Rutile and its applications in earth sciences

Transcription

Earth-Science Reviews 102 (2010) 1–28
Contents lists available at ScienceDirect
Earth-Science Reviews
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / e a r s c i r ev
Rutile and its applications in earth sciences
Guido Meinhold
CASP, University of Cambridge, West Building, 181a Huntingdon Road, Cambridge CB3 0DH, UK
a r t i c l e
i n f o
Article history:
Received 5 August 2009
Accepted 7 June 2010
Available online 12 June 2010
Keywords:
rutile
mineral geochemistry
geothermometry
oxygen isotopes
geochronology
thermochronology
Lu–Hf isotopes
a b s t r a c t
Rutile is the most common naturally occurring titanium dioxide polymorph and is widely distributed as an
accessory mineral in metamorphic rocks ranging from greenschist to eclogite and granulite facies but is also
present in igneous rocks, mantle xenoliths, lunar rocks and meteorites. It is one of the most stable heavy
minerals in the sedimentary cycle, widespread both in ancient and modern clastic sediments.
Rutile has a wide range of applications in earth sciences. It is a major host mineral for Nb, Ta and other high
field strength elements, which are widely used as a monitor of geochemical processes in the Earth's crust and
mantle. Great interest has focused recently on rutile geochemistry because rutile varies not only by bulk
composition reflected, for instance, in its Cr and Nb contents but also by the temperature of crystallisation,
expressed in the Zr content incorporated into the rutile lattice during crystallisation. Rutile geochemistry and
Zr-in-rutile thermometry yield diagnostic data on the lithology and metamorphic facies of sediment source
areas even in highly modified sandstones that may have lost significant amounts of provenance information.
Rutile may therefore serve as a key mineral in sediment provenance analysis in the future, similar to zircon,
which has been widely applied in recent decades. Importantly, rutile from high-grade metamorphic rocks
can contain sufficient uranium to allow U–Pb geochronology and (U–Th)/He thermochronology.
Furthermore, in situ Lu–Hf isotope analysis of rutile permits insights into the evolution of the Earth's crust
and mantle. Besides that, rutile is also of great economic importance because it is one of the favoured natural
minerals used in the manufacture of white titanium dioxide pigment, which is a major constituent in various
products of our daily life. Heavy mineral sands containing a significant percentage of rutile are therefore the
focus of exploration worldwide.
This paper aims to provide an overview of the applications of rutile in earth sciences, based on a review of
data published in recent years. After giving a summary of various rutile-bearing lithologies, the focus lies on
rutile geochemistry, Zr-in-rutile thermometry, O isotope analysis, U–Pb geochronology, (U–Th)/He
thermochronology and Lu–Hf isotope analysis. A final outline of the economic importance of rutile
highlights the demand for further rutile-related research in earth sciences.
© 2010 Elsevier B.V. All rights reserved.
Contents
1.
2.
3.
4.
Introduction . . . . . . . . . . . . . . . . . .
Physical properties and geochemical composition
2.1.
General description . . . . . . . . . . .
2.2.
Crystal structure. . . . . . . . . . . . .
2.3.
Crystal chemistry . . . . . . . . . . . .
Occurrences . . . . . . . . . . . . . . . . . .
3.1.
Rutile in metamorphic rocks . . . . . . .
3.2.
Rutile in igneous rocks and mineralisation
3.3.
Rutile in sedimentary rocks . . . . . . .
3.4.
Rutile in extraterrestrial rocks . . . . . .
Applications of rutile in earth sciences . . . . .
4.1.
Rutile geochemistry . . . . . . . . . . .
4.1.1.
Introduction . . . . . . . . . .
4.1.2.
Fe content . . . . . . . . . . .
4.1.3.
Nb and Ta contents . . . . . . .
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E-mail address: [email protected].
0012-8252/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.earscirev.2010.06.001
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2
G. Meinhold / Earth-Science Reviews 102 (2010) 1–28
4.1.4.
Cr and Nb contents .
4.1.5.
Other trace elements
4.1.6.
Examples . . . . . .
4.2.
Zr-in-rutile thermometry . . .
4.2.1.
Introduction . . . .
4.2.2.
4.2.3.
Zr diffusion . . . . .
4.3.
Oxygen isotopes . . . . . . .
4.3.1.
4.3.2.
4.4.
U–Pb geochronology . . . . .
4.4.1.
4.4.2.
4.4.3.
Pb diffusion . . . . .
4.5.
(U–Th)/He thermochronology
4.5.1.
4.5.2.
4.6.
Lu–Hf isotopes . . . . . . . .
4.6.1.
4.6.2.
5.
Economic importance of rutile. . . .
5.1.
Introduction . . . . . . . . .
5.2.
Economic importance . . . .
6.
Summary . . . . . . . . . . . . .
Acknowledgements . . . . . . . . . . .
References . . . . . . . . . . . . . . .
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1. Introduction
With an estimated TiO2 concentration of about 0.7 wt.% (Rudnick
and Fountain, 1995), titanium is the ninth most abundant element of the
Earth's continental crust. The most important titanium minerals are
rutile (TiO2), ilmenite (FeTiO3) and titanite (CaTiSiO5) (Figs. 1 and 2).
Rutile is an accessory mineral in a variety of metamorphic and igneous
rocks and occurs as a detrital mineral in clastic sediments. Although the
main formula of rutile is TiO2, there are commonly several possible
substitutions for titanium, for example, Al, V, Cr, Fe, Zr, Nb, Sn, Sb, Hf, Ta,
W and U (e.g. Graham and Morris, 1973; Hassan, 1994; Fett, 1995;
Murad et al., 1995; Smith and Perseil, 1997; Rice et al., 1998; Zack et al.,
2002; Bromiley and Hilairet, 2005; Scott, 2005; Carruzzo et al., 2006).
Variations in the geochemical composition are host rock specific and
allow the rutile source to be traced and the chemical and physical
properties during rutile formation to be characterised.
Great interest has focused on rutile geochemistry, because rutile is
a major host mineral for high field strength elements (HFSE), amongst
others Nb and Ta, which are widely used as geochemical fingerprints
of geological processes such as magma evolution and subductionzone metamorphism (e.g. Foley et al., 2000; Rudnick et al., 2000). For
many years, the significance of Nb and Ta concentrations and Nb/Ta
values of crustal and mantle rocks and the Earth's hidden suprachondritic Nb/Ta reservoir have been the subject of a lively debate (e.g.
Green, 1995; Foley et al., 2000; Rudnick et al., 2000; Kalfoun et al.,
2002; Zack et al., 2002; Xiao et al., 2006; Miller et al., 2007; Aulbach et
al., 2008; Baier et al., 2008; Bromiley and Redfern, 2008; Schmidt et
al., 2009).
Besides that, the Cr and Nb contents of rutile allow discrimination
between various rutile source lithologies such as metapelitic rocks
(e.g. mica-schists, paragneisses and felsic granulites) and metamafic
rocks (e.g. eclogites and mafic granulites) (Zack et al., 2004b; Triebold
et al., 2007; Meinhold et al., 2008). Furthermore, the incorporation of
Zr into the rutile crystal lattice has a strong dependence on
temperature and pressure, which has allowed the development of
Zr-in-rutile geothermometers (Zack et al., 2004a; Watson et al., 2006;
Tomkins et al., 2007). Several studies have already shown that Zr-inrutile thermometry is an attractive method to calculate temperatures
of high-grade and ultrahigh-grade metamorphic rocks (e.g. Spear et
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al., 2006; Zack and Luvizotto, 2006; Baldwin and Brown, 2008;
Luvizotto and Zack, 2009). Moreover, rutile geochemistry combined
with Zr-in-rutile thermometry can help to constrain the sediment
provenance and has therefore already been applied successfully to
sedimentary strata from the Precambrian to the Holocene worldwide
(e.g. Zack et al., 2004b; Stendal et al., 2006; Triebold et al., 2007;
Meinhold et al., 2008; Morton and Chenery, 2009).
Rocks exposed on the Earth's surface are prone to weathering and
erosion. These processes have continuously modified the Earth's
surface for probably more than 3.9 billion years producing clastic
sediments. Some of the key pieces of evidence for that may record
detrital zircons as old as 4.4 Ga from metaquartzites and metaconglomerates of the Yilgarn Craton, Western Australia (Mojzsis et al., 2001;
Wilde et al., 2001). Clastic sediments are composed of various minerals
(e.g. quartz, feldspar and mica) and lithic fragments and additionally
contain a minor amount of heavy minerals. The sediment composition
is primarily affected by the mineralogy of the primary source rock and
by a complex set of parameters such as weathering, transport,
deposition and diagenesis that modify the sediment during the
sedimentary cycle (e.g. Morton, 1985; Morton and Hallsworth, 1999).
Besides whole-rock petrography and heavy-mineral analysis,
geochemical studies of whole rock and specific detrital minerals are
powerful tools in provenance characterisation. Understanding clastic
sediment provenance is important for exploration of mineral
resources, basin analysis and palaeotectonic reconstructions. The
most common heavy minerals such as zircon, tourmaline, garnet and
chrome spinel have long been used as provenance indicators by virtue
of their geochemical and isotope signatures (e.g. Morton, 1991; von
Eynatten and Gaupp, 1999; Morton et al., 2004, 2005; Mange and
Morton, 2007). The exception is rutile, which received only minor
attention until 2002 (Götze, 1996; Preston et al., 1998, 2002).
However, rutile geochemistry, geothermometry and geochronology
yield diagnostic data on source-rock lithology and metamorphic facies
even in highly modified sandstones that may have lost significant
amounts of provenance information. Rutile may therefore serve as a
key mineral in sediment provenance analysis in the future, similar to
zircon, which has been widely applied in recent decades.
Studying the geochemical and physical parameters of rutile is not
only of scientific value. Rutile is an economically important mineral
3
Fig. 2. Theoretical TiO2 content in various Fe–Ti oxide phases (modified from Reyneke
and Wallmach, 2007). Titanite, a calcium titanium silicate, is shown for comparison.
Both methods are evaluated in unravelling specific source characteristics and in use as a chemostratigraphic indicator. Furthermore,
oxygen isotope analysis using the quartz–rutile mineral pair is
discussed. In the past, powerful new analytical methods such as in
situ U–Pb and Hf isotope analyses have been developed, which
significantly contribute to unravelling the geological history of natural
rutile and its host lithologies and are therefore addressed here too.
Finally, Section 5 summarises the economic importance of rutile and
shows the need for further rutile-related scientific research.
Fig. 1. Transmitted light photomicrographs showing rutile crystals (a) in eclogite from
the Cabo Ortegal complex, NW Spain (Harker Collection no. 146227) and (b) in mafic
granulite from the Saxonian Granulite Massif, Germany (Harker Collection no. 26002).
© 2009. Sedgwick Museum of Earth Sciences, University of Cambridge. The
photomicrographs were taken by the author and are reproduced with permission.
Mineral abbreviations (Kretz, 1983) are as follows: Cpx — clinopyroxene, Grt — garnet,
Rt — rutile, and Zo — zoisite.
because of its use in the manufacture of white titanium dioxide
pigment (Stanaway, 1994; Korneliussen et al., 2000), which is a
component in products of our daily life such as paint, paper, plastics,
toothpaste and sunscreen cream (Pearson, 1999; Carp et al., 2004;
Gambogi, 2008). Mineral sands containing large percentages of rutile
are therefore a focus of exploration worldwide (e.g. Goldsmith and
Force, 1978; Force, 1991; Pirkle et al., 2007; Schlüter, 2008).
Recently, the search for secondary standards of natural rutile to
assess measurement methods and demonstrate the quality of
acquired geochemical data (Luvizotto et al., 2009b) has also been a
focus of scientific study. Hence, the scope of this paper is to provide an
overview of the applications of rutile in earth sciences, introduced
with an outline of the physical properties and geochemical composition of rutile and a brief overview of various source lithologies for
rutile. The latter part is relative brief because Force (1991) already
gave a comprehensive overview of specific rutile sources, except for
extraterrestrial material.
The current paper has the following structure: Section 1 states the
objectives of this work; Section 2 presents a review of the physical
properties and geochemical composition of natural rutile and other
TiO2 polymorphs; Section 3 provides an overview of possible source
lithologies including metamorphic rocks, igneous rocks, mineralisation, sedimentary rocks and extraterrestrial rocks; Section 4 discusses
the applications of rutile geochemistry and Zr-in-rutile thermometry.
2. Physical properties and geochemical composition
2.1. General description
Abraham Gottlob Werner created the name rutile (Ludwig, 1803),
which he assigned to a mineral originally known as “red schorl”. The
first description of “red schorl” is commonly attributed to Romé de
l'Isle (1783); however, von Born (1772), as pointed out by Papp
(2007), already mentioned “red schorl” a few years earlier. Klaproth
(1795) used “red schorl” (rutile) for the description of the element
titanium, which he named after the Titans of Greek mythology. Note
that William Gregor originally discovered titanium (which he named
menackanite) in ilmenite in 1791 (Trengove, 1972).
Although it has long been thought that Horcajuelo (also called
Cajuelo) in the province of Burgos in Spain is the type locality of rutile,
a thorough study by Papp (2007) has recently revealed that the type
locality of rutile is Revúca in Slovakia.
The name “rutile” is derived from the Latin rutilus because of the
deep red colour observed in some specimens in transmitted light.
Rutile can be translucent or opaque. Yellowish and brownish colours
are also very common. A rarity is natural rutile with blue colour,
which has only been described so far as needle-like inclusions in
garnet from ultrahigh-pressure metasedimentary rocks of the Greek
Rhodope Massif (Mposkos and Kostopoulos, 2001). In reflected light
rutile with bluish colour has been reported from several meteorites
(El Goresy, 1971). The blue colour of meteoritic rutile may be due to a
stoichiometric deficiency of oxygen in the rutile structure (El Goresy,
1971). Experiments on synthetic rutile have shown that blue colours
occur in rutile samples grown or annealed under reducing conditions
(Bromiley and Hilairet, 2005). Khomenko et al. (1998) demonstrated
that the colour of blue rutile is mainly due to intervalence charge
4
Fig. 3. Ternary system FeO–Fe2O3–TiO2 showing the major high-temperature solidsolution series magnetite–ulvöspinel, haematite–ilmenite, pseudobrookite–ferropseudobrookite (modified from Buddington and Lindsley, 1964). Phases were plotted on
mole percentage basis.
transfer between Ti3+ and Ti4+ ions on adjacent interstitial and
octahedral sites (see Bromiley and Hilairet, 2005).
Rutile has a density of 4.23 g cm− 3, but can range up to 5.50 g cm− 3
(Deer et al., 1992), and thus belongs to the heavy mineral suite, which
are minerals with density N2.8 g cm− 3. Rutile is commonly diamagnetic
(non-magnetic), and therefore, it can easily be separated from the
paramagnetic (weakly magnetic) and ferromagnetic (strongly magnetic) heavy mineral fraction using the Frantz isodynamic separator (Buist,
1963a). However, rutile can also contain a high proportion of Fe making
it magnetic, and hence it could remain in the magnetic heavy mineral
fraction (Buist, 1963a; Hassan, 1994). Bramdeo and Dunlevey (2000)
mentioned anomalous behaviour of detrital rutile (due to substitution of
cations other than Ti4+ in the rutile crystal lattice; Fig. 8) during
industrial magnetic and electrostatic mineral separation, which can
cause rutile loss. Recent studies show that Co-implanted rutile can
become ferromagnetic (Akdogan et al., 2006). The melting point of pure
rutile is around 1825–1830 °C (MacChesney and Muan, 1959; Deer
et al., 1992). Note that synthetic rutile can be produced by heating a
solution of TiCl4 to 950 °C or by heating anatase to above 730 °C (Deer
et al., 1992).
2.2. Crystal structure
In nature, titanium dioxide mainly occurs in three structural
states: rutile, anatase and brookite (Fig. 2). Together they form the
TiO2 end-member of the ternary system FeO–Fe2O3–TiO2 (Fig. 3).
Fig. 4. Structure of rutile (after Baur, 2007) approximately parallel [100], rotated by 4°
around [001] and 8° around [010]. (a) Perspective view; one unit cell. (b) Perspective
polyhedral view; three unit cells in [001] direction, corner sharing between two
octahedral rutile type chains.
Rutile crystallises in the tetragonal space group P42/mnm and is the
most common phase, with unit cell parameters a = 4.594 Å and
c = 2.959 Å for pure rutile (Baur, 1956) (Table 1). Natural rutile,
however, commonly contains various trace elements such as Nb, V
and Fe, as outlined in Section 2.3, and hence has distinctly higher unit
cell parameters (e.g. Černý et al., 1999). The structure of pure rutile is
shown schematically in Fig. 4. In the unit cell, each Ti4+ ion is
surrounded by six oxygens at the corners of a slightly distorted,
regular octahedron while each oxygen surrounded by three Ti4+ ions
is lying in a plane at the corners of an approximately equilateral
triangle (Deer et al., 1992; Baur, 2007). Baur (2007) gives a more
detailed crystallographic description.
Rutile is a high-pressure and high-temperature polymorph and is
isostructural with stishovite, a high-pressure silica polymorph (Fig. 5).
Stishovite is a major phase in subducting oceanic crust under lower
mantle conditions (Ono et al., 2001) and has also been described from
impact-related rocks (Chao et al., 1962) and meteorites (Sharp et al.,
1999). The behaviour of rutile at high and ultrahigh pressures
therefore offers an analogy to explore post-stishovite phase transitions
(El Goresy et al., 2001; Bromiley et al., 2004). The low-temperature
polymorphs of titanium dioxide are anatase (tetragonal) and brookite
(orthorhombic). Under relatively low temperatures and pressures,
rutile is metastable with respect to anatase when the TiO2 crystal size
is less than ∼ 14 nm, because the surface energy of rutile is then much
higher than that of anatase (see Smith et al., 2009 for discussion).
Besides rutile, anatase and brookite, there are at least three
additional TiO2 polymorphs (Table 1). The TiO2(B) polymorph has a
structure closely related to that of VO2(B) (Marchand et al., 1980), the
TiO2(II) polymorph has an α-PbO2-type structure (Simons and
Table 1
Physical parameters of selected TiO2 polymorphs.
Density (g cm− 3)
Crystal system
Space group
Unit cell parameters (Å)
Comment
Reference
Rutile
Anatase
Brookite
TiO2(B)
TiO2(II)
TiO2(H)
4.23–5.5
Tetragonal
P42/mnm
a = 4.594
c = 2.959
3.82–3.97
Tetragonal
I41/amd
a = 3.785
c = 9.514
4.08–4.18
Orthorhombic
Pbca
a = 9.184
b = 5.447
c = 5.145
4.33
Orthorhombic
Pbcn
a = 4.59
b = 5.44
c = 4.94
3.46
Tetragonal
I4/m
a = 10.18
c = 2.97
(1)
(2)
(3)
3.64
Monoclinic
C2/m
a = 12.16
b = 3.74
c = 6.51
β = 107.29°
VO2(B)-related structure
(4)
α-PbO2-type structure
(5)
Hollandite-type structure
(6)
References: (1) Cromer and Herrington (1955), Baur (1956), Deer et al. (1992); (2) Cromer and Herrington (1955), Deer et al. (1992); Howard et al. (1991); (3) Baur (1961), Deer et
al. (1992); (4) Marchand et al. (1980); (5) Simons and Dachille (1967), Hwang et al. (2000); (6) Latroche et al. (1989).
5
1965) and reflected light microscopy (Mader, 1980) have to be used.
The most reliable technique to identify mineral polymorphs is laser
micro-Raman spectroscopy. A compilation of Raman bands for the
three major structural TiO2 polymorphs is shown in Fig. 6. Rutile can
be identified by bands at wavenumbers 143, 247, 447 and 612 cm− 1
(Porto et al., 1967; Tompsett et al., 1995) and anatase by bands at
wavenumbers 144, 197, 400, 516 and 640 cm− 1 (Ohsaka et al., 1978).
Brookite is characterised by several bands. Strong bands are at
wavenumbers 153, 247, 322 and 636 cm− 1 (Tompsett et al., 1995).
2.3. Crystal chemistry
Presently, analysis of rutile can be routinely performed by
sophisticated techniques such as electron microprobe (EMP), proton
microprobe (PIXE) and laser ablation inductively coupled plasma mass
spectrometry (LA-ICP-MS) so that differences in geochemical composition can easily be identified (Fig. 7). The disadvantage of the LA-ICPMS technique is that it makes a crater often several tens of
micrometres in diameter whereas the first two techniques are
nondestructive to the sample, but they have higher detection limits
(especially EMP) for the concentration of certain elements compared
with LA-ICP-MS facilities. For very tiny rutile crystals analysed in thin
sections, it is recommended that the Si content is measured in order to
identify beam interferences with adjacent silicate minerals (Carruzzo
et al., 2006; Baldwin and Brown, 2008). Smith and Perseil (1997)
considered Si substitution in rutile as “highly contentious at non-ultrahigh pressure” and thus if Si is detected in rutile of non-ultrahighpressure rocks it is likely to be due to analytical error, microinclusions,
or introduction into defective parts of the crystal structure (Smith and
Perseil, 1997). Moreover, very fine zircon lamellae can occur in rutile
(Schmitz and Bowring, 2003; Downes et al., 2007), which may cause
Fig. 5. Pressure–temperature diagram (after Okamoto and Maruyama, 2004; Baldwin et
al., 2004). Phase boundaries for rutile and TiO2(II) are based on phase equilibrium
experiments, nominally dry synthesis experiments and reference data (after Withers et
al., 2003). A range of geotherms is also shown. Abbreviations: GS, greenschist facies;
AM, amphibolite facies; GR, granulite facies; BS, blueschist facies; EC, epidote facies.
Dachille, 1967) and the highly metastable TiO2(H) polymorph has a
hollandite-type structure (Latroche et al., 1989). For several decades,
the last two were only known from synthetic polymorphs. However,
Hwang et al. (2000) described an epitaxial (about 8 nm thick) slab of
the TiO2(II) polymorph between twinned rutile bicrystals as inclusion
in garnet of diamondiferous quartzofeldspathic rocks from the
Saxonian Erzgebirge, Germany, which was the first natural TiO2(II)
polymorph found on Earth. This occurrence was explained by Hwang
et al. (2000) to have formed during ultrahigh-pressure prograde
metamorphism close to the rutile–α-PbO2 phase boundary in the
diamond stability field at depths of at least 130 km. The rocks
containing this TiO2(II) polymorph may have equilibrated at pressures in excess of 70 kbar (Withers et al., 2003) (Fig. 5). Another
natural TiO2(II) polymorph was reported in omphacite from a coesitebearing eclogite in the Dabie Mountains, China (Wu et al., 2005). Wu
et al. (2005) suggested subduction of continental material to depths of
over 200 km. El Goresy et al. (2001) discovered a natural shockinduced TiO2(II) polymorph from shocked garnet–cordierite–sillimanite gneiss clasts of the Ries crater, Germany. Its petrographic
setting is entirely different from that of the epitaxial slab in the
Saxonian diamondiferous gneisses (see description in El Goresy et al.,
2001 for further details). Another natural shock-induced TiO2(II)
polymorph has been identified in breccias from the Chesapeake Bay
impact structure in Virginia, U.S.A. (Jackson et al., 2006).
Because the mineral polymorphs of TiO2 cannot be distinguished
by their geochemical composition other identification methods such
as X-ray diffraction (Spurr and Myers, 1957; Raman and Jackson,
Fig. 6. Raman spectra of the TiO 2 polymorphs rutile, anatase and brookite.
Wavenumbers of main Raman bands are indicated (see text for explanation).
6
elevated Zr contents if such zircon lamellae-rich rutiles are analysed.
Thus, rutile measurements with Si contents N300 ppm showing
abnormally high Zr contents should be excluded from the data set
(see Zack et al., 2004a; Luvizotto and Zack, 2009 for further
discussion). Rutiles from diamondiferous kyanite-bearing eclogites
can contain elevated Al contents, which can be explained by several
tiny rods of corundum (Sobolev and Yefimova, 2000). Ilmenite and
magnetite may also occur as tiny lamellae in rutile. In general, if such
mineral rods are smaller than the electron beam size a mixture of them
and rutile is analysed. Literature data show a wide range of certain
trace elements, in particular Al and Fe, in rutile from crustal and mantle
eclogites, which most likely reflects the presence of corundum and
ilmenite lamellae (Sobolev and Yefimova, 2000).
Most naturally occurring rutile corresponds to the general formula
TiO2, with titanium occurring as Ti4+. Note that titanium also exists in
different states of oxidation: besides Ti4+, there are also Ti3+, Ti2+ and
Ti0 (MacChesney and Muan, 1959). In rutile, there are commonly several
possible substitutions for titanium such as hexavalent (W6+ and U6+),
pentavalent (Nb5+, Sb5+ and Ta5+), tetravalent (Zr4+, Mo4+, Sn4+, Hf4+
and U4+), trivalent (Al3+, Sc3+, V3+, Cr3+, Fe3+ and Y3+) and divalent
(Fe2+, and to a lesser degree Mg2+, Mn2+ and Zn2+) cations (Graham
and Morris, 1973; Brenan et al., 1994; Hassan, 1994; Fett, 1995; Murad et
al., 1995; Smith and Perseil, 1997; Rice et al., 1998; Zack et al., 2002;
Bromiley and Hilairet, 2005; Scott, 2005; Carruzzo et al., 2006). For
instance, Fe3+ and Nb5+ incorporation (Fe3+ + Nb5+ ↔ 2Ti4+) maintaining charge neutrality can compensate for substitution of tetravalent
Ti4+ ions. Several further examples can be found in the literature (e.g.
Urban et al., 1992; Michailidis, 1997; Smith and Perseil, 1997; Rice et al.,
1998; Scott and Radford, 2007). Substitution of Ti4+ in the rutile crystal
lattice is based on the ionic radius and ionic charge of the substituted
cation (Fig. 8). Cathodoluminescence (CL) and backscattered electron
(BSE) images of polished rutile grains can reveal complex oscillatory
zonation patterns or patchy zoned crystals (e.g. Michailidis, 1997;
Carruzzo et al., 2006; Birch et al., 2007), which indicate variations in the
geochemical composition in the rutile crystal lattice. Thus, a single-spot
Fig. 7. Comparison of Nb concentrations in rutiles analysed by EMP and LA-ICP-MS. Data
were taken from Zack et al. (2002) and Xiao et al. (2006). Dark grey diamonds are
rutiles from eclogites, grey squares represent rutiles from quartz veins, and the white
circles represent rutiles from garnet–mica schists. Solid line represents a 1:1
correlation; dotted lines are the upper and lower range of 20% and 30% deviations
from the 1:1 line respectively. Note that EMP gives a slightly lower value compared to
LA-ICP-MS for most of the analysed rutiles, also recognised by Xiao et al. (2006). Future
studies may help clarifying if this is an analytical artefact.
Fig. 8. Ionic charge versus ionic radius (Shannon, 1976) for elements that substitute Ti
in natural rutile (see text for explanation and references). Note that the ionic radius of
Ta5+ is about 0.015 Å smaller than that of Nb5+ (Tiepolo et al., 2000).
analysis may not be representative for the bulk composition of a rutile
grain. That is particularly critical for calculating the crystallisation
temperatures using Zr-in-rutile thermometry and for in situ isotope
analysis.
Rutile is the dominant carrier of HFSE (e.g. Foley et al., 2000; Kalfoun
et al., 2002; Zack et al., 2002). For example, in eclogites 1 modal-% of
rutile can carry more than 90% of the whole-rock content for Ti, Nb, Sb,
Ta and W and considerable amounts (5–45% of the whole-rock content)
of V, Cr, Mo and Sn (Rudnick et al., 2000; Zack et al., 2002). Because rutile
dominates the budget of Nb and Ta, Nb + Ta concentrations and Nb/Ta
values of rutile should be identical to that of the host rock (Rudnick et al.,
2000; Zack et al., 2002; Carruzzo et al., 2006). Schmidt et al. (2009)
recently made a critical note on this subject, based on Nb/Ta zoning in
eclogitic rutile. In general, the rutile structure can accommodate up to
37 wt.% Nb2O2 in solid solution (Roth and Coughanour, 1955; Tien et al.,
1969). Villaseca et al. (2007) suggested that around 10–35% of the
whole-rock Zr content of peraluminous granulites could be contained in
rutile. The needle-like blue rutile inclusions in garnet from ultrahighpressure metasedimentary rocks of the Greek Rhodope Massif contain a
small but significant amount of SiO2 (Mposkos and Kostopoulos, 2001)
that indicates high-temperature/high-pressure (HT/HP) conditions and
represents stishovite component in rutile (H.-J. Massonne, in Mposkos
and Kostopoulos, 2001).
Rutile can also contain considerable amounts (tens to thousands of
ppm) of H2O, structurally bounded as hydroxyl (OH), which has been
reported from both synthetic rutile (Bromiley et al., 2004; Bromiley
and Hilairet, 2005) and natural rutile (Rossman and Smyth, 1990;
Hammer and Beran, 1991; Vlassopoulos et al., 1993; Zhang et al.,
2001). Vlassopoulos et al. (1993) pointed out that rutile is one of the
most “hydrous” nominally anhydrous minerals (NAMs: Bell and
Rossman, 1992) so far identified. Experimental investigations have
shown that OH solubility in NAMs increases with pressure (e.g. Lu and
Keppler, 1997; Bromiley et al., 2004; Mierdel and Keppler, 2004;
Rauch and Keppler, 2004). Zhang et al. (2001) presented values of
about 4300 to 9600 ppm H2O in rutile from eclogites of the Dabie
Mountains, China. Therefore, besides pyroxene and garnet, rutile is
also an important NAM to recycle water into the mantle (Zhang et al.,
2001; Zheng et al., 2003; Bromiley et al., 2004).
3. Occurrences
3.1. Rutile in metamorphic rocks
Rutile is mainly formed during medium- to high-grade metamorphic processes (e.g. Goldsmith and Force, 1978; Force, 1980, 1991)
(Fig. 9), but it can also form in low-grade metamorphic rocks (e.g.
Fig. 9. Illustrations showing the main stages of rutile crystallisation from ilmenite and
biotite during prograde metamorphism. (a) Rutile crystallisation from ilmenite in lowto medium-grade metasedimentary rocks of the Erzgebirge (modified from Luvizotto et
al., 2009a). (b) Rutile crystallisation from biotite in granulite facies paragneisses of the
Ivrea–Verbano Zone (modified from Luvizotto and Zack, 2009). Mineral abbreviations
(Kretz, 1983) are as follows: Bt = Biotite, Chl = Chlorite, Ilm = Ilmenite, Rt = Rutile.
7
sample of the Rocciavre Massif, Western Alps. Smythe et al. (2008)
noted that ilmenite lamellae are abundantly present in mantlederived rutile.
Eclogite is the major rock type under high-grade metamorphic
rocks containing large percentages of rutile (Korneliussen and Foslie,
1985; Liou et al., 1998; Korneliussen et al., 2000; Zack et al., 2002;
Chen et al., 2005; Huang et al., 2006; Zhang et al., 2006). Korneliussen
and Foslie (1985) estimated that about 90% of the titanium in
eclogites of the Sunnfjord region of the Western Gneiss Region
(WGR), Norway, is hosted in rutile. Eclogite from the Western
Ligurian Alps contains up to 4 vol.% of rutile (Liou et al., 1998). Eclogite
is a plagioclase-free metamorphic rock composed of ≥75 vol.% of
garnet and Na-rich clinopyroxene (omphacite) and mainly forms by
subduction of gabbroic or basaltic rocks to great depths where rutile
crystallises from Fe–Ti oxides and Ti-bearing silicates during metamorphic recrystallisation (Krogh, 1980, 1982; Korneliussen and
Foslie, 1985; Liou et al., 1998; Korneliussen et al., 2000; Miller et al.,
2007; Figs. 5 and 10). Eclogite has a density of up to 3.6 g cm− 3 (Hills
and Haggerty, 1989; Rudnick and Fountain, 1995), higher than any
other crustal rock (Hacker, 1996), even peridotite, which it exceeds by
0.2–0.4 g cm− 3 (Rudnick and Fountain, 1995). Experimental data
suggest that rutile is the main Ti carrier in eclogite below 150 kbar
under sub-solidus conditions, even in relatively Ti-poor systems
(Okamoto and Maruyama, 2004). However, under ultrahigh-pressure
metamorphic conditions close to the coesite–stishovite phase boundary it is more likely to be the TiO2(II) polymorph instead of rutile
(Withers et al., 2003; Fig. 5). In general, the stability of rutile in
subducted lithosphere is a complex function of whole-rock composition, temperature and pressure (e.g. Zhang et al., 2003; Klemme et
al., 2005; Bromiley and Redfern, 2008; Fig. 10).
Since rutile is a major accessory mineral in eclogite and plays a
major role in the Earth's HFSE budget (in particular Nb and Ta) (see
Section 2.3), in the last decade, eclogite has received much attention
regarding its whole-rock and mineral geochemical composition (e.g.
Rudnick et al., 2000; Zack et al., 2002; Xiao et al., 2006; Miller et al.,
2007; Schmidt et al., 2009). In addition, the processes returning
Banfield and Veblen, 1991; Luvizotto et al., 2009a). Rutile in low- to
medium-grade metamorphic rocks typically occurs as small (∼20–
100 μm), scattered grains, generally needle-like crystals, or polycrystalline aggregates. Banfield and Veblen (1991) recognised that within
each sample analysed, the rutile crystals are uniform in size, but they
are smaller in samples from the chlorite and chloritoid zones than in
samples from the garnet and staurolite zones. The needle-like,
euhedral morphology of the crystals show that rutile grew during
metamorphism, rather than being detrital in origin (Banfield and
Veblen, 1991). Luvizotto et al. (2009a) recently described prograde
rutile crystallisation in low- to medium-grade metasedimentary rocks
from the Saxonian Erzgebirge, Germany. The rutiles form polycrystalline aggregates made of fine-grained intergrowths of rutile and
chlorite that replaces ilmenite (Fig. 9). Luvizotto et al. (2009a)
suggested that rutile has been derived from ilmenite breakdown due
to following simplified reaction:
Ilmenite þ Silicates þ H2 O→Rutile þ Chlorite
Rutile in high-grade and ultrahigh-grade metamorphic rocks (e.g.
eclogites, granulites) forms mainly single crystals in the matrix but
also occurs as inclusion in other minerals such as garnet, pyroxene,
amphibole and zircon (Fig. 1). These rutile grains can show euhedral
to subhedral forms with oval shapes or irregular shapes, with grain
sizes from a few μm up to a few mm (Hills and Haggerty, 1989; Brenan
et al., 1994; Zack et al., 2002; Huang et al., 2006; Xiao et al., 2006;
Janoušek et al., 2007; Chen and Li, 2008). Brenan et al. (1994)
described large (1–5 mm in size), euhedral single crystals of rutile
that contain fine exsolution lamellae of ilmenite from an eclogite vein
Fig. 10. Experimentally determined formation of rutile, titanite and ilmenite for a midocean ridge basalt–H2O system (after Liou et al., 1998). The P–T field phase boundaries
were not reversed and hence should be considered as synthesis boundaries, although
they are topologically consistent with natural occurrences of Ti-phases. Liou et al.
(1998) furthermore pointed out that these Ti-rich phases are not related to one another
by simple polymorphic transition, and thus two or even three of them may coexist
under certain physicochemical conditions, but this was not investigated
experimentally.
8
extremely dense eclogite from great depths back to the Earth's surface
(e.g. Guillot et al., 2000; Neufeld et al., 2008), supplemented by
geochronological studies (e.g. Baldwin et al., 2004; Glodny et al.,
2005; Kylander-Clark et al., 2008), have been much discussed.
Unfortunately, the original mineral assemblage of lower crustal
rocks such as eclogite and eclogite facies rocks are subject to
retrogression during their ascent from great depths to the Earth's
surface. For example, in eclogites and eclogite facies rocks from the
Western Ligurian Alps, rutile was subsequently replaced by ilmenite
and titanite along margins and cracks (Liou et al., 1998). Xiao et al.
(2006) described thin titanite (10–20 μm) replacement surrounding
rutile and a thin ilmenite (a few μm) rim at the rutile margin from an
eclogite and nearby quartz vein, respectively, of the Dabie–Sulu
ultrahigh-pressure terrane in east-central China. Note that, under
conditions of rapid exhumation (as fast as subduction; Rubatto and
Hermann, 2001; Baldwin et al., 2004) the original mineral assemblage
is largely preserved and allows insights into the pressure, temperature
and geochemical conditions present at great depths. Rutile in eclogitic
(E-type) diamonds and diamondiferous eclogites (Prinz et al., 1975;
Mvuemba Ntanda et al., 1982; Sobolev et al., 1997; Sobolev and
Yefimova, 2000) are accessible at the Earth's surface due to fast ascent
from the Earth's mantle as xenoliths in kimberlite pipes. The extensive
studies of the composition of eclogite in recent years have significantly contributed to the increase of geochemical data for natural
rutile, and thus they have opened new ways for rutile characterisation
such as rutile geochemistry and Zr-in-rutile thermometry, as outlined
in Section 4.
Rutile also occurs in the form of oriented, needle-like rods, known
as sagenitic texture. Shau et al. (1991) described these from matrix
biotite of an orthogneiss of the Tananao metamorphic complex, NE
Taiwan. Van Roermund et al. (2000) described oriented, needle-like
rutile rods of 2–15 μm in diameter and up to 200–300 μm in length
from protogranular and porphyroclastic garnet from garnet peridotite
of the WGR. Attoh and Nude (2008) recently described spindle shaped
rutile rods of b3 μm in diameter, b50 μm long and arranged in a
rectilinear pattern in garnet megacrystals from mafic granulites of the
Pan-African Dahomeyide suture zone, SE Ghana. Oriented, needle-like
rutile rods in garnet are commonly taken as an indicator for UHP
metamorphism (Ye et al., 2000; Mposkos and Kostopoulos, 2001;
Hwang et al., 2007; Attoh and Nude, 2008). They show crystallographically controlled growth of the exsolution rods and suggest
transformation in the garnet crystal structure involving substitution
of Ti4+ in the precursor garnet structure (Zhang et al., 2003). Hwang
et al. (2007) investigated the origin of oriented, needle-like rutile rods
in garnet from eclogitic rocks of Sulu, from diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge and from felsic granulite
of Bohemia. Their results argue against a simple solid-state precipitation scenario. The authors favour a mechanism where oriented
rutile needles form by cleaving and healing of garnet with rutile
deposition because of the natural analogue of oriented titanite
needles in biotite. Nonetheless, their study clearly shows the need
for further investigation of the origin of oriented rutile needles in
garnet of high-grade and ultrahigh-grade metamorphic rocks (see
Griffin, 2008).
3.2. Rutile in igneous rocks and mineralisation
Additional sources of rutile can be quartz veins (e.g. Watson, 1922;
Deer et al., 1992), granites (e.g. Force, 1980; Scott, 1988; Force, 1991;
Michailidis, 1997; von Quadt et al., 2005), pegmatites (e.g. Force,
1980; Černý et al., 1989; Force, 1991; Deer et al., 1992; Okrusch et al.,
2003), carbonatites (e.g. Bailey, 1961; Ripp et al., 2006; Doroshkevich
et al., 2007), kimberlites and xenoliths of metasomatised peridotite
(e.g. McGetchin and Silver, 1970; Dawson and Smith, 1977; Jones
et al., 1982; Kramers et al., 1983; Tollo and Haggerty, 1987; Schulze,
1990; Rudnick et al., 2000; Grégoire et al., 2002; Kalfoun et al., 2002;
Choukroun et al., 2005; Downes et al., 2007; Smythe et al., 2008) and
metallic ore deposits (e.g. Bayley, 1923; Force, 1980; Czamanske et al.,
1981; Force, 1991; Rice et al., 1998; Clark and Williams-Jones, 2004;
Scott, 2005; von Quadt et al., 2005; Scott and Radford, 2007). The
occurrence of large rutile crystals (up to 4 cm in size and larger) is
limited to some granitic pegmatites and vein mineralisation (Watson,
1922; Deer et al., 1992; Černý et al., 1999, 2007) and are described
from syn-metamorphic quartz veins of eclogite facies (Franz et al.,
2001; Gao et al., 2007).
In alpine fissures, rutile can occur as reddish needles in transparent
quartz crystals. They are then called rutilated quartz or “fléches
d'amour” (“arrows of love”) and are classified as gemstones, with
known localities in Brazil, Switzerland and U.S.A. (Pough, 1998).
Blue quartz is another type of rutilated quartz (e.g. Wise, 1981).
The “blue” colour of quartz is derived from Rayleigh scattering of light
by abundant inclusions of nanometre-scale acicular rutile, but other
minerals may also occur as inclusions, for instance, ilmenite (e.g.
Wise, 1981; Zolensky et al., 1988). In many cases, acicular rutile in
quartz has been formed by exsolution of Ti from the quartz crystal
lattice (Cherniak et al., 2007a). Rutilated blue quartz has been
described, for example, from granites, granodiorites, rhyolites,
charnockites and gneisses (Wise, 1981; Zolensky et al., 1988, and
references therein), and is restricted in occurrence mainly to the
Precambrian, in particularly to middle to late Proterozoic rocks
(Zolensky et al., 1988) of the Grenville province. Note that blue quartz
incorporated into detritus eroded from these rocks has proven to be a
reliable provenance indicator with stratigraphic significance both in
the Scottish Highlands, in western Ireland and in the eastern parts of
North America (Phillips, 1973; Fitches et al., 1990; Kline, 1991; Dewey
and Mange, 1999; Maria Mange, pers. comm., 2010).
Rutile in granitic rocks can have several origins; it can be a primary
igneous, peritectic, xenocrystic, or secondary phase (Carruzzo et al.,
2006; Clarke and Carruzzo, 2007). Secondary rutile can form because
of hydrothermal alteration (chloritisation) of Ti-rich biotite (Carruzzo
et al., 2006), by oxidation of ilmenite (Sakoma and Martin, 2002) or by
exsolution from Ti-bearing phases such as clinopyroxene and garnet
(Zhang et al., 2003).
Primary igneous rutile can have significant concentrations of HFSE
(e.g. Nb and Ta). Niobian rutile (also known as ilmenorutile) is a
variety of rutile with an atomic ratio of Nb/Ta N 1, while tantalian rutile
(also known as strüvertite) has an atomic ratio of Nb/Ta b 1 (Černý et
al., 1964). Both are accessory minerals in peraluminous to peralkaline
granites and substantial components of hydrothermal assemblages
associated with alkaline intrusive rocks (Černý et al., 1964, 1999;
Černý and Chapman, 2001). In both rutile varieties, Fe3+ is always
present to accommodate the overcharged (Ti4+, Nb5+ and Ta5+)
cation population (Smith and Perseil, 1997).
According to Bailey (1961) and Marvin (1971), in alkaline rocks,
carbonatites and carbonate veins in particular, rutile tends to be
enriched in Nb and poor in Ta. However, primary rutiles from
carbonatites can be free of Nb, and have ubiquitous V and elevated Fe
contents (Ripp et al., 2006). Chrome-rich rutile in carbonatites is
commonly related to mantle-derived xenoliths (Ripp et al., 2006).
Anderson (1960) mentioned niobian rutile from the carbonate-rich
metamorphic zone of the Idaho batholith. Tollo and Haggerty (1987)
described niobian rutile from nodules of the Orapa kimberlite,
Botswana. Kimberlitic rutile in general has higher Nb/Ta ratios
compared with rutile from granites and granitic pegmatites (Tollo and
Haggerty, 1987). Metasomatised mantle peridotite and continental
lithospheric mantle have Nb/Ta ratios N17.5, chondritic to suprachondritic (Kalfoun et al., 2002). Unmetasomatised peridotites commonly
have Nb/Ta ratios b17.5, subchondritic (Kalfoun et al., 2002).
Michailidis (1997) studied niobian rutile (some with substantial
tungsten content) from the Fanos aplitic granite, northern Greece. Černý
et al. (1999) described niobian rutile from the McGuire pegmatite,
Colorado, and its breakdown into secondary minerals such as
pseudobrookite, ferropseudobrookite, titanian ferrocolumbite and
ilmenite. Further examples of exsolution and breakdown of niobian
rutile are found in the literature (Uher et al., 1998; Černý and Chapman,
2001; Černý et al., 2007). Carruzzo et al. (2006) described several rutile
types from peraluminous granite of the late Devonian South Mountain
Batholith, Nova Scotia. The size of the primary igneous rutile
grains ranges from 0.04 to 0.28 mm (with minor larger grains),
with rare euhedral to commonly anhedral shapes. Carruzzo et al.
(2006) recognised that these grains have increasing concentrations of
Fe+ Mn, Zr, Nb, Sn, Ta and W with increasing chemical differentiation of
the South Mountain Batholith and concluded that rutile is a sensitive
monitor of Nb–Ta–Sn–W in the batholith. Rutile with high Nb+ Ta
concentrations and low Nb/Ta values, reflecting variable partitioning of
Nb and Ta into a fluid phase, is commonly associated with granitic
pegmatites and in case of the South Mountain Batholith may represent
crystallisation during H2O-oversaturated conditions (Carruzzo et al.,
2006).
Concentrations of boron and H2O can increase in granite magmas
during the late stage of emplacement and can led to explosive release
of volatiles forming tourmaline breccia dykes and pipes, some of
which have rutile as the main accessory phase (e.g. Müller and Halls,
2005). Such rutile has highly variable amounts of V, Fe, Nb, Sn and W
(Müller and Halls, 2005). Putnis (1978) and Putnis and Wilson (1978)
noted that rutile formed at low temperatures (less than 450 °C,
hydrothermal) contains notable Fe concentrations. Such rutile is
susceptible to exsolution of a Fe-bearing phase such as hematite
(Putnis, 1978; Putnis and Wilson, 1978).
9
(Reyneke and Wallmach, 2007). Authigenic rutile can often be identified
by its polysynthetic twin lamellae (Mader, 1980).
Rutile has been recognised as an important component of heavy
mineral suites since the very early days of sedimentary petrography
(e.g. Boswell, 1933, and references therein). Hubert (1962) introduced the zircon–tourmaline–rutile (ZTR) index as a quantitative
indicator of the mineralogical maturity of the heavy mineral suite in
sandstones. Buist (1963a,b) determined the rutile concentration of
heavy mineral separations of beach sands from southern Australia
using a Frantz isodynamic separator and Geiger counter X-ray
diffractometer. Raman and Jackson (1965) used X-ray diffraction
after sample treatment with hydrofluoric acid for the qualitative
detection and quantitative estimation of rutile in small amounts in
sediment. From the 1980s, microprobe techniques were used for
single-grain chemical analyses supplying additional information to
conventional heavy mineral analysis for sediment provenance studies
(e.g. Morton, 1985, 1991). This caused a resurgence of interest in
heavy mineral analysis both in academic research and in industry.
Rutile is chemically and physically stable and not prone to
destruction during the sedimentation cycle and can therefore provide
important information about source area lithologies. Rutile has similar
hydraulic and diagenetic behaviour as zircon, and Morton and
Hallsworth (1994) therefore introduced the rutile–zircon index
(RuZi) for provenance characterisation, defined as:
RuZi =
Rutile
× 100
Rutile + Zircon
3.3. Rutile in sedimentary rocks
The largest sedimentary sources of rutile are fine-grained clastic
sediment and heavy mineral sands (placer deposits). For example,
Valentine and Commeau (1990) studied the TiO2 whole-rock content
of Pleistocene and Holocene sediments from surficial and several core
samples of the Gulf of Maine where rutile is the main titanium source
present in the silt and clay fraction. Based on their data, the authors
estimated the amount of TiO2 to exceed 647 million metric tons (t) and
could show that the Gulf of Maine hosts a large titanium resource.
Placer deposits commonly contain high percentages of zircon, rutile
and ilmenite that are concentrated to economic grade (e.g. Force,
1991; Roy, 1999; Dill, 2007a). Examples are marine placer deposits in
southeastern Australia (e.g. Roy, 1999) and along the NW coast of
South Africa (e.g. Dill, 2007a; see Section 5). In continental placer
deposits, titanium minerals occur mainly in rutile–ilmenite aggregates
called “nigrine” (Clark, 1993; Dill, 2007a; Dill et al., 2007). Nigrine is a
variety of rutile with high iron concentration (Clark, 1993).
Pseudorutile (Fe2Ti3O9; Temple, 1966; Teufer and Temple, 1966) is
formed by Fe2+ removal during oxidation of ilmenite (FeTiO3) (Teufer
and Temple, 1966; Grey and Reid, 1975; Mücke and Chaudhuri, 1991;
Grey et al., 1994). Its status as a distinct mineral phase is still a subject of
lively debate (Dill, 2007a, and references therein). Removal of Fe3+ from
pseudorutile due to leaching and hydrolisation results in leucoxene
(Mücke and Chaudhuri, 1991). The latter term, introduced by Gümbel
(1874), had long been applied to alteration products with high Ti
concentration. In present usage, leucoxene refers to a mineral
concentrate with about 65–90 wt.% TiO2 (Fig. 2) and is a mixture of
pseudorutile and rutile (Grey et al., 1994; Reyneke and Wallmach, 2007).
In conclusion, pseudorutile and leucoxene indicate more oxidising
supergene or hypogene conditions in the provenance area (Dill, 2007a).
In sedimentary rocks rutile, anatase and brookite can form diagenetically from Ti-rich pore-solutions, which may derive from
alteration of ilmenite, titanite and biotite (Mader, 1980; Morad, 1986;
Valentine and Commeau, 1990). Paine et al. (2005) ascribed alteration
of ilmenite to pseudorutile and anatase in Pliocene placer deposits
of southeastern Australia to postdepositional weathering. The TiO2
polymorphs are commonly alteration endmembers of Fe–Ti oxides
with rutile and zircon given as counts per sample. This index is based
on the premise that ratios of minerals with similar hydraulic and
diagenetic behaviour most likely reflect provenance characteristics
(Morton and Hallsworth, 1994). Use of the rutile–zircon index as a
guide to provenance is especially important in clastic sediments that
have undergone advanced burial diagenesis and hence may have lost
significant amounts of provenance information (Morton and Hallsworth, 1994, 1999). Sands with high RuZi indicate that rutile-bearing
lithologies (metapelitic and/or metamafic rocks) are abundant in the
source region, whereas low RuZi indicates a prevalence of rutile-poor
lithologies (such as igneous rocks). Since rutile and zircon are both
stable minerals (Pettijohn, 1941; Hubert, 1962; Morton and Hallsworth, 1994, 1999), RuZi values can also reflect inheritance from preexisting clastic sediment. To date, the method has successfully been
applied in several conventional heavy mineral studies (e.g. Whitham
et al., 2004; Morton et al., 2005; Morton and Chenery, 2009).
Sophisticated methods for rutile provenance characterisation are discussed in Section 4.
3.4. Rutile in extraterrestrial rocks
Rutile has also been described from extraterrestrial material such
as lunar rocks and meteorites. Extraterrestrial rutile can have several
origins, such as reduction from ilmenite, exsolution from chromite
and primary crystallisation as a minor accessory mineral (Buseck and
Keil, 1966; Harper, 1996). Rutiles from lunar rocks were described, for
example, in Apollo 11, 12, 14 and 17 samples (Keil et al., 1970; Wood
et al., 1970; Marvin, 1971; Hlava et al., 1972; Hill et al., 2006). They
occur within ilmenite as thin exsolution lamellae of less than 2 μm
(Keil et al., 1970) and 2–5 μm (Wood et al., 1970) in size. They also
occur as small anhedral grains less than 20 μm in diameter adjacent to
or enclosed by ilmenite (Keil et al., 1970; Marvin, 1971; Hlava et al.,
1972). Marvin (1971) identified a niobium-enriched mineral from
lunar rocks and soils, which was a niobian rutile (6.4% Nb2O5) in a
microbreccia fragment of an Apollo 12 sample. That rutile was also
enriched in Ta, La and Ce. Hlava et al. (1972) found niobian rutile (7.1%
Nb2O5) in a lithic fragment of KREEP composition (K — potassium,
10
REE — rare earth elements and P — phosphorus) with basaltic texture
in an Apollo 14 sample.
One of the pioneers studying meteoritic rutile was Paul Ramdohr
who identified rutile in the Mt. Browne chondrite and in several
mesosiderites (Ramdohr, 1963, 1965). El Goresy (1965) mentioned a
euhedral rutile crystal enclosed in troilite of the Odessa iron meteorite
and accessory rutile in the Dalgaranga iron meteorite. Buseck and Keil
(1966) described rutile associated primarily with ilmenite and
chromite from several meteorites (Allegan, Bondoc, Esterville, Farmington and Vaca Muerta) (see Kimura et al., 1991). Rutile is most
abundant in the Farmington L-group chondrite where it occurs in fine
lamellae in polycrystalline ilmenite (Buseck and Keil, 1966). Referring
to Ramdohr (1963, 1965), Buseck and Keil (1966) suggested that this
rutile was derived from ilmenite breakdown due to the following
reaction:
2FeTiO3 →2TiO2 þ 2Fe þ O2
Experimental studies revealed that ilmenite could not coexist with
rutile and remain stable at high temperatures as they react to form
FeTi2O5 (Fig. 3), a mineral in the pseudobrookite solid solution series
(MacChesney and Muan, 1959; Buseck and Keil, 1966). During cooling
pseudobrookite decomposes to rutile + ilmenite at and below 1140 ±
10 °C (Lindsley, 1965), indicating that the mineral assemblage observed in the Farmington meteorite formed below that temperature
(Buseck and Keil, 1966).
In the Vaca Muerta mesosiderite the rutile occurs together with
ilmenite and chromite, both in thin bands within ilmenite (Kimura et
al., 1991) and in fine lamellae in chromite, as well as in individual
grains of up to 65 μm in diameter (Buseck and Keil, 1966). Nazarov et
al. (2002) reported rutile from the Dhofar 303 lunar highland
meteorite. El Goresy (1971) described Nb-rich rutile from the Toluca
iron meteorite in both silicate-bearing and silicate-free sulphide
inclusions. Later, Harper (1996) also analysed niobian rutiles from this
meteorite and discovered formerly live 92Nb, which forms in supernovae by p-processes (Harper, 1996) and decays by electron capture
to 92Zr with a half-life of about 36 Ma (Nethaway et al., 1978).
Extraterrestrial rutile may therefore bring quantitative data for the
initial abundance of short-lived, now extinct, radionuclides (e.g. 92Nb)
in the solar system's parental molecular cloud, which has been the
subject of recent discussion (Schönbächler et al., 2002, 2005; Wadhwa
et al., 2007, and references therein). The most interesting application
of short-lived radionuclides is their potential usage as fine-scale
chronometers to study processes in the early solar system (Harper,
1996; Wadhwa et al., 2007).
4. Applications of rutile in earth sciences
4.1. Rutile geochemistry
4.1.1. Introduction
Rutile is a major host mineral for Nb, Ta and other HFSE, which are
widely used as geochemical fingerprints of geological processes such
as magma evolution and subduction-zone metamorphism (e.g. Foley
et al., 2000; Rudnick et al., 2000). Although Nb/Ta values of crustal and
mantle rocks have been studied for a long time, processes that lead to
the fractionation of Nb and Ta and to the formation of the Earth's
hidden suprachondritic Nb/Ta reservoir are still the subject of a lively
debate, as outlined in Section 4.1.3.
Besides its application in igneous and metamorphic petrology,
rutile geochemistry can also be applied in sedimentary provenance
studies. Banfield and Veblen (1991) were one of the first who
suggested that rutile geochemistry may be useful in determining the
provenance of rutile. Nevertheless, until 2002, only a few papers
related to the mineral geochemistry of rutile and its application to
sedimentary provenance studies (Götze, 1996; Preston et al., 1998,
2002) were published. This was probably because of the lack of majorelement composition, in conjunction with a scarcity of rutile
geochemical data from potential source lithologies. For example,
Götze (1996) suggested that rutile with elevated concentrations of Sn
and W implies ore-bearing source rocks. Preston et al. (1998, 2002)
demonstrated that detrital rutile in Triassic continental red-beds in
the Beryl Field, North Sea, comprises almost pure TiO2, with only a
small proportion containing appreciable Nb2O5 or FeO.
More recently, however, rutile has attracted a lot of interest as new
studies have demonstrated the high potential of the trace-element
signature of rutile, including Zr-in-rutile thermometry, for characterising sediment source areas and hence for quantitative provenance
analysis, as will be shown in the following sections.
4.1.2. Fe content
The Fe content has been suggested to be an indicator of metamorphic origin since metamorphic rutile contains mostly N1000 ppm Fe
(Zack et al., 2004a). However, lamellae-rich regions in rutile can show
considerable Fe enrichment (Banfield and Veblen, 1991; Liou et al.,
1998; Sobolev and Yefimova, 2000). Therefore, careful examination of
rutile at the microscale is necessary to ensure that measurements
yielding elevated Fe contents were carried out in a homogeneous part
of the grain, as discussed in Section 2.3.
Banfield and Veblen (1991) recognised that the Fe content in rutile
generally increases with metamorphic grade, although they cautioned
that this observation needs further research to determine whether the
correlation is independent of whole-rock composition and other aspects
of metamorphic history. They suggested the potential of such a
correlation might be applicable as a thermometer in rocks that have
experienced temperatures less than 500 °C. However, rutile formed at
low temperatures (less than 450 °C, hydrothermal) also contains high
concentration (N0.5 wt.%) of Fe (Putnis, 1978; Putnis and Wilson, 1978;
Müller and Halls, 2005), which suggests that the Fe content cannot be
used to identify metamorphic rutile in heavy mineral separates.
Dawson and Smith (1977) assumed that their mica–amphibole–
rutile–ilmenite–diopside (MARID) group of xenoliths resulted from
crystallisation of an oxidised magma in the uppermost mantle, and
that all the Fe in rutile from these rocks is trivalent. Sobolev and
Yefimova (2000) noted that the Fe content in rutile from crustal and
mantle eclogites and diamond inclusions depends on whole-rock
composition, oxygen fugacity (fO2) and pressure and temperature
conditions. Hence, it is worthwhile to calculate the ferric Fe content of
rutile by either partitioning the measured total iron content into Fe2O3
and FeO using the stoichiometric method of Droop (1987) or by using
Mössbauer spectroscopy. The Fe+ 3 content is controlled by fO2 (e.g.
Buddington and Lindsley, 1964), and thus, presence of Fe+ 3 indicates
high fO2 during crystal growth. For example, many ultrahigh
temperature (UHT) terrains contain oxidised (high fO2) mineral
assemblages (Harley, 2008, and references therein). Zhao et al. (1999)
used fO2 as barometer for rutile–ilmenite assemblages in mantle
xenoliths from kimberlites.
4.1.3. Nb and Ta contents
Nb and Ta have the same oxidation state and nearly identical ionic
radii (Shannon, 1976; Tiepolo et al., 2000; Fig. 8) and thus should
remain tightly coupled during chemical processes within the crust–
mantle system. This should lead to relatively constant Nb/Ta ratios of
minerals and rocks, close to the chondritic value of about 17.65
(McDonough and Sun, 1995). However, continental crust, island arc
volcanic rocks and many oceanic basalts are characterised by
subchondritic Nb/Ta values (e.g. Green, 1995; Rudnick and Fountain,
1995; Rudnick et al., 2000; Foley et al., 2002; Schmidt et al., 2009). A
geochemically complementary reservoir is therefore required to
accommodate the mass imbalance in Nb and Ta between continental
crust and depleted mantle (McDonough, 1991; Rudnick et al., 2000).
The processes leading to major fractionation of Nb and Ta, and thus
to subchondritic Nb/Ta values, have been the subject of prolonged
debate because they are important for understanding the formation of
the continental crust (e.g. Foley et al., 2002; Xiao et al., 2006). As
outlined in Section 3.1, rutile is a major accessory mineral in eclogite,
which mainly forms by subduction of gabbroic or basaltic rocks to
great depths. During metamorphic recrystallisation, rutile crystallises
from Fe–Ti oxides and Ti-bearing silicates. It dominates the budget of
Nb and Ta in eclogite, and thus Nb/Ta of whole-rock eclogite reflects
this ratio in rutile (Rudnick et al., 2000; Zack et al., 2002). Experimental
studies by Brenan et al. (1994) have shown that a small amount of
rutile (∼0.2 wt.%) is enough to prevent HFSE enrichment in the mantle
wedge by fluids generated during subduction zone metamorphism.
Thus, rutile has long been regarded as a major factor controlling the
slab-to-mantle flux of HFSE (e.g. Brenan et al., 1994; Green, 1995).
Subchondritic Nb/Ta of the continental crust and island arc volcanic
rocks has been ascribed to melting of subducted slabs in the presence
of rutile (e.g. Rudnick et al., 2000). Rudnick et al. (2000) suggested that
refractory eclogite produced by slab melting is the “missing reservoir”
to accommodate the mass imbalance in Nb/Ta between continental
crust and depleted mantle. This reservoir possibly exists in the Earth's
deep mantle (Rudnick et al., 2000). Alternatively, it may be in the
Earth's core (Wade and Wood, 2001).
Experimental studies on the partitioning of Nb and Ta between
rutile and melts have shown that rutile favors Ta over Nb (e.g. Foley et
al., 2000, 2002; Klemme et al., 2005). Consequently, partial melting of
subducted rutile-bearing eclogite with chondritic Nb/Ta results in
melts with suprachondritic Nb/Ta and a residue depleted in Nb that
cannot be the “missing reservoir” with suprachondritic Nb/Ta (e.g.
Foley et al., 2002; Klemme et al., 2005).
Xiao et al. (2006) studied Nb and Ta in eclogites from the Dubi–Sulu
UHP metamorphic belt in east-central China and suggested the
following model: During the early stage of subduction, hotter regions
of the subducting slab will experience significant dehydration in the
presence of amphibole and absence of rutile (b15 kbar; Fig. 10), which
leads to suprachondritic Nb/Ta in the residual amphibole eclogites
with complementary subchondritic Nb/Ta in the released fluids. A
large proportion of these fluids (containing Nb, Ta, Ti, etc.) can be
retained in cold regions inside the subducting slab, forming hydrated
cold eclogites with subchondritic Nb/Ta. Subduction continues and the
slab, consisting of these hydrated cold eclogites, reaches greater
depths where rutile finally appears (N15 kbar; Fig. 10) and controls the
Nb and Ta budget. Thus, melting of these hydrated cold eclogites will
form magmas with negative Nb and Ta anomalies and subchondritic
Nb/Ta values. Because early-dehydrated slab with suprachondritic Nb/
Ta rations cannot be melted, refractory residual eclogites have highly
variable Nb/Ta from subchondritic to suprachondritic (Xiao et al.,
2006). Nonetheless, Xiao et al. (2006) suggested that they form the
geochemically complementary reservoir to the continental crust since
their overall average Nb/Ta is suprachondritic.
4.1.4. Cr and Nb contents
Zack et al. (2002, 2004b) suggested that Cr and Nb abundances in
rutile (Fig. 11a) can effectively distinguish between metamafic and
metapelitic source lithologies. For simplification, Triebold et al. (2007)
introduced log(Cr/Nb) values to discriminate between metamafic and
metapelitic source lithologies (“1:1” line; Fig. 11b). This method is
applicable except for low Cr and low Nb contents. Based on literature
data of Nb/TiO2 ratios of whole rock for pelites, Zack et al. (2002,
2004b) calculated that rutile in metapelites contains 900–2700 ppm
Nb. Combined with reference data, Meinhold et al. (2008) proposed
that the lower limit of Nb in metapelitic rutiles should be set at
800 ppm and that the discriminant boundaries between metamafic
and metapelitic source lithologies should therefore be modified as
shown in Fig. 11c. Rutiles with Cr b Nb accompanied by Nb N 800 ppm
are interpreted to be derived from metapelitic rocks (e.g. mica-schists,
11
Fig. 11. Nb versus Cr discrimination diagrams for rutile from different metamorphic
lithologies. (a) According to Zack et al. (2004b). Note that rutile from felsic granulite
facies rocks can have exceptionally high Nb contents up to 28,000 ppm and more.
(b) According to Triebold et al. (2007). Positive log(Cr/Nb) values mostly indicate a
metamafic source for rutile while negative values suggest derivation from metapelitic
rocks. (c) According to Meinhold et al. (2008). Note that Zack et al. (2002, 2004b)
introduced the terms “metamafic” and “metapelitic” to discriminate the rutile source,
although, for simplification, it seems more appropriate to use the terms “mafic” and
“felsic” respectively.
paragneisses, felsic granulites). Rutiles with Cr N Nb and those with
Cr b Nb, the latter however accompanied by Nb b 800 ppm, are
interpreted to be derived from metamafic rocks (e.g. eclogites and
mafic granulites). Rutiles from amphibolites plot in both fields
because the protoliths of amphibolites are of either sedimentary or
mafic igneous origin.
4.1.5. Other trace elements
Smythe et al. (2008) noted that Mg and Al contents distinguish
rutile derived from crustal and mantle sources (Fig. 12), and Al, Cr and
Nb contents further allow distinction between various mantlederived rocks such as eclogite, metasomatic rutile-dominated nodules
and mica–amphibole–rutile–ilmenite–diopside (MARID: Dawson and
12
Table 2
List of natural rocks containing rutile with economically important elements (compiled
from Williams and Cesbron, 1977; Scott, 1988; Urban et al., 1992; Clark and WilliamsJones, 2004; Scott, 2005). For example, elevated concentrations of W and Sb in rutile
strongly suggest a source from a mesothermal gold deposit (see Fig. 13). The V content
in rutile can be used as a guide to mineralisation even in highly weathered rocks (Scott,
2005). Geochemical data of rutile from ancient and modern clastic sedimentary rocks
can therefore provide useful fingerprints to identify the type of mineralisation.
Fig. 12. Discrimination between rutile derived from crustal and mantle sources,
according to Al and Mg contents in rutile (after Smythe et al., 2008).
Smith, 1977) xenoliths. Magnesium is one of the least compatible
elements in rutile (see Fig. 8). Therefore, Mg-rich rutile is most likely
to be found under HP and UHP conditions and hence in mantle rocks.
Moreover, rutile from mantle rocks (e.g. diamondiferous eclogite) can
contain an elevated Al content, which can be explained by a number of
tiny rods of corundum (Sobolev and Yefimova, 2000). These rods are
smaller than the electron beam size a mixture of them and rutile is
analysed.
Besides the major discriminants, Cr and Nb, there are also other
trace elements that can characterise the source of rutile. For example,
when elements such as V, Ni, Cu, Sn, Sb and W are detected in high
concentration in rutile, they can be considered to be anomalous and
suggest a source from metallic ore deposits (e.g. Urban et al., 1992;
Clark and Williams-Jones, 2004; Scott, 2005) (Fig. 13). For instance,
rutile from mesothermal gold mineralisation commonly contains
between 0.12 and 5.9 wt.% WO3. Table 2 shows a compilation of
various rutile-bearing deposits and the characteristic trace elements
incorporated into the rutile crystal lattice.
4.1.6. Examples
As outlined in Section 4.1.3, Nb and Ta concentrations in rutile
allow tracing the formation and evolution of the continental crust.
Hence, a large number of publications exists discussing Nb and Ta
values and Nb/Ta ratios of crustal and mantle rocks and the Earth's
Fig. 13. Summary of Ti, Fe, Cr, V and W contents of rutile from variably metamorphosed
mesothermal gold deposits (after Clark and Williams-Jones, 2004).
Type of deposit
Characteristic elements in rutile
Volcanogenic massive sulphide Cu–Zn deposits
Mesothermal and related gold deposits
Magmatic–hydrothermal Pd–Ni–Cu deposits
Granite-related Sn deposits
Granite–pegmatite Sn–W deposits
Porphyry and skarn Cu and Cu–Au deposits
Sn (W and/or Cu)
Sb, W and/or V
Ni, Cu
Sn, W
Sn, W, Nb, Ta
Cu, W (and sometimes V)
hidden suprachondritic Nb/Ta reservoir. Here, the reader is referred to
a selection of recent literature for further information (e.g. Xiao et al.,
2006; Aulbach et al., 2008; Baier et al., 2008; Bromiley and Redfern,
2008; Schmidt et al., 2009).
Since the work of Zack et al. (2004b), rutile geochemical
constraints on sediment provenance have been included in several
publications related to sedimentary strata from the Neoproterozoic to
the Holocene worldwide.
Stendal et al. (2006) used rutile geochemistry to establish that the
rutiles in young alluvial and eluvial heavy mineral deposits of the
Yaoundé region in southern Cameroon were derived from the
adjacent Neoproterozoic micaschists of the Yaoundé Group.
Triebold et al. (2007) analysed detrital rutile from Early Palaeozoic
metasedimentary rocks and Holocene river sediments of the Erzgebirge, Germany. They demonstrated that rutile compositions in river
sediments mirror those of the surrounding country rocks. This led
them to conclude that rutile is an accurate tracer of source rock
characterisation in sedimentary provenance studies.
Uher et al. (2007) analysed niobium–tantalum mineral assemblages (including Nb–Ta-rich rutile) from alluvial placer deposits in
southwest Slovakia, which were most likely sourced from granitic
pegmatites of the Bratislava Granitic Massif.
Meinhold et al. (2008) investigated detrital rutile from Carboniferous to Early Triassic sandstones of Chios Island, Greece. They
recognised a change in source rock lithology from the Carboniferous
with dominantly metamafic rutile to the Early Triassic with more
metapelitic rutile. Zr-in-rutile thermometry has confirmed this
change in the sediment source, which was explained by plate-tectonic
reorganisation during the subduction of Palaeotethys at the southern
margin of Laurussia in the Late Palaeozoic (Meinhold et al., 2008).
Morton and Chenery (2009) studied the rutile source of Jurassic to
Palaeocene sandstones in hydrocarbon exploration wells of the
Norwegian Sea. Their rutile data confirm the presence of five distinct
sand types sourced from different parts of the Norwegian and
Greenland landmasses to the east and west of the basin, established
by previous studies, concentrating on provenance-sensitive heavy
mineral ratios, garnet geochemistry, tourmaline geochemistry and
detrital zircon geochronology (Morton and Chenery, 2009). Moreover,
these authors demonstrated the importance of rutile geochemistry as
a provenance tracer, since the method yields diagnostic data on
source rock lithology and metamorphic facies even in highly modified
sandstones that may have lost significant amounts of provenance
information. This is because of the ultrastable nature of rutile under
both diagenetic and surficial weathering conditions (Pettijohn, 1941;
Hubert, 1962; Morton and Hallsworth, 1999, 2007).
Although the successful application of rutile geochemistry to
single-mineral provenance studies has been shown above, there are at
least two publications that clearly demonstrate that the discrimination diagrams based on Cr and Nb may not be strictly valid. BakunCzubarow et al. (2005) pointed out that the Cr–Nb discrimination
diagram of Zack et al. (2002, 2004b) is not applicable for rutile from
the Sudetes Fe–Ti-rich eclogites, which plot in the metapelite field.
Rutiles from eclogite of the ultrahigh-pressure metamorphic area at
the Saidenbach reservoir of the Erzgebirge in Germany (Massonne,
2001) also plot in the field of metapelitic source lithologies (Triebold
et al., 2007; their fig. 5). Based on whole-rock geochemical data,
Massonne and Czambor (2007) suggested that the protoliths of the
Saidenbach eclogites were basaltic to trachyandesitic in composition
and formed in a within-plate geotectonic setting with a relatively low
degree of melting. The Saidenbach eclogites have high Nb/Ti ratios.
Rutile dominates the Nb and Ti budget in eclogites, and rutiles in the
Saidenbach eclogites inevitably have high Nb concentrations, and
thus, they plot in the field for metapelitic rutile. Despite these
shortcomings, the Cr–Nb discrimination diagram, as it stands now, is
useful and should be applied in sediment provenance analysis until
more rutile data of various source rock lithologies are available to
place better constraints on its discrimination boundaries.
4.2. Zr-in-rutile thermometry
4.2.1. Introduction
The partitioning of zirconium (Zr) into rutile coexisting with
zircon or other Zr-rich phases has a strong dependence on
temperature (T) (Zack et al., 2004a; Watson et al., 2006; Tomkins et
al., 2007). Zack et al. (2004a) were the first presenting an empirically
calibrated Zr-in-rutile thermometer (Fig. 14), expressing temperature
as:
T ðBCÞ = 127:8 × ln Zrppm −10
with an error of ±50 °C. The calibration is based on analyses of rutile
grains from 31 metamorphic rocks with rutile–quartz–zircon assemblages spanning a temperature range from 430 to 1100 °C.
Watson et al. (2006) presented a revised Zr-in-rutile thermometer
based on experimental data (at ∼10 kbar) and constrained by natural
rutiles from metamorphic rocks (Fig. 14), expressing temperature as:
T ðBCÞ =
4470
Zrppm −273
7:36− log10
with an error of ±20 °C. The two thermometers intersect at a temperature of about 540 °C but diverge significantly both at lower and
higher temperatures (Fig. 14). Watson et al. (2006) considered this
behaviour to indicate possible pressure dependence and emphasised
the need for further investigation.
Fig. 14. Comparison of Zr-in-rutile thermometers of Zack et al. (2004a), Watson et al.
(2006) and Tomkins et al. (2007). For the latter thermometer, only calculations at 10,
30 and 60 kbar are shown.
13
Ferry and Watson (2007) suggested that the Zr content of rutile
depends on the activity of SiO2 as well as temperature, which had
been confirmed by experimental data. This observation let them to
conclude that the Zr-in-rutile thermometer may now be applied to
rocks without quartz, if the activity of SiO2 is estimated. The
maximum introduced uncertainty by unconstrained activity of SiO2
was given with about 60–70 °C at 750 °C (Ferry and Watson, 2007).
The new calibration of the Zr-in-rutile thermometer is remarkably
similar to that described by Watson et al. (2006). Ferry and Watson
(2007) gave examples showing that the Zr contents of rutile that
record 1100, 750 and 500 °C using the thermometer of Watson et al.
(2006) record 1093, 750 and 502 °C with the revised calibration for an
activity of SiO2 = 1. Ferry and Watson (2007) also gave a preliminary
evaluation of the dependence of Zr-in-rutile thermometers on
pressure.
Tomkins et al. (2007) discussed the pressure dependence, already
emphasised by Watson et al. (2006), and presented three new Zr-inrutile thermometers based on experimental data (Fig. 14). They
clearly demonstrate that pressure, especially ultrahigh pressure (see
also discussion in Chen and Li, 2008), does have an effect on the
uptake of Zr in rutile. The new thermometer equations by Tomkins et
al. (2007) are, in the α-quartz field
T ðBCÞ =
83:9 + 0:410 × P
−273
0:1428−R × ln Zrppm
in the β-quartz field
T ðBCÞ =
85:7 + 0:473 × P
−273
and in the coesite field
T ðBCÞ =
88:1 + 0:206 × P
−273
with P in kbar, and R is the gas constant, 0.0083144 kJ K− 1. An obvious
input parameter in their equation is the pressure. Hence, this
thermometer is suitable for rutiles of known source, meaning of
known pressure during rutile crystallisation. For detrital rutile,
however, the pressure under which the source rock had formed is
commonly unknown. To avoid speculation about the input parameter
‘pressure’, the equation of Watson et al. (2006) should be used for
detrital rutile or for rutile of unknown origin in general. Although it
was originally thought that the Zr-in-rutile thermometer is only valid
for metapelitic rutile (Zack et al., 2004a), recent studies have
demonstrated that it is also valid for rutile from metamafic lithologies
(e.g. Zack and Luvizotto, 2006; Triebold et al., 2007) and for detrital
metamafic rutile (e.g. Meinhold et al., 2008; Morton and Chenery,
2009).
Chen and Li (2008) have shown that the Zr-in-rutile thermometers
by Watson et al. (2006) and Tomkins et al. (2007) yield similar shapes of
the frequency histograms of temperatures (Fig. 15). However, the Zr-inrutile thermometer of Watson et al. (2006) gives about 70 °C lower
temperatures compared with the Zr-in-rutile thermometer of Tomkins
et al. (2007) for eclogitic rutile from the central Dabie UHP metamorphic
zone. The thermometer of Zack et al. (2004a) shows a wider spread in
the frequency histograms of temperatures. The differences in shape and
range of the frequency histograms of temperatures reflect the different
approaches of the various Zr-in-rutile thermometers to calculate the
temperature. Hereby, the pressure dependence of Zr incorporation into
the rutile crystal lattice is an important factor to be considered, which is
well illustrated in Fig. 14. The thermometers of Zack et al. (2004a) and
Watson et al. (2006) intersect at a temperature of about 540 °C
but diverge significantly both at lower and higher temperatures. The
14
thermometer of Tomkins et al. (2007) with overestimation of the
maximum temperature point for the Zack et al. (2004a) empirical
calibration.
In general, overestimation of temperature with Zr-in-rutile
thermometry is only possible where mineral assemblages in equilibrium with rutile are quartz-free while underestimation can occur by
absence of zircon and/or in partly reset mineral assemblages (Zack et
al., 2004a; Baldwin and Brown, 2008; Harley, 2008; Luvizotto and
Zack, 2009). Although Tomkins et al. (2007) noted that “Zr-in-rutile
thermometry is not going to be a magic bullet in thermometry”,
clearly it is an attractive method to calculate temperatures of highgrade and ultrahigh-grade metamorphic rocks (Spear et al., 2006;
Zack and Luvizotto, 2006; Miller et al., 2007; Baldwin and Brown,
2008; Harley, 2008; Luvizotto and Zack, 2009). In the case of detrital
rutile, Zr-in-rutile thermometry is an important technique in
sediment provenance analysis especially in highly modified sandstones that may have lost significant amounts of provenance
information (Morton and Chenery, 2009).
Fig. 15. Frequency histograms (bin width = 25 °C) showing calculated formation
temperatures for eclogitic rutile from the central Dabie UHP metamorphic zone with
data from Chen and Li (2008). Abbreviations TZ, TW and TT correspond to the Zr-in-rutile
thermometers of Zack et al. (2004a), Watson et al. (2006) and Tomkins et al. (2007)
respectively. TZ was calculated from Eq. (3) in Zack et al. (2004a); TT was calculated at
28 kbar. Besides histograms, some statistical parameters are also given. n — number of
data used, Min — minimun value, Max — maximum value, Med — Median, Avg — average
(arithmetic mean), Std — Standard deviation (1σ), Sk — Skewness, Ku — Kurtosis.
thermometer of Watson et al. (2006) gives nearly identical results to the
thermometer of Tomkins et al. (2007) using the α-quartz equation at
10 kbar, which is the pressure at that the Zr-in-rutile thermometer of
Watson et al. (2006) was experimentally calibrated. In the temperature
range between 750 °C and 1150 °C the thermometer of Zack et al.
(2004a) yields comparable results to the Tomkins et al. (2007) coesitefield equation at 30 kbar. Nonetheless, the thermometer of Zack et al.
(2004a) shows a wider spread in the frequency histograms of
temperatures (Chen and Li, 2008; Meinhold et al., 2008) which supports
the use of the Zr-in-rutile thermometer of Watson et al. (2006) for
sediment provenance studies of detrital rutile. Baldwin and Brown
(2008) explain the trend that the Zr-in-rutile thermometer of Zack et al.
(2004a) always gives a higher temperature than, for instance, the
4.2.2. Examples
The reliability of the new Zr-in-rutile thermometers of Zack et al.
(2004a) was demonstrated, for example, for eclogites and granulites
from the Sudetes of SW Poland (Bakun-Czubarow et al., 2005) and for a
wide variety of eclogites from Germany, Greece, Italy, Norway,
Switzerland and Turkey (Zack and Luvizotto, 2006). Spear et al. (2006)
showed the successful application of the Watson et al. (2006) calibration
on blueschist facies rocks from Sifnos Island, Greece and Vaggelli et al.
(2007) on high-pressure rocks from the Western Alps, Italy.
Zack et al. (2004b) first applied the combined use of detrital rutile
geochemistry and Zr-in-rutile thermometry for quantitative sediment
provenance analysis. Subsequent studies by Triebold et al. (2007) and
von Eynatten et al. (2005) have demonstrated that the trace element
composition of detrital rutile is unrelated to the grain size of the host
sediment. They furthermore revealed that high-grade metamorphic
rutile might preserve its geochemical signature to much lower
temperatures, suggesting that rutile may survive metamorphic conditions on a retrograde path below 550 °C. Stendal et al. (2006) have also
shown that relic rutile can retain its original composition during low- to
medium-grade metamorphism, indicating that it can survive temperatures as high as 620 °C. Thus, the generally accepted views of rutile
breakdown during low-grade metamorphism at greenschist facies and
formation during medium-grade metamorphic conditions (Force, 1980;
Zack et al., 2004b) may not be strictly valid. Luvizotto et al. (2009a) who
recognised prograde rutile growth from ilmenite in low- to mediumgrade metasedimentary rocks of the Erzgebirge, Germany, as outlined in
Section 3.1, have recently addressed this subject.
Meinhold et al. (2008) compared results obtained by using the Zrin-rutile thermometers of Zack et al. (2004a) and Watson et al. (2006)
on detrital rutile from Carboniferous to Early Triassic sandstones of
Chios Island, Greece. They demonstrated the discrepancy between
both thermometers, with the Zr-in-rutile thermometer of Zack et al.
(2004a) giving a wider spread in the frequency histograms of
temperatures compared with the thermometer of Watson et al.
(2006), which was also pointed out by Chen and Li (2008), as discussed
in Section 4.2.1.
Morton and Chenery (2009) successfully used Zr-in-rutile thermometry to characterise the rutile source of Jurassic to Palaeocene
sandstones in hydrocarbon exploration wells of the Norwegian Sea,
accompanied with application of rutile geochemistry, as outlined in
Section 4.1.6.
Note that for provenance identification of detrital rutile the
possibility of polyphase recycling has to be kept in mind.
4.2.3. Zr diffusion
Cherniak et al. (2007b) studied the Zr diffusion in natural and
synthetic rutile and provided evidence that Zr concentrations in rutile
15
juvenile mantle-derived magmas, which contrast with those from
“contaminants” that experienced low temperature and surficial process
such as hydrothermal alteration and sedimentary recycling and hence
have elevated δ18O values (e.g. Mojzsis et al., 2001; Wilde et al., 2001;
Valley, 2003; Valley et al., 2005). The isotopes used are 18O and 16O,
which are incorporated into the lattice during crystallisation. In current
studies, oxygen isotope analyses on minerals are commonly performed
by secondary ion mass spectrometry (SIMS) (e.g. Valley, 2003) and
various laser techniques (e.g. Li et al., 2003; Valley, 2003; Zhang et al.,
2006). The O isotope composition of a mineral is reported in delta
notation (δ18O) relative to VSMOW (Vienna Standard Mean Ocean
Water), which has an 18O/16O value of (2005.2 ±0.45) × 10− 6 (Gononfiantini, 1978). The corresponding equation is as follows:
2
3
16
O= O
3
sample
6
7
−15 × 10
δ O = 418 16 O = O VSMOW
18
18
Fig. 16. Zr centre-retention criteria for rutile of different radii cooling at a linear rate
from a range of maximum temperatures (after Cherniak et al., 2007b). The critical
cooling rate depends on the maximum temperature, grain radius and diffusion
parameters. When cooling rates are slower than this critical value, the peaktemperature Zr signature in the centre of a rutile grain is not preserved over the
cooling path. For illustration purposes, the field of ultrahigh-temperature (UHT)
metamorphism (Harley, 1998) is marked in grey.
can be affected by later thermal disturbance, although, based on
observations made by Watson et al. (2006), this is not likely to be as
rapid as Sasaki et al. (1985) suggested. Cherniak et al. (2007b) pointed
out that Zr diffusion in rutile is significantly slower than diffusion of
divalent and trivalent cation substitutions and seems little affected by
variations in trace element composition. The authors, however, made
a cautionary remark that under a broad range of geological conditions,
the Zr-in-rutile thermometry is less resistant to resetting than Ti-inzircon and Zr-in-titanite thermometry. They demonstrated that Zr
diffusion in rutile depends on the grain size and the cooling rate
(Fig. 16). For example, a rutile grain formed under ultrahightemperature (UHT) metamorphic conditions at about 945 °C with a
grain radius of 500 μm will preserve its Zr signature in the centre of
the grain when the cooling rate exceeds 100 °C Ma− 1. Hence, rutile
formed under UHT conditions will retain its Zr signature only under
certain circumstances such as rapid cooling (Cherniak et al., 2007b;
Fig. 16). Therefore, UHT source lithologies may be underestimated in
sedimentary provenance studies with Zr-in-rutile thermometry. Chen
and Li (2008) analysed eclogitic rutile from the Dabie–Sulu UHP
metamorphic zone in east-central China and suggested that retrogression (with fluid presence) can release Zr from the rutile crystal
lattice. This consequently causes lower calculated temperatures and
does not provide the peak metamorphic temperature. Luvizotto and
Zack (2009) observed large spreads in Zr concentrations for rutile
grains from granulite facies metapelitic rocks of the Ivrea–Verbano
Zone, Southern Alps, which they explained by Zr mobilisation due to
slow cooling rates and/or fluid presence. All these points have to be
kept in mind when using Zr-in-rutile thermometry.
with δ18O values in per mil (‰).
Experimental studies by Moore et al. (1998) on synthetic and
natural rutile have shown that the closure temperatures for O
diffusion in rutile are high (Fig. 17), with about 650 °C for a crystal
with a 100-μm radius and a cooling rate of 10 °C Ma− 1. That means a
rutile crystal with a 100-μm radius loses its initial core composition
only after heating at 600 °C for just over 10 Ma. Moore et al. (1998)
finally concluded that rutile retains its O isotope composition during a
wide range of thermal events.
Various minerals effectively fractionate the O isotopes. As for all
stable isotopes, this fractionation process is a strong function of
temperature and is time-independent. For example, quartz, calcite and
albite more strongly partition 18O while diopside, hornblende, zircon,
almandine and rutile more strongly partition 16O (Matthews et al.,
1979; Chacko et al., 1996; Moore et al., 1998, and references therein).
Fig. 18 demonstrates the O isotope fractionation in a coesite-bearing
eclogite of the Dabie Mountains, with δ18O values of about +1.1‰ for
quartz, − 2.3‰ for garnet and −6.1‰ for rutile (Li et al., 2003). A
compilation of literature data reveals that eclogitic rutile shows δ18O
values from − 8.9 to + 7.1‰, with values from 3.6 to 8.0‰ for oxygen
isotope fractionation between quartz and rutile (Fig. 19). Fig. 20
compares the quartz–rutile geothermometers of Agrinier (1991),
Zheng (1991) and Chacko et al. (1996). Quartz–rutile geothermometry
is a reliable method because both minerals are relatively resistant to
post-formation oxygen exchange (Agrinier, 1991; Chacko et al., 1996).
4.3. Oxygen isotopes
4.3.1. Introduction
The oxygen (O) isotope composition of minerals can yield information regarding the extent and nature of fluid–mineral interactions and
the temperature at the time of crystallisation or alteration (e.g. Matthews
et al., 1979; Agrinier, 1991; Zheng, 1991; Chacko et al., 1996; Moore et al.,
1998; Zheng et al., 1999, 2003). Many studies have shown that O isotopes
are a good fingerprint to identify the derivation of certain minerals from
Fig. 17. Dependence of the closure temperature for O isotope exchange in rutile from
crystal size and cooling rate (after Moore et al., 1998).
16
Fig. 18. Oxygen isotope composition of garnet, quartz and rutile from a coesite-bearing
eclogite of the Dabie Mountains. Data were taken from Li et al. (2003).
Quartz–rutile geothermometry yields reliable temperatures for blueschist and eclogite facies rocks but may not work for granulite facies
rocks due to extensive re-equilibration (Chacko et al., 1996).
4.3.2. Examples
Vogel and Garlick (1970) analysed the O isotope composition of
various minerals, amongst others rutile and quartz, from eclogites in
Europe, Venezuela and California, and they pointed out that O isotope
fractionations between quartz and rutile are relatively large. Thus, the
quartz–rutile pair is particularly suitable for geothermometry because
analytical errors involved in the determination of δ18O values would
Fig. 20. Comparison of the quartz–rutile oxygen isotope geothermometers of Agrinier
(1991), Zheng (1991) and Chacko et al. (1996).
not lead to large errors in the calculated isotope temperatures
(Matthews et al., 1979). Hence, Addy and Garlick (1974) and
Matthews et al. (1979) carried out experimental studies of O isotope
fractionation between rutile and water and tested their quartz–rutile
geothermometers on a number of eclogites. Desmons and O'Neil
(1978) reported O isotope data of various minerals from eclogites of
the Western Alps, Italy, and calculated for these eclogites an average
formation temperature of 540 °C, using quartz–rutile and quartz–
phengite geothermometry. Studies by Agrinier et al. (1985) have
shown that in eclogites of the WGR, Norway, the O isotope
fractionation between rutile and quartz is small (Δ18O ∼ 4.3–5.0‰),
with quartz–rutile geothermometry yielding formation temperatures
of about 680 to 715 °C. Zheng et al. (1999) analysed the O isotope
composition of various minerals (i.a. rutile and quartz) from HP and
UHP eclogites of the Dabie Mountains and calculated formation
temperatures using amongst others quartz–rutile geothermometry.
Quartz–rutile pairs from some of the eclogites yielded isotope
temperatures lower than the temperatures of eclogite facies metamorphism, suggesting O isotope exchange due to retrograde fluid–
rock interaction (Zheng et al., 1999). Li et al. (2003) used O isotope
analysis of rutile to test the validity of rutile U–Pb isochron dating on
coesite-bearing eclogite from the Dabie Mountains. They determined
almost identical δ18O values for different rutile grains from the same
specimen (Fig. 18), which suggests attainment of O isotope homogenisation in rutile during eclogite facies metamorphism and preservation during amphibolite facies retrograde metamorphism (Li et al.,
2003). Gao et al. (2006) also studied the O isotope composition of
mineral pairs in eclogite from the Dabie Mountains, with the quartz–
rutile pair yielding an isotope temperature of 530 °C. Chen and Li
(2008) emphasised the potential of quartz–rutile geothermometry to
place constraints on rutile U–Pb cooling ages since O diffusion in rutile
is similar to that of Pb under hydrous conditions (Moore et al., 1998;
Cherniak, 2000).
4.4. U–Pb geochronology
Fig. 19. Cross plot showing δ18O values of rutile and quartz–rutile fractionation values
in various eclogites (n = 38). The frequency histogram (bin width = 0.5‰) shows the
distribution of quartz–rutile fractionation values. Data were taken from Vogel and
Garlick (1970), Desmons and O'Neil (1978), Matthews et al. (1979), Agrinier et al.
(1985), Zheng et al. (1999), Li et al. (2003) and Gao et al. (2006). The terms ‘hot’ and
‘cold’ refer to the temperature conditions during eclogite facies metamorphism, based
on quartz–rutile geothermometry. Note that a number of samples from the ‘cold’
eclogite suite experienced retrograde isotope exchange subsequent to the eclogite
facies metamorphism (see Section 4.3.2).
4.4.1. Introduction
Rutile typically contains between 3 and 130 ppm of uranium
(Mezger et al., 1989) (Table 3; Fig. 21), but higher concentrations also
occur, making Pb–Pb and U–Pb dating possible (e.g. Mezger et al.,
1989, 1991; Möller et al., 2000; Vry and Baker, 2006). Radiometric
dating of rutile is based on the occurrences of unstable (radioactive)
uranium isotopes 238U and 235U incorporated into the rutile crystal
structure, which decay over several stages (decay chain) into stable
daughter lead isotopes 206Pb and 207Pb, respectively (Jaffey et al.,
1971; Table 4). By measuring the parent/daughter ratios and known
Table 3
U values (in ppm) for rutile from different source lithologies compiled from literature.
Note that the lowermost concentrations for U (minimum values) are defined by the
detection limit of the technique applied for analysis. Felsic granulite comprises here
granulite and granulite facies gneiss. Quartz vein data are mainly from eclogite facies
quartz veins (n = 75), supplemented by low-temperature (hydrothermal) quartz vein
mineralisation (n = 9) and a single granitic pegmatite vein sample (n = 1).
Felsic granulite
Eclogite
Quartz vein
Metasediment
Table 4
Half-life and decay constant values of parent–daughter pairs of uranium and thorium
(data from Jaffey et al., 1971; Stacey and Kramers, 1975).
Isotope decay
U → 206Pb + 84He + 6β−
U → 207Pb + 7 4He + 4β−
232
Th → 208Pb + 6 4He + 4β−
238
235
n
Min
Max
Med
Avg
Std
Ref
185
0.01
390
19
24
33
(1)
91
0.01
170
1
5
22
(2)
85
0.15
176
7
9
19
(3)
40
0.70
143
10
21
27
(4)
Abbreviations: n — number of data, Min — minimum value, Max — maximum value,
Med — Median, Avg — average (arithmetic mean), Std — Standard deviation (1σ). Ref —
References: (1) Mezger et al. (1989, 1991), Romer and Rötzler (2001), Luvizotto and
Zack (2009); (2) Zack et al. (2002), Li et al. (2003), Schärer and Labrousse (2003), Xiao
et al. (2006), Gao et al. (2007), Miller et al. (2007), Kylander-Clark et al. (2008); (3)
Richards et al. (1988), Uher et al. (1998), Franz et al. (2001), Xiao et al. (2006), Gao et al.
(2007), Kylander-Clark et al. (2008); (4) Mezger et al. (1989, 1991), Corfu et al. (1994),
Möller et al. (1995, 2000), Bibikova et al. (2001), Zack et al. (2002), Luvizotto et al.
(2009a).
decay constants, it is possible to calculate the age when rutile cooled
below its “blocking” or closure temperature. The latter is around
600 °C for rutile grains larger than about 0.2 mm in diameter
(Cherniak, 2000; Vry and Baker, 2006), which is much higher than
previously thought (370–500 °C: Mezger et al., 1989). The mathematical expression to determine the age of a rutile sample, as applied
to any closed system, is given as:
t=
1
D
ln 1 +
λ
P
where t is the elapsed time, λ the decay constant of the parent isotope,
ln the natural logarithm, D the number of atoms of the daughter
isotope in the sample, and P the number of atoms of the parent isotope
in the sample.
Fig. 21. Box and whisker plots showing U values for rutile from different source
lithologies. The box represents the middle 50%; the bar inside the box represents the
median. ‘Outliers’ are represented by black rectangles. n — number of data used. See
Table 3 for references. Although included in the calculation, note that for illustration
purpose the high U value of 390 ppm of a single granulite facies rutile grain is not
shown here.
17
Half-life value
Decay constant
t1/2
(yr)
λ
(yr− 1)
4.4683 × 109
0.70381 × 109
14.01 × 109
1.55125 × 10− 10
9.8485 × 10− 10
0.49475 × 10− 10
Measurements to determine the required parent/daughter ratios are
performed by conventional isotope dilution-thermal ionisation mass
spectrometry (ID-TIMS), secondary ion mass spectrometry (SIMS), of
which the sensitive high-resolution ion microprobe (SHRIMP) is an
example, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Rutile has some advantages compared with
zircon for U–Pb dating. Firstly, rutile from granulite facies rocks contains
almost no Th, allowing common lead correction via 208Pb (Allen and
Campbell, 2007; Zack et al., 2008; see also Ireland and Williams, 2003).
Secondly, the isotope composition of Pb in rutile is usually highly
radiogenic, and U–Pb ages are mostly concordant (Mezger et al., 1989,
1991; Mukasa et al., 1998; Möller et al., 2000; Bibikova et al., 2001).
Thirdly, rutile appears to be resistant to subsequent resetting of Pb
values (Vry and Baker, 2006).
Rutile has also some disadvantages compared with zircon for U–Pb
dating. Rutile usually has lower U contents compared with zircon.
Furthermore, there is a lack of large, isotopically homogeneous and
commonly available natural rutile standards to assess measurement
methods and demonstrate the quality of acquired geochemical data,
although this may change in the future (Luvizotto et al., 2009b).
Eclogitic rutile commonly has low U contents (Table 3; Fig. 21),
which in turn leads to low radiogenic Pb contents, and can contain a
relatively large proportion of common (nonradiogenic) Pb (Cherniak,
2000; Franz et al., 2001; Schärer and Labrousse, 2003). Therefore,
common Pb correction is important in age calculation, based on the
isotope composition of rutile in a single analysis (Cherniak, 2000; Li et
al., 2003). Correction for common Pb for the U–Pb data can be made
using the measured 238U/206Pb and 207Pb/206Pb ratios following TeraWasserburg (1972) as outlined, for example, in Williams (1998).
Further possibilities are the use of a Pb growth model (Stacey and
Kramers, 1975) and a numerical solution if measurement of 204Pb is
not possible (Andersen, 2002). Common Pb correction is also possible
by using Pb ratios obtained from leached K-feldspars or the host
whole-rock sample (e.g. Mezger et al., 1989). The latter method is
only applicable for rutile of known igneous or metamorphic host rocks
and not for detrital rutile. The problem of common Pb correction can
be avoided if there is the chance to construct an isochron (e.g. Schandl
et al., 1990; Li et al., 2003; Stendal et al., 2006). This, however, requires
analyses of a sufficient number of coexisting minerals with large U/Pb
fractionation (e.g. Mukasa et al., 1998; Li et al., 2003; Schärer and
Labrousse, 2003). Fig. 22 schematically illustrates the interpretation of
U/Pb ratios of rutile in the conventional (Wetherill) concordia plot
and in a U–Pb isochron diagram.
4.4.2. Examples
Radiometric dating of rutile has been successfully carried out for
more than two decades (e.g. Corfu and Andrews, 1986; Schärer et al.,
1986; Richards et al., 1988). For example, Mezger et al. (1989) applied
the rutile geochronometer to reconstruct the pressure–temperature
evolution of Archaean and Proterozoic high-grade polymetamorphic
terrains in North America. They recognised that within a single handspecimen larger rutile grains give older ages than do smaller ones and
explained this observation with volume diffusion directly related to
the dimensions of the rutile crystal. Mezger et al. (1989) furthermore
defined that at a cooling rate of about 0.5–1 °C Ma− 1 the closure
18
Fig. 22. (a) Conventional concordia plot after Wetherill (1956) illustrating the U–Pb
systematic of rutile for various stages of Pb loss. Assuming a simple two-stage history,
the upper concordia intercept of a best-fit line gives the crystallisation age of the rutile
while the lower intercept gives the age of isotopic disturbance. Discordance is
commonly caused by Pb loss due to radiation damage of the crystal structure. Schmitz
and Bowring (2003) and Kramers et al. (2009) discuss causes of Pb loss in detail.
(b) Schematic 238U/204Pb–206Pb/204Pb isochron diagram for a suite of co-genetic rutile
grains. For example, this method has successfully been applied by Li et al. (2003). In a
closed system, the 206Pb/204Pb ratios (y-axis) plotted against the 238U/204Pb ratios (xaxis) should ideally define a straight line, termed an ‘isochron’. This, however, is
normally not the case because of analytical uncertainties. Hence, the analytical errors
must be considered when the best-fit line through the analytical data points is
determined by least-squares regression techniques (York, 1967, 1969). The intercept
with the y-axis gives the initial 206Pb/204Pb ratio of the system (t = 0). The slope of the
best-fit line (regression line) yields the age of the co-genetic rutile grains. Note that the
interpretation of a Pb–Pb isochron diagram is more complex (e.g. Patterson, 1956).
temperature for U–Pb diffusion in rutile is about 420 °C for grains with
a radius of 90–210 μm and about 380 °C for grains with a radius of 70–
90 μm. The significance of these conclusions has been debated, as
discussed later in this section.
Romer and Rötzler (2001) analysed rutile grains from granulite
facies rocks of the Saxonian Granulite Massif. The grains had low
radiogenic Pb contents and yielded a broad range in apparent 206Pb/
238
U ages, which was interpreted by the authors as being due to initial
isotope heterogeneity. Franz et al. (2001) and Chen et al. (2005) had a
similar problem with eclogitic rutile from Dabie and Sulu respectively.
Heterogeneity of the initial Pb isotopic composition in combination
with the inability to make a sufficiently good common Pb correction
for each individual rutile U–Pb analysis will lead to ambiguous results.
Wong et al. (1991) used the ID-TIMS method to carry out U–Pb
isotope dating on rutile from Archaean greenstones and gold mineralisation in the Val d'Or region of Quebec. They determined a U–Pb age of
2684 ± 7 Ma, which overlaps within the analytical error with previous
40
Ar/39Ar ages on hornblende (2693 ± 17 Ma and 2672 ± 23 Ma) and
thus shows the successful application of U–Pb rutile dating. Hydrothermal rutile from the alteration zone around a quartz vein gave a Pb–Pb
isochron age of about 2600 Ma that was interpreted as the time of rutile
growth during vein emplacement and constrains the age of gold
mineralisation.
Bibikova et al. (2001) dated rutile from various rocks of the
Archaean domain of the Belomorian Belt and its junction zone with
the Karelian Protocraton of the Baltic Shield. The analysed rutiles gave
concordant U–Pb ages between 1740 and 1810 Ma and are about 50–
100 Ma younger than the coexisting titanite, with smaller age
difference in the junction zone and larger age difference in the main
body of the Belomorian Belt. The difference in U–Pb ages may reflect
different cooling histories of both units (see Bibikova et al., 2001 for
discussion).
Hirdes and Davis (2002) carried out a multigrain ID-TIMS analysis
of rutile from garnet-hornblende gneiss of southeastern Ghana. The
206
Pb/238U age of 576 ± 2 Ma corrected for common Pb is concordant
and was interpreted by them as a younger limit on metamorphism
when the cooling isograd passed through the closure temperature of
rutile.
Li et al. (2003) reported the first high-precision U–Pb age for
metamorphic rutile of about 218 Ma (ID-TIMS) from coesite-bearing
eclogite of the Dabie Mountains using conventional U–Pb dating and
the isochron dating method (see also Chen et al., 2006). They analysed
two colour types of rutile, light red and reddish brown, which showed
no systematic difference in the concentrations of U and Pb or of Pb
isotope ratios. In addition, they showed that omphacite in eclogite has
a low U/Pb ratio and thus suggested that the Pb composition of
omphacite can be used for common Pb correction in U–Pb dating of
rutile from eclogites.
Flowers et al. (2005) obtained 206Pb/238U ages of rutile (and titanite
and apatite) from a Mesozoic magmatic arc in New Zealand to constrain
the timing and duration of exhumation. Franz and Romer (2007) dated
syn-eclogite facies rutile from the Strona–Ceneri Zone of the Southern
Alps using the ID-TIMS method to constrain the tectonometamorphic
evolution at the northern margin of Gondwana during Early Palaeozoic
time. Further U–Pb ages of rutile (and titanite) were obtained from
eclogites of the WGR to assess the style and timing of exhumation and
cooling of that UHP terrane (Kylander-Clark et al., 2008). There seem to
be fundamental differences in the mechanisms controlling the evolution
of large UHP terranes (Dabie–Sulu, WGR) that undergo protracted
subduction and exhumation, and smaller UHP terranes (e.g. Dora Maira
in the Western Alps) that undergo rapid subduction and exhumation
(Kylander-Clark et al., 2008, and references therein).
Besides isotopic dating of rutile from metamorphic rocks, a
number of studies have also been already shown the power of
radiometric rutile dating in sedimentary successions from the
Palaeoproterozoic to the Holocene worldwide.
SHRIMP U–Pb work by Sircombe (1995, 1997) on rutile from
mineral sands in eastern Australia has shown a predominance of Late
Proterozoic/Early Cambrian grains that are exotic to the local continental hinterland (Williams, 1998).
Harrison et al. (2007) used a SIMS multi-collector facility to
determine 207Pb/206Pb ages of detrital rutile from the famous Jack
Hills quartzite of Western Australia. They recognised a distinct age
peak at 2.5 Ga, which corresponds to regional metamorphism and
local granite emplacement in the Archaean Narryer Gneiss Complex.
Stendal et al. (2006) carried out lead isotope analyses using a step
leaching process on rutile grains from alluvial heavy mineral deposits
and from a Neoproterozoic garnet–kyanite micaschist of the Yaoundé
Group, southern Cameroon. The 207Pb/204Pb and 206Pb/204Pb data for
most rutiles from heavy mineral concentrates yielded scattered plots
on the Pb–Pb isochron diagram, with no possibility to define a clear
age. However, those from the micaschist defined an age of about
950 Ma, which suggests that rutile in the Yaoundé Group formed
during early Pan-African metamorphism or was inherited as detrital
rutile from an early Pan-African source (Stendal et al., 2006).
Birch et al. (2007) used LA-ICP-MS to date detrital rutile from the
Late Cretaceous–Tertiary gold-bearing White Hills Gravel placer
deposits of the Victorian uplands in Australia. The analysed rutiles
show up to 5.5 wt.% Nb2O5 and 2.9 wt.% WO3 and together with their
weighted mean 206Pb/238U age of 393 ± 10 Ma (2σ) suggest an origin
associated with granite intrusion in the St Arnaud district (Birch et al.,
2007).
Allen and Campbell (2007) analysed rutiles from a sand sample of
the lower Mississippi River in the U.S.A. using LA-ICP-MS. They
identified a major Appalachian source and noted that some trace
elements (i.e. Cr, V and Zr) show strong correlation with age. The
latter effect is probably caused by diffusion of cation substitutions for
Ti4+ in the crystal lattice of rutile under slow cooling conditions (see
Cherniak et al., 2007b).
Taylor (2008) used an excimer laser system coupled to a
quadrupole ICP-MS to date rutile from the North Kimberley kimberlite
province of northwestern Australia and from a present-day stream
catchment within the Georgina Basin, Northern Territory, Australia.
He identified potential source areas and discussed the application of
rutile dating to diamond exploration.
4.4.3. Pb diffusion
The closure temperature for U in rutile is strongly dependent on
grain size (Mezger et al., 1991; Cherniak, 2000; see equation below).
Thus, if rutile grains of different sizes are dated, as is commonly the
case in sedimentary provenance studies, different rutile ages may not
necessarily represent different igneous or metamorphic events, but
may reflect the cooling history of each individual rutile grain.
However, the differences between closure temperatures for rutile
grains of different sizes are only of minor significance (few tens of
degrees for cooling rates between 1 and 10 °C Ma− 1 and grain sizes
up to a few millimetres) (Cherniak, 2000). The corresponding
mathematical expression to determine the closure temperature (Tc)
of rutile, as applied to any other mineral, is given as:
Tc =
E=R
ln A × R × Tc2 × D0 = a2 = E × Cr Þ
where R is the gas constant, E the activation energy, A the geometric
factor, D the factor for diffusion of the relevant species, a the effective
diffusion radius and Cr the cooling rate (Dodson, 1973). Cherniak (2000)
gave examples of closure temperature values of 567 °C for 70 μm-size
grains and 617 °C for 200 μm-size grains, for a cooling rate of 1 °C Ma− 1
with grains of spherical geometry. Moreover, it is likely that under some
conditions of slow cooling, rutile will record significantly younger U–Pb
ages compared to coexisting zircon (Cherniak, 2000). Li et al. (2003)
pointed out that a number of field-based studies on rutile of slowly
cooled terrains have demonstrated younger U–Pb ages compared with
coexisting titanite and hornblende Ar–Ar ages (Mezger et al., 1989;
Bibikova et al., 2001; Hirdes and Davis, 2002; Schmitz and Bowring,
2003). Although the causes of the disagreement between the experimental Pb diffusion data and the field-based observations remained
unclear, Li et al. (2003) expressed their preference for the field-based
rutile closure temperature estimates by Mezger et al. (1989).
Kramers et al. (2009) recently discussed the valence state of Pb in
zircon and suggested that radiogenic Pb is tetravalent, being similar in
ionic charge and effective ionic radius to U and Th, and hence has an
extremely low diffusivity. In general, the loss of radiogenic Pb causes
younger U–Pb ages. However, “radiogenic Pb cannot be lost from zircon
crystals except by being reduced to the divalent state” that can be caused
19
by hydrothermal fluids and natural leaching by groundwater, “after
which it would become both incompatible in the lattice and highly
mobile in solution” (Kramers et al., 2009). Although data are still
pending, it is likely that in rutile radiogenic Pb is also tetravalent. In
conclusion, fluids are more likely to affect rutile in slowly cooled than in
rapidly cooled terrains. The change from tetravalent to divalent Pb
causes loss of radiogenic Pb and thus of “age” (Kramers et al., 2009). This
may explain why rutile from slowly cooled terrains often has younger
U–Pb ages compared with coexisting titanite and hornblende Ar–Ar
ages. The disagreement between the experimental Pb diffusion data and
the field-based observations may be because the experiments do not
fully reflect the conditions for slowly cooled terrains and hence a change
of the valence state of radiogenic Pb does not occur in the experiments.
4.5. (U–Th)/He thermochronology
4.5.1. Introduction
The application of (U–Th)/He thermochronology to rutile is still in
its preliminary stages. In general, thermochronology is a temperaturesensitive radiometric dating technique, which constrains low-temperature, upper crustal processes such as timing and duration of
mineralisation, rate of exhumation and erosion of igneous and
metamorphic rocks (Farley, 2002; McInnes et al., 2005; Reiners and
Brandon, 2006, and references therein). The method is based on the
measurement of radiogenic 4He produced from 238U, 235U and 232Th
decay (Farley, 2002; Reiners and Brandon, 2006; Table 4). The
daughter helium is retained in the rutile crystal lattice until the grain
is heated above the closure temperature where the lattice becomes
weak for helium loss. Preliminary (U–Th)/He thermochronology on
rutile by Crowhurst et al. (2002) has suggested a closure temperature
of N180–200 °C, which is about 100 °C higher than the closure
temperature for apatite (75–100 °C; Farley, 2002) but in the range of
the closure temperature for zircon (171–196 °C; Reiners et al., 2004).
Initial step-heating He diffusion experiments by Stockli et al. (2005,
2007) and Wolfe et al. (2007) suggest a closure temperature of about
220–235 °C. As already documented in the previous section, the
closure temperature is dependent on a series of parameters such as
grain size, shape and cooling rate. In the case of rapid cooling of the
sample, the (U–Th)/He age reflects cooling of the sample through its
closure temperature and can often be related to a particular geological
event (Dodson, 1973; McInnes et al., 2005). Slow cooling over a longer
time interval, however, will give an age that is not necessarily related
to any specific geological event (McInnes et al., 2005). Further details
about the dependence of closure temperature from cooling rate can be
found, for instance, in Reiners and Brandon (2006).
4.5.2. Examples
Only a few applications of (U–Th)/He thermochronology to rutile
have been published. Crowhurst et al. (2002) analysed rutile from a
metamorphic rock in South Australia and determined an average (U–
Th)/He age of 472 ± 20 Ma that they interpreted as later stage cooling
related to the Delamerian Orogeny. McInnes et al. (2005) presented
preliminary rutile and zircon age data of a porphyry copper deposit
from Iran, which yielded identical ages within error supporting the
predicted similarity in rutile and zircon He closure temperatures.
Stockli et al. (2007) analysed rutile from mantle and lower crustal
xenoliths from Cenozoic volcanic rocks in the western U.S.A. and
demonstrated that the determined (U–Th)/He ages are in excellent
agreement with both 40Ar/39Ar and zircon (U–Th)/He data. To quantify
the position of the rutile He partial retention zone (e.g. Reiners and
Brandon, 2006) and to constrain the thermal history of Variscan
basement rocks, Wolfe et al. (2007) determined rutile (U–Th)/He ages
of amphibolites from the borehole of German Continental Deep
Drilling Project, which is, at 9101 m and a cost of about US$350 million,
the deepest and most expensive borehole for research in Germany
(Emmermann and Lauterjung, 1997). Dunkl and von Eynatten (2009)
20
Fig. 23. Schematic diagram for thermal history of specific minerals in an idealised rock
during uplift. The temperature represents the closure temperature for each radiometric
system of the individual mineral. The closure temperatures were taken from Cherniak
(2000), Möller et al. (2000) and Crowhurst et al. (2002).
used anchizonal–hydrothermal grown rutile crystals from the subgreenschist facies metamorphosed Mesozoic sandstones of Oman for
(U–Th)/He thermochronology, which allowed them to determine fluid
and thermal events after Late Cretaceous ophiolite emplacement.
Although the results outlined above are preliminary studies only, it
seems obvious that (U–Th)/He thermochronology on rutile can place
important constraints on the igneous and metamorphic evolution of a
region. Moreover, as already applied for zircon (McInnes et al., 2005,
and references therein), combined U–Pb dating and (U–Th)/He
thermochronology on rutile grains can provide information on their
age of formation and cooling history (Fig. 23). Note at the time of
writing this paper no study had been published about (U–Th)/He
thermochronology on detrital rutile. Nonetheless, this might change
in the future since (U–Th)/He thermochronology seems useful in
sediment provenance analysis to reconstruct both the age of potential
source lithologies and the timing of tectonic uplift in the source area.
4.6. Lu–Hf isotopes
4.6.1. Introduction
Rutile typically has Hf concentrations between b5 and 120 ppm,
but also higher amounts occur (Table 5; Fig. 24), and low Lu/Hf ratios,
so that correction for in situ radiogenic growth is negligible. Hafnium
isotope studies of single minerals are based on the occurrences of the
Table 5
Hf values (in ppm) for rutile from different source lithologies compiled from literature.
Note that the lowermost concentrations for Hf (minimum values) are defined by the
detection limit of the technique applied for analysis. Felsic granulite comprises here
granulite facies gneiss. Quartz vein data are mainly from eclogite facies quartz veins
(n = 74), supplemented by a single low-temperature (hydrothermal) quartz vein
sample (n = 1).
n
Min
Max
Med
Avg
Std
Ref
Felsic granulite
Eclogite
Quartz vein
Metasediment
173
0.05
194
68
76
43
(1)
368
1.65
189
12
12
11
(2)
75
1.34
86
9
10
9
(3)
19
1.08
21
4
6
5
(4)
Abbreviations: n — number of data, Min — minimum value, Max — maximum value,
Med — Median, Avg — average (arithmetic mean), Std — Standard deviation (1σ). Ref —
References: (1) Luvizotto and Zack (2009); (2) Zack et al. (2002), Xiao et al. (2006), Gao
et al. (2007), Miller et al. (2007), Schmidt et al. (2009); (3) Zack et al. (2002), Xiao et al.
(2006), Gao et al. (2007), John et al. (2008); (4) Zack et al. (2002), Luvizotto et al.
(2009a).
Fig. 24. Box and whisker plots showing Hf values for rutile from different source
lithologies. The box represents the middle 50%; the bar inside the box represents the
median. ‘Outliers’ are represented by black rectangles. n — number of data used. See
Table 5 for references.
unstable (radioactive) 176Lu isotope incorporated into the crystal
lattice, which undergoes spontaneous β-decay to the stable daughter
176
Hf isotope, with a decay constant of 1.93 × 10− 11 year− 1 (Sguigna
et al., 1982). The decay constant of 176Lu, however, has currently been
under review, which led to proposals of revised decay constants, i.e.
1.865 × 10− 11 year− 1 (Scherer et al., 2001), 1.983 × 10− 11 year− 1
(Bizzarro et al., 2003) and 1.945 × 10− 11 year− 1 (Luo and Kong,
2006). Owing to the large half-life of 176Lu of about 35–40 billion
years, the Lu–Hf system is suitable for tracing the history of the solar
system and the evolution of the Earth's crust–mantle system (Patchett
et al., 1981; Patchett, 1983; Salters and Zindler, 1995; Blichert-Toft
and Albarède, 1997; Amelin et al., 1999; Griffin et al., 2000;
Choukroun et al., 2005; Amelin, 2006; Aulbach et al., 2008).
The Lu–Hf isotope system is generally less disturbed by alteration
processes than other isotope systems such as Rb–Sr, Sm–Nd and U–Pb
(see discussions in Patchett, 1983; Griffin et al., 2000; Kinny and Maas,
2003). Experimental studies have shown that Hf diffusion is
significantly slower than diffusion of divalent and trivalent cation
substitutions; for example, it is about an order of magnitude slower
than Pb diffusion (Cherniak et al., 2007b). However, Luvizotto and
Zack (2009) have recently shown for granulite facies metapelitic rocks
from the Ivrea–Verbano Zone that Hf incorporation in rutile is temperature dependent.
The Lu–Hf isotope system has been widely applied in earth sciences
over the last decades. Its application is based on the fact that Lu and Hf
partition differently into specific minerals such as garnet, zircon and
rutile, and Lu/Hf ratios are thereby strongly fractionated during partial
melting, metamorphism and metasomatism (Salters and Zindler, 1995;
Amelin et al., 1999; Griffin et al., 2000; Kinny and Maas, 2003).
Therefore, the Hf isotope composition of the Earth's crust–mantle
system varies widely between the depleted mantle (Lu/Hf N chondritic),
the enriched crust (Lu/Hf b chondritic) and any remaining unfractionated source (Lu/Hf = chondritic), as shown in Fig. 25. Different Lu/Hf
ratios reflect the long-term evolution of these reservoirs (Patchett et al.,
1981; Choukroun et al., 2005). Hafnium preferentially enters the melt
phase, which leaves a residuum with relatively higher Lu/Hf ratios for
the subcontinental lithospheric mantle. However, metasomatism by
melts derived from the asthenospheric mantle can introduce Hf, which
produces lithospheric mantle with relatively low Lu/Hf ratios (Choukukroun et al., 2005). The deviations of the Hf isotope composition of a
Fig. 25. (a) Schematic illustration of Lu–Hf isotope evolution in the Earth's crust–mantle
system (modified from Patchett et al., 1981; Kinny and Maas, 2003). Partial melting in
the Earth's mantle at time t1 results in divergent Hf isotope evolution paths for the
newly generated crust (low Lu/Hf) and the residual mantle (high Lu/Hf). This is because
Hf enters the melt phase and Lu is preferentially retained in the mantle, which becomes
more radiogenic with time. Hence, any rutile formed within the crust has extremely
low Lu/Hf, which over time diverges in composition from the remainder of the host
rock. At time t2, a variety of possible sources may contribute to newly formed crust.
(b) Schematic illustration showing εHf as function of crystallisation age. The 176Hf/177Hf
ratio and the εHf value of a sample (calculated for the age of the sample) can be used to
produce a growth line that indicates the depleted mantle curve. The intersection yields
a depleted mantle (TDM) model age. This model age could reflect the time (t1) at which
the source of the magma from which a mineral (e.g. rutile) crystallised was extracted
from the depleted mantle reservoir. Alternatively, the model age may reflect a mixing
age of more ancient (e.g. with TDM model age of t1) with more juvenile (with a TDM
model age of t3) crust.
sample from that of the chondritic uniform reservoir (CHUR) are commonly expressed in epsilon units (εHf) as given by following equation
(Patchett et al., 1981):
2
3
Hf
4
sample
7
−15 × 10
Hf = 177 Hf chondrite
176
εHf
6
= 4176
Hf =
177
Samples with higher than chondritic 176Hf/177Hf at time t have
positive εHf values; those with lower than chondritic 176Hf/177Hf have
negative εHf values, and hence chondrites per definition have εHf = 0.
The 176Hf/177Hf ratios are used to determine Hf model ages, which are
a measure of the average time since the source of the magma from
which a mineral (e.g. rutile) crystallised was extracted from the
depleted mantle reservoir (Fig. 25b).
21
4.6.2. Examples
The use of in situ Lu–Hf isotope analysis has rapidly increased in
recent years because of an increase in sophisticated laser ablation
multi-collector ICP-MS facilities, which allow precise isotope analysis
of samples with Hf quantities as low as 25 ng (Blichert-Toft and
Albarède, 1997; Amelin et al., 1999). Choukroun et al. (2005) analysed
the Hf isotope composition of rutile from MARID xenoliths of the
Kimberley area, South Africa. The 176Hf/177Hf ratios are highly variable
(0.2811–0.2858, εHf = − 55 to +110), with much of this range found
in single samples and even within single grains. They noted that such
a wide range of Hf isotope composition within single samples and
within single rutile grains could not be generated by radioactive decay
of 176Lu in the rutile within the age of the Earth. Choukroun et al.
(2005) therefore interpreted the ranges in Hf isotope composition as
reflecting primary interaction of an asthenospheric-derived melt with
ancient depleted harzburgitic mantle, which was later overprinted by
metasomatism. The authors explained low 176Hf/177Hf ratios still
preserved in some MARID rutile grains by mixing between an
asthenospheric-derived melt and the ancient subcontinental lithospheric mantle.
Aulbach et al. (2008) analysed 176Hf/177Hf of rutile in eclogite
xenoliths from kimberlites of the Lac de Gras area, northern Canada.
They received similar, highly variable 176Hf/177Hf ratios (0.28156–
0.28568, εHf = − 43 to + 103), with negligible intergrowth of
radiogenic Hf in rutile since emplacement of the kimberlite, as
shown by low 176Lu/177Hf ratio of 0.000039 ± 0.000077 (1σ). They
recognised a correlation between Nb/Ta and minimum 176Hf/177Hf of
eclogitic rutiles, and interpreted the low 176Hf/177Hf and suprachondritic Nb/Ta values as acquired during interaction with a component
derived from ancient metasomatised subcontinental lithospheric
mantle. By contrast, they interpreted rutile with high 176Hf/177Hf
and subchondritic Nb/Ta values as having preserved its primary HFSE
concentrations and isotope characteristics. Their study clearly shows
that Lu–Hf isotope analysis combined with trace element geochemical
data of rutile is particularly helpful for a better understanding of the
evolution of the Earth's crust and mantle. New studies are under way
to improve Lu–Hf isotope analysis on rutile (Ewing et al., 2009).
At the time of writing this paper, no study had been published
about Lu–Hf isotope analysis of detrital rutile. However, this might
change in the future since the Lu–Hf isotope composition of rutile
represents an estimate of the protolith composition at the time of
crystallisation and therefore is helpful in tracing potential source
rocks in sediment provenance studies.
5. Economic importance of rutile
5.1. Introduction
Although the primary purpose of this paper is to provide
information on various applications of rutile in earth sciences, an
outline of the economic importance of rutile is essential because the
academic issues mentioned above have also important commercial
implications.
One of the major subjects for earth scientists is the exploration and
evaluation of mineral raw materials, including hydrocarbons, gold,
diamonds, chromium, iron, nickel and platinum group metals but also
titanium minerals. The world total rutile reserves are estimated to
be 45 million t and those of ilmenite are about 680 million t, with
ilmenite supplying about 92% of the world's demand for titanium
minerals (Gambogi, 2009). Titanium minerals are commercially
important because they are processed to titanium metal, which is
used, for instance, in the aerospace industry because of its low weight,
high strength and resistance to heat and corrosion. Rutile is one of the
favoured minerals for the production of titanium dioxide white
pigment, dominantly through the chloride manufacturing process
(Stanaway, 1994; Korneliussen et al., 2000). The main applications of
22
titanium dioxide white pigment are in the manufacture of paint (51%
of total production), paper (19%) and plastics (17%) (Pearson, 1999;
Carp et al., 2004; Gambogi, 2008). Other uses include ceramics, coated
fabrics and textiles, floor coverings, printing ink, roofing granules,
food colouring (E171), tablet coating, toothpaste and as a UV absorber
in sunscreen cream with high sun protection factors (Carp et al., 2004;
Gambogi, 2008, and references therein). Thus, titanium dioxide
(rutile) is always present in our daily life. Moreover, since Fujishima
and Honda (1972) successfully showed the application of TiO2 as a
photoanode to decompose water by visible light, anatase has received
much attention in photocatalysis (Carp et al., 2004). This use has also
been extended to rutile (e.g. Lu et al., 2004; Chuan et al., 2008),
although its reaction rate is a fifth of anatase (Chuan et al., 2008). In
contrast to rutile containing, for example, V and Fe, pure rutile shows
no photoactivity (Lu et al., 2004). Chuan et al. (2008) used natural Vbearing rutile from a rutile mine in the Shaanxi Province, China, to
decompose methylene blue and suggested the application of rutile for
large-scale photocatalytic decomposition of organic pollutants in
quiet and still waters.
5.2. Economic importance
Most of the natural rutile used in industry comes from heavy mineral
sands (placer deposits) enriched in ilmenite and rutile (e.g. Force, 1991;
Roy, 1999; Pirkle et al., 2007). The world's largest sedimentary deposits
of rutile and the largest rutile mine are both in Sierra Leone. Before its
closure in 1995, the rutile operation in Sierra Leone supplied 137,000 t
(Mobbs, 1996), which was about two-thirds of the world's rutile output
in 1994. Although rutile is commercially important, rutile mining causes
drastic changes to the environment (Akiwumi and Butler, 2008). The
Sierra Rutile Mine reopened in 2006, and Sierra Leone may become one
of the world's leading rutile producers in the future. In 2006, 70,360 t of
rutile (worth US$28.5 million) was exported (Bermúdez-Lugo, 2008).
Other African rutile placer deposits occur in Cameroon (exploited
between 1935 and 1955 near Yaoundé), Gambia (mined in the 1950s),
Guinea (deposits not yet exploited), Kenya (to commence in the near
future), Malawi (exploration has been conducted in recent years) and
South Africa (Stendal et al., 2006; Dill, 2007b; Schlüter, 2008). Rutile
placer deposits are also mined in Australia, India, Ceylon and U.S.A.
(Goldsmith and Force, 1978; Force, 1991; Roy, 1999; Force, 2000; Pirkle
et al., 2007).
Fig. 26 shows the world largest producers of natural rutile and the
trend of growth between 2006 and 2008. For example, in 2008, the
world production of natural rutile was about 608,000 t, with Australia
(309,000 t), South Africa (121,000 t) and Sierra Leone (95,000 t)
being the three largest producers (Gambogi, 2009). However, rutile
placer deposits are limited in volume and are rapidly being depleted,
and therefore, the current producers may not be able to fulfil the
world's need in the future (Korneliussen, 1980; Korneliussen et al.,
Fig. 26. World production of natural rutile by country between 2006 and 2008,
according to data in Gambogi (2008, 2009).
2000), with Sierra Leone being an exception. Thus, an alternative
source for high-grade TiO2 ores (such as eclogite) has to be found.
The eclogites of the Western Gneiss Region, Norway, contain
several million tons of rutile, and are therefore a large rutile resource
(Korneliussen and Foslie, 1985; Korneliussen et al., 2000). The
eclogites occur as pods and lenses within amphibolite to granulite
facies metamorphosed Proterozoic/sub-Caledonian gneisses and have
rutile concentrations in the range of 1 to 4 wt.%, although higher
concentrations occur locally (Korneliussen, 1980; Korneliussen and
Foslie, 1985). Ilmenite is important in the economic evaluation of
rutile-rich eclogite deposits, for two main reasons (Korneliussen and
Foslie, 1985). First, intergrowths of less-valuable ilmenite will lower
the purity, and accordingly the values of the rutile concentrate that can
be produced. Second, an increase in the ilmenite concentration in
eclogite will lead to a correspondingly smaller amount of Ti available to
form rutile (Korneliussen and Foslie, 1985). Moreover, the grain size of
the rutile and the CaO content in the concentrates (should be less than
0.2%) are of considerable importance in the economic evaluation of
rutile-rich eclogite deposits (Korneliussen et al., 2000). Further
examples of rutile-bearing eclogite of economic importance are
known from the Piampaludo deposit, Italy (Force, 1991; Liou et al.,
1998), the Shubino deposit, Russia (Force, 1991) and from the Dabie–
Sulu deposits, China (Chen et al., 2005; Huang et al., 2006; Zhang et al.,
2006). For instance, in the Sulu UHP metamorphic terrane the rutile
modal content in eclogite is 2–5 vol.% and can be as high as 8–10 vol.%
(Chen et al., 2005).
Minor economically important sources of natural rutile are ore
deposits (Czamanske et al., 1981; Clark and Williams-Jones, 2004),
amphibolitic rocks (Korneliussen et al., 2000: 40), granitic pegmatites
and rare-earth element mineralisation (Scott, 1988; Černý et al., 1999;
Černý and Chapman, 2001). Clark and Williams-Jones (2004)
discussed anomalous compositions of rutile at certain deposits for
their potential as indicators of metallic mineralisation (see Scott,
1988, 2005; Scott and Radford, 2007). Thus, detrital rutile can be used
as pathfinder mineral in stream sediments to guide the exploration
geologists to metallic mineralisation. Table 2 shows a compilation of
various rutile-bearing deposits and the characteristic trace elements
incorporated into the rutile crystal lattice. Moreover, besides pyrope
garnet, chrome diopside and chrome spinel, rutile can also be used as
a kimberlite indicator mineral (Smythe et al., 2008) and therefore
plays an important role in diamond exploration.
Table 6
Key elements in natural rutile useful for a wide range of applications in earth sciences
(see text for explanation).
Key elements
Applications
Cr and Nb
Source rock
characterisation
Comment
These elements allow discrimination
between rutile derived from metamafic
lithologies (high Cr, low Nb) or metapelitic
lithologies (low Cr, high Nb).
V, Ni, Cu, Nb, Sn, Source rock
Rutile containing these elements is useful as
Sb, Ta and W
characterisation
pathfinder mineral in stream sediments to
identify and trace the type of metallic
mineralisation.
Zr
Zr-in-rutile
Zr in rutile can yield the temperature of
thermometry
rutile crystallisation.
O
O isotopy
O isotope data can yield information about
the temperature of rutile crystallisation and
the extent and nature of fluid–mineral
interactions.
U and Pb
U–Pb
U/Pb and Pb/Pb isotope ratios can yield the
geochronology
age of rutile crystallisation.
U, Th and He
(U–Th)/He
(U–Th)/He isotope ratios are used to
thermochronology calculate an age related to the time the
rutile cooled through about 200 °C.
Lu and Hf
Lu–Hf isotopy
The Hf isotope composition of rutile allows
identifying the magmatic source by
reference to an Earth model.
6. Summary
Rutile is widely distributed as an accessory mineral in igneous,
metamorphic and sedimentary rocks. Its geochemical composition
allows tracing the formation and evolution of the Earth's continental
crust because rutile is a major host mineral for Nb, Ta and other HFSE,
which are widely used as a monitor of geochemical processes in the
crust and mantle such as magma evolution and subduction-zone
metamorphism. Processes influencing the Nb/Ta ratio of minerals (e.g.
rutile) and rocks are continuously topics of scientific debate. In recent
years, many data have been generated which significantly increased
our knowledge about rutile and its host lithologies. Table 6 gives a
summary of key elements in natural rutile that are useful for a wide
range of applications in earth sciences. For example, elements such as
Cr, Nb, Sb and W are used to trace the provenance of rutile. A number of
publications have already shown that rutile geochemistry, Zr-in-rutile
thermometry and isotope studies of rutile are useful methods in both
hard and soft rock geology. Rutile is also of economic importance
because of its use in the manufacture of white titanium dioxide
pigment, which is a major constituent in various products of our daily
life. Heavy mineral sands containing a significant percentage of rutile
are therefore the focus of exploration worldwide. Because these
mineral sands are limited in volume and are rapidly being depleted, an
alternative source for high-grade TiO2 ores has to be found. This clearly
shows the growing demand for further rutile-related research in earth
sciences. I hope that this review will serve as a good source of reference
for earth scientists both in academic research and in industry.
Acknowledgements
I would like to thank all the scientists who have been interested in
natural rutile in the last years producing helpful data used in this paper.
Thanks go also to everyone who provided me with literature. Arzu
Arslan and Hong Tan made helpful suggestions during the preparation
of the manuscript. Robert Scott improved the English style and
grammar of the manuscript. Thanks go also to Sally Gibson and Dirk
Frei for reading Sections 4.1.3 and 4.4. respectively. The thin section
photomicrographs of rutile-bearing rocks have been reproduced with
permission of the Sedgwick Museum of Earth Sciences, University of
Cambridge. Finally, I am grateful to Maria Mange and Andrew Morton
for their helpful comments on a previous version of the manuscript.
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Rutile and its applications in earth sciences

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