Spatial, temporal and geochemical evolution of

Transcription

GR-00742; No of Pages 26
Gondwana Research xxx (2012) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Gondwana Research
journal homepage: www.elsevier.com/locate/gr
GR focus review
Spatial, temporal and geochemical evolution of Oligo–Miocene granitoid magmatism
in western Anatolia, Turkey
Şafak Altunkaynak a,⁎, Yıldırım Dilek b, Can Ş. Genç a, Gürsel Sunal a, Ralf Gertisser c, Harald Furnes d,
Kenneth A. Foland e, Jingsui Yang f
a
Department of Geology Engineering, Istanbul Technical University, Maslak 34469, Istanbul, Turkey
Department of Geology, 116 Shideler Hall, Miami University, Oxford, OH 45056, USA
School of Physical and Geographical Sciences, Earth Sciences and Geography, Keele University, Keele, Staffordshire, ST5 5BG, United Kingdom
d
Department of Earth Science and Centre for Geobiology, University of Bergen, Allegt. 41, 5007 Bergen, Norway
e
School of Earth Sciences, Ohio State University,125 South Oval Mall, Columbus, OH 43210, USA
f
State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825,Beijing 100029, China
b
c
a r t i c l e
i n f o
Article history:
Received 15 June 2011
Received in revised form 10 October 2011
Accepted 26 October 2011
Available online xxxx
Handling Editor: M. Santosh
Keywords:
Oligo–Miocene granitoids
Western Anatolia
Post-collisional magmatism
Open system processes
Thermal weakening and synconvergent
extension
a b s t r a c t
Western Anatolia (Turkey) experienced widespread Cenozoic magmatism after the collision between the Sakarya (SC) and Anatolide–Tauride continental blocks (ATP) in the pre-middle Eocene. Voluminous granitic
magmas were generated and emplaced into the crystalline basement rocks of the Rhodope (RM) and Sakarya
continent to the north and Anatolide–Tauride Platform to the south of the ~ E–W-trending Izmir–Ankara suture zone (IASZ) during the late Oligocene–middle Miocene. We report here a comprehensive geochronological (combined zircon U–Pb and 40Ar–39Ar dating) and geochemical (major and trace element geochemistry,
and Sr–Nd isotopes) dataset from the Oligo–Miocene granitoids in order to evaluate the nature and the spatial–temporal distribution of the Cenozoic magmatism in the Aegean extensional province. Zircon SHRIMP
U–Pb dating of these plutons yields ages between 19.48 ± 0.29 and 23.94 ± 0.31 Ma as the timing of their emplacement, whereas 39Ar/40Ar dating of biotite separates from these plutons reveals cooling ages of 18.9 ±
0.1–24.8 ± 0.1 Ma. Regardless of the lithological make-up of the collided blocks, the RMG, SCG and NATPG
granitoids that were emplaced into the RM, SC and ATP, respectively, show similar major and trace element
and Sr–Nd isotopic compositions, indicating common mantle melt sources and magmatic evolutionary trends.
The isotopic signatures and trace element characteristics of these granitoids indicate that both lithospheric
and asthenospheric mantle melts appear to have contributed to source region of the RMG, SCG and NATPG
magmas. The compositional variations observed in these granitoids are interpreted as a result of opensystem processes (AFC and/or MASH) rather than a reflection of different compositions of crustal lithologies
through which RMG and SCG, ATPG magmas migrated. On the other hand, the SATPG with crustal signatures
stronger than the other groups may have been produced by crustal melting or significant contributions from
the ATP crystalline basement. The isotopic compositions and cooling age relationships of western Anatolian
granitoids indicate an increasing crustal signature from 24 to 18 Ma coinciding with crustal exhumation (Kazdag and Menderes core complexes) and extension in western Anatolia. Asthenospheric upwelling caused by
partial delamination or convective thinning of lithosphere led to underplating of mantle-derived magmas
that provided melts and heat to induce partial melting of sub-continental lithospheric mantle. Stalling of
mantle-derived melts in the crust triggered open system processes in separate magma chambers, resulting
in the production of granitic magmas. This inferred melt source and magma evolution readily explains the Itype granitoid nature of most late Oligocene to middle Miocene plutons in western Anatolia regardless of
their temporal and spatial position. The widespread early to middle Cenozoic magmatism caused thermal
weakening and played a significant role for the initiation of synconvergent extension, exhumation and thinning in the hinterland of a young Tethyan orogen in western Anatolia and the broader Aegean region.
© 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
⁎ Corresponding author. Tel.: + 90 212 2856272; fax: + 90 212 2856080.
E-mail address: [email protected] (Ş. Altunkaynak).
1342-937X/$ – see front matter © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.gr.2011.10.010
Please cite this article as: Altunkaynak, Ş., et al., Spatial, temporal and geochemical evolution of Oligo–Miocene granitoid magmatism in western
Anatolia, Turkey, Gondwana Res. (2012), doi:10.1016/j.gr.2011.10.010
Ş. Altunkaynak et al. / Gondwana Research xxx (2012) xxx–xxx
2
Contents
1.
2.
3.
4.
Introduction . . . . . . . . . . . . . . . . . . . . . . .
Regional geology . . . . . . . . . . . . . . . . . . . . .
Synopsis of Cenozoic plutonism in western Anatolia . . . .
Analytical techniques . . . . . . . . . . . . . . . . . . .
4.1.
SHRIMP dating. . . . . . . . . . . . . . . . . . .
40
Ar/39Ar dating . . . . . . . . . . . . . . . . . .
4.2.
4.3.
Major, trace elements and Sr–Nd isotope analyses . .
5.
Geochronology . . . . . . . . . . . . . . . . . . . . . .
5.1.
U–Pb zircon ages. . . . . . . . . . . . . . . . . .
40
Ar/39Ar dates . . . . . . . . . . . . . . . . . .
5.2.
6.
Geochemistry . . . . . . . . . . . . . . . . . . . . . .
6.1.
Major and trace element characteristics . . . . . . .
6.2.
Sr and Nd isotopic signatures and Nd model ages . .
7.
Petrogenesis . . . . . . . . . . . . . . . . . . . . . . .
7.1.
Source characteristics . . . . . . . . . . . . . . .
7.2.
Magma evolution . . . . . . . . . . . . . . . . .
7.3.
Petrogenetic modeling . . . . . . . . . . . . . . .
8.
Interplay between syn-convergent extension and magmatism
9.
Conclusions . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . .
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in western Anatolia
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1. Introduction
Western Anatolia is one of the best natural laboratories in the
broader Alpine–Himalayan orogenic system to investigate in fourdimensions the nature and distribution of post-collisional magmatism, the interplay between tectonic and magmatic processes, and
the crust–mantle interactions in a young mountain belt.
The consumption of a Neo-Tethyan oceanic lithosphere at a subduction zone dipping northwards beneath the Sakarya continent during the
late Cretaceous resulted in a continent–continent collision between the
Sakarya and Anatolide–Tauride continental fragments in the eastern
Mediterranean region (Şengör and Yılmaz, 1981). The timing of this collision has been well established in the literature as pre-middle Eocene
(Harris et al., 1994; Okay and Tüysüz, 1999). The widespread magmatic
activity in NW Anatolia postdates this continental collisional event in
the region (Yılmaz, 1989, 1990; Güleç, 1991; Şengör et al., 1993;
Harris et al., 1994; Seyitoğlu and Scott, 1996). The first products of
post-collisional magmatism are the middle Eocene granitic plutons
and andesitic extrusive rocks (Harris et al., 1994; Genç and Yılmaz,
1997; Delaloye and Bingöl, 2000; Köprübaşı and Aldanmaz, 2004;
Altunkaynak and Dilek, 2006; Okay and Satır, 2006; Altunkaynak,
2007). The following magmatic episode during the Oligocene and
Early Miocene is known to have produced the widespread granitic plutons (i.e., Kozak, Evciler, Cataldag, Kestanbol, Ilica-Samli, Eybek, Egrigoz,
Koyunoba) and associated volcanic rocks in western Anatolia (Yılmaz,
1989; Altunkaynak and Yılmaz, 1998, 1999; Genç, 1998; Yılmaz et al.,
2001; Özgenç and İlbeyli, 2008; Akay, 2009).
The relationships between tectonics and magmatism and their variation in time and space since the beginning of the Neogene remain
some of the most fundamental questions in the geodynamic evolution
of western Turkey and the broader Aegean extensional province. Although some geochemical data exist from this region (Harris et al.,
1994; Genç and Yılmaz 1997; Altunkaynak and Yılmaz, 1998, 1999;
Genç, 1998; Karacık and Yılmaz, 1998; Delaloye and Bingöl, 2000;
Köprübaşı and Aldanmaz, 2004; Okay and Satır, 2006; Altunkaynak,
2007; Altunkaynak and Genç, 2008; Özgenç and İlbeyli, 2008; Akay,
2009; Altunkaynak et al., 2010; Hasözbek et al., 2010; Mackintosh and
Robertson, 2011), it is not systematic and it does not contain sufficient
isotopic and geochronological information to develop a regionally coherent and viable geochemical and geodynamic model for the postcollisional magmatic evolution of NW Anatolia.
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We have investigated the geochronology, geochemistry and petrogenesis (magma sources, magma genesis and crust–magma interaction) of post-collisional granitic plutons and stocks emplaced into
the Anatolide–Tauride and Sakarya continental blocks on both sides
of the Izmir–Ankara suture zone (Fig. 1). Straddling one of the
major continental collision zones in the eastern Mediterranean region, the granitoids we have investigated provide us with an opportunity to evaluate the geochemical fingerprint and melt evolution of
post-collisional magmatism in and across a suture zone, and to document, for the first time, the different isotopic domains beneath the
early Tertiary western Anatolia. In this paper, we present our new
geochemical data, Sr–Nd isotope compositions, 40Ar– 39Ar and zircon
Shrimp ages from the late Oligocene to middle Miocene granitoid plutons, and the petrogenesis of thirteen granitoids to constrain the
magmatic evolution and melt sources of the post-collisional magmatism in the region. We then discuss the mantle dynamics and the melt
evolution beneath western Anatolia as a case study of alpine-style
collision zone magmatism.
2. Regional geology
The crustal architecture of western Anatolia and the broader Aegean region is formed from a collage of continental blocks, separated by
ophiolites and suture zones that are nearly parallel to each other
(IPSZ, VS_IASZ, PS in Fig. 1). The basement geology of NW Anatolia includes five tectonic units. These are, from north to south, the Rhodope
massif (RM), the Intra-Pontide Suture zone (IPSZ), the Sakarya continent (SC), the Izmir_Ankara suture zone (IASZ) and the Anatolide–
Tauride platform (ATP) (Şengör and Yılmaz, 1981; Okay and Satır,
2000 and references therein).
The Çamlıca micaschist which is a part of the Rhodope massif
(Okay and Satır, 2000) is exposed around the Ezine and Karabiga
(Fig. 2) in northwestern areas. The Sakarya continent (Şengör and
Yılmaz, 1981) consists of two types of rock associations; a) Palaeozoic
continental metamorphic rocks (i.e. the Uludağ and Kazdağ metamorphic massifs and the Söğüt basement) and b) Triassic metamorphic rocks (mainly the Karakaya complex, Bingöl et al., 1975; Okay
et al., 1990; Genç, 2004). The Çamlıca micaschist and the Sakarya continent are separated by a high-angle fault zone, marked by ophiolitic
fragments of IPSZ (Okay and Satır, 2000, 2006). The Anatolide–Tauride platform farther south is composed of carbonates and intercalated
3
30°E
E U R A S I A N P L AT E
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2
1
4
EB
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40°N
10
13
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Chios
AEGEAN
Athens
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n
s
SEA
?
Aegean Sea
PS
A
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Istanbul
Zone
Sea of
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IAS
20°E
Anatolia
Samos
S
Menderes M.
Study area
T
iinoss
Tinos
Patm
tm
Patmos
Milos
Santorini
Bodrum
Kos
36°N
Crete Massif
HELLENIC SUBDUCTION ZONE
32°N
Neogene granitoids
Suture zones
AFRICAN
P L AT E
Fig. 1. Generalized map of the Aegean region showing the distribution of Neogene granitoids, metamorphic massifs and major structural elements (modified from Pe-Piper and
Piper, 2001, 2006).
volcanosedimentary and epiclastic rocks ranging in age from CambroOrdovician (and older?) to Lower Cretaceous (Ricou et al., 1975;
Demirtasli et al., 1984), and is tectonically overlain by Cretaceous
ophiolite nappes derived from a Tethyan seaway to the north
(Juteau, 1980; Şengör and Yılmaz, 1981; Dilek and Moores, 1990;
Dilek et al., 1999).
The Kazdag and Menderes metamorphic massifs representing core
complexes of western Anatolia (Bozkurt and Park, 1994; Hetzel et al.,
1995; Hetzel and Reischmann, 1996; Bozkurt and Satır, 2000) consist
of high-grade lower crustal rocks that were exhumed during the postcollisional extensional tectonic evolution of the region. They are overlain by relatively unmetamorphosed cover sequences and are intruded by granitoids (Hetzel and Reischmann 1996; Bozkurt and Park,
1994; Okay and Satır, 2000; Gessner et al. 2004). The Menderes metamorphic massif (i.e. Şengör et al., 1984) was formed mainly from
continent-type metamorphic rocks (micaschists and gneisses) and
separated from the Sakarya continent by the Izmir–Ankara suture
zone (Şengör and Yılmaz, 1981; Okay and Tüysüz, 1999) (Fig. 2).
The IPSZ marks the collision zone between the RM (to the north)
and SC (to the south) in northern Turkey (Okay and Tüysüz, 1999;
Okay and Satır, 2006). These continental blocks collided as the
Intra-Pontide ocean was consumed at a north-dipping subduction
zone throughout the Cretaceous (Şengör and Yılmaz, 1981). All
these tectonic entities juxtaposed to form a tectonic mosaic prior to
the deposition of the Upper Campanian–Maastrichtian successions
that form the first common non-metamorphic cover (Yılmaz et al.,
1995). Following this event, a new sedimentation phase accompanied
by rigorous andesitic volcanism and co-eval granitic plutonism
started at the beginning of the middle Eocene (Lutetian, 48–39 Ma;
Gulmez and Genc, 2009; Genc et al., unpublished age data). These
4
granitic rocks and the volcano-sedimentary succession were described as “post-collisional” magmatic activity (Genç and Yılmaz,
1997; Yılmaz et al., 1997).
The Izmir–Ankara suture zone in western Anatolia represents
the collision zone between the Sakarya continent and Anatolide–
Tauride platform (Şengör and Yılmaz, 1981). The Izmir–Ankara suture zone includes two different tectonostratigraphic units. In its
northwestern and western parts, it consists of a wild-flysch sequence (Bornova flysch of Okay and Siyako, 1993), which contains
abundant platform type carbonate olistholiths and olistostromes
together with the ophiolitic slices and blocks embedded in finegrained flysch-type sediments. In the northern and eastern areas
(i.e. south of Uludağ, near the Orhaneli and its east continuation)
the Izmir–Ankara suture zone is represented mainly by the dismembered and tectonically mixed ophiolitic rocks. These tectonic
units were juxtaposed with each other as a consequence of the collision between the Sakarya continent to the north and the Anatolide–Tauride Platform to the south during the late Cretaceous–
Paleocene (Şengör and Yılmaz, 1981; Okay and Tüysüz, 1999). The
northern branch of the Neo-Tethyan ocean, located between the Sakarya continent and the Anatolide–Tauride Platform, was totally
consumed at the beginning of the pre-middle Eocene at a subduction zone dipping northwards beneath the Sakarya continent
(Harris et al., 1994; Okay and Tüysüz, 1999). Following the collision, the units of the Sakarya continent and the Bornova flysch
were covered unconformably by continental to shallow marine
sedimentary rocks (Baslamis Formation; Akdeniz, 1980 and Gebeler Formation; Akyurek and Soysal, 1983) during middle Eocene.
This stratigraphic relationship indicates that the timing of the collision in NW Anatolia was earlier than the middle Eocene.
After the continental collision, two major magmatic episodes
occurred in the region. The first was developed during the middle–late Eocene, and produced extensive plutonic and volcanic associations in different parts of NW Anatolia. The middle Eocene
magmatic associations have been studied in detail previously
(Genç and Yılmaz, 1997; Köprübaşı and Aldanmaz, 2004;
Altunkaynak, 2007; Dilek and Altunkaynak, 2007). The second
magmatic phase occurred during the late Oligocene–middle Miocene. It is represented by granitic plutons and co-eval volcanic
rocks, similar to those of the middle Eocene magmatic associations.
Our study focuses mainly on the Late Oligocene–middle Miocene
granitic rocks.
We studied thirteen granitic bodies (Fig. 2), including, from
northwest to southeast, the Kestanbol, Evciler, Karakoy, Katrandag,
Yenice, Hıdırlar, Ilica-Samlı, Kozak, Çataldag, Eybek, Çamlık, Eğrigöz
and Salihli granitoids. The Katrandağ, Yenice, Hıdırlar and Salihli
granites are represented by stocks, whereas the others are large
plutons. The Kestanbol granite was emplaced into the Sakarya
basement rocks (Karacık and Yılmaz, 1998), which are imbricated
with the Çamlıca micaschists of the Rhodope belt. The Kozak, Evciler, Ilıca-Şamlı, Eybek, Çataldağ, Hıdırlar and Katrandağ granites
were emplaced into the metamorphic basement rocks of the
Fig. 2. Simplified geological map of W Anatolia showing the distribution of granitoids (Modified from Yılmaz et al., 2000; Okay and Satir, 2006). IAESZ; Izmir–Ankara–Erzincan
suture zone, RM: Rhodope Massif, SC: Sakarya Continent, and ATP—Anatolide–Tauride platform). E1 to 7: Eocene granitoids, 1-Kestanbol, 2-Evciler, 3-Hıdırlar-Katrandag
4-Eybek, 5-Yenice, 6-Danisment, 7-Sarıoluk, 8-Kozak 9-Uludag, 10- Ilica-Samli 11-Davutlar, 12-Çataldag, 13-Egrigoz, 14-Koyunaoba, 15-Çamlik, 16-Turgutlu, 17-Salihli granitoids.
Data for radiometric ages: This study; Bingol et al., 1982; Hetzel et al., 1995; Delaloye and Bingöl, 2000; Işık et al., 2004; Ring and Collins 2005; Glodny and Hetzel 2007; Karacik
et al., 2008; Boztuğ et al., 2009.
Sakarya continent. The Çamlık, Eğrigöz and Salihli granitoids are
the representatives of the granites that were emplaced into the
Anatolide–Tauride Platform (i.e. the metamorphic rocks of the
Menderes Massif).
The late Oligocene–middle Miocene plutons are magmatic bodies
that were emplaced at shallow depths in the crust. They crosscut
the metamorphic country rocks and have well developed contact aureoles around their periphery. Along the border zone, the plutons
contain numerous metamorphic xenoliths and mafic microgranular
enclaves. Many of the late Oligocene–middle Miocene granites have
been described as caldera type, sub-volcanic plutons showing close
relationships with their co-genetic volcanic rocks in time and space
(Yılmaz, 1989; Altunkaynak and Yılmaz, 1998, 1999; Genç, 1998;
Yılmaz et al., 2001).
3. Synopsis of Cenozoic plutonism in western Anatolia
Cenozoic plutonism in western Anatolia has been the subject
of many studies. The models and interpretations derived from
these studies support different and often conflicting views about
the nature, origin and evolution of Cenozoic magmatism in the
region.
Borsi et al. (1972), Fytikas et al. (1976) and Delaloye and Bingöl
(2000) have argued that the western Anatolian plutons originated
from the Paleocene and younger magmatism associated with the Hellenic subduction zone. The Kozak, Kestanbol, Evciler and Karaköy plutons are post-collisional in character and are likely to have been
derived from the mantle and contaminated by thickened orogenic
crust, and may have evolved from a mixed magma source under a
compressional regime (Altunkaynak and Yılmaz, 1998, 1999; Genç,
1998; Karacık and Yılmaz, 1998; Yılmaz et al., 2001; Yılmaz-Şahin
et al., 2010). The Ilıca, Cataldag and Kozak granitoids were derived
from different magma sources generated by partial melting of various
sources including metasomatized mantle and crustal material in a
post-collisional extensional setting as a result of slab break-off event
following the collision between the SC and the ATP (Boztuğ et al.,
2009). Işık et al. (2004) reported that the syn-extensional Egrigöz
and Koyunoba plutons in the footwall of the Simav Detachment
were emplaced in the early stages of continental extension in the Aegean province. These granitoids are hybrid in nature with dominantly
upper crustal compositions similar to the coeval Oligo–Miocene granitoids in the central Aegean Sea region. For the same granitoids, Akay
(2009) and Hasözbek et al. (2010) argued for a hybrid magma source
produced under a compressional regime. Özgenç and İlbeyli (2008)
proposed that the Egrigöz pluton formed by partial melting of mafic,
lower crustal rocks during post-collisional extensional tectonics in
the region. Catlos et al. (2008) suggested that the trace-element geochemical features of the Salihli and Turgutlu granitoids are consistent
with a continental arc origin and that the magmas were generated
under a compressional regime above the north-dipping Hellenic
subduction zone. Dilek et al. (2009) and Öner et al. (2010) proposed
that the Salihli and Turgutlu granitoids represent syn-extensional
intrusions and formed by partial melting of the subductionmetasomatized lithospheric mantle and the overlying lower–middle
crust. Altunkaynak and Dilek (2006), Altunkaynak (2007) and Dilek
and Altunkaynak (2007, 2009) suggested that partial melting of
enriched, subcontinental lithospheric mantle-derived melts and subsequent fractional crystallization, accompanied by crustal assimilation, were important processes in the genesis and evolution of the
magmas. They demonstrated that mantle-derived melts experienced
decreasing subduction influence and increasing crustal contamination during the evolution of the Eocene and Oligo–Miocene volcanoplutonic associations. They further argued that collision-induced
slab break-off allowed an influx of asthenospheric heat that resulted
in partial melting of the orogenic lithospheric mantle, which was previously metasomatized by slab-derived fluids beneath the Izmir–
5
Ankara suture zone, producing the Eocene and Oligo–Miocene igneous suites.
4. Analytical techniques
4.1. SHRIMP dating
Zircons were extracted from 5 to 10 kg of rock samples by standard mineral separation techniques, mainly grinding, sieving, Frantz
isodynamic separator and heavy liquids. Separated zircons were
handpicked under a binocular microscope, and then a fraction with
grain sizes of 63–200 μm was selected and sorted according to their
crystal properties (i.e. euhedral morphology, lack of overgrowth and
visible inclusions). Zircons were mounted in epoxy resin and polished
down to expose grain interiors for cathodoluminescence (CL) and
SHRIMP studies. Zircons were dated on the SHRIMP II ion microprobe
at the Beijing SHRIMP Centre, Institute of Geology, Chinese Academy
of Geological Sciences. The analytical procedures were similar to
those described by Williams (1998). Mass resolution during the analytical sessions was ~5000 (1% definition), and the intensity of the
primary ion beam was 5–8 nA. Primary beam size was 25–30 μm,
and each site was rastered for 120–200 s prior to analysis. Five
scans through the mass stations were made for each age determination. U abundance was calibrated using the standard SL13
(U = 238 ppm, Williams, 1998) and 206Pb/ 238U was calibrated using
the standard TEMORA ( 206Pb/ 238U age = 417 Ma; Black et al., 2003).
The decay constants used for age calculation are those recommended
by the Subcommission on Geochronology of IUGS (Steiger and Jager,
1977). Measured 204Pb was applied for the common lead correction,
and data processing was carried out using the Squid and Isoplot programs (Ludwig, 2001). The uncertainties for individual analyses are
quoted at the 1 sigma confidence level, whereas errors for weighted
mean ages are quoted at 95% confidence.
4.2.
40
Ar/ 39Ar dating
Incremental step-heating 40Ar/ 39Ar age measurements were performed on amphibole and biotite mineral separates from the western Anatolian Oligo–Miocene granitoids. The analyses were
performed in the Radiogenic Isotopes Laboratory at Ohio State University. The general procedures have been described by Foland et
al. (1993) and references therein, except for the use of a new
noble-gas mass analysis system. Sized aliquots (~ 1–15 mg) of biotite
or amphibole were irradiated in the L-67 position of Ford Nuclear
Reactor, Phoenix Memorial Laboratory, at the University of Michigan
for 36 h. They were subsequently heated incrementally to successively higher temperatures using a custom-built, resistance-heating,
high-vacuum, low-blank furnace. The step heating was continuous
with ramp times from one temperature to another of about 1 min
and with dwell times of about 30 min at each temperature. These
incremental-heating fractions were analyzed by static gas mass analysis with a MAP 215-50 mass spectrometer. Corrections for interfering reactions producing Ar from K, Ca, and Cl were made using
factors determined. The monitor used was an intra-laboratory muscovite standard (“PM-1”) with an 40Ar/ 39Ar age of 165.3 Ma; an uncertainty of ±1% is assigned to this age in order to allow for
uncertainties in the standards against which PM-1 was calibrated.
The age for this monitor was determined by simultaneous cross calibration with several monitors including the Fish Canyon Tuff biotite
standard (FCT-3) with an age of 27.84 Ma.
4.3. Major, trace elements and Sr–Nd isotope analyses
Major and trace-element (V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr) analyses were carried out using a Philips PW 1140 X-ray fluorescence
spectrometry (XRF), and inductively-coupled plasma source mass
6
Fig. 3. CL images of dated zircon crystals from; a—the Çataldağ, b—the Eybek, c—the Çamlık, and d—Eğrigöz plutons. SHRIMP sites are marked by circles. The numbers refer to analytical data in Tables 1, 2, 3 and 4. The size of the scale bars is 100 μm.
spectrometry (ICP-MS) was used for the analysis of Sc, Cs, Ba, REEs,
Hf, Ta, Nb, U, Pb, Th and U at the Department of Earth Science, University of Bergen, Norway. The glass-bead technique of Padfield and Gray
(1971) was used for major elements and pressed-powder pellets for
trace elements, utilizing international standards and the recommended or certified concentrations of Govindaraju (1994) for calibration. The USGS standards BCR2 and W2 were run regularly to
establish reproducibility. For the major elements it is generally b2%,
but for Na2O, K2O and P2O5 around 4%. For the XRF-analyzed trace
elements the reproducibility is generally b10%.
The ICP-MS analyses were performed on a Thermo Fisher Scientific ELEMENT2 HR-ICP-MS. 100 mg of dry sample powders were
digested in a microwave sample container using a mixture of concentrated HNO3 (4 ml), HF (1 ml) and HCL (5Ml). After digestion, the
samples were transferred to 30 ml Savillex beakers and evaporated
to dryness at 90 °C overnight. The residue was dissolved in 2 N
HNO3, transferred to 50 ml volumetric flasks and diluted to volume
with pure water. Before analysis the samples were diluted further
and Indium (In) was used as an internal standard. For Nb, Cs, Ba, Hf,
Ta, Pb, Th, U, and REE the reproducibility is ~ 5%, and ~9–13% for Pr,
Tb, Ba, Th and U.
Rb/Sr and Sm/Nd ratios were determined using a Finnegan 262
mass spectrometer and isotope dilution techniques at UoB. The chemical processing was carried out in a clean-room environment with
reagents purified in two-bottle Teflon stills. Samples were dissolved
in a mixture of HF and HNO3. Rb–Sr and REE were separated by specific extraction chromatography using the method described by Pin et
al. (1994). Sm and Nd were subsequently separated using a modified
version of the method described by Richard et al. (1976). Sm, Nd, Rb
and Sr were loaded on a double filament, and Sm, Rb and Sr were analyzed in static mode and Nd in multi-collector dynamic mode.
Table 1
Summary chart of Ar–Ar and U–Pb Shrimp ages obtained from Oligo–Miocene granitoids of the western Anatolia. Ar–Ar ages are given as plateau ages.
Unit
Group
Evciler
SCG
Ilıca
Eybek
Hıdırlar
Çataldağ
Kestanbol
Eğrigöz
Çamlık
SCG
SCG
SCG
SCG
RMG
NATPG
NATPG
40
Ar/39Ar
(Ma)
238
U–206 Pb Shrimp
(Ma)
Hornblende
Biotite
28.0 ± 0.1
27.7 ± 0.1
22.3 ± 0.1
24.8 ± 0.1
24.8 ± 0.1
21.9 ± 0.1
23.5 ± 0.2
23.0 ± 0.1
20.4 ± 0.1
22.3 ± 0.2
18.9 ± 0.1
20.3 ± 0.1
K-Feldspar
Zircon
23.94 ± 0.31
22.8 ± 0.2
19.0 ± 0.1
20.6 ± 0.1
21.91 ± 0.33
19.48 ± 0.29
22.60 ± 0.77
7
Table 2
Zircon U–Pb Shrimp data of the Çataldağ pluton.
Spot
1–1.1
1–2.1
1–3.1
1–4.1
1–5.1
1–6.1
1–7.1
1–8.1
1–9.1
1–10.1
2–1.1
2–2.1
2–3.1
2–4.1
2–5.1
2–6.1
U
Th
Th/U 206Pb* %206 (1)
±% (1)
±% Total
±% Total
±% (1) 206Pb/
207
207
238
238
(ppm) (ppm)
(ppm) Pbc 206Pb*/238U
Pb*/235U
Pb/206Pb
U/206Pb
U age
567
662
2835
1413
1912
4276
2192
1997
2215
3849
1611
1008
614
2809
909
736
419
171
1057
353
563
6678
756
663
726
5887
374
771
1094
609
1046
597
0.76 1.77
0.27 1.94
0.39 8.80
0.26 4.21
0.30 5.62
1.61 12.3
0.36 6.09
0.34 6.08
0.34 6.53
1.58 14.2
0.24 4.39
0.79 2.79
1.84 1.84
0.22 8.50
1.19 2.59
0.84 2.22
6.38
3.01
1.02
1.51
2.00
–
0.93
2.68
1.04
2.36
1.60
1.60
1.30
0.37
1.39
6.90
0.003380
0.003303
0.003567
0.003465
0.003294
0.003327
0.003219
0.003480
0.003405
0.004220
0.003116
0.003183
0.003409
0.003499
0.003279
0.003337
3.1
2.4
2.1
2.2
2.3
2.1
2.2
2.2
2.1
5.7
2.3
2.3
2.4
2.2
2.4
2.5
0.0223
0.0227
0.0217
0.02753
0.0133
0.0201
0.02319
0.0232
0.0266
0.0305
0.0204
0.0235
0.0195
0.02278
0.0243
0.0251
38
16
7.5
3.5
26
5.2
3.9
11
4.2
9.3
13
6.6
14
3.4
12
16
0.1019
0.0769
0.0544
0.0576
0.0594
0.04879
0.0552
0.0633
0.0623
0.0682
0.0618
0.0633
0.0608
0.0527
0.0624
0.0935
7.3
5.7
2.3
2.7
2.9
1.8
2.4
2.2
2.2
3.4
4.8
3.6
7.1
2.2
3.8
3.3
275.7
292.3
276.7
288.6
292.3
298.7
309.4
282.0
291.5
232
315.1
310.3
286.2
283.8
301.6
284.7
2.3
2.3
2.1
2.2
2.1
2.1
2.2
2.1
2.1
5.7
2.2
2.3
2.4
2.2
2.3
2.3
21.74
21.26
22.96
22.30
21.20
21.41
20.72
22.39
21.91
27.1
20.06
20.49
21.94
22.52
21.11
21.48
(2) 206Pb/
U age
(3) 206Pb/
U age
238
± 0.68
± 0.52
± 0.49
± 0.48
± 0.49
± 0.45
± 0.45
± 0.49
± 0.46
± 1.5
± 0.45
± 0.47
± 0.53
± 0.49
± 0.51
± 0.54
21.71
21.17
23.02
21.99
21.66
21.48
20.57
22.34
21.63
26.9
20.03
20.30
22.08
22.49
20.91
21.26
238
±0.55
±0.50
±0.48
±0.47
±0.46
±0.45
±0.44
±0.48
±0.46
±1.5
±0.44
±0.46
±0.54
±0.49
±0.49
±0.50
21.85
21.35
23.02
21.96
21.58
21.58
20.60
22.21
21.84
27.0
20.10
20.41
22.19
22.59
21.05
21.05
± 0.70
± 0.55
± 0.52
± 0.51
± 0.50
± 0.62
± 0.48
± 0.52
± 0.49
± 2.2
± 0.47
± 0.55
± 0.82
± 0.51
± 0.63
± 0.65
Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively.
Error in standard calibration was 0.54% (not included in above errors but required when comparing data from different mounts).
(1) Common Pb corrected using measured 204Pb.
(2) Common Pb corrected by assuming 206Pb/238U–207Pb/235U age-concordance.
(3) Common Pb corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.
Repeated measurements of the La Jolla standard (Nd-isotopes) and
the NIST SRM 987 standard (Sr-isotopes) yielded average ratios of
0.511669 ± 5 (2 SE) for 143Nd/ 144Nd, and 0.710254 ± 5 (2 SE)
for 87Sr/ 86Sr, respectively.
0.10
5. Geochronology
We dated seven plutons (Evciler, Ilıca, Hıdırlar, Kestanbol, Eğrigöz,
Çamlık, and Çataldağ) using the 39Ar/ 40Ar method, and four plutons
0.10
a
Mean = 21.91 ± 0.33 Ma [1.5%] 2s
12 spots,MSWD = 1.11
spots 1.7.1, 1.10.1, 2.1.1, and 2.2.1
were excluded
0.09
Mean = 23.94 ± 0.31 Ma [1.3%] 2s
11 spots, MSWD = 1.6
spots 1.4.1, 2.1.1, and 2.4.1
were excluded
0.09
0.08
0.08
207Pb/206Pb
207Pb/206Pb
b
0.07
0.07
0.06
0.06
0.05
0.05
25
24
0.04
250
23
270
22
290
21
20
310
30
19
330
0.04
210
350
28
26
230
250
270
238U/206Pb
c
0.064
22
24
20
290
310
330
238U/206Pb
d
Mean = 22.60 ± 0.77Ma [3.4%] 2s
16 spots, MSWD = 13
Mean = 19.48 ± 0.29 Ma [1.5%] 2s
16 spots, MSWD = 0.93
0.12
0.060
207Pb/206Pb
207Pb/206Pb
0.10
0.056
0.052
0.08
0.048
28
26
24
22
20
0.06
18
0.044
0.040
220
260
300
238U/206Pb
340
380
0.04
280
22
21
300
20
320
19
340
18
360
17
380
238U/206Pb
Fig. 4. Tera-Wasserburg 206Pb/238U versus 207Pb/206Pb diagrams with errors depicted at the 1-sigma level. a—the Çataldağ, b—the Eybek, c—the Çamlık, and d—Eğrigöz plutons.
Uncertainties on all weighted average age calculations are 2-sigma confidence levels.
8
Table 3
Zircon U–Pb Shrimp data of the Eybek pluton.
Spot
U
Th
Th/U 206Pb* %206Pbc (1)
±% (1)
±%
206
207
(ppm) (ppm)
(ppm)
Pb*/238U
Pb*/235U
1–1.1
479
1–2.1
417
1–3.1
619
1–4.1 1046
1–5.1
547
1–6.1
290
1–6.2
700
1–7.1
711
1–8.1
956
2–1.1 1775
2–2.1
539
2–3.1
611
2–4.1
811
2–5.1
816
293
237
386
768
351
173
448
444
1600
1214
337
427
602
563
0.63
0.59
0.64
0.76
0.66
0.62
0.66
0.64
1.73
0.71
0.65
0.72
0.77
0.71
1.68
1.50
2.16
3.61
1.86
1.11
2.37
2.39
3.16
6.54
1.73
1.95
2.11
2.44
8.14
4.58
6.59
2.16
4.56
16.07
5.01
5.29
1.76
1.49
1.40
2.19
–
4.13
0.00369
0.00387
0.003774
0.003865
0.003814
0.00353
0.003701
0.003579
0.003739
0.004199
0.003681
0.003490
0.002862
0.00340
3.2
3.1
2.2
1.6
1.9
4.8
2.0
2.7
1.4
1.4
1.3
2.4
3.3
3.4
0.018
0.014
0.0222
0.0195
0.0289
0.0239
0.011
0.0214
0.0224
0.0224
0.0071
0.0219
Total
±%
Pb/206Pb
207
67
76
43
28
23
0.1101
0.084
0.097
0.0667
0.0845
0.173
29
0.0936
97
0.0900
17
0.0645
13
0.0555
8.5 0.0570
100
0.0639
0.0408
23
0.0653
7.7
12
12
5.4
7.8
11
6.4
8.9
3.3
3.0
4.5
4.0
9.5
14
Total
±% (1) 206Pb/
238
238
U/206Pb
U age
245.8
239.6
246.8
249.0
252.3
225.3
254.2
256.1
259.7
233.1
267.3
269.4
330.3
287.4
1.7
2.4
1.4
1.1
1.4
1.9
1.3
1.3
1.1
1.3
1.3
1.6
2.9
3.3
23.72
24.91
24.28
24.87
24.54
22.7
23.81
23.03
24.06
27.01
23.68
22.46
18.42
21.87
±0.75
±0.78
±0.53
±0.40
±0.48
±1.1
±0.47
±0.62
±0.34
±0.38
±0.32
±0.53
±0.60
±0.74
(2) 206Pb/
U age
238
24.08
25.56
24.40
25.18
24.28
24.00
23.80
23.74
24.21
27.28
23.75
23.36
19.63
21.86
± 0.50
± 0.71
± 0.50
± 0.30
± 0.41
± 0.83
± 0.37
± 0.40
± 0.29
± 0.35
± 0.32
± 0.37
± 0.57
± 0.78
(3) 206Pb/
U age
238
24.05
25.62
24.35
25.28
24.34
24.0
24.04
23.80
24.34
27.18
23.74
23.36
20.13
21.46
± 0.67
± 0.77
± 0.57
± 0.34
± 0.48
± 1.0
± 0.44
± 0.44
± 0.47
± 0.44
± 0.37
± 0.44
± 0.66
± 0.90
(Eğrigöz, Çamlık, Çataldağ and Eybek) using the Shrimp U–Pb method. Cathodoluminescence (CL) images and summary of the age data
are presented in Fig. 3 and Table 1, respectively.
5.1. U–Pb zircon ages
The zircons separated from the Çataldağ pluton have mostly euhedral and transparent grains with aspect ratios ranging from 1:1.5 to
1:3.5 (Fig. 3a). The majority of these zircons show magmatic growth
zoning with patchy recrystallization zones and local cores. Some
grains are represented by faint oscillatory and sector zoning (e.g.
Grains 1–6.1 and 2–1.1, Fig. 3a). Recrystallization zones in some of
the grains truncate the previously formed oscillatory zones (Grains
1–7.1, 1–8.1, 2–2.1, 2–3.1, and 2–6.1). Grains 1–3.1 and 1–8.1 have
xenocrystic cores with weakly developed Cl intensity. Laser spots
were concentrated on thin oscillatory zoned parts. All of the spots
(16 measurements) yielded ages between 20 and 23 Ma, except
Spot 1–10.1 that provided an age of ~27 Ma (Table 2). A coherent
group of 12 measurements has been used to calculate a mean age of
21.91 ± 0.33 Ma (Fig. 4a) for the emplacement age of the Çataldağ
pluton.
Zircons grains from the Eybek pluton are idiomorphic and transparent. Their aspect ratio ranges between 1:2 and 1:4 (Fig. 3b).
Most zircon grains exhibit clear oscillatory and sector zoning, indicating a magmatic origin. Some of the grains such as 1–1.1, 1–2.1, 1–3.1,
1–4.1, 2–2.1, and 2–3.1 have apparent inner cores. Laser spots are located on the oscillatory zoned parts (Fig. 3b). Except for one spot
(2–1.1), all results from the Eybek zircons gave ages between 20
and 26 Ma (Table 3; Fig. 4b). Spot 2–1.1 yielded an age of 27.18
± 0.44 Ma. This particular age and the age obtained from Spot 1 to
4.1 were excluded from the mean age calculation because of their
high U and Th values (Table 3). The corrected ages obtained from
Spot 2 to 4.1 are highly discordant, and hence this measurement
was not included in the mean age calculation either. The rest of the
measurements that represent a coherent age group were used to calculate a mean age of 23.94 ± 0.31 Ma for the timing of the emplacement of the Eybek pluton (Fig. 4b).
Zircon grains from the Çamlık pluton have long prismatic or stubby,
idiomorphic crystals (Fig. 3c). The outer rims of these grains display
Table 4
Zircon U–Pb Shrimp data of the Çamlık pluton.
Spot
1–1.1
1–2.1
1–3.1
1–4.1
1–5.1
1–6.1
1–7.1
1–8.1
1–9.1
1–10.1
1–11.1
2–1.1
2–2.1
2–3.1
2–4.1
2–5.1
U
Th
Th/U 206Pb* %206Pbc (1) 206Pb*/ ±% (1) 207Pb*/
238
235
(ppm) (ppm)
(ppm)
U
U
±%
4458
3151
1497
3375
4510
997
5046
2797
2324
3484
3130
2020
2546
3519
1142
2462
3.6
3.1
11
9.0
2.4
12
3.6
4.4
4.5
3.8
4.1
9.9
3.7
5.6
14
3.8
2433
1887
832
1584
3232
362
1621
1729
625
1469
935
498
638
1364
434
799
0.56
0.62
0.57
0.48
0.74
0.38
0.33
0.64
0.28
0.44
0.31
0.25
0.26
0.40
0.39
0.34
14.0
10.5
4.44
9.47
15.0
2.68
16.5
7.85
7.08
10.4
9.65
5.63
7.85
11.1
3.22
7.44
0.40
1.91
1.85
0.71
1.12
0.24
1.15
0.34
0.40
0.39
0.69
0.33
0.21
1.25
0.71
0.003650
0.003870
0.003410
0.003229
0.003857
0.00308
0.003790
0.003247
0.003516
0.003461
0.003574
0.003220
0.003571
0.003644
0.003221
0.003492
1.5
1.5
1.7
1.9
1.5
6.0
1.5
1.6
1.6
1.5
1.5
1.7
1.6
1.5
2.0
1.6
0.02408
0.02573
0.0204
0.0177
0.02532
0.0195
0.02409
0.02111
0.02119
0.02216
0.02191
0.0202
0.02258
0.0243
0.0208
0.02373
Total
±% Total
±% (1) 206Pb/
238
238
Pb/206Pb
U/206Pb
U age
207
0.05054
0.0499
0.0538
0.0490
0.04890
0.0592
0.04868
0.0516
0.0499
0.0481
0.0473
0.0510
0.0496
0.0532
0.0618
0.0545
1.9
2.1
5.1
4.5
1.7
7.1
1.7
2.8
2.6
2.2
2.3
4.5
2.6
4.1
3.8
2.7
273.0
257.8
289.5
306.1
258.8
320
263.0
306.3
282.2
288.3
278.8
308.4
278.7
272.8
304.6
284.5
1.5
1.5
1.7
1.8
1.5
6.0
1.5
1.6
1.6
1.5
1.5
1.7
1.6
1.5
1.8
1.6
23.49
24.90
21.94
20.78
24.82
19.8
24.38
20.89
22.63
22.27
23.00
20.72
22.98
23.45
20.73
22.47
± 0.35
± 0.37
± 0.38
± 0.39
± 0.36
± 1.2
± 0.36
± 0.33
± 0.35
± 0.34
± 0.35
± 0.36
± 0.36
± 0.36
± 0.40
± 0.36
(2) 206Pb/
U age
238
23.45
24.85
22.03
20.96
24.78
19.8
24.40
20.88
22.71
22.27
23.06
20.75
23.00
23.39
20.72
22.39
±0.35
±0.37
±0.37
±0.39
±0.36
±1.2
±0.36
±0.33
±0.36
±0.34
±0.35
±0.35
±0.36
±0.36
±0.38
±0.36
(3) 206Pb/
U age
238
23.48
25.16
21.81
20.64
24.68
19.9
24.41
20.77
22.73
22.23
23.00
20.72
23.01
23.54
20.86
22.46
± 0.38
± 0.42
± 0.41
± 0.43
± 0.41
± 1.3
± 0.38
± 0.37
± 0.37
± 0.36
± 0.37
± 0.37
± 0.38
± 0.39
± 0.41
± 0.38
9
Table 5
Zircon U–Pb Shrimp data of the Eğrigöz pluton.
U
Th
Th/U 206Pb* %206Pbc (1) 206Pb*/ ±% (1) 207Pb*/ ±%
238
235
(ppm) (ppm)
(ppm)
U
U
Spot
1–1.1
608
1–2.1
1225
1–3.1
918
1–4.1
629
1–5.1
459
1–6.1
278
1–7.1
318
1–8.1
1025
1–9.1
511
1–10.1
951
1–11.1
559
1–12.1
676
1–13.1
527
1–14.1
807
1–15.1
674
1–16.1
940
375
739
448
326
300
140
191
489
214
599
322
294
276
350
312
418
0.64
0.62
0.50
0.54
0.68
0.52
0.62
0.49
0.43
0.65
0.60
0.45
0.54
0.45
0.48
0.46
1.61
3.42
2.46
1.66
1.25
0.756
0.865
2.71
1.49
2.55
1.58
1.84
1.39
2.19
1.79
2.49
4.93
1.44
3.55
4.16
5.53
7.86
6.82
2.81
6.76
3.52
8.99
5.25
5.02
1.50
2.18
0.93
0.002848
0.003201
0.002988
0.002973
0.00292
0.00293
0.00286
0.002957
0.00310
0.00304
0.00292
0.00296
0.00297
0.003089
0.003017
0.00302
3.2
2.0
2.5
2.5
3.5
3.8
5.9
2.4
3.9
3.4
4.7
3.6
3.8
2.1
2.4
3.3
0.0246
0.0131
0.0221
0.0105
0.0221
9.5
40
18
86
43
0.0178
0.017
0.0202
25
62
13
0.0146
0.0274
0.0225
0.0157
0.0173
68
22
11
26
22
Total 207Pb/ ±%
Pb
206
0.0779
0.0668
0.0668
0.0807
0.0893
0.115
0.1040
0.0745
0.107
0.0665
0.118
0.0883
0.0914
0.0686
0.0587
0.0587
8.1
3.4
7.0
5.4
8.5
9.8
5.8
6.1
11
5.5
14
8.9
9.5
5.9
6.3
4.3
Total 238U/ ±% (1) 206Pb/
238
Pb
U age
206
325.0
307.9
320.1
324.9
315.5
315.4
315.6
325.0
295.6
321
303.8
315.6
326
317.2
322.8
324
2.3
1.9
2.1
2.3
2.4
2.9
2.8
2.1
2.9
3.3
3.0
2.3
3.6
2.1
2.1
3.1
18.33
20.60
19.23
19.14
18.81
18.83
18.4
19.03
19.95
19.59
18.78
19.06
19.13
19.88
19.42
19.46
± 0.59
± 0.41
± 0.49
± 0.48
± 0.66
± 0.72
± 1.1
± 0.46
± 0.78
± 0.66
± 0.89
± 0.69
± 0.73
± 0.43
± 0.47
± 0.65
(2) 206Pb/
U age
238
19.02
20.36
19.59
18.96
19.29
18.64
18.91
19.10
20.11
19.55
19.26
19.31
18.63
19.73
19.63
19.58
±0.47
±0.39
±0.42
±0.44
±0.50
±0.61
±0.54
±0.41
±0.66
±0.66
±0.72
±0.48
±0.70
±0.42
±0.43
±0.62
(3) 206Pb/
U age
238
18.83
20.60
19.39
18.99
19.27
18.80
19.00
19.25
20.30
19.35
19.28
19.32
18.76
19.99
19.50
19.71
± 0.57
± 0.45
± 0.48
± 0.53
± 0.62
± 0.70
± 0.76
± 0.45
± 0.70
± 0.76
± 0.84
± 0.54
± 0.79
± 0.46
± 0.48
± 0.68
magmatic oscillatory zoning and locally developed irregular recrystallization zones with low CL (Grains 1–5.1, 1–11.1, 2–3.1 and 2–4.1;
Fig. 3c). The inner parts of the grains show xenocrystic cores (e.g. Grains
1–6.1, 1–7.1, and 2–5.1) and some recrystallization zones (e.g. Grains
1–2.1 and 2–2.1). Grains 1–10.1 and 2–1.1 exhibit convoluted and
curved zoning. The obtained ages range from 19 to 25 Ma (Table 4).
The calculated mean age from the whole data set is 22.60 ± 0.77 Ma
(Fig. 4c), representing the emplacement age of the pluton.
Zircons from the Eğrigöz pluton have idiomorphic and transparent
crystals with aspect ratios between 1:1.1 and 1:2.5. The CL images of
the dated zircons commonly show magmatic oscillatory zoning with
locally developed sector zoning (Fig. 3d). The majority of the zircon
grains display ordinary magmatic growth zoning, and some growth
zoning around the inclusion boundaries (Grains 1.9.1 and 1.12.1;
Fig. 2d). A total of 16 measurements, taken from the outer oscillatory
zones (Fig. 3d), have revealed ages ranging from 18 Ma to 21 Ma
(Table 5). The calculated mean age of the Egrigöz pluton is 19.48 ±
0.29 Ma (Fig. 4d).
5.2.
40
Ar/ 39Ar dates
The 40Ar/ 39Ar ages of the plutons, obtained from hornblende, biotite, and K-feldspar separates, are given in Table 1, and the age spectrum plots are shown in Fig. 5.
The two biotite separates from the Evciler granitoid display plateau age of 24.8 ± 0.1 Ma (Fig. 5a and b), whereas the two hornblende
separates yield plateau ages of 28.0 ± 0.1 Ma and 27.7 ± 0.1 Ma
(Fig. 5c and d). The younger biotite ages likely represent the cooling
ages, while the slightly older amphibole ages are close to the emplacement age of the Evciler pluton.
We obtained hornblende and biotite plateau ages of 22.3 ± 0.1 Ma
and 21.9 ± 0.1 Ma (respectively, Fig. 5e–f) from the Ilıca granitoid,
and of 23.5 ± 0.2 Ma and 23.0 ± 0.1 Ma (respectively, Fig. 5g–h)
from Hıdırlar granitoid. The plateau ages of hornblende and biotite
separates from the Kestanbol granitoid are 22.8 ± 0.2 and 22.3 ±
0.2 Ma, respectively (Fig. 5i–j).
The hornblende and biotite separates from the Eğrigöz pluton
yielded plateau ages of 19.0 ± 0.1 Ma and 18.9 ± 0.1 Ma (respectively,
Fig. 5k–l), and the biotite and K-feldspar separates from the Çataldağ
pluton gave plateau ages of 20.4 ± 0.1 and 20.6 ± 0.1 Ma (respectively,
Fig. 5m–n). The biotite separates from the Çamlık pluton yielded a plateau age of 20.3 ± 0.1 Ma (Fig. 5o).
6. Geochemistry
We have studied a total of thirteen plutons in NW Anatolia and
have categorized them into three groups based on the nature and distribution of the tectonic units into which they were intruded. These
groups include the granitoids of the 1—Rhodope metamorphic massif
(RMG), 2—Sakarya continent (SCG) and 3—Anatolide–Tauride platform (ATP). The RMG group is represented by the Kestanbol pluton,
while the SCG includes the Eybek, Evciler, Karakoy, Kozak, and IlicaSamli plutons and the Hidirlar, Katrandag and Yenice stocks (Fig. 1).
All these granitoids of the RMG and SCG occur north of the Izmir–Ankara–Erzincan suture zone. To the south of this suture zone, the granitoids of the ATPG are further subdivided into the Northern (NATPG)
and Southern (SATPG) sub-groups. The Camlik and Egrigoz plutons
are part of the NATPG, whereas the Salihli and Turgutlu granitoids
in the Menderes metamorphic massif occur in the SATPG (Fig. 2).
The major and trace element compositions and Sr–Nd isotopic concentrations of representative samples from the RMG, SCG and ATPG
are listed in Table 6.
We also analyzed the major and trace element compositions and
Sr–Nd isotopic concentrations of representative metamorphic basement rocks from the Sakarya continent (Kazdağ core complex and
cover rocks; Altunkaynak et al., unpublished data) and the Anatolide–Tauride platform (Menderes core complex and cover rocks;
Altunkaynak et al., unpublished data) to better evaluate the nature
and extent of continental crust–magma interaction. In addition, we
evaluated metamorphic rocks of the Pelagonian zone in Greece (Brique et al., 1986; Pe-Piper et al., 2002; Anders, 2005), the central Pontides of northern Turkey (Nzegge et al., 2006) and the Istranca massif
in northwestern Turkey (G. Sunal, unpublished data) as possible analogs for the rocks in which the different groups of granitoids, north
and south of the IASZ were emplaced. Kula alkaline basalts representing the depleted mantle-derived melts (Aldanmaz et al., 2000, Alıcı et
al., 2002, Dilek and Altunkaynak 2010), dioritic enclaves and lavas
representing enriched mantle melts (EMM) from China and western
Anatolia (Yang et al., 2004; Altunkaynak et al., 2010) and granitoids
emplaced into other metamorphic core complexes in the northern
(Rhodope massif) and central (Cyclades) Aegean province are also
10
a
32
28
28
24
24
Age (Ma)
Age (Ma)
32
20
16
b
20
16
Evciler-Biotite-2
12
Plateau age = 24.8 ± 0.1 Ma
(1σ, including J-error of .25%)
Evciler-Biotite-1
12
8
MSWD = 0.60, probability=0.94
39
Includes 99.69% of the Ar
4
0.0
0.2
0.4
Cumulative
39
0.8
4
0.0
1.0
c
50
40
40
30
10
0
0.0
Evciler-Hornblende-1
0.4
0.6
0.8
1.0
Ar Fraction
Evciler-Hornblende-2
0
0.0
1.0
0.8
30
10
39
0.6
39
d
20
0.2
0.4
Cumulative
60
50
20
0.2
Ar Fraction
Age (Ma)
Age (Ma)
60
0.6
39
8
39
0.2
0.4
0.6
0.8
1.0
Cumulative 39 Ar Fraction
50
30
f
e
Age (Ma)
Age (Ma)
40
20
Ilıca-Biotite
10
0.4
Cumulative
0.6
39
0.8
0
0.0
1.0
0.6
39
0.8
1.0
0.8
1.0
Ar Fraction
h
40
Age (Ma)
Age (Ma)
40
30
0
0.0
0.4
Cumulative
50
g
10
0.2
Ar Fraction
50
20
39
10
39
0.2
20
Ilıca-Hornblende
(1σ
, including J-error of .25%)
0
0.0
30
Hıdırlar-Biotite
10
39
0.4
0.6
20
Hıdırlar-Hornblende
0.2
30
0.8
1.0
0
0.0
39
0.2
0.4
0.6
Fig. 5. 39Ar/40Ar plateau age spectrums of western Anatolian granitoids. Summary of the ages are listed in Table 1. Plateau steps are shown as white color whereas rejected ones are
black. Box heights are 1 sigma errors.
i
j
k
l
m
n
11
o
Fig. 5 (continued).
12
Fig. 6. a—Total alkali vs. SiO2 classification diagram (Cox et al., 1979) and b—AFM diagram of western Anatolian granitoids (Irvine and Baragar, 1971).
The SiO2 contents of the RMG and SCG groups vary between 52.74
and 66.77 wt.%, whereas those of the ATPG group ranges from 65.78
to 72.13 wt.%. The SiO2 contents of magmatic enclave from the ATPG
contains only 58.91 wt.% SiO2. The RMG and SCG plutons are hence
represented mainly by intermediate and silicic rocks based on their
SiO2 contents, whereas the ATPG plutons are mostly silicic in composition. On a TAS diagram (Fig. 6a; Cox et al., 1979), the RMG plutons
range from granodiorite, monzonite to syenite. Samples from the
SCG plutons span a wide range of rock types, extending from syenodiorite, monzonite and diorite to granodiorite. The ATPG plutons
plot in the granodiorite and granite fields. One of the magmatic enclaves analyzed from the ATPG is classified as monzodiorite.
The majority of the samples are subalkaline in nature and display a calc-alkaline trend (Irvine and Baragar, 1971; Fig. 6b), except
for the two alkaline samples from the RMG and one sample from a
SCG pluton (Katrandağ granite) (Fig. 6a). On the K2O vs. SiO2 classification diagram of Peccerillo and Taylor (1976), all pluton samples from the RMG, some samples from the SCG plutons (Evciler,
Karakoy, and Yenice granitoids), and one sample from the ATPG
pluton (Çamlik granitoid) are classified as shoshonitic, while the
others are high-K calc-alkaline in character. Two samples from the
Katrandağ and Yenice granitoids (SCG) are medium-K in character
(Fig. 7). The A/CNK [Al2O3/(CaO + Na2O + K2O) molecular ratio]
values of the analyzed granitoids range between 0.70 and 1.0. All
samples of the RMG and SCG plutons are metaluminous (Fig. 8;
Shand 1927). The least evolved members of the ATPG plutons and
their enclave are predominantly metaluminous, although some
more evolved samples exhibit slightly peraluminous signatures
with A/CNK ratios ranging from 1.1 to 1.2. In the same diagram,
Fig. 7. K2O vs. SiO2 diagram of western Anatolian granitoids using the classification
scheme of Peccerillo and Taylor (1976). See Fig. 6 for the symbols.
Fig. 8. A/CNK vs. A/NK plot of western Anatolian granitoids (Shand, 1927).
used for comparison (Fig. 1; Christofides et al., 1998; Pe-Piper and
Piper, 2001; Pe-Piper et al., 2002).
6.1. Major and trace element characteristics
a
1000
13
RMG
SCG
Av. Lower crust
Av. Middle crust
RBROM-N/KCO
Av. Upper crust
100
Av. Kula basalt
10
1
0.1
Cs RbBa Th U Nb Ta K La CePb Pr Sr P Nd Zr SmEu Ti Dy Y Yb Lu
b
1000
SATPG
NATPG
Av. Lower crust
Av. Middle crust
ROCK/N-MORB
Av. Upper crust
100
Av. Kula basalt
10
1
0.1
Cs Rb Ba Th U Nb Ta K La Ce Pb Pr Sr P Nd Zr SmEu Ti Dy Y Yb Lu
Fig. 10. N-MORB normalized multi-element patterns for the RMG and SCG (a) and
ATPG (b). N-MORB normalizing values are from Sun and McDonough (1989).
Fig. 9. Major and trace element versus SiO2 variation diagrams for western Anatolian
granitoids. See Fig. 6 for the symbols.
the metamorphic basement rocks of the Sakarya continent and the
ATP are predominantly peraluminous (A/CNK = 1.1–1.9), with the
exception of three samples from the SC basement that are metaluminous (A/CNK = 0.9–1.0) (Fig. 8). Both the basement and granitic
rocks have similar A/NK (Al2O3/Na2O + K2O) ratios between 1.1 and
2.5. All of the granitoid samples display I-type granite affinity, although two haplogranite sample of the ATPG pluton shows S-type
affinity (Fig. 8).
In the SiO2 variation diagrams (Fig. 9), the TiO2 (0.37–0.79 and
0.21–0.62 wt.%, respectively), Al2O3 (15.27–17.58 and 14.35–
16.66 wt.%), FeO* (3.49–7.09 and 1.86–3.83 wt.%), MgO (1.60–3.38 and
0.42–1.50 wt.%), CaO (3.67–7.08 and 1.04–4.56 wt.%) and P2O5
(0.12–0.75 and 0.08–0.25 wt.%) contents of the SCG and ATPG pluton
samples decrease with increasing SiO2 (52.74–66.77and 65.20–
72.13 wt.%, respectively). In these diagrams, the RMG samples display
trends that differ from those of the other groups. For example, the TiO2
(0.44–0.48 wt.%), FeO*(3.85–4.50 wt.%) and CaO (3.44–3.95 wt.%) contents of the RMG pluton samples remain nearly constant with increasing
SiO2 (57.09–65.51 wt.%) contents, and these rocks display two separate
trends in the diagrams of K2O (5.09–6.99 wt.%), MgO (1.38–1.71 wt.%)
and Al2O3 (15.42–18.55 wt.%) against SiO2. The SCG samples (Katrandag
and Yenice granitoids) and the magmatic enclave from the ATPG are the
least evolved samples with the highest MgO (2.70 wt.%), TiO2
(1.19 wt.%) and FeO* (7.89 wt.%) contents. The ATPG contains the most
silicic compositions. The Sr (695–1573 ppm and 163–671 ppm, respectively) and Zr (235–391 ppm and 114–224 ppm, respectively) contents
of the RMG and ATPG plutons decrease whereas the SCG samples (Sr:
421–785 ppm, Zr: 95–164 ppm) stay almost constant (or slightly decrease) with increasing SiO2 contents. The Rb contents (38–160 ppm,
178–268 ppm and 75–155 ppm, respectively) of the SCG, RMG and
ATPG display a positive correlation with SiO2 (Fig. 9).
On N-MORB normalized spider diagrams (Fig. 10a and b), all groups
(RMG, SCG and ATPG) display similar patterns with enrichment in the
most incompatible elements (e.g., Rb, Ba, Th, U, K, La and Ce) and depletion in Nb, Ta, Ti, P and Zr. All of the granitoid groups are strongly
enriched in LILE and LREE compared to the average lower crust, and display trace element compositions similar to average middle and upper
5
Hidirlar
Kozak
Evciler
Katrandag
Nd(20)
0
100
OIB
Ave.
EMM
-5
-10
Dy Ho
Er
Tm Yb
100
Ave. Kula Basalt
Ave. Lower Crust
Ave. Middle Crust
Ave. Upper Crust
Eybek
Yenice
Karaköy
SCG
SC basement
0.710
0.715
0.720
0.725
87Sr/ 86Sr(20)
Fig. 12. εNd(20) vs. 87Sr/86Sr(20) diagram for western Anatolian granitoids. Data source:
ATP (Menderes core and cover rocks) and SC (Kazdağ core and cover rocks) middle–
upper crustal compositions: Altunkaynak (unpub. data), Pelagonian Upper Crust : Anders
(2005), Santorini UC: Briqueu et al. (1986), Rhodope granites: Christofides et al. (1998),
Cyclades granitoids and Hercinian protoliths: Pe-Piper and Piper (2001, 2006), Kula basalts: Dilek and Altunkaynak (2010), average EMM (enriched mantle melts: Yang et al.
(2004) and Altunkaynak et al. (2010)), lithospheric mantle melting array: Davis and von
Blanckenburg (1995), Aegean Sea sediments: Altherr et al. (1988) and Global River Average: Goldstein and Jacobsen (1988).
on the basis of their Eu anomalies (Fig. 11a and b), whereas the syenitic
samples show positive Eu anomalies.
10
6.2. Sr and Nd isotopic signatures and Nd model ages
1
b
La
Ce
Pr
Nd Pm Sm Eu Gd Tb
Dy Ho
Er
Tm Yb
Lu
Fig. 11. Chondrite-normalized REE patterns for the RMG and SCG (a), and ATPG
(b). Chondrite normalizing values are from Boynton (1984).
crustal values. They also display a significant positive Pb anomaly,
which is not shown by the Kula basalts. Compared to N-MORB, the
ATPG samples and the SCG and RMG samples show a ~300 times and
a ~100 times enrichment in Pb, respectively. The granitoid groups
have variable Ce/Pb ratios ranging from 1.1 to 4.4 that are similar to
the Ce/Pb ratios of the average middle continental crust (Ce: 43 ppm,
Pb: 11 ppm; Ce/Pb = 3.9) and average upper crustal values (Ce:
63 ppm, Pb: 17 ppm, Ce/Pb = 3.7; Rudnick and Gao, 2003).
On chondrite-normalized spider diagrams (Fig. 11a and b), the REE
distributions of the SCG samples display considerable LREE enrichments
with respect to MREE and HREE (Lan/Ybn = 10.5–24.8) with some minor
depletions in MREE (Gdn/Ybn =1.2–2.4; Fig. 10a). Their HREE patterns
show nearly flat trends. The overall REE concentrations of these samples
fall between those of the Kula basalts and the average middle–upper
continental crust. The SCG group is characterized by either minor negative or slightly positive Eu anomalies. (Eu/Eu*= 0.80–1.25). Only three
samples from the SCG intrusions (Ilıca-Şamlı granite, one sample from
Hidirlar) display pronounced negative Eu anomalies (Eu/
Eu*= 0.51–0.61). In contrast, the ATPG samples show REE patterns similar to those of the average upper crust with significant negative Eu
anomalies (Eu/Eu* =0.30–0.60). The granodioritic samples of the RMG
group are transitional between those of the SCG and the ATPG groups
Sr and Nd isotopic data for the analyzed samples are shown in
Table 6. The initial Sr and Nd isotopic ratios ( 87Sr/ 86Sr(i); 143Nd/
144
Nd(i)) were calculated for the RMG, SCG and ATPG groups assuming a mean magma crystallization age of 20 Ma. The 87Sr/ 86Sr(i) ratios
vary from 0.705248 to 0.711428, and 143Nd/ 144Nd(i) values range
from 0.512619 to 0.512184. The Karakoy granitoid of the SCG group
is characterized by the lowest 87Sr/ 86Sr(i) = 705248–0.706106 and
the highest 143Nd/ 144Nd(i) = 0.512619–0.512548 values. The samples
8
6
RMG
SCG
NATPG
SATPG
Kula basalts
4
2
Ave.
EMM
0
Nd
ROCK/CHONDRITE
0.705
Lu
ATPG
ATPG
Global river average
Cyclades Granites
1
Nd Pm Sm Eu Gd Tb
1000
Pr
NATPG
(SATPG)
ATP basement
Aegean Sea Sediments
0.700
Ce
RMG
SCLM melting array
Rhodope
granites
(N. Greece)
a
La
Kestanbol
Camlik
Egrigoz
Salihli
Kula Basalts
RMG
SCG
Ave. Kula Basalt
Ave. Lower Crust
Ave. Middle Crust
Ave. Upper Crust
10
ROCK/CHONDRITE
1000
14
-2
-4
NATPG ATP
basement
Rhodope
granites
(Greece)
-6
-8
Cyclades granitoids
-10
Hercynian protoliths
-12
SATPG SC basement
-14
0
0.5
1
1.5
2
TDM (Ga)
Fig. 13. εNd(i) vs. TDM (Nd-model ages) diagram of the RMG, SCG and ATPG. See Fig. 12
for data source.
15
Kestanbol
Camlik
Egrigoz
Salihli
(SATPG)
Hidirlar
Kozak
Evciler
Katrandag
Eybek
Ilıca
Yenice
Karaköy
RMG
NATPG
0.2
Nb/Zr0.1
ATPG
SCG
Kula Basalts
Pa
rti
al
m
el
tin
g
30
20
La /Yb(n)
40
Pa
rtia
lm
elt
ing
50
MMA
10
FC
0.0
FC
MMA
Kula Basalts
20 Nb (ppm)30
40
0
10
20
40
60
80
100
120
La (ppm)
Fig. 14. La/Yb versus La (ppm) diagram illustrating the effects of partial melting in comparison to fractional crystallization. The inset diagram shows the variations of Nb/Zr with
changing Nb contents of the rocks. Vectors for FC and PM are from Thirlwall et al. (1994).
from the southern sub-group (SATPG) of the ATPG display higher
87
Sr/ 86Sr(i) ( 87Sr/ 86Sr(i) = 0.711428–0.71080) and lower 143Nd/
144
Nd(i) ( 143Nd/ 144Nd(i) = 0.51227–0.512184) ratios compared to
those of the RMG samples ( 87Sr/ 86Sr(i) = 0.707966–0.708799, 143Nd/
144
Nd(i) = 0.512408–0.512335) and SCG (average: 87Sr/ 86Sr(i) =
0.707540, 143Nd/ 144Nd(i) = 0.512450). The samples from the northern sub-group (NATPG) of the ATPG have initial Sr and Nd isotopic ratios of 0.708001–0.709039 and 0.512370–0.512348, respectively,
which are similar to those of the RMG and SCG samples (Table 6).
The calculated εNd(i) values for the western Anatolian granites
range from − 0.2 to − 8.35, with one sample from the SCG (Karakoy
pluton) showing a value of +0.12. The SATPG samples have the lowest εNd(i) values varying from − 8.4 to − 7.6, whereas the SCG samples have the relatively highest εNd(i) values between +0.12 to
−6.3. The RMG and NATPG groups have values intermediate between
these other two groups (Fig. 12). The Kula basalts from western Anatolia have εNd(i) values varying from + 5.2 to +6.5 (average: 6.1).
The RMG, SCG and NATPG samples lie on an array between the Kula
basalt field, representative of the partial melts of depleted Aegean
mantle (Aldanmaz et al., 2000; Alıcı et al., 2002), and the metamorphic basement rocks occurring to the north (SC) and the south
(ATP) of the Izmir–Ankara–Erzincan suture zone (Fig. 12), which
are similar to the Rhodope granites from northern Greece–Bulgaria.
In contrast, the Cyclades granitoids from the Aegean Sea, as well as
the SATPG samples from our study area plot in the field of the ATP
basement rocks. The ATP crystalline basement rocks have εNd(i)
values ranging from − 11.5 to −6.3 (average: −7.5). The SC crystalline basement rocks have more restricted values of εNd(i) ranging
from −11.3 to − 7.1 (average: −8.8) (Fig. 12).
The Nd depleted mantle model (TDM) and the εNd values of the
late Oligocene–middle Miocene granitoids are plotted together in
Fig. 13. The RMG and SCG plutons, which were emplaced into the
metamorphic basement rocks to the north of the suture zone (IASZ)
have younger TDM ages in comparison to those of the ATPG plutons
that were emplaced into the basement rocks in the ATP south of the
suture zone. The TDM of RMG and SCG plutons range from 0.6 to
1.2 Ga, corresponding to a Proterozoic age, similar to the Rhodope
granites from northern Greece–Bulgaria. This time constraint is consistent with the inferred extraction age of the K-enriched subcontinental lithospheric mantle source of the post-collisional lavas in
western Anatolia (0.9–1.0 Ga; Altunkaynak, 2007) and of the Rhodope granites in northern Greece (Christofides et al., 1998; Pe-Piper and
Piper, 2001; Pe-Piper et al., 2002). The TDM ages of the ATPG plutons
range from 1.2 to 1.6 Ga and constrain the residence age of their
source in the continental crust as the middle Proterozoic. This
model age is consistent with those of the Cyclades granitoids and
the ATP, representative of the Pan-African crust (Fig. 13) (Pe-Piper
and Piper, 2001, 2006; Pe-Piper et al., 2002).
7. Petrogenesis
7.1. Source characteristics
All pluton groups are subalkaline in nature, as revealed by their
major and trace element characteristics (Fig. 6a). Only two syenitic
samples from the RMG plutons and one sample from the SCG are alkaline. All groups are also potassic in character (high K-calcalkaline
to shoshonitic), resembling the compositions of those granitoids
commonly known as post-collisional in origin. The granitoids have
moderately to highly evolved compositions, as shown by their Mgnumbers (Fig. 8, average Mg# = 50 and 35, respectively) and silica
contents. All of the granitoid groups are represented by metaluminous to slightly peraluminous, I-type granitoids, whereas two haplogranite samples representing the most evolved members of the
NATPG are slightly to moderately peraluminous, S-Type granitoid
(Fig. 8). The RMG, SCG, and NATPG plutons, which were emplaced
into different tectonostratigraphic units, show similar major and
trace element characteristics and overlapping Sr–Nd isotopic ratios.
These observations may be attributed to similar evolutionary trends
and/or common melt sources. The SATPG plutons show higher Sr
and lower Nd isotopic compositions than those of the other groups.
Given the geochemical affinities among the RMG, SCG and NATPG
plutons (Figs. 12 and 13) and their distinctive isotopic differences
0.711
Kula basalts
(Ave. Nb/La:2.3
Ave. Ba/Rb: 12)
0.709
Open System
0.708
/ 86Sr
10
0.706
a
100
0.705
0.2
0.0
1.0
0.707
Crustal contamination
Ave.
EMM
UC
0.1
87Sr
0.8
Subduction zone
enrichment
0.4
0.6
Nb/La
1.0
0.710
1.2
1.4
16
1000
Closed system
b
0.002
0
0.004
0.006
0.008
0.010
1/Sr
Ave. Kula Basalt
(Ce/Pb=20)
40
Ave. Kula Basalt
30
c
d
0
Ave. SC
basement
10
2
20
4
Zr/Sm
Ce/Pb
6
8
Ba/Rb
0.705
0.710
0.705
0.715
0.710
87Sr/86Sr(i)
0.715
87Sr/86Sr(i)
Fig. 15. a—Nb/La versus Ba/Rb diagram illustrating the effects of crustal contamination and subduction metasomatism during evolution of the MEG. CC (Average Continental Crust):
McLennan (2001), EMM (average enriched mantle melts): Yang et al. (2004) and Altunkaynak et al. (2010), Kula basalts: Dilek and Altunkaynak (2010). b—87Sr/86Sr vs. 1/Sr diagram, c—Ce/Pb vs. 87Sr/86Sr(i) diagram and d—Zr/Sm vs. 87Sr/86Sr(i) diagram for RMG, SCG and ATPG.
1
Calc-alkaline volcanism associated with plutonism
KESTANBOL (RMG)
-5
-6
-7
re
ls
ig
na
tu
ILICA
SCG
us
ta
EYBEK
g
cr
YENICE
HIDIRLAR
in
-4
KOZAK
as
εNdi
-3
KARAKOY
cr
e
-2
EVCILER
In
-1
Initiation of mildly alkaline volcanism
Initiation of alkaline volcanism
0
SALIHLI (SATPG)
CAMLIK
EGRIGOZ
-8
NATPG
Exhumation of MM and
KD core complexes
-9
10
12
14
16
18
20
22
24
26
28
Average age (Ma)
Fig. 16. εNd(i) vs. average age diagram for western Anatolian granitoids. MM: Menderes core complex, KD: Kazdağ core complex. See Fig. 2 for data source.
17
Ave. Kula basalt
EMM
Ave. upper crust (Nzegge et al., 2006)
RMG
Ave. upper crust (Sunal, unpub. data)
0.73
0.74
a
SC basement
SCG
(20 Ma)
G
Ave. gneiss; Kazdag Massif
0.72
H
(H)
(G)
(H)
0.71
(G)
J
I
45
0.72
H
A
0.70
50
55
60
65
70
75
J
I
B
(J)
(I)
A
0.70
G
0.71
(J)
(I)
B
c
0.73
Ave. amphibolite, Kazdag Massif
87Sr/86Sr
87Sr/86Sr
(20 Ma)
0.74
45
80
50
55
SiO2 (wt%)
0.5134
b
(20 Ma)
A
0.5130
(I)
I
B
0.5126
(J)
(I)
(J)
(G)
J
0.5122
H
65
70
75
80
SiO2 (wt%)
G
(G)
(H)
143Nd/144Nd
143Nd/144Nd
(20 Ma)
0.5134
60
d
A
0.5130
I
0.5126
J
B
G
0.5122
H
0.5118
0.5118
45
50
55
60
65
70
75
80
SiO2 (wt%)
45
50
55
60
65
70
75
80
SiO2 (wt%)
Fig.17. Plots of 87Sr/86Sr(i) and 143Nd/144Nd(i), calculated at 20 Ma, versus SiO2 (wt.%), showing the results of AFC and bulk mixing modeling for the SCG and RMG. For the AFC
models (a–b), an average Kula basalt (A), representative of a depleted mantle-derived melt, and a melt derived from an enriched mantle source (EMM; B) were used as starting
magmas and different crustal compositions as contaminants: average upper crust (Nzegge et al., 2006) (G); average upper crust (Sunal, unpub. data) (H), average amphibolite
from the Kazdag Massif (Altunkaynak, unpub. data) (I), and average gneiss from the Kazdag Massif (Altunkaynak, unpub. data) (J). AFC model input parameters were: r = 0.8,
DSiO2 = 0.9, DSr = 1.1, DNd = 1.2. The dots along the AFC curves represent F (fraction of melt remaining) values decreasing in steps of 0.1 from left to right. The crustal contaminant
for each AFC curve is indicated in brackets. Bulk mixing arrays between the same endmembers with the dots along the lines at 20% intervals are shown in c–d.
from the SATPG plutons, we focus the remaining discussion on these
two distinct magmatic groups.
The RMG–SCG–NATPG plutons are isotopically depleted (εNd(i) =
+0.12 to −6.3, 87Sr/86Sr(i) =0.705248–0.709900), with respect to the
samples from the SATPG (87Sr/86Sr(i) =0.711428–0.71080, εNd(i) =
−8.4 to −7.6). These isotopic features imply either different source materials or different degrees of crustal contamination. The RMG, SCG and
NATPG samples have low εNd values and relatively high 87Sr/86Sr(i) compositions and display relatively high Mg-numbers and high abundances
of many incompatible elements, suggesting derivation of their melt
from a mantle source (Figs. 12 and 13). In Fig. 12, RMG–SCG–NATPG exhibit systematic co-variations within the lithospheric mantle array which
lies between the Kula basalts and the metamorphic basement rocks and
look similar to those of Rhodope granites in northern Greece and enriched
lithospheric mantle melts (EMM) from China and Turkey (Yang et al.,
2004, Altunkaynak et al., 2010). These features indicate that melting of
an enriched lithospheric mantle was involved in the evolution of RMG–
SCG–NATPG magmas. However, some of these granitoids have lower
87
Sr/86Sr ratios and higher εNd(i) values (+0.12 to −1.50) compared to
the enriched mantle melts (EMM). Hence, they display transitional values
between the depleted and enriched mantle melts. Similarly, it can be inferred from Fig. 13 that the RMG–SCG and some NATPG plutons have isotopic compositions and TDM ages (TDM =0.6–1.2 Ga) transitional between
those of the Kula basalts (TDM =0.3 Ga), EMM (TDM =0.9–1.1 Ga) and
the crystalline basement rocks (TDM =1.2 to 2 Ga). Therefore, these
model ages may indicate mixed model ages between the two endmembers rather than crustal extraction ages for each end-member.
Based on these lines of evidence, we deduce that melting of enriched lithospheric mantle and/or depleted mantle melts (at least partly) have contributed to the RMG–SCG–NATPG source region. The systematic covariation between mantle and crustal components and the large range
of the TDM ages is also consistent with the evolution of the RMG–SCG–
NATPG granitoid magmas through various degrees of crustal assimilation
or mixing of mantle melt with an evolved crustal component in different
proportions (McCulloch and Chappell, 1982; Arndt and Goldstein, 1987;
Chappell, 1996; Jwa, 2004, Sun et al., 2010). It is also apparent from
Fig. 12, for the genesis of the RMG–SCG–NATPG magmas, a potential contribution of crustal materials would have been lower in comparison to
those of the SATPG magmas. On the other hand, the SATPG samples
with crust-like geochemical signatures may have been produced by crustal melting or significant contributions from the ATP crystalline basement.
(Figs. 12 and 13)
Both the SC and ATP metamorphic basement rocks have higher A/
CNK values and lower Mg-numbers in comparison to the granitoid samples from the RMG–SCG. As the SC and ATP metamorphic basement
rocks are dominantly peraluminous (Fig. 8), crustal melting or a large degree of crustal contamination of the magmas would further increase
their A/CNK ratios and cause the formation of strongly peraluminous S-
18
0.74
D
ATP basement
(20 Ma)
ATPG
(D)
Ave. upper crust (Anders, 2005)
Ave. amphibolite, Menderes Massif
0.72
87Sr/86Sr
Ave. gneiss; Menderes Massif
C
F
(C)
87
(F)
0.71
E
0.73
0.72
F C
0.71
B
E
(E)
A
0.70
c
D
EMM
0.73
Sr/86Sr (20 Ma)
0.74
a
Ave. Kula basalt
45
B
A
0.70
50
55
60
65
70
75
45
80
50
55
SiO2 (wt%)
75
80
75
80
A
(E)
B
(C)
(E)
(C)
E
(F)
(F)
0.5122
F
C
D
(20 Ma)
d
0.5130
143Nd/144Nd
(20 Ma)
143Nd/144Nd
70
0.5134
b
0.5126
65
SiO2 (wt%)
0.5134
0.5130
60
0.5126
A
B
E
0.5122
F
(D)
C
D
0.5118
0.5118
45
50
55
60
65
70
75
80
SiO2 (wt%)
45
50
55
60
65
70
SiO2 (wt%)
Fig. 18. Plots of (87Sr/86Sr)i and (143Nd/144Nd)i, calculated at 20 Ma, versus SiO2 (wt%), showing the results of AFC and bulk mixing modeling for the ATPG. As in Fig. 17, an average
Kula basalt (A), representative of a depleted mantle-derived melt, and a melt derived from an enriched mantle source (EMM; B) were used as starting magmas in the AFC models
(a–b), alongside amphibolite from the Menderes Massif (E). Chosen crustal contaminants are: average upper crust (Anders, 2005) (C), upper crustal composition (UC9 from Anders,
2005) (D), average amphibolite from the Menderes Massif (Altunkaynak, unpub. data) (E), and average gneiss from the Menderes Massif (Altunkaynak, unpub. data) (F). AFC model
input parameters and explanations as in Fig. 17. Bulk mixing arrays between the same endmembers with the dots along the lines at 20% intervals are shown in c–d.
type granitoids. Therefore, we infer that none of the analyzed granitoids
could have been produced solely by these basement units. The metaluminous to slightly peraluminous I-type character of the RMG–SCG–
NATPG plutons precludes metapelitic rocks of the RM-SC and ATP basement as suitable source materials. Instead, it points to an igneous protolith such as metabasalt, juvenile K-rich basaltic underplate magma, and/
or mantle rocks (Roberts and Clemens, 1993; Tepper et al., 1993; Pearce,
1996; Patiño Douce and McCarthy, 1998; Von Blanckenburg et al., 1998;
Altherr and Siebel, 2002; Ashwall et al., 2002). On the other hand, the
geochemical and isotopic compositions and TDM ages of SATPG samples
overlap with those of the middle to upper crustal rocks of the ATP basement indicating a significant crustal contribution from the ATP crystalline basement (Figs. 8, 12 and 13).
Experimental studies report that hydrous melting of amphibolites
or basalts could produce tonalitic magmas and subsequent magma–
crust interaction and/or fractional crystallization of these magmas
yields granodioritic to granitic compositions. (Rapp and Watson,
1995Patiño Douce, 1996, 1999; Patiño Douce and McCarthy, 1998).
These studies also demonstrate that, regardless of the degree of partial melting, partial melts of metabasalts are characterized by relatively high Na2O (>4 wt.%) and low Mg numbers . The low Na2O
contents (b4) and relatively high Mg numbers of RMG–SCG–NATPG
samples eliminates metabasalts as a suitable source material. Besides
that, some researchers have argued that metabasaltic rocks are not
suitable source rocks for the generation of high-K calc-alkaline, Itype granitoids as metabasalts contain low-K2O and insufficient
incompatible trace elements to form appreciable volumes of granitic
melts (Roberts and Clemens, 1993; Ashwall et al., 2002). Therefore,
the high-K calc-alkaline, and incompatible element-enriched nature
of the RMG–SCG–NATPG and SATPG suggest that a purely metabasalt
source is not suitable for their magmas.
The REE patterns of all granitoid groups are parallel to each other
and define a trend between Kula basalts and middle–upper crustal
rocks. The majority of the plutons display concave-upward patterns
with only minor or no negative Eu anomalies, indicating a
plagioclase- and garnet-poor and amphibole-, clinopyroxene- and
titanite-rich residual source (Altherr and Siebel, 2002) (Fig. 11a, b).
Although some samples from NATPG display weakly to moderately
peraluminous S-type affinity, isotopic compositions of these samples
overlap with those of I-type granitoid samples from NATPG and SCG
(Fig. 12). The REE patterns of these samples display more pronounced
negative Eu anomalies in comparison to other granitoids groups.
Using the REE patterns of the ATPG samples, we can infer that these
rocks show evidence for amphibole and feldspar fractionation during
magma evolution, rather than a garnet bearing mantle source. Partial
melting models show that steep partial melting trajectories observed
in Nb/Zr vs. Nb and La/Yb vs. La plots (Fig. 14) can only be produced
by partial melting of a residual garnet-bearing mantle source
(Thirwall et al., 1994), and that the effect of partial melting was
more important than the sole influence of fractional crystallization
in controlling the compositional variations in both RMG–SCG and
ATPG plutons.
19
Fig. 19. Schematic model for the spatial, temporal and geochemical evolution of late Oligocene to middle Miocene magmatism in western Anatolia and the Aegean region.
7.2. Magma evolution
The RMG–SCG–NATPG and SATPG samples display LILE enrichment
and negative Nb, Ta, Ti, and P anomalies (Fig. 10a, b). These features
are consistent with derivation of their magmas from an incompatible element enriched source similar to those of rocks that form at convergent
margin settings (Pearce, 1982; McDonough, 1990; Pearce et al., 1990;
Thirlwall et al., 1994; Pearce and Peate, 1995; Eyuboglu et al., 2011)
and/or post-collisional granitoids (von Blanckenburg and Davies,
1995). The subduction-related enrichment of the mantle source may
have been a result of either arc-derived magmas or a subduction component inherited from earlier convergent margin events. Source enrichment through previous subduction events in the region has been
suggested for the western Anatolian plutons and related volcanism by
some authors (Yılmaz and Polat, 1998; Aldanmaz et al., 2000; Yılmaz et
al., 2000; Dilek and Altunkaynak, 2007). Although subduction-induced
mantle metasomatism can account for enriched source characteristics
of the studied granitoids, it can be argued that the multi-element patterns and isotopic compositions shown by the Oligo–Miocene granitoids
could have also been inherited from crustal contamination (Figs. 10–13).
The analyzed samples display similar trace-element patterns, comparable to those of the middle–upper continental crust (Fig. 10), which
might have been inherited from crustal melts of variable magma sources
and source compositions. In the Nb/La vs. Ba/Rb plot (Fig. 15a), observed
in these samples cannot be explained solely by this mechanism. The vertical trend between continental crust and mantle derived melts (Kula basalts and EMM) suggests mixing or AFC of a mantle derived magma with
a crustal component, rather than the sole influence of subduction generated fluids (Tatsumi et al., 1986; Pecerillo, 1999; Wang et al., 1999;
Marchev et al., 2004). Therefore, a critical evaluation of possible contamination by crustal material is crucial to understand granitoid magma generation in western Anatolia.
The relatively constant 1/Sr ratios, increasing Zr/Sm and decreasing Ce/Pb ratios with increasing 87Sr/ 86Sr(i) suggest that opensystem evolutionary processes played an important role in the generation of these granitoids (Fig. 15a–d). Individually, each granitoid
group displays isotopically uniform signatures but dispersed variation
patterns in the Rb, Sr, Zr and Mg-number vs. SiO2 diagrams (Fig. 9).
This may have been caused by heterogeneity in the source and/or different compositions of the overlying crust, through which the RMG,
SCG, and ATPG granitoid magmas migrated. Therefore, the observed
geochemical features of the late Oligocene–middle Miocene granitoids may indicate that both varying degrees of crustal contamination
of mafic parental magmas and/or different compositions of the overlying crust were in part responsible for the geochemical differences
between these granitoid suites. In order to test these alternative
20
processes, we evaluated εNd(i) vs. TDM (depleted mantle model age) relationships (Fig. 13).
On the εNd(i) vs. TDM diagram, the RMG and SCG granitoids plot on
an array between the fields of the Kula basalts and the metamorphic
basement rocks of the SC (north of the suture zone) which overlaps
with the fields of the Hercynian protoliths and the Pelagonian upper
crust and the crystalline basement of the ATP (south of the suture).
The RMG and SCG granitoids have generally younger TDM values
(0.6–1.2 Ga) compared to the SC basement and ATPG granitoids
(1.2–1.6 Ga). The RMG and SCG granitoids with the youngest TDM
values are characterized by a high amount of mantle-derived protoliths in the mixed source, and the extraction age of their mantle material is younger than 1.2 Ga. Based on the patterns observed in
Figs. 12 and 13, we conclude that the samples from the RMG and
SCG granitoids have isotopic compositions and TDM ages similar to
those of the Rhodope granites in Bulgaria–Greece. Christofides et al.
(1998), Pe-Piper and Piper (2001) and Pe-Piper et al. (2002) suggested that fractionation of mafic magmas and/or their mixing with
felsic crustal material, some of which was derived by crustal anatexis
could produce the granitoid plutons of the Rhodope massif. The distribution of the TDM values of the NATPG samples shows a slight overlap with those of the RMG and SCG plutons, and they generally have
older TDM values (>1.2 Ga) that are similar to those of ATP basement.
On the same diagrams, it can be inferred that the NATPG samples
have a higher amount of crustal and a minor mantle component in
the mixed source in comparison to the RMG–SCG samples. It is also
apparent from Fig. 13 that the SATPG samples plot in the field of the
metamorphic basement rocks from the ATP and the Hercynian protoliths, and show close similarities to the Cyclades granites from the
central Aegean Sea. We can deduce that the extraction age of crustal
source rocks might be slightly older than 1.2 Ga, which is consistent
with the TDM model ages of the crystalline basement rocks representing those occurring south of the suture zone (IASZ). This inferred
age is consistent with that of the Pan-African crustal rocks and indicates that the both the NATPG and SATPG magmas were strongly affected by the ATP basement units. Alternatively, as the isotopic
compositions and TDM ages of the SATPG samples overlap with
those of middle–upper crustal rocks of ATP basement rocks an origin
as a middle crustal melt cannot be discarded. Some authors suggested
a metasedimentary crustal source for the generation of the I- and Stype granitoid plutons in the Cyclades, which shows similar geochemical and isotopic features to those of the ATPG samples
(Altherr and Siebel, 2002; Stouraiti et al., 2010).
The isotopic compositions vs. average cooling ages of the RMG, SCG
and NATPG granitoids as reported by previous workers and in this study
(Table 1) suggest an increasing crustal signature (crustal contamination) with time (Fig. 16). The youngest granitoid group in northwestern
Anatolia, SATPG (16 Ma; Catlos et al. ., 2008), displays a strong crustal
signature, and the timing of its formation corresponds to the time interval between the initiation of mildly alkaline and strongly alkaline volcanism in western Anatolia (Altunkaynak and Dilek, 2006).
7.3. Petrogenetic modeling
In order to test quantitatively whether open-system processes can
explain the geochemical and isotopic variations and magmatic evolution of the western Anatolian granitoids, we conducted assimilation
and fractional crystallization (AFC) and simple bulk mixing modeling
(Figs. 17 and 18) and evaluate these contrasting models for the SCG–
RMG and the ATPG, respectively. In the AFC models (Figs. 17a–b and
18a–b), calculated using the equations of DePaolo (1981), it is assumed that a primary magma with an isotopic composition similar
to an average Kula basalt (representative of a melt derived from depleted mantle) and a melt derived from an enriched mantle source
(EMM) evolved by crystal fractionation to give rise to a series of derivative magmas, which subsequently assimilated different amounts
of crustal material, thus increasing the effects of crustal contamination with the degree of differentiation. To account for the variable
composition of the crustal basement in western Turkey and for the
different rock types into which the granitoids were emplaced, we
used different crustal lithologies and compositions as potential contaminants in the models (Figs. 17a–b and 18a–b). For the ATPG, a
lower crustal amphibolite from the Menderes Massif (Altunkaynak,
unpub. data) was also used as a starting composition in the AFC
models. Bulk mixing arrays (Figs. 17c–d and 18c–d) were calculated
between the same endmembers.
The AFC models for the SCG–RMG presented in the 87Sr/ 86Sri and
143
Nd/ 144Ndi vs. SiO2 plots (Fig. 17a–b) show that the variations within these granitoids can be modeled successfully, using both depleted
and enriched mantle melts as starting compositions, although the
models critically depend on the contaminant chosen. Suitable crustal
contaminants include the gneisses from the Kazdag Massif and the
middle and upper crustal rocks from Altunkaynak (unpub. data) and
Sunal (unpub. data) (Fig. 17a–b). Lower crust amphibolite can be
ruled out as a potential contaminant, based on the models presented.
Realistic models indicate relatively high rates of assimilation to fractional crystallization (r; all AFC models were calculated with
r = 0.8). High values for r suggest a comparatively minor role for fractional crystallization; however, as all r values are b1.0, fractional crystallization still dominates over assimilation of crustal rocks. In all AFC
models, the extent of differentiation that the parental magmas underwent to reach the values similar to those of the SCG–RMG depends
largely on the chosen contaminant. Fractions of original melt remaining (F) are ~ 0.6 for the most contaminated samples of the SCG–RMG,
although higher values of “F” (or less crystallization) may be required
for particular potential contaminants. Bulk mixing trends between
depleted or enriched mantle melts and most of the crustal compositions chosen for the AFC models mostly fail to reproduce the observed
compositional variations (in 87Sr/ 86Sr(i) and 143Nd/ 144Nd(i) vs. SiO2
space) of the SCG–RMG, although multi-component mixtures between mantle melts (both depleted and enriched) and/or amphibolites and silicic crustal lithologies remain a possibility (Fig. 17c–d).
AFC and bulk mixing models for the ATPG are illustrated in 87Sr/
86
Sr(i) and 143Nd/ 144Nd(i) vs. SiO2 plots (Fig. 18a–d). Using the same
depleted and enriched mantle melts as above as well as a lower crustal amphibolite from the Menderes Massif as starting compositions
and several crustal lithologies as potential contaminants in the AFC
calculations (Fig. 18a–b), the best-fit models for the observed compositional variations of the ATPG are obtained with the same high rates
of assimilation versus fractionation (r = 0.8). Models using a depleted
mantle melt or lower mafic crust (amphibolites) as starting compositions and upper crustal values and the Menderes Massif gneisses as
contaminants reproduce best the observed compositional variations
of the ATPG (with fractions of original melt remaining (F) of ~0.6
(or higher)), although derivation of the ATPG magmas from an
enriched mantle source and subsequent AFC processes are also feasible. As for the SCG–RMG, lower crust amphibolite can be ruled out as
a potential contaminant of any mantle-derived melt, based on the
models presented. Bulk mixing models between depleted and
enriched mantle-derived melts and crustal rocks (Fig. 18c–d) largely
fail to reproduce the observed compositional variations of the relatively silicic ATPG, although these models do not exclude the possibility of mixtures of mantle-derived melts (or Menderes Massif
amphibolite) with more SiO2-rich partial crustal melts.
8. Interplay between syn-convergent extension and magmatism in
western Anatolia
Convergence between the Eurasian and African plates played an
important role in shaping the crustal architecture of the western Anatolia and broader Aegean region during the late Mesozoic–Cenozoic
(e.g., Kalvoda and Babek, 2010). This crustal architecture formed from
a collage of continental blocks, separated by suture zones (IPS, VS_IASZ,
PS in Fig. 1). The continental fragments (RM, SC, ATP) were amalgamated through collisional events starting in the Cretaceous (Şengör and
Yılmaz 1981; Dilek and Moores, 1990; Okay et al., 1996; Okay and
Tüysüz, 1999).
The multiple episodes of continental collision in the Aegean region
caused orogen-wide burial metamorphism in the late Paleocene–
early Eocene. This regional metamorphism was responsible for the
development of high-grade metamorphic rocks in the Rhodope, Kazdağ and Menderes massifs. Continental collision events also produced
thick orogenic crust and heterogeneous mantle that affected the
mode and nature of syn- to post collisional magmatism and extension
in the Aegean region (Seyitoğlu and Scott, 1996; Aldanmaz et al.,
2000; Yılmaz et al., 2001; Altunkaynak and Dilek, 2006).
In western Anatolia, magmatism occurred in distinct episodes
since the early Eocene and appears to have changed in nature from
calc-alkaline to alkaline over time. The interpretations explaining
the mode and nature of multiple episodes of Cenozoic magmatism
through time are subject to discussions and further testing. The current models are; a) active subduction zone magmatism, b) regionwide extension and magmatism caused by orogenic collapse and c)
syn-convergent extension and magma generation driven by slab
break-off, delamination or convective removal of the lithosphere.
The variations in tectonic regimes were a result of feedback mechanisms between the tectonically driven crustal processes and mantle
dynamics in the late-stage evolution of the western Anatolian orogenic belt.
Current subduction zone models suggest that the Cenozoic magmatism was either a product of the north-dipping subduction of a Tethyan ocean floor (Borsi et al., 1972; Fytikas et al., 1984; Pe-Piper and
Piper, 1989; Gülen, 1990; Delaloye and Bingöl, 2000; Okay and Satır,
2000; 2006) or that the Cretaceous subduction along the Izmir–Ankara–Erzincan suture zone and the Miocene subduction along the Hellenic trench could have been related in space and time through slab
retreat (Spakman, 1990; van Hinsbergen et al., 2005; Pe-Piper and
Piper, 2006). Although magmatic rocks of western Anatolia display
a geochemical subduction fingerprint, there is no convincing geological evidence for a subduction event such as the formation of an
ophiolithic melange, accretionary prism or blueschist facies metamorphic rocks synchronous with Cenozoic magmatic activity in the
region during the middle Eocene through middle Miocene (Harris et
al., 1994; Genç and Yılmaz, 1997; Yılmaz et al., 2000, 2001 and references therein). Cretaceous subduction of the Tethyan seafloor beneath the Sakarya continent was halted and terminated by the
partial subduction of the Anatolide–Tauride continental margin, following the emplacement of the Cretaceous ophiolites exposed along
the Izmir–Ankara–Erzincan suture zone (Harris et al., 1994; Okay et
al., 1998; Sherlock et al., 1999; Dilek et al., 2007). The isostatic rebound of this partially subducted continental material in the lower
plate was the driving force for the uplift and exhumation of the blueschist rocks in the Paleogene (Sherlock et al., 1999). Time constraints
on the obduction of the ophiolite fragments exposed along the collision zone and accretionary processes (Harris et al., 1994; Okay and
Tüysüz, 1999; Sherlock et al., 1999; Önen and Hall, 2000) indicate
that the timing of collision SC and ATP in NW Anatolia was preearly Eocene. Following the collision, the units of the SC and the suture zone units were covered unconformably by a continental to shallow marine sedimentary rocks of Baslamis (Akdeniz, 1980) and
Gebeler Formations (Akyurek and Soysal, 1983) during middle Eocene. This stratigraphic relationship also supports the timing of collision in NW Anatolia was earlier than the middle Eocene. This
continental collision resulted in the development of the western Anatolian orogenic belt (Şengör et al., 1985; Dilek and Whitney, 2000).
As subduction of African lithosphere beneath Eurasia along the Hellenic trench south of the Anatolide–Tauride and Cyclades belts started
around ~ 12 Ma (Meulenkamp et al., 1988), the Eocene to middle
21
Miocene magmatism was not related to any active subduction processes at that time. Therefore, the Oligo–Miocene granitoids were
most likely generated in a post-collisional setting rather than in an active continental margin setting, and subduction-related enrichment
of the western Anatolian lithospheric mantle was associated with
the previous, late Cretaceous subduction of the Neo-Tethyan oceanic
lithosphere beneath the Sakarya continent, as suggested by previous
researchers (Yılmaz and Polat, 1998; Yılmaz et al., 2000; Aldanmaz
et al., 2000; Altunkaynak and Genç, 2008).
The orogenic collapse models suggest that the Late Oligocene–
Miocene magmatism in western Anatolia was a consequence of extensional tectonics associated with the collapse of the overthickened
western Anatolian orogenic belt (Seyitoğlu and Scott, 1991, 1992,
1996; Seyitoğlu et al., 1997). The inferred catastrophic orogenic collapse caused crustal attenuation and magmatism associated with
decompressional melting. This model does not explain the mode
and nature of earlier Eocene magmatism in the region and has limited
applications to the Cenozoic evolution of western Anatolia.
Synconvergent extension and associated magma generation is widely recognized within the interiors of modern convergent orogens (e.g.,
Dalmayrac and Molnar, 1981; Molnar and Chen, 1983; Molnar and
Lyon-Caen, 1988, England and Houseman, 1989; Platt and England,
1994; McCaffrey and Nabelek, 1998; Seghedi and Downes, 2011) and
the young Tethyan orogen in Anatolia (Turkey) and the broader Aegean
region (Aldanmaz et al., 2000; Keskin, 2003; Köprübaşı and Aldanmaz,
2004; Dilek and Altunkaynak, 2007; Altunkaynak and Genç, 2008). Different driving mechanisms such as slab break-off, extensive delamination, partial delamination or convective removal of lithosphere have
all been invoked to explain the interplay between syn-convergent extension and magma generation in the region. Some researchers have
suggested that the Cenozoic magmatism in western Anatolia displays
compositionally distinct magmatic episodes controlled by slab breakoff
(Köprübaşı and Aldanmaz, 2004; Altunkaynak and Dilek, 2006;
Altunkaynak 2007; Dilek and Altunkaynak, 2007; Boztuğ et al., 2009).
Others have proposed that lithospheric delamination (Aldanmaz et al.,
2000) and/or partial convective removal of the subcontinental lithospheric mantle resulting in asthenospheric upwelling and decompressional melting were important processes during the post collisional
build up of Cenozoic western Anatolia (Altunkaynak and Genç, 2008).
We think that the long-lived Cenozoic magmatism in western Anatolia was spatially and temporally associated with different tectonic
events driven by crustal- and mantle-scale processes and their interactions. The first episode of granitoid magmatism and its volcanic
equivalents evolved during the early to late Eocene (54–35 Ma) and
produced medium to high-K calc-alkaline I type granitoids. The emplacement of localized granitoid plutons along the IASZ and into the
Sakarya continent has been interpreted to have resulted from slab
breakoff-related asthenospheric upwelling and associated partial
melting of the subduction-metasomatized continental lithospheric
mantle by previous studies (Köprübaşı and Aldanmaz, 2004;
Altunkaynak, 2007; Dilek and Altunkaynak 2007). Partial underplating of the leading edge of the buoyant Anatolide–Tauride platform beneath the Sakarya continent jammed the north-dipping Tethyan
subduction temporarily, while the continued sinking of lithospheric
mantle resulted in slab breakoff in NW Anatolia. This interpretation
is supported by the seismic tomography model of Dilek and Sandvol
(2009) demonstrating the existence of a second high-velocity (cold)
slab near the 660 km discontinuity in the lower mantle north of the
Hellenic slab, which is interpreted as a detached Tethyan slab dipping
beneath the western Anatolian orogenic belt. Slab detachment and
breakoff is a natural consequence of the gravitational settling of subducted lithosphere in continental collision zones, as a result of a decrease
in the subduction rate caused by the positive buoyancy of partially subducted continental lithosphere (Davis and Von Blanckenburg, 1995;
Von Blanckenburg and Davies, 1995; Wortel and Spakman, 2000;
Gerya et al., 2004).
22
The second magmatic episode produced widespread I-type plutonic
and associated volcanic rocks in western Anatolia during the late Oligocene to middle Miocene. This time interval coincides with the exhumation of lower to middle crustal rocks in western Anatolia (as in the
Menderes and Kazdağ core complexes) and in the Aegean province
(Naxos, Cyclades) (Fig. 19). The initial exhumation age of the Kazdağ
core complex has been suggested as the latest Oligocene–early Miocene
(Okay and Satır, 2000) and that of the Menderes core complex as the
earliest Miocene (Işık et al., 2004; Thomson and Ring, 2006; Bozkurt,
2007; Dilek and Altunkaynak, 2007; Altunkaynak and Genç, 2008). In
general, tectonic extension also appears to have migrated southward
in time. Following the exhumation of the Kazdag and Menderes metamorphic core complexes, the Tauride block in SW Anatolia was uplifted
(Dilek et al. 1999b) and the blueschist rocks in Crete and the Cyclades in
the South Aegean region (Ring and Layer, 2003) were exhumed in the
Miocene and onwards (Fig. 19).
Zircon SHRIMP U–Pb dating of NATPG and SCG groups yields ages
between 19.48 ± 0.29 and 23.94 ± 0.31 Ma as the timing of their emplacement, whereas 39Ar/ 40Ar dating of hornblende and biotite separates from the SCG, RMG and NATPG groups reveals cooling ages of
18.9 ± 0.1–24.8 ± 0.1. These results are consistent with the radiometric ages (mostly K/Ar ages) obtained in previous studies and indicate
that the extensional deformation was spatially and temporally associated with voluminous granitoid magmatism which is represented by
metaluminous to slightly peraluminous, I-type granitoids. The Sr–Nd
isotopic signatures and trace element characteristics of these granitoids indicate that the melts derived from both lithospheric mantle
and depleted mantle (at least for the SCG and RMG magmas) contributed to magma source region of the parental magmas. The asthenospheric melt contribution in addition to lithospheric mantle melts
most likely resulted from lithospheric delamination or partial convective removal of the subcontinental lithospheric mantle. Although the
extensional tectonic regime was operating fully during the latest Oligocene–Early Miocene, the relationships between the isotopic compositions and cooling ages as documented in this study indicate an
increasing crustal signature from 24 to 18 Ma (Fig. 16).
We propose that asthenospheric upwelling caused by partial delamination or convective thinning of lithospheric mantle led to
underplating of mantle-derived magmas providing melt and heat to
induce partial melting of the lithospheric mantle (Fig. 19). Invasion
of the crust by melts derived from both asthenospheric (depleted)
and enriched lithospheric mantle triggered open system processes
(AFC and/or MASH (melting, assimilation, storage, homogenization;
Hildreth and Moorbath, 1988)) in separate magma chambers, resulting in the production of mildly to highly evolved Oligo–Miocene
granitoid magmas. This inferred melt source and magma evolution
readily explains the I-type granitoid nature of most Cenozoic plutons
in western Anatolia, regardless of their temporal and spatial position.
This widespread early to middle Cenozoic magmatism caused thermal weakening of the young orogenic crust and played a significant
role for the initiation of syn-convergent extension and crustal exhumation as early as in the latest Oligocene–early Miocene (Fig. 19).
The absence of large volumes of alkaline basaltic lavas in western Anatolia during this period also contradict extensive lithospheric delamination models. Moreover, previous workers suggested that the
crustal thickness in the Aegean province ranges from 16 km in the
Crete Sea to 25–35 km in the Cyclades and W Turkey (Makris and
Stobbe1984; Doglioni et al. 2002; Tirel et al. 2004; Zhu et al. 2006).
Variations in crustal thickness may indicate that extensional thinning
has not been uniform in western Anatolia and the Aegean region, consistent with the proposed models of convective removal and partial
delamination of lithospheric mantle.
The effects of convective removal or partial delamination of the
cold mantle lithosphere and its replacement by hot asthenosphere
are well documented in other orogenic belts and in eastern Anatolia,
where the lower–middle crust has been remobilized upwards,
causing exhumation, surface uplift, and overall net extension (Bird,
1979; England and Houseman, 1989; Molnar et al., 1993; Houseman
and Molnar, 1997; Keskin 2003; Şengör et al., 2003; Dokuz, 2011).
The degree of crustal contribution appears to have increased in
plutonic rocks by middle Miocene (Fig. 16). The age of the youngest
granitoid group (SATPG; 13–16 Ma; Hetzel et al., 1995), which displays a strong crustal signature, corresponds to the time interval between the initiation of, mildly alkaline (associated with bimodal
volcanism) and strongly alkaline volcanism in western Anatolia.
Thus, both asthenospheric- and lithospheric mantle and crustal
melts were involved in the evolution of magmatism in the middle
Miocene and onwards. Therefore, the geochemical variations in the
late Cenozoic post-collisional magmatism in western Anatolia reflect
the increasing intensity of regional extension through time (Altunkaynak and Dilek 2006, Altunkaynak and Genç 2008, Altunkaynak et
al., 2010). This shift in the geochemical affinity of magmatism is interpreted as a result of tectonically driven asthenospheric upwelling beneath this highly extended terrane, following a period of extreme
crustal thinning after the exhumation of core complexes in western
Anatolia and the Aegean region in response to rapid slab rollback at
the Hellenic trench (Meulenkamp et al., 1988; Spakman et al., 1988;
Pe-Piper and Piper 2006). Pn velocity and Sn attenuation tomography
models indicate that the uppermost mantle is anomalously hot and
thin, consistent with the existence of a shallow asthenosphere beneath western Anatolia (Sandvol et al., 2003).
The close temporal and spatial relationships between the late Cenozoic tectonic extension and magmatism suggest that the widespread early to middle Cenozoic magmatism caused thermal
weakening and played a significant role in the initiation of synconvergent extension, crustal exhumation and thinning in the hinterland of
a young Tethyan orogen in western Anatolia and the broader Aegean
region.
9. Conclusions
The majority of the Oligo–Miocene granitoids are represented by
metaluminous to slightly peraluminous, I-type granitoids. Isotopic
signatures and major-trace element characteristics of the RMG–SCG
and NATPG granitoids which emplaced into different tectonic units
of western Anatolia indicate that both lithospheric- and asthenospheric mantle (at least partly for the SCG–RMG magmas) melts appear to have contributed to source region of mafic parental magmas
which evolve toward granodioritic to granitic compositions. The compositional variations observed in the RMG, SCG and NATPG granitoids
are interpreted as a result of open-system processes during evolution
of these granitoids rather than a reflection of different compositions
of crustal lithologies through which the RMG and SCG, ATPG magmas
migrated. The TDM ages of the RMG and SCG suggest a high amount of
mantle-derived protoliths in the mixed source and the extraction age
of the mantle material to be younger than 1.2 Ga. The calculated TDM
ages of the NATPG samples are consistent with those of the PanAfrican crustal rocks, and indicate that these granitoids, characterized
by stronger crustal signatures than the other groups, were affected by
the crystalline basement of the Anatolide–Tauride platform. By contrast, the SATPG samples with crust-like geochemical signatures
may have been produced by crustal melting or, at least, significant
contributions from the ATP crystalline basement.
The observed isotopic characteristics and variations with indices
of differentiation suggest that the crustal signature within the
Oligo–Miocene granitoids developed predominantly through simultaneous assimilation of upper–middle crustal rocks and fractional
crystallization (AFC) of mantle derived melts during magma ascent.
Assimilation and fractional crystallization models explain the compositions of the Oligo–Miocene granitoids slightly better than bulk mixing between different mantle and crustal components, although
mixing between mantle-derived melts and partial crustal melts
cannot be entirely ruled out. Thus, the observed range in isotopic variations is not solely a feature of the inferred mantle melt source.
Zircon SHRIMP U–Pb dating of the NATPG and SCG groups yields
ages between 19.48 and 23.94 Ma as the timing of their emplacement, whereas cooling ages of same granitoids range between 20.6
and 18.9. 39Ar/ 40Ar dating of biotite separates from the SCG, RMG
and NATPG groups reveals cooling ages of 18.9–28.0 Ma. The isotopic
compositions and cooling ages of the western Anatolian granitoids
suggest a progressive increase in the amount of crustal signature (assimilation of crustal rocks) from 24 to 18 Ma, coinciding with the timing of crustal exhumation and core complex formation (Kazdağ and
Menderes massifs) in western Anatolia. The heat and basaltic material
to induce partial melting, which led to the generation of granitoid
magmas, were provided by asthenospheric upwelling caused by partial lithospheric delamination and/or convective thinning beneath
western Anatolia. This widespread early to middle Cenozoic magmatism caused thermal weakening of the young orogenic crust and
played a significant role for the initiation of syn-convergent extension
and crustal exhumation as early as in the latest Oligocene–early
Miocene.
The age of the youngest granitoid group (SATPG; 13–16 Ma; Hetzel et
al., 1995; Glodny and Hetzel 2007), which displays a strong crustal signature, corresponds to the time interval between the initiation of mildly alkaline and strongly alkaline volcanism in western Anatolia. This shift in
the geochemical affinity of magmatism is interpreted as a result of tectonically driven asthenospheric upwelling beneath this highly extended terrane, following a period of extreme crustal thinning after the exhumation
of core complexes in western Anatolia and the Aegean region.
Supplementary materials related to this article can be found online
at doi:10.1016/j.gr.2011.10.010.
Acknowledgments
This study has been funded by grants from the Istanbul Technical
University (BAP Project No: 35691) and the Turkish Research Council
(TUBITAK-CAYDAG-109Y010) that are gratefully acknowledged. Constructive and insightful comments by P.T. Robinson and Y. Eyupoglu
helped us to improve the paper. We would like to thank the Editorin-Chief, Professor M. Santosh, for inviting us to prepare this contribution as a Focus Paper in Gondwana Research.
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Şafak Altunkaynak is an Associate Professor in the Department of Geology at Istanbul Technical University (Turkey).
She received her PhD from Istanbul Technical University in
1997. She was a visiting scientist at the Open University
(UK) in 2003 and the University of Nevada Las Vegas
(USA) in 2009. She has worked on the geology, petrology
and geochemistry of post-collisional volcanic and plutonic
rocks, volcanic–plutonic connections in Turkey, the Aegean
region and the Lesser Caucasus (Azerbaijan). Her current research projects involve Cenozoic crustal evolution and mantle dynamics of post-collisional magmatism in western
Anatolia and the Aegean extensional province; thermobarometry and geochronology of magmatic and metamorphic rocks of Çataldağ, Kazdağ and Menderes core complexes; and petrology and geodynamics of adakitic
magmatism in NW Turkey. She has published a number of
refereed papers on these topics in international journals.
Yıldırım Dilek is a Professor of Tectonics in the Department
of Geology and a Harrison Scholars Professor at Miami University (USA). He received his PhD from the University of
California-Davis (1989), worked as a Senior Research Fellow
(1989–90) at the Getty Conservation Institute (Los Angeles,
CA), and taught at Vassar College (New York) until 1996. The
focus of his research is mostly on the structure, petrology,
and tectonics of modern oceanic crust and ophiolites, postcollisional igneous complexes in orogenic belts, and metamorphic core complexes. He has also worked extensively
in the western U.S. Cordillera, Northern Appalachians, Norwegian Caledonides, Caucasus Mountains, Arabian–Nubian
Shield, and Central Asian orogenic belts. He is an expert scientist for the NATO Science for Peace Programme and a
member of the United States Science Advisory Committee.
Ş. Can Genç is a Professor of Geology at the Istanbul Technical University, Istanbul (Turkey) since 2004. Genc received his BSc (1981) and MSc (1987) from Istanbul
University, and PhD (1993) from the Istanbul Technical
University, Turkey. Genc's main research topics include
magmatic petrology, petrogenesis, and volcanology. He
has published over 20 research papers.
Ralf Gertisser is a lecturer in Mineralogy and Petrology at
Keele University, UK, since 2005. He studied geology at
the University of Freiburg, Germany, and the University of
Oregon, USA, and received his diploma (M.Sc.) in geology
from the University of Freiburg in 1996. In 2001, he was
awarded a doctorate (Dr. rer. nat.) “with highest honors”
(summa cum laude) in Earth Sciences from the University
of Freiburg. Before joining Keele University, he held postdoctoral positions at the University of Freiburg and The Open
University, UK. Gertisser's main research interests include
magma generation and differentiation in subduction-zone
(and other geodynamic) settings, rates and timescales of
magmatic processes using short-lived isotopes, magma
chamber processes, volatile behavior in volcanic systems,
and the generation and emplacement mechanisms of
small-volume pyroclastic flows. Study areas have included
the Aeolian Islands (Italy), the Azores (Portugal), Santorini
(Greece), the Sunda arc in Indonesia and the Chilean Andes.
Harald Furnes is Professor at the Department of Earth Science, University of Bergen, Norway, since 1985. He received his D.Phil. at the University of Oxford, UK, in
1978. His main research interest has been connected to
volcanic rocks. This involves physical volcanology, geochemistry and petrology of volcanic rocks, mainly connected to ophiolitic and island arc development of
various ages. Another research focus has been related to
the alteration of volcanic glass, which again led to a
long-term study on the interaction between microorganisms and glassy rocks, and the search for traces of
early life. On these topics he has published a number of
refereed papers in international journals.
Kenneth A. Foland is Professor Emeritus in the School of
Earth Sciences at Ohio State University. He received a B.S.
from Bucknell University (1967) and M.S. (1969) and Ph.D.
(1972) degrees from Brown University. He joined Geology
faculty at the University of Pennsylvania in 1972, leaving in
1980 for Ohio State University in Columbus. There he developed new facilities for high-precision, low-blank measurements of radiogenic isotopes and noble gases. After more
than 40 years of research in isotope geochemistry and geochronology, he recently retired from active lab work and
teaching. His research includes laboratory, experimental,
field, and clinical studies on isotopic compositions of a broad
range of natural and modified materials including rock, mineral, water, gas, and blood samples.
Jingsui Yang graduated from Dalhousie University in
Canada in 1992 with a PhD in geology. In 1995 he became a Research Professor and now is a chief scientist
at the National Key Laboratory for Continental Tectonics
and Dynamics, Institute of Geology, Chinese Academy of
Geological Sciences. He has carried out a number of research projects on the tectonics and petrology of the orogenic zones of the Qinghai-Tibet Plateau. His research
work has mainly been focused on the ultra-high pressure
metamorphic zones, terrane amalgamation and collision,
and deep mantle processes. Yang with collaborators has
published 325 research papers and two books and became GSA Fellow in 2011.
Gürsel Sunal is an Assistant Professor in the Department
of Geology at İstanbul Technical University, İstanbul,
Turkey, since 2009. Sunal received his BSc (1993) and MSc
(1997) from Istanbul Technical University, Turkey, and
PhD (2008) from the University of Tübingen, Germany. His
main research interests include geochronology of metamorphic and magmatic rocks and exhumation history of tectonically active belts. He has published a number of research
papers on these topics.

Spatial, temporal and geochemical evolution of

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