Fault and fold growth of the Amenthes uplift

Earth and Planetary Science Letters 408 (2014) 100–109
Contents lists available at ScienceDirect
Earth and Planetary Science Letters
www.elsevier.com/locate/epsl
Fault and fold growth of the Amenthes uplift: Implications for Late
Noachian crustal rheology and heat flow on Mars
Karl Mueller a,∗ , Arwen Vidal a , Stuart Robbins b , Matthew Golombek c , Colin West d
a
Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, United States
c
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United States
d
Department of Applied Mathematics, University of Colorado, Boulder, CO 80309, United States
b
a r t i c l e
i n f o
Article history:
Received 30 November 2013
Received in revised form 20 September
2014
Accepted 29 September 2014
Available online xxxx
Editor: C. Sotin
Keywords:
Amenthes Rupes
thrust fault
heat flow
brittle–ductile transition
MOLA
a b s t r a c t
Determining the rheologic conditions that control growth of compressive structures on Mars is an elusive
problem, one limited by the lack of seismologic and other data commonly available for comparable
active uplifts on Earth. In some instances however, the geometry of faults on Mars that offset impact
craters can be deduced from surface topography alone. With this aim, construction of a balanced and
restorable structural cross section across the Late Noachian Amenthes uplift, or fault-related fold suggest
it forms above a deeply penetrating blind thrust with a gently curved or listric geometry that flattens
downward. Preferred structural solutions suggest the thrust dips between 41.5◦ and 56.1◦ at the surface
and flattens into a horizontal decollement at depths of ∼33–48 km. The range of values for depth to
detachment are greater than previous estimates for the Amenthes thrust based on elastic modeling for a
range of planar thrust geometries. Using the inference that the decollement corresponds to the onset of
plasticity in the crust, the depth to detachment is consistent with surface heat flow of 24–33 mW m−2
based on average values for heat production and the temperature threshold for the transition from brittle
faulting to ductile shear on Mars. This suggests the crust at Amenthes during the Late Noachian may be
slightly cooler than previously thought, similar to recent estimates derived from studies of lithospheric
strength.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
The formation and structure of Amenthes Rupes has long been
recognized as having important implications for the rheology of
the Martian crust early in its history (Watters, 2003). Central to
this idea is the interpretation that the depth the Amenthes thrust
penetrates corresponds to a change in brittle to ductile behavior
in the Martian crust (Schultz and Watters, 2001; Ruiz et al., 2008).
Evidence that large thrusts may flatten into the brittle to ductile
transition on Earth includes direct imaging from seismic reflection profiles (Smithson et al., 1978; Bloxsom Lynn et al., 1983;
Allmendinger and Shaw, 2000; Munoz, 2008), focal mechanisms
of large earthquakes and aftershock sequences (Pujol et al., 2006;
Verges et al., 2007) and the temperature threshold for plasticity in
quartz rich rocks (Coward, 1984; Scholtz, 1988; Munoz, 2008).
*
Corresponding author. Tel.: +1 303 552 7067.
E-mail address: [email protected] (K. Mueller).
http://dx.doi.org/10.1016/j.epsl.2014.09.047
0012-821X/© 2014 Elsevier B.V. All rights reserved.
The onset of plasticity on faults is chiefly controlled by the
mineralogy of rocks they deform, pressure and temperature conditions, and the presence of water (for a review of terrestrial examples see Burgmann and Dresen, 2008). Compressive structures
such as Amenthes can thus yield insight into the physical conditions that control their development. This offers an opportunity to
constrain the ambient conditions in the Martian crust by analysis
of large compressive uplifts and inferences for appropriate mineralogy and flow laws (Schultz and Watters, 2001; Grott et al., 2007;
Ruiz et al., 2008).
This depends however, on knowledge of fault geometry and requires direct information of the dip of the fault near the surface,
something that can be determined for Amenthes where it offsets
a large impact crater, allowing both the vertical and horizontal
components of shortening to be measured (Vidal, 2008). Armed
with this information, solutions for the depth the Amenthes thrust
penetrates and flattens can be constrained using fault-related fold
theory, where mass balanced structural solutions of nonrecoverable strain can be restored to a starting condition (Suppe, 1983;
Allmendinger, 1998; Seeber and Sorlien, 2000). Results of this
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
101
Fig. 1. Geologic map of the Amenthes uplift illustrating surface deposits, major thrust faults, impact craters and their ejecta. The main Amenthes Rupes lobate scarp extends
across the center of the image. Line of dots denotes MOLA shot points used to construct topographic profile for structural analysis. Mapping was conducted on existing
THEMIS global thermal mosaics, MOLA shaded relief maps and MOC imagery and comparisons to existing geologic mapping by Hiller (1979).
3. Mapping offset at Amenthes
3.1. Methods
Several methods were used to characterize the structural geology of Amenthes, based on techniques developed to determine
the geometry of thrust faults on Earth. These include basic tenets
of fault-related fold theory that relate the shape of thrust faults
to the geometry and style of folds formed simultaneously above
them (Suppe, 1983; Allmendinger, 1998; Seeber and Sorlien, 2000;
Johnson and Johnson, 2002). In addition, a large impact crater offset by the Amenthes thrust was exploited to determine the horizontal and vertical components of surface displacement, and hence
the dip of the fault at the surface. This was then combined with
area balancing of the Amenthes uplift to define the geometry of
the thrust at deeper levels in the crust and to test the goodness of
fit for an ensemble of restorations.
Fig. 2. Oblique view of Amenthes scarp overlain with trace of thrust. Note discontinuous fault strands and rollover of forelimb as a 5 km wide fold. Arrows denote
sense of rotation of forelimb. Mars digital image map (MDIM 2.1) draped over MOLA
topography.
paper thus build on previous studies that use elastic solutions to
fit a wide range of possible planar fault orientations to the pattern
of surface uplift (Schultz and Watters, 2001; Ruiz et al., 2008).
2. Regional setting
Amenthes Rupes is a 380 km long lobate scarp or surface thrust
rupture and fold with ∼1 km of vertical surface relief located in
the equatorial eastern hemisphere of Mars (Fig. 1). The scarp is
formed above a northeast dipping thrust fault and offsets heavily
cratered highlands terrain of Late Noachian age (Fig. 2). The exact
age of the Amenthes uplift is difficult to closely constrain, but must
postdate the Late Noachian crust it displaces and predate Early
Hesperian volcanic rocks deposited across its leading edge (Fig. 1).
3.2. Mapping surface topography
Raw MOLA shot points were used from over 2000 orbit tracks
to create a digital elevation model of the Amenthes region using the natural neighbor interpolation method (Vidal, 2008). The
resulting DEM was then used to characterize the topography of
the Amenthes region with the aim of identifying subtle changes
in surface slope related to folding above the thrust. The approach
is an offshoot of methods originally developed in terrestrial thrust
belts for mapping the edges of folds with seismic reflection profiles (Shaw et al., 1994; Shaw and Suppe, 1996; Bergen and Shaw,
2010). Termed axial surface mapping, the method uses the morphology of fault-related folds to predict the geometry and distribution of slip on underlying blind thrusts. The method was adapted
to map the edges of the Amenthes uplift as defined by topography
by creating first derivative (slope) and second derivative (curvature) maps of the region. The derivative maps were created by
calculating a bi-directional average slope for individual MOLA shot
points relative to values for nearest neighbor points. MOLA orbit
102
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
Fig. 3. Topographic profile and corresponding slope values for transect across Amenthes uplift. Location of transect shown in Fig. 1. Figure is highly vertically exaggerated.
tracks are spaced unevenly across the Amenthes region, as illustrated by significant gaps between orbit tracks. This allowed the
most ideal transect across the Amenthes uplift to be defined with
the closest spacing between orbit tracks (see location of transect
on Fig. 1). It was also located away from a large crater and associated ejecta blanket that altered the topography of Amenthes after
it was formed (Fig. 1).
3.3. Morphology of the Amenthes uplift
Maps of surface topography suggest the Amenthes uplift is inclined on average ∼1◦ to the northeast across its entire width.
Closer examination of detrended topography suggests however,
that the surface of the Amenthes uplift is comprised of two dip
domains, one dipping 0.4◦ to the northeast that defines its broad,
nearly flat top and a second 20 km-wide panel that dips 2.2◦
between the plateau-like crest and the base of the uplift to the
northeast (Fig. 3). The dip of each panel was determined by regressions of the MOLA shotpoints and the axial surface mapping
(Vidal, 2008; Fig. 3). The 58 km width of the Amenthes uplift is
remarkably broad with respect to terrestrial structures with comparable fault displacement. This illustrates the importance of back
limb width in the restorations, where the tradeoff between the dip
of the thrust and the geometry and depth at which the thrust flattens is consistent with observed fold geometry at the surface.
In contrast to the crest and backlimb of the Amenthes uplift, the forelimb of the structure (i.e. the lobate scarp itself) is
much more steeply inclined, and typically dips between 5–15◦
(Fig. 3). Second derivative mapping suggests the scarp has a gentle
S-shaped morphology along much of its length and is ∼5 km wide
near the offset crater.
3.4. Fault dip and displacement from crater offset
Craters have previously been used as finite strain markers to
measure offset across faults on Mars (Golombek et al., 1996). This
opportunity is also available at Amenthes where the lobate scarp,
or surface thrust rupture and fold deforms a large, 33 km-diameter
crater located at 110.19◦ E, 2.3◦ N (Figs. 1, 2). This allows the vertical and horizontal displacement across the crater to be measured
and combined to estimate the dip of the Amenthes thrust at the
surface. This is required to develop robust solutions of the geometry of the thrust and the depth at which it flattens in the brittle
crust.
The average elevation and offset of the rim of the displaced
impact crater was first measured using 10 topographic profiles derived from the digital elevation model; this yielded an average
value for vertical displacement of 1.00 ± 0.07 km. This is similar
to the ∼920 m of vertical relief measured across the scarp using
individual MOLA shot points along the transect used in the structural restoration (Fig. 3).
Horizontal displacement across the crater was determined by
measuring how the shape of the originally circular crater was deformed (i.e., shortened) across the Amenthes scarp (Fig. 4). This
was first undertaken by manually mapping the rim of the crater on
both sides of the thrust using THEMIS imagery. The crater rim is
marked by shadows on the footwall side of the crater wall (illuminated from the west) and conversely is brightened on the opposite
side of the crater (Fig. 4). Whereas the portion of the offset crater
rim (i.e. about one half of the original) in the footwall of the thrust
is well preserved, about 40% of the crater rim on the hanging wall
of the thrust has been modified by an ejecta blanket produced by
a subsequent large impact located immediately towards the northeast (Figs. 1, 4).
After manually picking well defined points on the crater rim,
semicircles on both sides of the thrust were fitted to the points
to define two circles using a crater mapping algorithm. The center
of each circle was then calculated and the horizontal displacement
and slip direction were determined by measuring the difference in
their locations. Results of this indicate about 1040 m of horizontal
offset along a slip vector at 23◦ azimuth, a direction oriented 74◦
from the strike of the thrust at the location of the transect (Fig. 4).
While significant error exists in the measurement, the calculated
slip direction is oriented within 16◦ of that expected for pure dip
slip across the thrust.
In addition to mapping in the THEMIS image, offset across the
crater was measured by mapping the crater rim using topographic
profiles on individual MOLA orbits (Fig. 4). Using the 30 orbit
tracks that cross the crater, and fitting to circles, 720 m of horizontal displacement was determined along an azimuth of 27◦ . The
azimuth of the resulting transport direction is 78◦ from the strike
of the thrust – comparable to the results from mapping on the
THEMIS image.
The circle-fitting code used to determine the centers of circles
fit to each half of the crater also outputs formal χ 2 uncertainties. The difference in latitude between fits to the two halves of
the crater is 0.032◦ , while the difference in longitude is 0.014◦ .
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
103
Fig. 4. MOLA orbit tracks used to map the offset crater. Curved line denotes rim of crater mapped on the underlying THEMIS image. Circles mark locations of offset crater
rim as mapped on individual orbit tracks. Straight gray segment shows area of offset crater rim obscured by younger crater ejecta.
Table 1
Values for combinations of vertical and horizontal offset, slip at the surface, fault dip at surface and radii of curvature used to construct cross section.
Vertical
offset
Horizontal
offset
Y/X
Slip
920
920
1000
1000
720
1040
720
1040
1.28
0.89
1.39
0.96
1168
1389
1232
1442
m
m
m
m
m
m
m
m
m
m
m
m
However, the χ 2 uncertainties are approximately 0.05◦ and 0.15◦ ,
respectively. The large formal uncertainties are due to a large degree of scalloping on the southwest side and the lesser amount of
the original rim remaining on the northeast side (due to being obscured by the large younger crater). These 1σ uncertainties were
alternatively added to and subtracted from the crater centers and
new offset distances calculated. When doing this, the standard deviation from the mean of the various offsets was ±0.73 km.
Using vertical displacements and shortening determined across
the offset crater, the dip of the thrust at the surface can be calculated using:
θ = tan−1 (μv /μh )
(1)
where θ is the dip of the fault at the surface, μv is the vertical
separation and μh is the horizontal separation. Similarly, dip slip
across the fault was calculated using:
U=
μ2v + μ2h
1/2
(2)
Fault
dip
Radius of
curvature
upper ramp
Radius of
curvature
lower ramp
Depth to
Detach.
52.0◦
41.5◦
54.3◦
43.8◦
167
198
176
206
30.4
36.2
32.0
37.5
43.1
32.6
47.8
36.2
km
km
km
km
km
km
km
km
km
km
km
km
where U is the total slip along the fault. Based on 920 and 1000 m
of vertical separation across the scarp, and shortening of 720 and
1040 m, the Amenthes thrust dips between 41.5–54.3◦ at the surface and accommodated between 1168 to 1442 m of slip (Table 1).
Preferred values of 41.5◦ to 52.0◦ for fault dip at the surface based
on 920 m of vertical separation measured on the topographic profile across Amenthes yields 1168 and 1389 m of slip.
4. Structural analysis
The structural analysis presented here is based on basic tenets
of fault-related fold theory for compressive structures on Earth
using first order assumptions for conservation of mass and nonrecoverable (i.e. non-elastic) strain. These include a rigid footwall
block that does not deform during shortening and translation of
rocks in the hangingwall, parallel to the surface of the thrust. Internal strain in fault-related folds on Earth has been shown to occur
by a number of physical deformation mechanisms (Suppe, 1983;
104
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
Fig. 5. Balanced cross section through Amenthes uplift. Four fault geometries are based on combinations of vertical and horizontal separation across offset crater (920 and
1000 m vertical, 720 and 1040 m horizontal) through which fault dip at the surface is determined. Curvature of each fault solution equals slip at the surface divided by
inclination of the broad crest and backlimb of the fold (0.4◦ and 2.2◦ or 0.007 and 0.0384 radians). See Table 1 with values for these solutions and Seeber and Sorlien
(2000) for methods. Slip is conserved through both curved segments on each model and equals displacement at surface. Change in curvature in each fault surface occurs at
upper axial surface (dashed line) at top of backlimb. Solid line defines base of ramp on all four models and lies directly beneath foot of backlimb at the surface. Stars denote
predicted location of base of backlimb for each fault model. MOLA topography defined by open circles (i.e. individual data points along line of transect). Line of cross section
shown on Fig. 1. Surface topography exaggerated 500%.
Fig. 6. Cross section of the Wind Rivers thrust, a deeply penetrating thrust fault in the Laramide province of Wyoming. Simplified from Stone (1993).
Erslev, 1986), but for Mars it is assumed that rocks are penetratively deformed by widely distributed brittle fracturing, producing
a broad fold above a dipping fault (Seeber and Sorlien, 2000).
Fracturing is likely to be concentrated within the forelimb of the
fold in response to increased shear along the blind thrust. While
other deformation mechanisms have been shown to occur in layered sedimentary rocks in thin-skinned thrust belts on Earth such
as layer parallel shear, this is inappropriate for deformation of
Noachian age crust on Mars, which is assumed to be largely igneous in origin. Detrended topography across Amenthes suggests
the base of its forelimb (i.e. the lobate scarp) is at the same elevation as the base of its backlimb (Fig. 5). This implies the width of
the curved thrust ramp is contained between these two points and
that the base of the back limb marks the point where the thrust
flattens into a horizontal detachment.
Examination of the Amenthes uplift from MOLA topography suggests its most likely terrestrial analogues are isolated,
basement-cored structures, such as the Wind River Mountains in
the Laramide province of the western USA (Fig. 6; Erslev, 1986;
Mitra, 1990; Stone, 1993). These structures, or fault-propagation
folds are typified by steeply dipping or overturned forelimbs where
shear is localized in a downward tightening, triangular envelope
(Erslev, 1986; Allmendinger, 1998). Numerous studies suggest that
shear in the forelimbs of these structures is accommodated by
early folding followed by displacement on a thrust that propagates
upward from depth. MOLA topography suggests the forelimb of
Amenthes is about 5 km wide and dips 5–15◦ (Figs. 3, 5). This
and the detailed morphology of the forelimb or lobate scarp as
shown on THEMIS and other imagery (Fig. 2) both suggest it is a
broad flexure offset by short discontinuous fault ruptures, consistent with an origin as a fault propagation, or trishear fold formed
above a blind thrust. Alternatively a simple thrust rupture at the
surface without broad prior folding would require a much narrower and steeper forelimb where limb width is comparable to
fault slip and limb dip is greater than fault dip. Here the observed
limb width is 5 km versus less than 1.5 km (i.e. fault slip) as might
be expected for a simple rupture. Similarly for a simple thrust rupture with no prior folding, forelimb dip would be greater than the
∼40–55◦ dip of the thrust as opposed to 5–15◦ as observed from
MOLA topography.
Further, at larger scales, these asymmetric structures have been
shown to form by displacement on gently curved, moderatelydipping thrust ramps (Fig. 6; Erslev, 1986; Stone, 1993) where fault
slip is a small fraction of the width of their backlimbs. This is an
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
important distinction, one that indicates Amenthes did not form
above a thrust with abrupt changes in its dip, as would be associated with sharp, kink-like folds whose limbs matched fault slip
(Suppe, 1983). This includes an abrupt step up from a flat-lying
decollement onto the base of a planar thrust ramp, as has been
previously modeled for Amenthes (Schultz and Watters, 2001;
Ruiz et al., 2008). Additionally, while such ramp and flat thrusts
are common in thin-skinned thrust belts that deform sedimentary
basins on Earth (Suppe, 1983) and in regions characterized by volcanic rocks on Venus (Suppe and Connors, 1992), they typically
accommodate shortening at shallow levels in layered sedimentary
or volcanic strata as opposed to more isotropic (i.e. less well bedded) rocks as might be expected in late Noachian highlands crust
on Mars.
Given the range of fault offset estimated at the surface, and the
broad width of the backlimb of Amenthes, any structural model
must therefore include a listric geometry for the thrust ramp beneath the uplift. The broad, nearly flat top of the Amenthes uplift
(i.e. the panel dipping 0.4◦ ) can be related to a very gently curved
and wide thrust ramp, one on which rocks are translated upward.
In contrast, the 2.2◦ panel marking the backlimb located immediately to the east implies a relatively greater amount of uplift
produced by folding over a shorter distance (i.e. the width of the
backlimb) and greater fault curvature at depth. As a basis for comparison, either a shorter radius of curvature that describes a ramp
segment or greater fault displacement can both act to produce a
more steeply inclined fold limb above a listric fault. In addition,
the width of a thrust ramp segment can be directly related to the
edge of associated fold limbs at the surface because a change in
the dip of one corresponds with a change in the other.
Active examples of fault propagation folds have been shown
to grow upward from the base of the seismogenic crust, suggesting a link between the depth to detachment and the brittle
ductile transition (Allmendinger and Shaw, 2000). This has previously been invoked for Amenthes, namely the assumption that the
depth the thrust flattens corresponds with the rheological threshold for plasticity in the Martian crust (Schultz and Watters, 2001;
Ruiz et al., 2008).
4.1. Balanced cross section construction
Studies of well constrained listric thrusts on Earth have derived
a set of relationships that allow fault geometry to be related to
fault displacement, radius of curvature and the dip of backlimbs on
the folds produced above them (Seeber and Sorlien, 2000; Amos
et al., 2007). For a thrust ramp of constant curvature, a circular
listric fault is connected tangentially to a horizontal detachment
at depth, (i.e. the depth to detachment) which we relate to the
brittle–ductile transition. In this case, the hanging wall above the
thrust rotates about a horizontal axis, parallel to the strike of the
fault and requires uplift at the base of the ramp where it starts to
steepen upward. For this case, fault slip S = R α , where R is the
radius of curvature of the fault and α is the cumulative rotation
angle (in radians) of the hanging wall block (i.e. the dip of the
backlimb, Erslev, 1986).
The trajectory, or shape of four fault solutions derived from
combinations of fault slip and dip at the surface and the dip of
the broad crest and backlimb of the Amenthes uplift (Fig. 5) was
determined as follows. The upper tip of the thrust was pinned at
the midpoint of the forelimb or lobate scarp, consistent with a trishear envelope centered symmetrically across an upwardly propagating fault. Radii of curvature for sections of the underlying thrust
were then calculated for the two dip panels (2.2◦ backlimb =
0.0384 rad; 0.4◦ broad crest = 0.007 rad; Table 1) and four possible combinations of vertical (920 and 1000 m) and horizontal (720
and 1040 m) offset measured across the scarp and offset crater
105
(i.e. fault slip). The resulting circular arcs were then used to define
overall fault geometry in each of the four models.
The upper circular arc in each model was constructed for the
shape of the thrust beneath the broad crest that ended at the axial surface that marks the top of the backlimb (Fig. 5). These were
then fit to a lower circular arc consistent with similar fault slip and
the dip of the backlimb. The dip of the thrust was similar where
the two circular arcs in each model meet, producing a smooth
transition where curvature changes at the vertical axial surface at
the top of the backlimb. It follows that continuity of slip is required through synclinal axial surfaces to conserve mass, a basic
tenet for constructing balanced cross sections of curved or listric
thrust faults. The predicted location of the base of the fault ramp
for each model (i.e. where they flatten to horizontal; see stars on
Fig. 5) was then plotted and compared to the location of the synclinal axial surface at the base of the backlimb.
Results of the fault modeling suggest that solutions for fault geometry are relatively insensitive to fault dip as shown by all four
cases where predicted fold geometry can be closely fit to surface
topography (Fig. 5). Note that the balancing method solves for surface dips that exactly match the 0.4 and 2.2◦ dip of the panels
at the surface that are themselves based on regressions of MOLA
shotpoints (Vidal, 2008). These solutions thus easily match MOLA
topography within limits posed by the inherent roughness of the
cratered late Noachian surface and spacing of MOLA shotpoints in
the cross section.
The resulting area balancing thus lends credence to the fault
models, and indicates a curved thrust at depth that steepens above
a horizontal decollement as depicted in the cross sections (Fig. 5).
Further, the depth to detachment in the models can be related to
slip at the surface where uncertainty is dictated by measurements
of fault displacement, in particular horizontal shortening across
the offset crater (Fig. 4). For the four models, shallower depths of
detachment correspond to estimates with the greater value for horizontal shortening (i.e. 1040 m) and range from ∼32.6–36.2 km in
depth based on fault dips at the surface of 41.5–43.8◦ (Fig. 5). Alternatively smaller values for horizontal shortening yield greater
depths to detachment that range from 43.1–47.8 km. Curvature
is greatest at the deepest part of the thrust ramp, where models
for thrust geometry suggest the ramp steepens between 26.9 and
33.5◦ over 3.7–5.7 km of the crust. The goodness of fit of the solutions can be defined by comparing the horizontal distance between
the predicted location of the base of the thrust ramp with the synclinal axial surface marked by the solid line on Fig. 5. These misfits
range from 0.2–0.3 km for values with 920 m of vertical displacement across the scarp, and 2.1–2.2 km for values with 1000 m of
vertical displacement.
4.2. Previous results from fault modeling
Results of the modeling presented here differ from previous
studies that also sought to determine the geometry of the Amenthes thrust (Schultz and Watters, 2001; Ruiz et al., 2008). These
studies used the elastic dislocation method with the program,
Coulomb (Toda et al., 1998), to test whether an optimally oriented,
planar thrust fault could produce surface folding similar to that
measured by MOLA topography. Coulomb is typically used in studies of active faults on Earth to predict instantaneous changes in an
elastic stress field following a large earthquake (for a review see
Freed, 2005).
Schultz and Watters (2001) assumed a planar fault for modeling
the Amenthes thrust. Their model consisted of a fault embedded in
the upper crust, one that was not linked with a horizontal decollement at depth. The term depth of penetration is used here to
describe the lower limit of the thrust modeled in their analysis and
that of Ruiz et al. (2008). In contrast, the term depth of detachment
106
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
is used in our model to describe the level where faults in the models flatten to horizontal as defined by area balancing techniques
(Fig. 5).
Schultz and Watters (2001) considered an ensemble of models
with a broad range of assumed values for fault dip, displacement
and depth of penetration in order to match surface topography.
This analysis was based on a topographic profile from a single orbit
acquired soon after MOLA data were first acquired as part of the
Mars Global Surveyor program, before a gridded DEM was available. The profile used in the study was oriented about 61◦ from
the average strike of the Amenthes scarp. Results of the analysis
argue for a depth of penetration ranging from 25–30 km for Amenthes, overlapping with, or less than the 32.7–47.8 km determined
here for the depth to detachment using area balancing techniques
(Fig. 5). In a subsequent test of the depth of penetration of the
Amenthes thrust, Grott et al. (2007) also used the elastic dislocation method to model surface topography across the uplift. Using
increments for 1 km for depth of penetration and 2◦ for fault dip,
their solutions suggested a higher range of values for the thickness
of the brittle crust, about 32–40 km, corresponding with fault dips
of 30–35◦ .
Subsequent work by Ruiz et al. (2008) again used Coulomb
elastic modeling to constrain the depth of penetration of a planar thrust, using the same methods and assumptions as Schultz
and Watters (2001) and Grott et al. (2007). The topographic profile
used in this analysis was oriented perpendicular to the Amenthes uplift and derived from the MOLA 1/128◦ digital elevation
model. Comparison of the set of parameters used in their analysis was based on determining RMS error for the goodness of fit
between surface topography from MOLA data and that calculated
from the elastic models. RMS were lowest for the range of values
that include 19–24◦ for the dip of the thrust, 1900–2300 m of displacement on it and 27–35 km for the depth it penetrates.
While Ruiz et al. (2008) calculate a range of temperatures for
the onset of plasticity in the crust based on estimations of strength
at this depth, the brittle–ductile transition is determined here using a different method of structural analysis. This refinement offers
the advantage of directly determining the dip of the thrust and
slip across it by measuring the vertical and horizontal displacement across a large crater it offsets. These provide a starting point
for constructing mass balanced models based on well established
relationships between fault and fold shape (Fig. 5). The resulting
balanced structural models are thus internally consistent, where
fault dip and curvature match more detailed surface slope, displacement and most importantly depth to detachment. Similar to
previous studies, it is then argued that the flat decollement of the
thrust formed at the brittle to ductile transition and surface heat
flow calculated accordingly.
In contrast, previous studies of Amenthes use elastic dislocation theory to explore a broad set of models, each of which is
comprised of some combination of values for fault dip, displacement and depth of penetration. Each model produces surface deformation that is compared to MOLA topography. These are then
assessed for goodness of fit between the geometry of the fold predicted by the model versus surface topography. This thus narrows
the most likely combinations of fault orientation, displacement and
depth of penetration, forming the basis for determining a range
of values for heat flow. Elastic dislocation theory generally predicts slip on thrust faults to increase towards the surface (see
model setup in Fig. 4 of Schultz and Watters, 2001), whereas models based on fault-related fold theory conserve slip on the fault
through the entire brittle crust (i.e. displacement is constant with
depth).
Although values obtained for horizontal displacement across
the thrust have some uncertainty from crater rim mapping (Fig. 4),
results in this study predict an average depth to detachment equal
to or significantly greater than values derived from the previous
studies. This has implications for estimates of Late Noachian heat
flow, which are outlined in the following section.
5. Depth to detachment and the brittle–ductile transition
Previous studies of Amenthes have all sought to relate the
depth to detachment, or penetration of the Amenthes thrust to the
temperature of the brittle–ductile transition, to estimate surface
heat flow during the Late Noachian in this part of Mars (Schultz
and Watters, 2001; Grott et al., 2007; Ruiz et al., 2008). Whereas
uncertainty in the depth of detachment of the Amenthes thrust is
considered in the previous sections, estimations of the temperature
of the brittle–ductile transition, and it’s likely variation depend
largely on the composition and thermal properties of the Martian
crust, which have been assumed for Mars. It is beyond the scope of
this paper to comment on the suitability of assumptions for rheology and strain rate used to calculate surface heat flow at Amenthes
and the reader is referred instead to the comprehensive consideration of heat flow in Ruiz et al. (2008) and methods and parameters
used in that analysis, which are adopted here. For the purposes
of comparison, the temperature of the brittle to ductile transition,
surface heat flow and thermal gradients are recalculated using the
range of depth to detachment determined from the structural analysis. These are based on a range of values for thermal conductivity
and heat production in the crust, strain rate and crustal density
(Ruiz et al., 2008).
5.1. Surface heat flow
Ruiz et al. (2008) first estimate the temperature of the brittle–
ductile transition using the thermal dependence of ductile strength
where brittle failure transitions to plastic creep. See equations and
solutions in their Section 4. Heat flow from the depth of the Amenthes Rupes-related thrust fault (Ruiz et al., 2008). The temperature
of the brittle ductile transition is determined for zero pore fluid
pressure, a stress coefficient for compression, a range of crustal
densities (2700–3100 kg m−3 ) and strain rates (10−16 –10−19 s−1 ),
gravity on Mars and empirically derived values for the activation energy of creep for flow of wet diabase. The resulting values
for the temperature of the brittle ductile transition range from
530–610 K. This then permits surface heat flow to be estimated
using the previously determined temperature of the brittle–ductile
transition and surface temperature as well as a range of values
for volumetric heat production (0.46–0.60 μW m−3 ), and thermal
conductivity in the crust (2.0 W m−1 K−1 ; Ruiz et al., 2008). For
a depth range of 27–35 km to the brittle ductile transition, Ruiz
et al. (2008) calculate surface heat flow of 26–37 mW m−2 and
thermal gradients of 9–14 K km−1 . They also determine surface
heat flow for zero crustal heat production with resulting values
of 18–29 mW m−2 .
Using the assumption that the height of the lower ramp in the
four models (3.7–5.7 km) represents the depth interval over which
the full onset of plasticity occurs, it is possible to determine the
corresponding difference in temperature over this thickness of the
crust. For a temperature range of 530–610 K at the brittle ductile
transition (Ruiz et al., 2008), this indicates the change in temperature ranges between ∼26–47 K (i.e. over the depth range of
3.7–5.7 km).
For comparative purposes, we also plot surface heat flow as
bounded by the same range of parameters listed above with respect to our work and that of the previous studies for the depth
of the brittle ductile transition at Amenthes (Fig. 7). The plot illustrates how surface heat flow varies as a function of the depth
to detachment, using the range of values for thermal conductivity, heat production, strain rate, crustal density, etc. used by
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
107
Fig. 7. Curves that plot surface heat flow versus depth of detachment or depth of penetration of the Amenthes thrust. Range of values from the previous studies shown by
arrows. Area between the two curves contains solutions for surface heat flow using all possible combinations of volumetric heat production, strain rate and density of the
crust listed in text box. Combination of upper set of values yield maximum possible surface heat flow (upper curve). The lower set of values yield minimum possible heat
flow, shown as the lower curve. See Ruiz et al. (2008) for flow law constants and other variables.
Ruiz et al. (2008); Fig. 7. The plot considers a range from estimates
of the brittle–ductile transition, including that of Schultz and Watters (2001) of 25–30 km, Ruiz et al. (2008) of 27–35 km, and our
results of 32.6–47.8 km (Fig. 7). Although the rate of change in
surface heat flow decreases with increasing depth (i.e. the curve
shown in Fig. 7 flattens with increasing depth to detachment),
our results yield lower heat flow estimates than previous studies.
For example, surface heat flow predicted by three previous studies range from 28–38 mW m−2 at 25–30 km (Schultz and Watters,
2001) and 26–37 mW m−2 for depths of 27–35 km (Ruiz et al.,
2008; Grott et al., 2007; Figs. 7). In contrast, the greater depth to
the brittle ductile transition estimated in this study yields shifted,
generally lower surface heat flows that range from 24–33 mW m−2
(Fig. 7).
6. Discussion
MOLA surface topography indicates the Amenthes uplift is an
asymmetric fold with a broad, gently inclined backlimb formed
above a wide (58 km), moderately to steeply dipping listric thrust
ramp. The absence of narrow dip panels on the uplift, combined
with values for fault slip indicates the thrust is not comprised
of ramp and flat segments, as is common in thin-skinned fold
belts that deform layered deposits with large strength contrasts
on Earth (Suppe, 1983). In addition no correlation exists between
the shape of the thrust and a shallow weak layer between the
surface and 1–3 km depth, as might be expected for the thickness of megaregolith in Noachian age crust (Hartmann et al., 2001;
Ward, 2002). It can therefore be argued the upper crust in the
Amenthes region is largely homogeneous with regards to rock
strength and that crustal scale layering with widely different mechanical properties is not present within the upper 30–40 km. Balanced cross sections are robust and can be restored such that the
predicted location of the base of the thrust ramp closely matches
its location as inferred by surface topography (i.e. the base of the
back limb). The area uplifted above the thrust in the fault models
similarly closely matches detrended topography, within the limits
of ambient surface roughness.
The balanced cross section and structural reconstruction argues that the fault that produced Amenthes penetrated to the
base of the brittle lithosphere and that the structure is most
closely analogous to basement cored uplifts of the Rocky Mountains that formed via fault-propagation folding (Fig. 6; Erslev, 1986;
Mitra, 1990; Stone, 1993). Interpretations of the subsurface structure and depth of penetration of faults beneath wrinkle ridges has
been argued to be thin-skinned in which faults only extend several
kilometers deep or thick-skinned in which the faults extend to the
brittle ductile transition (e.g., see review in Golombek and Phillips,
2010 and references therein). We do note, however, that the broad
backlimbs of wrinkle ridges (similar to the backlimb of Amenthes)
also argues that faults beneath wrinkle ridges penetrate deeply
and may extend to the brittle ductile transition analogous to large
fault-propagation folds on Earth (Fig. 6; Golombek et al., 2001;
Mueller and Golombek, 2004).
A significant change in the otherwise gently listric geometry
of the Amenthes thrust inferred from the structural models is the
more sharply curved 3.7–5.7 km-high and 16 km-wide section of
the thrust that forms the base of the ramp above the basal detachment. This smaller ramp is required to balance uplift above
the backlimb and marks the transition from the flat detachment
to the main thrust ramp. As in many compressive orogens, thrust
ramps step upward at the base of stronger units, especially in fold
belts that deform rocks of widely different strength. We attribute
the sharper curvature at the base of the thrust ramp to form in
response to displacement across the brittle to ductile transition.
The thickness over which the thrust curves sharply upward must
therefore be related to a gradual increase in fault strength, over a
thickness of ∼ 4–6 km in the crust. While the transition from brittle to plastic deformation mechanisms can be affected by a variety
of rheological conditions (see previous discussion), an increase in
temperature is the most likely cause over this thickness of the
crust, in particular as it might affect rocks of appropriate composition for Mars. The middle crust on Mars is most likely mafic in
composition, perhaps similar to Nahklite meteorites that consist of
clinopyroxene, minor olivine and interstitial mesostatic plagioclase
108
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
Our results are similar to recent estimates by Ruiz et al. (2011)
who consider the thermal evolution of Mars using lithospheric
strength as derived by estimates in the literature of the depth of
penetration of large thrust faults and the effective elastic thickness
of the lithosphere. Their work suggests that surface heat flow as
implied by lithospheric strength in many regions on Mars is lower
than those derived from radioactive heat production. This is interpreted to suggest that the contribution of secular cooling to heat
flow on Mars is lower than previously thought, consistent with
presently high effective elastic thickness shown by the lack of deflection from loading of its north polar ice cap and extensive recent
volcanism. Further, work by Ruedas et al. (2013a, 2013b) suggests
low values for surface heat flow early in Mars history as defined by
models of the thermal and compositional evolution of its mantle.
These results are comparable to ours. Taken as a whole, these results suggest Mars is cooling more slowly than previously thought,
perhaps as a result of a more stagnant convective mantle and more
inefficient heat loss (Ruiz et al., 2011). This further suggests that
Mars may have had higher internal temperatures throughout much
of its history.
Fig. 8. Graph of surface heat flow curves for Mars from the previous studies. Results shown as follows. Coupled thermal-magmatic model (solid line; Hauck and
Phillips, 2002), radiogenic heat production balanced with chemistry (dashed lines,
Montesi and Zuber, 2003; Laul et al., 1986; Treiman et al., 1986), lithospheric cooling (Montesi and Zuber, 2003). Boxes are results from analysis of buckling instability
(dashed) and gravity and topography (solid) by Montesi and Zuber (2003). Light
gray envelope in background is from admittance analysis in many regions of Mars
(McGovern et al., 2002; 2004; see Solomon et al., 2005 and Golombek and Phillips,
2010 for reviews) whereas dots are values from McKenzie et al. (2002). Results from
this study shown as small, dark gray rectangle labeled “This Study”; other studies
at Amenthes are labeled “Prev. Work”. Results from Ruiz et al. (2011) shown as star.
Values for all studies that relate depth to detachment, or depth to penetration of
the thrust at Amenthes are shown in the insert at the upper right and include the
work of Schultz and Watters (2001), Grott et al. (2007) and Ruiz et al. (2008).
(Berkeley et al., 1980). Of these minerals plagioclase is the phase
that controls the onset of plasticity (Kirby and Kronenberg, 1984;
Stunitz, 1993; Dimanov and Dresen, 2005).
The 33–48 km depth to detachment determined for Amenthes is greater than the 30 km depth estimated by Schultz and
Watters (2001) and mostly greater than the 27–35 km depth derived by Ruiz et al. (2008). Given the range of applicable temperatures for the brittle–ductile transition, results in this study
imply correspondingly lower heat flow. It is thus useful to consider other independent estimates of heat flow early in Mars history as determined from other methods. A recent compilation of
elastic lithosphere thickness from a variety of tectonic models suggest a thin lithosphere (10–35 km) in the Noachian and a progressively thicker lithosphere in the Hesperian (10–65 km) and
Amazonian (20–300 km) (e.g., see Golombek and Phillips, 2010).
As an example, in an analysis of local conditions that lead to
the development of younger, Early Hesperian wrinkle ridges on
Solis Planum, Montesi and Zuber (2003) used modeling of buckling instabilities to argue for surface heat flow of 30–48 mW m−2 ,
a geotherm of 12 ± 3 K km−1 and a brittle–ductile transition as
deep at 60 km. Depth to the brittle–ductile transition is greater
in this work than is presented here, although the structures on
Solis Planum may be considerably younger than Amenthes and
formed under a correspondingly lower thermal gradient in the
crust. Studies based on lithospheric cooling models (Montesi and
Zuber, 2003) are generally consistent with estimates of heat flow
presented here (Fig. 8). However estimates here are considerably
lower than most other previous studies including coupled thermalmagmatic models (Hauck and Phillips, 2002) and models of radiogenic heat production balanced with chemistry (Laul et al., 1986;
Treiman et al., 1986; Fig. 8).
7. Summary
We use a large impact crater offset by the Amenthes Rupes
thrust fault and the shape of the region uplifted above it to determine its geometry and the depth it flattens in Late Noachian
crust on Mars. Measurements of vertical displacement across the
fault scarp and horizontal shortening across the crater define the
dip of the fault at the surface, which ranges from 42–54◦ with
slip of ∼1170–1440 m. MOLA surface topography suggests the region uplifted above the thrust is similar to fault propagation folds
formed above curved or listric faults, like those associated with
basement cored uplifts developed in continental crust on Earth. As
defined by detrended MOLA topography the area uplifted above
the thrust is marked by a moderately dipping forelimb formed
above the fault tip, a wide and flat crest, and a gently inclined
backlimb. Structural modeling based on fault-related fold theory
suggests that surface topography is best fit by a deeply penetrating
thrust ramp that flattens into a horizontal detachment at depths of
33–48 km. Solutions for fault dip, curvature and slip are fully balanced and restorable, meaning that the uplifted area predicted in
the models can be closely matched to the width and inclination
of the back limb as seen in surface topography. The depth range
over which the thrust steepens above the detachment can be related to a gradual change in brittle to plastic behavior over a depth
of ∼ 4–6 km, and the most likely cause for this change is temperature for a range of reasonable geothermal gradients. Calculations
of surface heat flow based on an applicable range of temperatures
for the brittle–ductile transition and the structural modeling yield
values similar to some estimates of lithospheric strength and modeling of the thermal and compositional evolution of the martian
mantle.
Acknowledgements
Support for this work was provided by NASA’s Planetary Geology and Geophysics Program to M. Golombek and K. Mueller (grant
1241698). Work at the Jet Propulsion Laboratory, California Institute of Technology was done under a contract with NASA.
References
Allmendinger, R.W., 1998. Inverse and forward numerical modeling of trishear faultpropagation folds. Tectonics 17, 640–656.
Allmendinger, R.W., Shaw, J.H., 2000. Estimation of fault propagation distance
from fold shape: implications for earthquake hazard assessment. Geology 28,
1099–1102.
K. Mueller et al. / Earth and Planetary Science Letters 408 (2014) 100–109
Amos, C.B., Burbank, D.W., Nobes, D.C., Read, S.A.L., 2007. Geomorphic constraints
on listric thrust faulting: implications for active deformation in the Mackenzie Basin, South Island, New Zealand. J. Geophys. Res. 112, B03S11. http://
dx.doi.org/10.1029/2006JB004291.
Bergen, K.J., Shaw, J.H., 2010. Displacement profiles and displacement-length scaling
relationships of thrust faults constrained by seismic-reflection data. Geol. Soc.
Am. Bull. 122, 1209–1219. http://dx.doi.org/10.1130/B26373.1.
Berkeley, J.L., Keil, K., Prinz, M., 1980. Comparative petrology and origin of Governador Valadares and other nahklites. In: Proc. 11th Lunar and Planet. Sci.,
pp. 1089–1102.
Bloxsom Lynn, H., Quam, S., Thompson, G.A., 1983. Depth migration and interpretation of the COCORP Wind River, Wyoming seismic reflection data. Geology 11,
462–469.
Burgmann, R., Dresen, G., 2008. Rheology of the lower crust and upper mantle: evidence from rock mechanics, geodesy, and field observations. Annu. Rev. Earth
Planet. Sci. 36, 531–567.
Coward, M.P., 1984. Major shear zones in the Precambrian crust: examples from NW
Scotland and southern Africa and their significance. In: Kröner, A., Greiling, R.
(Eds.), Precambrian Tectonics Illustrated. Schweizerbart’sche Verlagsbuchhandlung (Nagele U. Obermiller), Stuttgart, pp. 207–235.
Dimanov, G., Dresen, G., 2005. Rheology of synthetic anorthite–diopside aggregates:
implications for ductile shear zones. J. Geophys. Res. 110. http://dx.doi.org/
10.1029/2004JB003431.
Erslev, E., 1986. Basement balancing of Rocky-Mountain foreland uplifts. Geology 14,
259–262.
Freed, A.M., 2005. Earthquake triggering by static, dynamic and postseismic stress
transfer. Annu. Rev. Earth Planet. Sci. 33, 335–367.
Golombek, M.P., Phillips, R.J., 2010. Mars tectonics. Chapter 5 In: Watters,
T.R., Schultz, R.A. (Eds.), Planetary Tectonics. Cambridge University Press,
pp. 183–232.
Golombek, M.P., Tanaka, K.L., Franklin, B.J., 1996. Extension across Tempe Terra,
Mars, from measurements of fault scarp widths and deformed craters. J. Geophys. Res. 101, 26,119–26,130. http://dx.doi.org/10.1029/96JE02709.
Golombek, M.P., Anderson, F.S., Zuber, M.T., 2001. Martian wrinkle ridge topography:
evidence for subsurface faults from MOLA. J. Geophys. Res. 106, 23811–23821.
Grott, M., Hauber, E., Werner, S.C., Kronberg, P., Neukum, G., 2007. Mechanical
modeling of thrust faults in the Thaumasia region, Mars, and implications for
Noachian heat flux. Icarus 186, 517–526.
Hartmann, W.K.J., Anguita, M.A., de la Casa, D.C., Berman, C., Ryan, E.V., 2001. Martian cratering 7. The role of impact cratering. Icarus 149, 37–53.
Hauck II, S.A., Phillips, R.J., 2002. Thermal and crustal evolution of Mars. J. Geophys.
Res. 107. http://dx.doi.org/10.1029/2001JE001801.
Hiller, K.H., 1979. Geologic map of the Amenthes quadrangle of Mars: USGS Map
I-1110 (MC-14). United States Geological Survey.
Johnson, K.M., Johnson, A.M., 2002. Mechanical models of trishear-like folds.
J. Struct. Geol. 24, 277–287.
Kirby, S.H., Kronenberg, A.K., 1984. Deformation of clinopyroxenite: evidence for
a transition in flow mechanisms and semibrittle behavior. J. Geophys. Res. 89,
3177–3192.
Laul, J.C., Smith, M.R., Waenke, H., Jagoutz, E., Dreibus, G., Palme, H., Spettel, B.,
Burghele, A., Lipschutz, M.E., Verkouteren, R.M., 1986. Chemical systematics
of the Shergotty Meteorite and the composition of its parent body (Mars).
Geochim. Cosmochim. Acta 50, 909–926.
McGovern, P.J., Solomon, S.C., Smith, D.E., Zuber, M.T., Simmons, M., Wieczorek,
M.A., Phillips, R.J., Neumann, G.A., Aharonson, O., Head, J.W., 2002. Localized gravity/topography admittance and correlation spectra on Mars: implications for regional and global evolution. J. Geophys. Res. 107. http://dx.doi.org/
10.1029/2002JE001854.
McGovern, P.J., Solomon, S.C., Smith, D.E., Zuber, M.T., Simmons, M., Wieczorek,
M.A., Phillips, R.J., Neumann, G.A., Aharonson, O., Head, J.H., 2004. Correction
to “Localized gravity/topography admittance and correlation spectra on Mars:
implications for regional and global evolution”. J. Geophys. Res. 109. http://
dx.doi.org/10.1029/2004JE002286.
McKenzie, D., Barnett, D.N., Yuan, D.N., 2002. The relationship between Martian
gravity and topography. Earth Planet. Sci. Lett. 195, 1–16.
Mitra, S., 1990. Fault-propagation folds: geometry, kinematic evolution, and hydrocarbon traps. Am. Assoc. Pet. Geol. Bull. 74, 921–945.
Montesi, L.G.J., Zuber, M.T., 2003. Clues to the lithospheric structure of Mars from
wrinkle ridge sets and localization instability. J. Geophys. Res. 108. http://dx.
doi.org/10.1029/2002JE001974.
109
Mueller, K., Golombek, M.P., 2004. Compressional structures on Mars. Annu.
Rev. Earth Planet. Sci. 32, 435–464. http://dx.doi.org/10.1146/annurev.earth.32.
101802.120553.
Munoz, M., 2008. The brittle/ductile transition in the lithosphere of the Andes region and its relationship with seismogenesis. In: 7th International Symposium
of Andean Geodynamics. ISAG 2008, Nice, pp. 361–364.
Pujol, J., Mueller, K., Shen, P., Chitupolu, V., 2006. High-resolution 3-D P-wave velocity model for the East Ventura – San Fernando basin, California, and relocation
of events in the Northridge and San Fernando aftershock sequences. Bull. Seismol. Soc. Am. 96, 2269–2280.
Ruedas, T., Tackley, P.J., Solomon, S.C., 2013a. Thermal and compositional evolution
of the martian mantle: effects of phase transitions and melting. Phys. Earth
Planet. Inter. 216, 32–58.
Ruedas, T., Tackley, P.J., Solomon, S.C., 2013b. Thermal and compositional evolution of the martian mantle: effects of water. Phys. Earth Planet. Inter. 220,
50–72.
Ruiz, J., Fernandez, C., Gomez-Ortiz, D., Dohm, J.M., Lopez, V., Tejero, R., 2008.
Ancient heat flow, crustal thickness, and lithospheric mantle rheology in the
Amenthes region, Mars. Earth Planet. Sci. Lett. 270, 1–12. http://dx.doi.org/
10.1016/j.epsl.2008.02.015.
Ruiz, J., McGovern, P.J., Jimenez-Diaz, A., Williams, J., Hahn, B.C., Tejero, R., 2011.
The thermal evolution of Mars as constrained by paleo-heat flows. Icarus 2115,
508–517.
Scholtz, C.H., 1988. The brittle–plastic transition and the depth of seismic faulting.
Geol. Rundsch. 77, 319–328.
Schultz, R.A., Watters, T.R., 2001. Forward mechanical modeling of Amenthes Rupes
thrust fault on Mars. Geophys. Res. Lett. 28, 4659–4662.
Seeber, L., Sorlien, C., 2000. Listric thrusts in the western Transverse Ranges, California. Geol. Soc. Am. Bull. 112, 1067–1079.
Shaw, J.H., Suppe, J., 1996. Earthquake hazards of active blind-thrust faults under
the central Los Angeles basin, California. J. Geophys. Res. 101, 8623–8642. http://
dx.doi.org/10.1029/95JB03453.
Shaw, J.H., Hook, S., Suppe, J., 1994. Structural trend analysis by axial surface mapping. Am. Assoc. Pet. Geol. Bull. 78, 700–721.
Smithson, S.B., Brewer, J., Kaufman, S., Oliver, J., 1978. Nature of the Wind River
thrust, Wyoming, from COCORP deep-reflection data and from gravity data. Geology 6, 648–652.
Solomon, S.C., Aharonson, O., Aurou, J.M., Banerdt, W.B., Carr, M.H., Dombard, A.J.,
Frey, H.V., Golombek, M.P., Hauck, S.A., Head, J.W., Jakosky, B.M., Johnson, C.J.,
McGovern, P.J., Neumann, G.A., Phillips, R.J., Smith, D.E., Zuber, M.T., 2005. New
perspectives on ancient Mars. Science 307, 1214–1219.
Stone, D.S., 1993. Basement-involved thrust-generated folds as seismically imaged
in the subsurface of the central Rocky Mountain foreland. Spec. Pap., Geol. Soc.
Am. 280, 271–318.
Stunitz, H., 1993. Transition from fracturing to viscous flow in a naturally deformed
metagabbro. In: Boland, J.N., Fitz Gerald, J.D. (Eds.), Defects and Processes in the
Solid State: Geosciences Applications, pp. 121–149.
Suppe, J., 1983. Geometry and kinematics of fault-bend folding. Am. J. Sci. 283,
648–721.
Suppe, J., Connors, C., 1992. Critical taper wedge mechanics of fold-and-thrust belts
on Venus: initial results from Magellan. J. Geophys. Res. 97, 13,545–13,561.
Toda, S., Stein, R.S., Reasenberg, P.A., Dieterich, J.H., Yoshido, A., 1998. Stress transferred by the 1995 Mw = 6.9 Kobe, Japan, shock: effects on aftershocks and
future earthquake probabilities. J. Geophys. Res. 103 (24), 543–24566.
Treiman, A.H., Drake, M.J., Janssens, M.J., Wolf, R., Ebihara, M., 1986. Core formation
in the Earth and shergottite parent body (SPB): chemical evidence from basalts.
Geochim. Cosmochim. Acta 50, 1071–1091.
Verges, J., Ramos, V.A., Meigs, A., Cristallini, E., Bettini, F.H., Cortes, J.M., 2007. Crustal
wedging triggering recent deformation in the Andean thrust front between 31◦ S
and 33◦ S: Sierras Pampeanas–Precordillera interaction. J. Geophys. Res. 112,
B03S15. http://dx.doi.org/10.1029/2006JB004287.
Vidal, A., 2008. Thrust faulting on Mars: implications for early Martian heat flux.
PhD. University of Colorado, Boulder, Colorado, p. 121.
Ward, S.N., 2002. Planetary cratering: a probabilistic approach. J. Geophys. Res. 107
(E4), 5023. http://dx.doi.org/10.1029/2000JE001343.
Watters, T.R., 2003. Thrust faults along the dichotomy boundary in the eastern hemisphere of Mars. J. Geophys. Res. 108. http://dx.doi.org/10.1029/2002JE001934.