subsidence, and sedimentation derived from the rising mountain belt, geodynamics models have been
used to derive important parameters like the rheology
of the lithosphere, thrusting rates, or erosion rates
(DeCelles and DeCelles, 2001; Jordan and Watts,
2005; Pelletier, 2007). Numerical models of foreland
basin successfully combined the effects of fold-andthrust belt migration, flexural subsidence, and sedimentation including three-dimensional geometries
and nonlinear crustal rheology (Garcia-Castellanos
et al., 1997, Clevis et al., 2004).
(ii) A fold-and-thrust belt consists in intensely thrusted
and folded unmetamorphosed or low-grade sediments, derived from the passive margins of the
downgoing continent. In cross section, the fold-andthrust belt has a wedge-shaped geometry with a sole
fault (décollement) at its base. The deformation generally propagates outwards in a sequence so that the
deformation near the core of the orogen and at high
structural levels is older than the deformation near
the foreland at the structural base of the thrust stack.
The décollement characteristically contains weak
rocks like shales or salt along which the deformation
of the overlying wedge is decoupled from the underlying rocks, which frequently consists of crystalline
basement rocks. This style of deformation where
strongly shortened sedimentary rocks are detached
from a basement is called thin-skinned tectonics. At
the contrary, thick-skin tectonics describes a foldand-thrust belt in which the basement is also
deformed (typically by reactivation of normal faults
as thrusts).
The shape of the wedge has been explained by the
mechanics of a deformable sequence above a basal
décollement, generally known as the critical Coulomb wedge theory (Davis et al., 1983). Critical
parameters, which influence the deformation within
the wedge, are the dip angle of the décollement, the
basal traction along the décollement, the friction
angle of the décollement, and the pore fluid pressure,
which counteracts the overburden. Numerous physical and numerical models have tested the influence of
various parameters on the development and geometry of fold-and-thrust belts like the décollement layer
thickness, intermediate décollements within the sedimentary sequence and syn-shortening erosion
(Costa and Vendeville, 2002; Ellis et al., 2004;
Sherkati et al., 2006, Cruz et al., 2010, Fillon et al.,
2013).
Since fold-and-thrust belts are estimated to contain 15 % of the undiscovered global recoverable
hydrocarbons, numerous studies focused on the
development of balanced cross-section techniques,
which aimed to geometrically constrain the style of
folding and thrusting and to kinematically model
palinspastic reconstructions by unfolding and retrodeforming the stratigraphic sequence (Dahlstrom,
1969; Elliot, 1983; Groshong, 1994; Homza and
Wallace, 1995). However, recent studies have demonstrated that the characteristics and the wavelength
of folding in fold-and-thrust belts are strongly
influenced by rheological parameters and mechanical
isotropies of the stratigraphic pile (Yamato et al.,
2011; Ruh et al., 2012). Therefore, future research
will focus on mechanical reconstructions of foldand-thrust belts (Simpson, 2009; Frehner et al.,
2012; Vidal-Royo et al., 2012) including threedimensional mechanical interaction of fold and fault
growth (Schmid et al., 2008a; Grasemann and
Schmalholz, 2012).
(iii) A crystalline core zone forms the central and highest
part of a mountain belt, usually above the orogenic
root, where the crust is the thickest. It mainly consists
of metamorphic and magmatic rocks derived from the
upper crust of the lower plate. Lower crustal rocks are
rare (Jolivet et al., 2003). Units of oceanic material
involved earlier in the subduction zone can also be
found, overthrusting the continental units. The crystalline zone is mainly deformed by ductile flow, resulting
in large shear zones and folded nappes recording complex multiple deformation events. Metamorphism
reaching the amphibolite and eclogite facies is widespread. The metamorphic evolution is, however,
very heterogeneous in time and space. Frequently
the high-grade metamorphic nappes preserve an
inverted metamorphic field gradient, showing an
increase of the metamorphic pressure and temperature
conditions towards structural higher levels. The presence of eclogites, some of which experienced
ultrahigh-pressure metamorphism, suggests that at
least parts of the core zone of mountain belts have
been involved in continental subduction at mantle
depth and later exhumed back to the surface
(Chopin, 1984; Hacker and Peacock, 1995; Hacker
and Liou, 1998; Jolivet et al., 2003).
Structural field observations demonstrate that the
high-grade rocks are exhumed above high-strain shear
zones with thrusting kinematic at the base and below
normal shear zones at the top. Physical and numerical
models together with geological data resulted in several
extrusion wedge models accounting for more or less
complex internal nappe stack structures (Grujic et al.,
1996; Grasemann et al., 1999; Beaumont et al., 2001;
Grujic et al., 2002; Gerya et al., 2008; Yamato et al.,
2008), which have been applied to most Phanerozoic
orogens (Himalayas, Alps, Hellenides, Dabie Shan,
Ural, Hindu Kush, or Caledonides; Ernst, 2001; Law
et al., 2006). Most of these models have in common
that the extrusion of the high-grade rocks has to be at
least partly balanced by surface erosion (Froitzheim
et al., 2003; Beaumont et al., 2004; Schulmann et al.,
2008) requiring huge sediment accumulations in the
foreland of the orogen (White et al., 2002).
Synorogenic S-type granites result from partial
melting of metasedimentary source rocks from the
lower part of the continental crust that has been
OROGENY
605
used to derive important parameters like the rheology
of the lithosphere, thrusting rates, or erosion rates
(DeCelles and DeCelles, 2001; Jordan and Watts,
2005; Pelletier, 2007). Numerical models of foreland
basin successfully combined the effects of fold-andthrust belt migration, flexural subsidence, and sedimentation including three-dimensional geometries
and nonlinear crustal rheology (Garcia-Castellanos
et al., 1997, Clevis et al., 2004).
(ii) A fold-and-thrust belt consists in intensely thrusted
and folded unmetamorphosed or low-grade sediments, derived from the passive margins of the
downgoing continent. In cross section, the fold-andthrust belt has a wedge-shaped geometry with a sole
fault (décollement) at its base. The deformation generally propagates outwards in a sequence so that the
deformation near the core of the orogen and at high
structural levels is older than the deformation near
the foreland at the structural base of the thrust stack.
The décollement characteristically contains weak
rocks like shales or salt along which the deformation
of the overlying wedge is decoupled from the underlying rocks, which frequently consists of crystalline
basement rocks. This style of deformation where
strongly shortened sedimentary rocks are detached
from a basement is called thin-skinned tectonics. At
the contrary, thick-skin tectonics describes a foldand-thrust belt in which the basement is also
deformed (typically by reactivation of normal faults
as thrusts).
The shape of the wedge has been explained by the
mechanics of a deformable sequence above a basal
décollement, generally known as the critical Coulomb wedge theory (Davis et al., 1983). Critical
parameters, which influence the deformation within
the wedge, are the dip angle of the décollement, the
basal traction along the décollement, the friction
angle of the décollement, and the pore fluid pressure,
which counteracts the overburden. Numerous physical and numerical models have tested the influence of
various parameters on the development and geometry of fold-and-thrust belts like the décollement layer
thickness, intermediate décollements within the sedimentary sequence and syn-shortening erosion
(Costa and Vendeville, 2002; Ellis et al., 2004;
Sherkati et al., 2006, Cruz et al., 2010, Fillon et al.,
2013).
Since fold-and-thrust belts are estimated to contain 15 % of the undiscovered global recoverable
hydrocarbons, numerous studies focused on the
development of balanced cross-section techniques,
which aimed to geometrically constrain the style of
folding and thrusting and to kinematically model
palinspastic reconstructions by unfolding and retrodeforming the stratigraphic sequence (Dahlstrom,
1969; Elliot, 1983; Groshong, 1994; Homza and
Wallace, 1995). However, recent studies have demonstrated that the characteristics and the wavelength
of folding in fold-and-thrust belts are strongly
influenced by rheological parameters and mechanical
isotropies of the stratigraphic pile (Yamato et al.,
2011; Ruh et al., 2012). Therefore, future research
will focus on mechanical reconstructions of foldand-thrust belts (Simpson, 2009; Frehner et al.,
2012; Vidal-Royo et al., 2012) including threedimensional mechanical interaction of fold and fault
growth (Schmid et al., 2008a; Grasemann and
Schmalholz, 2012).
(iii) A crystalline core zone forms the central and highest
part of a mountain belt, usually above the orogenic
root, where the crust is the thickest. It mainly consists
of metamorphic and magmatic rocks derived from the
upper crust of the lower plate. Lower crustal rocks are
rare (Jolivet et al., 2003). Units of oceanic material
involved earlier in the subduction zone can also be
found, overthrusting the continental units. The crystalline zone is mainly deformed by ductile flow, resulting
in large shear zones and folded nappes recording complex multiple deformation events. Metamorphism
reaching the amphibolite and eclogite facies is widespread. The metamorphic evolution is, however,
very heterogeneous in time and space. Frequently
the high-grade metamorphic nappes preserve an
inverted metamorphic field gradient, showing an
increase of the metamorphic pressure and temperature
conditions towards structural higher levels. The presence of eclogites, some of which experienced
ultrahigh-pressure metamorphism, suggests that at
least parts of the core zone of mountain belts have
been involved in continental subduction at mantle
depth and later exhumed back to the surface
(Chopin, 1984; Hacker and Peacock, 1995; Hacker
and Liou, 1998; Jolivet et al., 2003).
Structural field observations demonstrate that the
high-grade rocks are exhumed above high-strain shear
zones with thrusting kinematic at the base and below
normal shear zones at the top. Physical and numerical
models together with geological data resulted in several
extrusion wedge models accounting for more or less
complex internal nappe stack structures (Grujic et al.,
1996; Grasemann et al., 1999; Beaumont et al., 2001;
Grujic et al., 2002; Gerya et al., 2008; Yamato et al.,
2008), which have been applied to most Phanerozoic
orogens (Himalayas, Alps, Hellenides, Dabie Shan,
Ural, Hindu Kush, or Caledonides; Ernst, 2001; Law
et al., 2006). Most of these models have in common
that the extrusion of the high-grade rocks has to be at
least partly balanced by surface erosion (Froitzheim
et al., 2003; Beaumont et al., 2004; Schulmann et al.,
2008) requiring huge sediment accumulations in the
foreland of the orogen (White et al., 2002).
Synorogenic S-type granites result from partial
melting of metasedimentary source rocks from the
lower part of the continental crust that has been
OROGENY
605