Impact of Surface Processes on the Growth of ... - Pages perso de

1 downloads 0 Views 1MB Size Report
stop developing a Coulomb thrust wedge during con vergence. Scaling, and ...... ley, and Y. G. Chen, “Mountain Building in Taiwan: A. Thermokinematic Model ...
ISSN 00168521, Geotectonics, 2010, Vol. 44, No. 6, pp. 541–558. © Pleiades Publishing, Inc., 2010.

Impact of Surface Processes on the Growth of Orogenic Wedges: Insights from Analog Models and Case Studies1 J. Malavieillea and E. Konstantinovskayab a

Université Montpellier 2, CNRS UMR 5243, Lab. Géosciences Montpellier, 34095 Montpellier cedex 5, France, and International Laboratory, (LIA) “ADEPT”, CNRSNSC, FranceTaiwan email: [email protected]montp2.fr b Institut National de la Recherche Scientifique, Centre Eau, Terre et Environnement (INRSETE), 490 rue de la Couronne, Quebec City, Quebec, Canada G1K 9A9 email: [email protected] Received March 23, 2010

Abstract—Interaction between surface processes and deep tectonic processes plays a key role in the structural evolution, kinematics and exhumation of rocks in orogenic wedges. The deformation patterns observed in analogue models applied to natural cases of present active or ancient mountain belts reflect several first order processes that result of these interactions. Internal strain partitioning due to mechanical behaviour of a thrust wedge has a strong impact on the vertical component of displacement of tectonic units that in return favour erosion in domains of important uplift. Such strain partitioning is first controlled by tectonic processes, but surface processes exert a strong feed back on wedge dynamics. Indeed, material transfer in thrust wedges not only depends on its internal dynamics, it is also influenced by climate controlled surface processes involving erosion and sedimentation. Effects of erosion are multiple: they allow long term localization of deformed domains, they favour important exhumation above areas of deep underplating and combined with sedimen tation in the foreland they contribute to maintain the wedge in a critical state for long time periods. The sim ple models illustrate well how mountain belts structure, kinematics of tectonic units and exhumation are determined by these complex interactions. DOI: 10.1134/S0016852110060075 1

INTRODUCTION

The geologic history of orogenic wedges records both the main phases of tectonic evolution and the coupled influence of deep geological (rheology and kinematics, metamorphism, magmatism) and surface processes (climate dependent erosion–sedimenta tion) active along convergent margins. In recent years more attention has been paid on the mechanical and thermormechanical aspects of mountain building offering a better understanding of the behaviour and deformation of the continental lithosphere in subduc tion settings. Today, the major role of surface processes is highlighted in numerous studies dealing with the evolution of orogens at different time and space scales. For example, the role of erosion and sedimentation on fault growth, exhumation processes and deformation history of accretionary orogens is widely studied through geological, experimental and numerical approaches [e.g. 6, 14, 60, 79, 90, 93]. Here, insights from simple sandbox models are used to show how the interactions between surface processes and the mechanical behavior of the orogenic wedge influence its structures, kinematics of deformation, exhumation mechanisms, and global evolution. Several case stud 1 The article is published in the original.

ies chosen in various settings characterizing first order tectonic processes (Taiwan, Alps and Variscan belt) are then discussed in the light of the experiments. GROWTH OF OROGENIC WEDGES DURING CONTINENTAL SUBDUCTION Orogenic wedges develop in subduction settings due to plate convergence involving large shortening and deformation of the crust (Fig. 1a). Two main sub duction settings characterize mountain building. The first one, oceanic subduction, concerns Andean type mountain belts formed by subduction of an oceanic plate below a deforming continental margin upper plate. Continental subduction, the second one, con cerns most of other mountain belts. This paper focuses on orogenic wedges of the second type, either due to subduction of a continental margin under a continen tal plate following an Andean type oceanic subduc tion, or due to subduction of a continental margin under an intraoceanic volcanic arc (oceanic lithos phere upperplate) following intraoceanic subduc tion [64, 66]. Continental subduction occurs after clo sure of an oceanic domain that can be wide or narrow depending on the geodynamic setting. Subduction of the lithospheric mantle induces deformation of the

541

542

MALAVIEILLE, KONSTANTINOVSKAYA (a) orogenic wedge 0 30 km

input

U.P.

o u t pu

S

continental crust

lithospheric mantle

U.P. = Upper Plate L.P. = Lower Plate

t

L.P.

Svelocity discontinuity

(b) rigid buttress

sedimentation

glass sidewall

deformable U.P. erosion surface plastic sheet

sand cake S

10 cm

engine

décollement layer

rigid base L.P.

3m

Fig. 1. (a) Kinematic setting of continental subduction and (b) Schematic setting used for analogue modeling of thrust wedges. Backstop geometries and rheologies can be modified. Dotted line represents the chosen erosion surface. Sedimentation (when integrated) is performed by sprinkling sand.

continental crust and controls the structural asymme try of the mountain belt [33, 68]. This is well illustrated today by various geophysical data (wide angle seismic transects and seismic tomography) from different mountain chains [5, 10, 98]. They clearly show the subduction of the lithospheric mantle and suggest that it could drag the continental crust or part of it. The study of oceanic accretionary wedges has played a great role in the understanding of mountain building processes. What do we learn from oceanic accretion? Two major tectonic processes act along subduction zones: tectonic erosion (when material is removed from the upperplate margin and dragged through the subduction channel) and accretion (when material is removed from the subducting lowerplate and accreted to the upperplate) [e.g., 56]. During continental accretion, the whole or only part of the incoming rock sequences is incorporated to the wedge depending on the location of the décollements that allow crustal material to be detached from the sub ducting plate. The part which is not involved in wedge growth is dragged deeper into the mantle. At lithos pheric scale, oceanic and continental subduction have been described by a simple setting [e.g. 62] that was used as a first order kinematic boundary condition for many modeling approaches (Fig. 1). The location of a velocity discontinuity (the “S point” in numerical models, e.g., [9]) determines the amount of accreted material (input) vs. subducted material (output) and controls which part of the continental crust is sub ducted with the mantle (the whole crust or part of uppercrust). In a thrust wedge, several kinematic sin gularities exist mainly due to the mechanical layering

of the continental crust, they can be activated (simul taneously or not) during the evolution of the orogen. Such a layering can be lithologic (e.g., basement cover interface, or weak layers in a sedimentary sequence), rheologic (e.g., thermomechanical changes during subduction or fluids pressure changes) or inherited from the early tectonic history (e.g., the structural her itage of an extended margin prior to continental sub duction). During mountain building, these weak zones have a major impact on the mechanical behavior of the wedge [16, 87] as they constitute potential déc ollement zones. How and where these décollements develop and how they influence the mechanics and structural evolution of the orogenic wedge are major questions [90]. Since the fundating works by Davis, Dahlen, and Suppe in the 1980s [30, 31], mountain belts have been often considered by geologists as crustal scale accre tionary wedges [62, 78, 92] which deformation mech anisms can be satisfactorily described by a simple Coulomb behaviour. The Coulomb theory gives a sim ple mechanical setting allowing the definition of dif ferent tectonic regimes depending on wedge stability: critical, undercritical, overcritical [e.g. 25]. Then, it has been shown that orogens commonly adopt a dis tinct geometry with a lowtapered prowedge facing the subducting plate, and a hightapered retrowedge on the internal side [62]. This concept of doubly ver gent accretionary wedge widely explored in the 1990s [8, 35, 97] is still explored now [e.g., 74, 77, 81]. Ero sion has rapidly been added as a major parameter to the theory [26–29] because it exerts a significant con trol on wedge mechanics. Removing material from the GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

wedge surface induces a continuous deformation of the wedge changing the way for the critical state to be maintained. If the tectonic (shortening) and climatic conditions (erosional potential] remain stable, the wedge reach a dynamic steady state [6, 27, 44, 47, 95, 96] in which the incoming fluxes (accreted material) are compensated by the outgoing fluxes (material removed by erosion). According to these models, the velocity field of the crust and, hence, the exhumation paths of rock particles, depends on erosion at the sur face [e.g. 45, 76]. Consequently, any changes in ero sion rates potentially result in a modification of the strain pattern [80] and thus the internal evolution of the wedge [63]. The topography of mountain belts depends of the behaviour of continental rock units, depending itself on fault grow and evolution. Models involving plastic [20, 97] or viscous [22] behaviour account well for dis placements and produce velocity fields close to what are observed in mountain belts, but they do not gener ate clear displacement discontinuities as faults did [67]. Thus, although the Coulomb wedge model gives a rigorous mechanical frame to study the dynamics of orogenic wedges, it presents some limits when study ing the internal structure and kinematics of deforma tion which are mainly controlled by the heterogeneous nature of tectonic units and subsequent fault zones development. The critical wedge theory, is based on the hypothesis that orogens are everywhere on the verge of internal failure along potential slip planes [31] which do not allow strain localization along fault zones. Thus it does not account for deformation pro cesses at the scale of individual tectonic instabilities [e.g. 74]. Analysis becomes much more complex when introducing surface processes which interactions with tectonics induce changes in the mechanical state of the wedge at different time and length scales. MODELING PRINCIPLES AND TECHNIQUES A lot of analogue experiments dealing with the growth of thrust wedges have been performed since many years at Geosciences Montpellier laboratory giving insights for the general ideas discussed in this article. The analogue modeling approach presents sig nificant advantages providing quantitative and/or qualitative estimations of experimental models [40]. It accounts for tectonic instabilities, providing comple mentary informations on accretion processes and deformation at the scale of discrete tectonic struc tures. Large convergence can be tested, that is neces sary to take into account the widespread deformations observed in subduction related mountain belts. In addition, experiments can integrate erosion and sedi mentation allowing us to characterize the impact of surface processes on the foreland/hinterland structure and evolution of mountain wedges. They provide a dynamic view of long term processes involved in mountain building that is complementary to geology GEOTECTONICS

Vol. 44

No. 6

2010

543

and geophysics that are able to produce a global view at a lithospheric scale, but this image is a “snap shot” in time. The classical sandbox devices used (Fig. 1b) are made by a flat basal plate bound by two lateral glass walls (see detail in: [14, 50, 51, 62]). A motor pulls a plastic sheet with a surface on which basal friction can be chosen. A polished plastic film produces low basal friction and a rough plastic sheet surface simulates a high basal friction at the base of the layered incoming sand. The analogue granular materials deposited on the plastic sheet have frictional properties satisfying the Coulomb theory and they correctly mimic non linear deformation behaviour of crustal rocks in the brittle field. The aeolian sand used in the experiments is rounded with a grain size of less than 300 mm and a density of 1690 kg/m3. The internal coefficient of fric tion is 0.57 and the cohesion Co = 20 Pa. The weak décollement levels are created by introducing in the model thin (1–2 mm) layers of glass microbeads. They are a Coulomb material and their density and size are almost the same as those of dry sand, however due to their close to perfect roundness their coefficient of internal friction is about 23% smaller (0.44), with cohesion almost negligible. The successive colored sand layers are generally accreted against a rigid back stop developing a Coulomb thrust wedge during con vergence. Scaling, and characterization of models and analogue materials are discussed in [21, 32, 42, 43, 54, 57, 61] and a clear synthesis is given in [41]. The rigid backstop simulates the undeformed part of the upper plate lithosphere. The basal plate length is 2.8 m allowing large convergence to be tested. It represents the subducting lowerplate lithosphere. An equivalent setup is used to study the influence of erosion and sedimentation on the internal structure and fault kinematics of model thrust wedges while maintaining a constant taper angle [14, 15, 50, 51]. Erosion is performed by hand with a thin metal plate (the sand being removed using a vacuum cleaner) to maintain the slope of the wedge at a constant angle reflecting the mean taper angle imposed by wedge mechanics. Erosion of the units was applied in a con stant manner, independently of their compositional nature, as a function only of topography. Thus higher topographies and topographic anomalies were eroded leading to erosion that is distributed and linearly dependant on elevation. Generally this means that erosion is increasing towards higher topographies. This is supported by other analogue models [e.g. 24, 46], and also by observations from natural situations where erosion can be positively correlated with eleva tion [91]. Sedimentation (when integrated) is per formed in the foreland in the basin and on the deform ing orogenic front (developing piggyback basins) by sprinkling sand [48, 58, 65] to fill the same average surface as used for erosion. Thus, results of models are usefull to discuss the effects of several first order mechanical parameters on the deformation and struc

544

MALAVIEILLE, KONSTANTINOVSKAYA backthrusting high angle taper accretion of new tectonic units by underthrusting

10 cm (a)

HIGH BASAL FRICTION low angle taper

backthrust

frontal accretion of new tectonic units

10 cm (b)

LOW BASAL FRICTION backstop

“basal décollement”

variable taper

basal accretion

frontal accretion “décollement 2”

10 cm (c)

“décollement 1”

DECOLLEMENTS

mean surface slope

(d)

“décollement 1”

10 cm

“décollement 2”

Fig. 2. Models without erosion showing the main mechanisms of wedge growth and corresponding critical taper: (a) high basal friction model, (b) low friction, (c) multiple décollements, (d) picture of a model with décollement.

tural evolution of orogenic wedges submitted to ero sion. GENERAL CHARACTERISTICS OF EXPERIMENTAL WEDGES SUBMITTED TO EROSIONSEDIMENTATION A selection of 2D experiments without erosion is first used to discuss the main mechanisms that are involved in wedge growth and a second series involving erosion and sedimentation, to highlight the impact of surface processes on wedge development. Experiments without Erosion Figure 2 shows the geometry, structure and kine matics of simple endmember model wedges formed by accretion only. Three main mechanisms account

for wedge growth: frontal accretion (décollement), underthrusting (high basal coupling) and underplating (different decoupling levels acting at different depths within the wedge). High friction wedges are character ized by a high taper angle and by growth occuring through underthrusting of long tectonic units bounded by lowangle thrusts. A major backthrust develops along the backstop whereas only few minor back thrusts develop within the body of the wedge. Low fric tion wedges are characterized by a low taper angle and by growth through frontal accretion of new tectonic units involving forward propagation of a basal décolle ment. As the stress field is more symmetrical in the wedge (the main principal stress axis is close to hori zontal), deformation commonly involves conjugate thrust faults leading to popup structures formation [e.g. 89]. Many backthrusts develop within the body of the wedge allowing continuous thickening. In the both GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

types of experiments, the birth and activity of thrusts is not continuous during shortening. As new thrusts grow to propagate the deformation forward, former thrusts or newly formed thrusts can be activated out of sequence inside the wedge to allow the wedge to main tain an ideal “accretionary” critical) taper. The similar wedge geometry was observed in experimental models with both for high and low basal friction even if the rigid backstop was vertical [50, 51]. Wedges involving more than a basal decoupling level present a more complex behavior (Fig. 2c). The presence of a weak décollement within the incoming material will influence the thickening mechanisms of the wedge right from the start. Two main growth mechanisms will act simultaneously in different places of the wedge: 1—frontal accretion above the décolle ment located within the incoming material and, 2— deep underplating of thrust slices (basal accretion) at the rear of the wedge due to duplex formation along a basal detachment. The resulting geometry and kine matics of these two types of tectonic units are very dif ferent. These accretionary processes will exert a strong influence on wedge topography which does not follow a simple slope (Fig. 2d). Various taper angles charac terize different domains that directly depend of defor mation partitioning in the thrust wedge. The low angle slope at the frontal part of the wedge is a consequence of the low friction décollement, whereas the high angle slope above the domain of underplating reflects the high friction behaviour of the lower basal detach ment. In addition, a cyclical behaviour of the thrusting regime has been recognized, with model wedges growth fluctuating between periods of frontal accre tion and internal deformation by underplating [43]. Experiments with Erosion Experiments accounting for surface processes behave differently as erosion and sedimentation involve large material transfer which modify the wedge dynamics. Many parameters or boundary conditions have been tested in order to determine their relative importance [14, 15, 50, 51]. Only several experiments giving significant insights for the understanding of actual orogenic wedges will be described there. In these experiments, a model thrust wedge is submitted to erosion under flux steady state conditions as defined in [96], i.e.: the volume of eroded material remains equal to the volume of newly accreted material, main taining a constant surface slope during shortening. The slope angles, that reflect the basal frictional strength, are maintained during shortening in the experiments with erosion and are further considered to be “ideal” critical angles for accretionary wedge growth. Then, analysis of material transfer kinematics across model thrust wedges allows an identification of the different modes of exhumation in response to ero sion. GEOTECTONICS

Vol. 44

No. 6

2010

545

Two simple models, based on accretion of a homo geneous material sequence (Fig. 3), illustrate the direct effect of erosion on structure and material trans fer. They can be compared to the similar experiments without erosion of Fig. 2. In the eroded thrust wedges, the diversity of exhumation patterns is controlled by the mode of fault propagation, itself depending on the basal friction (high or low). The vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges. The uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction. The material is exhumed along a series of inclined (20–50°) thrusts in the rear of the high friction wedge. The zone of maximum exhuma tion is generally localized in the central portion of the thrust wedge and migrates towards the backstop with continued shortening. The vertical exhumation rate increases with time, and the material accreted later is rapidly transferred to the main exhumation zone, compared to the material accreted during the early stages. To analyze the impact of a décollement layer, a model wedge is constructed with a high basal friction detachment and the presence of a low friction décolle ment level (thin layer of glass microbeads) within the incoming sand layer (Fig. 3d). A 6° slope angle has been chosen for the imposed erosion profile to repre sent an overcritical taper for a low basal friction wedge. The material located at depth below the weak layer is underplated under the rear part of the wedge, while above the décollement the thrust wedge front is deformed mainly by frontal accretion (typical mecha nism for low friction wedge). After a large amount of shortening, the structure of the wedge is characterized by a particular organization of main thrust units. From the frontal part of the wedge to the backstop respec tively, we have (Fig. 3d): (1) frontal imbricate of thrust sheets, (2) a synformal klippe of thrust units previously accreted to the front and progressively deformed, and, (3) an antiformal stack of underplated thrust units refolding the upper décollement layer. During contin uous shortening, the kinematics of deformation reflects the complex interaction between wedge mechanics and erosion. Underplating of the basal lay ers (below the weak décollement level) is localized under the frontal part of the protowedge inducing the formation of a domeshaped structure. With contin ued shortening, uplift and subsequent exhumation of the underthrust units occurs along a series of inclined thrusts (20–40°). They progressively become steeper (up to 60–70°) due to vertical shearing that develops as a consequence of material uplift at the back of the growing wedge. A highangle backthrust develops at the rear of the thrust wedge affecting the protowedge at the final stages of shortening. It controls the further upward transfer of the basal layers material within the area of maximum exhumation. The upper thrust wedge develops above the décollement leading to fron

546

MALAVIEILLE, KONSTANTINOVSKAYA

(a) LOW BASAL FRICTION

backthrust maximum exhumation

décollement frontal accretion 102 cm (b) HIGH BASAL FRICTION

protoslope maximum exhumation erosion slope

accretion by underthrusting 96 cm (c)

+ SEDIMENTATION

82 cm (shortening) (d)

décollement

DECOLLEMENTS

1 duplexing 21 cm 20 cm

frontal accretion

maximum exhumation antiformal stack

basal accretion

particle paths 2 frontal accretion

68 cm

1

2

2+1

synformal klippe décollement 3

underplating

frontal accretion

115 cm (shortening)

Fig. 3. Models with erosion (flux steady state) showing particle paths (dotted lines) and domains of maximum exhumation: (a) low friction wedge (asymmetric divergent orogen), (b) high friction wedge (monovergent orogen), (c) syntectonic sedimentation and erosion, syntectonic sedimentary layers (yellow in color) are involved in the wedge structure, (d) impact of décollements. Model evolution shows the partition of deformation, particle paths (dotted lines) and domains of maximum exhumation: 1— frontal accretion and basal duplex formation, 2—and stacking of basal units (underplating), 3—frontal accretion, growth of the antiformal stack, passive refolding of former imbricate thrusts of the upperwedge and backthrusting. One segment of the scale bar is 1 cm for (a), (b) and (d) and 5 cm for (c). GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

547

upperplate rocks (orogenic lid) 1

L–P

erosion su rface

U–P

2 1 2

1 2

antiformal stack

frontal imbricate

vertical shear brittle

1

1 2 3

3 2 3

underplating

ductile

ZOOM 1 2 3 4

4 1 2 3

4

Fig. 4. Sketch showing four stages of wedge development outlining deformation partitioning and kinematics of thrust units. Sim plified from models with décollements and submitted to erosion. Notice the passive deformation of upper plate (orogenic lid) resting on top of the former refolded décollement . Early folds are suggested to show evolution of U–P geometry. A possible defor mation mechanism responsible for vertical shear inducing stretching and thinning of the underplated units is schematized. Resulting strain is shown by the green ellipsoids. U–Pprestructured upperplate passively deformed during underplating (parts of the foreland basin can be included in); L–P—basement rocks lowerplate.

tal imbrication of thrust sheets. When incorporated to the wedge, the thrust units are deformed and become progressively steeper, to near vertical due to continued shortening and surface erosion. The former thrust units of the upper wedge are compressed, between the growing antiformal stack and the frontal imbricate, leading to the formation of a synformal “klippe” com pletely detached from the basal layers of the model (Fig. 3d). A detailed analysis of the experiment and a movie showing an experimental run is available in [50, 51]. The singular kinematics of “décollements type expériments” is illustrated as a sketch in Fig. 4. GEOTECTONICS

Vol. 44

No. 6

2010

From Submarine to SubAerial Wedges, Impact of Surface Processes on Tectonics The series of experiments examined here shows that simple thrust wedges can behave in a complex manner, even when simple and homogeneous materi als are used. They also outline the impact of material transfer (erosion–sedimentation) on wedge structure and dynamics. Thus, when applied to nature, models suggest that erosion can strongly modify the structural evolution of subaerial wedges relative to submarine ones [85, 86].

548

MALAVIEILLE, KONSTANTINOVSKAYA

Impact on Structure, Strain Partitioning, Faults Kinematics and Exhumation Analog models have shown that simple accretion ary wedges can behave according to tectonically com plex patterns. They present a punctuated thrust activ ity during convergence and they show sustained local ized deformation. Internal deformation mechanisms and faults control the shape, topography, taper vari ability and structural evolution of the wedge. décolle ments play a major role allowing duplex formation and underplating at different structural levels within the wedge whereas frontal accretion characterizes defor mation in the piedmont (foreland zone). As strong partitioning of deformation occurs in thrust wedges, this exerts a major influence on topography and as a direct consequence on the degree of local erosion. In return, erosion and sedimentation which influence material transfer from the surface have a direct control on the internal dynamics of the experimental wedge, and so one can obtain a feedback loop. Exhumation of metamorphic rocks remains a major question for geologists working in mountain belts. Many papers dealing with exhumation problems have been published to date, some focusing on early exhumation of very highpressure rocks in subduction channel settings [79], others on exhumation processes in the frame of the orogenic wedge itself. We focus here on material transfer in orogenic wedges submitted to erosion. To analyze the kinematics of material transfer, particle paths have been studied in numerical [e.g. 29] or experimental wedges [e.g. 50, 51]. They define an accretionary flux directed from bottom to top in the wedge body explaining the vertical advection of mate rial at the origin of thickening and relief development. Without erosion, these paths do not represent exhu mation paths; they only reflect uplift of material or uplift of topography [e.g. 36]. Thus, exhumation in orogenic wedges requires erosion (or at least normal faulting). Indeed, the type of exhumation depends on the internal dynamics of thrust wedges and conversely, on how this dynamics is modified by erosion [e.g. 17, 45]. Experiments with erosion show that local uplift induced by underplating can generate localized high angle slopes in the wedge. If applied to nature, such deformation mechanisms occurring at depth in oro genic wedges would favor strong erosion and high den udation rates above domains of underplating. In the same manner, that the portion of the wedge located between the underplating domain and the domain of active frontal accretion does not undergo strong defor mation, its angle of slope remains low, inducing only minor erosion and consequently minor exhumation. Thus, due to internal strain partitioning [e.g. 49], den udation rates will vary along a mountain belt transect because erosion controlled exhumation is very sensi tive to the vertical component of displacements in the wedge.

Coulomb wedge theory supports the idea that when the mechanical state of a wedge changes from critical to overcritical, gravitational forces may cause local extension and subsequent normal faulting [e.g. 30]. Indeed, if there is no (or only minor) erosion, normal faults are required in the wedge body for exhumation to occur, for example in submarine prisms where grav ity induced material transfer can occur. Such explana tions have been widely extended to mountain belts [e.g. 78]. Nevertheless, it is sometimes difficult to explain why a purely extensional deformation would have initiated during convergence in deep parts of mountain belts. If we check the effect of erosion and piedmont sedimentation on wedge dynamics in a sta bility field diagram [25], it decreases the slope angle and as a consequence displaces the stability field, favoring an evolution from overcritical to stable or from stable to undercritical state [e.g. 59]. This trend does not favor extension. Thus, although extension is commonly invoked to explain exhumation of meta morphic rocks and synchronous enigmatic normal faults observed in orogenic wedges, in many cases, this cannot be the dominant mechanism [72]. Experi ments suggest an interesting alternative way to develop deep crustal scale normal shear zones and superim posed brittle normal faults in the uppermost crust dur ing compressional tectonics associated to continental subduction. Normal faulting could be the result of a purely kinematic effect of the vertical shear induced by strain partitioning in the orogenic wedge (Fig. 4). Such partitioning being the direct consequence of deep underplating processes which combined with surface erosion induces strong uplift within discrete areas. Differential motion of underplated crustal units relative to surrounding material induces vertical shear and as a consequence a strong stretching and layer par allel thinning of the stacked tectonic units. At depth these zones are characterized by the development of shear zones with normal sense shearing evolving to brittle normal faults when reaching uppercrustal domains during continuous synconvergence erosion assisted uplift. CASE STUDIES Three case studies taken from different orogens are discussed here, each of them being chosen to outline specific processes enlighted by results of analogue models. The Taiwan case illustrates well the strong partitioning of deformation that develops during rapid convergence. The Western Alps case shows the role of sedimentation in the foreland and the impact of Mesozoic extensional structural heritage. The last Variscan case shows how the interpretations of major geologic features in a mountain belt may evolve through time depending on the processes that are enlighted. GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

549

(a) Foothills ~4 cm/yr

W

Central Range exhumation ~3 cm/yr

2nd zone of underplating

Volcanic arc

km 10

~9 cm/yr

U.P.

L.P. Eurasian Plate 0

1st zone of underplating

50 km

maximum exhumation

(b)

refolded décollement

U.P. cm 5

L.P. basement Tectonic units

backstop

20

0

E

~2 cm/yr

décollement frontal imbricate

synformal thrust stack

underplated units U.P. = Upper Plate antiformal stack L.P. = Lower Plate

Fig. 5. (a) Interpretive geological section of Taiwan orogenic wedge inspired by (b) experiment with décollement and erosion. Mediumterm shortening rates on main active faults are indicated.

Taiwan: Partition of Deformation in a Young and Very Active Mountain Belt Taiwan is recognized as one of the best places in the world to address major questions concerning mecha nisms of lithospheric deformation in convergent set tings, processes of mountain building (from oceanic subduction to continental subduction), and subse quent deformation involving large seismogenic faults. In this area, the obliquity of the plate convergence involves the progressive subduction of the continental margin of China inducing the fast growth of the Tai wan mountain belt. Due to the high convergence rate (~8 cm/yr) and the complex interaction (doublyverg ing oceanic and continental subduction) between the converging Eurasia and Philippine Sea plates (PSP), deformation rates and erosion rates are extreme (hor izontal shortening > 2 cm/yr on major faults, local ver tical motions up to 3 cm/yr). In fact, erosion processes triggered by the subtropical climate can often be cata strophic (landslides induced by Typhoons and earth quakes, flooding), thus sculpting the sharp relief of the Island. Today, the orogen culminates at about 4000 meters, having risen from sealevel in only a few million years. The impact of climate and surface pro cesses are thus particularly well expressed allowing GEOTECTONICS

Vol. 44

No. 6

2010

detailed study of their interaction with active tectonic processes on the Island. In the domain of active continental subduction, where the subaerial orogenic wedge is growing today, estimates of longterm shortening rates on active faults and wedge deformation show a surprising behavior (Fig. 5a). Most of the shortening is accounted for by just a few major faults, on the western side of the wedge in the foreland and on its backside against the Philip pine Sea upperplate onland along the Longitudinal Valley and offshore the Coastal Range, the accreted part of the Luzon Volcanic arc. Indeed, recent studies along a transect in Central Taiwan have revealed that ~4 cm/yr of the total convergence across the plate boundary have been absorbed on the longterm across the most frontal faults of the sole foreland [83]. On the other side of the wedge, further east, about 3 cm/yr of shortening is accounted for by the active faults of the Longitudinal Valley [3, 82] and offshore within the PSP (~2–3 cm/yr) along the submerged flank of the Coastal Range [66]. This is confirmed by the intense seismic activity, both onshore and offshore eastern Taiwan reflecting deformation of the backside of the orogenic wedge against the Philippine Sea upperplate indenter. Thus most part of the bulk shortening occurs today on foreland faults and along the backside of the

550

MALAVIEILLE, KONSTANTINOVSKAYA

10 cm

Upper Plate

Duplexing

(a)

Syntectonic deposits

10 cm

U.P. Klippe

antiformal stack Upper Plate

(b)

Lower Plate

Underplating

NW Alps presentday cross section [18]

NW km –10

Jura

Subalpine Prealpes Molasse Molasse klippen basin

Helvetic nappes Penninic nappes

SE

Upper Plate

Autochthonous European basement midcru

–20

stal deta

Crystalline Massifs c h m e nt

(c) 0

50

100

150

200 km

Fig. 6. (a) Model simulating structural heritage of a continental margin without erosion to be compared to (b) same model with erosion and syntectonic sedimentation applied to the Alps, (c) present day geologic section across the Swiss Alps (from [18]).

mountain belt, leaving little (if any) horizontal short ening within the body of the wedge. Estimates of the vertical and horizontal components of deformation, compared at different spatial and time scales (ranging from longterm to shortterm evolution), suggest a strong partitioning of deformation. If compared with analog models of erosional wedges, such a kinematic pattern and deformation partitioning matches closely the behavior of experiments with décollement s (Fig. 5b). This suggests that the main mechanisms of growth can be described by frontal accretion in the foreland Foot hills and underplating of tectonic units at depth under the hinterland, involving strong uplift, exhumation and backthrusting in the Philippine Sea upperplate. Intracrustal décollements localized within the sub ducting continental margin of Eurasia favor such a style of deformation partitioning and wedge growth. Normal faulting that affects the eastern flank of the Central Range [23], could be related to the strong dif ferential uplift occurring between the growing range and the volcanic arc upperplate (as schematized on Fig. 4). Together with new constraints on the thermal evolution [11] and exhumation of the Central Range,

analog models and thermokinematic numerical models [84] involving erosion in which underplating at depth sustains the growth of the orogenic wedge, account well for the observed geologic structure, recent kinematic evolution and exhumation. Alps: Subduction of a PreStructured Continental Margin and Foreland Basin Evolution Examination of classical geologic sections across the Swiss Alps [37], reveals how the current structural pattern has been controlled by the structural and sedi mentary features inherited from Mesozoic extensional tectonics. It also underscores the importance of sur face processes in the structural evolution of a moun tain belt. To better characterize deformation mecha nisms involved in the subduction of a prestructured continental margin, a series of analogue experiments have been conducted [13–15]. The initial geometry and rheologic structure of the basic models (Fig. 3, [14]) have been designed using data from a restored section across the western Alps proposed by [18]. The aim of our experiments was threefold: GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

—to better understand the impact of erosion—sedi mentation changes on the tectonic structure and the evolution of the Alpine wedge, —to analyse the role played by former structural heritage in the tectonic evolution, and —to determine the relative influence of these parameters on the main tectonic events recorded in a foreland during the evolution of an orogenic belt. Here two analogue models are compared to the geological section, the first is run without erosion and the second with erosion (Fig. 6). Without surface processes, we obtain a classically shaped high friction wedge. In response to shortening, basement imbricates first overthrust each other using inherited weaknesses. Then, the unstructured part of the basement sponta neously underthrusts allowing a critical taper to be maintained. With erosion and sedimentation, the models grow differently by frontal accretion in the foreland basin and by simple underthrusting and sub sequent underplating in the hinterland. The combined effect of tectonics and erosion leads to strong focus sing of exhumation in the domain of underplating. Subsequent uplift isolates the front of the lid forming a synformal klippen nappe composed of former imbri cated thrust units. Frontal accretion therefore leads to a cyclic syndeformational removal of a substantial vol ume of foreland sediments. At the end of shortening, the different units have been largely eroded and partic ularly the foreland basin and the orogenic lid including its frontal klippe come to rest upon syntectonic depos its. Underplated duplexes lead to the formation of an antiformal nappe stack where the displacement is accommodated along thrust ramps, favoring localized rapid synconvergence exhumation. Then, the anti formal structure reaches the surface where it appears as a tectonic window. In the experiments, the structural heritage of the lower plate (weak levels of glass beads in the basement) defines the size of thrust units and favors the initiation of underplating, but the process then continues spon taneously in the homogeneous part of the basement due to burial and increasing “lithostatic” stress at depth (Fig. 6b). Models suggest that for natural oro genic wedges, when convergence can no longer be mechanically accommodated by subduction of lower plate basement units at depth, deformation is taken up by underplating. This mechanism allows the tectonic units detached from the subducting lowerplate to be accreted to the upper plate, contributing to wedge growth. It requires intracrustal décollement zones, the location of which is controlled by the kinematics of subduction, the thermomechanical conditions in the wedge, the structural heritage and by erosion. Various processes of crustal decoupling exist during continen tal subduction, at great depth [e.g., 19], or in the oro genic wedge due either to fluid overpressure inducing weak crustal zones of strain concentration along brittle or plastic shear zones or weak décollement layers in the sedimentary cover. Thus, underplating can develop GEOTECTONICS

Vol. 44

No. 6

2010

551

at different structural levels in a thrust wedge and can affect simultaneously or successively different parts of the subducted crust. Décollement induced deformation partitioning largely controls particle trajectories and strain pat terns. One way to investigate orogen dynamics is to look at the ages recorded by different thermochro nometers across it [53, 96]. Exhumation of rocks means the approaching of a rock particle to the Earth’s surface, which is, e.g. recorded by cooling rates calcu lated from thermochronologic data [e.g. 39], whereas uplift of rocks means the displacement of rocks with respect to the geoid, or less accurately with respect to the mean sea level [36]. The study of material paths (trajectories) in mountain belts may provide useful insight on their kinematic evolution. Surface processes strongly influence the timing, localization and ampli tude of rock displacements in the varying members of an orogenic wedge. The comparison of their trajecto ries in experiments performed with and without ero sion–sedimentation underscores the influence of sur face processes on material transfer in the model wedge [e.g. 24]. The variations in rates of erosion and sedi mentation modify the extent, the morphology, the structures, the timing of development and the material paths in the different models. Particles located in the converging lowerplate or in the upperplate show complex uplift paths related to deformation partition ing and various tectonic stages. Thus, exhumation rates calculated on the basis of simulated thermochronometry without knowledge of the particle trajectories and internal structure may result in erroneous estimations. Indeed, at the scale of a mountain belt each tectonic unit may record an indi vidual specific exhumation path. Experiments involving sedimentation show the effect of erosion on the development of a foreland basin. They outline that if the erosion/sedimentation budget is not balanced in the sense that much more material is removed from the system than is deposited (output > input), an important record of the tectonic history of the orogenic wedge is missing. This is equiv alent to the natural situation in the Alpine foreland basin, where more than half of the sediments have been carried out of the system by large rivers into the neighbouring sinks that are the Black Sea, North Sea and Mediterranean Sea [52]. In addition, as parts or entire units of the foreland basin are incorporated to the orogenic prism [e.g. 73], and then vanish during mountain growth, section balancing techniques are frequently inappropriate and can lead to a significant underestimation of the amount of shortening recorded in a foreland. Specific models suggest that depending on the behavior of the backstop upperplate, underplating induced deformation at the back part of the wedge and associated material transfer paths will change during continuous shortening. During the growth of an anti formal stack, the tectonic units are first strongly

552

MALAVIEILLE, KONSTANTINOVSKAYA Permian basin

Albigeois nappes U.P.

(a)

(b)

NS

FRANCE

Stephanian basin

AZ Massif central

L.P.

VFB SFN

500 km

Visean flysch basin 10 km

section

(c)

normal shear zone U.P.

N PCB

NS

S AZ

SFN VFB

L.P.

Underthrust basement

10 km

Fig. 7. (a) Location of the Montagne Noire in the French Massif Central. (b) Structural map of the area showing the main tec tonostratigraphic units: PCB, Permian and UpperCarboniferous basins; NS, Northern Slope; AZ, Axial Zone; SFN, Southern Fold Nappes; VFB, Visean Foreland Basin. (c) Interpretive cross section of the Montagne Noire showing an alternative hypoth esis for dome formation and enigmatic normal shear zone and faults observed on its northern flank. The southern recumbent fold nappes emplaced on the foreland basin are passively deformed during development of the Axial Zone antiformal stack.

stretched and thinned to accomodate the differential uplift imposed by the combination of stacking mecha nisms and surficial erosion. Then, when the upper plate becomes thinner due to the effect of uplift and continuous erosion, more localized backthrusting deformation may develop, changing the material transfer path. Such an evolution may apply to the final evolution of the Alpine orogenic wedge (Fig. 6c). Variscan Montagne Noire: Formation of Gneiss Domes and Enigmatic Normal Faults The Variscan orogen developed during the Gond wana–Laurasia collision with progressive migration of crustal thickening to external parts of the belt from Devonian to Middle Carboniferous times accompa nied by a Barroviantype metamorphism and progres sive southward thrusting [e.g., 69]. The Montagne Noire forms the southernmost part of the French Massif Central resulting from this Variscan history (Fig. 7a). It consists of a core of gneisses, migmatites

and micaschists (lowerplate) of Proterozoic to Cam brian age, flanked and overlain by lowgrade Palaeo zoic cover series (upperplate). The area has tradition ally been subdivided into three main tectonostrati graphic units from the internal domains of the belt to the foreland respectively: 1—the Northern Slope upperplate with a southward tectonic vergence is composed by lowgrade lower Paleozoic foldeciand faulted metasedimentary units; 2—the Axial Zone lowerplate is a highgrade metamorphic antiform of foliation made of gneisses, migmatites and micaschists of Proterozoic to Ordovician age. The gneissic rocks of the dome are characterized by a complex deformation pattern with superimposed shearing deformation and a coaxial strain in the core of the antiformal structure: 3—the kilometer scale recumbent fold nappes of the Southern Slope (upperplate) are composed of low grade Paleozoic sequences. Visean flysch sediments including synorogenic olistolites are involved in the nappe deformation. These sediments characterize the GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

553

(a) 0 U–P 30 km

crust

L–P

UHP rocks subduction channel

mantle

(b) 0 crust

30 km underplating

mantle

(c) 0 crust

30 km underplating

mantle

backthrusting

(d)

Klippe

0 crust 30 km

U–P Upper Plate L–P Lower Plate

underplating mantle

UH–P rocks domains of important uplift and strong erosion

Fig. 8. Conceptual model showing the impact of surface processes on deformation partitioning, kinematics and exhumation dur ing orogenic wedge growth: (a) end of oceanic subduction stage (early exhumation of high pressure rocks in the subduction chan nel), (b) subduction of the continental margin involving deep stacking of underplated crust units and strong uplift controlled ero sion of the upper plate, (c) deep underplating continue and a new stage of underplating begins in the foreland involving inverted inherited features of the margin, (d) during the late stage, the foreland basin is involved in frontal accretion whereas major back thrusting develops at the back of the wedge due to strong thinning of the upper plate lid by erosion.

foreland basin developed during the final growth of the Variscan orogenic wedge. The upperplate nappes units are separated from highgrade lowerplate basement units by major fault zones that have recorded a complex pattern (or his tory) of deformation (see detailed tectonic analysis in GEOTECTONICS

Vol. 44

No. 6

2010

[1, 2]). The steep north dipping fault zone bounding the Axial Zone–Northern Slope tectonic units is characterized by polyphase deformation including a later outstanding normal sense shearing. Molassetype sediments of StephanianB (Upper Carboniferous) age are exposed in a narrow strip north of this bound

554

MALAVIEILLE, KONSTANTINOVSKAYA U.P.

W

erosion level

foreland basin E

2 1

Underplating

L.P. basement 50 km

Fig. 9. Interpretive cross section of the variscan belt from NW Spain, modified from [75], suggesting that two different domains of underplating (1 in the hinterland, 2 in the foreland) controls the structure of the wedge and the location of uplift related normal sense shear zones.

ary. The deposition of these rocks in intermontane basin and the development of normal shear zones have been related to lateorogenic extension [34] involving the growth of an extensional metamorphic core com plex, the Axial zone [94]. The Montagne Noire may be a sort of “Metamorphic core complex”, but how was it formed? The large variety of models proposed for this unique structure, do not take into account the proba bly fundamental role of erosion. Some invoke: a com pressive anticline (tectonic forces dominant, e.g., [4]), diapiric uplift or wrenching and diapirism (combined tectonic and buoyancy forces, [38]), transtensional Metamorphic Core Complex (tectonic forces domi nant and buoyancy forces, e.g., [34, 88]), extensional Metamorphic Core Complex (buoyancy forces domi nant during late orogenic extension, e.g., [94]), or, ductile thickening and gravitational collapse (com bined tectonic and buoyancy forces, e.g., [2]). Obser vation of experiments with erosion now allows discus sion of two endmember hypotheses. In the Metamor phic Core Complex model, exhumation is mainly related to the development of a crustal scale lowangle detachment fault during widespread lateorogenic extensional tectonics. The suggested alternative inter pretation (Fig. 7) favors combined uplift (induced by underplating of basement units) and erosion acting simultaneously during the main events of the conver gent history of the orogen as a dominant process driv ing exhumation. This synconvergence mechanism accounts well for the geometry of tectonic units, fault kinematics and metamorphic relationships between the high grade core zone and the surrounding low grade nappes. This tectonic history does not exclude the late orogenic reworking of the area by extensional and/or wrench faulting which characterize late stage Variscan tectonics. Misleading may also concern the interpretation of normal faults or ductile normal sense shear zones observed in Alpine type mountain belts. Indeed, many antiformal gneissic domes (Gran Paradiso, Ambin, Dora Maira, Tauern window) from the internal Alps are locally bounded by normal sense shear zones and brittle normal faults, leading to interpretations in terms of a relatively late and deepseated extensional faulting due to gravitational collapse (extensional metamorphic core complexes) could be revisited in

the light of the above suggested alternative explana tion, which does not require such major changes in the general compressional tectonic regimes. CONCLUSIONS Interaction between surface processes and deep tectonic deformation processes plays a key role in the structural evolution, kinematics and exhumation of rocks in orogenic wedges. Insights from analog models applied to natural cases of present active or ancient mountain belts allow us to emphasize several first order processes that result from these interactions. Internal strain partitioning due to mechanical behav ior of the thrust wedge has a strong impact on the ver tical component of displacement of tectonic units, which in turn favors erosion in domains of strong uplift. During continental subduction, the role of déc ollements can be major as they permit strain partition ing in the orogenic wedge as it is shown in the example of the Taiwan orogen. They can result from the struc tural heritage of the continental margin (inherited structures from the rifting event that preceeds ocean opening), and/or from the rheologic layering of the crust (either due to thermomechanical behavior of the continental crust or weak zones in sedimentary cover rocks). Such a strain partitioning is first controlled by tec tonic processes, but surface processes exert a strong feedback on wedge dynamics. Indeed, material trans fer in thrust wedges not only depends on its internal dynamics, it is also influenced by climate controlled surface processes including erosion and sedimenta tion. The effects of erosion are multiple: erosion allows long term localization of uplifted domains, it favors strong exhumation above areas of deep under plating and combined with sedimentation in the fore land can contribute to maintain the wedge in a critical state for long periods of time. Our simple models illus trate well how mountain belts structure, kinematics of tectonic units and exhumation can be determined by these complex interactions (Fig. 8). In addition, they offer an explanation for syncontractional development of normal sense shear zones and faults at the backside of underplated tectonic units observed in the discussed examples of the orogenic wedges of Taiwan, Alps and GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES

Variscan Montagne Noire. Many other mountain belts where underplating is suspected, such as the Alps, Himalaya [12], Variscan belt of NW Spain ([7]; see Fig. 9, modified from [75]), Oman [70], New Cale donia [55], Alpine Corsica [71] and many other places exposing similar structures such as exhumed antifor mal metamorphic domes bounded by normal fault zones need to be revisited in the light of the general mechanisms here outlined. ACKNOWLEDGMENTS During the last ten years, the modeling method and the techniques in Montpellier have been considerably improved, in particular due to the contribution of S. Dominguez with the technical assistance of C. Romano. A. Delplanque is acknowledged for improvements of the figures. We are grateful to Yu.A. Morozov and M.A. Goncharov for constructive remarks that helped to improve the manuscript. REFERENCES 1. D. G. A. M. Aerden, “Tectonic Evolution of the Mon tagne Noire and a Possible Orogenic Model for Syn Collisional Exhumation of Deep Rocks, Hercynian Belt,” France Tectonics 17, 62–79 (1988). 2. D. Aerden and J. Malavieille, “Origin of a LargeScale Fold Nappe in the Montagne Noire, Variscan belt, France,” J. Struct. Geol. 21, 1321–1333 (1999). 3. J. Angelier, H.T. Chu, J.C. Lee, and J.C. Hu, “Active Faulting and Earthquake Risk: the Chihshang Fault Case,” Taiwan. J. Geodyn. 29, 151–185 (2000). 4. F. Arthaud, “Etude Tectonique et Microtectonique Comparée de Deux Domaines Hercyniens: les Nappes de la Montage Noire (France) et l’Anticlinorium de l’Iglesiente (Sardaigne), Publications de l’Université des Sciences et Techniques du Languedoc, Montpel lier, Serie Géologie Structurale 1, 175 (1970). 5. J.P. Avouac, “Mountain Building, Erosion, and the Seismic Cycle in the Nepal Himalaya,” Advances Geo phys. 46, 1–80 (2003). 6. J. P. Avouac and E. G. Burov, “Erosion as a Driving Mechanism of Intracontinental Growth,” J. Geophys. Res. 101 (8), 17747–17769 (1996). 7. C. J. Banks and J. Warburton, “MidCrustal Detach ment in the Betic System of Southeast Spain,” Tec tonophysics 191, 275–289 (1991). 8. C. Beaumont, P. Fullsack, and J. Hamilton, “Erosional Control of Active Compressional Orogens,” in Thrust Tectonics, Ed. by K. R. McClay (Chapman and Hall, London, 1992), pp. 1–18. 9. C. Beaumont, P. Fullsack, and J. Hamilton, “Styles of Crustal Deformation in Compressional Orogens Caused by Subduction of the Underlying Lithosphere,” Tectonophysics 232, 119–132 (1994). 10. C. Beaumont, J. A. Munoz, J. Hamilton, and P. Full sack, “Factors Controlling the Alpine Evolution of the Central Pyrenees Inferred from a Comparison of Observations and Geodynamical Models,” J. Geophys. Res. 105, 8121–8145 (2000). GEOTECTONICS

Vol. 44

No. 6

2010

555

11. O. Beyssac, M. Simoes, J. P. Avouac, K. A. Farley, Y. G. Chen, Y. C. Chan, and B. Goffé, “Late Cenozoic Metamorphic Evolution and Exhumation of Taiwan,” 26, TC6001, (2007) doi: Tectonics 10.1029/2006TC002064. 12. L. Bollinger, J. P. Avouac, O. Beyssac, E. J. Catlos, T. M. Harrison, M. Grove, B. Goffé, and S. Sapkota, “Thermal Structure and Exhumation History of the Lesser Himalaya in Central Nepal,” Tectonics 23, TC5015 (2004), doi: 10.1029/2003TC001564. 13. C. Bonnet, Interactions between Tectonics and Surface Processes in the Alpine Foreland: Insights from Analogue Model and Analysis of Recent Faulting (Geofocus, Uni versite de Fribourg (Suisse), Fribourg, 2007), vol. 17, No. 1551, p. 196. 14. C. Bonnet, J. Malavieille, and J. Mosar, “Interactions between Tectonics, Erosion, and Sedimentation during the Recent Evolution of the Alpine Orogen: Analogue Modeling Insights,” Tectonics 26, TC6016 (2007), doi: 10.1029/2006TC002048. 15. C. Bonnet, J. Malavieille, and J. Mosar, “Surface Pro cesses Versus Kinematics of Thrust Belts: Impact on Rates of Erosion, Sedimentation, and Exhumation— Insights from Analogue Models,” Bull. Soc. Geol. France 179 (3), 179–192 (2008). 16. J. P. Brun, “Deformation of the Continental Litho sphere: Insights from BrittleDuctile Modes,” Geol. Soc. Spec. Publ. 200, 355–370 (2002). 17. D. W. Burbank, “Rates of Erosion and Their Implica tions for Exhumation,” Mineral. Mag. 66, 25–52 (2002). 18. M. Burkhard and A. Sommaruga, “Evolution of the Western Swiss Molasse Basin: Structural Relations with the Alps and the Jura Belt,” Geol. Soc. Spec. Publ. 134, 279–298 (1998). 19. N. Carry, F. Gueydan, J. P. Brun, and D. Marquer, “Mechanical Decoupling of HighPressure Crustal Units During Continental Subduction,” Earth Planet. Sci. Lett. 278 (1–2), 13–25 (2009), doi: 10.1016/j.epsl.2008.11.019. 20. W. M. Chappie, “Mechanics of ThinSkinned Fold andThrust Belts,” Geol. Soc. Am. Bull. 89, 1189– 1198 (1978). 21. P. R. Cobbold, S. Durand, and R. Mourgues, “Sandbox Modelling of Thrust Wedges with FluidAssisted Detachments,” Tectonophysics 334, 245–258 (2001). 22. D. S. Cowan and R. M. Silling, “A Dynamic, Scaled Model of Accretion at Trenches and Its Implications for the Tectonic Evolution of Subduction Complexes,” J. Geophys. Res. 83 (B11), 5389–5396 (1978). 23. J. M. Crespi, Y.C. Chan, and M. S. Swaim, “Synoro genic Extension and Exhumation of the Taiwan Hinter land,” Geology 24, 247–250 (1996). 24. L. Cruz, C. Teyssier, L. Perg, A. Take, and A. Fayon, “Deformation, Exhumation, and Topography of Experimental DoublyVergent Orogenic Wedges Sub jected to Asymmetric Erosion,” J. Structural Geol. 30, 98–115 (2008). 25. F. A. Dahlen, “Non Cohesive Critical Coulomb Wedges: An Exact Solution,” J. Geophys. Res. 89 (B12), 10125–10133 (1984).

556

MALAVIEILLE, KONSTANTINOVSKAYA

26. F. A. Dahlen, “Mechanical Energy Budget of a Fold andThrust Belt,” Nature 331, 335–337 (1988). 27. F. A. Dahlen, “Critical Taper Model of Foldand Thrust Belts and Accretionary Wedges,” Ann. Rev. Earth Planetary Sci. 18, 55–99 (1990). 28. F. A. Dahlen and T. D. Barr, “Brittle Frictional Moun tain Building, 1: Deformation and Mechanical Energy Budget,” J. Geophys. Res. 94, 3906–3922 (1989). 29. F. A. Dahlen and J. Suppe, “Mechanics, Growth, and Erosion of Mountain Belts,” Geol. Soc. Am., Special Paper 218, 161–178 (1988). 30. F. A. Dahlen, J. Suppe, and D. Davis, “Mechanics of FoldandThrust Belts and Accretionary Wedges: Cohesive Coulomb Theory,” J. Geophys. Res. 89 (B12), 10087–10101 (1984). 31. D. Davis, J. Suppe, and F. A. Dahlen, “Mechanics of FoldandThrust Belts and Accretionary Wedges,” J. Geophys. Res. 88 (B12), 1153–1172 (1983). 32. P. Davy and P. R. Cobbold, “Experiments on Shorten ing of a 4Layer Model of the Continental Lithos phere,” Tectonophysics 188, 1–25 (1991). 33. J. Dewey and J. Bird, “Mountain Belts and the New Global Tectonics,” J. Geophys. Res. 75, 2625–2647 (1970). 34. H. Echtler and J. Malavieille, “Extensional Tectonics, Basement Uplift and Stephano Permian Collapse Basin in a Late Variscan Metamorphic Core Complex (Mon tagne Noire, Southern Massif Central),” Tectonophys ics 177, 125–138 (1990). 35. S. Ellis and C. Beaumont, “Models of Convergent Boundary Tectonics: Implications for the Interpreta tion of Lithoprobe Data,” Can. J. Earth Sci. 36, 1711– 1745 (1999). 36. P. C. England and P. Molnar, “Surface Uplift, Uplift of Rocks and Exhumation of Rock,” Geology 18 (12), 1173–1177 (1990). 37. A. Escher, J. Hunziker, M. Marthaler, H. Masson, M. Sartori, and A. Steck, “Geologic Framework and Structural Evolution of the Western SwisssItalian Alps,” in Deep Structure of the Swiss Alps—Results of the National Research Program 20 (NRP 20), Ed. by O. A. Pfiffher, P. Lehner, P. Heitzmann, S. Mueller, and A. Steck (Birkhauser, Basel, 1997), pp. 205–222. 38. M. Faure and N. Cottereau, “Kinematic Data on the Emplacement of the Middle Carboniferous Migmatitic Dome in the Axial Zone of the Montagne Noire, Massif Central, France,” Comptes Rendus, Academie des Sciences, Ser. II 307 (16), 1787–1794 (1988). 39. D. A. Foster and B. E. John, “Quantifying Tectonic Exhumation in an Extensional Orogen with Thermo chronology: Examples from the Southern Basin and Range Province,” Geol. Soc. London Sp. Publ. 154, 343–364 (1999). 40. M. A. Goncharov, “Applicability of Similarity Condi tions to Analoque Modeling of Tectonic Structures,” Geodynamics Tectonophys. 1 (2), 148–168 (2010). 41. F. Graveleau, Interactions Tectonique, Erosion, Sédi mentation Dans les Avantpays de Chanes: Modélisa tion Analogique et Étude des Piémonts de l’est du Tian Shan (Asie centrale), Thesis, UniversitéMontpellier II, Sciences et Techniques du Languedoc, 2008, p. 487.

42. M. Gutscher, N. Kukowski, J. Malavieille, and S. Lallemand, “Cyclical Behavior of Thrust Wedges: Insights from High Basal Friction Sandbox Experi ments,” Geology 24, 135–138 (1996). 43. M. A. Gutscher, N. Kukowski, J. Malavieille, and S. Lallemand, “Episodic Imbricate Thrusting and Underthrusting: Analog Experiments and Mechanical Analysis Applied to the Alaskan Accretionary Wedge,” J. Geophys. Res. 103, 10161–10176 (1998). 44. G. E. Hilley and M. R. Strecker, “Steady State Erosion of Critical Coulomb Wedges with Applications to Tai wan and the Himalaya,” J. Geophys. Res. 109, B01411 (2004), doi: 10.1029/2002JB002284. 45. B. K. Horton, “Erosional Control on the Geometry and Kinematics of Thrust Belt Development in the Central Andes,” Tectonics 18, 1292–1304 (1999). 46. S. Hoth, J. Adam, N. Kukowski, and O. Oncken, “Influence of Erosion on the Kinematics of Bivergent Orogens, Results from Scaled SandboxSimulations,” Geol. Soc. Am. Sp. Pap. 398, 201–225(2004). 47. R. A. Jamieson and C. Beaumont, “Deformation and Metamorphism in Convergent Orogens: a Model for Uplift and Exhumation of Metamorphic Terranes,” Geol. Soc. Spec. Publ. 43, 17–129 (1989). 48. M. Jolivet and J. Malavieille, Role de l’héritage sédi mentaire sur la cinématique des systémes chev auchants: Modélisation analogique et application a l’avantpays Andin, Scientific report, EP/T/EXP/GDP, No. 9730rs, ELF Aquitaine Exploration Production, France, 1997, p. 85. 49. R. R. Jonesa, R. E. Holdsworth, J. Kenneth, W. McCaffrey, P. Clegg, and E. Tavarnelli, “Scale Dependence, Strain Compatibility and Heterogeneity of ThreeDimensional Deformation During Mountain Building: a Discussion,” J. Struct. Geol. 27, 1190– 1204 (2005). 50. E. Konstantinovskaya and J. Malavieille, “Erosion and Exhumation in Accretionary Orogens: Experimental and Geological Approaches,” Geochemistry, Geo physics Geosystems 6, Q02006 (2005), doi: 10.1029/2004GC000794. 51. E. A. Konstantinovskaya and J. Malavieille, “Accre tionary Orogens: Erosion and Exhumation,” Geotec tonics 39 (1), 69–86 (2005). 52. J. Kuhlemann, W. Frisch, B. Székely, and I. Dunkl, “PostCollisional Sediment Budget History of the Alps: Tectonic Versus Climatic Control,” Int. J. Earth Sci. 91, 818–837 (2002). 53. A. Kühni and O. A. Pfiffner, “Drainage Patterns and Tectonic Forcing: A Model Study for the Swiss Alps,” Basin Res. 13, 169–197 (2001). 54. N. Kukowski, S. Lallemand, J. Malavieille, M.A. Guts cher, and T. J. Reston, “Mechanical Decoupling and Basal Duplex Formation Observed in Sandbox Experi ments with Application to the Mediterranean Ridge Accretionary Complex,” Marine Geol. 186, 29–42 (2002). 55. Y. Lagabrielle and A. Chauvet, “The Role of Exten sional Tectonics in Shaping Cenozoic NewCale donia,” Bull. Soc. Geol. France 179, 315–329 (2008). GEOTECTONICS

Vol. 44

No. 6

2010

IMPACT OF SURFACE PROCESSES ON THE GROWTH OF OROGENIC WEDGES 56. S. Lallemand and J. Malavieille, “Coulomb Theory Applied to Accretionary and NonAccretionary Wedges,” Eos, Trans., AGU 73 (14), 7–23 (1992). 57. S. E. Lallemand, P. Schnurle, and J. Malavieille, “Cou lomb Theory Applied to Accretionary and NonAccre tionary Wedges—Possible Causes for Tectonic Erosion and/or Frontal Accretion,” J. Geophys. Res. 99 (B6), 12033–12055 (1994). 58. C. Larroque, S. Calassou, J. Malavieille, and F. Chanier, “Experimental Modeling of Forearc Basin Develop ment During Accretionary Wedge Growth,” Basin Res. 7, 255–268 (1995). 59. P. Leturmy, J. L. Mugnier, P. Vinour, P. Baby, B. Col letta, and E. Chabron, “Piggyback Basin Development Above a ThinSkinned Thrust Belt with Two Detach ment Levels as a Function of Interactions between Tec tonic and Superficial Mass Transfer: the Case of the Subandean Zone (Bolivia),” Tectonophysics 320, 45– 67 (2000). 60. L. I. Lobkovsky, Geodynamics of Spreading and Subduc tion Zones and TwoLevel Plate Tectonics (Nauka, Mos cow, 1988), p. 253 [in Russian]. 61. J. Lohrmann, N. Kukowski, J. Adam, and O. Oncken, “The Impact of Analogue Material Properties on the Geometry, Kinematics, and Dynamics of Convergent Sand Wedges,” J. Struct. Geol. 25 (10), 1691–1711 (2003). 62. J. Malavieille, “Modélisation Expérimental des Chev auchements Imbriqués: Application aux Chanes de Montagnes,” Bull. Soc. Geol. France 26, 129–138 (1984). 63. J. Malavieille, “Impact of Erosion, Sedimentation and Structural Heritage on the Structure and Kinematics of Orogenic Wedges: Analog Models and Case Studies,” Geol. Soc. Am. 20 (1), 4–10 (2010), doi: 10.1130/GSATG48A.1. 64. J. Malavieille, and A. Chemenda, “Impact of Initial Geodynamic Settings on the Structure, Ophiolite Emplacement and Tectonic Evolution of Collisional Belts,” Ofioliti 22 (1), 3–13 (1997). 65. J. Malavieille, S. Calassou, and C. Larroque, “Modeli sation Experimentale des Relations Tectonique Sedi mentation Entre Bassin Avantarc et Prisme D’Accre tion,” C. R., Acad., Sci. Paris 316, 1131–1137 (1993). 66. J. Malavieille, S. E. Lallemand, S. Dominguez, A. Des champs, C.Y. Lu, C.S. Liu, P. Schnürle, and the ACT Scientific Crew, ArcContinent Collision in Taiwan: New Marine Observations and Tectonic Evolution," Geol. Soc. Am. Spec. Pap. 358, 187–211 (2002). 67. J. G. Masek and C. C. Duncan, “MinimumWork Mountain Building,” J. Geophys. Res. 103 (B1), 907– 917 (1998). 68. M. Mattauer, “Intracrustal Subduction, CrustMantle décollement and CrustalStacking Wedge in the Hima layas and Other Collision Belts,” Geol. Soc. London, Collision Tectonics 19, 37–50 (1986). 69. P. Matte, “Variscan Thrust Nappes, Detachments, and StrikeSlip Faults in the French Massif Central: Inter pretation of the Lineations,” in Memoir 200: 4D Framework of Continental Crust., 2007, Vol. 200, pp. 391–402. GEOTECTONICS

Vol. 44

No. 6

2010

557

70. A. Michard, B. Goffé, O. Saddiqi, R. Oberhansli, and A. S. Wendt, “Late Cretaceous Exhumation of the Oman Blueschists and Eclogites: a TwoStage Exten sional Mechanism,” Terra Nova 6, 404–413 (1994). 71. G. Molli, R. Tribuzio, and D. Marquer, “Deformation and Metamorphism at the Eastern Border of the Tenda Massif (NE Corsica): a Record of Subduction and Exhumation of Continental Crust,” J. Struct. Geol. 29, 1748–1766 (2006). 72. Yu. A. Morozov, An Inverse Kinematic Effect of Thrusting and Its Structural and Tectonic Implica tions," Trans. (Dokl.) Rus. Acad. Sci. 384 (4), 382–385 (2002). 73. J. Mosar, “PresentDay and Future Tectonic Under plating in the Western Swiss Alps: Reconciliation of Basement WrenchFaulting and décollement Folding of the Jura and Molasse Basin in the Alpine Foreland,” Earth Planet. Sci. Lett. 173, 143–145 (1999). 74. M. Naylor, H. D. Sinclair, S. Willett, and P. A. Cowie, “A Discrete Element Model for Orogenesis and Accre tionary Wedge Growth,” J. Geophys. Res. 110, B12403 (2005), doi: 10.1029/2003JB002940. 75. A. PérezEstaün, J. R. MartinezCatalan, and F. Bas tida, “Crustal Thickening and Deformation Sequence in the Footwall to the Suture of the Variscan Belt of Northwest Spain,” Tectonophysics 191, 243–253 (1991). 76. K. S. Persson and D. Sokoutis, “Analogue Models of Orogenic Wedges Controlled by Erosion,” Tectono physics 356, 323–336 (2002). 77. O. A. Pfiffner, S. Ellis, and C. Beaumont, “Collision Tectonics in the Swiss Alps: Insight from Geodynamic Modeling,” Tectonics 19 (6), 1065–1094 (2000). 78. J. P. Platt, “Dynamics of Orogenic Wedges and the Uplift of HighPressure Metamorphic Rocks,” Geol. Soc. Am. Bull. 97, 1037–1053 (1986). 79. D. M. Robinson and O. N. Pearson, “Thrust in Nepal: Implications for Channel Flow Exhumation of Greater Himalayan Rock Along the Main Central,” Geol. Soc. Spec. Publ. 268, 255–267 (2006). 80. F. Schlunegger and M. Hinderer, “Crustal Uplift in the Alps: Why the Drainage Pattern Matters,” Terra Nova 13, 425–432 (2001). 81. C. Selzer, S. J. H. Buiter, and O. A. Pfiffner, “Numeri cal Modeling of Frontal and Basal Accretion at Colli sional Margins,” Tectonics 27, TC3001 (2008), doi: 10.1029/2007TC002169. 82. J. B. H. Shyu, K. Sieh, Y.G. Chen, and L.H. Chung, “Geomorphic Analysis of the Central Range Fault, the Second Major Active Structure of the Longitudinal Val ley Suture, Eastern Taiwan,” Geol. Soc. Am. Bull. 118 (11/12), 1447–1462 (2006), doi: 10.1130/B25905.1. 83. M. Simoés and J. P. Avouac, “Investigating the Kine matics of Mountain Building in Taiwan from the Spa tiotemporal Evolution of the Foreland Basin and West ern Foothills,” J. Geophys. Res. 111 (B10) (2006), doi: 10.1029/2005JB004209. 84. M. Simoés, J. P. Avouac, O. Beyssac, B. Goffe, K. Far ley, and Y. G. Chen, “Mountain Building in Taiwan: A Thermokinematic Model,” J. Geophys. Res. 112, B11405 (2007), doi: 10.1029/20066JB004824.

558

MALAVIEILLE, KONSTANTINOVSKAYA

85. G. D. H. Simpson, “How and to what Extent does the Emergence of Orogens above Sea Level Influence Their Tectonic Development?,” Terra Nova 18, 447–451 (2006a), doi: 10.1111/j.13653121.2006.00711. 86. G. D. H. Simpson, “Influence of Erosion and Deposi tion on Deformation in Fold Belts,” Geol. Soc. Am. Spec. Pap. 398, 267–281 (2006b). 87. A. Sommaruga, “décollement Tectonics in the Jura Foreland FoldandThrust Belt,” Mar. Petrol. Geol. 16 (2), 111–134 (1999). 88. J.C. Soula, P. Debat, S. Brusset, G. Bessiére, F. Chris tophoul, and J. Déramond, “ThrustRelated, Diapiric, and Extensional Doming in a Frontal Orogenic Wedge: Example of the Montagne Noire, Southern French Hercynian Belt,” J. Struct. Geol. 23 (11), 1677–1699 (2001). 89. G. S. Stockmal, “Modeling of Large Scale Accretion ary Wedge Deformation,” J. Geophys. Res. 88, 8271– 8287 (1983). 90. G. S. Stockmal, C. Beaumont, M. Nguyen, and B. Lee, “Mechanics of ThinSkinned FoldandThrust Belts: Insights from Numerical Models,” Geol. Soc. Am. Spec. Pap. 433, 63–98 (2007). 91. M. A. Summerfield and N. J. Hulton, “Natural Con trols of Fluvial Denudation Rates in Major World

92.

93.

94.

95.

96. 97.

98.

Drainage Basins,” J. Geophys. Res. 99 (B7), 13871– 13884 (1994). J. Suppe, “Mechanics of Mountain Building and Meta morphism in Taiwan,” Memoir Geol. Soc. China 4, 67–89 (1981). G. Toussaint, E. Burov, and J.P. Avouac, “Tectonic Evolution of a Continental Collision Zone: A Thermo mechanical Numerical Model,” Tectonics 23, TC6003 (2004), doi: 10.1029/2003TC001604. J. Van den Driessche and J. P. Brun, “Tectonic Evolu tion of the Montagne Noire (French Massif Central): a Model of Extensional Gneiss Dome,” Geodinamica Acta 5, 85–99 (1992). S. D. Willett, “Orogeny and Orography: The Effects of Erosion on the Structure of Mountain Belts,” J. Geo phys. Res. 104 (B12), 28957–28982 (1999). S. D. Willett and M. T. Brandon, “On Steady States in Mountain Belts,” Geology 30, 175–178 (2002). S. D. Willett, C. Beaumont, and P. Fullsack, “Mechan ical Model for the Tectonics of Doubly Vergent Com pressional Orogens,” Geology 21 (4), 371–374 (1993). W. Zhao, K. D. Nelson, and project INDEPTH team, “Deep SeismicReflection Evidence for Continental Underthrusting Beneath Southern Tibet,” Nature 366, 557–559 (1993).

GEOTECTONICS

Vol. 44

No. 6

2010