Effect of unbalanced topography and overloading on Coulomb wedge kinematics: Insights from sandbox modeling

Abstract

[1] This study addresses the effect of variable unbalanced topography and overload on the kinematics of a fold and thrust belt developed within a collisional belt that underwent a subduction polarity reversal event. This was done by physical modeling of doubly vergent Coulomb wedges, using sand as an analogue material. During the experimental procedure a preexisting topography was generated by a first phase of subduction in one direction. A second phase of subduction was then initiated in the opposite direction (simulating a subduction flip). An anomalous, strong frontal growth for the wedge during the second phase was experimentally shown to be dependent upon surface slope breaks and the critical asymmetrical architecture achieved by the wedge at mature stages of deformation. The latter is suggested to be the rule for doubly vergent orogens at steady state, even after a subduction flip. During the experiments, surface processes, like syntectonic erosion and sedimentation, markedly altered mass transfer within the wedge. In particular, lowering the surface slope by syntectonic erosion favored cycling between accretion and underthrusting modes. By contrast, a sudden syntectonic sediment load in the prowedge region promoted prolonged phases of underthrusting, retarding accretion of new imbricates at the prowedge toe. However, at later stages of deformation the prowedge was forced to regain its characteristic minimum critical taper as predicted by theory and did so by the sudden nucleation of long, flat thrust units, rapidly rebalancing the asymmetry between prowedge and retrowedge regions. The experiments suggest that given a fixed critical taper related to time-invariant frictional properties along the wedge bounding surfaces, deformation does vary within the wedge according to time-varying location of normal stress surpluses and unbalanced topography acting on potential failure surfaces. These, in turn, alter the equilibrium between prowedge and retrowedge basal detachments that is here considered to be a major factor controlling the self-regulating dynamics of collisional orogens.

The Fossil Accretionary Wedge of the Bay of Biscay: Critical Wedge Analysis on Depth-Migrated Seismic Sections and Geodynamical Implications

“…However, based on the results from the geometry of the wedge, it appears that the Biscay wedge was behaving similarly to active accretionary wedges and therefore would also have a decollement partially weakened by elevated fluid pressure. In the east, the decreased number of imbricates may simply be the direct consequence of higher sedimentation (Smit et al 2003;Del Castello 2004;Selzer et al 2008). …”

“…This would agree with a negative buoyancy of the thickened crust producing the bending in the Iberian plate. Analog models predict the creation of a new set of thrusts and a related wedge with inverse polarity under these conditions (Shemenda 1992), a process catalyzed by the unbalanced topography acting on the inherited detachment surfaces (Del Castello et al 2004). In the Bay of Biscay, unbalanced topography and inherited extensional detachments (Boillot and Froitzheim 2001;Lavier and Manatschal 2006;Reston et al 2007) were available when the wedge initiated ( fig.…”

“…Large extensional detachments can develop as areas of embrittlement of the entire crust in magma-poor rifted margins, explaining the exhumation of the mantle and serpentinization at the continent-ocean transition (PerezGussinye and Reston 2001;Jammes et al 2009;Peron-Pinvidic and Manastchal 2009). This extensional detachment, originally seaward, would change its dip easily and become the basal thrust of a newly forming accretionay wedge (i.e., Del Castello et al 2004) when the regime changed to compressional ( fig. 9b).…”

Late Oligocene–early Miocene olistostromes (sedimentary mélanges) as tectono-stratigraphic constraints to the geodynamic evolution of the exhumed Ligurian accretionary complex (Northern Apennines, NW Italy)

“…Observations on modern accretionary complexes in convergent plate boundaries show that the outer wedge is highly sensitive to changes of the dynamic equilibrium (e.g., Davis et al 1983;Platt, 1986;Del Castello et al 2004von Huene et al 2004;Sage et al 2006;Vannucchi et al 2012). In this framework, mass-transport processes are leading agents in maintaining the dynamic equilibrium by reshaping the accretionary wedge topography and producing high concentration of small-to medium-scale submarine landslide accumulations (McAdoo et al 2004;Mosher et al 2008;Camerlenghi et al 2009;Moore et al 2009;Harders et al 2011;Strasser et al 2011) and megaslides (Moore et al 1976;Golfinger et al 2000;Cochonat et al 2002;von Huene et al 2004;Hühnerbach et al 2005;von Huene, 2008;Yamada et al 2010).…”

Forearc Basin Stratigraphy Resulting From Syntectonic Sedimentation During Accretionary Wedge Growth: Insights From Sandbox Analog Experiments

“…The formation of a forearc basin at an accretionary margin is controlled by deformation of the accretionary wedge, which depends on various factors including the material properties of the wedge and the décollement (friction, cohesion, and pore fluid pressure), plate convergence (obliquity and velocity), isostatic response (uplift and subsidence), and external surface processes (erosion and sedimentation) (e.g., Byrne et al, ; Fuller et al, ; Graveleau & Dominguez, ; Gutscher et al, ; Malavieille et al, ; Mannu et al, ; Noda, , ; Simpson, ; Wang & Davis, ). Among these factors, external surface processes can strongly influence deformation of the accretionary wedge (e.g., Cruz et al, , ; Simpson, ; Storti & McClay, ) by (1) concentrating deformation at the rear of the wedge (Hardy et al, ; Storti & McClay, ), (2) reducing the taper angle (Bigi et al, ; Simpson, ; Storti & McClay, ), (3) decreasing the number of thrusts and widening the thrust spacing, which is likely caused by a reduction in differential stress in the wedge due to an increase in normal stress (Bigi et al, ; Fillon et al, ; Liu et al, ; Simpson, ; Zhang et al, ), (4) increasing the duration of folding at the upper ramp tip (Storti et al, ), (5) prolonging the phase of underthrusting and limiting the forward propagation of thrust activity (Del Castello et al, ; Hardy et al, ), (6) forming a trishear zone and causing limb rotation (Wu & McClay, ), (7) creating and reactivating out‐of‐sequence thrusts (Mannu et al, ; Storti et al, ), (8) stabilizing the rear of the wedge and increasing the rate of migration of the deformation front (Fillon et al, ), and (9) causing a switch from frontal accretion to synchronous thrusting and underthrusting due to local heterogeneity of the basal shear stress (Bigi et al, ; Del Castello et al, ; Storti et al, ).…”