Abstract
Abstract. Focused, rapid exhumation of rocks is observed at some orogen syntaxes, but the driving mechanisms remain poorly understood and contested. In this study, we use a fully coupled thermomechanical numerical model to investigate the effect of upper-plate advance and different erosion scenarios on overriding plate deformation. The subducting slab in the model is curved in 3-D, analogous to the indenter geometry observed in seismic studies. We find that the amount of upper-plate advance toward the trench dramatically changes the orientation of major shear zones in the upper plate and the location of rock uplift. Shear along the subduction interface facilitates the formation of a basal detachment situated above the indenter, causing localized rock uplift there. We conclude that the change in orientation and dip angle set by the indenter geometry creates a region of localized uplift as long as subduction of the down-going plate is active. Switching from flat (total) erosion to more realistic fluvial erosion using a landscape evolution model leads to variations in rock uplift at the scale of large catchments. In this case, deepest exhumation again occurs above the indenter apex, but tectonic uplift is modulated on even smaller scales by lithostatic pressure from the overburden of the growing orogen. Highest rock uplift can occur when a strong tectonic uplift field spatially coincides with large erosion potential. This implies that both the geometry of the subducting plate and the geomorphic and climatic conditions are important for the creation of focused, rapid exhumation.
Highlights
The deformation around orogen syntaxes has been the subject of widespread attention over the last years due to the observed high, sustained, and spatially focused exhumation with rates in excess of 5 mm a−1 over million-year timescales
At the model front and back (y < 200 and y > 600 km), which correspond to the geometry of the straight-slab models, shortening is accommodated by a lithospheric scale pop-up structure formed by two broad shear zones, indicated by strain rates above 5.0 × 10−15 s−1
The simulations with a rigid subducting plate presented here indicate that shortening is accommodated by a lithosphericscale pop-up structure formed by two broad shear zones rooting to the S line
Summary
The deformation around orogen syntaxes has been the subject of widespread attention over the last years due to the observed high, sustained, and spatially focused exhumation with rates in excess of 5 mm a−1 over million-year timescales. We use the term “plate corners” in this study to refer to all short, convex bends that separate the longer, straight to slightly concave plate boundary segments. This alternation between bends in the subducting plate and straight segments is a direct consequence of the slab bending that is required to accommodate subduction on a sphere (Frank, 1968; Mahadevan et al, 2010). The change in orientation of neighboring subducting slab segments ef-
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