The influence of upper-plate advance and erosion on overriding plate deformation in orogen syntaxes

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.

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter‐Shaped Plate: Insights Into Localized Exhumation at Orogen Syntaxes

“…See the numerical methods section in supporting information for governing equations and material properties used in the model, and additional details. We also refer readers to Braun and Yamato (), Whipp et al () and Nettesheim et al () for further information.…”

“…This has been done by means of analogue (e.g., Willingshofer et al, ) and numerical modeling (e.g., Burov et al, ; Erdos et al, ; Jammes & Huismans, ; Vogt et al, , ). In view of these advances, the subduction of a down‐going plate with a convex‐upward‐shaped indenter (as investigated by Bendick & Ehlers, ) has been further explored (Nettesheim et al, ) with a series of numerical thermomechanical experiments assuming a viscoplastic rheology and stratification of the overriding continental lithosphere. In these models, the highest rock uplift rates are localized within elongated areas above both the indenter bulge and straight segments of the subducting plate and thus not reproducing the observed concentric bull's‐eye pattern of vertical uplift as described in Bendick and Ehlers () and observed in some syntaxial orogens.…”

“…In these models, the highest rock uplift rates are localized within elongated areas above both the indenter bulge and straight segments of the subducting plate and thus not reproducing the observed concentric bull's‐eye pattern of vertical uplift as described in Bendick and Ehlers () and observed in some syntaxial orogens. Here we build upon the work of Nettesheim et al () with particular focus on variations in the style of deformation and associated rock uplift in syntaxial orogens as a function of the degree of rheological (de)coupling of the upper plate (see, e.g., Brun, ; Koptev et al, ; Tetreault & Buiter, ). In contrast to the work of Nettesheim et al () who focused on the effect of variable velocity boundary conditions and erosion mechanisms, we investigate the effect of different thermorheological lithospheric profiles ranging from mechanically decoupled to completely coupled by varying the lithology of the lower crust and the initial crustal geotherm in order to identify the role of rheological structure on the spatial localization of rock uplift.…”

“…Here we build upon the work of Nettesheim et al () with particular focus on variations in the style of deformation and associated rock uplift in syntaxial orogens as a function of the degree of rheological (de)coupling of the upper plate (see, e.g., Brun, ; Koptev et al, ; Tetreault & Buiter, ). In contrast to the work of Nettesheim et al () who focused on the effect of variable velocity boundary conditions and erosion mechanisms, we investigate the effect of different thermorheological lithospheric profiles ranging from mechanically decoupled to completely coupled by varying the lithology of the lower crust and the initial crustal geotherm in order to identify the role of rheological structure on the spatial localization of rock uplift. Similar to Nettesheim et al (), we have also tested different contributions in the total shortening by subduction of the down‐going plate and migration of the overriding plate toward the trench (Capitanio et al, ; Heuret & Lallemand, ; Schellart et al, ) through the introduction of variable rates of upper plate advance ( V Adv ) that refers to the relation between boundary velocities applied at the opposite sides of the model.…”

“…In contrast to the work of Nettesheim et al () who focused on the effect of variable velocity boundary conditions and erosion mechanisms, we investigate the effect of different thermorheological lithospheric profiles ranging from mechanically decoupled to completely coupled by varying the lithology of the lower crust and the initial crustal geotherm in order to identify the role of rheological structure on the spatial localization of rock uplift. Similar to Nettesheim et al (), we have also tested different contributions in the total shortening by subduction of the down‐going plate and migration of the overriding plate toward the trench (Capitanio et al, ; Heuret & Lallemand, ; Schellart et al, ) through the introduction of variable rates of upper plate advance ( V Adv ) that refers to the relation between boundary velocities applied at the opposite sides of the model. Finally, given the large uncertainty in seismic images of subducting plate geometries, various configurations of the flexural bulge geometry are also investigated here.…”