Slow Propagation of Slab Tearing at Collisional Boundaries: Implications for Foreland Basin Evolution and Adjacent Mountain Uplift

Slab detachment and its lateral propagation (slab tearing) have been hypothesized to cause along-strike migration of foreland basin depocenters, sedimentary facies belts and adjacent mountain uplift in many collisional orogens. However, existing numerical models of continental collision suggest that lateral propagation of slab tearing is a geologically very fast process (up to 120 cm yr^-1), often inconsistent with tear velocity estimated from foreland basin depocenter migration data ( <20 cm yr^-1). Moreover, the spatial and temporal effects of slab tearing on surface processes including the along-strike differential evolution of foreland basins and lateral facies belt migration remain poorly understood. Here, we present 3D thermo-mechanical numerical models, coupled with surface processes, such as diffusion-controlled erosion and sedimentation, to address under what conditions lateral migration of slab detachment along-plate boundaries slows down, if so, how it influences the evolution of foreland basins and the adjacent mountain topography. Our results indicate that lateral crustal heterogeneities, such as micro-continents, can trigger the initiation of slab detachment at one end earlier than the other. However, once a slab tear begins, it propagates to the opposite end almost instantaneously. Strikingly, an asymmetric oceanic age along the strike of the subducting passive margin, resulting in lateral lithospheric strength variations,  plays the most significant role in slowing down the lateral propagation of slab tearing (8-12 cm yr^-1)—to rates similar to those obtained from collisional orogens. Finally, we compare our model results with Alps-Carpathians mountain chain and adjacent foreland basins, and emphasize the necessity to take into account subducting passive margin’s structural and oceanic age heterogeneities to explain slower slab tear propagation and observed surface geological fingerprints.