Lower Crustal Rheology Controls the Development of Large Offset Strike‐Slip Faults During the Himalayan‐Tibetan Orogeny
Geophysical Research Letters
The mechanism of crustal deformation and the development of large offset strike-slip faults during continental collision, such as the India-Eurasia zone, remains poorly understood. Previous mechanical models were simplified which are either (quasi-)2-D approximations or made the a priori assumption that the rheology of the lithosphere was either purely viscous (distributed deformation) or purely localized. Here we present three-dimensional visco-elasto-plastic thermo-mechanical simulations,
... h can produce both distributed and highly localized deformation, to investigate crustal deformation during continental indentation. Our results show that large-scale shear zones develop as a result of frictional plasticity, which have many similarities with observed shear zones. Yet localized deformation requires both a strong upper crust (>10 22 Pa·s) and a moderately weak middle/lower crust (~10 20 Pa·s) in Tibet. The brittle shear zones in our models develop low viscosity zones directly beneath them, consistent with geological observations of exhumed faults, and geophysical observations across active faults. Plain Language Summary Large offset strike-slip faults are one of the key surface features of continental collision, such as in Tibet. These narrow belts of strike-slip faults accommodate strong deformation, and deciphering their mechanism of formation helps to understand the complex dynamics of India-Eurasia collision. Yet previous models developed to address this either assumed simplified rheologies or employed low numerical resolutions that is insufficient to simulate the spontaneous formation of localized zones. Here, we present high-resolution 3-D visco-elasto-plastic thermo-mechanical models that simulate the formation of large-scale strike-slip faults during Indian indentation, while also taking distributed deformation into account. Our simulations show that a combination of a strong upper crust and a moderately weak middle/lower crust produces faults that are, to first order, consistent with observed ones in the Tibet region. Localized deformation usually initiates at the brittle-ductile transition, and a weak middle/lower crust facilitates subsequent shear localization such that the shear zones cut through the whole crust. The craton-like strong terranes can sustain large stresses and initiate large offset faults along their boundaries.