Normal faulting and viscous buckling in the Tibetan Plateau induced by a weak lower crust

Sarah H Bischoff,Lucy M Flesch

doi:10.1038/s41467-018-07312-9

Sarah H Bischoff, Lucy M Flesch

Open Access

https://doi.org/10.1038/s41467-018-07312-9

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Journal: Nature Communications	Publication Date: Nov 23, 2018
Citations: 36	License type: open-access

Affiliation: Purdue University West Lafayette

Abstract

Flow of weak lower crust has been invoked to reconcile observed topographic gradients, uniform elevations, slow seismic velocity, and high conductivity measured in the Tibetan Plateau, with viscosity estimates of 1016–1021 Pa·s. Here we investigate the dynamic response resulting from a range of lower crust viscosities in a 3-D lithospheric-scale geodynamic simulation of the India–Eurasia collision zone to determine bounds of physically viable lower crustal strengths. We show that thickening of the plateau is accommodated through viscous buckling of the upper crust in response to lower crustal flow for a lower crustal viscosity on the order of 1020 Pa·s. This generates two east–west trending bands of surface subsidence and dilatation consistent with observed normal faulting and estimates of vertical velocity. These results suggest viscous buckling of the upper crust, induced by lower crustal flow from gravitational pressure gradients due to high topography, is responsible for the observed extension in Tibet.

Highlights

Flow of weak lower crust has been invoked to reconcile observed topographic gradients, uniform elevations, slow seismic velocity, and high conductivity measured in the Tibetan Plateau, with viscosity estimates of 1016–1021 Pa·s
Geodynamic simulations are governed by incompressible steady state Stokes-flow within a 100 km thick spherical cap simulation driven by edge velocity conditions and gravity acting on 3-D varying material properties
Becaus several studies have demonstrated the importance of lateral strength heterogeneity and pre-existing lithospheric structure in generating geophysical features that correlate with the Tibetan Plateau[1,20,23,24,30], we use the lateral strength heterogeneity based on the updated vertically-averaged lithospheric effective viscosity estimates of Flesch et al.[1,30] (Fig. 1)

Summary

Introduction

Flow of weak lower crust has been invoked to reconcile observed topographic gradients, uniform elevations, slow seismic velocity, and high conductivity measured in the Tibetan Plateau, with viscosity estimates of 1016–1021 Pa·s. We find Poiseuille flow of a weak lower crust, on the order of 1020 Pa·s, induced by gradients of gravitational potential energy resulting from high topography causes the strong upper crust to viscously buckle generating bands of east–west uplift, surface subsidence and dilatation that drives normal faulting in southern and central Tibet.

Results

Conclusion