Publication 198

Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

Dong, H., W. Wenbo, S. Jin, G. Ye, A.G. Jones, L. Zhang, J. Jing, C. Xie, and Y. Yin

Abstract

The ongoing India‐Asia collision since the Paleogene created the Tibetan Plateau, the most prominent elevated plateau on our planet. This convergence also contributed to the formation of two distinct types of active surface deformation of the plateau, namely, north–south trending normal fault systems and “ conjugate” strike‐slip fault systems. The tectonics and geodynamic mechanism(s) behind this curious combination are still unclear, despite numerous theories proposed over past decades. Here we present a new three‐dimensional, lithospheric‐scale, electrical conductivity model with unprecedented resolution of the central part of Tibetan Plateau derived from the SINOPROBE magnetotelluric array data set and discuss its inferences related to this question. Our model reveals contrasting conductivity structures corresponding to the surface deformation patterns, namely, highly conductive lower crustal anomalies beneath the graben systems in the Lhasa and Qiangtang terranes and moderately resistive crustal features in the strike‐slip region near Bangong‐Nujiang Suture Zone. With the help of experimentally calibrated constraints between conductivity and melt fraction, the conductivity model and the inferred lateral viscosity distribution together suggest a weak lower crust beneath the graben regions, compared to a stronger crustal rheology associated with the strike‐slip zone. Here we expand the previously proposed “ extensional extrusion” tectonic model in central Tibet to interpret our conductivity model and other geophysical/geodesic observations. The weak rheology under a N‐S directed primary stress may have caused the east–west extension of the graben regions, which further aides the eastward extrusion of the conjugate strike‐slip zone and eventually shapes the surface deformation of central Tibetan Plateau into its current, complex pattern.

Source

[Journal link] [PDF]

MTNet Home Page Alan's Home Page

Alan G Jones / 01 September 2020 / alan.jones.geophysics -at- gmail.com