The rheological structure of East Asian continental lithosphere

Abstract

The rheological structure of the East Asia continent is the key to understanding its broad, heterogeneous, and intense Cenozoic deformation. Based on a refined three-dimensional thermal structure of the lithosphere in this region and the latest strain rate data, we derived a model of the rheological structure of the East Asian continental lithosphere. The strength envelopes, defined by the yield strength of frictional, fractural, and plastic creep, are constrained by the lithological stratification based on previous studies and the depth distribution of earthquakes. The results show large vertical and lateral variations of lithospheric strength in the East Asian continent. A weak lower crust with low effective viscosity is ubiquitous. The rheological structure agrees with the jelly sandwich model in cratons, where the mantle lithosphere is relatively strong. The Tibetan Plateau has the weakest lower crust, with its effective viscosity ranging from 10¹⁹ to 10²⁰ Pa∙s. Its mantle lithosphere is weakened by relatively high temperature; hence, its rheological structure can be described by the crème brûlée model. The lithospheric scale faults and suture zones in and around the Tibetan Plateau, with low strength or viscosity, correspond to the banana split model. The strength of the lithosphere in the Tibetan Plateau and other zones of active Cenozoic tectonics mainly derive from the crust, while the strength of the cratonic lithosphere is dominated by that of the mantle lithosphere. The rheological heterogeneity controls the lateral growth of the Tibetan Plateau and the widespread and differential deformation in the East Asian continent.