Heterogeneities of the lithospheric thermal structure and rheology control Cenozoic intracontinental deformation in southeast China

Abstract

It still remains elusive how the rheology of the lithosphere influences intracontinental deformation. We constructed a thermo-rheological model of the lithosphere in southeast China, a typical intracontinental deformation area, to address this issue. The thermal model was derived from updated heat flow data assuming steady-state heat conduction, using xenoliths and Pn seismic velocity data as constraints. This thermal model was integrated with a compositional and structural model of the lithosphere to estimate the strength distribution. Remarkable heterogeneities in the thermo-rheological structure were obtained. Most of southeast China is characterized by a large mantle heat flow and high temperature, thin and weak lithosphere, except for the western Yangtze Craton where a cold and rigid lithosphere exists. The lithosphere thins southeastward from 200 km in the craton interior to 70 km in the northern South China Sea. Both the ‘jelly sandwich’ and ‘crème brûlée’ rheological profiles for the continental lithosphere exist in southeast China, depending on the geothermal condition. The seismicity in southeast China is restricted to areas cooler than 600 °C, which are rheologically weak and characterized by strength transition zones. The Mesozoic flat-slab subduction of the Paleo-Pacific Ocean and far-field effects of the Cenozoic Indo-Asia collision influence the thermo-rheological pattern in southeast China, and the thermo-rheological heterogeneities control the Cenozoic intracontinental deformation.