Multi-oriented and layered structures of lith osphere in orogenic belt and their effects on Cenozoic magmatism

Abstract

Integrating the surface structures with the reinterpretations of 3-D velocity images, this paper puts forward a kind of multi-oriented and layered structure for those of the upper and mid-lower crust, lithospheric and asthenospheric mantle in Tethyan orogenic belt of western Yunnan and Sichuan, China (Sanjiang belt). There exists a detachment between upper and mid-lower crust. The lithospheric mantle is a rigid and competent body unable to be deformed which preserved the older tectonic framework. The asthenosphere is an imcompetent layer that is easy to be deformed, and behaves as an initiation region of deformation, and its structural patterns reflect younger tectonics. The Cenozoic intracontinental magmatism of this region is controlled by: (i) sub-meridional and NNE trending asthenospheric upwelling around the western margin of Yangtze block; (ii) crust-mantle transitional layer formed by underplating of ascending melts; and (iii) intersection or transformation of regional structures such as major faults.