ABSTRACT
The Qinling Orogenic Belt is a polyphase collisional belt between the North China and Yangtze blocks in central China, in which the Tongbai-Dabie segment is considered to be the eastern partion or root belt of the orogenic belt. The crystalline axial belt in the Tongbai-Dabie segment represents Precambrian middle-lower continental crust exhumed at the surface through syn-orogenic tectonic processes and late-or post-orogenic extensional processes. The rheological features of the ancient middle-lower crust are assessed on the basis of the frictional failure in the brittle regime, and power-law creep in the ductile regime. The present-day and Mid-Late Proterozoic rheological profiles showing variation of rock strength with depth in the crust of the Tongbai-Dabie segment are qualitatively constructed and compared, respectively. The profiles suggest that the crustal texture, composition and deformation have been strongly heterogeneous and partitioned with the rheological stratification since Mid-Late Proterozoic times at least. The formation of the Luotian old metamorphic core complex in the Dabie area is interpreted in terms of mechanical instabilities arising from sialic partial melting in the middle crust in the Mid-Late Proterocoicx.
