Geologic framework and tectonic evolution of the Qinling orogen, central China

Abstract

The geologic framework of the Qinling orogen was built up through interplay of three blocks, the North China block (including the North Qinling), the South Qinling, and the South China block, separated by the Shangdan and Mianlue sutures. The Shangdan suture resulted from Middle Paleozoic collision of the North China block and the South Qinling. The Mianlue suture resulted from Late Triassic collision of the South Qinling and the South China block. Present upper crust of the Qinling is structured dominantly by thrust–fold systems. The North Qinling displays thick-skinned deformation with crystalline basement involved, whilst the South Qinling is characterized by thin-skinned thrusts and folds detached above the Lower Sinian. Two types of Precambrian basement, crystalline and transitional, are defined according to lithology and metamorphic grade and different in age. Stratigraphic and sedimentary architecture is characterized by distinct zonation. The Qinling orogen experienced a prolonged continental divergence and convergence between blocks. During the period from Late Neoproterozoic to Early Paleozoic times, the South Qinling was the northern margin of the South China block, and the North Qinling was the southern margin of the North China block, separated by a Proto-Tethyan Qinling Ocean. The North Qinling evolved into an active margin when the Proto-Tethyan Qinling Ocean subducted northward during Ordovician time. Collision of the South and North Qinling took place in Middle Paleozoic along the Shangdan suture. Synchronous with the collision, rifting occurred at the southern rim of the South Qinling and was followed by the opening of the Paleo-Tethyan Qinling Ocean during the Late Paleozoic, resulting in the splitting of the South China block from the South Qinling. Collision of the South Qinling and the South China block came about in the Late Triassic along the Mianlue suture. The Late Triassic collisional orogeny caused extensive fold-and-thrust deformation and granitoid intrusions throughout the Qinling, and led to final amalgamation of the North and South China blocks.