Structural and geochronological constraints on the Mesozoic tectonic evolution of the North Dabashan zone, South Qinling, central China

Abstract

Structural and 40Ar/39Ar data from the mylonitic rocks of the North Dabashan zone (NDZ) document kinematic and tectonothermal characteristics of the Mesozoic collisional and intra-continental orogenesis in the southern part of the Qinling orogenic belt. The NDZ underwent two deformational phases during the Mesozoic period. The earlier one is characterized by top-to-the-SW thrust ductile shearing along a NW-trending shear zone (DSZ-1), while the later one is featured by dextral strike-slip ductile shearing along another NNW-trending shear zone (DSZ-2). The timing of the two deformation events have been constrained to be 245–189 Ma and 178–143 Ma respectively, by using mica 40Ar/39Ar geochronology. It is proposed that the earlier deformation event was associated with the Middle Triassic–Early Jurassic collision between the North and South China Blocks, which generated the initial framework of the NDZ; and the later one was related to the Middle Jurassic to Early Cretaceous intra-continental orogeny in East Asia, which caused a significant eastward extrusion of the South Qinling and led to the formation of the SW-convex Dabashan foreland orocline. The distinguishing between these two deformation events sheds a new insight into the Mesozoic tectonic evolution of the Qinling orogenic belt.