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

摘要

Structural and ~(40)Ar/~(39)Ar 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 ~(40)Ar/~(39)Ar 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.