Abstract:

Southern Qinling belt is located in the south part of the Qinling orogen, which experienced the complex intra-continental deformation in Mesozoic. In the Late Mesozoic period, there were a series of strike-slip faults developed along the orogen in the southern Qinling belt. At present, the understanding of the deformation features, superposition relationship and dynamic mechanism for these strike-slip faults on different location is not sufficient. Structural studies show that the Ningshan fault and the Ankang fault are characterized by the A type fold and subhorizontal stretching lineation, which indicated the southern Qinling belt underwent a tectonic stage dominated with the strike-slip shear deformation. Kinematic studies revealed the Ningshan fault was characterized by a sinistral shear deformation, while the Ankang fault by dextral characteristics. We chose the typical rock samples for isotopic dating to limit the fault activity time. The zircon SHRIMP U-Pb age of the syn-tectonic granite vein in the Ningshan fault was (186.0±4.0) Ma, and the mica ⁴⁰Ar-³⁹Ar dating results in the Ankang fault are 161.2-173.5 Ma. Although the kinematic features are opposite between the Ningshan fault and the Ankang fault, the geochronological results defined that the deformation time of these two faults is the same, e.g. Early-Middle Jurassic, both of which constitute a eastward extrusion for the central block of southern Qinling belt. This tectonic characteristic also indicated that the deformation of the orogen was soon transformed into the intra-continental deformation stage, which was dominant with the lateral extrusion and strike-slip displacement along the orogen.

Key words: southern Qinling belt, intra-continental deformation, lateral extrusion, Ningshan fault, Ankang fault, Qinling orogen