Cenozoic faulting of the Ganzi-Yushu (Xianshuihe) fault from apatite (U-Th)/He ages and its implications for the tectonic reorganization in the southeastern Tibetan plateau

Abstract

The Ganzi-Yushu-Xianshuihe fault that lies along the northeastern boundary of the Chuan-Dian crustal fragment provides the opportunity to study the tectonic evolution and geodynamic mechanisms of the southeastern Tibetan Plateau. Apatite (U-Th)/He data from an elevation transect provide robust evidence for the initiation of the Ganzi-Yushu fault. The consistent AHe ages of the lower samples constrain the onset of fault activity to 9.4 ± 1.5 Ma. Moreover, the zircon U-Pb dating and rare earth element (REE) analysis confirm that the Queer Shan and Gaogong granitic plutons were emplaced as a whole and then displaced by the Ganzi-Yushu fault. Combining the total offset of these two plutons and the onset timing of the fault activity yields a long-term average left-lateral strike-slip rate of 7.3–10.8 mm/yr for the Ganzi-Yushu fault. Based on the summarized synchronous deformation in the southeastern Tibetan Plateau, including the initiation of fault activity along the whole Ganzi-Yushu-Xianshuihe fault, the slip reversal of the Red River fault, and the fault activity along a series of left-slip faults in the Indochina block, we suggest that the southward extrusion of the Chuan-Dian crustal fragment and clockwise rotation around the Eastern Himalayan Syntaxis initiated at the middle-late Miocene (15-10 Ma).