U-Pb (SHRIMP) and 40Ar/39Ar geochronological constraints on the evolution of the Xingxingxia shear zone, NW China: A Triassic segment of the Altyn Tagh fault system

摘要

The development of structures and their age along the segment of the Altyn Tagh fault system, and the eastward extension of the Tianshan orogenic belt, remain speculative. Recent investigations on the structural framework, granitic intrusions, and metamorphic rocks in the eastern Tianshan and adjacent areas show that the NE-striking Xingxingxia sinistral ductile shear zone, NW China, is subparallel to the Altyn Tagh fault zone and is superposed on the eastern Tianshan orogenic belt. U-Pb zircon sensitive high-resolution ion microprobe (SHRIMP) dating, and muscovite, biotite, and K-feldspar 40Ar/39Ar thermochronology indicate that sinistral shear along the Xingxingxia shear zone initiated at 240–235 Ma, broadly at the same time as initial formation of the Altyn Tagh fault zone, but later than initiation of dextral strike-slip motion along EW-trending eastern Tianshan orogenic belt at 270–245 Ma. Formation of the Xingxingxia ductile shear zone was associated with Gondwanaland convergence along the southern margin of the Eurasian continent during the Late Permian–Early Triassic.