Late Paleozoic strike-slip shear zones in eastern central Asia (NW China): New structural and geochronological data

Abstract

New structural studies and 40 Ar/ 39 Ar dating in northwest China provide information about late Paleozoic strike-slip motions subsequent to accretional events, which built eastern central Asia during the Paleozoic. Two principal areas were affected by these large transcurrent motions. First, in the Tianshan range, main east-west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism. Associated biotites give ages ranging from 290 Ma to 245 Ma. The earlier N110 shearing occurred in western Tianshan, while the last one, dextral in whole Tianshan, occurred 250-245 Myr ago. Second, in the Chinese Altay region several NW-SE shear zones structured the area. The main motion is sinistral and occurred along the Erqishi zone at 280-290 Ma. It is followed by a complex succession of dextral and sinistral shearing episodes, leading to the northwestward structuring, dated at 245 Ma, of a metamorphic zone that was folded during a compressive event.