Dextral shear initiation of the Kangguer Shear Zone in the East Tianshan: Constraints from a “porphyroclast” system

Abstract

The Kangguer Shear Zone, located in the East Tianshan, is one of the key faults for understanding the final amalgamation processes of the southwestern margin of the Central Asian Orogenic Belt. Magmatism was active in the Tuwu area of the Kangguer Shear Zone during the late Early Permian. LA–ICP–MS U–Pb dating analyses of the magmatic zircons from three monzogranite plutons, a felsic dyke, and a diorite dyke show ages of 286.9±0.78, 282.8±0.62, 281.7±0.89, 278.0±0.61, and 278.1±1.2 Ma, respectively. Detailed field and microscopic observations reveal that these intrusions form a “porphyroclast” system, and this area has undergone ductile dextral strike-slip deformation, with foliations dipping steeply to the south and subhorizontal stretching lineations trending to the east. Further structural analysis indicates that the three monzogranite plutons intruded into the Kangguer Shear Zone and cooled into rigid bodies before regional dextral strike-slip deformation, which limited the deformation that occurred after 282 Ma. The felsic dykes exhibit synkinematic characteristics, and the diorite dyke may have intruded before or at the same time as dextral strike-slip deformation, implying that regional dextral shear was initiated at ca. 278 Ma. These data, combined with previous studies, suggest that the initiation of dextral shear in the Kangguer Shear Zone occurred after the closure of the Kangguer Ocean and was the result of regional nearly N–S compression caused by the convergence of the Tarim Craton and plates north of the Kangguer Shear Zone.