Deformational History of the Kanguer Subduction Complex in the Eastern Tianshan (NW China): Implications for Paleozoic-Triassic Multiple Accretionary Tectonics of the Southern Altaids

The Kanguer Subduction Complex in the Eastern Tianshan is critical to understanding the tectonic evolution of the southern Altaids as it marks the terminal suture along which the Paleo-Asian Ocean was consumed. However, the nature and timing of this final collision, as well as the mechanism of shearing and related magmatism, remain enigmatic. The Kanguer Subduction Complex demonstrates obvious sinistral transtensional and dextral compressional deformation in different tectonic events along the Qiugemingtash Shear Zone in Huangshan area. Three sets of asymmetric plunging folds (e.g., basin-like, S-shaped and Z(W)-shaped) were recognized in the sedimentary rocks. Locally, the folds are offset by dextral strike-slip faults, indicating that they were formed by dextral shearing. The Huangshandong mafic-ultramafic complex experienced brittle dextral shearing partitioned around the margins of the intrusion. Detrital zircon U-Pb dates for deformed sedimentary rocks have maximum deposit ages (MDA) of 251 and 290 Ma, respectively, and syn-compressional shearing conjugate granitic dikes that intruded into the deformed sedimentary rocks yield crystallization ages of 249 and 245 Ma, respectively. These ages reveal that the extensional and/or transtensional sedimentary basins formed between ca. 290–249 Ma, and dextral compressional shearing started ca. 249 Ma. Combining deformed units with transtensional basins and mantle-derived magmatism, we suggest that ocean-ridge subduction induced a sinistral transtensional regime in a forearc/intraarc setting related to the Tuva-Mongol Orocline in the Permian. The oblique convergence between the Tarim Craton and southern Altaids triggered the Qiugemingtash dextral compressional shearing in the Early Triassic (ca. 249 Ma).