Paleozoic Subduction‐Accretion in the Southern Central Asian Orogenic Belt: Insights From the Wuwamen Accretionary Complex of the Chinese South Tianshan

Abstract

AbstractAccretionary complexes are a major component of the Central Asian Orogenic Belt (CAOB) and are important for understanding its architecture and evolution. The Wuwamen accretionary complex in the Chinese South Tianshan contains a tectonic mélange that witnessed the dynamic evolution from early accretion to final collision of the western CAOB with the Tarim Craton. We present geochronological and geochemical studies on the exotic blocks and metasedimentary matrix of the tectonic mélange in order to refine the subduction‐accretion processes in the CAOB. Geochemical and age data reveal that the exotic blocks are of diverse origins, including arc‐related granite and arc basalt‐like garnet amphibolite from the upper plate, and MORB‐like amphibolite from the subducting slab. The blocks underwent subduction‐related high‐temperature metamorphism between ca. 397 and 340 Ma. Detrital zircons in the metasedimentary matrix are dominated by Paleozoic ages corresponding to the continuous arc magmatism in the Yili‐Central Tianshan Block. This finding is consistent with the accretion of the Wuwamen complex on the southern margin of the Yili‐Central Tianshan Block above the northward subducting South Tianshan Ocean. A ca. 307 Ma post‐accretion granite dyke intruded the Wuwamen complex, thereby providing a minimum age limit for its terminal accretion. In conjunction with subduction‐related magmatism, metamorphism, and sedimentation, the accretion of the Wuwamen accretionary complex was active during the early Ordovician to the late Carboniferous. Our new results reiterate that long‐lasting accretionary processes in the South Tianshan Ocean and the terminal collision due to its closure exert a major control on the architecture of the southwestern CAOB.