The detrital zircon LA-ICP-MS U-Pb age of Early Permian Shoushangou Formation in Hanwula area of Xi Ujimqin Banner, Inner Mongolia, and its significance

There exist different opinions concerning the structural setting of southern Central Asia Orogenic Belt (CAOB) in the Permian period. The authors studied the Shoushangou Formation in Hanwula area of Xi Ujimqin Banner, Inner Mongolia, in such aspects as field occurrence, petrology, and detrital zircon U-Pb isotopic geochronology. The result shows that the cathodoluminescence (CL) images of analyzed zircons of two samples from Shoushangou Formation and their Th/U ratios imply the igneous origin. And the ages of total 103 detrital zircons can be mainly divided into 5 groups:285~328Ma (peak age being 302Ma), 338~361Ma, 455~490Ma (Early Paleozoic), 757Ma (Neoproterozoic)and the fifth group including 1278Ma and 2380Ma (Mesoproterozoic- Paleoproterozoic).The youngest age of dating zircons is 285Ma. Together with the age of the granite that intruded into it, the authors have come to the conclusion that the sedimentary age of the Shoushangou Formation ranges from 285Ma to 280Ma, with the main deposition epoch being the Sakmarian -Artinskian stage of Early Permian. The detrital zircons of Shoushangou Formation indicate that the investigated rocks are immature, probably due to the results of rapid erosion, transport, and diagenetic process and nearby supply derived from the nearby source. Additionally, lots of volcanic clastics were found in the provenance of the Shoushangou Formation. All these characteristics suggest that the Shoushangou Formation was most probably formed in a back-arc spreading environment triggered by oceanic crust subduction before closure of the Paleoasian Ocean in Early Permian. Combined with the regional geology and timing of the magmatism, it is concluded that the detrital zircons of the Shoushangou Formation reflect the information of the metamorphic basement and following tectonomagmatic event in Northeast China, and the provenance of Shoushangou Formation mainly came from the Paleozoic granitoids and volcanic rocks in the Sonid Zuoqi-Xilin Hot-Xi Ujimqin Banner area, with the probable addition of materials from Hegenshan-Dong Ujimqin Banner area. Therefore, the suture zone between the North China and Siberia plate is situated in the south of Shoushangou Formation, which is located along the the Solonker suture zone, and the timing for the final collision might be Late Permian-Early Triassic.