Time constraints on the closure of the Paleo-Asian Ocean on the northern margin of North China Craton: Evidence from Xihouhaozisyn-collisional granites in Siziwang Qi area

Xihouhaozi pluton is located in the north of Siziwang Qi area, northern North China Craton. Cameca IMS-1280-SIMS zircon U-Pb dating indicates that it was emplaced at 266Ma±2Ma. Monzogranite, as the dominant composition, has abundant large-size muscovites. Geochemical analyses show that the pluton is characterized by high SiO2 (75.21%-76.69%), A/CNK ratios (mostly>1.1) and normative corundum abundances (mostly>1%). Furthermore, the Xihouhaozi granite displays strong negative Eu anomalies (δEu=0.03-0.11), striking Ba, Nb, Sr and Ti depletions, and slight Cs, Rb, Th and Pb enrichments. It presents a spectacular M-type tetrad effect in the REE distribution patterns as well as non-CHARAC (charge-and-radius-controlled) trace element behavior. Tectonic discrimination diagram shows that the pluton might have been formed in a syn-collisional tectonic setting. In combination with regional geology, the authors hold that the Xihouhaozi granite belongs to highly fractionated peraluminous S-type granite and was generated during the continent-continent collision in the late Permian period. During 270-260Ma, a syn-conllisional granitic belt was formed in Siziwangqi area, which constrained the closure of the Solonker suture of the North China Craton with southern Mongolia in the late Permian period.