LA-ICP-MS zircon U-Pb dating of Wulanhada middle Permian alkali-feldspar granites in Xianghuang Banner, central Inner Mongolia, and its geochemical characteristics

Wulanhada pluton, located in Xianghuang Banner of Inner Mongolia, belongs to the middle section of the northern edge of theNorth China Craton (NCC). It is mainly composed of middle-fine to middle-coarse grained alkali-feldspar granites. LA-ICP-MS zircon U-Pb dating indicates that the pluton was emplaced in the middle Permian (265.1Ma±1.5Ma, MSWD=1.5). These granites have high SiO2 (73.63%~75.47%) and are enriched in alkali (Na2O+K2O=9.25%~9.49%), belonging to high-K calc-alkaline rocks as shown in the plot of SiO2-K2O. They are weakly peraluminous with ACNK of 1.00~1.03. The Wulanhada granites show high REE content (94×10-6~383×10-6) and are relatively enriched in LREE ((La/Yb)N=6.59~13.20), with evident negative Eu anomalies (δEu=0.22~0.38). Their trace elements are characterized by distinct negative Ba, Sr, Nb, Ti and P anomalies, with high HFSE content (Zr+Nb+Ce+Y>350×10-6) and relatively high 10000×Ga/Al ratios (2.36~2.79). In conclusion, the Wulanhada alkali-feldspar granites show typical A-type geochemical affinity. Furthermore, the relatively low Nb content implies that the pluton is A2 subtype granite. Based on the plots of R1-R2 and Y+Nb-Rb, the authors hold that the pluton was probably emplaced in an extensional post-collision setting. The results obtained by the authors suggest that the collision between NCC and Siberian Craton took place as early as 265.1Ma.