Geochronological and geochemical characteristics of the late Early Cretaceous granitic porphyry in the Ulanhot area and its tectonic setting

Two granitic porphyry belts outcropped in the Ulanhot area, Inner Mongolia, occur mainly in the sinistral strike-slip shear zone related to the Nenjiang-Balihan fault. LA-ICP-MS zircon U-Pb dating shows that granitic porphyry formed at 124.99±0.99 Ma, which belongs to the late Early Cretaceous. Geochemical characteristics show that the granitic porphyry has SiO₂content of 70.56%～78.34% and(Na₂O+K₂O)content of 7.10%～8.99%, with A/CNK ratio of 0.94～1.20, and enrichment in Si and alkaline suggests that it belongs to subluminous-peraluminous granite. Granitic porphyry is characterized by medium REE contents, distinct fractionation of LREE and HREE((La/Yb)_N=9.49～14.71), strong negative Eu anomaly(δEu=0.33～0.73), relative enrichment of large ion lithophile elements(Rb and Ba)and of high field strength-elements(Th and U), but relative depletion of Sr, Nb and Ti, with distinct negative anomaly, suggesting that it belongs to highly fractionated I-type granite. It can be concluded in this study that the Nenjiang-Balihan fault in the Ulanhot area experienced a short-period extension in the late Early Cretaceous.