Zircon U-Pb Ages and Geochemical Characteristics of Quartz Diorite Porphyrite from Suoerkuli Area in Altyn Tagh and their Geological Significance

In order to confirm the genesis and formation age of quartz diorite porphyrite from Suoerkuli area in Altyn Tagh, its geochemical characteristics and LA-ICP-MS zircon U-Pb age have been studied in this paper. The LA-ICP-MS zircon U-Pb dating indicates that these quartz diorite porphyrites was formed at (375.7±2.2) Ma. The geochemical data show that these rocks are relatively rich in SiO₂ (61.41%~69.93%) and Al₂O₃ (13.48%~15.57%) contents, but low in TFeO (3.47%~4.53%), MgO (0.66%~1.83%) and CaO (2.81%~4.21%) contents, showing the features of calc-alkaline I-type granites. These rocks have relative high total REE concentration (∑REE=129.32×10^-6~253.63×10^-6), with fractionated REE(La/Yb)_N=6.25~8.51 and no remarkable Eu anomalies. Furthermore, they are enriched in LILE (e.g. Rb, Pb, Th and U), but depleted in HFSE (e.g. Nb, Ta and Ti). The geochemical characteristics suggest that these quartz diorite porphyrites were generated by the partial melting of basic rocks in lower crust and formed by the fractional crystallization, and the parental magma was caused by the underplating of mantle-derived materials. Based on the regional geological investigations and the spatial-temporal distribution of the coeval igneous rocks, it's considered that the quartz diorite porphyrite was emplaced in a post-orogenic extensional environment, which is related with the strike slip of Altyn Tagh Fault.