Geochemistry, zircon U-Pb age and Hf isotopic characteristics of the Asiha diorite in Dulan County, Qinghai Province

The Asiha diorite in Dulan County is batholith shaped output. The whole rock samples have characteristics by SiO₂ (56.82%~61.15%), rich alkali (Na₂O+K₂O=5.31%~6.02%), low total iron (TFeO=6.09%~6.65%) and low TiO₂ (1.02%~1.25%). Therefore, the diorite belongs to of high-K calc-alkaline rocks. The values of Cr (24.6×10^-6~47.6×10^-6) and Ni (12.8×10^-6~17.6×10^-6) are not high. The diorite is enriched in the LILE such as K, Ba, Rb, Th, U and LREE and depleted in HFSE such as Nb, Ta, P and Ti. LA-ICP-MS zircon U-Pb dating results show that the crystallization age of the diorite is 232.6+1.4Ma, and the age belongs to the Middle Triassic. The zircons have relatively low ε_Hf(t) values (t=232Ma, ε_Hf(t)=-3.71~-0.84, -2.31 on average) and relatively old t_2DM (1.32~1.50Ga, 1.41Ga on average), thus the magma should be derived from Proterozoic subducted crust. In summary, the magma had crust-mantle mixing characteristics, and the diorite was mainly derived from granitic magma of crust (Proterozoic subducted crust) and experienced activity of basic magma of the mantle. The rock was formed under the geodynamic background of conversion from subduction to collision, which represented the magma records of oceanic crust subduction from Late Paleozoic to Early Mesozoic in East Kunlun.