Zircon U-Pb age, petrogenesis and teceonic setting of the Yabulai adakite, northern Alxa Block, Inner Mongolia

Yabulai adakite is located in the western part of Yabulai-Nuorigong-Honggueryulin belt, northern Alxa Block.The main rock types of the Yabulai adakite are diorite and quartz diorite.The LA-ICP-MS zircon U-Pb dating results are 275±1 Ma(MSWD=1.00, n=27, diorite) and 277±2 Ma(MSWD=0.64, n=26, quartz diorite), which shows that the ages of the adakite are between 275 Ma and 277 Ma, suggesting a product of Early Permian.Geochemical characteristics show that the Yabulai adakite with high content of SiO₂(60.56%~63.41%), Al₂O₃ (15.86%~17.33%), Sr(572×10^-6~758×10^-6) and low content of MgO(1.45%~3.06%), Y(11.1×10^-6~14.7×10^-6), Yb(1.06×10^-6~1.55×10^-6), enrichment of large ion lithophile elements(such as K, Rb, Ba and Sr), and depletion of high field-strength elements(such as Ta, Nb, Ti and P).The Yabulai adakite is typical C-type adakite with high content of Mg#(38~53), the ratio of Y/Yb is between 7.35 and 11.89, and Na₂O/K₂O is between 1.18 and 1.77;in addition, it exhibits significant fractionation between LREE and HREE and is depleted in HREE with slight Eu anomaly(0.81 < δEu < 1.04).The authors hold that the Yabulai adakite was formed by partial melting of delaminated lower crust and interaction with the mantle peridotite, and magmatic mixing was experienced during diagenesis.Combined with previous studies, the authors hold that the Yabulai adakite might have been formed in a post-collision extension stage.