Zircon U-Pb age, geochemical characteristics, and tectonic implications of the Early Permian ultrabasic dykes in the Harlik Mountain,East Tianshan, Xinjiang

[ Objective ]During multiple stages of magmatic activity in the Halrick Mountains of the East Tianshan, extensive granitic and mafic dyke swarms were formed.To limit the closure time of the ancient Asian Ocean in this area and to elucidate the tectonic environment in which ultrabasic rock walls were formed. [ Methods ]This study reports on the petrography, geochemistry, and zircon U-Pb ages of a particular type of ultrabasic dyke swarm (amphibolites) in Qincheng, Hami.[ Results ] The results show that the amphibolites have SiO₂ contents ranging from 39.00% to 45.48%, TiO₂ contents ranging from 1.60% to 3.01%, and Mg# values ranging from 50 to 60, They are relatively weakly enriched in light rare earth elements ((La/Yb)_N = 1.34~2.25) and show no Eu anomalies (δEu = 0.76~1.12). They are enriched in large ion lithophile elements (LILEs: Rb, Ba, K, Sr) and depleted in high field strength elements (HFSEs: Nb, Zr, Hf). The amphibolites belong to the alkaline series rocks. The LA-MC-ICPMS zircon U-Pb ages reveal that these three amphibolites crystallized at 298.4±1.7 Ma, 297.7±1.6 Ma, and 295.5±1.6 Ma, respectively. The whole-rock Sr-Nd compositions indicate initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7047 to 0.7051 and ε_Nd(t) values ranging from -2.63 to 1.81. [ Conclusion ]Based on comprehensive analysis of regional geology, chronology, geochemistry, and Sr-Nd isotopes, it is suggested that the primitive magma of the Early Permian amphibolites in Qincheng possibly originated from partial melting of the lithospheric mantle and these rocks were formed in a post-collisional extensional tectonic setting.At the same time, it implies that the ancient Asian Ocean in the Harlik Mountains region closed before the Early Permian.