Zircon U-Pb dating, geochemistry and tectonic implications of Akechukesai gabbro in East Kunlun orogenic belt

The study of basite and ultrabasite in East Kunlun is relatively limited, which results in a lack of an overall understanding of mantle-source magmatic activities and magmatic evolution in East Kunlun. This paper presents geochemical, U-Pb chronological and Hf isotopic studies of gabbro in Akechukesai. The results indicate that the rock was formed in early Late Triassic(219.3±1.1Ma, MSWD=0.80). The rock belongs to calc-alkaline series. The content of SiO₂ is 49.03%~57.26% and the values of Mg^# are 49~57. The REE distribution curve shows right-dipping feature of LREE. The rock is enriched in LILE(Rb, Ba, K)and depleted in HFSE (Nb, Ta, Ti). The ε_Hf(t)values vary from -1.81 to 3.25 and the Hf model age of zircon is older than the crystallizational age of zircon. Geochemical features of the rock indicate that the Akechukesai gabbro originated from partial melting of the metasomatized lithospheric mantle caused by the dehydration of the subducting slab. Combined with the analysis of regional tectonic setting, the authors hold that the Akechukesai gabbro was formed in an extensional regime of the Late Indosinian, inheriting the characteristics of mantle source altered by early subduction of slab.