Geochronology, geochemistry, and Hf isotopic compositions of the Early Devonian Heihaibei granite in the East Kunlun Orogen, Northwest China

Abstract

The East Kunlun Orogen (EKO) is located in the western part of the Central Asian Orogenic Belt, and it records the Neoproterozoic–Early Devonian tectonic evolution involving the subduction and extinction of the Proto-Tethys Ocean. The Heihaibei granite is located in the South Kunlun belt within EKO. In this study, geochronology, geochemistry, and Hf isotope analysis of Heihaibei monzogranite and granodiorite were carried out. Their LA-ICP-MS zircon U-Pb results yielded ages of 414.1 ± 2.0 and 417.8 ± 2.0 Ma. The Heihaibei granite is peraluminous (A/CNK = 0.99–1.30), with high alkali contents (7.76–9.14 wt.%) and 10 000 Ga/Al (2.60–3.38), FeOT/MgO (27.6–49.5), and Y/Nb ratios (1.93–2.93), suggesting that the Heihaibei granite is an A2-type granite. The Heihaibei granite samples have zircon εHf(t) values ranging from −6.3 to −0.3, which suggests that the Early Devonian granite was derived from partial melting of Mesoproterozoic ( TDM2 = 1797–1415 Ma) crust. When considering data on contemporaneous granites, geochronological and geochemical data for the Heihaibei granite indicate that it was emplaced in a post-collisional extension environment following the closure of the Proto-Tethys Ocean. The Heihaibei granite was formed by extension of the southern subduction accretionary complex as part of the post-collisional setting during the closure of the Proto-Tethys Ocean.