The Middle–Late Silurian granitoids in the Eastern Kunlun Orogenic Belt, NW China: petrogenesis and implications for tectonic evolution

Abstract

The Eastern Kunlun Orogenic Belt lay on a significant tectonic boundary between Gondwana and Eurasia, produced widespread granitoids, and recorded at least two orogenic episodes since the Phanerozoic eon. In this paper, we provided new petrography, geochemistry, zircon U–Pb dating, and Lu–Hf isotopic research on the Middle–Late Silurian granitoids from the eastern segment of The Eastern Kunlun Orogenic Belt. These granitoids comprised of Zhongzhigou granodiorites and Xintuo alkali-feldspar granites, formed in the Middle–Late Silurian (420–425 Ma). Geochemically, the granodiorites exhibit high Sr/Y (31.2–35.2) as adakitic affinities, and alkali-feldspar granites belong to highly fractionated I-type granites. Additionally, granodiorites have zircon eHf(t) values show limited positive variations from − 0.5 to + 3.2, with two-stage Hf model ages (TDM2) of 1105–1306 Ma, while alkali-feldspar granites show negative zircon eHf(t) values ranged from − 4.6 to − 0.1 with two-stage Hf model ages (TDM2) of 1289–1541 Ma, implying that their primary magma originated from different sources. Taken together, we conclude that granodiorites had been derived from partial melting of the juvenile newly underplated mafic lower crust, while alkali-feldspar granites were derived from partial melting of the shallower ancient crustal source. Combined with temporal and spatial distribution of magmatic activities, sedimentation, and metamorphism, it can be concluded that the whole EKOB underwent a transition from syn-collision compression to post-collision extension and extensive crustal reworking occurred during the Middle–Late Silurian.