Late Paleozoic intrusive rocks from the southeastern Lhasa terrane, Tibetan Plateau, and their Late Mesozoic metamorphism and tectonic implications

Abstract The Lhasa terrane in southern Tibet experienced Late Paleozoic and Mesozoic–Cenozoic composite orogenesis. This work reports a study on the petrology, geochemistry, zircon U–Pb chronology and Hf isotopes of Late Paleozoic and Late Mesozoic intrusive rocks from the southeastern Lhasa terrane. The Late Paleozoic intrusive rocks crystallized in the Late Devonian–Early Carboniferous of 371 to 355 Ma, representing a bimodal igneous association formed in the back-arc extensional setting. The mafic end-member originated from the enriched mantle and experienced contamination of crustal materials, characterized by a slight enrichment of LREE, positive anomalies of U, K and Pb and negative anomalies of Th, Nb, Ta and Ti. The felsic end-member was derived from the partial melting of the ancient continental crust, characterized by metaluminous, positive anomalies of Th, Zr and Hf, negative anomalies of Ba, Sr, Nb, Ta and Ti and negative εHf(t) values of zircon with TDM2 ages from 1.90 to 1.40 Ga. The Late Cretaceous (ca. 107 Ma) mafic intrusions, along with the Late Paleozoic intrusive rocks, underwent nearly syn-intrusion amphibolite-facies metamorphism under P–T conditions of 0.56 to 0.69 GPa and 692 to 735 °C during the Andean-type orogeny correlated with the subduction of the Neo-Tethyan oceanic slab beneath the Lhasa terrane. This study provides a new insight into the pre-Cenozoic tectonic evolution of the Lhasa terrane.