Middle Permian adakitic granite dikes in the Sumdo region, central Lhasa terrane, central Tibet: Implications for the subduction of the Sumdo Paleo-Tethys Ocean

Abstract

Abstract The Sumdo Paleo-Tethys Ocean was the southernmost part of the Paleo-Tethys Ocean, located on the Qinghai–Tibet Plateau. However, the evolution of the Sumdo Paleo-Tethys Ocean and the origin of eclogites in the Sumdo area of Tibet are still matters of debate. Here we report newly discovered adakitic granite dikes from the Sumdo area of the central Lhasa terrane. The rocks have high SiO2, Al2O3, and Sr contents, high Sr/Y and La/Yb ratios, enrichment in light rare-earth elements (REEs), and depletion in Y, Yb, Th, and heavy REEs. They are characterized by low 87Sr/86Sr (0.703678–0.704427) and high 143Nd/144Nd (0.512825–0.512904) ratios, and positive eNd(t) (+6.41 to +7.38) and eHf(t) (+13.8 to +15.7) values. Zircon U–Pb dating yielded ages of 269.1 ± 4.1 and 266.4 ± 2.0 Ma for the rocks. Our data indicate that the Sumdo adakitic granite dikes were derived from partial melting of subducted oceanic slab, with the magma being influenced by slab-derived fluids and slight interaction with peridotite in the mantle wedge during ascent. By combining our new geochemical data with results of previous studies, we infer a subduction event involving the Sumdo Paleo-Tethys Ocean during the middle Permian, which led to the formation of the Sumdo adakitic granite dikes and the Sumdo, Jilang, and Xindaduo eclogites.