Geological significance of the newly discovered Middle Permian ocean island basalt‐type gabbros in Ewulang, Nianqing‐Sumdo area, Tibet

Abstract

Numerous research data have been obtained about the Sumdo Palaeo‐Tethys, but the reports on the occurrence of Permian Ocean islands are relatively scarce. Here, we present the zircon U–Pb geochronology, geochemistry, and in situ zircon Hf isotopic characteristics of the ocean island basalt (OIB)‐type gabbros from Ewulang in Nianqing‐Sumdo, Tibet. The zircon U–Pb age obtained from Ewulang OIB‐type gabbros is 263 Ma (the Middle Permian), representing the formation age of the gabbros. The geochemical characteristics of the samples show no contamination by crustal material. Meanwhile, all samples are enriched in light rare earths (LREEs) and large‐ionic lithophile elements (LILEs), which are similar to the typical OIB. In various geochemical discriminant diagrams, all samples fall into the fields of OIB and related tectonic settings, indicating that the rocks were formed in the oceanic island environment within the oceanic plate. Various geochemical indicators imply that the OIB‐type gabbros may originate from mantle plume and the in situ zircon εHf(t) values of Ewulang gabbros range from −0.34 to +4.30, suggesting that the magmas derived from an enriched mantle source. Combined with regional data and previous studies, this article further confirms that Sumdo Palaeo‐Tethys extends west to Nianqing‐Sumdo area and the Tangjia (Zhikong)‐Sumdo Palaeo‐Tethys was still an ocean basin with a certain scale during the Middle Permian.