Origin of the Paleocene Granite in the Lhasa Terrane of the Qinghai-Tibet Plateau and Its Constraints on the Evolution of the Neo-Tethys Ocean

Abstract

Large-scale Cenozoic magmatic rocks in the southern Qinghai-Tibet Plateau show a key chapter of geological evolution, especially the northward subduction and gradual melting in the Neo-Tethys Sea plate during the collision between the Asian continent and the Indian plate, which reveals its geological importance. Although some progress has been made in the study of the Linzizong volcanic rocks in southern Lhasa during the India-Asia collision, the closure time of the Neo-Tethys Sea and the exact timing of the first India-Asia collision are still controversial in the geological community. This study focuses on the formation age, geochemical characteristics, and tectonic environment of the granitic diorite in the Duodigou area, central southern Lhasa. LA-ICP-MS U–Pb dating of zircons reveals that the diorite was formed in the Paleogene, with a specific age of 57.20 ± 0.56 Ma. Geochemical analysis indicates that the granite was formed in an island-arc magmatic environment and belongs to peraluminous I-type granite. Under the background of the continuous northward subduction in the Neo-Tethys plate, the interaction of marine sediment dehydration and melting led to the intrusion of basaltic magma into the crust, which led to the remelting of the lower crust and the formation of granitic magma. Through this study, we have further improved the chronological framework of Cenozoic magmatism in southern Lhasa and provided new geological constraints for the analysis of the Neo-Tethys Sea's evolution during the period.