Final closure of the Paleo-Tethys Ocean: Insights from Triassic granitoids in the central Qiangtang area, northern Tibetan Plateau

Author:

Zhai Qingguo1,Hu Peiyuan1,Liu Yiming1,Tang Yue1,Lee Haoyang2

Affiliation:

1. 1SinoProbe Laboratory, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

2. 2Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan

Abstract

The geodynamic evolution during the closure of the Paleo-Tethys Ocean in the Tibetan Plateau remains to be fully understood. The Longmu Co−Shuanghu suture zone in the northern Tibetan Plateau has usually been considered to represent the main ocean basin of the Paleo-Tethys Ocean, so it plays a key role in understanding the evolution of the Paleo-Tethys Ocean. In this study, we focused on the Gacuo and Bensong batholiths on the north and south sides of the Longmu Co−Shuanghu suture zone, respectively. We conducted detailed zircon geochronology and whole-rock geochemical and Sr-Nd isotopic analyses, as well as zircon Hf isotope studies. Zircon U-Pb dating indicates that the Gacuo batholith was formed ca. 223−209 Ma, and the age of the Bensong batholith is ca. 213−203 Ma. The Gacuo batholith is mainly composed of I-type granitoids, which are most likely attributed to partial melting of ancient sedimentary materials of the North Qiangtang terrane with a mixture of ∼0%−30% amounts of mantle-derived components. In contrast, the Bensong batholith has granitoids of A-type affinity, and it was probably generated by partial melting of Mesoproterozoic crust of the South Qiangtang terrane with limited mantle contribution (<5%). Finally, we suggest that the Gacuo batholith was probably generated by the break-off of the oceanic slab beneath the North Qiangtang terrane, while the Bensong batholith was related to a possible lithospheric delamination process of the South Qiangtang terrane after continental collision. Therefore, the Gacuo and Bensong batholiths both developed in a postcollisional tectonic setting, and they recorded the evolutionary process of the subduction and closure of the Paleo-Tethys Ocean during the Late Triassic.

Publisher

Geological Society of America

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