Early Triassic Volcanic Rocks in the Western Yarlung Zangbo Suture Zone: Implications for the Opening of the Neo-Tethys Ocean

Abstract

In this study, zircon U-Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone (YZSZ) in southern Xizang (Tibet) yielded an age of 247 ± 3 Ma. According to whole rock geochemical and Sr-Nd-Pb isotopic data, the Early Triassic samples could be divided into two groups: Group 1 with P-MORB affinity, showing initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70253–0.70602, ε_Nd(t) values of 4.2–5.3, (²⁰⁶Pb/²⁰⁴Pb)_t ratios of 16.353–18.222, (²⁰⁷Pb/²⁰⁴Pb)_t ratios of 15.454–15.564, and (²⁰⁸Pb/²⁰⁴Pb)_t ratios of 35.665–38.136; Group 2 with OIB affinity, showing initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70249–0.70513, ε_Nd(t) values of 4.4–4.9, (²⁰⁶Pb/²⁰⁴Pb)_t ratios of 17.140–18.328, (²⁰⁷Pb/²⁰⁴Pb)_t ratios of 15.491–15.575, and (²⁰⁸Pb/²⁰⁴Pb)_t ratios of 36.051–38.247. Group 2 rocks formed by partial melting of the mantle source enriched by a former plume, and assimilated continental crustal material during melt ascension. The formation of Group 1 rocks corresponds to the mixing of OIB melts, with the same components as Group 2 and N-MORBs. The Zhongba Early Triassic rocks belong to the continental margin type ophiolite and formed in the continental–oceanic transition zone during the initial opening of the Neo-Tethys in southern Xizang (Tibet).

Keywords

rift / Early Triassic magmatism / Yarlung Zangbo Suture Zone / Neo-Tethys / Southern Xizang / Tibet

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2023 2023 Geological Society of China