Zircon U-Pb age and Hf isotopic characteristics of Qushenla Formation volcanic rocks in the middle part of the Bangong Co-Nujiang suture, Tibet

Mesozoic magmatic activities are widely distributed in the Bangong Co-Nujiang suture zone in Tibet, and it is important to study them for understanding the evolution of the Tethys Ocean. This paper reports the zircon U-Pb dating and zircon Hf isotope data of the andesites of the Qushenla Formation in the Dongkaco microcontinental block of the middle Bangong Co-Nujiang suture zone. The zircon ²⁰⁶Pb/²³⁸U weighted age of the andesites obtained from 21 sites is 110.3±0.7Ma. Zircon Hf isotope analysis shows that the zircon ε_Hf(t) varies in the range of -5.66~1.05, and second stage Hf model ages are 1020~1448Ma, showing the characteristics of crust-mantle mixing. Considering regional tectonic sedimentary evolution and previous research results, the authors hold that the volcanic rocks of the Qushenla Formation were probably related to the slab break-offduring southward subduction of the Bangong Co-Nujiang oceanic crust in the Early Cretaceous, and were produced in an intraplate extensional environment. The magma was derived from the mixing of acidic melt formed by deep melting or remelting of mature crustal material in Nyainrong microcontinent with basic melt formed by partial melting of ancient lithospheric mantle.