Late Triassic granitic magmatism in the Eastern Qiangtang, Eastern Tibetan Plateau: Geochronology, petrogenesis and implications for the tectonic evolution of the Paleo-Tethys

摘要

Triassic granites are widely exposed in the central Qiangtang, northern Tibetan Plateau. They, therefore, made an important contribution to the growth of the Tibetan Plateau. In this paper, we present zircon U-Pb dating and Hf isotopic results, and whole-rock elemental and Sr-Nd isotopic analyses of the Dongdashan (DDS) batholith in the central Qiangtang in order to understand their petrogenesis and tectonic setting. LA-MC-ICP-MS zircon U-Pb results show that the DDS batholith was emplaced at 220.3 +/- 0.7 Ma. All the granites in the DDS possess high A/ CNK values (>1.0) and display peraluminous characteristics, similar to S-type granite. Their strongly fractionated REE patterns ((La/Vb)(N) = 6.98-13.9) with conspicuous negative Eu anomalies (Eu*/Eu = 051-0.67), together with negative epsilon(Nd)(t) and epsilon(Nd)(t) values, and depleted Nd and Hf model ages, suggest that the DDS granitic magma had a dominantly crustal source, likely the Paleoproterozoic basement (i.e., the Ningduo and Caoqu group metasediments) in the area.