Eocene magmatism in the Gaoligong orogen, southwestern Yunnan, and its response to the collision of the India-Eurasia

The Gaoligong orogen is the eastern boundary of the Tengchong block, and the Cenozoic granites outcropped in this orogen are related to the collision of the Indian and Eurasian plates. Here we report a new chronological and petrochemical study for the Eocene granites from the Gaoligong orogen in eastern Tengchong block. The zircon LA-ICP-MS U-Pb dating from three granites yielded weighted mean Pb-206/U-238 ages ranging from 47Ma to 43Ma. The zircon epsilon(Hf)(t) values show a range of -8.4 similar to -0.8 with t(DMC) of 1317 similar to 1730Ma for Jiujinliang and Dazhongshan granites, and -7.0 similar to + 5.7 with tDMC of 907 similar to 1531Ma for Dongjiayuan granite. These rocks are characteristized by high-K calc-alkaline, high SiO2, K2O and low CaO, P2O5 contents, metaluminous to peraluminous, enrichment of LILE and LREE, with strongly negative Ba, Nb, Sr, P and Ti anomalies, indicating a collision affinity. These features shows that the granitic magmas for the Jiujinliang and Dazhongshan granites are derived from the partial melting of the Mid-Neoproterozoic metasedimentary rocks, while the Dongjiayuan granite was considered to be derived from melting of metaigneous and metasedimentary rocks. According to petrological and geochemical characteristics of these granites together with the tectonic diagram analysis, all of these granites are formed within a collision-related tectonic setting. The Eocene magmatism is the response to the collision of the Indian and Tengchong blocks.