Geochronology, geochemistry and tectonic evolution of the basaltic trachyandesite in Huize, northeastern Yunnan Province

Several small-scale basalt trachyandesite rock masses were found in NNE direction in Emeishan basalts of Huize area, northeastern Yunnan Province. Based on detailed field geological survey, microscopic petrographic analysis, zircon U-Pb dating and rock geochemical test, the authors studied the formation age and geochemical characteristics of these basalt trachyandesites and their tectonic evolution process. LA-ICP-MS zircon U-Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U age of(251.6±4.2)Ma (MSWD=0.20) for the basalt trachyandesite, and the alteration ages are(143.5±1.9) Ma and(150.5±2.4) Ma, respectively. The content of SiO₂ in basalt trachyandesite is between 52.09%-54.10%, implying that it belongs to the intermediate basic volcanic rock. The Mg^# values of basalt trachyandesite are from 19.88 to 40.86, and the TAS diagram generally shows that it belongs to alkali basalt trachyandesite series. The characteristics of REE and trace elements show that the basalt trachyandesite of Huize was derived from enriched mantle source. In the process of magmatic evolution, a part of clinopyroxene, plagioclase and magnetite experienced fractional crystallization. It is considered that the basalt trachyandesite of Huize is a part of Emeishan basalts, and that it might have been the product of the extinction of Emeishan mantle plume.