Petrogenesis of late Eocene high Ba-Sr potassic rocks from western Yangtze Block, SE Tibet: A magmatic response to the Indo-Asian collision

Abstract

The Indo–Asian collision resulted in extrusion of the Indochina Block along the Ailao Shan–Red River (ASRR) shear zone in the Cenozoic, with the emplacement of widespread potassic magmatic rocks. In this contribution, we investigated five potassic felsic intrusions exposed in the western Yangtze Block adjacent to the ASRR shear zone, including the Xiaoqiaotou, Jianchuan, Yuzhaokuai, Laojunshan and South Taohuacun intrusions. New LA–ICP–MS zircon U–Pb results in combination with previous data indicate that these felsic rocks have identical crystallization ages of ∼36–35Ma. They are characterized by high Ba (mostly >1500ppm) and Sr (mostly >1000ppm) abundances, with high K2O contents and K2O/Na2O ratios. They exhibit similar Sr-Nd isotopic components as the coeval shoshonitic mafic rocks exposed in the studied area. Elemental and isotopic data suggest that the five intrusions were likely derived from fractional crystallization of shoshonitic mafic magmas originating from an enriched lithospheric mantle. On the basis of previously published data and results in this paper, we considered that the lithospheric mantle underneath the western Yangtze might have undergone enrichment events twice at least, including the Neoproterozoic oceanic subduction and the Neo-Tethyan oceanic subduction.