Early Carboniferous continental margin magmatism in central Qiangtang, Tibet: Implications for the geological evolution of the Paleo‐Tethys Ocean

Abstract

We report zircon U-Pb age and Hf isotopic data, and whole-rock major and trace element data for diverse volcanic rocks from the Riwanchaka region of central Qiangtang, Tibet, including andesite and dacite. Zircon U-Pb dating of andesite yielded a magmatic crystallization age of 358.5 Ma, indicating that the volcanic rocks were erupted in the early Carboniferous. The zircons from the andesite samples have εHf(t) values from +8.27 to +11.5 and single-stage Hf model ages of 533-670 Ma. All of the samples are calc-alkaline, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta, Ti, and P, which are geochemical features typical of arc volcanic rocks. Geochemical and isotopic data indicate that the andesites were generated by partial melting of a mantle wedge, whereas the dacites originated by fractional crystallization of coeval andesitic melt. Compared with typical arc rocks, the Riwanchaka volcanic rocks resemble those from active continental margins. Our new and previously published data enable us to correlate the subduction-related volcanic arc rocks in the Riwanchaka area to the northward subduction of the Paleo-Tethys oceanic lithosphere.