Mid-Neoproterozoic arc magmatism in the northeastern margin of the Indochina block, SW China: Geochronological and petrogenetic constraints and implications for Gondwana assembly

Abstract

The mid-Neoproterozoic high-K calc-alkaline granitoids in the northeastern margin of the Indochina block, SW China, provide important insights into the relationship of the Indochina block with the Gond- wana supercontinent. Here we report zircon LA-ICP-MS U–Pb data from the granitoids which show weighted mean 206 Pb/ 238 U ages ranging from 754 to 767 Ma, representing their timing of emplacement. The zircons from the granitoids have ε Hf (t) values ranging from −0.2 to −7.9, with a mean of −1.9 to −4.6, and T C DM varying from 1713 to 2156 Ma. The granitoids are characteristized by high Mg # , weakly negative Eu anomalies, enrichment of LILE (Rb, Ba, Th and K) and LREE (La, Ce, Nd), strong depletion of HFSE (Nb, Ta, Sr, P and Ti), with most of the samples falling within the field of volcanic arc granitoids. The Hf isotopic data and geochemical signatures compare these granitoids with typical calc-alkaline mag- mas generated in active continental margins within a subduction-related (island-arc or continental-arc) tectonic setting, with the magma mainly sourced from the partial melting of the ancient crust together with a minor mantle-derived component. The rocks reported in our study and their ages are similar to those occurring along the northwestern margin of Greater India, and suggest the juxtaposition of India and Indochina within the Gondwana reconstruction.