Petrogenesis of 1000 Ma Felsic Tuffs, Chhattisgarh and Indravati Basins, Bastar Craton, India: Geochemical and Hf Isotope Constraints

摘要

The 1000 Ma felsic tuffs that occur near the top of both the Chhattisgarh and Indravati Basins in peninsular India have been attributed to a "rhyolite flare-up" occasioned by the collision of parts of East Antarctica with India, in what is now the Eastern Ghats Mobile Belt, and the suturing of the North and South Indian cratonic blocks along the Central Indian Tectonic Zone, all during the assembly of Rodinia. In this study we present (1) new U-Pb SHRIMP ages of zircons from the granitic basement; (2) Hf isotopic compositions (laser ablation multicollector ICP-MS) from previously dated zircons from a number of tuff samples and a sample of the Archean basement (Bastar craton); and (3) major, minor, trace, and rare earth element compositions of these and a randomly collected additional set of samples from the Bastar craton basement. We have used these data to infer the petrogenesis of the tuffs. The Hf isotopic data preclude derivation of the parent magmas of the tuffs from simple melting of the basement rocks; geochemical data constrain the source to include garnet, a titanium mineral, and in some cases plagioclase. It is likely that the source was a mafic granulite, possibly in the lower crust, and that the triggering mechanism was farfield stress release during collisional orogenies to the southeast and to the north.