Multiple stages of melting and melt-solid interaction in the lower crust: new evidence from UHT granulites of Eastern Ghats Belt, India

Abstract

This study documents contrasting style of melt-solid interaction during different stages of evolution from two samples of UHT aluminous granulites from the central part of the Proterozoic Eastern Ghats Belt, India. While the early phase melt (M₁-melt) has largely been lost from the granulitic restite, the secondary melt (M₂-melt) remained in-situ in both the rocks. The M₁-melt is granitic in composition and was produced during the prograde heating stage when the rocks were evolving along an anticlockwise P-T path and could be documented from the sparse occurrence of quartz-plagioclase-perthite leucosome layers in the migmatitic aluminous granulites. The M₂-melt, on the other hand was produced during retrograde decompressive stage, incipient in nature, and evidenced by the presence of undeformed symplectites consisting of cordierite-K-feldspar-quartz. Estimated melt chemistry shows peraluminous and ultrapotassic character. Such incipient melting possibly took place in presence of CO₂-rich fluid during the post-peak decompressive stage and its possible interaction with the solid phases furnishes nature of crustal reworking during the post-Grenvillian age evolution of the lower crust.