Controls of evolution of mineral assemblages in ultrahigh-temperature metamorphosed Mn-carbonate-silicate rocks from the Eastern Ghats Belt, India

Abstract

A unique suite of Mn-silicate-carbonate rocks from the Eastern Ghats Belt, India, were metamorphosed under ultrahigh temperatures and exhibit contrasting mineral assemblages in closely spaced domains. Development of contrasting assemblages under isothermal-isobaric conditions is attributed to initial variations in fluid composition particularly a_CO2, and bulk-rock Mn:Mg:Al:Si:Ca ratios. The fO₂ was buffered near the QFM buffer during peak metamorphism. Garnet shows a sharp increase in Fe⁺³ content towards the rim, which is interpreted to be the result of increased a_CO2 during later stages of evolutions of the rocks due to channelled fluid flux. At the terminal stage of evolution, the rocks suffered hydration at lower temperatures.