Phase equilibria modelling, fluid inclusion study, and U-Pb zircon dating of ultra-high temperature mafic granulites from Rampur domain, Eastern Ghats province: implications for the Indo-Antarctic correlation

Abstract

The study area (Rampur domain) is situated to the east of the Eastern Ghats Boundary Shear Zone (EGBSZ) and encompasses portions of the granulite facies rocks of the exhumed Proterozoic Eastern Ghats Province (EGP), India. The EGP is characterized by a diverse array of rock types, featuring a wide variety of mineral parageneses and chemical compositions, including charnockite, mafic granulite, Mg-Al granulite, felsic granulites, amphibolite, khondalite and anorthosite. In this study, we report for the first time evidence of ultra-high temperature (UHT) metamorphism within the mafic granulites of the relatively unexplored Rampur domain of the Eastern Ghats Province, using the two-pyroxene assemblage. The stable mineral assemblage present during peak metamorphism typically includes garnet, orthopyroxene₁, clinopyroxene, hornblende₁, quartz, and plagioclase₁. The consumption of garnet observed in different reaction textures, alongside the formation of striking orthopyroxene₂–plagioclase₂ and hornblende₂–plagioclase₂ symplectites, represent the later phases of metamorphism. By applying TWQ calculation procedures to the mineral core compositions, we have determined peak metamorphic conditions of approximately 970 °C at a pressure of 10.5 kbar. Zircon dating results from LA-HR-ICP-MS indicate upper intercept ages of 2509.9 ± 21.7 Ma and 2479.9 ± 21.0 Ma for the protolith, while lower intercept ages of 965.7 ± 40.7 Ma and 979.8 ± 18.1 Ma correspond to the metamorphic age of the analyzed samples E-185 and E-186, respectively. Based on the textural relationship, derived zircon ages, fluid-P-T constraints, and P-T pseudosection model, we propose a decompressional evolutionary P-T-t path that supports the Neo-Proterozoic assembly of the Indo-Antarctic region.