Metamorphic evolution of sapphirine-and sodicgedrite-anorthite-bearing granulites, Rampur domain, Eastern Ghats Province, India
Description
The Eastern Ghats Belt (EGB) have been extensively explored by the geoscientific community since few decades, however, there still prevail some gaps regarding the unique mineral assemblage reported through this communication. This study documents the occurrence of sapphirine, spinel, orthopyroxene, sodic-gedrite, calcic-amphibole, biotite, and plagioclase assemblage resulting in UHT metamorphic conditions. The significance of this study lies in the peculiarity of sapphirine being present within anorthite matrix which has been reported for the first time from the Indian subcontinent. The studied assemblage has also been correlated with the more or less similar assemblage of rock called ‘Sakenites’ reported from southern Madagascar to unravel the most probable source rock anorthosites which led to such rare UHT mineral assemblage. Also, the gedrite present in the assemblage is Na-rich representing high-grade phase sodic-gedrite which had traversed across the amphibolite facies before attaining conditions of UHT granulites. The P-T path estimated also reveals decompression path with almost uniformly decreasing P-T conditions in contrast to the commonly reported isothermal decompression path from various other domains and provinces of the EGB. Another important aspect that needs to be highlighted is the UHT conditions of metamorphism at low to moderate pressures of 5.5 kbar. The corresponding retrograde assemblage has been recalibrated by the sequential removal of sapphirine and spinel while T-X (H2O) diagram is also constrained that suggests low water contents in the assemblage during the peak metamorphic condition. Conversely, high-water contents during retrograde history of the studied granulites have been reported through T-X (H2O) constraints. The introduced source of fluid is thought to be external during the later stages of exhumation and subsequent upliftment. The analysed EMP U-Th-total Pb monazite chemical age constraints also suggest Mesoproterozoic to Neoproterozoic episodes corresponding to ~846 Ma to ~959 Ma pair of thermal events. These metamorphic events have also been correlated to reconstruct the Rodinian supercontinent at ~959 Ma and the initiation of its subsequent break-up at ~846 Ma.