Mafic magmatism in an arc setting: evidence from the Eastern Ghats Province, India and its implication on the tectonic evolution of the Rayner-Eastern Ghats Orogen

Integrated petrological, phase equilibria modelling, whole-rock geochemistry, zircon trace element, and U–Pb geochronology from mafic granulite enclaves within coarse-grained charnockite and felsic gneisses of the Eastern Ghats Province show a complex evolutionary history. Petrological data suggest that the garnet-free (type-A) and the garnet-bearing (type-B) mafic granulites were metamorphosed (M 1 ) to ∼890–900 °C/5.8–6 kbar, and 820–860 °C/7.4−7.8 kbar, respectively. A reworking involved limited dehydration melting of hornblende to tiny intergrowth of pyroxenes and plagioclase. Phase equilibria modelling suggests that the peak mineral assemblages were stabilized at suprasolidus conditions subsequent to crystallization from mafic magmas emplaced into the lower crust. Whole-rock geochemical data indicate a mantle-derived origin of both the mafic magmas, characterized by LILE and LREE enrichment, negative Ti anomalies, and mixed arc-related and enriched MORB–within-plate affinities. Trace-element data suggest derivation of the mafic magma from a fertile mantle source variably influenced by subduction-related processes. Zircon U–Pb ages suggest magmatic crystallization at ca. 953–942 Ma, overlapping with the retrogressive stage of the M 1 metamorphism and second phase of charnockite emplacement in the province, with younger zircon domains recording age of reworking at ca. 915–906 Ma. Spatial and temporal associations of mafic and felsic magmas during the late Neoproterozoic time and their geochemical characteristics imply origin from root zones of a continental arc setting. Their present occurrence as enclaves within charnockite likely reflects tectonic juxtaposition and exhumation of deep crustal levels during accretionary to collisional processes related to the Rayner-Eastern Ghats orogeny.