Slab melt metasomatisation of a Paleo-Proterozoic mantle wedge: An insight from the geochemistry of rare Nb-enriched basalt of Singhbhum craton, India

The Paleoproterozoic volcanic sequences of the Singhbhum Craton, Eastern India, encompass a broad compositional range, from ultramafic to felsic lithologies, and preserve important records of early subduction-related magmatism. This study investigates the petrogenesis of a newly identified Nb-enriched basalt (NEB) from the Kanjipani-Telkoi (KT) region, associated with the Malangtoli volcanics, offering key insights into mantle heterogeneity and slab melt-mantle interaction during the Paleo-Proterozoic era. The KT NEB is characterized by high niobium (Nb) levels, ranging from 7 to 29 ppm, along with elevated ratios of (Nb/Th)_PM (0.40-1.86), (Nb/La)_PM (0.29-0.82), and Nb/U (6.99-22.43). These geochemical features suggest that the NEB originated from the partial melting of a metasomatized mantle wedge that had interacted with subducting slab melts. Petrogenetic modeling suggests that the NEB compositions can be generated by ~5–20% partial melting of a metasomatized mantle wedge modified by interaction with high-silica, adakitic slab melts produced by ~15% partial melting of subducting oceanic crust. Furthermore, the chemistry of clinopyroxene in the NEB suggests crystallization at high temperatures, around 1016 to 1141 °C, at shallow to intermediate depths (1.6-7.6 kbar), consistent with conditions typical of a hot subduction environment. Collectively, these results provide robust evidence for Neoarchean–Paleoproterozoic arc magmatism in the Singhbhum Craton and underscore the critical role of slab-melt metasomatism of the mantle wedge in generating Nb-enriched magmas and promoting early continental crustal growth.

Keywords: Singhbhum craton, Nb-enriched basalt, clinopyroxene, slab melts, metasomatized mantle wedge, Partial melting.