Petrogenesis of Paleoproterozoic Khalari Hornblende-Pyroxenite Intrusion Within the Dongargarh Supergroup, Bastar Craton: Insights From Petrological and Geochemical Studies

Abstract

This study investigates Paleoproterozoic hornblende pyroxenite, a lithological unit within the Khalari Ultramafic-Mafic Complex (KUMC), which is intruded into the Neoarchean-Paleoproterozoic Dongargarh Supergroup near Khalari village in the northern Bastar Craton. A comprehensive characterisation has been conducted through petrological analysis, bulk-rock geochemistry, mineral chemistry, and platinum group elements (PGEs)-Au geochemical studies to understand its petrogenesis and geotectonic implications. The presence of primary amphibole, specific pyroxene chemistry (low Ti and Cr), and enriched LILE, LREE and fluid-mobile elements alongside negative Nb–Ta–Ti anomalies suggest these rocks were crystallised from a mantle melt originated from a metasomatized sub-continental lithospheric mantle (SCLM) source. This metasomatization could be due to fluids derived from a subduction event predating the emplacement of the studied rocks. The proposed melt composition is estimated to have formed from 5% to 10% partial melting of a garnet-rich peridotite mantle source. The crystallisation conditions are estimated to have occurred at an average pressure of 7.85 kbar and a temperature of 902°C, indicating moderately shallow depths influenced by fractional crystallisation and slow cooling rates. The emplacement of the KUMC is contemporaneous with several other magmatic activities in the Bastar Craton, around ca. 2.50–2.47 Ga, suggesting that mantle plume might have played a significant role in their formation. Low concentrations of PGEs in the studied samples indicate a PGE-depleted mantle source.