Arc-Related Pyroxenites Derived from a Long-Lived Neoarchean Subduction System at the Southwestern Margin of the Cuddapah Basin: Geodynamic Implications for the Evolution of the Eastern Dharwar Craton, Southern India

AbstractMineralogy and bulk-rock geochemistry (including Sr and Nd isotopes) of two ultramafic (pyroxenite) intrusions at Gurramkonda, situated adjacent to the southwestern margin of the Paleo-Mesoproterozoic Cuddapah Basin within the Eastern Dharwar Craton, southern India, are presented. The pyroxenites have a characteristic cumulate texture, with a predominance of pyroxene (augite) and amphibole (hornblende and actinolite), whereas chromite is present mostly as inclusions in pyroxene. Mineral chemistry of these ultramafics is akin to that of arc cumulate rocks, particularly those associated with the Alaskan-type complexes, formed in suprasubduction zones. High Mg#’s (72–74), coupled with high bulk-rock Ni (830–1130 ppm) and Cr (1110–1,360 ppm), strikingly correspond to those of continental arc cumulates. The enrichment of large ion lithophile elements over high field strength elements, conspicuous negative Nb-Ta, Zr-Hf, and Ti anomalies, and chondrite-normalized light rare earth element patterns highlig...