A fresh look at the physicochemical evolution of the lithospheric mantle beneath the Dharwar craton (India)

The physicochemical evolution of cratonic lithosphere reflects the impacts of tectonomagmatic processes over its lifetime that may be deciphered using kimberlite-borne xenoliths and xenocrysts, but remain poorly constrained for the Indian Dharwar craton, owing to the dearth of fresh mantle material. This study examines detailed petrography and geochemical composition of six eclogite xenoliths, and additional eclogitic and peridotitic garnet separates, from the Wajrakarur kimberlites in the Eastern Dharwar Craton (EDC). Clinopyroxene in eclogite xenoliths is too altered to permit contamination-free sampling during laser ablation for trace element analysis. We overcome this limitation by exploiting relationships of clinopyroxene-garnet distribution coefficients with garnet Ca#, clinopyroxene jadeite content, and temperature. This allows a more accurate delineation of their petrogenesis from reconstructed bulk rocks and indicates their origin from variably plagioclase-rich oceanic crustal protoliths, with weak subsequent metasomatic overprint. In contrast, estimates of Fe³⁺ in garnet from peridotite xenoliths indicate an oxygen fugacity shift towards more oxidized conditions beneath the EDC linked to enrichment in melt-mobile elements (Ti, Zr) in the barren or weakly diamondiferous P1 and P3 kimberlites. The most depleted and reduced sample [ΔlogfO₂ (FMQ) of -4.3; where FMQ corresponds to the fayalite-quartz-magnetite buffer] derives from diamondiferous kimberlite P7, suggesting oxidative melt metasomatism as a key control on the regional diamond inventory, although more data are needed. EDC eclogites and peridotites have estimated P-wave velocities of 8.46–8.63 km/s and 8.21–8.22 km/s, respectively, which are lower than present-day observed bulk P-wave velocities, and may point to lithological or thermal changes since Mesoproterozoic entrainment.