Provenance of Neoarchaean metagreywackes on the western margin of the Western Dharwar Craton, South India: Implications for Madagascar − Western Dharwar Craton connection

Abstract

Neoarchaean, low-grade metamorphic greywackes of the Ranibennur Formation of Chitradurga Group of Dharwar Supergroup, from the Western Dharwar Craton (WDC) were studied to understand their provenance. The metagreywackes consist of detrital quartz, feldspar and volcanic and plutonic lithic fragments in a chlorite-sericite-dominated matrix. They have low to moderate chemical indices of alteration (CIA) (50 to 60.4). The metagreywackes are characterized by fractionated light rare earth element (LREE) and moderately fractionated heavy rare earth element (HREE) patterns (Gd_N/Yb_N 1.0–3.97) and negative Eu/Eu* anomaly (∼0.79). The detrital zircon ages indicate an overwhelming contribution from 2.56 − 2.57 Ga and 2.67–2.68 Ga sources. Integration of their petrographic and geochemical characteristics suggests a provenance composed of a mix of recycled and arc-derived sediments. A four component mixing model indicated ∼55 % of tonalitic-trondhjemitic to granodioritic; 17 to 20 % of granitic, 20–22 % mafic volcanic and 3–5 % ultramafic rocks constituted the provenance composition. The rarity of igneous 2.67–2.68 Ga source rocks in the Dharwar Craton and the presence of such rocks in the eastern part of Madagascar suggest that the detrital zircon grains of that age were mainly derived from eastern Madagascar. This would imply that eastern Madagascar was part of the Dharwar Craton.