Platinum group element geochemistry and whole‐rock systematics of the Vempalle sills, Cuddapah Basin, India: Implications on sulphur saturation history, mantle processes, and tectonic setting

Th. Dhanakumar Singh, C. Manikyamba

The intracratonic Cuddapah Basin of southern peninsular India has multiple phases of magmatism exposed as mafic intrusives and extrusives in the Vempalle and Tadpatri formations. We report platinum group element geochemistry along with whole‐rock systematics of the mafic sills from the Vempalle Formation to understand their sulphur saturation history, source characteristics, and tectonic setting. These sills are medium‐ to fine‐grained dolerites with plagioclase and pyroxenes as essential minerals exhibiting sub‐ophitic to intergranular texture. Geochemically, they are characterized by moderate MgO (6.3–8.5 wt.%), Ni (55–105 ppm), Cr (20–130 ppm), and ∑PGE (22–61 ppb) contents and exhibit transitional to calc‐alkaline in nature. Primitive mantle‐ and chondrite‐normalized trace and rare earth element patterns display relative enrichment of LILE–LREE over HFSE, suggesting plume‐related intraplate magmatism with contributions from subcontinental lithospheric mantle (SCLM), lithosphere–asthenosphere interaction, crustal contamination, and fractional crystallization. Their REE relationship indicates the generation of parent magma from a heterogeneous source marked by 10–25% polybaric partial melting within spinel and garnet lherzolite domain. Platinum group elements (PGE) geochemistry reveals their sulphur‐undersaturated nature, and sulphide fractionation played a key role in the distribution of PGEs, which is evidenced by their enriched character, moderate degrees of partial melting, and crustal contamination. Further, the negative platinum anomalies in these sills indicate its removal during fractional crystallization, and the enrichment of Pd over Pt endorses the decoupling nature of these elements prior to their emplacement. Diagnostic trace element signatures and their relationship corroborate a riftogenic intraplate tectonic regime for the emplacement of the Vempalle sills through an ocean–continent transition zone.

Map of study area

Geological Journal. 2020;55:1300–1319

DOI: 10.1002/gj.3459