Petrogenesis and Emplacement Age of Karamadai Granites, Southern India: Evidence from Geochemistry, Zircon Typology and U-Pb SHRIMP Geochronology

ABSTRACT

Geochemistry, zircon typology, and U-Pb geochronology of Karamadai granites (KG) forming the KG pluton in the Palghat-Cauvery Shear Zone (PCSZ), Tamil Nadu, India, have been investigated to decipher the petrogenesis and timing of KG magmatism and crustal growth. KG is classified as slightly metaluminous (I-type), with enrichment in SiO2 (70.88-75.5 wt.%) and alkalies (K2O+Na2O=8.29-9.85 wt.%). It belongs to the alkalic and alkali-calcic series and formed within syn-collisional to late-orogenic tectonic regimes. Zircon grains from the KG sample (19-3) are subhedral to euhedral, display oscillatory zoning, and show diverse typology (mainly S2-S3 types) reflecting magmatic evolution in crust-derived granite melts. Zircon U-Pb SHRIMP data from a granite sample (19-3) indicate high Th/U (>0.1) and yield a weighted mean age of 554±16 Ma, interpreted as the zircon crystallization age or emplacement age of the KG pluton. This age corresponds to late Neoproterozoic-early Cambrian Pan-African magmatism, suggesting that KG formed during crustal reworking and magmatic activity linked to syn- to late-orogenic tectonic regimes during Gondwana assembly and growth.