Geochemistry of Granitoids Adjoining the Raichur Belt, Eastern Dharwar Craton: Implications on Crustal Evolution

ABSTRACT The Dharwar Craton in southern India represents one of the most ancient and extensively studied segments of the Indian shield, characterised by a complex and prolonged geological evolution spanning from the early Archaean to the Proterozoic. It comprises a wide array of granitoids and gneisses, reflecting multiple episodes of magmatism, crustal reworking, and tectonic deformation. Based on geochronological and metamorphic evidence, the craton is subdivided into the Palaeo- to Mesoarchaean Western Dharwar Craton (WDC) and the predominantly Neoarchaean Eastern Dharwar Craton (EDC), separated by a major shear zone along the Chitradurga greenstone belt. The EDC features narrow, linear schist belts (e.g., Kolar, Raichur, Hutti, and Ramagiri) characterised by gold mineralisation and widespread granitoid intrusions. In this paper, granitoid plutons adjoining the Raichur belt are studied from their petrographic and geochemical aspects. These granitoids include tonalite-granodiorite, sanukitoid, biotite granite, two-mica granite, and hybrid varieties. SiO2 in these granitoids ranges from 58 to 74 wt%, and A/CNK 0.68 to 1.31. Further, they are characterised by a fractionated Rare Earth Element (REE) pattern (LaN/YbN=12-91) and a distinct negative Eu anomaly. Their geochemical characteristics suggest complex petrogenetic processes involving partial melting of mantle and crustal sources, magma mixing, and crustal reworking. Their spatial distribution and geochemical signatures indicate a dynamic tectonic environment involving terrane accretion, crustal thickening, and thermal perturbations during the late Archaean to early Proterozoic transition.