Crustal thickening-driven late Archean adakitic alkaline magmatism: A marker of Archean-Proterozoic tectonic transition in the Eastern Dharwar Craton

Archean alkaline magmatism is volumetrically minor yet provides critical insights into early crust-mantle interactions and the evolution of the continental lithosphere. This study investigates the origin and geodynamic significance of Late Archean alkaline syenite from the Danduvaripalle area, Eastern Dharwar Craton (EDC), using integrated bulk-rock geochemistry, in situ titanite geochemistry, and U-Pb geochronology. Titanites exhibit low Al/Fe ratios and high rare earth element (REE) contents, indicating an igneous origin. These magmatic titanites yield a well-constrained Late Neoarchean crystallization age of ∼2520 Ma. Strongly fractionated REE patterns in titanites and in the bulk rock indicate persistent garnet control during melt generation. Bulk-rock geochemistry shows classic adakitic features, including high Sr/Y and La/Yb ratios, depleted Y and heavier REE, and strong negative Nb-Ta-Ti anomalies. However, very low MgO, Ni, Cr, and Co contents, together with high Th/U and K 2 O/Na 2 O ratios, rule out slab melting or interaction of slab-derived melt with the mantle. Age-corrected near-chondritic to slightly unradiogenic ε Nd values, overlapping to that observed in the basement rocks, further support a crustal rather than a mantle source. These characteristics together with geochemical and phase-equilibrium modelling point to partial melting of a thickened, compositionally heterogeneous mafic lower continental crust, with garnet, clinopyroxene, and amphibole as stable residual phases during melt generation. We interpret the ∼2520 Ma emplacement of the Danduvaripalle adakitic syenite as a late- to post-collisional event, following crustal thickening and collision between the Eastern and Western Dharwar Cratons. This Late Archean adakitic alkaline magmatism marks a critical tectonic transition from arc-dominated crustal growth to intracontinental reworking and stabilization during cratonization, making it a key marker of the Archean-Proterozoic boundary in the EDC. The Danduvaripalle syenite thus represents a rare Archean example of adakitic alkaline magmatism generated entirely within the continental crust. This finding has broader implications for understanding the thermal and compositional maturation of early continental lithosphere during this pivotal tectonic transition. In addition, the notable REE enrichment in these rocks opens new avenues for future prospecting to evaluate their economic potential for REE extraction.