Assessing Thermal Gradients Across Archean Stratigraphy Using Raman Spectra of Carbonaceous Material Thermometry and Mineral Chemistry in the Western Dharwar Craton, India

Abstract

This study investigates the metamorphic evolution of the Chitradurga Schist Belt (CSB) in the Western Dharwar Craton, India, emphasising its relationship with tectonic processes. Due to the limited availability of ideal mineral assemblages for calculating metamorphic temperatures, we selected metasedimentary rocks containing carbonaceous material (CM) from each stratigraphic unit in the CSB to understand the tectono-metamorphic evolution. Raman spectra of carbonaceous material (RSCM) thermometry was integrated with mineral chemical analyses to elucidate the regional metamorphic conditions. These findings were then coupled with the microstructural evolution and deformation history of the CSB to clarify the tectonic evolution of the terrane. Our findings reveal a distinct metamorphic gradient, with the Bababudan Group exhibiting amphibolite-facies metamorphism at temperatures exceeding 500°C. Other stratigraphic units in the study area recorded greenschist-facies metamorphism at temperatures below 450°C. Detailed examinations of metamorphic mineral assemblages align with RSCM temperature estimates; hornblende is a major constituent in the Bababudan Group and is replaced by actinolite and chlorite during D₂ or D₃ deformation. Hydrous minerals such as muscovite and chlorite are distributed across all stratigraphic units, appearing along S₂ or S₃ foliation. The metamorphism in the Bababudan Group is likely linked to the early stages of collisional events/metamorphism of pre-rift sequences. In contrast, the pervasive hydration and lower-grade metamorphism are associated with the later stages of hinterland-thrust belt formation. This study highlights the significant influence of plate tectonic processes on regional-scale metamorphism and deformation in the Meso-Neoarchean Dharwar Craton.