Petrography and Geochemistry Study of the Madharam Lamprophyre Dyke, Western Margin of the Proterozoic Pakhal Basin Within Eastern Dharwar Craton, Khammam, Telangana, India

Abstract

Various lamprophyre types are prevalent throughout the Cuddapah Igneous Province (CIP) and Prakasam Alkaline Province (PAP) in the Eastern Dharwar Craton (EDC), located in southern India. This study focuses on a newly identified lamprophyre dyke situated near the Madharam area in Khammam District, Telangana, India (coordinates 80°15ʹ:17°32ʹ) on the northeastern edge of the EDC. The paper provides an in-depth analysis of the petrography and geochemistry of this lamprophyre. The study area predominantly comprises granitoids from the Peninsular Gneissic Complex (PGC) within the EDC. Geographically, it is flanked by the Proterozoic sedimentary basins of Pakhal to the east and Cuddapah to the south. The Madharam lamprophyre exhibits a characteristic porphyritic-panidiomorphic texture, with clinopyroxene phenocrysts occurring alongside feldspar in the groundmass. Amphiboles present in the rock are of calcic variety (mainly actinolite group). Clinopyroxene is found to be diopside in nature (Wo48-50 En40-41 Fs9-10) and the feldspars show albitic (Or0Ab85-92 An 6-14) nature. Lower TiO2 content in the amphibole and clinopyroxene suggests the nature of the lamprophyre is calc-alkaline. The geochemical signatures, such as variable Ba/La ratios and low Nb/La values, suggest minimal to no crustal contamination in the lamprophyre magma. These findings are significant for understanding the evolution of the EDC and provide important constraints on the geodynamics of southern peninsular India.