Dimension-scaling relationships of Pachmarhi dyke swarm and their implications on Deccan magma emplacement

Abstract

The Continental flood basalts of the Deccan Volcanic Province in India contain three major dyke swarms, namely the Narmada-Satpura-Tapi (N-S-T), the Western Coastal and the Nasik-Pune dyke swarm. The current study area is around Pachmarhi town, Madhya Pradesh, which marks the eastern end of the N-S-T dyke swarm. There are ∼244 mappable doleritic and basaltic dykes around Pachmarhi. The shortest and longest dykes in the area are 140 m and 22 km respectively. The mean length of all the studied dykes is ∼5.15 km. The dykes are in general shorter than those exposed in the western end of the NST swarm in the Dhule-Nandurbar area in Maharashtra. The thickness of the Pachmarhi dykes varies between 3.5 m and 35 m. The dykes exhibit a preferred orientation of N82°E that is parallel to the general trend of the Narmada-Son Lineament (NSL) and perpendicular to the N-S trending paleo extension. In this paper, we present detailed documentation of the scaling relationships of Pachmarhi dyke dimensions, calculate magmatic overpressures during emplacement of dykes and therefore infer magma source depth. Further, we compare the inferred magma source depths among Pachmarhi and Dhule-Nandurbar dykes of Deccan with Early-Neoarchean to Late-Paleoproterozoic Newer dolerite dykes of the Singhbhum craton. Finally, we discuss some possible scenarios of magma emplacement mechanisms for Pachmarhi dykes and relate them to the larger geodynamics of Deccan volcanism.