Structural attributes of Pachmarhi Deccan dykes and Newer Dolerite dykes of Singhbhum Craton: implications in magma emplacement mechanism

The Deccan Continental flood basalts are associated with three major dyke swarms, namely the Narmada-Satpura-Tapi (N-S-T), the Western Coastal and the Nasik-Pune dyke swarm. The Pachmarhi dykes are located in the eastern part of the Narmada-Satpura-Tapi (N-S-T) dyke swarm in Madhya Pradesh, India. Here, we used the structural attributes of Pachmarhi dykes to quantify the magmatic overpressure and the source depth of the magma chamber and further compared the results with the Newer dolerite dykes (NDDs) of Singhbhum. There are ~244 mappable doleritic and basaltic dykes around Pachmarhi with the shortest and longest dykes of 140 m and 22 km, respectively (Shukla et al., 2022). The mean dyke length is ~5.15 km. The Pachmarhi dykes are in general shorter than those exposed in the Western end of the N-S-T swarm in the Dhule-Nandurbar area in Maharashtra (Das et al., 2021; Ray et al., 2007). The thickness of the Pachmarhi dykes varies between 3.5 m and 35 m. The Pachmarhi dykes exhibit a preferred orientation of N82°E that is parallel to the general trend of the Narmada-Son Lineament (NSL). The calculated magmatic overpressure for Pachmarhi dykes varies between 3.71 MPa to 52.22 MPa, with an average of 23.08 MPa, whereas the source depth of the magma chamber varies between 1.81 km to 25.38 km with an average of 11.21 km; considering average Young’s modulus of 11 GPa (Shukla et al., 2022). We compared the inferred magma source depths of the Pachmarhi and Dhule - Nandurbar dykes of Deccan (Ray et al., 2007); confirming the presence of numerous shallow magma chambers in the upper crustal levels for both cases (Shukla et al., 2022). The Singhbhum NDDs have fewer shallow crustal magma chambers compared to the Pachmarhi and Nandurbar-Dhule dykes. The emplacement of NDDs could be directly from the plume-induced Sub-Continental Lithospheric Mantle (SCLM; Pandey et al., 2021) and/or from the shallow crustal magma chambers, which can serve as a trap or barrier to store the magma from deeper magma sources (Shukla et al., 2022).References: Das, A., Mallik, J., Banerjee, S., 2021. Characterization of the magma flow direction in the Nandurbar-Dhule Deccan dyke swarm inferred from magnetic fabric analysis. Phys. Earth Planet. Inter. 319, 106782. https://doi.org/10.1016/j.pepi.2021.106782 Pandey, O.P., Mezger, K., Upadhyay, D., Paul, D., Singh, A.K., Söderlund, U., Gumsley, A., 2021. Major-trace element and Sr-Nd isotope compositions of mafic dykes of the Singhbhum Craton: Insights into evolution of the lithospheric mantle. Lithos 382–383, 105959. https://doi.org/10.1016/j.lithos.2020.105959 Ray, R., Sheth, H.C., Mallik, J., 2007. Structure and emplacement of the Nandurbar-Dhule mafic dyke swarm, Deccan Traps, and the tectonomagmatic evolution of flood basalts. Bull. Volcanol. 69, 537–551. https://doi.org/10.1007/s00445-006-0089-y Shukla, G., Mallik, J., Mondal, P., 2022. Dimension-scaling relationships of Pachmarhi dyke swarm and their implications on Deccan magma emplacement. Tectonophysics 843. https://doi.org/10.1016/j.tecto.2022.229602