Insights into the magma dynamics of the multi-pulsed ca. 2.08 Ga Devarabanda dyke swarm, eastern Dharwar craton: Constraints from integrated geochemical, magnetic fabric and emplacement studies

Abstract

The ca. 2.08 Ga Devarabanda mafic dyke swarm in the eastern Dharwar craton exhibits a spectacular radiating geometry spanning 167˚. This study focuses on unravelling the intra-swarm variability in geochemistry and emplacement systematics across its three distinct sub-swarms designated as SS-1, SS-2 and SS-3, trending N, NW, and NE, respectively. Through an integrated study that includes whole rock geochemistry, anisotropy of magnetic susceptibility (AMS), and available geochronology and gravity data, we identify shared differentiation trends across all the sub-swarms, suggesting a common genetic linkage. While crustal influence is evident, the SS-3 displays relatively primitive geochemical signatures, the other two sub-swarms signify more highly differentiated pulses, indicating multiple magma pulses in the ca. 2.08 Ga dyke swarm. AMS analyses reveal lateral magma flow for SS-3, while vertical injection feeds the other two sub-swarms. Based on this study, we propose the role of a mantle plume for the formation of the three sub-swarms; SS-3 formed from a shallow crustal magma chamber during the pre-rift phase, due to a central domal uplift. Subsequently, SS-1 and SS-2 were emplaced at a later rift phase, where SS-2 was emplaced along a pre-existing NW-trending rift, and SS-1 formed during active rifting and crustal thinning. Evidence supporting an older NW-trending rifting event in the region corresponding to the SS-2 exposures was observed from available gravity data. The presence of discrete crustal magma reservoirs, separate for each sub-swarm, surrounding the domal uplift, explains the intervening dyke-poor areas, and suggests the formation of an apical graben as a precursor to the Proterozoic Cuddapah basin.