Lateral, polycentric flow of the Nandurbar-Dhule Deccan dyke swarm inferred from magnetic fabric analysis: Evidence of ‘fissure-fed’ volcanism

The emplacement mechanism of the Deccan province in India had been argued by researchers to a great extent. One of the most favoured hypotheses is “” facilitated by major pre or syn-Deccan crustal extension i.e. the Deccan flood basalts are dyke fed. Determination of flow direction, not only provides indirect evidence in proving or disproving the hypothesis, it also provides clues on its association with a mantle plume, depth of the feeder chambers, etc. In this paper, we have studied Nandurbar-Dhule (DND) Deccan dyke swarm (~210 mappable dykes) from Western India, that intruded compound basaltic (older than dykes) lava flows. Multiple oriented samples were collected from fourteen dykes of the swarm and their magnetic fabrics were delineated by Anisotropy of Magnetic Susceptibility (AMS) technique. The study was complemented by petrography and rock magnetic analysis to decipher the magnetic mineralogy and domain structure. AMS analysis suggests that most of the studied dykes display inclined/lateral flows which are likely in most large dyke swarms. Moreover, the cumulative flow geometry suggests the dominance of polycentric flow i.e. there were multiple magma sources and there were no preferable flow direction. Our results are strongly in line with the geochemical and isotopic signatures (that also establishes lateral, polycentric flow and indicates that the dykes are feeders to the younger Deccan flow) found independently by other groups of researchers. Finally, we discuss the merit of “eruption through fissures” hypothesis and its likely association with a mantle plume in the light of our results.