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