Anisotropy of magnetic susceptibility (AMS) and rock magnetic data for Pachmarhi dyke swarm of Deccan

The Pachmarhi dyke swarms, situated in the Eastern part of the Narmada-Satpura-Tapi (N-S-T) dykes of the Deccan Continental Flood Basalt (DCFB), are studied using the Anisotropy of Magnetic Susceptibility (AMS) technique. Here, we determine the direction and sense of magma flow within the dykes to gain insights into the depth, number, and location of magma chambers, as well as the geodynamics of their plumbing system. Petrography and rock magnetism analyses revealed high-titanium magnetite particles, predominantly of Pseudo-Single Domain (PSD) nature, with a smaller proportion of Multi-Domain (MD) grains. We identified four distinct magnetic fabric types (I-IV) within the Pachmarhi dykes. The imbrication of magnetic foliation (for oblate fabric) and magnetic lineation (for prolate fabric) has been employed to discern the direction of magma flow which revealed multiple trends of magma flow, ranging from vertical/sub-vertical to inclined, with one particular dyke exhibiting lateral flow. The intersection of imbrication within the dyke margins provided valuable information about the presence of multiple shallow sub-crustal magma chambers which are supported by independent geophysical evidence and are similar to those of the Nandurbar-Dhule dyke swarms in the western region of the N-S-T dykes. Consequently, it can be inferred that the emplacement of dykes in the Pachmarhi region of the NSL, which were possible feeders to the late-stage Deccan volcanism, was primarily facilitated by a "polycentric flow" mechanism, wherein magma was injected vertically through shallow crustal fissures, potentially feeding into the late-stage Deccan flow units like Ambenali or Mahabaleshwar formation.

Methods
The Anisotropy of Magnetic Susceptibility (AMS) data were acquired from AGICO-made MFK2-FA Kappabridge instrument and data was analysed from Anisoft software (version 5.1.08.) by AGICO, Inc, Brno, Czech Republic (https://agico.cz/text/software/anisoft/anisoft.php ). The AMS data contains orientation of principal susceptibility axes (k1,k2,k3) along with shape parameter (T) and degree of anisotropy (p') etc. The research is motivated to decipher the magma flow pattern in these dykes, whether they were directly related to Reunion hotspot or fed by the fissures.

The Rock Magnetic data were acquired from SQUID-VSM at IISER Bhopal and analysed from RockMag Analyzer 1.1 software by Leonhardt, 2006 (http://earthref.org/tools/rockmaganalyzer/ ).