Establishment of Correlation between Anisotropy of Magnetic Susceptibility and Magma Flow Fabric:An Insight from Nandurbar–Dhule Dyke Swarm of Deccan Volcanic Province

Abstract

There are rising concerns about the robustness of interpretation from Anisotropy of Magnetic Susceptibility (AMS) studies, because often correlation between AMS and geological fabric is not properly established before a wide regional- scale interpretation is made. Here, we document case studies on two dykes from the Nandurbar–Dhule dyke swarm (western India) of Deccan Volcanic Province (Figure 1 a), where we have tested if shape-preferred orientation of the elongated mineral grains (flow fabric) is actually represented by AMS fabric. In one of the dykes, we observed that AMS fabric is coplanar with the fabric of major constituent silicate minerals; hence it represents magma flow fabric. In the other dyke, AMS fabric largely represents the shape fabric of the opaque minerals which were deposited in the interstitial spaces of the mineral grains after the dyke was emplaced; hence it does not correspond to the primary magma flow fabric. These findings reinforce the need for detailed understanding of rock fabric in order to make robust interpretation of AMS data.