AMS studies on a 450 km long 2216 Ma dyke from Dharwar craton, India: Implications to magma flow

Anisotropy of magnetic susceptibility (AMS) studies were carried out on a precisely dated (2216.0±0.9 Ma), 450 km long N-S striking dyke in the Dharwar Craton, to determine the magma flow direction along the dyke length. In order to use the imbrication of the magnetic foliation, forty eight samples were collected from 13 locations along the length of the dyke. Magnetogranulometry studies show that AMS fabric is dominated by medium grained interstitial Ti-poor multidomain magnetite. The corrected anisotropy degree (P_j) of the samples was found to be low to moderate, between 1.007 and 1.072, which indicates primary magnetic fabric. The magnetic ellipsoid is either triaxial, prolate or oblate and clearly defines normal, intermediate and inverse magnetic fabrics related to magma flow during the dyke emplacement. The maximum susceptibility axes (K_max) of the AMS tensor of the dyke is predom inantly inclined at low angles (<30°), with no systematic variation in depth along the N-S profile, indicating sub-horizontal flow even at mid crustal levels which could probably be governed by location of the focal region of the magma source (mantle plume?), flow dynamics together with the compressive stresses exerted by the overlying crust.