Magnetic fabrics and magnetic mineralogical variations in Lava Channel: an example from the Deccan Volcanic Province, India

Abstract

A ~3000 m long exposure of paleo-lava channel body within the Deccan volcanic province (India) has been investigated for mineral magnetism and anisotropy of magnetic susceptibility (AMS) to examine the lava flow-related fabrics. Distinct gradient from ferrimagnetic to antiferromagnetic mineralogy along the channel indicated progressive oxidative mixing. The AMS studies along and across the channel profiles decipher a combination of factors responsible for the resultant fabrics. Various dominating mechanisms including gravity settling, grain imbrications, viscous shear and competitive mineral readjustments penultimate to cooling appears to have imparted the final/resultant fabric. The orientation of principle susceptibility axes (K1-K2-K3) and petrographic observations define three major types of fabrics as: (I) mineral lineation, (II) crystal settling and (III) crystal-matrix-re-adjustment. The resultant of type I along with imbrications is generally observed along the axial part, while type II are developed during lava residency; and the opaque−non-opaque interlocking with groundmass resulted in type III fabrics. A three-stage model is produced to resolve the plausible sequence of fabric development during various stages of the lava flow formation. More detailed AMS studies on the Deccan lavas are envisaged to lead semi-quantitative information on fluid dynamical forces governed by slope gradients and gravity, dynamic thermal changes in viscosity, shear and the effects of paleotopography.