Magnetic fabric analysis of meta-ultramafic rocks and associated gneisses from the Moyar Shear Zone, Southern Granulite Terrane, India

Abstract

The magnetic fabric of the meta-ultramafic rocks and the associated gneisses in the Wayanad district, in the Moyar Shear Zone (MOSZ) of the Southern Granulite Terrane (SGT) of the state of Kerala, in India has been investigated using Anisotropy of Magnetic Susceptibility (AMS) and its low-field variation, as well as temperature variation of magnetic susceptibility vs temperature (Tc). The dominant magnetic minerals that control and contribute to the magnitude of the AMS were quantified and the regional deformation in the area and its effects on the rock types deciphered. The mean bulk susceptibility of the two rock types indicates the ferromagnetic character in the area. Ferromagnetic and ferrimagnetic minerals – magnetite and maghemite – are the major magnetic mineral contributors of AMS in the meta-ultramafic rocks of Wayanad whereas the mafic minerals – garnet, hornblende, biotite, and pyroxene – influence the magnetic bulk susceptibility in the gneisses. The development of fabric in the meta-ultramafics of Wayanad has an intimate evolutionary relationship with the gneisses and the shear zone itself. This has been demonstrated by magnetic and field-based studies. Both the magnetic foliation of the meta-ultramafics and the gneisses have orientations that fit well with the occurrence of the meta-ultramafic body in the field within the orientation of the Moyar Shear Zone.