Insights into the crustal architecture from the analysis of gravity and magnetic data across Salem-Attur Shear Zone (SASZ), Southern Granulite Terrane (SGT), India: an evidence of accretional tectonics

Abstract

The gravity and magnetic surveys were carried out across E-W trending Salem-Attur Shear Zone (SASZ), Southern Granulite Terrane (SGT), India. The study envisages detail crustal architecture/ fabric across the SASZ from the analysis of potential field data. The Bouguer gravity map shows a circular gravity high closure over ultramafics complex of Chalk hill. Gravity model indicates that the complex is a spherical plug type body with depth extension of ~7-8 km. The SASZ is reflected by dominantly E-W trending elongated isogals with low gravity values and depth extension of 3-4 km. The gravity high anomaly at the southeastern part of the SASZ indicates a high-density crustal unit that might have accreted along the southern margin of the shear zone. The magnetic map shows a high anomaly zone in the north-western block of the study area and bordered by a predominantly low anomaly zone at the southeastern boundary. The gravity-magnetic joint modelling reveals that a plane in south of the SASZ separates two upper crustal unit of contrasting density and susceptibility. The study indicates evidence of accretional tectonic in the southern margin of Dharwar Craton (DC) through arc magmatism. The SASZ has a shallow vertical extension (~4 km) and is characterized by diamagnetic rock.