Tectonic significance of the shear zones in Southern Granulite Terrane: An integrated geophysical study

Abstract

• The crustal models derived reveal Moho depth at ∼40 km near MBSASZ. • The increased crustal thickness near MBSASZ can be related to collision. • MBSASZ and PCSZ have different tectono-magmatic history. • Eastward marine prolongation of MBSASZ and PCSZ up to the COB. • The tectonic events in SGT are vital to understand the Precambrian shields. The tectonics of Southern Granulite Terrane (SGT), one of the most important Archean- Neoproterozoic terrain, is unveiled by the gravity-magnetic signatures associated with the complex shear zone system. The significance of gravity and magnetic anomalies and the comparison between the two anomalies elucidate the structural complexity of the region. Though Moyar Bhavani Salem Attur Shear Zone (MBSASZ) and Palghat Cauvery Shear zone (PCSZ) have been identified as the major crustal scale shears, it shows significant difference in their anomaly pattern. A four-layer crustal model derived from gravity and magnetic anomalies is further constrained by seismic information. Along the PCSZ, gravity gradient was subdued and magnetic gradient shows a low in contrast to the magnetic high associated with the MBSASZ suggesting that it might belong to two different crustal terranes. The increase in crustal thickness along MBSASZ also could be explained on the context of the compressional tectonic regime. It is evident that the major shear zones of SGT is extending to the offshore region which suggest that deformation might have extended to the adjacent continents in the geologic past. This leads to an important conclusion that the tectonic events portrayed by SGT is not confined to the terrane alone, but plays an important role in understanding the tectonics in the context of the East Gondwana fragmentation and dispersal.