Contrasting metamorphism across cauvery shear zone, south India

Abstract

The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating the metamorphic history of the southern granulite terrane (SGT). In the mafic granulites occurring to the south of CSZ, evidence of garnet breaking down during near isothermal decompression (ITD) is indicated by the development of orthopyroxene + plagioclase moats in between quartz and garnet. The presence of comparatively small elongated second generation garnet embedded in pyroxenes from the mafic granulites occurring to the north of CSZ is indicative of the garnet formation via reaction between pyroxenes and plagioclase, which occurred during isobaric cooling (IBC). Rocks occurring to the south of CSZ have recorded comparatively higher temperature and pressure (849‡C and 9.6kbar) than those occurring to the north of the CSZ (731‡C and 8.6kbar) using conventional geothermobarometry. The rocks occurring to the north of CSZ have suffered more complex metamorphic histories in comparison to the southern part. Integrating the results of the present field and metamorphic studies with the earlier investigations and available geochronological data we suggest that the CSZ could represent a suture zone between two different continental blocks that underwent distinct metamorphic evolution.