Tectonic implications of seismic reflectivity pattern observed over the Precambrian Southern Granulite Terrain, India

Abstract

The Southern Granulite Terrain (SGT) constitutes a large part of the South Indian Precambrian shield. A study of the crustal reflectivity and tectonic framework of the Madurai Block of the SGT has been carried out using multifold seismic reflection survey along the Vattalkundu–Kalugumalai transect. The seismic stack sections along the profile, showing conspicuous changes in reflectivity pattern, indicate the presence of several structurally distinct crustal blocks. It is apparent from the north dipping reflectors near Vattalkundu that the Kodaikanal massif extends 5 km further south of Vattalkundu, where the dip direction changes towards south. The reflectivity pattern in the crustal column of central part of the profile, between Sedapatti and Sarvathapuram suggests block uplift accompanied by internal domal deformation of the crust in Madurai Block. The dip on the southern flank of the dome is steeper than that of northern side. The south dipping reflections in the southern part of the profile, between Sivakasi and Kalugumalai in the upper crust are strong and continuous. The presence of the ultrahigh-temperature–pressure (UHT–P) metamorphic layering reported in the region might be contributing to the increased reflectivity. However, the relationship between the reflectivity and the UHT–P is enigmatic and yet to be established. In general, the region is characterized by distinct upper and mid crustal reflectivity, but the Reflection Moho identifiable at 13.0–13.5 s two-way travel time (TWT) is diffuse.