Seismic signatures of a proterozoic thermal plume below southwestern part of the Cuddapah Basin, Dharwar craton

摘要

Origin and evolutionary history of the Cuddapah Basin in SE India has remained a subject of considerable speculation whether it was evolved through vertical tectonic movements, extentional stretching or even cometary impact. Based on detailed seismic and other geophysical studies (Gravity, magnetotelluric and heat flow), we have delineated signatures of a possible deep seated mantle plume below southwestern part of the Cuddapah Basin, which may have been responsible for the 1.1 Ga kimberlitic magmatism in the eastern part of the Dharwar craton (EDC). The thermal anomaly associated with this mantle plume appears to have resulted into 15–20 km thick magmatic underplating (Vp: 7.10–7.30 km/s; density 3.07–3.16 g/cm3) below the Parnapalle region of the southwestern Cuddapah Basin, which also coincides with the high gravity and high conductivity anomaly. The massive underplating led to thickening of the crust to about 40–44 km below southwestern part of the Cuddapah Basin, compared to about 34± 2 km in the surrounding regions of EDC, indicating thermal restructuring of the crust / mantle boundary. This plume, which was apparently active in an area of about 500 km radius, may have also affected the Closepet granitic region, which is ∼100 km west of Cuddapah Basin.