Tectonosedimentary evolution of Cuddapah basin and Eastern Ghats mobile belt (India) as Proterozoic collision: gravity, seismic and geodynamic constraints

Abstract

The crustal scale terrane boundary shear zone along the eastern margin of the Dharwar craton, marked by an eastward dipping thrust fault, defines a cryptic suture between the middle to late Proterozoic Eastern Ghats mobile belt (EGMB) and the contemporary Cuddapah basin west of it. The contact zone of these two geologically distinct terranes is characterized by bipolar gravity anomaly with a relative gravity high over the EGMB and low over the eastern part of the Cuddapah basin. Two available seismic sections across the EGMB and the Cuddapah basin have been integrated with the modelling of Bouguer anomalies along these profiles. The density model along these two profiles suggest a high-density (2.90 g/cm3) oblique ridge-like structure at a depth of about 12 km under the EGMB and a thick sedimentary sequence of 10–11 km and a thick crust of about 40 km under the eastern part of the Cuddapah basin. These models also provide a basic lopolith over the basement under the western part of the Cuddapah basin, where large basic sills are exposed. The high-density oblique ridge-like body along with the deep seated intrusives such as anorthosites and carbonatites, and occurrences of ophiolite melange and highly disturbed sediments of the Cuddapah basin along the EGMB may indicate a collision zone along the eastern margin of the Dharwar craton. The exposed charnockite and khondalite rocks along the EGMB suggest that the inferred eastward dipping high-density body under it may represent lower crustal rock upthrusted from the east to the west. A thick crust with eastward dipping horizons under the eastern part of the Cuddapah basin and the westward thrusting of lower crustal rocks under the EGMB indicate eastward subduction of the Dharwar craton. The thick sedimentary sequences of shelf marine origin indicate that the Cuddapah basin may represent a peripheral foreland basin. However, the presence of prominent seismic reflectors in the upper mantle under the Cuddapah basin may indicates that some crustal rocks might have also subducted towards the west suggesting bivergent collision along the EGMB.