Chapter 3 - Development of Gondwana Basins in Indian Shield

Abstract

Abstract The Gondwana basin belts in the Indian shield occur as discrete rectilinear belts, following the Proterozoic mobile belts that encapsule collisional sutures between the Archaean cratons. They also follow zones of Bouguer gravity anomaly and higher heat flow. The Gondwana basins generally have “half-graben” geometry; their boundary faults account for greater basin subsidence. The boundary fault zones generally show steep, dipping slickenlines, indicating the extensional nature of the Gondwana basins, which occur as rift basins in response to NNE-SSW directed extension acting over rigid Indian Shield. The Indian continent comprises a mosaic of a few Archaean cratons, which are mechanically strong, but have collisional junctions and bordering Proterozoic mobile belts that are mechanically weak. The Gondwana basin belts in the Indian shield overlie Proterozoic mobile belts that have encapsuled Archaean collisional sutures. The three main Gondwana basin belts in the Indian shield are: (i) broadly NW-SE trending Pranhita-Godavari Valley and (ii) Mahanadi Valley belts, and (iii) broadly E-W to ENE-WSW trending Damodar-Koel-Son Valley and Satpura Mountain belt. These are disposed at an oblique angle to each other. However, the Gondwana basin belts each initiated contemporaneously and show parallel Gondwana stratigraphy ( Table 2.3 ). It is logically and tectonostratigraphically difficult to conceive of a tectonic model to initiate opening up such obliquely disposed Gondwana basins contemporaneously. It is postulated that the Indian Shield was under NNE-SSW trending regional extension, and the Gondwana basins opened contemporaneously during the Late Paleozoic mimicking and inheriting the Proterozoic structural weaknesses and the Proterozoic fabric. The Proterozoic basin belts that are oriented oblique to the extension axis (~ 60 degrees) opened and developed contemporaneously during the Late Paleozoic-Mesozoic. The Gondwana basins, mimicked the Proterozoic structure, and was controlled by their deformed basement structures, and inherited the Precambrian fabrics. The Late Mesozoic faulting, mafic, ultramafic intrusion, and initiation of flood basalt signalled the Gondwana continental break up and the termination of the Gondwana geodynamic cycle. The presence of compressive structures like overturned folds and reverse faults developed especially close to some boundary fault zones indicate local effects of inversion tectonics.