Geosystems and Geoenvironment (May 2023)
A possible paleorift zone in the Central Dharwar Craton of South Indian Shield: Evidence from regional gravity anomalies
Abstract
A conspicuous zone marked with linear Bouguer gravity anomalies encompassed with overall regional gravity high zone spreads about 5° length and width of about 1 to 1 1/2° in the central part of Dharwar Craton is not entirely relatable to surface geological formations. This feature and geological studies have defined Central Dharwar Craton in the southern Indian Shield area as transitory block between the Western Dharwar Craton and Eastern Dharwar Craton occupying about 75,000 sq.km in the South Indian Shield area. Pronounced two-dimensional gravity high, covering this region to the bordering Deccan Volcanic Province and Southern Granulite Terrain has to be accounted for mid-crustal to Lithosphere-Aesthenosphere Boundary level changes as low-density Closepet Granitic Terrain cannot support this high zone and thus attributed as due to crustal doming which led to assumption that this region could be due to Midcontinent Rift (MCR). Elsewhere, MCRs are characterized with significant tectonic, magmatic and geophysical features. Though passive rift zones of early era may not retain all the topographic evidences such as central depression bordered with shoulder uplifts, the elongated narrow extensional features could be seen in this region in the form of long schist belts and elongated granite body. Bordering normal faults could be identified with abrupt shift in the regional background values.Further, modeling of gravity anomalies indicated lithospheric thinning and this feature supports a secondary process of uplifting of local features and crustal doming. Another important factor is the type of magmatic activity in this region with alkali basalts and bimodal volcanism. Bouguer gravity anomalies of this region possibly indicate that this may be a failed rift zone that has stopped before continental break up and filled with linear igneous granite body and volcanic rocks. Linear airborne magnetic anomalies also characterize this part of Dharwar Craton coinciding with gravity high zone. Variations in lithospheric thickness is noticeable in these areas from the other geophysical inputs also. Integrated study leads us to conclude that central part of Dharwar Craton is paleorift zone.
