Crustal structure and domain tectonics of the Dharwar Craton (India): insight from new gravity data

摘要

The Precambrian Dharwar Craton of Peninsular India comprises three distinct crustal domains, namely the Western Dharwar Craton (WDC), the Eastern Dharwar Craton (EDC) and the Eastern Ghats Mobile Belt (EGMB). The domain boundaries are demarcated by bipolar (positive and negative) gravity anomalies, measured along a 600 km long Udipi-Kavali seismic line. The two and half dimensional modelling of the gravity anomalies, well constrained by available seismic depth-sections, identified the two contact zones. One occurs between the WDC (relatively low density) and the EDC (intermediate density), to the east of the Chitradurga Schist Belt and the second occurs between the EDC and the EGMB (high density), to the east of Cuddapah Basin as west verging thrust faults. The three-layer crustal structure is up to 41 km thick beneath the WDC, thinning to 37 km beneath the west coast. Under the EDC, the depth of the Moho varies from 38 km towards the west to 40 km beneath the Cuddapah Basin, and decreases to a depth of 35 km beneath the EGMB. A high-density steeply inclined ridge-like body is modelled between 5 and 20 km depth beneath the Closepet Granite, and a similar body is modelled under the EGMB. It is suggested that the three domains of the Dharwar Craton were brought and welded together at the suture zones in the period from Late Archaean to Late Proterozoic through collisional tectonics. The apparent offsets in the Moho depth may be the imprint of the relative domain movement that probably was initiated by the convergent plate motion. The steeply inclined ridge-like high-density bodies are interpreted as stacked lower crustal blocks from the convergent tectonic setting. The Cuddapah Basin, with a 10 km thick shelf-marine sedimentary sequence, is interpreted as a peripheral foreland basin abutting the EGMB. A lopolith of likely mafic composition is modelled at 10 km depth, and is interpreted as a product of juvenile magmatism beneath the EDC.