Petrogenesis, Geochronology and Crustal Evolution of the Canacona Region of Southern Goa

Fernandes, Orlando A. and Widdowson, Mike (2009). Petrogenesis, Geochronology and Crustal Evolution of the Canacona Region of Southern Goa. In: Mascarenhas, Antonio and Kalavampara, Glenn eds. Natural Resources of Goa: A Geological Perspective. India: Geological Society of Goa, pp. 69–95.

Abstract

The South Indian shield is a complex mosaic of lithologies, which evolved through the middle to late Archaean and early Proterozoic. After this time, the crust attained stability, so forming the Western Dharwar craton (WDC) terrain in the west of peninsular India. Goa State comprises the small but important north-western part of the WDC terrain. In such terrains, where a variety of rock types have fused over a vast time span, careful study of these types of complexes can yield significant findings concerning Precambrian palaeo-tectonics and crustal evolution.

In Goa, this north-western continuation of the WDC consists of a varied suite of Precambrian igneous lithologies in close association with folded with supracrustal materials of low metamorphic grade. These igneous rocks include, notably, a series of large late Archaean – early Proterozoic granitoid plutonic bodies located on the coastal plain and extending inland toward the Western Ghats. In some instances, these granite bodies have been intruded by early Proterozoic doleritic dykes. The complex mosaic of granites, mafic bodies and associated lithologies of theGoa region presents a unique opportunity to investigate a regional Precambrian evolutionary trend of the north-western Dharwar craton; a dominantly igneous environment involving extensional tectonics is proposed.

Field observations, petrography, geochemistry and preliminary 40Ar/39Ar dating are here employed to distinguish and chronicle the emplacement of the mafic and felsic rocks in the Canacona region of south-western Goa, and to evaluate their role in crustal evolution of the region. A hypothesis involving sinistral transpressional displacement is advocated here in order to explain the extensional tectonic setting in which the porphyritic Canacona granite, and subsequent dolerite dykes, evolved.

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