The geology of Goa Group: Revisited

Abstract

The supracrustals that constitute the Goa Group of Gokul et al. (1985) can be divided into two lithostratigraphic sequences namely the Barcem Group and the Ponda Group. The former comprises predominantly greenstones (metabasalts) and rests on a basement of the 3300-3400 Ma Anmode Ghat trodhjemite gneiss with a crudely developed quartz-pebble conglomerate at the base, and shows lithological similarities with the lower part of the Bababudan Group. The younger sequence is dominated by clastics, and is assigned to a new stratigraphic group formally termed the Ponda Group which is equivalent to the Chitradurga Group of the Dharwar Supergroup. This group rests on a basement of the 2700-2900 Ma Chandranath granite gneiss with a distinct unconformity marked by a polymict, granite-clast metaconglomerate. The conglomerate displays many similarities with the Talya conglomerate that occurs at the base of the Chitradurga Group. It is overlain by a psamolitic sequence which is followed in ascending order by the chemogenic sediments that host the BIF and by the deep water turbidite sequence (argillite-graywacke association) with intercalations of mafic volcanics. The supracrustal sequence is intruded by the Bondla layered mafic-ultramafic complex along a major shear zone (NW-SE) that largely controls the course of the northwesterly flowing tributary of River Mandovi. The late intrusive, Canacona potassic granite marks the culmination of the sedimentation in the Shimoga-Goa basin.

The Origin and Tectonic Setting of Precambrian Greywacke of Ribandar‐Chimbel, Goa, India: Petrological and Geochemical Evidence

“…Goa, located at the northwestern part of the western Dharwar craton, forms part of the Shimoga-Goa supracrustal belt that probably extends up to the Narmada beneath the Deccan Traps, which terminates at the Narmada-Son lineament (Dessai, 2011). This supracrustal belt extends NNW-SSE for a length of over 250 km and the maximum width of 120 km is seen at Dharwar.…”

“…The Barcem Formation of Goa (Fig. 1) is equivalent to the Bababudan group whereas the Sanvordem, Bicholim and Vageri formations are comparable to the Chitradurga Group (Dessai, 2011). The Goa Group has undergone three stages of folding.…”

“…62-63 Ma (Widdowson et al, 2000, Patil andRao, 2002). The mafic intrusion followed the emplacement of the mafic-ultramafic layered complex and Canacona Granite (2395±390 Ma) and thus indicates the injection of the mafic dykes to be the last event (Dessai, 2011). These dykes could also be related to post-trappean tectonics that occurred at 63 Ma in the Seychelles, and which corresponds to the end of Deccan volcanism and/or to the initiation of the rifting of the Arabian Sea (Courtillot et al, 1986, Patil andRao, 2002).…”

“…It is of interest that the ultramafic-gabbro complex of the Dharwar Supergroup occurring in other parts of Goa (Jena, 1985) and the Pre-Cambrian metamorphic rocks of Sindhudurg, Maharashtra (to the north of Goa) (Chari andMaggirwar, 1968, Iyer et al, 2010) host significant amount of chromites. The Goa Group is divided in the order of superposition as Barcem (lowermost), Sanvordem, Bicholim-Rivona and the Vageri Formations (Gokul et al, 1985;Dessai, 2011). The general stratigraphy of the Goa group is given in Table 1 and Figure 1.…”

“…This supracrustal belt extends NNW-SSE for a length of over 250 km and the maximum width of 120 km is seen at Dharwar. The Dharwarian schist belt can be designated as the older Bababudan and younger Chitradurga schist belts (Group) (Dessai, 2011). The Barcem Formation of Goa (Fig.…”