Aashwini Shetye and Poornima Dhawaskar Sawant*

School of Earth Ocean and Atmospheric Sciences, Goa University, Goa – 403206 (GA), India (*Corresponding Author, E-mail: poornima@unigoa.ac.in)

Abstract

This study examines the mafic dyke swarm exposed along the Cacra coast, North Goa, to interpret its structural orientation, petrography, and magmatic evolution. Field mapping and geophysical data reveal nine doleritic dykes trending ENE–WSW, NW–SE, N–S, and NNW–SSE, with CD-1 confirmed as N–S oriented. Although dyke host contacts are obscured, adjacent metagreywacke exposures likely represent the country rock. Petrographic analysis indicates medium- to coarse-grained dolerite comprising plagioclase, clinopyroxene, opaques, and alteration minerals such as chlorite, biotite, and iddingsite. Textures including porphyritic, sub-ophitic, and symplectic intergrowths with zoned plagioclase suggest a two-stage crystallization slow cooling at depth followed by rapid quenching. These features collectively indicate emplacement under dynamic magmatic conditions governed by pre-existing fractures within the Proterozoic basement of the Dharwar Craton.

Keywords: Dykes, Dolerite, Petrographic Analysis, Geophysical Survey