Petrology of Picrodolerites from the Dedan Cluster, Gujarat

Picritic dykes of oceanite and ankaramite composition occur around Dedan in the Kathiawar peninsula of Gujarat State. They have been studied across their width, with reference to the distribution and crystallisation of olivine and pyroxene. Olivine and pyroxene occur both as large phenocrysts and as small crystals in the groundmass. Considerable variation in the concentration of olivine and pyroxene is observed from the central portion of the dykes to the margins. A gradual decrease in the grain size and content of these minerals is seen from the centre to the margin of the dykes It is also observed that the grain size of these two minerals shows a direct relationship with the percentage of these minerals. This is explained by flow differentiation proposed by Bhattacharji and Smith for the Muskox feeder dyke.