A Note on Inch Scale Layering in a Dolerite Dyke of the Deccan Trap of Saurashtra, India

Distinct vertical rhythmic layering is seen in one of the dykes 68 km southeast of Rajkot. The dyke extends for almost 50 km in length but has a limited width of 10 to 15 metres. The vertical layering is due to alternating layers rich in plagioclase and pyroxene, which is encountered mainly in the central part of the dyke. The layering is formed due to molecuIar diffusion at the front of cooling and crystallization with the temperature gradient catching up gradually to form the next layer. Alternatively it may be possible that layering is due to multiple injections of melt into the fracture that was responsible for disturbing the equilibrium from time to time.