Areal Variation of Anorthite Content of Plagioclase Feldspars from the Vajrat Gabbro, Ratnagiri District, Maharashtra State

The paper deals with the plagiodases occurring in the gabbro pluton of Vajrat. 133 twinned plagioclase grains from 26 rock samples of these gabbros are studied on the 4-axes universal stage. The anorthite content and the twin laws of these plagiodases have been determined on the lines of Reinhard. Areal variation map is prepared for the anorthite content of the plagioclases, on the lines of Dawson and Whitten. Petrographic studies of the gabbros indicate that the gabbros of the more central parts of the pluton are distinctly fine grained ru. compared to the grain size of those forming the peripheral portion. The areal variation pattern of the anorthite content together with the petrographic characters of the gabbros suggest more than one period of igneous activity in the formation of the Vajrat gabbro pluton.