Petrography and Major Oxide Geochemistry of Dolerite Dykes from Kunnam Region Villupuram, Tamil Nadu, Southern India

The mafic dolerite dyke crosscut the charnockite basement in the Kunnam region. The dykes throughout the area were highly fractured and there are various faults and joints are seen. The proper methodology was followed for collecting the unaltered rock samples in the study area. The rock reflects ophitic to sub-ophitic textures and is mainly composed of plagioclase feldspar, clino-pyroxene and opaque minerals (magnetite and titanomagnetite), olivine and quartz are observed as accessory minerals. The geochemical studies indicate that the rock has basic composition based on the percentage of silica. The TAS classification diagram for the mafic dyke shows that the samples fall under basaltic composition in the classification of the volcanic rock, and gabbroic composition in the classification of the plutonic rock. The K2O versus silica diagram shows that the rock samples fall under the category of calc-alkaline series. The rock weathering was examined with A–CN–K plot indicating that the dolerite rock samples fall under low weathering margin.