Petrogenetic significance of ferro-enstatite orthopyroxene in basaltic dikes from the Tapi rift, Deccan flood basalt province, India

Some basaltic dikes from the Tapi rift in the Deccan flood basalt province, India, contain abundant clusters of prismatic quench crystals of ferro-enstatite orthopyroxene (Fe39–42Mg53–57Ca2–4). Such profuse orthopyroxene clusters are not yet known from any other flood basalt province in the world. Based on petrography, mineral chemistry and whole-rock chemistry, we conclude that these crystals are formed due to assimilation of shale by Deccan basalt magma. This interpretation is consistent with the known bedrock geology of the area. These quench crystals constitute the first direct, petrographic evidence for crustal contamination in the Deccan province. The liquidus temperature for the dikes is estimated at 1220±10°C, with the crystallization temperature of the orthopyroxene at 1080°C or less.