Hybrid Acid Xenoliths in Dolerite Dykes Intruding Deccan Flood Basalts, Pune-Ahmednagar Region, Western India

The Deccan flood basalt in Pune - Ahmednagar region, western India, is intruded by NE-SW. NW-SE and E-W trending dolerite dyke swarms, post-dating the main eruptive phase. The NE-SW trending dykes host a number of large (∼1 to ›5 m across) ellipsoidal rhyolitic and granitic xenoliths that show effects of hybridization along their rims. Granitic xenoliths contain fractured and partially assimilated crystals. whereas in the fine-grained rhyolites hybridization is manifested in the development of flow structures and chlorophaeite-filled amygdules. Hybridization of the xenoliths has resulted in wide variation in silica abundance, whereas the REE patterns show remarkable similarity. This indicates that hybridization was limited only to the readjustment of relatively mobile elements, resulting in alkali exchange across the interface. The rhyolitic xenoliths might have resulted from the fusion of the crust by basic magma, while the granitic xenoliths possibly represent the basement component. Incomplete assimilation of xenoliths by the melt as evidenced by limited reaction, further corroborates the incorporation of xenoliths at a shallow level, when the uprising basic melt had considerably fractionated and cooled. The fractionated nature of host dolerite dyke is also confirmed by moderate MgO, high FeO and LREE enrichment.