Textural Variation in the Crustal Xenoliths in Basic Dykes, Western Deccan Volcanic Province, Maharashtra, India:Evidence of Partial Melting And Pyrometamorphism

Abstract

In flood basalt provinces that cover Precambrian terrains, crustal xenoliths are rare. But when present in lava flows and in intrusives, they provide direct information about the basement composition and upper lithospheric crust. Although dykes hosting xenoliths are not common in Deccan Volcanic Province, there are a few known occurrences of mantle and/or crustal xenoliths in some dykes from Maharashtra and Madhya Pradesh, India. The NE–SW dykes from Western Deccan Volcanic Province of upland Maharashtra host crustal xenoliths exhibiting textural variation. Petrographic studies of these xenoliths were not dealt with in detail earlier. We document here, a detailed petrographic work, signifying the importance of pyrometamorphic changes in xenoliths, to understand the composition and explain the textural variation. Presence of elongated quartz ribbons, neocrystallization, incorporation of basaltic melt into mineral cracks, complex twinning in feldspars, exsolved Fe-oxide and silica melt inclusions represent high temperature effects. Major oxide data is suggestive of peraluminous nature of the xenoliths while high temperature minerals tridymite and mullite observed from X-ray diffractograms indicate pyrometamorphic effects. The original rock is quite completely transformed by various processes like partial melting, incipient hybridization and pyrometamorphism, leaving very little mineralogical and textural traces that give evidence of the original protolith. These processes explain the textural variation observed in these upper crustal xenoliths, which could be termed as buchites or buchite rocks.