Pyroxenes from Alkaline Rocks of the Chhota Udaipur Carbonatite-Alkaiic Province, Gujarat, India

The Amba Dongar, Sirivasan and Panwad-Kawant carbonatite-alkalic complexes have close spatial relation. In Amba Dongar olivine-free nephelinite is the predominent type of alkaline rock with a few phonolite dykes; in Sirivasan tinguaite is more abundant than nephelinilte while in Panwad-Kawant region bulk of the alkaline rocks is made up of phonolite and tinguaite. The chemistry of the pyroxenes of these alkaline rocks has been interpreted and their evolutionary trends are discussed. The pyroxenes of Amba Dongar and Sirivasan complexes show early acmitic trend with phenocrysts being more calcic. The groundmass pyroxenes are more acmitic. The pyroxenes of the Panwad-Kawant complex, on the other hand, are less evolved diopsidic-salite type, showmg only slight initial hedenbcrgite enrichment and the final aemitic enrichment. These two trends are attributed to varying crystallizing conditions of the two batches of the same magma.