ANALCIME-PHONOLITE AND ASSOCIATED ALKALINE ROCKS OF PANWAD-KAWANT COMPLEX, GUJARAT, INDIA

In Panwad-Kawant complex large number of dykes and plugs of phonolite, pseudoleucite tinguaite, lamprophyre and syenite porphyry are encount ered. Mineralogical and geochemical data of different phonolites (mafi c and felsic types) indicate that these rocks were derived from two di fferent magma types. The genetic link between undersaturated and satur ated rocks is not well understood, but it could be assumed that the di fferentiating undersaturated magma may have acquired slight saturation due to the crustal contamination, as evidenced by abundant of rounded gneissic xenoliths. The origin of analcime-mafic-phonolites is discus sed with the help of field, petrographic and geochemical data. It is c oncluded that analcime in phonolites is not of primary origin but was formed from leucite by ion exchange with Na-rich marine fluids. The fo llowing observations support our conclusion: 1. Analcime occurs only a s microphenocrysts which are not euhedral but always rounded. Except f or analcime-phonolites all other rocks in the area are sodi-potassic i n nature. 3. Ion-exchange reaction involves liberation of K-rich fluid s which, in the present case, appear as K-feldspar veins within the an alcime-phonolite outcrop.