Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 1.03, Latitude: 18.87

This complex is built from six intrusive granite phases of which the fourth and fifth are peraluminous and the other four peralkaline, with successively younger intrusions emplaced inwards. It is oval in outline, 32x22 km, and with the first two intrusive phases forming partial ring-dykes of which the second is much the better developed. The first phase is a porphyritic microgranite with perthite phenocrysts in a microcrystalline groundmass. The second granite is medium-grained and of quartz, perthite, aegirine-augite and sodic and sodic-calcic amphiboles, while the third is of a similar mineralogy but is a coarser rock. Apatite, fluorite, cryolite, astrophyllite and chevkinite are accessory in these two granites. The two peraluminous granites are perthitic rocks with biotite and with calcic amphibole in one of them. The last granite is fine- to medium-grained and contains aegirine, arfvedsonite and astrophyllite. Evolution of the principal mafic minerals is discussed and illustrated by Ba et al. (1985) but numerical data are not given. Numerous 87Rb/86Sr and 87Sr/86Sr data are given by Liégeois and Black (1984) and Pb, Sr and O isotopic data by Weis et al. (1986). Oxygen isotope data for four rocks are presented and discussed by Javoy and Weis (1987).

21 whole rocks gave a Rb-Sr isochron of 549(6 Ma (Liégeois and Black, 1984; Weis et al., 1986) and the second authors determined a Pb-U age of 573(26 Ma based on four samples.
BA, H., BLACK, R., BENZIANE, B., DIOMBANA, D., HASCOET-FENDER, J., BONIN, B., FABRE, J. and LIÉGEOIS, J.P. 1985. La province des complexes annulaires alcalins sursaturés de l'Adrar des Iforas, Mali. Journal of African Earth Sciences, 3: 123-42.JAVOY, M. and WEIS, D. 1987. Oxygen isotopic composition of alkaline anorogenic granites as a clue to their origin: the problem of crustal oxygen. Earth and Planetary Science Letters, 84: 415-22.LIÉGEOIS, J.-P. and BLACK, R. 1984. Petrographie et geochronologie Rb-Sr de la transition calco-alcaline-alcaline fini-panafricaine dans l'Adrar des Iforas (Mali): accretion crustale au Precambrien superieur. In. J. Klerkx and J. Michot (eds), Geologie africaine - African Geology. 115-25.WEIS, D., LIEGOIS, J.P. and JAVOY, M. 1986. The Timedjelalen alkaline ring-complex and related N-S dyke swarms (Adrar des Iforas, Mali): a Pb-Sr-O isotopic study. Chemical Geology, 57: 201-15.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith