Alkaline Rocks and Carbonatites of the World

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Adrar Bous (Bous, Adrar Bouss)

stripes

Occurrence number: 
121-00-001
Country: 
Niger
Location: 
Longitude: 9, Latitude: 20.33

The most northerly of the alkaline complexes of Air, Adrar Bous has an elliptical form of 20x12 km. It comprises three units (Husch and Moreau, 1982), a western arc, of high relief, mainly of adamellites and monzonites; an extensive area in the south, east and west of low relief, consisting predominantly of gabbroic rocks with subsidiary amounts of more mafic and anorthositic rocks, within which are outcrops of metamorphosed basement shales and conglomeratyes which may be xenoliths or possibly septa between intrusions. A third unit forms interior and northern zones of peralkaline granite, monzonite and micromonzonite which is topographically high. The basic rocks display a weak layering which dips inwards with more olivine-rich rocks towards the base of the series. The micromonzonite includes varieties containing hastingsite and biotite which form dykes cutting the basic rocks. This was followed by emplacement of granites with sodic amphiboles followed by an aegirine granite that was partly obliterated by intrusion of a later sodic amphibole granite (Black et al., 1967). Mineral data on the basic rocks are given by Husch and Moreau (1982) who also include three whole rock analyses for this series.

Age: 
Karche and Vachette (1978) give a Rb-Sr date of 470(5 Ma. A Rb-Sr whole rock and alkali feldspar isochron age of 429(4 Ma was determined by Bowden et al. (1976), and Moreau et al. (1994) give a Rb-St isochron age, based on six granites, of 406(11 Ma..
References: 
BLACK, R., JAUJOU, M. and PELLATON, C. 1967. Notice explicative sur la carte geologique de l'Air à l'échelle du 1/500 000. Direction des Mines et de la Geologie. Republique du Niger, 1-57.BOWDEN, P., VAN BREEMEN, O., HUTCHINSON, J. and TURNER, D.C. 1976. Palaeozoic and Mesozoic age trends for some ring complexes in Niger and Nigeria. Nature, London, 259: 297-9.HUSCH, J.M. and MOREAU, C. 1982. Geology and major element geochemistry of anorthositic rocks associated with Paleozoic hypabyssal ring complexes, Air massif, Niger, West Africa. Journal of Volcanology and Geothermal Research, 14: 47-66.KARCHE, J.-P. and VACHETTE, M. 1978. Age et migration de l'activité magmatique dans les complexes paléozoïques du Niger. Consequences. Bulletin de la Société Géologique de France, 20: 941-53.MOREAU, C., DEMAIFFE, D., BELLION, Y. and BOULLIER, A.-M. 1994. A tectonic model for the location of palaeozoic ring complexes in Air (Niger, West Africa). Tectonophysics, 234: 129-46.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith