Alkaline Rocks and Carbonatites of the World

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The voluminous extrusive rocks of Cameroon together with a series of intrusions, which are principally granitic and syenitic, lie along a northeast-trending line which is known as the Cameroon Line. This alignment continues southwestwards into the Gulf of Guinea in the form of the islands of Bioko (Fernando Po), Principe, Sao Tome and Pagalu (Annobon) and northeastwards as far as Lake Chad. There are many papers on the Cameroon Line and useful reviews will be found in Fitton (1987), who is particularly concerned with the extrusive rocks and their chemistry, and Derruelle et al. (1991), who also cover the intrusive rocks, discuss the tectonic context, and present the various interpretations of the line. Four large volcanic complexes lie along the line within Cameroon and extend into Nigeria. They range from basaltic and nephelinitic to rhyolitic and trachytic rocks and are generally alkaline, the most extreme alkalinity being manifested by the lavas of Mount Etinde, some of which have unique compositions. Gèze (1943) describes in considerable detail the geography and geology of the southernmost volcanoes. There are about 60 intrusions lying along the Cameroon Line within Cameroon itself (Déruelle et al., 1991), but many of these are not alkaline. Apart from the reviews cited above a useful account of the intrusive complexes is that of Lasserre (1978) while many age data are given in papers by Cantagrel et al. (1978) and Fitton and Dunlop (1985). Halliday et al. (1988) give Nd, Sr, Pb and O isotopic data for a number of Cameroon Line centres and discuss the genesis of the line in some detail.



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