Ring-Complexes of Ofoud-Type in Aïr, Niger: A new Anorogenic-Type Anorthosite Association
A general review of the different types of Palaeozoic ring-structures in the Aïr was given in Chap. 10 by Moreau et al. in which three main types were distinguished. In this chapter we deal in detail with the third type called Ofoud type, in which basic (anorthositic) and salic rocks are closely associated. Seven ring-complexes of Ofoud-type with basic rocks outcrop in northern and central Aïr, namely from north to south: Bous, Tamgak, Meugueur-Meugueur, Ofoud, Tagueï, Abontorok and Iskou (Fig. 1 A). The proportions of basic rocks vary from complex to complex (Table 1), the highest proportions being found in Abontorok and Ofoud and in the Meugueur-Meugueur ring-dyke. By far the largest area of basic rocks is found in Ofoud.
KeywordsQuartz Zircon Depression Geochemistry Fractionation
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