Volcanic and intrusive structures in the Kila-Warji ring-complex, northern Nigeria

Abstract

The Kila-Warji massif is one of a large number of ring-complexes of Jurassic age which cut the basement rocks of northern Nigeria. It is the only large member of this Nigerian Younger Granite province in which rocks of intermediate composition are dominant over acidic rocks. Structurally the complex presents several features of interest. The southern part——Warji—is a cauldron subsidence structure of volcanic rocks invaded by partly concordant intrusions. In the north the Kila ring-complex consists of a cluster of almost superimposed intrusive ring-structures. The complex lies in the extreme north of the Nigerian Younger Granite province (Fig. 1) and forms a group of low hills rising from an almost level plain developed on basement rocks. Farther north a few small complexes are exposed near the southern fringes of the Plio-Pleistocene sediments of the Chad basin, on the northern flanks of which Younger Granites reappear as large massifs in the Zinder-Gouré area of Niger ( Black 1963 ) and at Matsena in Bornu Province (Turner, in press). The Kila-Warji complex, composed mainly of acid and intermediate volcanics, syenites and peralkaline granites, has closer affinities to these northern complexes than to the main part of the Nigerian province, where biotite-granites are the most abundant rock type. Previous work on the area includes a preliminary survey by Raeburn (Falconer & Raeburn 1923) and an account of the petrography of some of the rocks by Beer (1952) . Field work for the present study was carried out from October 1965 to January 1966. This paper