Rekkame Province

Over this very large area isolated occurrences of alkaline rocks take the form of lava flows and small volcanoes and craters; this is referred to as the Rekkame Province by Rachdi et al. (1997). Jérémine (1955) lists, and pinpoints on a map, 10 localities for which she gives brief notes and cites earlier work, but much more detail is given by Rachdi et al. (1997) whose map indicates that major areas of lava are notably concentrated in the western part of the province. The lava flows are up to several metres thick and tend to cap hills; they are associated with dykes and many contain xenoliths of peridotite and pyroxenite. Explosion craters and maars are circular structures filled with lava fragments and abundant crystals of pyroxene and magnetite. The lavas (Rachdi et al., 1997) are essentially melanephelinites, with or without melilite, and basanites. The nephelinites comprise phenocrysts of olivine, pyroxene and Fe-Ti oxides, and may contain microphenocrysts of melilite, set in a matrix of pyroxene, Fe-Ti oxides, perovskite, nepheline and phlogopite. The basanites are similar rocks but also contain a little apatite and rare microlites of labradorite-bytownite. The Tiskenit phonolite intrusion is an isolated dome in the extreme northeast of the province. It contains phenocrysts of sanidine, aegirine-augite and hauyne in a groundmass of sanidine laths with some plagioclase xenocrysts. Jérémine (1955) found melanite, calcite and zeolite in some rocks. Rachdi et al. (1997) give 33 rock analyses, including a range of trace elements.