Lithium in carbonatites — consequence of an enriched mantle source?

Abstract

AbstractThe rare Li-mica taeniolite is described from the Dicker Willem carbonatite complex, Namibia, and from the Alpine carbonatitic lamprophyre dyke swarm at Haast River, New Zealand. At Haast River, taeniolite occurs in sodic and ultrasodic fenites derived from quartzo-feldspathic schists and rarely in metabasites, adjacent to dykes of tinguaite, trachyte and a spectrum of carbonatites ranging from Ca- to Fe- rich types. In Namibia, taeniolite is present in potassic fenites derived from quartz-feldspathic gneisses and granitoids at the margin of an early sövite phase of the complex and in a radial sövite dyke emanating from this centre.The occurrence of taeniolite in these totally disparate carbonatite complexes, together with examples of lithian mica from other carbonatite complexes worldwide, raises the question of the status of Li as a ‘carbonatitic element’. We argue that lithium is not a consequence of crustal assimilation or interaction, but reflects the geochemical character of the magmatic source. Li, an overlooked and little-analysed element, may be an integral part of metasomatic enrichment in the mantle, and of magmas derived by partial melting of such a source.