... rares, 9.9% SiO 2 ) et un hydroxyde de Mn–Ba. Chimiquement, les filons ont une composition calciocarbonatitique, et montrent une forte teneur en F, Sr, Fe et Mn. Le total des alcalins est inférieur à 2%. En comparaison d’une natrocarbonatite saine, les teneurs en terres rares, Y, Zr, Th, Nb et Pb sont...

...Tibor Guzmics; Márta Berkesi; Robert J. Bodnar; András Fall; Enikő Bali; Ralf Milke; Enikő Vetlényi; Csaba Szabó Abstract Earth’s only active natrocarbonatite volcanism, occurring at Oldoinyo Lengai (OL), Tanzania, suggests that natrocarbonatite melts are formed through a unique geological process...

...Anatoly N. Zaitsev; Jörg Keller; John Spratt; Elena N. Perova; Anton Kearsley Abstract Samples of natrocarbonatite showing various degrees of alteration are preserved in an older carbonatite platform that existed before and until the 1917 explosive eruption at Oldoinyo Lengai volcano, in Tanzania...

... quenched trachytoidal and flow-banded textures and consist largely (90%) of calcite, plus apatite and magnetite. The principal primary constituent is inferred to have been nyerereite (cf. the natrocarbonatite of Oldoinyo Lengai) now pseudomorphed by calcite, and accompanied by primary tabular calcite...

...R. H. Mitchell; F. Belton Abstract Lapilli and spatter of natrocarbonatite extruded from the T56B cone of Oldoinyo Lengai (Tanzania) in August 2003 are unusually rich in apatite, silicate, oxide and sulphide minerals. These minerals occur primarily within inclusions of quenched natrocarbonatite...

...B. T. NGWENYA; D. K. BAILEY Abstract Fine grained carbonatite in the Kaluwe complex has been inferred, on textural grounds, to be calcified natrocarbonatite. Electron microprobe analysis, however, shows that the brown laths thought to be pseudo-nyerereite are dolomitic, with Sr values much higher...

...R. H. Mitchell; F. A. Belton Abstract A unique hybrid natrocarbonatite, collected from the new ash cone of the volcano Oldoinyo Lengai, Tanzania in July 2008, consists of phenocrysts of nyerereite and gregoryite together with xenocrysts of clinopyroxene, nepheline and Ti-andradite set...

... natrocarbonatite lava that has been erupted in more recent times. This proposition is difficult to reconcile with the currently fashionable hypothesis whereby the natrocarbonatite lava separated immiscibly from a type of nephelinite magma, most recently thought to be a wollastonite nephelinite. In 1993 Dawson...

... of premodern natrocarbonatite volcanism. The principal carbonate mineral was nyerereite, which is the dominant mineral in modern natrocarbonatite lava flows of the adjacent volcano Oldoinyo Lengai. The nyerereite of Kerimasi was leached of its alkalis by meteoric water and is now represented by calcite...

...Andrew D. Beard; Kieren Howard; Laura Carmody; Adrian P. Jones Abstract We report new observations of a clathrate mineral, melanophlogite [46SiO 2 ·6(N 2 ,CO 2 )·2(CH 4 ,N 2 )], as part of a tuffaceous layer within a sample of the 2006 natrocarbonatite lava, whose composition reflects the typical...

... the solidus at ~550°C, discrete exsolved inclusions of (Na,K)Cl ss occur in (K,Na)Cl ss and of (K,Na)Cl ss in (Na,K)Cl ss . These data are relevant to the differentiation and crystallization of the natrocarbonatitic melt at Oldoinyo Lengai under hypabyssal and plutonic conditions; they predict the formation...

...J. Gittins; B. C. Jago Abstract Natrocarbonatite magma, erupted as lava flows in the Tanzanian volcano Oldoinyo Lengai in June and November of 1988, has evolved chemically since its formation. The June and November flows of 1988 display increasing Cl, F, Ba, K, Mg and Mn, concomitantly with Na, Ca...

...R. H. Mitchell; J. B. Dawson Abstract The September 2007 ash eruption at Oldoinyo Lengai terminated a period of >30 y of relatively quiet extrusion of natrocarbonatite lavas. Ash erupted on the 24 th September comprised nuclei of ijolitic phases, surrounded by finer peralkaline, silica...

...R. H. Mitchell Abstract Stalactites formed by the chemical weathering of natrocarbonatite lava decorate the roofs of hollow inactive hornitos at Oldoinyo Lengai, Tanzania. The stalactites are composed principally of trona with lesser and very variable amounts of nahcolite, (NaHCO 3 ), thermonatrite...

...R. H. Mitchell Abstract Lapilli formed by a Strombolian eruption are associated with the formation of a large lava flow of natrocarbonatite on or about 21–22 July, 2000 at Oldoinyo Lengai volcano, Tanzania. Fresh lapilli consist of vesicular natrocarbonatite similar to that occurring in rapidly...

...R. H. Mitchell Abstract Natrocarbonatite lavas erupted from hornitos T37B and T49B at Oldoinyo Lengai (Tanzania) during 23–30 July, 2000 are unusual in containing sylvite and fluorite microcrysts together with fluorite-nyerereite intergrowths. The latter are relatively coarse grained and exhibit...

... differentiates that are not related to other carbonatites or their parental magmas. The origin and genetic relationships of the Oldoinyo Lengai natrocarbonatite cannot be unambiguously determined, although these rocks are regarded as a distinct variety of primary carbonatite. Carbonate-rich rocks associated...

...B. C. Jago; J. Gittins Several K-Fe sulphide minerals have been described from natrocarbonatite lavas erupted from the Tanzanian volcano Oldoinyo Lengai but uncertainty remains about their exact identity. They do not appear to be any of the established K-Fe sulphides according to Dawson et al...