Mineralogy, geochemistry and petrology of the phonolitic to nephelinitic Sadiman volcano, Crater Highlands, Tanzania

Zaitsev, Anatoly N.; Marks, Michael A.W.; Wenzel, Thomas J.; Spratt, John; Sharygin, Victor V.; Strekopytov, Stanislav; Markl, Gregor

doi:10.1016/j.lithos.2012.03.001

Cited by 39 publications

(32 citation statements)

References 57 publications

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“…The presence of pyrrhotite and S-bearing apatite in nephelinite indicates that sulphur was present as sulphide (S 2− ) and sulphate species (S 6+ ), respectively, and moderated oxidized condition above the fayalite-magnetitequartz buffer (FMQ) prevailed during crystallization (Jugo et al 2010). This redox state agrees with thermodynamic equilibrium between titanite, andradite and wollastonite and crystallization of titanite and andradite at high oxidation state (ΔFMQ = −0.5 to +2) for silica activity between 0.1 and 0.25, whereas wollastonite is stable at more reduced conditions (Marks et al 2008;Zaitsev et al 2012).…”

Section: Petrogenesis Of Hanang Nephelinitessupporting

confidence: 82%

“…The matrix of nephelinites did not contain any accessory minerals as observed in Sadiman nephelinites (e.g. götzenite, barytolamprophyllite, delhayelite; Zaitsev et al 2012).The lavas are normative nph >20 % (CIPWnph = 24-31 %), and can be defined as nephelinites sensus lato (i.e. Le Bas et al 1986).…”

Section: Resultsmentioning

confidence: 95%

“…3,4,5). The absence of wollastonite and perovskite in Hanang nephelinite compared to Oldoinyo Lengai nephelinites may suggest crystallization under slightly more oxidized conditions (Marks et al 2008;Zaitsev et al 2012).…”

Section: Carbonatite-nephelinite Association In North Tanzanian Divermentioning

confidence: 99%

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Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

Baudouin

Parat

Denis

et al. 2016

Contrib Mineral Petrol

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International audienceNorth Tanzanian Divergence is the first stage of continental break-up of East African Rift (<6 Ma) and is one of the most concentrated areas of carbonatite magmatism on Earth, with singular Oldoinyo Lengai and Kerimasi volcanoes. Hanang volcano is the southernmost volcano in the North Tanzanian Divergence and the earliest stage of rift initiation. Hanang volcano erupted silica-undersaturated alkaline lavas with zoned clinopyroxene, nepheline, andradite-schorlomite, titanite, apatite, and pyrrhotite. Lavas are low MgO-nephelinite with low Mg# and high silica content (Mg# = 22.4–35.2, SiO2 = 44.2–46.7 wt%, respectively), high incompatible element concentrations (e.g. REE, Ba, Sr) and display Nb–Ta fractionation (Nb/Ta = 36–61). Major elements of whole rock are consistent with magmatic differentiation by fractional crystallization from a parental melt with melilititic composition. Although fractional crystallization occurred at 9–12 km and can be considered as an important process leading to nephelinite magma, the complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) and trace element patterns of nephelinites recorded magmatic differentiation involving open system with carbonate–silicate immiscibility and primary melilititic melt replenishment. The low water content of clinopyroxene (3–25 ppm wt. H2O) indicates that at least 0.3 wt% H2O was present at depth during carbonate-rich nephelinite crystallization at 340–640 MPa and 1050–1100 °C. Mg-poor nephelinites from Hanang represent an early stage of the evolution path towards carbonatitic magmatism as observed in Oldoinyo Lengai. Paragenesis and geochemistry of Hanang nephelinites require the presence of CO2-rich melilititic liquid in the southern part of North Tanzanian Divergence and carbonate-rich melt percolations after deep partial melting of CO2-rich oxidized mantle source

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Section: Petrogenesis Of Hanang Nephelinitessupporting

confidence: 82%

Section: Resultsmentioning

confidence: 95%

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Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

Baudouin

Parat

Denis

et al. 2016

Contrib Mineral Petrol

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“…In addition to Oldoinyo Lengai, immiscible melt inclusions were previously described in nephelinite lavas of other carbonatite-related volcanoes of the Gregory rift (Bazarova et al, 1975;Rankin and Le Bas, 1974;Romanchev, 1972;Zaitsev et al, 2011Zaitsev et al, , 2012.…”

Section: Nephelinementioning

confidence: 94%

“…The study of silicate and carbonate melt inclusions trapped by minerals gives additional information to better understand the relationships between silicate and carbonatite melts, and PT-conditions of their formation. Recently melt inclusions have been routinely used in the studies of carbonatites and related rocks (e.g., Rankin and Le Bas, 1974 and references therein; Golovin et al, 2007;Guzmics et al, 2011;Kamenetsky et al, 2007;Mitchell, 2009;Mitchell and Dawson, 2012-this volume;Panina, 2005;Sharygin et al, 2011;Stoppa et al, 1997Stoppa et al, , 2009Veksler et al, 1998;Zaitsev, 2010b;Zaitsev et al, 2011Zaitsev et al, , 2012. This paper presents detailed data on silicate melt inclusions in minerals in a combeite-wollastonite nephelinite (CWN) lava flow from Oldoinyo Lengai, erupted in the period 1904-1917(Dawson et al, 1995a, 1995bKeller et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Silicate–natrocarbonatite liquid immiscibility in 1917 eruption combeite–wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

Sharygin

Kamenetsky

Zaitsev

et al. 2012

Lithos

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Widespread freshwater carbonate in the Olduvai Basin, a precursor to a major eruption in the East African Rift System

Ashley

Wet

Houser

et al. 2020

The Depositional Record

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Freshwater limestones are uncommon in the sedimentary record of the East African Rift System. Recent research in the Olduvai Basin, Tanzania has revealed an extensive carbonate unit ca 1.8 Ma in age that varies spatially in thickness, petrography, trace element and rare earth geochemistry, C and O isotope values and freshwater microfossils. Five distinct lithologies are recognized. Four reflect deposition in carbonate‐rich environments that occurred at the same time in a catena‐like pattern over a heterogeneous landscape: spring, wetland, freshwater lake/pond and saline playa lake. The fifth is carbonate nodular soil that formed by paedogenesis on areas of topographically higher terrane. The δ18O of the carbonate, as negative as −6.5‰, indicates that the groundwater is meteoritic derived. The origin of the carbonate comprising this thick, extensive, isochronostratigraphic deposit has not been determined, but it is believed that carbonatite volcanism may have supplied elevated levels of carbonate to the basin which then entered the groundwater system. The carbonate was deposited just prior to a major trachyte‐phonolite eruption of Mount Olmoti, and the deposition of a basin wide tuff, Tuff IF. The region is seismically active today and seismic events were likely associated with Olmoti volcanism. The widespread carbonate unit may have preceded the Olmoti eruption and formed from a recurring seismically induced increase in aquifer porosity and permeability. The carbonate‐enriched groundwater episodically discharged onto the land surface, interacting locally with both fresh and saline ponded water.

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Mineralogy, geochemistry and petrology of the phonolitic to nephelinitic Sadiman volcano, Crater Highlands, Tanzania

Cited by 39 publications

References 57 publications

Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

Silicate–natrocarbonatite liquid immiscibility in 1917 eruption combeite–wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

Widespread freshwater carbonate in the Olduvai Basin, a precursor to a major eruption in the East African Rift System

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