Chemical composition of nyerereite and gregoryite from natrocarbonatites of Oldoinyo Lengai volcano, Tanzania

Zaitsev, Anatoly N.; Keller, Jörg; Spratt, John; Jeffries, Teresa; Sharygin, Victor V.

doi:10.1134/s1075701509070095

Cited by 45 publications

(61 citation statements)

References 21 publications

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“…This mineral assemblage is similar to other inclusions observed in gregoryite crystals (Mitchell 2006). The outer rims of the gregoryites are generally more sodium rich compared to the cores (Peterson 1990;Zaitsev et al 2008). Fig.…”

Section: Petrography Of Natrocarbonatitic Lavassupporting

confidence: 62%

“…In a recent paper, Zaitsev et al (2008) reported that some samples of natrocarbonatite from Oldoinyo Lengai display distinctively different gregoryite compositions (i.e., lower Na 2 O and higher CaO content) than found in most lavas from the volcano. The sample (OL-3a in Zaitsev et al 2008) is fast quenched lapilli from the 1992 eruption of Oldoinyo Lengai.…”

Section: Discussion Phase Equilibria: Implications For Magma Ascentmentioning

confidence: 99%

“…The sample (OL-3a in Zaitsev et al 2008) is fast quenched lapilli from the 1992 eruption of Oldoinyo Lengai.…”

Section: Discussion Phase Equilibria: Implications For Magma Ascentmentioning

confidence: 99%

“…The lavas are generally crystal rich (30-85 vol.%; Dawson et al 1990Dawson et al , 1994Mattsson and Vuorinen 2009), although near-aphyric varieties also occur (Dawson et al 1995b). The main phenocryst phases in the lavas are the alkali carbonates nyerereite and gregoryite (Na 2 Ca[CO 3 ] 2 and [Na,Ca x ,K] 2 − x CO 3 respectively; McKie and Frankis 1977;Zaitsev et al 2008). The groundmass is predominantly composed of variable amounts of sylvite, fluorite, gregoryite, and alabandite (Peterson 1990;Mitchell 1997Mitchell , 2006.…”

Section: Petrography Of Natrocarbonatitic Lavasmentioning

confidence: 99%

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Experimental constraints on the crystallization of natrocarbonatitic lava flows

Mattsson

Caricchi

2009

Bull Volcanol

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Natrocarbonatitic magmas are characterized by their extremely low viscosities and fast elemental diffusion, and as a consequence of this, their chemistry and crystallinity can change significantly during residence in shallow reservoirs or even due to cooling during lava flow emplacement. Here, we present the results of a series of crystallization experiments conducted at 1-atm confining pressure and in a temperature range between 630°C and 300°C. The experiments were set up to characterize the chemistry and growth processes of the phenocryst phases present in natrocarbonatites. The results are applicable to (1) processes occurring during residence in shallow magma reservoirs and/or (2) during lava flow emplacement. We show that during crystallization of natrocarbonatites at atmospheric pressure, gregoryite is the first mineral to crystallize at 630°C, followed by nyerereite at 595°C. Crystal size distributions of the gregoryites show that the crystals grow rapidly by textural coarsening (i.e., Ostwald ripening). As the crystallization is a continuous process at this pressure, the composition of the residual melt changes in response to the crystallization. However, the experiments also show that individual crystals completely reequilibrate with the changes in melt composition in as little time as <11 min. We therefore conclude that crystallization and diffusion are extremely fast processes in the natrocarbonatitic system and that the measured chemical variations in phenocrysts from Oldoinyo Lengai can be explained by different cooling histories. Finally, we model the rheological control on the emplacement of highly crystallized natrocarbonatitic lavas at Oldoinyo Lengai.

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Section: Petrography Of Natrocarbonatitic Lavassupporting

confidence: 62%

Section: Discussion Phase Equilibria: Implications For Magma Ascentmentioning

confidence: 99%

“…The sample (OL-3a in Zaitsev et al 2008) is fast quenched lapilli from the 1992 eruption of Oldoinyo Lengai.…”

Section: Discussion Phase Equilibria: Implications For Magma Ascentmentioning

confidence: 99%

Section: Petrography Of Natrocarbonatitic Lavasmentioning

confidence: 99%

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Experimental constraints on the crystallization of natrocarbonatitic lava flows

Mattsson

Caricchi

2009

Bull Volcanol

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“…1). The volcano is famous for its unique low-temperature and lowviscosity natrocarbonatites (Keller and Krafft, 1990;Peterson, 1990;Zaitsev et al, 2009). However, the 3000 m high cone is made up of predominantly silicate lavas and pyroclastics (Donaldson et al, 1987;Dawson et al, 1989;Dawson, 1998;Klaudius and Keller, 2006).…”

Section: Introductionmentioning

confidence: 99%

Melilite-group minerals at Oldoinyo Lengai, Tanzania

Wiedenmann

Keller

Zaitsev

2010

Lithos

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Oldoinyo Lengai and the volcanic centres of the Lake Natron-Engaruka province contain melilite as a widespread mineral. Extraordinarily Na-Al-rich melilites (up to 6 wt.% Na 2 O and 9 wt.% Al 2 O 3 ) from recent explosive eruptions are among the most Na-rich ever reported. Their unusual mineral composition leads to optical properties with vivid birefringence colours of 2nd order. The continuous variation in mineral composition from common åkermanite to Na-Al-melilite (alumoåkermanite) is documented and reflects the whole peralkaline trend of Oldoinyo Lengai. The data presented allow the volcano's evolution from primitive olivine melilitites to highly evolved and peralkaline combeite-wollastonite nephelinites to be traced. Melilite compositions of Oldoinyo Lengai extend the magmatic field in the Ca 2 Fe(Si 2 O 7 )-Ca 2 Mg(Si 2 O 7 )-(CaNa)Al (Si 2 O 7 ) end-member ternary compositional diagram.

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In situ ambient and high‐temperature Raman spectroscopic studies of nyerereite (Na,K)₂Ca(CO₃)₂: can hexagonal zemkorite be stable at earth‐surface conditions?

Golovin

Korsakov

Zaitsev

2015

J Raman Spectroscopy

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In this study we present Raman spectroscopy data obtained from a naturally occurring orthorhombic nyerereite (Na,K)2Ca(CO3)2 from the Oldoinyo Lengai volcano (Tanzania) at ambient and high temperature. Nyerereite was heated up to 300 °C, 400 °C and 500 °C, and is believed to have been transformed at high temperatures to hexagonal β‐ and γ‐phases similar to zemkorite, (Na,K)2Ca(CO3)2. There are no major differences in the chemical composition of natural nyerereite and zemkorite. However, Raman spectra reveal significant differences between the nyerereite at ambient temperature and the phases obtained in the course of all our high‐temperature experiments. In situ measurements show that none of the high‐temperature hexagonal phases are quenchable, even at very high cooling rates (up to 50–80 °C/min), and they transform to nyerereite at ambient temperature. Contrary to previous studies even the presence of high K2O (up to 7.5 wt.%) did not stabilize the hexagonal structure during cooling. The cooling rates in our experiments were much higher than those at natural magmatic or hydrothermal systems; therefore hexagonal zemkorite is not likely to survive within natural systems as it transforms to nyerereite at ambient conditions. Thus, we do not expect to find zemkorite in any magmatic, metasomatic or hydrothermal rocks exposed at the Earth's surface. Copyright © 2015 John Wiley & Sons, Ltd.

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Chemical composition of nyerereite and gregoryite from natrocarbonatites of Oldoinyo Lengai volcano, Tanzania

Cited by 45 publications

References 21 publications

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Melilite-group minerals at Oldoinyo Lengai, Tanzania

In situ ambient and high‐temperature Raman spectroscopic studies of nyerereite (Na,K)₂Ca(CO₃)₂: can hexagonal zemkorite be stable at earth‐surface conditions?

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Chemical composition of nyerereite and gregoryite from natrocarbonatites of Oldoinyo Lengai volcano, Tanzania

Cited by 45 publications

References 21 publications

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Melilite-group minerals at Oldoinyo Lengai, Tanzania

In situ ambient and high‐temperature Raman spectroscopic studies of nyerereite (Na,K)2Ca(CO3)2: can hexagonal zemkorite be stable at earth‐surface conditions?

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In situ ambient and high‐temperature Raman spectroscopic studies of nyerereite (Na,K)₂Ca(CO₃)₂: can hexagonal zemkorite be stable at earth‐surface conditions?