The system Na 2 CO 3 -K 2 CO 3 -CaCO 3 at 1 kilobar and its significance in carbonatite petrogenesis

Cooper, Alan F.; Gittins, J.; Tuttle, O. F.

doi:10.2475/ajs.275.5.534

Cited by 141 publications

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“…Previous experimental work has shown that nyerereite is the first mineral on the liquidus of natrocarbonatitic magmas at 100 and 20 MPa (Cooper et al 1975;Gittins and McKie 1980;Petibon et al 1998). However, these experimental results also clearly indicate that as pressure is reduced, the stability field of gregoryite expands to higher temperature.…”

Section: Discussion Phase Equilibria: Implications For Magma Ascentcontrasting

confidence: 45%

“…The experimental charges were kept for 30 min at 750°C (i.e., above the liquidus of natrocarbonatitic melts; Cooper et al 1975;Peterson 1990) to homogenize and equilibrate the starting material before controlled cooling was initiated. Two sets of experiments were conducted: In the first, five samples were cooled at a fixed rate of 3.2°C/min and quenched at different final temperatures (ranging from 630°C to 490°C; Fig.…”

Section: Materials and Methods Experimental Starting Materials And Setupmentioning

confidence: 99%

“…However, the extremely low melt viscosities and high diffusion rates that characterize natrocarbonatitic magmas (Gaillard et al 2008) could favor rapid crystallization during emplacement of lava flows (e.g., the crystal content of a solidified lava flow is not identical to the crystal content during emplacement). Previous experimental studies focused on the crystallization of natrocarbonatitic magmas have been conducted at 100 and 20 MPa confining pressure (Cooper et al 1975;Petibon et al 1998). However, rapid magma drainage and formation of a pit crater at Oldoinyo Lengai following the March-April 2006 eruption shows that a significant volume of natrocarbonatitic magma has been stored at shallow levels beneath the hornitos inside the summit crater (i.e., the collapse exposed a network of several small interconnected magma reservoirs located at 0-40 m depth; Kervyn et al 2008).…”

Section: Introductionmentioning

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: Discussion Phase Equilibria: Implications For Magma Ascentcontrasting

confidence: 45%

Section: Materials and Methods Experimental Starting Materials And Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental constraints on the crystallization of natrocarbonatitic lava flows

Mattsson

Caricchi

2009

Bull Volcanol

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“…The crystal fraction in this fractionation process, mainly of calcite (or dolomite), together with other minerals such as magnetite, apatite, sulphides, pyrochlore, etc., which have been precipitated by the carbonatite liquid and then accumulated on the floor of the magma chambers are the raw material for the coarse-grained intrusive carbonatites which ultimately form the cores of many ring complexes. The liquidus phase diagram of Cooper et al (1975) is relevant to this process of accumulation of calcite; part of this diagram is shown on Fig. 8.…”

Section: Petrologymentioning

confidence: 99%

“…Three widely different models have been proposed suggesting that carbonatite magmas are: (1) a direct product of partial melting of mantle material (von Eckermann, 1948;Holmes, 1952;Dawson, 1962Dawson, , 1966Eggler, 1975;Koster Van Groos, 1975); (2) a differentiation product of a carbonated silicate liquid (King, 1949;King and Sutherland, 1960;Watkinson and Wyllie, 1971;Wyllie, 1987); (3) an immiscible carbonate liquid separated from an originally homogeneous carbonated silicate melt (von Eckermann, 1961;King, 1965;Koster Van Groos and Wyllie, 1966, 1968, 1973Middlemost, 1974;Cooper et al, 1975;Le Bas, 1977, 1981Freestone and Hamilton, 1980). The hypothesis of liquid immiscibility has recently been favoured by many authors, but a major objection is the contrasting evidence deduced from field and experimental relations.…”

Section: Introductionmentioning

confidence: 99%

Liquid immiscibility and the origin of alkali-poor carbonatites

1988

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The work on liquid immiscibility in carbonate-silicate systems of Freestone and Hamilton (1980) has been extended to include alkali-poor and alkali-free compositions. Immiscibility is shown to occur on the j oins albite-calcite and anorthite-calcite at 5 kbar. These results make it possible to interpret ocellar structure between calcite-rich spheroids in lamproite or kimberlite host rock as products of liquid immiscibility. The common sequence of rock types found in carbonatite complexes of melilitite-ijolite-urtite-phonolite is interpreted as being the result of both fractional crystallization and liquid fractionation, the corresponding carbonatite composition changing from nearly pure CaCO 3 ( + MgCO3) progressively to natrocarbonate. A carbonate melt cooling in isolation will suffer crystal fractionation, the residual liquid producing the rarer ferrocarbonatites, etc., whilst the crystal accumulate of calcite (dolomite) plus other phases such as magnetite, apatite, baryte, pyrochlore, etc., are the raw material for the coarse-grained intrusive carbonatites commonly found in ring complexes.

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High‐Pressure Na‐Ca Carbonates in the Deep Carbon Cycle

Rashchenko

Shatskiy

Litasov

2020

Geophysical Monograph Series

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Carbonates play a central role in the subduction transport of oxidized carbon from Earth's surface to the deep mantle. The melting of carbonated rocks also leads to the release of carbonate melts, regarded as important oxidizing and metasomatizing agents, from the subducting slab. Although at upper mantle conditions the chemistry of carbonates within the subducting slab is restricted to the thoroughly studied ternary CaCO 3 -MgCO 3 -FeCO 3 system, recent experimental and natural evidences strongly suggest that at conditions of the mantle transition zone, Na-Ca carbonates become the main host of oxidized carbon and define solidus temperatures and chemistry of deep melts. In this chapter, we discuss transport of carbonates to the mantle transition zone within the subducting slab, evidences of sodium migration from silicates into carbonates under high pressure, and crystal chemistry of currently known high-pressure Na-Ca carbonates. 13 13.

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The system Na 2 CO 3 -K 2 CO 3 -CaCO 3 at 1 kilobar and its significance in carbonatite petrogenesis

Cited by 141 publications

References 0 publications

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Liquid immiscibility and the origin of alkali-poor carbonatites

High‐Pressure Na‐Ca Carbonates in the Deep Carbon Cycle

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