Direct observation of complete miscibility in the albite–H2O system

Shen, Andy H.; Keppler, Hans

doi:10.1038/385710a0

Cited by 202 publications

(95 citation statements)

References 13 publications

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“…The heating and cooling rates were about 5°C∕s, which is comparable to those adopted in the studies on the observation of critical behavior between aqueous fluid and silicate melt using a hydrothermal diamond-anvil cell (27,28,32,36). The X-ray camera was on at all times during the experiment, and images were recorded from the beginning of the heating (i.e., room T) until quenching.…”

Section: Methodsmentioning

confidence: 70%

“…Under high-pressure (P) and high-temperature (T) conditions, it has been shown that the solubility of both water in silicate melt (13)(14)(15)(16) and silicate in aqueous fluid (13,(17)(18)(19)(20)(21)(22)(23)(24)(25) increases with increasing P. As a result, silicate melt and aqueous fluid in the interior of the Earth are expected to become SCF, and the hydrous solidus of the system can no longer be defined beyond a certain critical condition (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). This condition is called the second (or upper) critical endpoint (26) and is the point of intersection between the critical curve and hydrous solidus.…”

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confidence: 99%

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Slab melting versus slab dehydration in subduction-zone magmatism

Mibe

Kawamoto

Matsukage

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

156

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The second critical endpoint in the basalt-H 2 O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770°C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones.water | island arc | silicate melt | synchrotron X-ray | high-pressure research W ater plays an important role in subduction-zone magmatism because it can reduce the melting temperature of rocks in subduction zones and hence can generate magmas (1-7). There is a long-standing debate about whether the fluids released from a subducting slab are aqueous fluid, hydrous silicate melt, supercritical fluid (SCF), or a combination of these (2,4,(8)(9)(10)(11)(12). Whether the subducting slab melts or dehydrates depends on the thermal structure and the phase relation of slab materials under hydrous conditions. Therefore, this long-standing question cannot be answered until the detailed stability fields of these fluids are clarified.Under high-pressure (P) and high-temperature (T) conditions, it has been shown that the solubility of both water in silicate melt (13-16) and silicate in aqueous fluid (13, 17-25) increases with increasing P. As a result, silicate melt and aqueous fluid in the interior of the Earth are expected to become SCF, and the hydrous solidus of the system can no longer be defined beyond a certain critical condition (26-36). This condition is called the second (or upper) critical endpoint (26) and is the point of intersection between the critical curve and hydrous solidus. Basalt is one of the dominant constituents of a subducting slab and is considered the main carrier of water that triggers the melting of rocks in subduction zones. Therefore, the second critical endpoint in the basalt-H 2 O system has to be determined in order to understand fully the subduction-zone magmatism.In some silicic silicate-H 2 O systems, the location of the second critical endpoint has been reported [e.g., 1.0 GPa, 1,080°C in the SiO 2 -H 2 O system (13); 1.5 GPa, 670°C in the system NaAlSi 3 O 8 -H 2 O (21); 1.5 GPa, 800°C in the system KAlSi 3 O 8 -H 2 O (36)]. In mafic systems, however, the determination of the second critical endpoints is not easy because of the difficulty in identifying phases (aqueous fluid versus hydrous silicate melt) in the recovered samples quenched from high-P and high-T conditio...

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Section: Methodsmentioning

confidence: 70%

mentioning

confidence: 99%

Slab melting versus slab dehydration in subduction-zone magmatism

Mibe

Kawamoto

Matsukage

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

156

View full text Add to dashboard Cite

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“…While this is indeed verified for relatively small and cool planets (from Ganymede to the Earth), the question arises for planets that may be large and hot enough for their interior to be predominantly molten. Molten silicate and water are known to be miscible with each other at pressures above a few GPa and temperatures > ∼1000 K (Shen & Keppler 1997;Mibe et al 2007). Above ∼10 000 K, silicate and iron are also no longer immiscible (Stevenson 2008).…”

Section: Possibility Of An Undifferentiated Structurementioning

confidence: 99%

Composition and fate of short-period super-Earths

Valencia¹,

Ikoma

Guillot³

et al. 2010

A&A

232

294

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Context. The discovery of CoRoT-7b, a planet of a radius 1.68 ± 0.09 R ⊕ , a mass 4.8 ± 0.8 M ⊕ , and an orbital period of 0.854 days demonstrates that small planets can orbit extremely close to their star. Aims. Several questions arise concerning this planet, in particular concerning its possible composition, and fate. Methods. We use knowledge of hot Jupiters, mass loss estimates and models for the interior structure and evolution of planets to understand its composition, structure and evolution. Results. The inferred mass and radius of CoRoT-7b are consistent with a rocky planet that would be significantly depleted in iron relative to the Earth. However, a one sigma increase in mass (5.6 M ⊕ ) and one sigma decrease in size (1.59 R ⊕ ) would make the planet compatible with an Earth-like composition (33% iron, 67% silicates). Alternatively, it is possible that CoRoT-7b contains a significant amount of volatiles. For a planet made of an Earth-like interior and an outer volatile-rich vapour envelope, an equally good fit to the measured mass and radius is found for a mass of the vapour envelope equal to 3% (and up to 10% at most) of the planetary mass. Because of its intense irradiation and small size, we determine that the planet cannot possess an envelope of hydrogen and helium of more than 1/10 000 of its total mass. We show that a relatively significant mass loss ∼10 11 g s −1 is to be expected and that it should prevail independently of the planet's composition. This is because to first order, the hydrodynamical escape rate is independent of the mean molecular mass of the atmosphere, and because given the intense irradiation, even a bare rocky planet would be expected to possess an equilibrium vapour atmosphere thick enough to capture stellar UV photons. Clearly, this escape rate rules out the possibility that a hydrogen-helium envelope is present, as it would escape in only ∼1 Ma. A water vapour atmosphere would escape in ∼1 Ga, indicating that this is a plausible scenario. The origin of CoRoT-7b cannot be inferred from the present observations: It may have always had a rocky composition; it may be the remnant of a Uranus-like ice giant, or a gas giant with a small core that has been stripped of its gaseous envelope. Conclusions. With high enough sensitivity, spectroscopic transit observations of CoRoT-7 should constrain the composition of the evaporating flow and therefore allow us to distinguish between a rocky planet and a volatile-rich vapour planet. In addition, the theoretical tools developed in this study are applicable to any short-period transiting super-Earth and will be important to understanding their origins.

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“…8). The physical conditions in the system NaAlSi 3 O 8 -H 2 O with different fluxes (F, Cl, B, P) at variable pressures and incidence of this system in the residual pegmatitic system have been addressed experimentally by several authors (e.g., Swanson and Fenn 1992;Shen and Keppler 1997;Sowerby and Keppler 2002). From these works, it is known that the liquidus in the albite-H 2 O system is lowered considerably by the presence of F, B and P at ~800-600 ºC.…”

Section: Discussionmentioning

confidence: 99%

The anatomy of an albite-type granitic pegmatite from the Totoral pegmatite field, San Luis, Argentina

Galliski¹,

Márquez-Zavalía²,

Černý³

et al. 2015

J. Geosci.

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The Independencia Argentina albite-type granitic pegmatite is the most distal differentiate in the Cerro La Torre pegmatite group, located in the Eastern Pampean Ranges of Argentina. It is a zoned pegmatite formed at two main stages that probably shared the same origin but had separate evolutions. The product of the first stage was a pegmatite dominated by albite, quartz and muscovite, with rare K-feldspar and muscovite + albite pseudomorphs after spodumene, and accessory columbite-group minerals, beryl, fluorapatite as well as garnet. This first-stage pegmatite was emplaced forcefully and crystallized syn-kinematically. Resulting boudinage and necking-down produced the main body, bulbous in shape and asymmetric in zoning. This pegmatite was subsequently intruded by a melt that solidified to a very fine-grained, saccharoidal albite unit, composed in excess of 97 % by Ab 99.1-99.6 , with accessory columbite-group minerals and fluorapatite. The normative mineral composition of this unit corresponds very well with that of the experimental products of protracted fractionation of rare-element pegmatite melts, with high Na/K ratios and HFSE enrichment. The spatial and temporal association of the two pegmatitic melts, one enriched in H 2 O and the other one more evolved, Na-rich, almost alkaline and flux-bearing, strongly suggests that the two are cogenetic. They probably represent products of a rare-element pegmatite magma differentiation at depth that were extracted at different stages of its crystallization and emplaced at higher crustal levels.

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Direct observation of complete miscibility in the albite–H2O system

Cited by 202 publications

References 13 publications

Slab melting versus slab dehydration in subduction-zone magmatism

Slab melting versus slab dehydration in subduction-zone magmatism

Composition and fate of short-period super-Earths

The anatomy of an albite-type granitic pegmatite from the Totoral pegmatite field, San Luis, Argentina

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