Lead concentration and isotopic composition in five peridotite inclusions of probable mantle origin

Experimental and theoretical data from systems peridotite-$$CO_{2}-H_{2}O$$ and $$CaO-MgO-SiO_{2}-CO_{2}-H_{2}O$$ are combined, and extrapolated to 70 Kb for construction of partly schematic diagrams for subsolidus and near-solidus phase relationships of peridotite containing $$CO_{2}$$ and $$H_{2}O$$. The divariant solidus surface for peridotite-vapor in the presence of $$CO_{2} + H_{2}O$$ is traversed by a series of univariant lines marking the intersections of divariant subsolidus carbonation/decarbonation and hydration/dehydration reactions occurring in the presence of $$CO_{2}-H_{2}O$$ vapors. For$$H_{2}O-CO_{2}$$ contents up to certain limits, the vapor phase composition along these lines is buffered by carbonates or hydrous minerals, and liquid compositions are similarly defined. The approximate positions have been estimated for vapor-buffer lines on the solidus involving dolomite, amphibole, amphibole-dolomite, phlogopite, and phlogopite-dolomite. The buffering capacity of carbonate is far greater than that of hydrous minerals. Considering normal mantle peridotite with olivine, orthopyroxene and clinopyroxene, the maximum amounts of phlogopite and amphibole are produced by about 0.02% $$H_{2}O$$ and 0.4% $$H_{2}O$$., respectively. About 5% $$CO_{2}$$ is required to produce the maximum amount of dolomite without complete reaction of clinopyroxene and loss of peridotite mineralogy. The buffered curve for partly carbonated peridotite extends to lower temperatures and higher pressures from an invariant point near 26 Kb and 1,200°C Near this line there is a temperature-maximum on the peridotite-vapor solidus. On the high-pressure side of this maximum, $$CO_{2}/H_{2}O$$ is greater in liquid than in vapor; on the low-pressure side of the maximum (including all pressures below 26 Kb), $$CO_{2}/H_{2}O$$ is greater in vapor than in liquid. Because of this maximum, near-solidus magmas rising along an adiabat would evolve dissolved volatile components in the depth range 100-80 km; this could contribute to explosive eruptions. At pressures greater than 30 Kb, mantle peridotite with $$H_{2}O$$. and $$CO_{2}$$ melts along curves with vapor buffered to high $$CO_{2} /H_{2}O$$ by dolomite (magnesite at higher pressures) or dolomite + phlogopite, or a vapor-absent curve for dolomite-phlogopite-peridotite, producing low-$$SiO_{2}$$ magmas. The relationships among carbon, carbonate, and oxygen fugacity are important for determination of magma compositions.

Peridotite

Phlogopite

Amphibole

Solidus

10.1086/649737

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Citations (160)

Garnet pyroxenite lens within Ugelvik layered garnet peridotite

Earth and Planetary Science Letters (1973)

D. A. Carswell

Peridotite

Enstatite

Diopside

10.1016/0012-821x(73)90009-5

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Citations (46)

PARTIAL MELTING OF PHLOGOPITE–BEARING SYNTHETIC SPINEL– AND GARNET– LHERZOLITES

Elsevier eBooks (1975)

M.S. Bravo M. J. O’Hara

Phlogopite

Diopside

Enstatite

Forsterite

Metasomatism

Pyrope

Peridotite

10.1016/b978-0-08-018017-5.50058-4

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Citations (2)

Experimental Study of the Reaction Pyrope + Enstatite = Phlogopite in the Presence of H2O–KCl Fluid at 5 GPa in Application to the Problem of Modal Mantle Metasomatism

Springer proceedings in earth and environmental sciences (2019)

Е. В. Лиманов В. Г. Бутвина О. Г. Сафонов

Phlogopite

Enstatite

Metasomatism

Pyrope

Peridotite

10.1007/978-3-030-00925-0_18

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Citations (1)

Conditions of phlogopite formation upon interaction of carbonate melts with peridotite of the subcratonic lithosphere

Doklady Earth Sciences (2015)

Alexander G. Sokol Alexey N. Kruk Dmitry A. Chebotarev Yuri N. Palyanov N. V. Sobolev

Peridotite

Phlogopite

10.1134/s1028334x15060227

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Citations (7)

Dynamic Metasomatism Experiments Investigating the Interaction between Migrating Potassic Melt and Garnet Peridotite

Geosciences (2021)

Stephen F. Foley M. Pertermann

Dynamic metasomatism experiments were performed by reacting a lamproite melt with garnet peridotite by drawing melt through the peridotite into a vitreous carbon melt trap, ensuring the flow of melt through the peridotite and facilitating analysis of the melt. Pressure (2–3 GPa) and temperature (1050–1125 °C) conditions were chosen where the lamproite was molten but the peridotite was not. Phlogopite was formed and garnet and orthopyroxene reacted out, resulting in phlogopite wehrlite (2 GPa) and phlogopite harzburgite (3 GPa). Phlogopites in the peridotite have higher Mg/(Mg + Fe) and Cr2O3 and lower TiO2 than in the lamproite due to buffering by peridotite minerals, with Cr2O3 from the elimination of garnet. Compositional trends in phlogopites in the peridotite are similar to those in natural garnet peridotite xenoliths in kimberlites. Changes in melt composition resulting from the reaction show decreased TiO2 and increased Cr2O3 and Mg/(Mg + Fe). The loss of phlogopite components during migration through the peridotite results in low K2O/Na2O and K/Al in melts, indicating that chemical characteristics of lamproites are lost through reaction with peridotite so that emerging melts would be less extreme in composition. This indicates that lamproites are unlikely to be derived from a source rich in peridotite, and more likely originate in a source dominated by phlogopite-rich hydrous pyroxenites. Phlogopites from an experiment in which lamproite and peridotite were intimately mixed before the experiment did not produce the same phlogopite compositions, showing that care must be taken in the design of reaction experiments.

Peridotite

Phlogopite

Metasomatism

10.3390/geosciences11100432

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Citations (8)

Phlogopite Formation in the Orthopyroxene–Garnet System in the Presence of H2O–KCl Fluid in Application to the Processes of Mantle Metasomatism

Doklady Earth Sciences (2020)

Е. В. Лиманов В. Г. Бутвина О. Г. Сафонов К. В. Ван L. Ya. Aranovich

Phlogopite

Enstatite

Metasomatism