Geochemistry of ultrapotassic volcanic rocks in Xiaogulihe NE China: Implications for the role of ancient subducted sediments

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)

Breakdown of Phlogopite in Presence of Carbonate: Metasomatic Agents in the Sub-Continental Lithospheric

Christopher M. Scarfe Robert W. Luth

Summary First results in the phlogopite + magnesite (KMASH-CO2) system demonstrate that a potassiumbearing fluid will be the metasomatic agent at sub-continental-lithospheric-mantle conditions with a continental geotherm of 40 mWm -2 . In this case, phlogopite can be stable to a depth of 200 km in the presence of carbonate, and will coexist with potassic fluids. Assuming a hotter geotherm of 44 mWm -2 , these fluids can be present to a depth of about 180 km. Beyond this depth, at the base of a thick sub-continental lithospheric mantle, a hydrous, potassium- and CO2-rich silicate melt would be the metasomatic agent. In this system, garnet is present above solidus as a residual phase, which implies that a K-CO2-H2O-enriched metasomatic fluid or melt could react with garnet peridotite to form phlogopite.

Phlogopite

Metasomatism

Peridotite

Solidus

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Citations (1)

Implications of experimental petrology to the evolution of ultrapotassic rocks

Lithos (1992)

A. D. Edgar D. Vukadinovic

Phlogopite

Metasomatism

Amphibole

10.1016/0024-4937(92)90007-l

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Citations (48)

Phlogopite-Forming Reactions as Indicators of Metasomatism in the Lithospheric Mantle

Minerals (2019)

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

Phlogopite is widely accepted as a major mineral indicator of the modal metasomatism in the upper mantle within a very wide P–T range. The paper reviews data on various phlogopite-forming reactions in upper-mantle peridotites. The review includes both descriptions of naturally occurring reactions and results of experiments that model some of these reactions. Relations of phlogopite with other potassic phases, such as K-richterite, sanidine and K-titanates, are discussed. These data are taken as a basis for thermodynamic modeling of the phlogopite-forming reactions for specific mantle rocks in terms of log(aH2O) − log(aK2O) diagrams (pseudosections) using the Gibbs free energy minimization. These diagrams allow estimation of potassium-water activity relations during metasomatic transformations of mantle rocks, prediction sequences of mineral assemblages with respect to these parameters and comparison of metasomatic processes in the rocks of different composition. This approach is illustrated by examples from peridotite xenoliths from kimberlites.

Phlogopite

Metasomatism

Peridotite

Xenolith

10.3390/min9110685

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Citations (36)

Rb-Sr isotope systematics in a phlogopite-bearing spinel lherzolite and its implications for age and origin of metasomatism in the Horoman peridotite complex, Hokkaido, Japan.

JOURNAL OF MINERALOGY PETROLOGY AND ECONOMIC GEOLOGY (1993)

Masako Yoshikawa Eizo Nakamura Natsuko Takahashi

23.0±1.2 Ma was obtained by Rb-Sr method for a phlogopite-bearing spinel lherzolite from the Horoman peridotite complex in the Hidaka metamorphic belt, Hokkaido, Japan. The age is essentially identical to the oldest ages of the country metamorphic rocks reported so far in the Hidaka metamorphic belt, and may indicate the time of a metasomatic event which occurred in the wedge mantle. This metasomatic event may have occurred during uplift of this mantle fragment under mantle conditions contemporaneously with elevation of the Hidaka metamorphic belt resulting from collision between the Eurasian and North American plates.

Peridotite

Metasomatism

Phlogopite

10.2465/ganko.88.121

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Citations (35)

Metasomatic processes in the lithospheric mantle beneath the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province, Russia)

Russian Geology and Geophysics (2015)

Elena Shchukina A. M. Agashev S. I. Kostrovitsky N. P. Pokhilenko

Phlogopite

Metasomatism

Peridotite