Internal sources of CO2 during anatexis under conditions of high-temperature metamorphism (experimental data)

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Partial melting experiments of garnet-two-mica schist containing 0–20 wt. % graphite were carried out at 900°C and 500 MPa. Experiments have shown that at all graphite contents (within the specified range), metapelite melts are formed by peritectic melting reactions of biotite, muscovite and partly quartz: Bt + Ms + Qz → Kfs + Spl(Hc) + oAm + Sil + Gl. The decreasing Fe3+/(Fe3++Fe2+) ratio in Fe-Mg minerals with increasing graphite content reflects increasing reducing conditions. Oxygen released as a result of the oxidation-reduction reactions of iron reacts with graphite to form CO2. It partially dissolves in the melt to form carbonate complexes of Ca, Mg, K and accompanies it in the form of a free fluid phase. Experiments demonstrate that graphite-bearing metapelites can serve as efficient internal sources of CO2 during high-temperature metamorphism.

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Sobre autores

O. Safonov

D.S. Korzhinskii Institute of Experimental Mineralogy of the Russian Academy of Sciences; Lomonosov Moscow State University

Autor responsável pela correspondência
Email: khodorevskaya@mail.ru
Rússia, Chernogolovka, Moscow Region; Moscow

L. Khodorevskaya

D.S. Korzhinskii Institute of Experimental Mineralogy of the Russian Academy of Sciences

Email: khodorevskaya@mail.ru
Rússia, Chernogolovka, Moscow Region

S. Kosova

D.S. Korzhinskii Institute of Experimental Mineralogy of the Russian Academy of Sciences

Email: khodorevskaya@mail.ru
Rússia, Chernogolovka, Moscow Region

A. Spivak

D.S. Korzhinskii Institute of Experimental Mineralogy of the Russian Academy of Sciences

Email: khodorevskaya@mail.ru
Rússia, Chernogolovka, Moscow Region

L. Aranovich

D.S. Korzhinskii Institute of Experimental Mineralogy of the Russian Academy of Sciences; Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: khodorevskaya@mail.ru

Academician of the RAS

Rússia, Chernogolovka, Moscow Region; Moscow

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2. Fig. 1. Products of experiments in backscattered electrons (BSE): a ‒ chains of hercynite-magnetite spinel (Hc) around garnet, Gl, Ilm, Qz (experiment 14D, 4 wt. % graphite); b ‒ needle-shaped and prismatic orthoamphybole crystals among the products of melt quenching Gl, Qz (experiment 16D, 20 wt. % of graphite)

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3. Fig. 2. Characteristics of melts in experimental products. (a) Diagram in coordinates A/CNK and A/NK; a vertical solid line on A/CNK = 1.0 separates the fields of low-alumina (1) and high-alumina (plumasitic) (2) granites; a vertical dotted line on A/CNK = 1.1 separates the fields of type I and type S granites [6]; a horizontal solid line at A/NK = 1.0 separates the fields of low-alumina (1) and agpaitic (3) granites [7]. (b) Diagram in SiO2‒MALI coordinates according to [7]. The gray field in Fig. 2 a, b, outlined by a dashed line, corresponds to the field of melts obtained by melting various metapelites in the pressure range of 500-1500 MPa with and without the participation of an aqueous fluid ([8] and a review therein). Symbols for Fig. 2 a, b: 1 – experiments without graphite, 2-5 – experiments with graphite content of 4.2, 10.1, 14 and 18.6 wt, respectively. %

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4. Fig. 3. (a) Representative Raman spectrum of the hardened melt from sample 14D. (b) Section 1000-1650 cm–1 is the spectrum of the hardened melt from sample 15D. Carb* ‒ doublet 1082 and 1066 cm–1 of K2Sa(CO3)2 double carbonate, Cal – calcite, Gr – graphite, Q2, Q3 – groupings of (SiO44–)-tetrahedra of various degrees of polymerization [11], Gr(D), Gr(G) – bands characterizing the degree of disordered graphite structure [12]

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5. 4. Raman spectra of carbonates from samples 14D, 15D and 17D

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6. Fig. 5. Opened (a) and not opened (b) gas bubbles in glass

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7. Fig. 6. Raman spectrum of gas bubbles in the glass of sample 14D with characteristic peaks of CO2 — Fermi dyads

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