Инд. авторы:	Sokol A.G., Palyanova G.A., Palyanov Y.N., Tomilenko A.A., Melenevsky V.N.
Заглавие:	Fluid regime and diamond formation in the reduced mantle: Experimental constraints
Библ. ссылка:	Sokol A.G., Palyanova G.A., Palyanov Y.N., Tomilenko A.A., Melenevsky V.N. Fluid regime and diamond formation in the reduced mantle: Experimental constraints // Geochimica et Cosmochimica Acta. - 2009. - Vol.73. - Iss. 19. - P.5820-5834. - ISSN 0016-7037. - EISSN 1872-9533.
Внешние системы:	DOI: 10.1016/j.gca.2009.06.010; SCOPUS: 2-s2.0-69149099293;
Реферат:	eng: The composition and potential diamond productivity of C-O-H fluids that could exist in the reduced regions of the Earth's upper mantle and in the mantles of Uranus and Neptune were studied in experiments at 6.3 GPa and 1400-1600 °C and durations of 15-48 h. Hydrogen fugacity in the fluid phase was controlled by the Mo-MoO2 or Fe-FeO buffers, using a specially modified double-capsule method. The oxygen fugacity in the samples was controlled by adding different amounts of water, stearic acid, anthracene, and docosane to a graphite charge. At high P-T conditions, the degree of decomposition of the heavy hydrocarbons added to the charge was ≥99.9%. The composition of the fluids coexisting with graphite/diamond in the buffered experiments varied from H2O ≫ H2 > CH4 (at fO2 somewhat lower than the 'water maximum') to H2 > CH4 > (C2H4 + C2H6)>C3H8 (in C-H system). In the C-H system the maximum concentrations of major species in the synthesized fluid were: H2 = 79 mol.% and CH4 = 21 mol.%. The composition of the H2-rich fluids, which were synthesized at 6.3 GPa and 1400-1600 °C for the first time, differs considerably from that of the ultra-reduced CH4-rich fluids stable at 2.0-3.5 GPa and 1000-1300 °C. Thermodynamic calculations of the reduced C-O-H fluids at the P-T conditions of the experiments revealed CH4-rich compositions (CH4 ≫ H2 > (C2H4 + C2H6)>C3H8), which however drastically differed from the synthesized compositions. The rates of diamond nucleation and growth in the experiments depended on the fluid composition. Diamond crystallization had a maximum intensity in the pure aqueous fluids, while in the H2-rich fluids no diamond formation was observed. Only metastable graphite precipitated from the ultra-reduced fluids. The type of the initial hydrocarbon used for the fluid generation did not affect this process. © 2009 Elsevier Ltd. All rights reserved.
Ключевые слова:	thermodynamics; P-T conditions; Neptune; isotopic composition; hydrocarbon; Uranus; fluid inclusion; experimental study; diamond; crystallization; graphite;
Издано:	2009
Физ. характеристика:	с.5820-5834