TY - JOUR

T1 - Iron carbide as a source of carbon for graphite and diamond formation under lithospheric mantle P-T parameters

AU - Bataleva, Yuliya V.

AU - Palyanov, Yuri N.

AU - Borzdov, Yuri M.

AU - Bayukov, Oleg A.

AU - Zdrokov, Evgeniy V.

N1 - Publisher Copyright: © 2017 Elsevier B.V.

PY - 2017/8/1

Y1 - 2017/8/1

N2 - Experimental modeling of natural carbide-involving reactions, implicated in the graphite and diamond formation and estimation of the iron carbide stability in the presence of S-bearing fluids, sulfide melts as well as mantle silicates and oxides, was performed using a multi-anvil high-pressure split-sphere apparatus. Experiments were carried out in the carbide-sulfur (Fe3C-S), carbide-sulfur-oxide (Fe3C-S-SiO2-MgO) and carbide-sulfide (Fe3C-FeS2) systems, at pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–40 h. During the interaction of cohenite with S-rich reduced fluid or pyrite at 900–1100 °C, extraction of carbon from carbide was realized, resulting in the formation of graphite in assemblage with pyrrhotite and cohenite. At higher temperatures complete reaction of cohenite with newly-formed sulfide melt was found to produce metal-sulfide melt with dissolved carbon (Fe64S27C9 (1200 °C)–Fe54S40C6 (1500 °C), at.%), which acted as a crystallization medium for graphite (1200–1600 °C) and diamond growth on seeds (1300–1600 °C). Reactions of cohenite and oxides with S-rich reduced fluid resulted in the formation of graphite in assemblage with highly ferrous orthopyroxene and pyrrhotite (900–1100 °C) or in hypersthene formation, as well as graphite crystallization and diamond growth on seeds in the Fe-S-C melt (1200–1600 °C). We show that the main processes of carbide interaction with S-rich fluid or sulfide melt are recrystallization of cohenite (900–1100 °C), extraction of carbon and iron in the sulfide melt, and graphite formation and diamond growth in the metal-sulfide melt with dissolved carbon. Our results evidence that iron carbide can act as carbon source in the processes of natural graphite and diamond formation under reduced mantle conditions. We experimentally demonstrate that cohenite in natural environments can be partially consumed in the reactions with mantle silicates and oxides, and is absolutely unstable in the presence of S-bearing reduced fluid or sulfide melt at temperatures higher than 1100 °C, under lithospheric mantle pressures.

AB - Experimental modeling of natural carbide-involving reactions, implicated in the graphite and diamond formation and estimation of the iron carbide stability in the presence of S-bearing fluids, sulfide melts as well as mantle silicates and oxides, was performed using a multi-anvil high-pressure split-sphere apparatus. Experiments were carried out in the carbide-sulfur (Fe3C-S), carbide-sulfur-oxide (Fe3C-S-SiO2-MgO) and carbide-sulfide (Fe3C-FeS2) systems, at pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–40 h. During the interaction of cohenite with S-rich reduced fluid or pyrite at 900–1100 °C, extraction of carbon from carbide was realized, resulting in the formation of graphite in assemblage with pyrrhotite and cohenite. At higher temperatures complete reaction of cohenite with newly-formed sulfide melt was found to produce metal-sulfide melt with dissolved carbon (Fe64S27C9 (1200 °C)–Fe54S40C6 (1500 °C), at.%), which acted as a crystallization medium for graphite (1200–1600 °C) and diamond growth on seeds (1300–1600 °C). Reactions of cohenite and oxides with S-rich reduced fluid resulted in the formation of graphite in assemblage with highly ferrous orthopyroxene and pyrrhotite (900–1100 °C) or in hypersthene formation, as well as graphite crystallization and diamond growth on seeds in the Fe-S-C melt (1200–1600 °C). We show that the main processes of carbide interaction with S-rich fluid or sulfide melt are recrystallization of cohenite (900–1100 °C), extraction of carbon and iron in the sulfide melt, and graphite formation and diamond growth in the metal-sulfide melt with dissolved carbon. Our results evidence that iron carbide can act as carbon source in the processes of natural graphite and diamond formation under reduced mantle conditions. We experimentally demonstrate that cohenite in natural environments can be partially consumed in the reactions with mantle silicates and oxides, and is absolutely unstable in the presence of S-bearing reduced fluid or sulfide melt at temperatures higher than 1100 °C, under lithospheric mantle pressures.

KW - Diamond

KW - Graphite

KW - High-pressure experiment

KW - Iron carbide

KW - Mantle sulfides

KW - Sulfur-rich fluid

KW - CORE

KW - HIGH-PRESSURE

KW - INCLUSIONS

KW - SULFIDES

KW - SULFUR

KW - EARTHS DEEP MANTLE

KW - REDOX BUDGET

KW - EVOLUTION

KW - KAAPVAAL CRATON

KW - METAL

UR - http://www.scopus.com/inward/record.url?scp=85021730601&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2017.06.010

DO - 10.1016/j.lithos.2017.06.010

M3 - Article

AN - SCOPUS:85021730601

VL - 286-287

SP - 151

EP - 161

JO - Lithos

JF - Lithos

SN - 0024-4937

ER -