Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite

doi:10.2138/am.2014.4696

	Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite
	Lazar, Codi 1,2; Zhang, Chi 1,3; Manning, Craig E.2; Mysen, Bjorn O.1
刊名	AMERICAN MINERALOGIST
	2014-08-01
卷号	99 期号:8-9 页码:1604-1615
关键词	Carbon cycle subduction zones fluid-rock interaction serpentinization forearc mantle methanogenesis
ISSN号	0003-004X
DOI	10.2138/am.2014.4696
文献子类	Article
英文摘要	Oxygen fugacity (f(O2)) is a fundamental parameter that controls carbon mobility in aqueous fluids in geological environments such as subduction zones, where reduced serpentinite fluids have the potential to infiltrate oxidized carbonate-bearing lithologies. Using experiments and calculations, we describe how mineral-fluid equilibria evolve as f(O2) decreases in the model Ca-C-O-H system at forearc conditions (300-700 degrees C and 2-10 kbar). Experimental calcite solubility was constant at f(O2) values from quartz-fayalite-magnetite (QFM) to hematite-magnetite (HM). At lower f(O2) values of iron-magnetite (IM) or wustite-magnetite (WM), calcite reacted with H-2 to form methane plus portlandite or melt. These results were consistent with thermodynamic calculations and indicate that carbon mobility, as parameterized by total aqueous carbon ([C-TOT]), is strongly dependent on f(O2). At constant pressure and temperature, carbon mobility is minimized at oxidizing conditions, where [C-TOT] is controlled by calcite solubility. Carbon mobility is maximized at the most reducing conditions because all the carbon in the system is present as CH4. An intermediate region of carbon mobility exists in which calcite is stable with a CH4-bearing fluid. As pressure increases from 2 to 10 kbar, the f(O2) range over which calcite is stable with a methane-rich fluid shifts to more reducing conditions. The variety of geological conditions with the potential for redox enhancement of carbon mobility becomes more restricted with depth. Reduction melting was observed at 700 degrees C and 6 kbar, and at 650 degrees C and 10 kbar, due to the partial reaction of calcite to portlandite at conditions above the hydrous melting curve of calcite+portlandite. Although likely metastable in the present experiments, reduction melting may occur in nature whenever H-2 partially reduces carbonate minerals at pressures and temperatures above the hydrous melting curve of calcite+portlandite. Whether it causes melting or not, calcite reduction is likely an important mechanism for abiotic methanogenesis in natural systems such as subduction zone forearcs or similar environments with the potential for interaction of reduced fluids with carbonate minerals. Because calcite solubility at oxidized conditions is already known to increase substantially with pressure, the additional increase in carbon mobility provided by calcite reduction implies that subduction zones may host some of the most carbon-rich aqueous fluids on Earth.
WOS关键词	UPPER-MANTLE CONDITIONS ; HIGH-PRESSURES ; ROCK INTERACTION ; AQUEOUS FLUIDS ; SYSTEM CAO-CO2-H2O ; TEMPERATURES ; SOLUBILITY ; INCLUSIONS ; IRON ; SERPENTINIZATION
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
语种	英语
出版者	MINERALOGICAL SOC AMER
WOS记录号	WOS:000340580500010
资助机构	NSF(EAR-1049901) ; NSF(EAR-1049901) ; Deep Carbon Observatory ; Deep Carbon Observatory ; NSF(EAR-1049901) ; NSF(EAR-1049901) ; Deep Carbon Observatory ; Deep Carbon Observatory ; NSF(EAR-1049901) ; NSF(EAR-1049901) ; Deep Carbon Observatory ; Deep Carbon Observatory ; NSF(EAR-1049901) ; NSF(EAR-1049901) ; Deep Carbon Observatory ; Deep Carbon Observatory
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/85908]
专题	中国科学院地质与地球物理研究所
通讯作者	Lazar, Codi
作者单位	1.Carnegie Inst Sci, Geophys Lab, Washington, DC 20015 USA 2.Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90095 USA 3.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Earths Deep Interior, Beijing 100029, Peoples R China
推荐引用方式 GB/T 7714	Lazar, Codi,Zhang, Chi,Manning, Craig E.,et al. Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite[J]. AMERICAN MINERALOGIST,2014,99(8-9):1604-1615.
APA	Lazar, Codi,Zhang, Chi,Manning, Craig E.,&Mysen, Bjorn O..(2014).Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite.AMERICAN MINERALOGIST,99(8-9),1604-1615.
MLA	Lazar, Codi,et al."Redox effects on calcite-portlandite-fluid equilibria at forearc conditions: Carbon mobility, methanogenesis, and reduction melting of calcite".AMERICAN MINERALOGIST 99.8-9(2014):1604-1615.