Carbon in Reduced Mantle: Stability of Carbides and C-bearing Alloys in the System Fe-Ni-C

还原地幔中的碳：Fe-Ni-C 体系中碳化物和含碳合金的稳定性

• 批准号: 1119295
• 负责人: Marc Hirschmann
• 金额: $ 24.44万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119295&HistoricalAwards=false
• 关键词: Carbon; Reduced; Mantle; Stability; Carbides

In the deep Earth carbon cycle, carbon is exchanged between Earth's near surface reservoirs (including the oceans, atmosphere, and crust) and the mantle. The storage of carbon in different reservoirs and the fluxes between them are of key importance to maintenance of Earth's climate and habitability on times scales of millions to billions of years and also may have principal influence on the dynamics of Earth's interior, including the operation of plate tectonics, the locus of melting, the formation of distinct geochemical reservoirs, and the origin of diamonds. The majority of the carbon participating in the deep Earth carbon cycle is stored in the mantle, but the mode of storage is poorly understood. Possible phases include carbonates, diamonds, FeNi alloys, carbides, or carbide melts. The stable phases are likely to vary with depth and laterally, but these variations are also not well-constrained. In much of the mantle, carbon is likely in reduced form, for which phase relations in the system Fe-Ni-C have key influence on the stable phase assemblages. In this project, the team will conduct experimental determinations of phase relations in the system Fe-Ni-C and make thermodynamic determinations of the properties of possible mantle carbides Fe3C and Fe7C3.Apart from studies in a narrow pressure interval applicable to commercial diamond synthesis (5.4-5.7 GPa), high pressure experimental data for the system Fe-Ni-C are sparse. To improve understanding of the hosts of reduced carbon in the mantle, it is planned to conduct experimental and thermodynamic studies of the system Fe-Ni-C. Experiments will be conducted between 2 and 15 GPa with a focus at ≥6 GPa and will address (a) the topology of phase stability in the system Fe-Ni-C (b) the relative stabilities of (Fe,Ni)3C and (Fe,Ni)7C3 carbides (c) the locus of stability of Fe-Ni-C carbide melts and (d) the solubility of C in FeNi alloy as a function of temperature and pressure Analyses of C in FeNi alloy will be performed by electron microprobe, using carefully calibrated procedures and detailed attention to analytical blanks. Additionally, the alloys will be analyzed for C by SIMS. To better understand the stability of carbides in the mantle, it is proposed to perform a calorimetric study of the heat capacities and entropies of Fe3C and Fe7C3 from 4 to 1900 K. The heat capacities of Fe3C have not been measured in 75 years and those of Fe7C3 have never been measured. Calorimetry will be performed in collaboration with Jean Tangeman of 3M and Edgar Dachs of Universtät Salzburg. The experimental and calorimetric results will be combined with existing constraints on carbide and silicate phase equilibria to construct thermodynamic models of the stability of reduced carbon phases in equilibrium with peridotite close to the P-T-fO2 conditions applicable to the mantle. Broader impacts of the project include collaboration between the UMN experimental petrology laboratory and materials scientists at 3M, international collaboration between the UMN group and Edgar Dachs at the Universtät Salzburg and the training of undergraduate and graduate students.

在深层碳循环中，碳在地球近地面储层（包括海洋，大气和地壳）和地幔之间交换。 The storage of carbon in different reservoirs and the fluxes between them are of key importance to maintenance of Earth's climate and habitability on times scales of millions to billions of years and also may have principal influence on the dynamics of Earth's interior, including the operation of plate tectonics, the locus of melting, the formation of distinct geochemical reservoirs, and the origin of diamonds.参与深层碳循环的大多数碳都存储在地幔中，但对存储方式的了解很少。可能的阶段包括碳酸盐，钻石，Feni合金，碳化物或碳化物熔体。稳定的阶段可能会随着深度和横向而变化，但是这些变化也不是很大的约束。在大部分地幔中，碳可能以降低的形式减少，因为该系统中的相位关系对稳定的相组合具有关键影响。在该项目中，团队将对系统FE-NI-C中的相位关系进行实验确定，并对适用于商业钻石合成的狭窄压力间隔的研究对可能的地幔Carbides FE3C和FE7C3进行热力学确定（5.4-5.7 GPA）（5.4-5.7 GPA），系统Fe-Ni-C的高压实验数据。为了改善对地幔中碳减少的宿主的理解，计划对系统Fe-Ni-C进行实验和热力学研究。 Experiments will be conducted between 2 and 15 GPa with a focus at ≥6 GPa and will address (a) the topology of phase stability in the system Fe-Ni-C (b) the relative stability of (Fe,Ni)3C and (Fe,Ni)7C3 carbides (c) the locus of stability of Fe-Ni-C carbide melts and (d) the Solubility of C in FeNi alloy as a function of FENI合金中C的温度和压力分析将使用仔细校准的程序以及对分析空白的详细关注进行电子探针进行。此外，将通过SIMS分析合金。为了更好地了解地幔中碳化物的稳定性，提议对Fe3c和Fe7c3的热能和熵进行Calolimetric研究，从4到1900K。FE3C的热容量尚未在75年内测量，而FE7C3的热容量尚未测量。量热法将与3M的Jean Tangeman和SalzburgUniverstät的Edgar Dachs合作进行。实验和量热结果将与碳化物和硅酮相位的现有限制相等，以构建相等的碳相稳定性的热力学模型，而橄榄岩接近适用于地幔的p-t-fo2条件。该项目的更广泛影响包括UMN实验性质学实验室与3M的材料科学家之间的合作，UMN集团与萨尔茨堡大学的Edgar Dachs之间的国际合作以及对本科生和研究生的培训。