DOI: 10.1016/j.epsl.2020.116520
论文题名: Mixed incorporation of carbon and hydrogen in silicate melts under varying pressure and redox conditions
作者: Karki B.B. ; Ghosh D.B. ; Banjara D.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 549 语种: 英语
中文关键词: first-principles calculations
; high pressure
; magma ocean
; melt density
; silicate melts
; volatile speciation
英文关键词: Carbon dioxide
; Coordination reactions
; Iron
; Molecular dynamics
; Silicates
; Silicon
; Carbon and hydrogens
; Dissolution mechanism
; First principles molecular dynamics
; Lower mantle condition
; Oxidizing conditions
; Partial Molar volume
; Reducing conditions
; Volatile components
; Hydrogen bonds
; carbon
; computer simulation
; dissolution
; igneous geochemistry
; lower mantle
; magma
; mantle source
; nitrogen
; numerical model
; oxidation
; partial melting
; pressure effect
; redox conditions
; silicate melt
英文摘要: Volatiles including carbon and hydrogen are generally considered to be more soluble in silicate melts than in mantle rocks. How these melts contribute to the storage and distribution of key volatiles in Earth's interior today and during its early evolution, however, remains largely unknown. It is essential to improve our knowledge about volatiles-bearing silicate magmas over the entire mantle pressure regime. Here we investigate molten Mg1−xFexSiO3 (x=0, 0.25) containing both carbon and hydrogen using first-principles molecular dynamics simulations. Our results show that the dissolution mechanism of the binary volatiles in melts varies considerably under different conditions of pressure and redox. When incorporated as CO2 and H2O components (corresponding to oxidizing conditions) almost all carbon and hydrogen form bonds with oxygen. Their speciation at low pressure consists of predominantly isolated molecular CO2, carbonates, and hydroxyls. More oxygenated species, including tetrahedrally coordinated carbons, hydrogen (O-H-O) bridges, various oxygen-joined complexes appear as melt is further compressed. When two volatiles are incorporated as hydrocarbons CH4 and C2H6 (corresponding to reducing conditions), hydroxyls are prevalent with notable presence of molecular hydrogen. Carbon-oxygen bonding is almost completely suppressed. Instead carbon is directly correlated with itself, hydrogen, and silicon. Both volatiles also show strong affinity to iron. Reduced volatile speciation thus involves polymerized complexes comprising of carbon, hydrogen, silicon, and iron, which can be mostly represented by two forms: C1−4H1−5Si0−5O0−2 (iron-free) and C5−8H1−8Si0−6Fe5−8O0−2. The calculated partial molar volumes of binary volatiles in their oxidized and reduced incorporation decrease rapidly initially with pressure and then gradually at higher pressures, thereby systematically lowering silicate melt density. Our assessment of the calculated opposite effects of the volatile components and iron on melt density indicates that melt-crystal density crossovers are possible in the present-day mantle and also could have occurred in early magma ocean environments. Melts at upper mantle and transition zone conditions likely dissolve carbon and hydrogen in a wide variety of oxidized and non-oxygenated forms. Deep-seated partial melts and magma ocean remnants at lower mantle conditions may exsolve carbon as complex reduced species possibly to the core during core-mantle differentiation while retaining a majority of hydrogen as hydroxyls-associated species. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165072
Appears in Collections: 气候变化与战略
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作者单位: School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, LA 70803, United States; Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States; Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803, United States
Recommended Citation:
Karki B.B.,Ghosh D.B.,Banjara D.. Mixed incorporation of carbon and hydrogen in silicate melts under varying pressure and redox conditions[J]. Earth and Planetary Science Letters,2020-01-01,549