DOI: 10.1016/j.epsl.2020.116590
论文题名: Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: New constraints from Bi and Ag metal-silicate partitioning
作者: Righter K. ; Schönbächler M. ; Pando K. ; Rowland R. ; II ; Righter M. ; Lapen T.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 552 语种: 英语
中文关键词: accretion
; core formation
; differentiation
; mantle heterogeneity
; siderophile elements
; volatiles
英文关键词: Binary alloys
; Bismuth compounds
; Chromium alloys
; Inert gases
; Isotopes
; Manganese alloys
; Metals
; Palladium alloys
; Silicates
; Silicon alloys
; Silver compounds
; Structural geology
; Sulfur compounds
; Tungsten alloys
; Volatile organic compounds
; Element partitioning
; High-pressure and temperatures
; Isotopic composition
; Metal-silicate differentiation
; Metal-silicate partitioning
; Planetary differentiation
; Pressure and temperature
; Siderophile elements
; Silver alloys
; accretion
; bismuth
; heterogeneity
; isotopic composition
; mantle chemistry
; Mars
; partitioning
; siderophile element
; silver
; terrestrial environment
; volatile element
英文摘要: The Earth's timing of accretion and acquisition of moderately volatile compounds is uncertain. Hafnium-W and Mn-Cr isotopic data can bracket the timing of early planetary differentiation and core formation. The Ag-Pd system has also been utilized but its application has been limited by a lack of high pressure and temperature metal-silicate partitioning for Pd and Ag. Because Ag (and Bi) are volatile chalcophile siderophile elements, understanding their early distribution can constrain the origin of volatile elements in differentiated bodies and planets. Unfortunately, neither Ag or Bi have been studied across the wide range of pressure and temperature conditions that are relevant to accretion and core-mantle differentiation. Here, new high-pressure and temperature multi-anvil metal-silicate equilibrium experiments for Bi and Ag have been carried out at conditions relevant to planetary accretion and metal silicate differentiation that allow a more refined and complete understanding of element partitioning during core formation. The new metal-silicate partitioning data are combined with previously reported data, and utilized to predict the distributions of Bi, Pd, and Ag at conditions of accretion relevant for Earth and Mars. Application of the new partitioning results to Earth shows that D(Bi) and D(Ag) (D = metal/silicate concentration ratio) are lowered due to the effect of pressure and Si alloyed in the metallic liquid, resulting in higher predicted mantle Bi and Ag abundances than in the bulk silicate Earth (BSE), as well as high and variable Pd/Ag. The unradiogenic Ag isotopic composition of the BSE could have been generated by early accretion of volatile-poor (high Pd/Ag) pre-cursors, followed by later accretion of volatile–rich (low Pd/Ag) material, in agreement with earlier studies of Pd-Ag and Mn-Cr (Schönbächler et al., 2010). However, these main accretion phases would have to be followed by segregation of a sulfide liquid (at least 1.5% of magma ocean) at high pressures (>30 GPa), to explain the primitive upper mantle (PUM) Bi, Pd, and Ag, as well as Au, Pt, Cu and Ni concentrations as proposed previously. If the early accreted bulk Earth was volatile depleted with high Pd/Ag ratios, portions of the mantle may contain ancient domains that developed positive 107Ag isotopic anomalies (as also argued by noble gases, Nd, W, and Os isotopes). In comparison, Bi, Pd, and Ag concentrations in the martian mantle could have been set by simple metal-silicate equilibrium. Mars accreted and differentiated relatively rapidly, while also developing a deep magma ocean with a high Pd/Ag ratio that could have evolved positive 107Ag anomalies, in contrast to Earth. Measurements on shergottites may reveal these predicted Ag isotopic anomalies. © 2020 Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165237
Appears in Collections: 气候变化与战略
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作者单位: NASA-JSC, 2101 NASA Parkway, Houston, TX 77058, United States; ETH Zürich, Inst. Isotope Geology and Mineral Resources, Zürich, 8092, Switzerland; Jacobs JETS, NASA JSC, Houston, TX 77058, United States; Los Alamos National Laboratory, Mail Stop P952, Los Alamos, NM 87545, United States; Dept. of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, United States
Recommended Citation:
Righter K.,Schönbächler M.,Pando K.,et al. Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: New constraints from Bi and Ag metal-silicate partitioning[J]. Earth and Planetary Science Letters,2020-01-01,552