scholarly journals Reconciling metal–silicate partitioning and late accretion in the Earth

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Terry-Ann Suer ◽  
Julien Siebert ◽  
Laurent Remusat ◽  
James M. D. Day ◽  
Stephan Borensztajn ◽  
...  
Keyword(s):  
High Pressures ◽  
Platinum Metal ◽  
Core Formation ◽  
Enriched Mantle ◽  
Metal Silicate ◽  
Partitioning Coefficients ◽  
Diamond Anvil ◽  
Laser Heated ◽  
Geochemical Constraints ◽  
Island Basalt

AbstractHighly siderophile elements (HSE), including platinum, provide powerful geochemical tools for studying planet formation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE. However, core formation could also have contributed to the mantle’s HSE content. Here we present measurements of platinum metal-silicate partitioning coefficients, obtained from laser-heated diamond anvil cell experiments, which demonstrate that platinum partitioning into metal is lower at high pressures and temperatures. Consequently, the mantle was likely enriched in platinum immediately following core-mantle differentiation. Core formation models that incorporate these results and simultaneously account for collateral geochemical constraints, lead to excess platinum in the mantle. A subsequent process such as iron exsolution or sulfide segregation is therefore required to remove excess platinum and to explain the mantle’s modern HSE signature. A vestige of this platinum-enriched mantle can potentially account for 186Os-enriched ocean island basalt lavas.

scholarly journals The niobium and tantalum concentration in the mantle constrains the composition of Earth’s primordial magma ocean

2020 ◽  
Vol 117 (45) ◽  
pp. 27893-27898
Author(s):  
Dongyang Huang ◽  
James Badro ◽  
Julien Siebert
Keyword(s):  
Diamond Anvil Cell ◽  
Magma Ocean ◽  
Core Formation ◽  
The Core ◽  
Bulk Silicate Earth ◽  
Reducing Conditions ◽  
Metal Silicate ◽  
Diamond Anvil ◽  
Laser Heated ◽  
Tantalum Concentration

The bulk silicate Earth (BSE), and all its sampleable reservoirs, have a subchondritic niobium-to-tantalum ratio (Nb/Ta). Because both elements are refractory, and Nb/Ta is fairly constant across chondrite groups, this can only be explained by a preferential sequestration of Nb relative to Ta in a hidden (unsampled) reservoir. Experiments have shown that Nb becomes more siderophile than Ta under very reducing conditions, leading the way for the accepted hypothesis that Earth’s core could have stripped sufficient amounts of Nb during its formation to account for the subchondritic signature of the BSE. Consequently, this suggestion has been used as an argument that Earth accreted and differentiated, for most of its history, under very reducing conditions. Here, we present a series of metal–silicate partitioning experiments of Nb and Ta in a laser-heated diamond anvil cell, at pressure and temperature conditions directly comparable to those of core formation; we find that Nb is more siderophile than Ta under any conditions relevant to a deep magma ocean, confirming that BSE’s missing Nb is in the core. However, multistage core formation modeling only allows for moderately reducing or oxidizing accretionary conditions, ruling out the need for very reducing conditions, which lead to an overdepletion of Nb from the mantle (and a low Nb/Ta ratio) that is incompatible with geochemical observations. Earth’s primordial magma ocean cannot have contained less than 2% or more than 18% FeO since the onset of core formation.

scholarly journals The carbon content of Earth and its core

2020 ◽  
Vol 117 (16) ◽  
pp. 8743-8749 ◽  
Author(s):  
Rebecca A. Fischer ◽  
Elizabeth Cottrell ◽  
Erik Hauri ◽  
Kanani K. M. Lee ◽  
Marion Le Voyer
Keyword(s):  
Carbonaceous Chondrite ◽  
Magma Ocean ◽  
Core Formation ◽  
Earth’S Core ◽  
Multistage Model ◽  
Earth's Core ◽  
Metal Silicate ◽  
Diamond Anvil ◽  
Laser Heated ◽  
Carbon Inventory

Earth’s core is likely the largest reservoir of carbon (C) in the planet, but its C abundance has been poorly constrained because measurements of carbon’s preference for core versus mantle materials at the pressures and temperatures of core formation are lacking. Using metal–silicate partitioning experiments in a laser-heated diamond anvil cell, we show that carbon becomes significantly less siderophile as pressures and temperatures increase to those expected in a deep magma ocean during formation of Earth’s core. Based on a multistage model of core formation, the core likely contains a maximum of 0.09(4) to 0.20(10) wt% C, making carbon a negligible contributor to the core’s composition and density. However, this accounts for ∼80 to 90% of Earth’s overall carbon inventory, which totals 370(150) to 740(370) ppm. The bulk Earth’s carbon/sulfur ratio is best explained by the delivery of most of Earth’s volatiles from carbonaceous chondrite-like precursors.

scholarly journals Synthesis of clathrate cerium superhydride CeH9 at 80-100 GPa with atomic hydrogen sublattice

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Nilesh P. Salke ◽  
M. Mahdi Davari Esfahani ◽  
Youjun Zhang ◽  
Ivan A. Kruglov ◽  
Jianshi Zhou ◽  
...  
Keyword(s):  
Atomic Hydrogen ◽  
High Pressures ◽  
Structure Stability ◽  
X Ray Diffraction ◽  
Detailed Chemistry ◽  
X Ray ◽  
3 Dimensional ◽  
Diamond Anvil ◽  
Laser Heated ◽  
Very High

Abstract Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors. Recent experiments discovered superhydrides at very high pressures, e.g. FeH5 at 130 GPa and LaH10 at 170 GPa. With the motivation of discovering new hydrogen-rich high-Tc superconductors at lowest possible pressure, here we report the prediction and experimental synthesis of cerium superhydride CeH9 at 80–100 GPa in the laser-heated diamond anvil cell coupled with synchrotron X-ray diffraction. Ab initio calculations were carried out to evaluate the detailed chemistry of the Ce-H system and to understand the structure, stability and superconductivity of CeH9. CeH9 crystallizes in a P63/mmc clathrate structure with a very dense 3-dimensional atomic hydrogen sublattice at 100 GPa. These findings shed a significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. Discovery of superhydride CeH9 provides a practical platform to further investigate and understand conventional superconductivity in hydrogen rich superhydrides.

Fate of Carbon During the Formation of Earth’s Core

2020 ◽  
Author(s):  
Ingrid Blanchard ◽  
Eleanor Jennings ◽  
Ian Franchi ◽  
Zuchao Zhao ◽  
Sylvain Petitgirard ◽  
...  
Keyword(s):  
Focused Ion Beam ◽  
Early Stage ◽  
Ion Beam ◽  
Light Element ◽  
Major Elements ◽  
Core Formation ◽  
Crustal Rocks ◽  
The Earth ◽  
Diamond Anvil ◽  
Laser Heated

<p>Carbon is an element of great importance in the Earth, because it is intimately linked to the presence of life at the surface, and, as a light element, it may contribute to the density deficit of the Earth’s iron-rich core. Carbon is strongly siderophile at low pressures and temperatures (1), hence it should be stored mainly in the Earth’s core. Nevertheless, we still observe the existence of carbon at the surface, stored in crustal rocks, and in the mantle, as shown by the exhumation of diamonds. The presence of carbon in the crust and mantle could be the result of the arrival of carbon during late accretion, after the process of core formation ceased, or because of a change in its metal–silicate partitioning behavior at the conditions of core formation (P >40 GPa – T >3500 K). Previous studies reported metal–silicate partitioning of carbon based on experiments using large volume presses up to 8 GPa and 2200°C (2). Here, we performed laser-heated diamond anvil cell experiments in order to determine carbon partitioning between liquid metal and silicate at the extreme conditions of Earth’s core–mantle differentiation. We recovered our samples using the Focused Ion Beam technique and welded a 3 μm thick slice of each sample onto a TEM grid. Major elements were analyzed by electron microprobe, whereas the concentrations of carbon in the silicate were analyzed by nanoSIMS. We thus have obtained metal–silicate partitioning results for carbon at PT conditions relevant to planetary core formation, where C remains siderophile in all experiments, but partition coefficients are up to two orders of magnitude lower than in low PTexperiments. We derive a new parameterization of the pressure–temperature dependence of the metal–silicate partitioning of carbon and apply this in a state-of-the-art model of planet formation and differentiation (3,4) that is based on astrophysical N-body accretion simulations. Results show that BSE carbon concentrations increase strongly starting at a very early stage of Earth’s accretion and, depending on the concentration of carbon in accreting bodies, can easily reach or exceed estimated BSE values.</p><p> </p><p>(1) Dasgupta et al., 2013. Geochimica et Cosmochimica Acta 102, 191-212</p><p>(2) Li et al., 2016. Nature Geoscience 9, 781–785</p><p>(3) Rubie et al., 2015. Icarus 248, 89–108</p><p>(4) Rubie et al., 2016. Science 353, 1141–1144</p><p> </p>

scholarly journals Experimental Issues in In-Situ Synchrotron X-Ray Diffraction at High Pressure and Temperature by Using a Laser-Heated Diamond-Anvil Cell

1997 ◽  
Vol 499 ◽  
Author(s):  
C. S. Yoo ◽  
H. Cynn ◽  
A. Campbell ◽  
J.-Z. Hu
Keyword(s):  
Diamond Anvil Cell ◽  
High Pressures ◽  
Thermal Gradients ◽  
X Ray Diffraction ◽  
High Pressure And Temperature ◽  
X Ray ◽  
Diamond Anvil ◽  
Integrated Technique ◽  
Laser Heated

ABSTRACTAn integrated technique of diamond-anvil cell, laser-heating and synchrotron x-ray diffraction technologies is capable of structural investigation of condensed matter in an extended region of high pressures and temperatures above 100 GPa and 3000 K. The feasibility of this technique to obtain reliable data, however, strongly depends on several experimental issues, including optical and x-ray setups, thermal gradients, pressure homogeneity, preferred orientation, and chemical reaction. In this paper, we discuss about these experimental issues together with future perspectives of this technique for obtaining accurate data.

scholarly journals Raman Spectroscopy Study on Chemical Transformations of Propane at High Temperatures and High Pressures

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Daniil A. Kudryavtsev ◽  
Timofey М. Fedotenko ◽  
Egor G. Koemets ◽  
Saiana E. Khandarkhaeva ◽  
Vladimir G. Kutcherov ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Upper Mantle ◽  
High Pressures ◽  
Chemical Transformations ◽  
Spectroscopy Study ◽  
Heavy Hydrocarbons ◽  
Thermobaric Conditions ◽  
Diamond Anvil ◽  
Laser Heated

AbstractThis study is devoted to the detailed in situ Raman spectroscopy investigation of propane C3H8 in laser-heated diamond anvil cells in the range of pressures from 3 to 22 GPa and temperatures from 900 to 3000 K. We show that propane, while being exposed to particular thermobaric conditions, could react, leading to the formation of hydrocarbons, both saturated and unsaturated as well as soot. Our results suggest that propane could be a precursor of heavy hydrocarbons and will produce more than just sooty material when subjected to extreme conditions. These results could clarify the issue of the presence of heavy hydrocarbons in the Earth’s upper mantle.

scholarly journals Diamond Anvil Cell Partitioning Experiments for Accretion and Core Formation: Testing the Limitations of Electron Microprobe Analysis

2019 ◽  
Vol 25 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Eleanor S. Jennings ◽  
Jon Wade ◽  
Vera Laurenz ◽  
Sylvain Petitgirard
Keyword(s):  
Microprobe Analysis ◽  
Element Distribution ◽  
Planetary Scale ◽  
Element Partitioning ◽  
Metal Silicate ◽  
Diamond Anvil ◽  
Cell Partitioning ◽  
Two Phases ◽  
Laser Heated ◽  
Tem Grid

AbstractMetal–silicate partitioning studies performed in high-pressure, laser-heated diamond anvil cells (DAC) are commonly used to explore element distribution during planetary-scale core–mantle differentiation. The small run-products contain suitable areas for analysis commonly less than tens of microns in diameter and a few microns thick. Because high spatial resolution is required, quantitative chemical analyses of the quenched phases is usually performed by electron probe microanalysis (EPMA). Here, EPMA is being used at its spatial limits, and sample thickness and secondary fluorescence effects must be accounted for. By using simulations and synthetic samples, we assess the validity of these measurements, and find that in most studies DAC sample wafers are sufficiently thick to be characterized at 15 kVacc. Fluorescence from metal-hosted elements will, however, contaminate silicate measurements, and this becomes problematic if the concentration contrast between the two phases is in excess of 100. Element partitioning experiments are potentially compromised; we recommend simulating fluorescence and applying a data correction, if required, to such DAC studies. Other spurious analyses may originate from sources external to the sample, as exemplified by 0.5 to >1 wt% of Cu arising from continuum fluorescence of the Cu TEM grid the sample is typically mounted on.

scholarly journals Diamond and methane formation from the chemical decomposition of polyethylene at high pressures and temperatures

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
E. B. Watkins ◽  
R. C. Huber ◽  
C. M. Childs ◽  
A. Salamat ◽  
J. S. Pigott ◽  
...  
Keyword(s):  
High Pressures ◽  
Equations Of State ◽  
Spherical Particles ◽  
Radius Of Gyration ◽  
Methane Formation ◽  
Reaction Products ◽  
Chemical Decomposition ◽  
X Ray ◽  
Diamond Anvil ◽  
Laser Heated

AbstractPolyethylene (C2H4)n was compressed to pressures between 10 and 30 GPa in a diamond anvil cell (DAC) and laser heated above 2500 K for approximately one second. This resulted in the chemical decomposition of the polymer into carbon and hydrocarbon reaction products. After quenching to ambient temperature, the decomposition products were measured in the DAC at pressures ranging from ambient to 29 GPa using a combination of x-ray diffraction (XRD) and small angle x-ray scattering (SAXS). XRD identified cubic diamond and methane as the predominant product species with their pressure–volume relationships exhibiting strong correlations to the diamond and methane equations of state. Length scales associated with the diamond products, obtained from SAXS measurements, indicate the formation of nanodiamonds with a radius of gyration between 12 and 35 nm consistent with 32–90 nm diameter spherical particles. These results are in good agreement with the predicted product composition under thermodynamic and chemical equilibrium.

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