Modelling Mie scattering in pyrolite in the laser-heated diamond anvil cell: Implications to the core-mantle boundary temperature determination

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.

Download Full-text

Partitioning experiments in the laser-heated diamond anvil cell: volatile content in the Earth's core

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2008.0226 ◽

2008 ◽

Vol 366 (1883) ◽

pp. 4295-4314 ◽

Cited By ~ 12

Author(s):

Andrew P Jephcoat ◽

M. Ali Bouhifd ◽

Don Porcelli

Keyword(s):

Trace Elements ◽

Diamond Anvil Cell ◽

The Core ◽

The Earth ◽

Wide Range ◽

Recent Developments ◽

Mantle Reservoir ◽

History Of ◽

Diamond Anvil ◽

Laser Heated

The present state of the Earth evolved from energetic events that were determined early in the history of the Solar System. A key process in reconciling this state and the observable mantle composition with models of the original formation relies on understanding the planetary processing that has taken place over the past 4.5 Ga. Planetary size plays a key role and ultimately determines the pressure and temperature conditions at which the materials of the early solar nebular segregated. We summarize recent developments with the laser-heated diamond anvil cell that have made possible extension of the conventional pressure limit for partitioning experiments as well as the study of volatile trace elements. In particular, we discuss liquid–liquid, metal–silicate (M–Sil) partitioning results for several elements in a synthetic chondritic mixture, spanning a wide range of atomic number—helium to iodine. We examine the role of the core as a possible host of both siderophile and trace elements and the implications that early segregation processes at deep magma ocean conditions have for current mantle signatures, both compositional and isotopic. The results provide some of the first experimental evidence that the core is the obvious replacement for the long-sought, deep mantle reservoir. If so, they also indicate the need to understand the detailed nature and scale of core–mantle exchange processes, from atomic to macroscopic, throughout the age of the Earth to the present day.

Download Full-text

Strategy and enhanced temperature determination in a laser heated diamond anvil cell

Journal of Applied Physics ◽

10.1063/1.3117517 ◽

2009 ◽

Vol 105 (9) ◽

pp. 093543 ◽

Cited By ~ 10

Author(s):

Shanti Deemyad ◽

Anthony N. Papathanassiou ◽

Isaac F. Silvera

Keyword(s):

Diamond Anvil Cell ◽

Temperature Determination ◽

Diamond Anvil ◽

Laser Heated

Download Full-text

Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1821712116 ◽

2019 ◽

Vol 116 (21) ◽

pp. 10238-10243 ◽

Cited By ~ 4

Author(s):

Sarah M. Arveson ◽

Jie Deng ◽

Bijaya B. Karki ◽

Kanani K. M. Lee

Keyword(s):

Iron Alloy ◽

Liquid Immiscibility ◽

Outer Core ◽

Core Mantle Boundary ◽

The Core ◽

Earth Pressures ◽

Deep Earth ◽

Diamond Anvil ◽

Dynamics Simulations ◽

Laser Heated

Seismic observations suggest that the uppermost region of Earth’s liquid outer core is buoyant, with slower velocities than the bulk outer core. One possible mechanism for the formation of a stably stratified layer is immiscibility in molten iron alloy systems, which has yet to be demonstrated at core pressures. We find immiscibility between liquid Fe-Si and Fe-Si-O persisting to at least 140 GPa through a combination of laser-heated diamond-anvil cell experiments and first-principles molecular dynamics simulations. High-pressure immiscibility in the Fe-Si-O system may explain a stratified layer atop the outer core, complicate differentiation and evolution of the deep Earth, and affect the structure and intensity of Earth’s magnetic field. Our results support silicon and oxygen as coexisting light elements in the core and suggest that SiO2 does not crystallize out of molten Fe-Si-O at the core-mantle boundary.

Download Full-text

Melting of Fe–Ni–Si and Fe–Ni–S alloys at megabar pressures: implications for the core–mantle boundary temperature

Physics and Chemistry of Minerals ◽

10.1007/s00269-011-0449-9 ◽

2011 ◽

Vol 38 (10) ◽

pp. 767-776 ◽

Cited By ~ 52

Author(s):

Guillaume Morard ◽

Denis Andrault ◽

Nicolas Guignot ◽

Julien Siebert ◽

Gaston Garbarino ◽

...

Keyword(s):

Mantle Boundary ◽

Boundary Temperature ◽

Core Mantle Boundary ◽

The Core

Download Full-text

Interaction of mantle dregs with convection: Lateral heterogeneity at the core-mantle boundary

Geophysical Research Letters ◽

10.1029/gl013i013p01517 ◽

1986 ◽

Vol 13 (13) ◽

pp. 1517-1520 ◽

Cited By ~ 78

Author(s):

Geoffrey F. Davies ◽

Michael Gurnis

Keyword(s):

Lateral Heterogeneity ◽

Mantle Boundary ◽

Core Mantle Boundary ◽

The Core

Download Full-text

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

Geophysical Journal International ◽

10.1093/gji/ggu244 ◽

2014 ◽

Vol 199 (1) ◽

pp. 164-177 ◽

Cited By ~ 23

Author(s):

Sanne Cottaar ◽

Mingming Li ◽

Allen K. McNamara ◽

Barbara Romanowicz ◽

Hans-Rudolf Wenk

Keyword(s):

Seismic Anisotropy ◽

Mantle Boundary ◽

Core Mantle Boundary ◽

The Core

Download Full-text

Application of spherical Slepian functions to the inversion of virtual observatory satellite magnetic data into localised regions of flow on the core-mantle boundary

10.5194/egusphere-egu21-2857 ◽

2021 ◽

Author(s):

Hannah Rogers ◽

Ciaran Beggan ◽

Kathryn Whaler

Keyword(s):

Spherical Surface ◽

Surface Flow ◽

Magnetic Data ◽

Virtual Observatory ◽

Core Surface ◽

Flow Models ◽

Mantle Boundary ◽

Core Mantle Boundary ◽

The Core ◽

Slepian Functions

Spherical Slepian functions (or &#8216;Slepian functions&#8217;) are mathematical functions which can be used to decompose potential fields, as represented by spherical harmonics, into smaller regions covering part of a spherical surface. This allows a spatio-spectral trade-off between aliasing of the signal at the boundary edges while constraining it within a region of interest. While Slepian functions have previously been applied to geodetic and crustal magnetic data, this work further applies Slepian functions to flows on the core-mantle boundary. There are two main reasons for restricting flow models to certain parts of the core surface. Firstly, we have reason to believe that different dynamics operate in different parts of the core (such as under LLSVPs) while, secondly, the modelled flow is ambiguous over certain parts of the surface (when applying flow assumptions). Spherical Slepian functions retain many of the advantages of our usual flow description, concerning for example the boundary conditions it must satisfy, and allowing easy calculation of the power spectrum, although greater initial computational effort is required. In this work, we apply Slepian functions to core flow models by directly inverting from satellite virtual observatory magnetic data into regions of interest. We successfully demonstrate the technique and current short comings by showing whole core surface flow models, flow within a chosen region, and its corresponding complement. Unwanted spatial leakage is generated at the region edges in the separated flows but to less of an extent than when using spherical Slepian functions on existing flow models. The limited spectral content we can infer for core flows is responsible for most, if not all, of this leakage. Therefore, we present ongoing investigations into the cause of this leakage, and to highlight considerations when applying Slepian functions to core surface flow modelling.

Download Full-text

Multiple inner core reflections from a Novaya Zemlya explosion

Bulletin of the Seismological Society of America ◽

10.1785/bssa0620041063 ◽

1972 ◽

Vol 62 (4) ◽

pp. 1063-1071 ◽

Cited By ~ 2

Author(s):

R. D. Adams

Keyword(s):

Lower Bound ◽

Inner Core ◽

Nuclear Explosion ◽

Outer Core ◽

Low Velocity ◽

Mantle Boundary ◽

Core Mantle Boundary ◽

Novaya Zemlya ◽

The Core ◽

Velocity Channel

Abstract The phases P2KP, P3KP, and P4KP are well recorded from the Novaya Zemlya nuclear explosion of October 14, 1970, with the branch AB at distances of up to 20° beyond the theoretical end point A. This extension is attributed to diffraction around the core-mantle boundary. A slowness dT/dΔ = 4.56±0.02 sec/deg is determined for the AB branch of P4KP, in excellent agreement with recent determinations of the slowness of diffracted P. This slowness implies a velocity of 13.29±0.06 km/sec at the base of the mantle, and confirms recent suggestions of a low-velocity channel above the core-mantle boundary. There is evidence that arrivals recorded before the AB branch of P2KP may lie on two branches, with different slownesses. The ratio of amplitudes of successive orders of multiple inner core reflections gives a lower bound of about 2200 for Q in the outer core.

Download Full-text

Synthesis of InSb in a Laser Heated Diamond Anvil Cell.

The Review of High Pressure Science and Technology ◽

10.4131/jshpreview.7.1019 ◽

1998 ◽

Vol 7 ◽

pp. 1019-1021 ◽

Cited By ~ 1

Author(s):

N. V. Chandra Shekar ◽

K. Takemura ◽

H. Yusa

Keyword(s):

Diamond Anvil Cell ◽

Diamond Anvil ◽

Laser Heated

Download Full-text