Modelling clinopyroxene/melt partition coefficients for higher upper mantle pressures 

2021 ◽  
Author(s):  
Julia Marleen Schmidt ◽  
Lena Noack
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Thermodynamic Model ◽  
Upper Mantle ◽  
Partition Coefficients ◽  
Trace Element Partitioning ◽  
Partial Melt ◽  
Element Partitioning ◽  
Incompatible Trace Elements ◽  
Free Element

<p>When partial melt occurs in the mantle, redistribution of trace elements between the solid mantle material and partial melt takes place. Partition coefficients play an important role when determining the amount of trace elements that get redistributed into the melt. Due to a lower density compared to surrounding solid rock, partial melt that was generated in the upper mantle will rise towards the surface, leaving the upper mantle depleted in incompatible trace elements and an enriched crust. Studies investigating trace element partitioning in the mantle typically rely on constant partition coefficients throughout the mantle, even though it is known that partition coefficients depend on pressure, temperature, and composition. Between the pressures of 0-15 GPa, partition coefficients vary by two orders of magnitude along both, solidus and liquidus. Since partition coefficients exhibit a parabolic relationship in an Onuma diagram, a similar variation is expected for all trace element partition coefficients that can be derived from the sodium partition coefficients.</p><p>In this study, we developed a thermodynamic model for sodium in clinopyroxene after Blundy et al. (1995). With the thermodynamic model results, we were able to deduce a P-T dependent equation for sodium partitioning that is applicable up to 12 GPa between the peridotite solidus and liquidus. Because sodium is an almost strain-free element in jadeite, it can be used as a reference to model partition coefficients for other elements, including heat producing elements like K, Th, and U. This gives us the opportunity to insert P-T dependent partition coefficient calculations of any trace element into mantle melting models, which will have a big impact on the accuracy of elemental redistribution calculations and therefore, if the partitioning of the heat producing elements is taken into account, also the evolution of the mantle and crust.</p><p>Blundy, J. et al. (1995): Sodium partitioning between clinopyroxene and silicate melts, J. Geophys. Res., 100, 15501-15515.</p><p>Schmidt, J.M. and Noack, L. (2021): Parameterizing a model of clinopyroxene/melt partition coefficients for sodium to higher upper mantle pressures (to be submitted)</p>

Element Partitioning (Mineral-Melt, Metal-/Sulfide-Silicate) in Planetary Sciences

2021 ◽  
Author(s):  
Brandon Mahan
Keyword(s):  
Free Energy ◽  
Trace Elements ◽  
Partition Coefficient ◽  
Trace Element ◽  
Gibbs Free Energy ◽  
Major Element ◽  
Molar Fraction ◽  
Metal Sulfide ◽  
Trace Element Partitioning ◽  
Element Partitioning

Element partitioning—at its most basic—is the distribution of an element of interest between two constituent phases as a function of some process. Major constituent elements generally affect the thermodynamic environment (chemical equilibrium) and therefore trace element partitioning is often considered, as trace elements are present in minute quantities and their equilibrium exchange reactions do not impart significant changes to the larger system. Trace elements are responsive to thermodynamic conditions, and thus they act as passive tracers of chemical reactions without appreciably influencing the bulk reactions themselves. In planetary sciences, the phase pairs typically considered are mineral-melt, metal-silicate, and sulfide-silicate, owing largely to the ubiquity of their coexistence in planetary materials across scales and context, from the micrometer-sized components of meteorites up to the size of planets (thousands of kilometers). It is common to speak of trace elements in terms of their tendency toward forming metallic, sulfidic, or oxide phases, and the terms “siderophile,” “chalcophile,” and “lithophile” (respectively) are used to define these tendencies under what is known as the Goldschmidt Classification scheme. The metric of an element’s tendency to concentrate into one phase relative to another is expressed as the ratio of its concentration (as a weight or molar fraction) in one phase over another, where convention dictates the reference frame as solid over liquid, and metal or sulfide over silicate; this mathematical term is the element’s partition coefficient, or distribution coefficient, between the two respective phases,DMPhaseBPhaseA (where M is the element of interest, most often reported as molar fraction), or simply DM. In general, trace elements obey Henry’s Law, where the element’s activity and concentration are linearly proportional. Practically speaking, this means that the element is sufficiently dilute in the system such that its atoms interact negligibly with one another compared to their interactions with major element phases, and thus the trace element’s partition coefficient in most settings is not appreciably affected by its concentration. The radius and charge of an element’s ionized species (its ionic radius and valence state)—in relation to either the major element ion for which it is substituting or the lattice site vacancy or interstitial space it is filling—generally determine the likelihood of trace element substitution or vacancy/interstitial fill (along with the net charge of the lattice space). The key energy consideration that underlies an element’s partitioning is the Gibbs free energy of reaction between the phases involved. Gibbs free energy is the change in internal energy associated with a chemical reaction (at a given temperature and pressure) that can be used to do work, and is denoted as ΔGrxn. Reactions with negative ΔGrxn values are spontaneous, and the magnitude of this negative value for a given phase, for example, a metal oxide, denotes the relative affinity of the metal toward forming oxides. That is to say, an element with a highly negative ΔGrxn for its oxide species at relevant pressure-temperature conditions will tend to be found in oxide and silicate minerals, that is, it will be lithophile (and vice versa for siderophile elements). Trace element partitioning systematics in mineral-melt and metal-/sulfide-silicate systems have boundless applications in planetary science. A growing collective understanding of the partition coefficients of elements has been built on decades of physical chemistry, deterministic theory, petrology, experimental petrology, and natural observations. Leveraging this immense intellectual, technical, and methodological foundation, modern trace element partitioning research is particularly aimed at constraining the evolution of plate tectonics on Earth (conditions and timing of onset), understanding the formation history of planetary materials such as chondrite meteorites and their constituents (e.g., chondrules), and de-convolving the multiply operating processes at play during the accretion and differentiation of Earth and other terrestrial planets.

Partitioning of trace elements between garnet, clinopyroxene and diamond-forming carbonate-silicate melt at 7 GPa

2010 ◽  
Vol 74 (2) ◽  
pp. 227-239 ◽  
Author(s):  
A. V. Kuzyura ◽  
F. Wall ◽  
T. Jeffries ◽  
Yu. A. Litvin
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Element Distribution ◽  
Silicate Melt ◽  
Trace Element Distribution ◽  
Published Data ◽  
Trace Element Partitioning ◽  
Element Partitioning ◽  
Icp Ms ◽  
Melt Composition

AbstractConcentrations of trace elements in coexisting garnet, clinopyroxene and completely miscible carbonate-silicate melt (formed at 7 GPa from the Chagatai silicocarbonatite rock known to be diamondiferous) were determined using LA-ICP-MS. The partition coefficients for Li, Rb, Cs, Ba, Th, U, Ta, Nb, La, Ce, Pb, Pr, Sr, Nd, Zr, Hf, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, Lu, Sc and Zn were determined. The new experimental data for trace-element partitioning between garnet, clinopyroxene and carbonate-silicate melt have been compared with published data for partitioning between garnet, clinopyroxene and carbonatite melt, and garnet, clinopyroxene and silicate melt. The results show that the trace-element partitioning is not significantly altered by changes in melt composition, with HREE always concentrated in the garnet. Carbonate-silicate melt, as a diamond-forming medium, and carbonatite or silicate melt equilibrated with mantle silicate minerals, behave similarly in respect of trace-element distribution.

Trace element partitioning in mixed-habit diamonds

2013 ◽  
Vol 355 ◽  
pp. 134-143 ◽  
Author(s):  
D. Howell ◽  
W.L. Griffin ◽  
N.J. Pearson ◽  
W. Powell ◽  
P. Wieland ◽  
...  
Keyword(s):  
Trace Element ◽  
Trace Element Partitioning ◽  
Element Partitioning

Trace element partitioning between silicate melts – A molecular dynamics approach

2017 ◽  
Vol 205 ◽  
pp. 245-255 ◽  
Author(s):  
Johannes Wagner ◽  
Volker Haigis ◽  
Daniela Künzel ◽  
Sandro Jahn
Keyword(s):  
Molecular Dynamics ◽  
Trace Element ◽  
Silicate Melts ◽  
Trace Element Partitioning ◽  
Element Partitioning

Experimental study of trace element partitioning between enstatite and melt in enstatite chondrites at low oxygen fugacities and 5GPa

2014 ◽  
Vol 130 ◽  
pp. 167-187 ◽  
Author(s):  
Camille Cartier ◽  
Tahar Hammouda ◽  
Régis Doucelance ◽  
Maud Boyet ◽  
Jean-Luc Devidal ◽  
...  
Keyword(s):  
Experimental Study ◽  
Trace Element ◽  
Low Oxygen ◽  
Trace Element Partitioning ◽  
Element Partitioning ◽  
Enstatite Chondrites
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