Lithium defects and diffusivity in forsterite

Feiwu Zhang, Kate Wright

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Lithium is an important geochemical tracer used to infer the thermal and chemical evolution of minerals in the Earth's upper mantle. Knowledge of point defect chemistry and diffusion is critical for the interpretation of Li distribution in minerals. Using quantum mechanical methods we show that in forsterite Li will be incorporated as bound interstitial-substitutional pairs. Furthermore, there will be temperature dependent fractionation of its two isotopes between the different sites. The fractionation decreases dramatically from 87.1 parts per thousand at 300 K to 1.0 parts per thousand at 3000 K. Diffusion is predicted to occur via two inter-related mechanisms: Mg-Li exchange, and a second, vacancy assisted interstitial mechanism. This behaviour is complex, facilitates migration of the heavier isotope and offers insights into observations of Li mobility and zoning in olivine, the most volumetrically important upper mantle mineral. (C) 2012 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)32-39
Number of pages8
JournalGeochimica et Cosmochimica Acta
Volume91
DOIs
Publication statusPublished - 15 Aug 2012
Externally publishedYes

Cite this

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abstract = "Lithium is an important geochemical tracer used to infer the thermal and chemical evolution of minerals in the Earth's upper mantle. Knowledge of point defect chemistry and diffusion is critical for the interpretation of Li distribution in minerals. Using quantum mechanical methods we show that in forsterite Li will be incorporated as bound interstitial-substitutional pairs. Furthermore, there will be temperature dependent fractionation of its two isotopes between the different sites. The fractionation decreases dramatically from 87.1 parts per thousand at 300 K to 1.0 parts per thousand at 3000 K. Diffusion is predicted to occur via two inter-related mechanisms: Mg-Li exchange, and a second, vacancy assisted interstitial mechanism. This behaviour is complex, facilitates migration of the heavier isotope and offers insights into observations of Li mobility and zoning in olivine, the most volumetrically important upper mantle mineral. (C) 2012 Elsevier Ltd. All rights reserved.",
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Lithium defects and diffusivity in forsterite. / Zhang, Feiwu; Wright, Kate.

In: Geochimica et Cosmochimica Acta, Vol. 91, 15.08.2012, p. 32-39.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Lithium defects and diffusivity in forsterite

AU - Zhang, Feiwu

AU - Wright, Kate

PY - 2012/8/15

Y1 - 2012/8/15

N2 - Lithium is an important geochemical tracer used to infer the thermal and chemical evolution of minerals in the Earth's upper mantle. Knowledge of point defect chemistry and diffusion is critical for the interpretation of Li distribution in minerals. Using quantum mechanical methods we show that in forsterite Li will be incorporated as bound interstitial-substitutional pairs. Furthermore, there will be temperature dependent fractionation of its two isotopes between the different sites. The fractionation decreases dramatically from 87.1 parts per thousand at 300 K to 1.0 parts per thousand at 3000 K. Diffusion is predicted to occur via two inter-related mechanisms: Mg-Li exchange, and a second, vacancy assisted interstitial mechanism. This behaviour is complex, facilitates migration of the heavier isotope and offers insights into observations of Li mobility and zoning in olivine, the most volumetrically important upper mantle mineral. (C) 2012 Elsevier Ltd. All rights reserved.

AB - Lithium is an important geochemical tracer used to infer the thermal and chemical evolution of minerals in the Earth's upper mantle. Knowledge of point defect chemistry and diffusion is critical for the interpretation of Li distribution in minerals. Using quantum mechanical methods we show that in forsterite Li will be incorporated as bound interstitial-substitutional pairs. Furthermore, there will be temperature dependent fractionation of its two isotopes between the different sites. The fractionation decreases dramatically from 87.1 parts per thousand at 300 K to 1.0 parts per thousand at 3000 K. Diffusion is predicted to occur via two inter-related mechanisms: Mg-Li exchange, and a second, vacancy assisted interstitial mechanism. This behaviour is complex, facilitates migration of the heavier isotope and offers insights into observations of Li mobility and zoning in olivine, the most volumetrically important upper mantle mineral. (C) 2012 Elsevier Ltd. All rights reserved.

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KW - AB-INITIO

KW - LI

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KW - OLIVINE

KW - CASTEP

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DO - 10.1016/j.gca.2012.05.034

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JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

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