Magnesium isotopic variations in cratonic eclogites: Origins and implications

Wang, S.-J.; Teng, F.-Z.; Williams, H.; Li, S.-G.

doi:10.1016/j.epsl.2012.10.016

Magnesium isotopic variations in cratonic eclogites: Origins and implications

Wang, S.-J.; Teng, F.-Z.; Williams, H.; Li, S.-G.

Authors

S.-J. Wang

F.-Z. Teng

H. Williams

S.-G. Li

Abstract

Cratonic eclogites play an important role in the formation and dynamic evolution of the subcontinental lithospheric mantle. However, their origin, whether as fragments of subducted oceanic crust or high-pressure mantle cumulates, remains controversial. Here, we report Mg isotopic compositions (δ26Mg) for cratonic eclogites from Kaalvallei and Bellsbank kimberlite pipes, South Africa. We find that clinopyroxene is 0.375±0.069 to 0.676±0.075‰ heavier than coexisting garnet, which reflects equilibrium isotope fractionation between these phases, primarily driven by the difference in Mg coordination between clinopyroxene and garnet. Bulk eclogites have strikingly variable Mg isotopic compositions, which range from −0.797±0.075 to −0.139±0.061‰, values that are significantly lighter than the range displayed by global mantle peridotites to date (−0.25±0.07‰, 2SD). As significant Mg isotope fractionation is only known to occur during low-temperature water–rock interaction, our results provide further evidence for the derivation of cratonic eclogites from subducted altered oceanic crust. In addition, the lack of correlation between Δ26Mg and Δ57Fe provides evidence for redox control on equilibrium inter-mineral Fe isotope fractionation.

Citation

Wang, S., Teng, F., Williams, H., & Li, S. (2012). Magnesium isotopic variations in cratonic eclogites: Origins and implications. Earth and Planetary Science Letters, 359-360, 219-226. https://doi.org/10.1016/j.epsl.2012.10.016

Journal Article Type	Article
Publication Date	Dec 1, 2012
Deposit Date	Jan 21, 2015
Publicly Available Date	Feb 13, 2015
Journal	Earth and Planetary Science Letters
Print ISSN	0012-821X
Publisher	Elsevier
Peer Reviewed	Peer Reviewed
Volume	359-360
Pages	219-226
DOI	https://doi.org/10.1016/j.epsl.2012.10.016
Keywords	Magnesium isotopes, Iron isotopes, Isotope fractionation, Cratonic eclogite, Mantle
Public URL	https://durham-repository.worktribe.com/output/1414028

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Copyright Statement
NOTICE: this is the author’s version of a work that was accepted for publication in Earth and planetary science letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Earth and planetary science letters, 359-360, 2012, 10.1016/j.epsl.2012.10.016