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Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

Earth and Planetary Science Letters

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, , , ,
DOI: 10.1016/j.epsl.2013.02.037

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Abstract

he zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation.


The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰<δ66Zn<0.36‰; δ66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe–Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰<δ66Zn<0.33‰), however, the degree of fractionation caused by magmatic differentiation is less significant (only 0.07‰) and no correlation between isotope composition and degree of differentiation is seen. We conclude that high temperature magmatic differentiation can cause Zn isotope fractionation that is resolvable at current levels of precision, but only in compositionally-evolved lithologies. With regards to primitive (ultramafic and basaltic) material, this signifies that the terrestrial mantle is essentially homogeneous with respect to Zn isotopes. Utilizing basaltic and ultramafic sample analyses, from different geologic settings, we estimate that the average Zn isotopic composition of Bulk Silicate Earth is δ66Zn=0.28±0.05‰ (2s.d.).

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth
Series title:
Earth and Planetary Science Letters
DOI:
10.1016/j.epsl.2013.02.037
Volume
369-370
Year Published:
2013
Language:
English
Publisher:
North-Holland Pub. Co.
Publisher location:
Amsterdam
Description:
9 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
34
Last page:
42
Number of Pages:
9