Diffusion-driven chromium isotope fractionation in ultramafic cumulate minerals: Elemental and isotopic evidence from the Stillwater Complex

Bai, Yang; Su, B.-X.; Xiao, Y.; Chen, C.; Cui, M.-M.; He, X.-Q.; Qin, L.-P.; Charlier, Bernard

doi:10.1016/j.gca.2019.07.052

Article (Scientific journals)

Diffusion-driven chromium isotope fractionation in ultramafic cumulate minerals: Elemental and isotopic evidence from the Stillwater Complex

Bai, Yang; Su, B.-X.; Xiao, Y. et al.

2019 • In Geochimica et Cosmochimica Acta, 263, p. 167-181

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https://hdl.handle.net/2268/240253

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10.1016/j.gca.2019.07.052

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Keywords :

Chromium isotopes; Diffusion; Stillwater Complex

Abstract :

[en] To investigate chromium diffusion kinetics in ultramafic cumulate minerals, we analyzed the Cr elemental and isotopic compositions of olivine, orthopyroxene, and chromite from the Stillwater layered intrusion. Core-to-rim compositional profiles reveal that Cr elemental concentrations decrease from 60 to 20 ppm in olivine and from 5000–4600 to 2700–2400 ppm in orthopyroxene. These zoned Cr distributions in olivine and orthopyroxene suggest that Cr was lost by diffusion into the melt. Olivine and orthopyroxene have δ53Cr values ranging from –0.09 to 0.25‰ and from –0.11 to 0.07‰, respectively, higher than the values of coexisting chromite (–0.23 to –0.07‰). This isotopic disequilibrium can be explained by diffusion-driven kinetic fractionation during cooling. The preferential diffusion of light Cr isotopes from silicate minerals to the melt resulted in isotopically heavier olivine and orthopyroxene, but the kinetic diffusion between chromite and melt negligibly affected the isotopic compositions of chromite grains due to their high Cr concentrations. Modeling results based on the observed Cr contents and isotopic compositions of silicate minerals constrain the cooling time of the Peridotite Zone in the Stillwater magmatic system to have been 10–100 kyr. © 2019 Elsevier Ltd

Disciplines :

Earth sciences & physical geography

Author, co-author :

Bai, Yang ; Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing, 100029, China, University of Chinese Academy of Sciences, Beijing, 100049, China, Department of Geology, University of Liege, Liege, B-4000, Belgium

Su, B.-X.; Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing, 100029, China, University of Chinese Academy of Sciences, Beijing, 100049, China

Xiao, Y.; State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing, 100029, China

Chen, C.; Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing, 100029, China, University of Chinese Academy of Sciences, Beijing, 100049, China

Cui, M.-M.; University of Chinese Academy of Sciences, Beijing, 100049, China, Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008, China

He, X.-Q.; CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China

Qin, L.-P.; CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China

Charlier, Bernard ; Université de Liège - ULiège > Département de géologie > Pétrologie, géochimie endogènes et pétrophysique

Language :

English

Title :

Diffusion-driven chromium isotope fractionation in ultramafic cumulate minerals: Elemental and isotopic evidence from the Stillwater Complex

Publication date :

2019

Journal title :

Geochimica et Cosmochimica Acta

ISSN :

0016-7037

eISSN :

1872-9533

Publisher :

Elsevier Ltd

Volume :

263

Pages :

167-181

Peer reviewed :

Peer Reviewed verified by ORBi

Funders :

YIPA - Youth Innovation Promotion Association [CN]
CAS - Chinese Academy of Sciences
State Key Laboratory of Genetic Resources and Evolution
NSCF - National Natural Science Foundation of China [CN]

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