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Iron isotopic evolution during fractional crystallization of the uppermost Bushveld Complex layered mafic intrusion
dc.contributor.authorBilenker, Laura D.
dc.contributor.authorVanTongeren, Jill A.
dc.contributor.authorLundstrom, Craig C.
dc.contributor.authorSimon, Adam C.
dc.date.accessioned2017-05-10T17:47:37Z
dc.date.available2018-05-04T20:56:59Zen
dc.date.issued2017-03
dc.identifier.citationBilenker, Laura D.; VanTongeren, Jill A.; Lundstrom, Craig C.; Simon, Adam C. (2017). "Iron isotopic evolution during fractional crystallization of the uppermost Bushveld Complex layered mafic intrusion." Geochemistry, Geophysics, Geosystems 18(3): 956-972.
dc.identifier.issn1525-2027
dc.identifier.issn1525-2027
dc.identifier.urihttps://hdl.handle.net/2027.42/136675
dc.description.abstractWe present δ56Fe (56Fe/54Fe relative to standard IRMM‐014) data from whole rock and magnetite of the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex. With it, we assess the role of fractional crystallization in controlling the Fe isotopic evolution of a mafic magma. The UUMZ evolved by fractional crystallization of a dry tholeiitic magma to produce gabbros and diorites with cumulus magnetite and fayalitic olivine. Despite previous experimental work indicating a potential for magnetite crystallization to drastically change magma δ56Fe, we observe no change in whole rock δ56Fe above and below magnetite saturation. We also observe no systematic change in whole rock δ56Fe with increasing stratigraphic height, and only a small variation in δ56Fe in magnetite separates above magnetite saturation. Whole rock δ56Fe (errors twice standard deviation, ±2σ) throughout the UUMZ ranges from −0.01 ±0.03‰ to 0.21 ±0.09‰ (δ56FeaverageWR = 0.10 ±0.09‰; n = 21, isotopically light outlier: δ56FeWR = −0.15‰), and magnetites range from 0.28 ±0.04‰ to 0.86 ±0.07‰ (δ56FeaverageMgt = 0.50 ±0.15‰; n = 20), similar to values previously reported for other layered intrusions. We compare our measured δ56FeWR to a model that incorporates the changing normative mineralogy, calculated temperatures, and published fractionation factors of Fe‐bearing phases throughout the UUMZ and produces δ56FeWR values that evolve only in response to fractional crystallization. Our results show that the Fe isotopic composition of a multiply saturated (multiple phases on the liquidus) magma is unlikely to change significantly during fractional crystallization of magnetite due to the competing fractionation of other Fe‐bearing cumulus phases.Key PointsWhole rock and magnetite separates from the uppermost portion of the Bushveld Complex were analyzed for their Fe isotope compositionsWe find no systematic variation in whole rock or magnetite Fe isotope ratios with stratigraphic height85% crystallization of a dry tholeiitic multiply‐saturated magma does not significantly fractionate Fe isotopes
dc.publisherInst. of Min. Metall
dc.publisherWiley Periodicals, Inc.
dc.subject.otherBushveld Complex
dc.subject.otheriron isotope
dc.subject.otherlayered intrusion
dc.subject.otherfractional crystallization
dc.titleIron isotopic evolution during fractional crystallization of the uppermost Bushveld Complex layered mafic intrusion
dc.typeArticleen_US
dc.rights.robotsIndexNoFollow
dc.subject.hlbsecondlevelGeological Sciences
dc.subject.hlbtoplevelScience
dc.description.peerreviewedPeer Reviewed
dc.description.bitstreamurlhttps://deepblue.lib.umich.edu/bitstream/2027.42/136675/1/ggge21257_am.pdf
dc.description.bitstreamurlhttps://deepblue.lib.umich.edu/bitstream/2027.42/136675/2/ggge21257.pdf
dc.identifier.doi10.1002/2016GC006660
dc.identifier.sourceGeochemistry, Geophysics, Geosystems
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