Determination of Fe3+/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophiolite

Hdl Handle:
http://hdl.handle.net/10545/621503
Title:
Determination of Fe3+/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophiolite
Authors:
Lenaz, Davide; Adetunji, Jacob ( 0000-0002-8491-6440 ) ; Rollinson, Hugh ( 0000-0002-6553-8472 )
Abstract:
We present the results of a comparative study in which we have measured Fe3+/ΣFe ratios in chromites from mantle chromitites in the Oman ophiolite using Mössbauer spectroscopy and single-crystal X-ray diffraction. We have compared these results with ratios calculated from mineral stoichiometry and find that mineral stoichiometry calculations do not accurately reflect the measured Fe3+/ΣFe ratios. We have identified three groups of samples. The majority preserve Fe3+/ΣFe ratios which are thought to be magmatic, whereas a few samples are highly oxidized and have high Fe3+/ΣFe ratios. There is also a group of partially oxidized samples. The oxidized chromites show anomalously low cell edge (a0) values and their oxygen positional parameters among the lowest ever found for chromites. Site occupancy calculations show that some chromites are non-stoichiometric and contain vacancies in their structure randomly distributed between both the T and M sites. The field relationships suggest that the oxidation of the magmatic chromitites took place in association with a ductile shear zone in mantle harzburgites. Primary magmatic Fe3+/ΣFe ratios measured for the Oman mantle chromitites are between 0.193–0.285 (X-ray data) and 0.164–0.270 (Mössbauer data) and preserve a range of Fe3+/ΣFe ratios which we propose is real and reflects differences in the composition of the magmas parental to the chromitites. The range of values extends from those MORB melts (0.16 ± 0.1) to those for arc basalts (0.22–0.28).
Affiliation:
University of Derby
Citation:
Lenaz, D. et al (2014) 'Determination of Fe3+/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophiolite', Contributions to Mineralogy and Petrology, 167 (1)
Publisher:
Springer
Journal:
Contributions to Mineralogy and Petrology
Issue Date:
3-Jan-2014
URI:
http://hdl.handle.net/10545/621503
DOI:
10.1007/s00410-013-0958-2
Additional Links:
http://link.springer.com/10.1007/s00410-013-0958-2
Type:
Article
Language:
en
ISSN:
107999
EISSN:
14320967
Sponsors:
University of Derby, URSS fund
Appears in Collections:
Environmental Sustainability Research Centre

Full metadata record

DC FieldValue Language
dc.contributor.authorLenaz, Davideen
dc.contributor.authorAdetunji, Jacoben
dc.contributor.authorRollinson, Hughen
dc.date.accessioned2017-03-22T11:42:53Z-
dc.date.available2017-03-22T11:42:53Z-
dc.date.issued2014-01-03-
dc.identifier.citationLenaz, D. et al (2014) 'Determination of Fe3+/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophiolite', Contributions to Mineralogy and Petrology, 167 (1)en
dc.identifier.issn107999-
dc.identifier.doi10.1007/s00410-013-0958-2-
dc.identifier.urihttp://hdl.handle.net/10545/621503-
dc.description.abstractWe present the results of a comparative study in which we have measured Fe3+/ΣFe ratios in chromites from mantle chromitites in the Oman ophiolite using Mössbauer spectroscopy and single-crystal X-ray diffraction. We have compared these results with ratios calculated from mineral stoichiometry and find that mineral stoichiometry calculations do not accurately reflect the measured Fe3+/ΣFe ratios. We have identified three groups of samples. The majority preserve Fe3+/ΣFe ratios which are thought to be magmatic, whereas a few samples are highly oxidized and have high Fe3+/ΣFe ratios. There is also a group of partially oxidized samples. The oxidized chromites show anomalously low cell edge (a0) values and their oxygen positional parameters among the lowest ever found for chromites. Site occupancy calculations show that some chromites are non-stoichiometric and contain vacancies in their structure randomly distributed between both the T and M sites. The field relationships suggest that the oxidation of the magmatic chromitites took place in association with a ductile shear zone in mantle harzburgites. Primary magmatic Fe3+/ΣFe ratios measured for the Oman mantle chromitites are between 0.193–0.285 (X-ray data) and 0.164–0.270 (Mössbauer data) and preserve a range of Fe3+/ΣFe ratios which we propose is real and reflects differences in the composition of the magmas parental to the chromitites. The range of values extends from those MORB melts (0.16 ± 0.1) to those for arc basalts (0.22–0.28).en
dc.description.sponsorshipUniversity of Derby, URSS funden
dc.language.isoenen
dc.publisherSpringeren
dc.relation.urlhttp://link.springer.com/10.1007/s00410-013-0958-2en
dc.rightsArchived with thanks to Contributions to Mineralogy and Petrologyen
dc.subjectCr-spinel chromititeen
dc.subjectOmanen
dc.subjectX-ray single-crystal diffractionen
dc.subjectOxidation processesen
dc.titleDetermination of Fe3+/ΣFe ratios in chrome spinels using a combined Mössbauer and single-crystal X-ray approach: application to chromitites from the mantle section of the Oman ophioliteen
dc.typeArticleen
dc.identifier.eissn14320967-
dc.contributor.departmentUniversity of Derbyen
dc.identifier.journalContributions to Mineralogy and Petrologyen
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