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dc.contributor.authorLeroux, H.
dc.contributor.authorDevouard, B.
dc.contributor.authorCordier, P.
dc.contributor.authorGuyot, F.
dc.date.accessioned2021-02-12T20:56:41Z
dc.date.available2021-02-12T20:56:41Z
dc.date.issued2004-01-01
dc.identifier.citationLeroux, H., Devouard, B., Cordier, P., & Guyot, F. (2004). Pyroxene microstructure in the Northwest Africa 856 Martian meteorite. Meteoritics & Planetary Science, 39(5), 711-722.
dc.identifier.issn1945-5100
dc.identifier.doi10.1111/j.1945-5100.2004.tb00114.x
dc.identifier.urihttp://hdl.handle.net/10150/655835
dc.description.abstractTransmission electron microscopy was used to examine pyroxene microstructure in the Northwest Africa (NWA) 856 martian meteorite to construct its cooling and shock histories. All pyroxenes contain strained coherent pigeonite/augite exsolution lamellae on (001). The average width and periodicity of lamellae are 80 and 400 nm, respectively, indicating a cooling rate below 0.1 degrees C/hr for the parent rock. Pigeonite and augite are topotactic, with strained coherent interfaces parallel to (001). The closure temperature for Ca-Fe, Mg interdiffusion, estimated from the composition at the augite pigeonite interface, is about 700 degrees C. Tweed texture in augite reveals that a spinodal decomposition occurred. Locally, tweed evolved toward secondary pigeonite exsolutions on (001). Due to the decreasing diffusion rate with decreasing temperature, "M-shaped" concentration profiles developed in augite lamellae. Pigeonite contains antiphase boundaries resulting from the C2/c to P21/c space group transition that occurred during cooling. The reconstructive phase transition from P21/c clinopyroxene to orthopyroxene did not occur. The deformation (shock) history of the meteorites is revealed by the presence of dislocations and mechanical twins. Dislocations are found in glide configuration, with the [001](100) glide system preferentially activated. They exhibit strong interaction with the strained augite/pigeonite interfaces and did not propagate over large distances. Twins are found to be almost all parallel to (100) and show moderate interaction with the augite/pigeonite interfaces. These twins are responsible for the plastic deformation of the pyroxene grains. Comparison with microstructure of shocked clinopyroxene (experimentally or naturally shocked) suggests that NWA 856 pyroxenes are not strongly shocked.
dc.language.isoen
dc.publisherThe Meteoritical Society
dc.relation.urlhttps://meteoritical.org/
dc.rightsCopyright © The Meteoritical Society
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.subjectMars meteorites
dc.subjectshock metamorphism
dc.subjectelectron microscopy
dc.subjectCooling history
dc.titlePyroxene microstructure in the Northwest Africa 856 martian meteorite
dc.typeArticle
dc.typetext
dc.identifier.journalMeteoritics & Planetary Science
dc.description.collectioninformationThe Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information.
dc.eprint.versionFinal published version
dc.description.admin-noteMigrated from OJS platform February 2021
dc.source.volume39
dc.source.issue5
dc.source.beginpage711
dc.source.endpage722
refterms.dateFOA2021-02-12T20:56:41Z


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