LINK<\/strong><\/a><\/p>\n\n\n\n“Northwest Africa (NWA) 12379 is a new metal-rich chondrite with unique characteristics distinguishing it from all previously described meteorites. It contains high Fe,Ni-metal content (\u223c70\u2009vol.%) and completely lacks interchondrule matrix; these characteristics are typical only for metal-rich carbonaceous (CH and CB) and G chondrites. However, chondrule sizes (60 to 1200\u2009\u03bcm; mean\u2009=\u2009370\u2009\u03bcm), their predominantly porphyritic textures, nearly equilibrated chemical compositions of chondrule olivines (Fa18.1\u201328.3, average Fa24.9\u00b13.2, PMD\u2009=\u200912.8; Cr2O3\u2009=\u20090.03\u2009\u00b1\u20090.02\u2009wt.%; FeO\/MnO\u2009=\u200953.2\u2009\u00b1\u20096.5 (wt.-ratio); n\u2009=\u200928), less equilibrated compositions of low-Ca pyroxenes (Fs3.2\u201318.7Wo0.2\u20134.5; average Fs14.7\u00b13.7Wo1.4\u00b11.3; n\u2009=\u200920), oxygen-isotope compositions of chondrule olivine phenocrysts (\u039417O \u223c 0.2\u20121.4 \u2030, average \u223c 0.8 \u2030), and the presence of coarse-grained Ti-bearing chromite, Cl-apatite, and merrillite, all indicate affinity of NWA 12379 to unequilibrated (type 3.8) ordinary chondrites (OCs). Like most OCs, NWA 12379 experienced fluid-assisted thermal metamorphism that resulted in formation of secondary ferroan olivine (Fa27) that replaces low-Ca pyroxene grains in chondrules and in inclusions in Fe,Ni-metal grains. \u039417O of the ferroan olivine (\u223c 4 \u2030) is similar to those of aqueously-formed fayalite in type 3 OCs, but its \u03b418O is significantly higher (15\u201519 \u2030, average\u2009=\u200917 \u2030 vs. 3\u201512 \u2030, average\u2009=\u20098 \u2030, respectively). We suggest classifying NWA 12379 as the ungrouped metal-rich chondrite with affinities of its non-metal fraction to unequilibrated OCs and speculate that it may have formed by a collision between an OC-like body and a metal-rich body and subsequently experienced fluid-assisted thermal metamorphism. Trace siderophile element abundances and isotopic compositions (e.g., Mo, Ni, Fe) of the NWA 12379 metal could help to constrain its origin.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Christian A. Jansen, Frank E. Brenker, Jutta Zipfel, Andreas Pack, Luc Labenne, Kazuhide Nagashima, Alexander N. Krot, Martin Bizzarro, Martin Schiller Geochemistry In Press, Journal Pre-proof, Available online 10 September 2019 LINK “Northwest Africa (NWA)…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[59,7,951],"tags":[4840,4839,1731],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20404"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=20404"}],"version-history":[{"count":2,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20404\/revisions"}],"predecessor-version":[{"id":20406,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20404\/revisions\/20406"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20404"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=20404"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=20404"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}