LINK<\/strong><\/a><\/p>\n\n\n\n“The nature of oxygen-isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] from weakly metamorphosed chondrites is one of the outstanding problems in cosmochemistry. To obtain insights into possible processes resulting in O-isotope heterogeneity of refractory inclusions, we investigated the mineralogy, petrology, and oxygen isotopic compositions of six CAIs and two AOAs and aqueously formed fayalite grains within the matrix of the H3.1 chondrite Northwest Africa (NWA) 3358. Most of the refractory inclusions studied appear to be unmolten solar nebula condensates; some may have experienced partial melting and\/or high-temperature annealing. The NWA 3358 refractory inclusions nearly completely avoided metasomatic alteration on the H-chondrite parent body: nepheline grains replacing anorthite and\/or melilite are either very minor or absent. Five out of eight refractory inclusions studied have heterogeneous O-isotope composition: \u039417O ranges from \u223c \u221225\u2030 to \u223c 3.5\u00b12\u2030 (2\u03c3). This O-isotope heterogeneity appears to be mineralogically controlled with melilite and anorthite being systematically 16O-depleted compared to hibonite, spinel, Al,Ti-diopside, and forsterite all having similar solar-like \u039417O of \u223c \u221224\u00b12\u2030. In contrast to NWA 3358 refractory inclusions, the previously studied AOAs and a fine-grained CAI from the LL3.00 chondrite Semarkona have uniform \u039417O of \u223c \u221225\u2030 (McKeegan et al., 1998; Itoh et al., 2007). Because the mineralogically-controlled O-isotope heterogeneity in refractory inclusions from ordinary chondrites appears to correlate with petrologic type of a host meteorite experienced by aqueous alteration, we suggest O-isotope exchange in NWA 3358 CAIs and AOAs resulted from aqueous fluid-rock interaction on the H-chondrite parent asteroids. This is supported by the presence of 16O-depleted anorthite (\u039417O \u223c 3.5\u00b12\u2030) and aqueously formed fayalite similar depleted in 16O (\u039417O \u223c 4\u00b12\u2030). The \u039417O of NWA 3358 fayalite is comparable to that of magnetite and fayalite in Semarkona and other weakly metamorphosed L3 and LL3 chondrites (Choi et al., 1998; Doyle et al., 2015) suggesting similar \u039417O of aqueous fluids on the H, L, and LL chondrite parent asteroids.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Samuel Ebert, Kazuhide Nagashima, Alexander N. Krot, Addi Bischoff Geochimica et Cosmochimica ActaIn Press, Journal Pre-proof, Available online 21 May 2020 LINK “The nature of oxygen-isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[685,66,6,7,65,337,57],"tags":[1891,1846,4852,2416,5558,5555,5557,5556,4390],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/22073"}],"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=22073"}],"version-history":[{"count":2,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/22073\/revisions"}],"predecessor-version":[{"id":22075,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/22073\/revisions\/22075"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=22073"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=22073"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=22073"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}