LINK<\/strong><\/a><\/p>\n\n\n\n“The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05\u2030, 95% confidence interval), we systematically measured the K isotopic compositions and major\/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high\u2010temperature conditions in the solar nebula and were dominated by nominally K\u2010free refractory minerals, have the highest K2O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (\u03b441K: \u22120.30 to \u22120.25\u2030). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K2O content (0.003\u20130.17 wt%) and generally lighter K isotope compositions (\u03b441K: \u22120.87\u2030 to \u22120.24\u2030). The matrix and bulks are nearly identical in K2O content and K isotope compositions (0.02\u20130.05 wt%; \u03b441K: \u22120.62 to \u2212 0.46\u2030), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent\u2010body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1\u2030) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC\u2010ICP\u2010MS analyses of the components in ordinary chondrites, which also show an absence of large (10\u2030) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Yun Jiang, Piers Koefoed, Olga Pravdivtseva, Heng Chen, Chun\u2010Hui Li, Fang Huang, Li\u2010Ping Qin, Jia Liu, Kun Wang Meteoritics & Planetary ScienceVersion of Record online: 24 November 2020 LINK “The alkali element K is moderately…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[61,9,72,71],"tags":[108,1842,1846,3273,1839,3701,5103,3236,1015],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/25378"}],"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=25378"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/25378\/revisions"}],"predecessor-version":[{"id":25379,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/25378\/revisions\/25379"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25378"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25378"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25378"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}