{"id":34440,"date":"2023-10-26T10:37:55","date_gmt":"2023-10-26T08:37:55","guid":{"rendered":"https:\/\/karmaka.de\/?p=34440"},"modified":"2023-10-26T10:37:56","modified_gmt":"2023-10-26T08:37:56","slug":"nature-and-timing-of-a-significant-reduction-event-on-the-l-chondrite-parent-asteroid","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=34440","title":{"rendered":"Nature and timing of a significant reduction event on the L-chondrite parent asteroid<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"\n<p>Alan E. Rubin, Brent D. Turrin<\/p>\n\n\n\n<p>MAPS, Version of Record online: 26 October 2023<\/p>\n\n\n\n<p><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1111\/maps.14088\"><strong>LINK (OPEN ACCESS)<\/strong><\/a><br><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/epdf\/10.1111\/maps.14088\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>PDF (OPEN ACCESS)<\/strong><\/a><\/p>\n\n\n\n<p class=\"justify-text\">&#8220;About 17% of L6 chondrites (15\/87) show significant reduction features in BSE images in thin section. Because some thin sections of these meteorites do not show reduction features, this percentage is a lower limit. Reduction features include: (1) 4\u20135-\u03bcm-thick BSE-dark reduction rims on olivine and orthopyroxene grains and along fracture boundaries in these grains, (2) 4\u201312-\u03bcm-thick dark bands (probably poorly crystalline pyrrhotite) at the margins and along fractures in troilite grains, and (3) 2\u20135-\u03bcm-thick dark rinds of kamacite around some taenite grains. Only one of 70 L-group chondrites (1.4%) of lower petrologic type exhibits minor reduction. The L6 chondrites showing major reduction have 40Ar\/39Ar plateau ages ranging from 156\u2009\u00b1\u20091\u2009Ma for Guangnan to 4543\u2009\u00b1\u20093\u2009Ma for Thamaniyat Ajras. Reduction occurred after silicate, sulfide, and metal grains had attained their present sizes during parent-body thermal metamorphism (and had been fractured by parent-body collisions). The precise plateau age of Thamaniyat Ajras probably marks the timing of the L6 reduction event. It seems likely the reductant was a low-viscosity fluid, plausibly CO, derived from oxidation of poorly graphitized and amorphous carbon within fine-grained matrix. Water-ice that had accreted to the L-chondrite asteroid was heated and mobilized during metamorphism, causing oxidation. After peak metamorphism, ~75% of the water had been used up or lost; the remaining water facilitated continuing graphite oxidation so that, after this point, overall reduction effects exceeded those of oxidation. L chondrites of lower petrologic type were less affected by reduction due to their lower metamorphic temperatures.&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Alan E. Rubin, Brent D. Turrin MAPS, Version of Record online: 26 October 2023 LINK (OPEN ACCESS)PDF (OPEN ACCESS) &#8220;About 17% of L6 chondrites (15\/87) show significant reduction features in BSE images in thin section&#8230;.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23,7,337],"tags":[93,3188,325,490,1807],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/34440"}],"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=34440"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/34440\/revisions"}],"predecessor-version":[{"id":34441,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/34440\/revisions\/34441"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=34440"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=34440"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=34440"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}