{"id":38396,"date":"2025-05-25T00:23:51","date_gmt":"2025-05-24T22:23:51","guid":{"rendered":"https:\/\/karmaka.de\/?p=38396"},"modified":"2025-05-25T00:23:52","modified_gmt":"2025-05-24T22:23:52","slug":"oxygen-isotope-variations-in-refractory-inclusions-from-rumuruti-type-chondrites-evidence-for-nebular-gas-heterogeneity-and-parent-body-exchange","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=38396","title":{"rendered":"Oxygen-isotope variations in refractory inclusions from Rumuruti-type chondrites: Evidence for nebular gas heterogeneity and parent-body exchange<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"\n<p>Samuel Ebert, Kazuhide Nagashima, Alexander N. Krot, Addi Bischoff<\/p>\n\n\n\n<p>Geochimica et Cosmochimica Acta<br>In Press, Journal Pre-proof, Available online 24 May 2025<\/p>\n\n\n\n<p><a href=\"https:\/\/www.sciencedirect.com\/science\/article\/pii\/S001670372500273X\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>LINK + PDF (OPEN ACCESS)<\/strong><\/a><\/p>\n\n\n\n<p class=\"justify-text\">&#8220;Refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] in unmetamorphosed chondrites (petrologic type\u202f\u2264\u202f3.0) have typically uniform 16O-rich solar-like compositions. The origin of oxygen-isotope heterogeneity within individual refractory inclusions from weakly metamorphosed (petrologic type\u202f&gt;\u202f3.0) chondrites remains controversial. It may reflect (i) condensation from a nebular gas having variable O-isotope composition, (ii) gas\u2013solid or gas\u2013melt O-isotope exchange with this gas, and\/or (iii) O-isotope exchange with an 16O-depleted aqueous fluid in the host chondrite parent bodies. Here, we present the mineralogy, petrology and O-isotope compositions of refractory inclusions (12 CAIs and 2 AOAs) from the Rumuruti-type (R) chondrites of petrologic type 3 \u2013 Northwest Africa (NWA) 753, NWA 1471, and Dhofar 1123. The CAIs and AOAs are extensively altered: melilite is completely replaced by secondary minerals; perovskite is largely replaced by ilmenite; spinel and olivine are enriched in FeO. The polymineralic refractory inclusions have heterogeneous O-isotope compositions: \u039417O ranges from\u202f\u223c\u221225\u202f\u2030 to\u202f\u223c5\u202f\u2030 (2\u03c3\u202f=\u202f\u00b1\u223c2\u2030). The only exception is a spinel-hibonite inclusion having uniform 16O-depleted composition (\u039417O\u202f\u223c\u202f\u221214\u202f\u2030). Hibonite, most ferroan spinel, and some olivine and Al,(Ti)-diopside grains in Rumuruti-type chondrite (RC) fragments of low petrologic type (3.15\u202f\u2212\u202f3.2) retained their initial \u0394 17O values, which, however, range from\u202f\u221225\u202f\u2030 to\u202f\u223c\u202f\u221214\u202f\u2030, suggesting variations in O-isotope composition of nebular gas in the CAI-forming region. Most Al,Ti-diopside and some olivine and spinel grains in RC refractory inclusions are 16O-depleted compared to minerals most resistant to O-isotope exchange (hibonite and spinel) that retained their original compositions. The most 16O-depleted compositions of Al,Ti-diopside and ferroan olivine have \u039417O of \u223c +5\u2030 that is similar to \u039417O of the aqueously formed grossular and ferroan olivine. We infer that the 16O-depleted Al,Ti-diopside, olivine, and spinel in isotopically heterogeneous refractory inclusions experienced post-formation O-isotope exchange with aqueous fluids in the RC parent asteroid(s).&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Samuel Ebert, Kazuhide Nagashima, Alexander N. Krot, Addi Bischoff Geochimica et Cosmochimica ActaIn Press, Journal Pre-proof, Available online 24 May 2025 LINK + PDF (OPEN ACCESS) &#8220;Refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[685,66,65,27,57],"tags":[1635,1891,1846,6886,6885,4259,2779,3129,5365,5556],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/38396"}],"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=38396"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/38396\/revisions"}],"predecessor-version":[{"id":38397,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/38396\/revisions\/38397"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=38396"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=38396"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=38396"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}