LINK<\/strong><\/a><\/p>\n\n\n\n“The distribution of the short\u2010lived radionuclide 26Al in the early solar system remains a major topic of investigation in planetary science. Thousands of analyses are now available but grossite\u2010bearing Ca\u2010, Al\u2010rich inclusions (CAIs) are underrepresented in the database. Recently found grossite\u2010bearing inclusions in CO3 chondrites provide an opportunity to address this matter. We determined the oxygen and magnesium isotopic compositions of individual phases of 10 grossite\u2010bearing CAIs in the Dominion Range (DOM) 08006 (CO3.0) and DOM 08004 (CO3.1) chondrites. All minerals in DOM 08006 CAIs as well as hibonite, spinel, and pyroxene in DOM 08004 are uniformly 16O\u2010rich (\u039417O = \u221225 to \u221220\u2030) but grossite and melilite in DOM 08004 CAIs are not; \u039417O of grossite and melilite range from ~ \u221211 to ~0\u2030 and from ~ \u221223 up to ~0\u2030, respectively. Even within this small suite, in the two chondrites a bimodal distribution of the inferred initial 26Al\/27Al ratios (26Al\/27Al)0 is seen, with four having (26Al\/27Al)0 \u22641.1 \u00d7 10\u22125 and six having (26Al\/27Al)0 \u22653.7 \u00d7 10\u22125. Five of the 26Al\u2010rich CAIs have (26Al\/27Al)0 within error of 4.5 \u00d7 10\u22125; these values can probably be considered indistinguishable from the \u201ccanonical\u201d value of 5.2 \u00d7 10\u22125 given the uncertainty in the relative sensitivity factor for grossite measured by secondary ion mass spectrometry. We infer that the 26Al\u2010poor CAIs probably formed before the radionuclide was fully mixed into the solar nebula. All minerals in the DOM 08006 CAIs, as well as spinel, hibonite, and Al\u2010diopside in the DOM 08004 CAIs retained their initial oxygen isotopic compositions, indicating homogeneity of oxygen isotopic compositions in the nebular region where the CO grossite\u2010bearing CAIs originated. Oxygen isotopic heterogeneity in CAIs from DOM 08004 resulted from exchange between the initially 16O\u2010rich (\u039417O ~\u221224\u2030) melilite and grossite and 16O\u2010poor (\u039417O ~0\u2030) fluid during hydrothermal alteration on the CO chondrite parent body; hibonite, spinel, and Al\u2010diopside avoided oxygen isotopic exchange during the alteration. Grossite and melilite that underwent oxygen isotopic exchange avoided redistribution of radiogenic 26Mg and preserved undisturbed internal Al\u2010Mg isochrons. The \u039417O of the fluid can be inferred from O\u2010isotopic compositions of aqueously formed fayalite and magnetite that precipitated from the fluid on the CO parent asteroid. This and previous studies suggest that O\u2010isotope exchange during fluid\u2013rock interaction affected most CAIs in CO \u22653.1 chondrites.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Steven B. Simon, Alexander N. Krot, Kazuhide Nagashima Meteoritics & Planetary Science LINK “The distribution of the short\u2010lived radionuclide 26Al in the early solar system remains a major topic of investigation in planetary science. Thousands…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66,9,19,57],"tags":[1846,3273,1814,1388,973,4930,4929],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/18239"}],"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=18239"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/18239\/revisions"}],"predecessor-version":[{"id":18240,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/18239\/revisions\/18240"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18239"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18239"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18239"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}