LINK<\/strong><\/a><\/p>\n\n\n\n“We report on the mineralogy, petrology, oxygen, and aluminum\u2013magnesium isotopic systematics of the secondary corundum-bearing assemblages in type B CAIs 3529Z and 3529G and fluffy type A (FTA) CAI ALH-2 from Allende (CV\u2009>\u20093.6). In 3529Z and 3529G, 2\u20135\u2009\u03bcm-sized euhedral-to-subhedral corundum grains associate with secondary alumo\u00e5kermanite [(Ca,Na)2AlSi2O7], grossular, spinel, grossite, celsian, kushiroite, and wadalite. In ALH-2, 2\u20135\u2009\u03bcm-sized euhedral-to-subhedral corundum grains associate with secondary grossular, nepheline, spinel, and kushiroite. In 3529Z and 3529G, corundum and associated secondary grossite, spinel, alumo\u00e5kermanite, grossular, and kushiroite have similar 16O-poor compositions (\u039417O\u2009=\u2009\u22122.2\u2009\u00b1\u20091.5\u2030); primary spinel is 16O-rich (\u039417O\u2009~\u2009\u221223\u2030); Al,Ti-diopside shows a range of \u039417O (from ~ \u221224\u2030 to ~ \u221215\u2030); anorthite and melilite are 16O-depleted to various degrees (\u22126.5\u2030\u2009\u2264\u2009\u039417O\u2009\u2264\u2009\u22124.5\u2030 and \u039417O\u2009=\u2009\u22122.7\u2009\u00b1\u20090.8\u2030, respectively). In ALH-2, corundum shows a range of \u039417O, from ~ \u22129\u2030 to ~ \u22121\u2030; primary hibonite and spinel are 16O-rich (\u039417O\u2009~\u2009\u221223\u2030); melilite and perovskite are 16O-poor (\u039417O\u2009=\u2009\u22122.6\u2009\u00b1\u20091.5\u2030 and \u22123.1\u2009\u00b1\u20091.3\u2030, respectively). On the Al-Mg isotope diagram (26Mg* versus 27Al\/24Mg), primary Al,Ti-diopside, hibonite, melilite, and spinel in the Allende CAIs studied along the canonical isochron with inferred initial 26Al\/27Al ratio [(26Al\/27Al)0] of ~5\u2009\u00d7\u200910\u22125. All secondary minerals have resolved excesses of 26Mg*: alumo\u00e5kermanite, corundum, and grossite plot below the canonical isochron, whereas most spinel analyses plot above it. An internal isochron defined by the coexisting secondary corundum and alumo\u00e5kermanite in 3529Z has (26Al\/27Al)0\u2009=\u2009(7.5\u2009\u00b1\u20092.6)\u2009\u00d7\u200910\u22127. We conclude that the corundum-bearing assemblages in Allende CAIs resulted from metasomatic alteration of primary melilite and anorthite, ~4\u20135\u2009Ma after their crystallization. Metasomatic alteration of CAIs in the Allende parent asteroid by an aqueous fluid having \u039417O of ~ \u22123\u2009\u00b1\u20092\u2030 modified the O-isotope composition of their primary melilite, anorthite, and Ti-rich pyroxene; O-isotope compositions of primary hibonite, spinel, and low-Ti pyroxene escaped this modification.”<\/p>\n","protected":false},"excerpt":{"rendered":"
A. N. Krot, K. Nagashima, M. I. Petaev, E. Dobric\u0103, C. Ma, B. Jacobsen MAPS, Version of Record online: 22 August 2025 LINK “We report on the mineralogy, petrology, oxygen, and aluminum\u2013magnesium isotopic systematics of…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66,9,14,20,57],"tags":[448,2229,1532,108,1846,3273,2770,2401,727],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/39005"}],"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=39005"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/39005\/revisions"}],"predecessor-version":[{"id":39006,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/39005\/revisions\/39006"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=39005"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=39005"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=39005"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}