LINK<\/strong><\/a><\/p>\n\n\n\n“We report on the mineralogy, petrography, and in situ oxygen isotopic composition of twenty-five ultrarefractory calcium-aluminum-rich inclusions (UR CAIs) in CM2, CR2, CH3.0, CV3.1\u20153.6, CO3.0\u20153.6, MAC 88107 (CO3.1-like), and Acfer 094 (C3.0 ungrouped) carbonaceous chondrites. The UR CAIs studied are typically small, < 100 \u00b5m in size, and contain, sometimes dominated by, Zr-, Sc-, and Y-rich minerals, including allendeite (Sc4Zr3O12), and an unnamed ((Ti,Mg,Sc,Al)3O5) mineral, davisite (CaScAlSiO6), eringaite (Ca3(Sc,Y,Ti)2Si3O12), kangite ((Sc,Ti,Al,Zr,Mg,Ca,\u25a1)2O3), lakargiite (CaZrO3), warkite (Ca2Sc6Al6O20), panguite ((Ti,Al,Sc,Mg,Zr,Ca)1.8O3), Y-rich perovskite ((Ca,Y)TiO3), tazheranite ((Zr,Ti,Ca)O2\u2015x), thortveitite (Sc2Si2O7), zirconolite (orthorhombic CaZrTi2O7), and zirkelite (cubic CaZrTi2O7). These minerals are often associated with 50\u2015200 nm-sized nuggets of platinum group elements. The UR CAIs occur as: (i) individual irregularly-shaped, nodular-like inclusions; (ii) constituents of unmelted refractory inclusions \u2013 amoeboid olivine aggregates (AOAs) and Fluffy Type A CAIs; (iii) relict inclusions in coarse-grained igneous CAIs (forsterite-bearing Type Bs and compact Type As); and (iv) relict inclusions in chondrules. Most UR CAIs, except for relict inclusions, are surrounded by single or multilayered Wark-Lovering rims composed of Sc-rich clinopyroxene, \u00b1eringaite, Al-diopside, and \u00b1forsterite. Most of UR CAIs in carbonaceous chondrites of petrologic types 2\u20153.0 are uniformly 16O-rich (\u039417O \u02dc \u201523\u2030), except for one CH UR CAI, which is uniformly 16O-depleted (\u0394 17O \u02dc \u20155\u2030). Two UR CAIs in Murchison have heterogeneous \u039417O. These include: an intergrowth of corundum (\u02dc \u201224\u2030) and (Ti,Mg,Sc,Al)3O5 (\u02dc 0\u2030), and a thortveitite-bearing CAI (\u02dc \u201220 to \u02dc \u20125\u2030); the latter apparently experienced incomplete melting during chondrule formation. In contrast, most UR CAIs in metamorphosed chondrites are isotopically heterogeneous (\u039417O ranges from \u02dc \u201523\u2030 to \u02dc \u20152\u2030), with Zr- and Sc-rich oxides and silicates, melilite and perovskite being 16O-depleted to various degrees relative to uniformly 16O-rich (\u039417O \u02dc \u201523\u2030) hibonite, spinel, Al-diopside, and forsterite. We conclude that UR CAIs formed by evaporation\/condensation, aggregation and, in some cases, melting processes in a 16O-rich gas of approximately solar composition in the CAI-forming region(s), most likely near the protoSun, and were subsequently dispersed throughout the protoplanetary disk. One of the CH UR CAIs formed in an 16O-depleted gaseous reservoir providing an evidence for large variations in \u039417O of the nebular gas in the CH CAIs-forming region. Subsequently some UR CAIs experienced oxygen isotopic exchange during melting in 16O-depleted regions of the disk, most likely during the epoch of chondrule formation. In addition, UR CAIs in metamorphosed CO and CV chondrites, and, possibly, the corundum-(Ti,Mg,Sc,Al)3O5 intergrowth in Murchison experienced O-isotope exchange with aqueous fluids on the CO, CV, and CM chondrite parent asteroids. Thus, both nebular and planetary exchange with 16O-depleted reservoirs occurred.”<\/p>\n","protected":false},"excerpt":{"rendered":"
A.N. Krot, C. Ma, K. Nagashima, A.M. Davis, J.R. Beckett, S.B. Simon, M. Komatsu, T.J. Fagan, F. Brenker, M.A. Ivanova, A.Bischoff Geochemistry Available online 15 August 2019 LINK “We report on the mineralogy, petrography, and…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[685,66,9,583,18,19,12,14,65,57,2531,335],"tags":[3895,2958,568,1846,1718,3273,1887,105,1814,1810,1812,2132,107,4373,5141],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20291"}],"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=20291"}],"version-history":[{"count":2,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20291\/revisions"}],"predecessor-version":[{"id":20293,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20291\/revisions\/20293"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20291"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=20291"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=20291"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}