LINK<\/strong><\/a><\/p>\n\n\n\n“Chondrites consist of three major components: refractory inclusions (Ca,Al\u2010rich inclusions [CAIs] and amoeboid olivine aggregates), chondrules, and matrix. Here, I summarize recent results on the mineralogy, petrology, oxygen, and aluminum\u2010magnesium isotope systematics of the chondritic components (mainly CAIs in carbonaceous chondrites) and their significance for understanding processes in the protoplanetary disk (PPD) and on chondrite parent asteroids. CAIs are the oldest solids originated in the solar system: their U\u2010corrected Pb\u2010Pb absolute age of 4567.3 \u00b1 0.16 Ma is considered to represent time 0 of its evolution. CAIs formed by evaporation, condensation, and aggregation in a gas of approximately solar composition in a hot (ambient temperature >1300 K) disk region exposed to irradiation by solar energetic particles, probably near the protoSun; subsequently, some CAIs were melted in and outside their formation region during transient heating events of still unknown nature. In unmetamorphosed, type 2\u20133.0 chondrites, CAIs show large variations in the initial 26Al\/27Al ratios, from <5 \u00d7 10\u20136 to ~5.25 \u00d7 10\u20135. These variations and the inferred low initial abundance of 60Fe in the PPD suggest late injection of 26Al by a wind from a nearby Wolf\u2013Rayet star into the protosolar molecular cloud core prior to or during its collapse. Although there are multiple generations of CAIs characterized by distinct mineralogies, textures, and isotopic (O, Mg, Ca, Ti, Mo, etc.) compositions, the 26Al heterogeneity in the CAI\u2010forming region(s) precludes determining the duration of CAIs formation using 26Al\u201026Mg systematics. The existence of multiple generations of CAIs and the observed differences in CAI abundances in carbonaceous and noncarbonaceous chondrites may indicate that CAIs were episodically formed and ejected by a disk wind from near the Sun to the outer solar system and then spiraled inward due to gas drag. In type 2\u20133.0 chondrites, most CAIs surrounded by Wark\u2013Lovering rims have uniform \u039417O (= \u03b417O\u22120.52 \u00d7 \u03b418O) of ~ \u221224\u2030; however, there is a large range of \u039417O (from ~\u221240 to ~ \u22125\u2030) among them, suggesting the coexistence of 16O\u2010rich (low \u039417O) and 16O\u2010poor (high \u039417O) gaseous reservoirs at the earliest stages of the PPD evolution. The observed variations in \u039417O of CAIs may be explained if three major O\u2010bearing species in the solar system (CO, H2O, and silicate dust) had different O\u2010isotope compositions, with H2O and possibly silicate dust being 16O\u2010depleted relative to both the Genesis solar wind \u039417O of \u221228.4 \u00b1 3.6\u2030 and even more 16O\u2010enriched CO. Oxygen isotopic compositions of CO and H2O could have resulted from CO self\u2010shielding in the protosolar molecular cloud (PMC) and the outer PPD. The nature of 16O\u2010depleted dust at the earliest stages of PPD evolution remains unclear: it could have either been inherited from the PMC or the initially 16O\u2010rich (solar\u2010like) MC dust experienced O\u2010isotope exchange during thermal processing in the PPD. To understand the chemical and isotopic composition of the protosolar MC material and the degree of its thermal processing in PPD, samples of the primordial silicates and ices, which may have survived in the outer solar system, are required. In metamorphosed CO3 and CV3 chondrites, most CAIs exhibit O\u2010isotope heterogeneity that often appears to be mineralogically controlled: anorthite, melilite, grossite, krotite, perovskite, and Zr\u2010 and Sc\u2010rich oxides and silicates are 16O\u2010depleted relative to corundum, hibonite, spinel, Al,Ti\u2010diopside, forsterite, and enstatite. In texturally fine\u2010grained CAIs with grain sizes of ~10\u201320 \u03bcm, this O\u2010isotope heterogeneity is most likely due to O\u2010isotope exchange with 16O\u2010poor (\u039417O ~0\u2030) aqueous fluids on the CO and CV chondrite parent asteroids. In CO3.1 and CV3.1 chondrites, this process did not affect Al\u2010Mg isotope systematics of CAIs. In some coarse\u2010grained igneous CV CAIs, O\u2010isotope heterogeneity of anorthite, melilite, and igneously zoned Al,Ti\u2010diopside appears to be consistent with their crystallization from melts of isotopically evolving O\u2010isotope compositions. These CAIs could have recorded O\u2010isotope exchange during incomplete melting in nebular gaseous reservoir(s) with different O\u2010isotope compositions and during aqueous fluid\u2013rock interaction on the CV asteroid.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Alexander N. Krot Meteoritics & Planetary Science First Published: 23 July 2019 LINK “Chondrites consist of three major components: refractory inclusions (Ca,Al\u2010rich inclusions [CAIs] and amoeboid olivine aggregates), chondrules, and matrix. Here, I summarize recent…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66,9,19,14,57],"tags":[3895,2958,238,399,5108,1635,1846,1718,3273,1748,135,4390],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20118"}],"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=20118"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20118\/revisions"}],"predecessor-version":[{"id":20119,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/20118\/revisions\/20119"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=20118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=20118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}