LINK<\/strong><\/a><\/p>\n“The oldest solar system solids dated are refractory inclusions [Ca-Al\u2013rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)], which occur in chondritic meteorites and provide records of high-temperature processes in the early solar system. An ultrarefractory CAI and the silica-phase quartz occur in an AOA from the carbonaceous chondrite Yamato-793261, indicating formation over a temperature range exceeding 650 K. The minerals have 16O-rich compositions consistent with the nebular setting associated with refractory inclusions. This AOA provides direct evidence that silica condensed from gas in a CAI\/AOA-forming region in our solar system indicates that gas became Si-rich as Mg condensed and may explain the origin of silica detected from infrared spectroscopy of T Tauri and asymptotic giant branch stars.”<\/p>\n
“Calcium-aluminum\u2013rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (\u039417O \u223c \u221224\u2030) compositions, most likely near the protosun. Here we describe a 16O-rich (\u039417O \u223c \u221222 \u00b1 2\u2030) AOA from the carbonaceous Renazzo-type (CR) chondrite Yamato-793261 containing both (i) an ultrarefractory CAI and (ii) forsterite, low-Ca pyroxene, and silica, indicating formation by gas\u2013solid reactions over a wide temperature range from \u223c1,800 to \u223c1,150 K. This AOA provides direct evidence for gas\u2013solid condensation of silica in a CAI\/AOA-forming region. In a gas of solar composition, the Mg\/Si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the AOA formed in a parcel of gas with fractionated Mg\/Si ratio, most likely due to condensation of forsterite grains. Thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by \u223c10\u00d7 in H and He that cooled at 50 K\/hour at total pressure of 10\u22124 bar. Condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Mutsumi Komatsu, Timothy J. Fagan, Alexander N. Krot, Kazuhide Nagashima, Michail I. Petaev, Makoto Kimura, and Akira Yamaguchi PNAS July 2, 2018. 201722265; published ahead of print July 2, 2018. https:\/\/doi.org\/10.1073\/pnas.1722265115 LINK “The oldest solar…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[685,66,12,57],"tags":[1635,1891,1846,3273,1810,397,4657,3592],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/16150"}],"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=16150"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/16150\/revisions"}],"predecessor-version":[{"id":16151,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/16150\/revisions\/16151"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=16150"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=16150"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=16150"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}