LINK<\/strong><\/a><\/p>\n“We have analysed the petrography, major element abundances and bulk Al-Mg isotope systematics of 19 ferromagnesian chondrules from the CV3 chondrites Allende, Mokoia, and Vigarano, together with an Al-rich chondrule and refractory olivine from Mokoia. Co-variations of Al\/Mg with Na\/Mg and Ti\/Mg in our bulk chondrules suggest their compositions are dominantly controlled by reworking of different proportions of chondrule components (e.g. mafic minerals and mesostatis); their precursors are thus fragments from prior generations of chondrules. Our samples show a range in fractionation corrected 26Mg\/24Mg (\u0394\u201926Mg) \u223c60ppm, relative to precisions <\u00b15ppm (2se) and these values broadly covary with 27Al\/24Mg. The data can be used to calculate model initial 26Al\/27Al, or (26Al\/27Al)0, of the chondrule precursors. Our resolvably radiogenic chondrules yield model (26Al\/27Al)0 \u223c1-2x10-5, equivalent to model \u201cages\u201d of precursor formation \u22661Ma post CAI. However, many of our chondrules show near solar \u0394\u201926Mg and no variability despite a range in 27Al\/24Mg. This suggests their derivation either from younger precursor chondrules or open system behaviour once 26Al was effectively extinct ((26Al\/27Al)0<0.8x10-5, given the resolution here). Evidence for the latter explanation is provided by marked rims of orthopyroxene replacing olivine, indicating reaction of chondrules with a surrounding silicate vapour. Concurrent isotopic exchange of Mg with a near chondritic vapour during late reworking could explain their isotopic systematics. One ferromagnesian object is dominated by a high Mg# olivine with elevated Ti and Ca abundances. This refractory olivine has a markedly negative \u0394\u201926Mg = -16\u00b13 ppm (2se), reflecting its early removal (model age of <0.5Ma post CAI), from a reservoir with evolving \u0394\u201926Mg. If representative of the chondrule forming region, this grain defines a minimum interval of radiogenic ingrowth for CV chondrites commensurate with (26Al\/27Al)0>3.4\u00b10.6×10-5. Overall, our samples record a sequence of events from the formation of ferromagnesian objects within 0.5Ma of CAI to re-equilibration of chondrules and silicate vapour >2Ma post CAI, assuming an initially homogeneous 26Al\/27Al. Metamorphism on the asteroid parent body may have played a subsequent role in affecting Mg isotope composition, but we argue this had a minor influence on the observations here.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Hsin-Wei Chen, Jennifer L. Claydon, Tim Elliott, Christopher D. Coath, Yi-Jen Lai, Sara S. Russell Geochimica et Cosmochimica Acta In Press, Accepted Manuscript, Available online 16 February 2018 LINK “We have analysed the petrography, major…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,56,148,14],"tags":[2278,108,3273,1839,1812,833,1531,630,482],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/14326"}],"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=14326"}],"version-history":[{"count":3,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/14326\/revisions"}],"predecessor-version":[{"id":14329,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/14326\/revisions\/14329"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14326"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14326"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14326"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}