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|Title:||Chondrule fragments from Comet Wild2: Evidence for high temperature processing in the outer Solar System|
|Citation:||Earth and Planetary Science Letters, 2012, 341-344, pp. 186-194|
|Abstract:||Terminal grains from C2063,1,154,1,0 (Track 154) and C2061,1,113,5 (Track 113) from the Stardust collection of Comet Wild2's coma have been studied by TEM and NanoSIMS. Terminal grain 2 of C2063,1,154,1,0 consists of an Al-rich diopside (En 97–99%, Al[subscript 2]O[subscript 3] 9–11 wt%), pigeonite (En 85% Wo 15% with TiO[subscript 2] and Al[subscript 2]O[subscript 3] contents of 0.5 and 5.2 wt%) and minor forsterite and enstatite. The mineral assemblage and Al-rich, Ti-poor composition of the grain are consistent with being a fragment of an Al-rich chondrule, similar to those present in carbonaceous chondrites. The oxygen isotopic composition of the C2063,1,154,1,0 grain was determined by NanoSIMS analyses and found to be δ[superscript 17]O −10.6±5.7‰, δ[superscript 18]O −7.5±2.5‰ and δ[superscript 17]O +1.4±4.3‰, δ[superscript 18]O −6.5±1.6‰ (1σ errors) for the two sections. These figures are distinct from CAIs and consistent with an origin as Al-rich chondrule fragments. Terminal grain 5 of C2061,1,113,5 consists of low Ca pyroxene En 86–87% Fs 10–11% Wo 3–4% and ≤2 wt% Al[subscript 2]O[subscript 3] and in one section 5–10% of a Na-rich silicate phase. This assemblage may be a fragment of a low-Ca pyroxene-bearing chondrule and mesostasis. The original chondrule diameter for the C2063,1,154,1,0 and C2061,1,113,5 samples, by analogy with carbonaceous chondrite chondrules, might have been in the range 0.2–1.0 mm. If they were of that size, then the presence of large grains of high temperature material (e.g. ≥1500 K for such refractory assemblages) could be explained through commonly invoked models of radial drift from inner to outer Solar System, but only if the chondrules were first fragmented to dust within the inner Solar System. An alternative scenario is that some chondrule formation was associated with high temperature processing and planetesimals in the outer Solar System.|
|Description:||Full text of this item is not currently available on the LRA. The final published version may be available through the links above.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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