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(2020) CAI Formation: Processes and Ages Under Scopes of O Isotopes and Al-Mg Systematics Based on Crystal Growth
01g: Room 1, View in program
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Thank you Prof. Yurimoto. I kind of didn't understand, from page #10, how the calculated time scale of oxygen exchange between gas and liquid can reflect the oxygen isotope variation period of the gas itself? Could you explain a bit more, what process this "2 weeks" time scale represent? In your proposed model, the D17O of the gas seems oscillating between O-16 rich and O-16 poor, and this is recorded by CAI crystal growth. In the two cases you showed, both FTA mellilite and Type B pyroxene show decreasing D17O along with growth, or say from core to rim. Is there any mineral recorded a reverse trend, i.e., they crystallized or condensed when the gas D17O was increasing?
Regarding the difference between spinel and other phases, could it be explained by a much lower diffusion rate of O in spinel relative to other phases like melilite? For instance, we can find CAIs in Léoville (CV3red) where all phases but melilite are 16O-rich.
Regarding some of your unsolved issues, could you talk a little more about if the O isotope change of the nebular gas was independent or dependent from the heating phenomena?
Sasha Krot Comment: Not only spinel and hibonite in igneous CAIs from Allende have 16O-rich compositions, but forsterite in forsterite-bearing Type B CAIs as well. Question: In forsterite-bearing Type B CAIs and FUN Type B CAIs, minerals which crystallized from a CAI melt that experienced evaporation plot along mass-dependent fractionation line with d18O typically increasing with crystallization sequence: spinel,hibonite < forsterite < Al,Ti-diopside; D17O remains constant, ~ -24 permil. Melilite which is expected to crystallize after spinel, hibonite, or forsterite, but before Al,Ti-diopside plots near the terrestrial fractionation line, D17O ~ -2 permil. How can it be explained by gas-melt O-isotope exchange during melt crystallization?
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