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Abstract Details

(2020) Heterogeneous Nucleosynthetic 84Sr Anomalies within and Among CAIs

Di Y & Amelin Y

https://doi.org/10.46427/gold2020.570

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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.

Submitted by Noriko Kita on
Could you comment mineral phases related to leachates and residues? SJ101 is one of least melted FoB CAIs, according to Bullock et al. 2012 (MaPS 47, 2128–2147) that show relatively smaller grain sizes. Is it a problem for homogenization of 84Sr by melting?
The fraction we used for leaching experiment was a mixture of phases. Since the majority of Sr was released in the leachates, we suspect that the phases dissolved in the leachates are the Sr-rich soluble minerals i.e. mellilite and anothosite. The residue may consist of other acid-resist and low-Sr phases, like pyroxene, forstrite and spinel. Indeed, this CAI only experienced small degree partial melting. It is possible that the precursor of this CAI initially formed in a well-mixed reservoir with homogenized Sr isotopes.
Submitted by Alison Hunt on
Hi, on Slide 8, it looks like the data for CAI 3529-21 are not resolved relative to the grey 'Earth' bar. Can you comment this, and the implications for your conclusion of a deficit in u84Sr in some non-FUN CAIs?
Hi, thank you for pointing out this! As shown in that figure, we measured two fractions from this CAI: one finer-grained fraction yielded -80 +/- 72 ppm, and one coarser-grained fraction yielded -52 +/- 18 ppm. Our result for 33 analyses of terrestrial rock standards is -31 +/- 8 ppm. The finer-grained fraction has too large uncertainty due to small sample size, but the mu84Sr of the coarser-grained fraction is lower than the Earth by 21 +/- 20 ppm. This difference is indeed minor and is only marginally resolved from 0. There is also some debate on the true mu84Sr of the Earth. However, it is still true that this CAI has the lowest mu84Sr seen in normal CAIs, and the mu84Sr of normal CAIs cover a range from about -50 to +300 ppm. Our current conclusion may be better expressed "some non-FUN CAI may have 84Sr composition close to, or slightly depleted relative to the Earth".
Submitted by Quinn Shollenberger on
Very nice presentation! Do you have any thoughts on what the carrier phase may be in CAI 3529-49 that has the anomalous L1 leachate for 84Sr?
Thank you! We are currently not sure. The majority of Sr is released in that leachate, so the anomaly may reflect the existence of small amount of extreme p-/r- isotope carrier SN (or processed) grains; Charlier et al. (2019, GCA) also mentioned a nugget effect of 84Sr in CAIs. However how they survived the high-T condensation might be a problem. Another explanation is the Sr isotope heterogeneity of the CAI gas reservoirs. Probably, a large proportion of the soluble phases (and also Sr-enriched phases), like melilite, condensed from a domain with higher mu84Sr while the more refractory and resist phases mainly come from another gasous region.

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