4:45 PM - 5:00 PM
[PPS10-30] A combined study of Be-B and Al-Mg systematics on CH and CH/CB CAIs
Keywords:cosmic ray irradiation, solar protoplanetary disk, Ca, Al-rich inclusion, SIMS
We studied 8 CAIs from the Sayh al Uhaymir 290 (CH) and the Isheyevo (CB/CH) chondrites. Be-B and Al-Mg measurements were conducted with a NanoSIMS 50 at Atmosphere and Ocean Research Institute (AORI), The Univ. of Tokyo. Seven out of 8 CAIs show highly variable initial 10Be/9Be ratios ranging from 1.1 to 33 x 10-4. They cannot be explained by a molecular cloud origin [6, 7] or a stellar origin , suggesting that they have experienced solar cosmic ray irradiation near the proto-Sun. In contrast to Be-B systematics, all CAIs studied here do not show resolvable excesses in 26Mg. This could be attributed to: (1) heterogeneous distribution of 26Al in the protoplanetary disk, (2) formation prior to injection of 26Al, or (3) late formation after a significant decay of 26Al. (1) is unlikely because CH and CB/CH CAIs may have formed in the same region as that of CV CAIs (= near the proto-Sun) as inferred from the Be-B systematics [e.g., 8-12, this study]. (2) is possible because CH and CB/CH CAIs have highly refractory nature relative to CV canonical CAIs. (3) may be a simpler interpretation. If (3) is the case, the transportation mechanism from near the proto-Sun to the accretion region of CH and CB parent bodies must have existed at least until the timing of CH and CB/CH CAI formation.
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