Chondrules formation

In ordinary chondrites, Ca-Al rich inclusions are also present and give the canonical value (Russell et al. 1996), but other object like chondrules or mineral grains give reduced values by a factor of 5 to 100 (Hinton and Bischoff 1984 Hutcheon and Hutchison 1989). Delayed formation relative to CAIs is a probable cause. High precision ICPMS measurements of Mg have been used to address the timing of chondrule formation and show the importance of gas during the formation process (Galy et al. 2000). 

Alexander CMOD, Grossman JN, Wang J, Zanda B, Bourot-Denise M, Hewins RH (2000) The lack of potassium-isotopic fractionation in Bishunpur chondrules. Meteor Planet Sci 35 859-868 Alexander CMOD, Wang J (2001) Iron isotopes in chondrules implications for the role of evaporation during chondrule formation. Meteor Planet Sci 36 419-428... 

Alexander CMO D, Wang J (2001) Iron isotope in chondrules implications for the role of evaporation during chondrule formation. Meteoritics Planet Sci 36 419-428... 

Ion probe (SIMS) measurements of (26Al/27Al)0 for chondrules from several meteorite groups. The right axis shows the formation time relative to CAIs, the oldest solids formed in the solar system. These data indicate that chondrule formation started at least 1 Myr after CAIs formed and continued for 1-2 Myr. For CR chondrites, in addition to the plotted data, a similar number of chondrules show no resolvable evidence for 26Al. Data for unequilibrated ordinary chondrites (UDC) from Kita ef al. 

The highest of these ratios are the same as those measured in CAIs, which suggests that chondrule formation was contemporaneous with CAI formation in Allende. It is currently not clear why the ICPMS measurements of the 26Al-26Mg system give older ages for Allende chondrules than other types of measurements. 

As with the ordinary chondrites, the accretion times for CV and CO chondrite parent bodies can be estimated from the times of chondrule formation. The 26Al-26Mg and129I-129Xe data suggest chondrule formation extended to 4565 Ma, 3.2 Myr after CAIs. This is slightly later than, but within the uncertainties of, the time indicated for the accretion of ordinary chondrite parent bodies. 

Hutcheon, I. D., Marhas, . K., Krot, A. N., Goswami, J. N. and Jones, R. H. (2009) 26A1 in plagioclase-rich chondrules in carbonaceous chondrites evidence for extended duration of chondrule formation. Geochimica et Cosmochimica Acta, 73, 5080-5099. 

Kita, N. T., Nagahara, H., Togashi, S. and Morshita, Y. (2000) A short duration of chondrule formation in the solar nebula evidence from 26A1 in Semarkona ferromagnesian chondrules. Geochimica et Cosmochimica Acta, 64, 3913-3922. 

Rudraswami, N. G. and Goswami, J. N. (2007) 26A1 in chondrules from unequilibrated L chondrites onset and duration of chondrule formation in the early solar system. Earth and Planetary Science Letters, 257, 231—244. 

We may thus put constraints from chondrules on the presence of dust and gas 2 Myr after the first solid formation. Again, it is not possible at present to correlate directly the chondrule formation period with the evolutionary stage of the protoplanetary disk, but high-temperature events capable of melting chondrule precursors could have occurred during the active stage of the protoplanetary disk (classical T Tauri stage). 

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