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On type B CAI formation: experimental constraints on fO_2 variations in spinel minor element partitioning and reequilibration effects

Connolly, Harold C., Jr. and Burnett, D. S. (2003) On type B CAI formation: experimental constraints on fO_2 variations in spinel minor element partitioning and reequilibration effects. Geochimica et Cosmochimica Acta, 67 (22). pp. 4429-4434. ISSN 0016-7037. doi:10.1016/S0016-7037(03)00271-0.

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We report data from a series of dynamic crystallization experiments that focus on determining the partition coefficients (D’s) for V and Ti in the spinel + liquid system of an average type B1 CAI bulk composition for three different fO_2 conditions. Partitioning data for Ca and Si are also obtained. We show that the D’s for V and Ti are fO_2 dependent with D_(Ti) decreasing at low oxygen fugacity due to the presence of Ti^(3+). D_V is essentially 0 in air, rises to 2.2 at the Fe-FeO buffer and drops to 1.4 at the C-CO buffer. This indicates that V^(3+) is highly compatible in spinel and that higher and lower valence states are much less compatible. We also report data from isothermal experiments that determine diffusion times for V and Ti in same system at a temperature close to the T_(max) for type B1 CAIs. Diffusion of these elements between spinel and liquid is surprisingly rapid, with essentially total equilibration of Ti and V between spinel and liquid in 90 h run duration. Lack of equilibration of Cr, Si, and Ca shows that the Ti and V equilibration mechanism was diffusion and not dissolution and reprecipitation. Our experimental run durations set an upper limit of a few tens of hours on the time that type B1 CAIs were at their maximum temperature. Based on our data we argue that subsolidus reequilibration between spinel inclusion and host-silicate phases within type B CAIs likely explains the observed range of V and Ti concentrations in spinels which are inclusions in clinopyroxene.

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Burnett, D. S.0000-0001-9521-8675
Additional Information:© 2003 Elsevier Ltd. Received July 2, 2002; accepted in revised form April 17, 2003. We are grateful for helpful discussions with J. Beckett, G. MacPherson, A. Davis, and D. Mittelfeld. We thank A. El Groesy, an anonymous reviewer, and C. Koeberl for their helpful reviews that greatly improved the quality of this paper. This research was in part supported by NASA-NAG5-4319, D.S. Burnett P. I.
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Issue or Number:22
Record Number:CaltechAUTHORS:20150506-140725958
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Official Citation:Harold C Connolly Jr., D.S Burnett, On type B CAI formation: experimental constraints on fO2 variations in spinel minor element partitioning and reequilibration effects, Geochimica et Cosmochimica Acta, Volume 67, Issue 22, 15 November 2003, Pages 4429-4434, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57286
Deposited By: Tony Diaz
Deposited On:06 May 2015 22:12
Last Modified:10 Nov 2021 21:10

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