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Crystallization sequences of Ca-Al-rich inclusions from Allende: An experimental study

Stolper, Edward (1982) Crystallization sequences of Ca-Al-rich inclusions from Allende: An experimental study. Geochimica et Cosmochimica Acta, 46 (11). pp. 2159-2180. ISSN 0016-7037. doi:10.1016/0016-7037(82)90192-2.

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The equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of Type B Ca-Al-rich inclusions from the Allende meteorite is: spinel (1550°C) → melilite (1400°C; Åk22) → anorthite (1260°C) → Ti-Al-rich clinopyroxene (1230°C; “Ti-fassaite”). The melilite becomes increasingly åkermanitic with decreasing temperature. The pyroxene is similar in composition to fassaites from Type B inclusions. Preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron-wüstite buffer. The results of these experiments have been integrated with available phase equilibrium data in the system CaO-MgO-Al_2O_3-SiO_2TiO_2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse-grained Ca-Al-rich inclusions has been developed. Available bulk compositions of coarse-grained inclusions form a well-defined trend in terms of major elements, extending from Type A and Bl inclusions near the spinel-melilite join to more pyroxene-rich Type B2 inclusions. The trend deviates from the expected sequence of solid condensates from a nebular gas at P = 10^(−3) atm if pure diopside is assumed to be the clinopyroxene that condenses. The Type A-B1 end of the trend is similar in composition to calculated equilibrium condensates at 1202–1227°C and the trend as a whole parallels the sequence of condensates expected from diopside condensation at ~ 1170°C. The trend is consistent to first order with the condensation of solid Ti-rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense. Partially molten condensates may be likely in this case or if the nebular pressure is higher than 10^(−3) atm.

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Stolper, Edward0000-0001-8008-8804
Additional Information:© 1982 Pergamon Press Ltd. Received 14 December 1981. Accepted 15 July 1982. I have benefited from discussions with J. Armstrong, J. Beckett, L. Grossman, J. Huneke, J. Kerridge, and G. MacPherson. Reviews by J. Beckett, R. Brett, G. MacPherson, and R. J. Williams were helpful. Special thanks go to G. J. Wasserburg, both for suggesting the experiments reported in this paper and for his interest and encouragement. J. Paque assisted with the microprobe analyses. This work was supported by The President's Fund (PF-176) under NASA Contract NAS 7-100 and NASA Grant NAGW-257. Division of Geological and Planetary Sciences Contribution Number 3713.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Caltech President's FundPF-176
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Caltech Division of Geological and Planetary Sciences3713
Issue or Number:11
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Official Citation:Edward Stolper, Crystallization sequences of Ca-Al-rich inclusions from Allende: An experimental study, Geochimica et Cosmochimica Acta, Volume 46, Issue 11, November 1982, Pages 2159-2180, ISSN 0016-7037, 10.1016/0016-7037(82)90192-2. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33413
Deposited By: Ruth Sustaita
Deposited On:21 Aug 2012 21:36
Last Modified:09 Nov 2021 21:34

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