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| Titel |
An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| VerfasserIn |
S. Bouquain, N. T. Arndt, F. Faure, G. Libourel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 5, no. 2 ; Nr. 5, no. 2 (2014-07-09), S.641-650 |
| Datensatznummer |
250115314
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| Publikation (Nr.) |
 copernicus.org/se-5-641-2014.pdf |
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| Zusammenfassung |
| To investigate the crystallization of pyroxene in spinifex-textured
komatiites, we undertook a series of experiments in which compositions in the
CaO-MgO-Al2O3-SiO2 CMAS system were cooled rapidly in a thermal gradient. Cooling rates were
generally between 5 and 10 °C h−1, but some runs were made at
100–200 °C h−1; thermal gradients were between 10 and
20 °C cm−1. These conditions reproduced those at various depths in the
crust of komatiite lava flow. The starting composition was chosen to have
pigeonite on the liquidus, and most of the experimental charges crystallized
zoned pigeonite–diopside crystals like those in komatiite lavas. An
intriguing aspect of the experimental results was their lack of
reproducibility. Some experiments crystallized forsterite, whereas others that
were run under similar conditions crystallized two pyroxenes and no
forsterite; some experiments were totally glassy, but others crystallized
entirely to pyroxene. The degree of supercooling at the onset of pyroxene
crystallization was variable, from less than 25 °C to more than
110 °C. We attribute these results to the difficulty of nucleation
of pyroxene under the conditions of the experiments. In some cases forsterite
crystallized metastably and modified the liquid composition to inhibit
pyroxene crystallization; in others no nucleation took place until a large
degree of supercooling was achieved, and then pyroxene crystallized rapidly.
Pigeonite crystallized under a wide range of conditions, at cooling rates
from 3 to 100 °C h−1. The notion that this mineral only forms
at low cooling rates is not correct. |
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