An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites
To investigate the crystallization of pyroxene in spinifex-textured komatiites, we undertook a series of experiments in which compositions in the CaO-MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> CMAS system were cooled rapidly in a thermal gradient. Cooling rat...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-07-01
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| Series: | Solid Earth |
| Online Access: | http://www.solid-earth.net/5/641/2014/se-5-641-2014.pdf |
| _version_ | 1818508827532722176 |
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| author | S. Bouquain N. T. Arndt F. Faure G. Libourel |
| author_facet | S. Bouquain N. T. Arndt F. Faure G. Libourel |
| author_sort | S. Bouquain |
| collection | DOAJ |
| description | To investigate the crystallization of pyroxene in spinifex-textured
komatiites, we undertook a series of experiments in which compositions in the
CaO-MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> CMAS system were cooled rapidly in a thermal gradient. Cooling rates were
generally between 5 and 10 °C h<sup>−1</sup>, but some runs were made at
100–200 °C h<sup>−1</sup>; thermal gradients were between 10 and
20 °C cm<sup>−1</sup>. 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<sup>−1</sup>. The notion that this mineral only forms
at low cooling rates is not correct. |
| first_indexed | 2024-12-10T22:37:14Z |
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| id | doaj.art-d3b3725ea2374e26b86c6f4328b72402 |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-10T22:37:14Z |
| publishDate | 2014-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-d3b3725ea2374e26b86c6f4328b724022022-12-22T01:30:50ZengCopernicus PublicationsSolid Earth1869-95101869-95292014-07-015264165010.5194/se-5-641-2014An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiitesS. Bouquain0N. T. Arndt1F. Faure2G. Libourel3ISTerre, CNRS UMR5275, Université J. Fourier, BP53, 38041 Grenoble Cedex, FranceISTerre, CNRS UMR5275, Université J. Fourier, BP53, 38041 Grenoble Cedex, FranceNancy Université, CNRS/INSU, CRPG, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre-lès-Nancy, FranceNancy Université, CNRS/INSU, CRPG, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre-lès-Nancy, FranceTo investigate the crystallization of pyroxene in spinifex-textured komatiites, we undertook a series of experiments in which compositions in the CaO-MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> CMAS system were cooled rapidly in a thermal gradient. Cooling rates were generally between 5 and 10 °C h<sup>−1</sup>, but some runs were made at 100–200 °C h<sup>−1</sup>; thermal gradients were between 10 and 20 °C cm<sup>−1</sup>. 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<sup>−1</sup>. The notion that this mineral only forms at low cooling rates is not correct.http://www.solid-earth.net/5/641/2014/se-5-641-2014.pdf |
| spellingShingle | S. Bouquain N. T. Arndt F. Faure G. Libourel An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites Solid Earth |
| title | An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| title_full | An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| title_fullStr | An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| title_full_unstemmed | An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| title_short | An experimental study of pyroxene crystallization during rapid cooling in a thermal gradient: application to komatiites |
| title_sort | experimental study of pyroxene crystallization during rapid cooling in a thermal gradient application to komatiites |
| url | http://www.solid-earth.net/5/641/2014/se-5-641-2014.pdf |
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