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First in situ observation of crystallization processes in a basaltic-andesitic melt with the moissanite cell

Federica Schiavi, Nicolas Walte and Hans Keppler
First in situ observation of crystallization processes in a basaltic-andesitic melt with the moissanite cell
Geology (Boulder) (November 2009) 37 (11): 963-966

Abstract

The evolution of texture and crystal size distribution of igneous rocks is mainly determined by processes such as nucleation, grain growth, and Ostwald ripening. However, the role played by these processes on the final crystal size distribution is difficult to quantify with conventional methods. Here we present the first direct in situ observation of a crystallizing supercooled basaltic-andesitic liquid in order to directly assess the role of grain-scale processes occurring during magma solidification. The experiments were conducted at 900 degrees C and 1 bar with a new moissanite cell specifically designed for long-term high-temperature experiments. The method allowed the direct continuous observation of the crystallizing melt until the crystal fraction approached 0.7. Investigation of the evolving texture revealed that individual crystals followed distinct growth histories characterized by intervals of relatively uniform free growth, abrupt size increase due to grain coalescence, and growth reduction due to impingement; the latter played a dominant role at higher crystal fractions. Despite this growth dispersion, average growth rates calculated for single grains showed only little variation (4.9X10 (super -6) to 1.9X10 (super -6) mm/s). No clear relation between growth rate and crystal size was observed. Crystal coarsening through a combination of overgrowth and coalescence can also account for the counterclockwise rotation and the drop-off at smaller size fractions of the recovered crystal size distributions in our experiments. These results suggest that crystal size distributions of natural rocks do not record the original nucleation rates.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 37
Serial Issue: 11
Title: First in situ observation of crystallization processes in a basaltic-andesitic melt with the moissanite cell
Affiliation: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany
Pages: 963-966
Published: 200911
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 20
Accession Number: 2009-100334
Categories: Igneous and metamorphic petrologyGeneral mineralogy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2009245
Illustration Description: illus. incl. 1 table
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200953
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