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Magmatic crystallization experiments at 1 bar in systems closed to oxygen; a new/old experimental approach

Dominique Lattard and Georg M. Partzsch
Magmatic crystallization experiments at 1 bar in systems closed to oxygen; a new/old experimental approach (in Experimental mineralogy, petrology and geochemistry, Anonymous)
European Journal of Mineralogy (June 2001) 13 (3): 467-478

Abstract

Many controversial discussions on the control of the oxidation state of crystallizing magmas are hampered by the fact that there are no available experimental data gained in systems closed to all elements, inclusive oxygen. To fill this gap the old technique of conducting experiments in evacuated silica-glass ampoules at 1 bar has been revived and adapted to perform equilibrium crystallization experiments with basaltic melts at high temperatures under closed-system conditions. The experiments are conducted in two steps. Step 1: in order to fix the initial oxygen fugacity (f (sub O2) ), small charges of the glassy starting materials are either pressed onto a loop of thin Pt-wire or into a small AgPd crucible and equilibrated at super-liquidus temperatures (>1180 degrees C) with CO/CO (sub 2) gas mixtures. Step 2: to achieve equilibrium crystallization under closed-system conditions, the charges are subsequently placed together with their metal holder/container in evacuated silica-glass ampoules and re-equilibrated under sub-liquidus conditions (1050-1170 degrees C). To test whether this experimental approach really ensures closed-system conditions, a series of experiments was conducted at near-liquidus temperatures with a synthetic ferro-basaltic starting composition. Within the analytical uncertainties, the bulk ferrous iron contents of the samples remain constant during the step-2 experiments, pointing to systems closed to oxygen. There are, however, indications for a slight oxidation related to a small loss of iron from the sample to the AgPd container. Using the same synthetic ferro-basaltic composition, preliminary equilibrium crystallization experiments under closed-system conditions were performed at 1091-1146 degrees C with an initial superliquidus f (sub O2) corresponding to FMQ. The crystallization sequence of the mineral phases is the same as under open system conditions but magnetite (sub ss) appears at higher temperatures. The FeO (sub tot) content of the residual melt shows the same increase with decreasing temperature under closed and open system conditions down to about 1100 degrees C. At lower temperatures, however, the values drop drastically under closed-system conditions, in contradiction with previous modelling. This exemplifies the need for further experiments in closed systems.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 13
Serial Issue: 3
Title: Magmatic crystallization experiments at 1 bar in systems closed to oxygen; a new/old experimental approach
Title: Experimental mineralogy, petrology and geochemistry
Author(s): Lattard, DominiquePartzsch, Georg M.
Author(s): Anonymous
Affiliation: Universitaet Heidelberg, Mineralogisches Institut, Heidelberg, Federal Republic of Germany
Pages: 467-478
Published: 200106
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: Eighth international symposium on Experimental mineralogy, petrology and geochemistry
Meeting location: Bergamo, ITA, Italy
Meeting date: 20000416April 16-19, 2000
References: 34
Accession Number: 2001-055192
Categories: Igneous and metamorphic petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus. incl. 2 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200117
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