Experimentally observed iron redox kinetics in silicic liquids: Implications for Fe/sup 3 +//Fe/sup 2 +/ variations in rhyolite lava
Iron redox kinetics in silicate liquids were investigated by melting 100 mg pellets of compacted rhyolite, pantellerite, pantelleritic trachyte, and andesite rock powders at 1243 and 1343/degree/C in a moderately reducing furnace atmosphere (log fO/sub 2/ = /minus/7.83) for periods of 1 to 4320 minutes. The redox state of glasses produced by quenching these liquids was determined by colorimetric analysis of the ferrous iron and total iron content. Redox equilibrium, indicated by the attainment of a constant FeO/FeO/sub tot/ ratio, was observed for all temperature-composition conditions studied, except for 1243/degree/C experiments with USGS rhyolite standard RGM-1. This is consistent with the low diffusivity of reacting components in high viscosity rhyolite liquids. In the 1243/degree/C experiments with RGM-1, no change in the FeO/FeO/sub tot/ ratio was observed after 4320 minutes. This implies that redox equilibrium is not maintained in natural rhyolite lavas which erupt as significantly lower temperatures (720--850/degree/C). We conclude that sluggish redox kinetics precludes major changes in the oxidation state of a rhyolite magma during the eruption process. If this is true, then the quenched magma, represented by glassy rhyolites, preserves the pre-eruption redox signature of the magma. 2 refs.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5984389
- Report Number(s):
- CONF-890702-1; ON: DE89001521
- Resource Relation:
- Conference: 28. international geological congress, Washington, DC, USA, 9 Jul 1989; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
IRON
REDOX REACTIONS
VOLCANISM
REACTION KINETICS
EQUILIBRIUM
ERUPTION
GLASS
IRON OXIDES
LAVA
LIQUIDS
MAGMA
SILICATES
VOLCANOES
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
FLUIDS
IRON COMPOUNDS
KINETICS
METALS
OXIDES
OXYGEN COMPOUNDS
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
580202* - Geophysics- Volcanology- (1980-1989)
400201 - Chemical & Physicochemical Properties