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possibilities to deduce these conditions from Fe-bearing phases and phase assemblages found in magmatic rocks.
Conditions of magma genesis and their evolution are of major interest for the understanding of volcanic eruptions.
A brief overview on the most common methods used is given together with potential problems and limitations.
Fe equilibria are not only sensitive to changes in intensive parameters (especially T and fO2) and extensive
parameters like composition also have major effects, so that direct application of experimentally calibrated
equilibria to natural systems is not always possible. Best estimates for pre-eruptive conditions are certainly
achieved by studies that relate field observations directly to experimental observations for the composition of
interest using as many constraints as possible (phase stability relations, Fe-Ti oxides, Fe partitioning between
phases, Fe oxidation state in glass etc.). Local structural environment of Fe in silicate melts is an important parameter
that is needed to understand the relationship between melt transport properties and melt structure. Assignment
of Fe co-ordination and its relationship to the oxidation state seems not to be straightforward. In addition,
there is considerable evidence that the co-ordination of Fe in glass differs from that in the melt, which has
to be taken into account when linking melt structure to physical properties of silicate melts at T and P.
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