Fe in magma - An overview

Abstract

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