Ferric-ferrous ratios, H2O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

Article Abstract:

Detailed chemical surveys of phlogopite/biotite in diverse tectonic lavas provide a database to understand degassing-related variations in the ferric-ferrous ratios, O/H2O contents, and delta-D values. Cation/anion-based normalization techniques accurately unravel mineral formulae of most of the cations/anions, but seem unable to provide realistic estimates of Fe3+/Fe(super T) ratios. Analysis of the phenocrysts in arc-related lavas of western Mexico and eastern California reveals the highest ferric-ferrous ratios pointing to high magmatic oxygen fugacities.

Observations, Geology, Structural, Structural geology, Biotite, Porphyry

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Mineralogy and origin of stichtite in chromite-bearing serpentinites

Article Abstract:

Stichtite was characterized as an isostructural member of the Pyroaurite Group that possesses a structure that was similar to pyroaurite. Stichtite is composed of positively charged brucite-like layers with randomly distributed octahedral Mg and Cr that were separated by negatively charged interlayers containing disordered carbonate and water. Furthermore, chemical analysis of stichtite indicated the presence of serpentine and chromite.

Rocks, Metamorphic, Metamorphic rocks, Petrology, Serpentinite

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