A precise olivine-augite Mg-Fe-exchange geothermometer

Article Abstract:

The calibration of an Mg-Fe2+ cation-exchange geothermometer involves the use of olivine and augite that are experimentally equilibrated in natural basaltic and andesitic bulk compositions. The temperature interval for the experiment is 1175-1080 degrees celsius at pressure of 1 bar. The standard error of the geothermometer is plus or minus 6 degrees celsius over a wide range in olivine Mg/Fe ratio. Examples demonstrate that it can be applied to igneous equilibration temperature estimations in holocrystalline intrusives and extrusives and the intratelluric H2O content dissolved in magmas.

Innovations, Temperature measurements, Temperature measurement, Rocks, Igneous, Igneous rocks

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Thin intergranula melt films and melt pockets in spinel peridotite xenoliths from the Rhon area (Germany): early stage of melt generation by grain boundary melting

Article Abstract:

Fine irregular glass layers and pockets through mineral interfaces, cracks in olivine, within olivine crystals and in spongy rims of clinopyroxene were found using optical microscopy and transmission electron microscopy on porphyroclastic high temperature spinel peridotite from the Rhon area. The glass has a chemical composition deviating significantly from the composition of the host basanite. Its amorphous nature classifies it as a former melt.

Electron microscopy, Porphyry, Spinel group

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Thin amorphous films (1-2 nm) at olivine grain boundaries in mantle xenoliths from San Carlos, Arizona

Article Abstract:

Xenolith samples in basanite host rock from San Carlos show the presence of thin, amorphous intergranular layers along olivine grain boundaries when studied under microscope. The morphology and chemistry of the glass films indicate that partial melting at the interlayers was triggered by decompression and the energy supplied by the host rock during uplift. These results are used to suggest that mixing of melt occurs in melt veins or wider films.

Amorphous substances, Amorphous materials, Geochemistry, Electron microscopes

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