Pohorje marble is a metamorphic rock that forms lenses and smaller bodies and is outcropping predominantly on the eastern and southern parts of the Pohorje Mountains. Unlike for other metamorphic rocks from Pohorje, for marbles, we still do not know precisely what were the metamorphic conditions during the peak of the metamorphism. The partial reason for this is the exceptional purity of Pohorje marbles with very seldom non-carbonate minerals, which are crucial for determining metamorphic conditions at the time of rock formation.
The determination of these non-carbonate mineral phases in the Pohorje marbles was carried out by examining the polished thin sections using the optical microscope under plain polarized light. More precise investigations of non-carbonate mineral phases were carried out using electron microscopy in combination with X-ray diffraction spectroscopy (SEM / EDS) and electron microprobe in combination with X-ray diffraction spectroscopy (EPMA / WDS). Recognized non-carbonate mineral phases in marbles are: feldspars, pyroxenes, amphiboles, olivines, quartz, epidot, muscite, biotites, phlogopite, fengite, chlorites, serpentines, titanite, apatite, zoisite, zircon, turmalins, scapolite, rutile, hematite and pyrite. Pyroxene are Ca-Mg pyroxenes with 0,5 do 10,3 wt % FeO and various proportions of Ca and Mg oxide, and are determined mainly as endiopside, diopside, augite, and wollastonite.The feldspars are very different in composition varying from almost pure potassium feldspar with 93 mol% of the orthoclase component to completely pure anorthite, and in addition there are plagioclases with the composition of bytownite, labradorite, andesite and oligoclase. Among the amphiboles, Ca amphibole tremolite, actinolite, edenite, ferro-edenite and ferro-pargasite are predominant, containing from 3.8 to 14.1 wt % CaO, 4.5-24.1 wt % MgO, 0.6-31.2 wt % FeO and up to 0.2 wt % MnO and up to 1.5 wt % Na2O. Forstite is present with 85.2–97.4 mol. % of forsterite component.
Based on mineral paragenesis calcite + quartz + biotite + tremolite + forsterite + diopside + plagioclase or calcite + dolomite + quartz + biotite + tremolite + forsterite + diopside + plagioclase we conclude that marbles from Pohorje reached high matamorphic grade in the area of the regional metamorphism of the amphibolite facies.
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