Variation in chemical composition of V-bearing muscovite during metamorphic evolution of graphitic quartzites in the Moravian Moldanubicum
Three distinct morphological and paragenetic types of vanadium-bearing muscovite occur as common minor phases in graphitic quartzites in the Moravian Moldanubicum: Abundant V-bearing muscovite I (VM1) as green flakes up to 3 mm in size, commonly as intimate intergrowths with graphite and sillimanite I; rare V-bearing muscovite II (VM2) as green flakes up to 1 cm in size, exclusively in the ductile quartz-rich nests and veins enclosed in graphitic quartzite; fine-flaked V-bearing muscovite III (VM3) replacing sillimanite I and perhaps also the medium-flaked VM1. Electron-microprobe study gave: 0.03-0.84 apfu V (≤7.49 wt. % V2O3); 0.05-0.31 apfu Mg (≤ 1.52 wt. % MgO), 0.00-0.17 apfu Ti (≤ 1.59 wt. % TiO2). VM1 is characterized by high V, Mg and Ti contents; VM2 has low V and Ti, but high Mg concentrations; VM3 shows moderate V, low Ti, but variable Mg. Typical substitutions involve dominant VA1-1 and subordinate SiMgAl-2, both particularly in the early VM1. Mineral assemblages and textural relationships suggest that the mineral assemblage Qtz + Gr + Sil I + VM1 ± V-bearing dravite I is stable if XH2O = 0.5 for P < 700 MPa T < 650 °C, and for P < 300-400 MPa T < 570 °C. Mineral assemblage Qtz + Kfs + VM2 + Sil II ± V-bearing dravite II with VM2 is characterized by elevated activity of O2 and probably H2O (redistribution of graphite and degraphitization). Very low mobility of V during high- to medium-grade metamorphism is evident.
SNIP (Scopus, 2015): 0.700
IF (ISI, 2015): 1.326
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