TY - JOUR A1 - Novak,M. T1 - Blue dravite as an indicator of fluid composition during subsolidus replacement processes in Li-poor granitic pegmatites in the Moldanubicum, Czech Republic JF - Journal of the Czech Geological Society JA - J. Czech Geol. Soc. Y1 - 1998 VL - 43 IS - 1-2 SP - 24 EP - 30 CY - Prague PB - Czech Geological Society SN - 1803-1943 (online), 1802-6222 (print) AV - Free UR - http://www.jgeosci.org/index.php?pg=detail&ID=JCGS.746 L1 - http://www.jgeosci.org/content/JCGS.746_Novak.pdf KW - dravite KW - cordierite KW - electron microprobe KW - subsolidus replacement KW - fluid composition KW - granitic pegmatites KW - Moldanubicum KW - Czech Republic AB - Fibrous to needle-like blue dravite characterized by low and variable Fe/Mg ratios, low Ti, Mn, Li and F contents and locally elevated Ca contents was found at several localities of Li-poor granitic pegmatites in Moldanubicum, Czech Republic. These pegmatites commonly penetrate Ca, Mg-rich rocks such as dolomite-calcite marble and serpentinite. Blue dravite from Strazek and Vezna replaces cordierite in early stages of subsolidus crystallization at temperature above 450 to 500 °C, before relics of cordierite were completely replaced by a mixture of micaceous minerals. Simplified reaction may be expressed: 3Na0.4(Mg,Fe)2Al4Si5O18.nH2O + 3B(OH)3 + yH2O + zCaO = 2(Na,Ca)0.7(Mg,Fe)3Al6Si6O18(BO3)3(OH)4 + 3SiO2. Blue dravite from Blizna formed in relatively late stage of subsolidus process and it is closely associated with Ca, Mg-rich elbaite. Pegmatite-derived fluids in Li-poor pegmatites are characterized by high activity of B and low activities of F and Li. It is in a contrast with highly evolved Li-rich complex granitis pegmatites, where high activities of B, F and alkalis (Li, K, Rb, Cs) in pegmatite-derived fluids were observed. Metamorphic fluids are Ca, Mg-enriched, but their participation in the reaction is negligible to moderate. Significant influx of metamorphic fluids is assumed particularly during a low temperature formation of blue dravite in Blizna, but it was small during replacement of cordierite at localities Vezna and particularly Strazek. ER -