Turmalín v pegmatitech, aplitech a granitech ze západní granodioritové zóny brněnské masívu

Pages 112-118
Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze | 2010/18/2

Tourmaline granites, pegmatites and aplites in the Western Granodiorite area of Brno Massif are spatially related to the metapelite enclaves, which represents relict of the contact aureole around biotite granites to amphibol-biotite granodiorites of Tetčice Suite. Tourmaline forms anhedral aggregates inside the nodule core in the biotite granites (Qtz + Kfs + Pl + Bt ± Tu). Euhedral to subhedral grains are typical for the pegmatite dykes (Qtz + Kfs + Pl ± Ms ± Bt ± Grt ± And ± Tu). Small anhedral to subhedral grains tourmaline occurs as accessory phase in the same gneisses and leucosome of migmatites from contact aureole. The results of the calculations indicate breakdown tourmaline during partial melting metapelites related with contact metamorphosis (~730 °C and 4 - 3 kbar). The P-T conditions of crystallisation of pegmatites have been constrained by stability of andalusite and quartz-tourmaline isotope thermometry (~570 °C and < 3 kbar). The two main exchange vectors characterize the substitutions in studied tourmaline schorl-dravite series: XNa1 YAl1 XCa-1 YMg-1 and X□1 YAl2 WO1 XNa-1 YR2+ -2 W(OH)-1.

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