Publication details
Compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites: Examples from the Bohemian Massif, Czech Republic
| Authors | |
|---|---|
| Year of publication | 2007 |
| Type | Article in Periodical |
| Magazine / Source | Lithos |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | tourmaline granite |
| Description | Two distinct textural types of tourmaline were distinguished in leucocratic granites of the Bohemian Massif (Moldanubicum, Saxothuringicum): (i) commonly euhedral disseminated tourmaline (DT) crystallized in relatively early stage of the granite consolidation, and (ii) typically interstitial nodular tourmaline (NT) formed during the stage transitional from late solidus to early subsolidus crystallization. Very similar chemical composition and similar fractionation trends in both DT and NT tourmaline types indicate crystallization in a quasi-closed system from early solidus to early subsolidus stage of granite consolidation. The substitutions in tourmaline from NT granites in the Moldanubicum are more similar to the substitutions in tourmaline from Li-poor granitic pegmatites in the same region relative to tourmaline from DT granites. Plotting of EMP analyses of tourmaline in diverse diagrams strongly suggests using combination of ternary diagrams Al Fe Mg and Na Ca Xsite vacancy and simple plots involving single cations (elements) such as Na/Al, F/Na, Fe/Mg rather then more complicated diagrams (e.g., R1+R2/R3) to characterize chemical composition and to derive substitution mechanisms in Ca-poor tourmaline from granitic rocks. The complex diagrams e.g., R1+R2 versus R3 do not enable to investigate compositional evolution in the Xsite and Wsite properly and oversimplifies the real substitutions. We recommend using specific diagrams for specific tourmaline compositions (e.g., Carich, Lirich). |
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