Composition of trioctahedral micas in the Karlovy Vary pluton, Czech Republic and a comparison with those in the Coruubian batholith, SW England

Abstract

Trioctahedral micas in the Karlovy Vary pluton range in composition from Fe-biotites in the granites of the Older Intrusive Complex (OIC) through siderophyllite and lithian siderophyllite to zinnwaldite in the granites of the Younger Intrusive Complex (YIC). Li + AlVI + Si would appear to substitute for Fe2+ + AlIV in biotite with a formula similar to that given in Henderson et al. (1989), but Li + Si appears to substitute for Fe2+ + AlIV in the Li-micas. In mica vs. host rock plots, Rb and F show positive linear covariation except for the Li-mica granites, but femic constituents and tFeO/(tFeO + MgO) have separate trends for OIC and YIC granites and micas. Further differences between OIC and YIC granite micas are seen in their Ti and Mg contents and in plots like V vs. SiO2, AlIVvs. Fe/(Fe+Mg) and Li vs. total iron as Fe2+ and in the results of discriminant analysis. These reveal a geochemical hiatus between OIC and YIC granite micas that coincides with a major temporal hiatus.Biotite compositions in the YIC granites are similar to those in the granites of the Cornubian batholith and reveal a similar magmatic evolution and genesis in which later biotites evolve to lithian siderophyllites with some enrichment in trace alkalis and F. It is suggested that the biotite granites in the YIC were derived from the products of partial fusion of the OIC granites. A less well-marked geochemical hiatus exists between YIC biotites and zinnwaldites. In some plots (e.g. Si vs. Li, Li vs. tFe) apparent continuity between biotite and the Li-micas suggests continuous evolution, but in others (e.g. Rb vs. TiO2, Rb(biotite) vs. Rb(rock)), Li-mica data points stand apart from the biotites suggesting, like the whole rock data, a separate evolution. Comparison with the more abundant data for Li-micas of the Cornubian batholith suggests derivation of the Li-mica granites by partial fusion of the OIC/YIC granite residues.

Occurrence of primary almandine-spessartine-rich garnet and zinnwaldite phenocrysts in a Neogene rhyolite on the island of Chios, Aegean Sea, Greece

“…The volatile constituents required can be generated from a subcrustal (mantle or crust/mantle interface) source above an active mantle. Stone et al (1997) suggested that one way of generating Li-mica granites would be by partial fusion of earlier granite residues, in which case the garnet-zinnwaldite phenocrysts association would be easily explicable. That is provided that there is sufficient heat in the granite-generating system to melt residues from an earlier formed granite (but see Creaser et aI., 1991).…”

Lithium and trace-element concentrations in trioctahedral micas from granites of different geochemical types measured via laser ablation ICP-MS

“…Many authors addressed this deficiency using additional methods. For example Stone et al (1988Stone et al ( , 1997, du Bray (1994), Ford et al (1995), Černý et al (1995), Breiter (2002) and Brigatti et al (2003) prepared monomineralic separates of mica via crushing, sieving, magnetic separation, separation in heavy liquids and handpicking. Separates with 95%-99% purity were analysed for Li using classical wet chemistry methods, e.g.…”

Actual Fe-Li mica series as a series with ☐VI constant but not with AlIV or AlVI

“…The concept of the essential replacement is linear. However, as emphasized by Stone et al (1997) and Tischendorf (1997), strictly speaking, the relations between cations in tetrahedral and octahedral sheets are not linear (e.g. Fig.…”