The western Erzgebirge-Vogtland region (Saxony, Germany), which is part of the Saxothuringian Zone of the Variscan orogen, is characterized by the emplacement of large masses of granitic rocks during the Late Carboniferous having mixed I-S and mainly S-type affinities. Förster et al. (1995) recognized the occurrence of felsic subvolcanic rocks in this area, which share many features of non-peralkaline
A-type rocks generated in a post-collisional extensional collapse tectonic setting. Typical rocks are represented by the Gottesberg subvolcanic suite (Wasternack et al., 1995; Gottesmann et al., 1994a, 1995), that intruded into the large Eibenstock multiphase S-type pluton. The aim of this contribution is to discuss the compositional features of this suite, and to present electron microprobe data on their trioctahedral mica composition.
The Gottesberg A-type suite consists of two rhyolites and two microgranites emplaced at a subvolcanic level. All four rocks show similar petrographic and compositional features, which are markedly different from those of the older Eibenstock pluton. The highly differentiated Eibenstock granites are distinguished by higher concentrations of Sn,
Li, Rb, Cs, F, and P relative to the Gottesberg suite (Förster and Tischendorf, 1994), and may be classified as highphosphorus topaz granites. In contrast the A-type suite is comparatively higher in HREE, Y, Zr, Hf, Th, and Nb. The subvolcanic rocks often show intensive alteration, and features of brecciation, cataclasis, mylonitization etc. are common. Secondary processes, however, did not alter their primary magmatic compositional patterns, except of irregularly scattering fluorine and silica abundances.
Whereas the earlier intruded Eibenstock granites are characterized by the occurrence of Li-Fe siderophyllites and protolithionites (Gottesmann et al., 1994b) the trioctahedral micas of the Gottesberg suite are Mg-Fe siderophyllites. Their Fe+Mn/Fe+Mn+Mg ratio reflects a cyclic magma evolution, from rhyolite 1 (ratio ~78-81) to microgranite 1 (~86-88), and rhyolite 2 (~82-85) to microgranite 2
(~88-90). Fluorine concentrations are in the range of 1.5-3.2 wt.%.
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