Current research on granites in the Erzgebirge metallogenic province reveals that A-type silicic plutonic as well as volcanic rocks are more common than previously thought. These rocks are emplaced as small stocks, sills and dikes at shallow crustal levels, and are localized within and at intersections of major structural zones. The goal of this contribution is to compile the recent knowledge on the distribution and geochemical signatures of these rocks which share many important features of non-peralkaline A-type granites.
A-type rocks are preferentially located in the eastern Erzgebirge (Krusné hory). Known occurrences include the granite plutons, cupolas and stocks of Markersbach, Sadisdorf, Schellerhau, Sachsenhöhe-Bärenstein, Schenkenshöhe-Falkenhain, Altenberg, Zinnwald-Cinovec, Krupka, and Preiselberk. Presently proved A-type granites in the easternmost central Erzgebirge comprise the localities of Seiffen and Hora sv. Kateriny. In the western Erzgebirge-Vogtland region, affinity to A-type exists for the Gottesberg subvolcanic intrusions.
The Rb-Li-F-Sn specialized granites of the Erzgebirge can be divided into two compositionally and petrogenetically distinct sub-types which formerly were referred to a single group of Li-F granites named the Younger Intrusive Complex. We distinguish (a) - strongly peraluminous (A/CNK > 1.2) granites of S-type affinity which possess very low concentrations of REE, Y, Th, Zr, Hf, Sc, and Pb but elevated P contents, and (b) - weakly to moderately
peraluminous (A/CNK < 1.2) A-type felsic intrusives and extrusives displaying marked enrichments in HREE, (Y), Th, Hf, Sc, Nb, Ta, (Zr), (U), (Pb), and (Zn). An extreme depletion in P and comparatively lower Cs concentrations are
further diagnostic features of the latter rock type. Highly
differentiated intrusions within both groups, represented by albite-protolithionite(zinnwaldite) granites, match the
criteria of "high-P" and "low-P" sub-types of topaz granites.
The degree of element enrichment or depletion may vary considerably among individual A-type representatives. Specifically, rocks from the western Erzgebirge-Vogtland differ from those of the central and eastern Erzgebirge by showing lower fluorine (usually between 0.1 and 0.3 wt.%) and lithium (< 100 ppm) abundances. The Markersbach pluton is particularly notable for its depletion in Ba (< 20 ppm), Sr (< 6 ppm), P2O5 (commonly below 0.01 wt.%), and flat chondrite-normalized REE patterns (LaN/YbN = 0.8 - 2) with strong negative Eu-anomalies (Eu/Eu* = 0.002 - 0.01).
Most A-type rocks suffered intense fluid-rock interactions, particularly those related to Sn-(W) mineralization. Primary magmatic compositional patterns cannot always be easily distinguished from those superimposed by late- to post-magmatic processes.
The lack of age data prevents defining the accurate temporal position of the Erzgebirge A-type occurrences, and
relative age positions are conclusive only in places. The Altenberg stock has been tentatively dated as younger than 300 Ma based on Ar-Ar ages of K-feldspar from the contact aureole. The Gottesberg subvolcanic suite is intrusive into the S-type Eibenstock pluton. As recorded from other
complex orogenic settings, the A-type rocks were formed presumably late in the Variscan post-orogenic stage. Formation in a post-collision environment is more likely than an anorogenic setting s.s. (continental rift- and mantle plume-related). Whether the Erzgebirge A-types were
produced nearly simultaneously and always postdate the emplacement of I-(S)- and S-types remains unknown. The hypothesis that the A-type rocks are highly fractionated and volumetrically insignificant phases of large I- and S-type granite suites is not substantiated by geologic and geophysical evidence. A-type tendencies are rarely developed in aplitic dikes of multiphase I-(S)-type plutons (Kirchberg,
W-Erzgebirge), which represent extreme differentiation. The contrasting compositional features among the individual
A-type suites are suggested to be primarily source-related, although variably intense hydrothermal alteration may be also responsible to a certain extent (disturbances in U, Y, F, and Li abundances).