Nearly contemporaneous evolution of the A- and S-type fractionated granites in the Krušné hory/Erzgebirge Mts., Central Europe

Abstract

The Krušné hory/Erzgebirge Mountains is one of the best-known provinces of granite magmatism and associated metallogenesis in Europe. Variscan magmatic activity in the Krušné hory/Erzgebirge area spanned the period from 330 to 295Ma. For much of this time, two types of magma were generated and emplaced in close proximity in this province. Strongly peraluminous P-rich (S-type) melts were formed alongside slightly peraluminous P-poor melts (A-type). Two suites of strongly peraluminous P, F, Li, Rb, Cs, U, Sn-rich and Zr, Th, Y, HREE-poor magmas were intruded in rapid succession over a period of about 10Ma (about 330–320Ma) over the entire region of the Krušné hory. Several peraluminous rhyolitic dykes near Gottesberg mark an isolated event at about 295Ma. Slightly peraluminous F, Li, Rb, Cs, Sn, Zr, Y, HREE-rich and P-poor magmas were intruded in several events separated in space and time (325–295Ma). Both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions, accompanied by explosive brecciation and followed by Sn+W mineralization of greisen type. Successive volcanic eruption of rhyolites and dacites of S-type, and rhyolites of A-type form the fill of the Altenberg-Teplice Caldera (ATC), thus demonstrating the close temporal and spatial relationship between these two types of magma. When these two geochemically distinct types of rock are in direct contact, then the rocks of A-type are always younger. The absolute time difference between the two types can range from less than 1Ma (the first eruption of the Teplice rhyolite versus the Schönfeld dacite in the ATC) to about 15Ma (eruption of rhyolites at Gottesberg versus emplacement of the Eibenstock granite). The assumed protolith of all late-Variscan granites in the area of Krušné hory/Erzgebirge is a mixture of fertile quartzo-feldspathic rocks with micaceous metapelites enriched in LILE and Sn+W. The differences in chemical composition of S- and A-type melts originated from local changes in the proportion of quartzo-feldspathic and pelitic lithologies, different pT-conditions of melting, the degree of melting, and the degree of metamorphic dehydratation of the protolith prior to the melting.