Original paper

Age constraints for the late-Variscan magmatism in the Altenberg-Teplice Caldera (Eastern Erzgebirge/Krusne hory)

Romer, Rolf L.; Förster, Hans-Jürgen; Štemprok, Miroslav

Abstract

The late-Variscan peraluminous A-type Sn-bearing Li-mica granites of Altenberg and Zinnwald/Cínovec (Eastern Erzgebirge) intruded into the Teplice Rhyolite (TR) and the Altenberg microgranite (AM), which forms the eastern branch of the Altenberg-Frauenstein microgranite dike system. The maximum age of the TR and AM has been estimated from lithocorrelation of the rocks underlying the TR with biostratigraphically dated rocks from the Schönfeld-Hermsdorf area. The Westphalian B/C age of the Schönfeld Rhyolite (SR) implies that A-type granitic magmatism of the Altenberg-Teplice area is younger than c. 305-311 Ma. These age constraints are tested by dating the Písečný vrch microgranite that is part of the AM, cuts the TR, and is unaffected by the massive hydrothermal overprint related to the tin-bearing granites at the eastern contact of the TR. The Písečný vrch microgranite has a complex zircon population due to open-system behaviour of U-rich zircon and minor inheritance. The U-Pb age of 319.2±2.4 Ma (2σ) of this microgranite disagrees with earlier age estimates and provides a minimum age for the TR that is distinctly older than the one inferred from lithologic correlations with the Schönfeld area. Furthermore, the age of the Písečný vrch microgranite provides a maximum age for the intrusion of the A-type granites in the Eastern Erzgebirge, superseding earlier geochronologic constraints for an age younger than c. 305-311 Ma. Most importantly, the U-Pb age of this microgranite disqualifies earlier lithocorrelations of volcanic rocks from the Schönfeld area with volcanic rocks underlying the TR in the Mikulov area. In the Teplice-Altenberg Caldera, there occur besides the rocks of the TR volcanosedimentary rocks of at least two additional phases of volcanic activity, one predating the deposition of the TR (basal volcanic units in the Mikulov area) and one post-dating the emplacement of the TR (volcanic units in the Schönfeld area). Our new U-Pb age data imply that the Písečný vrch microgranite and the TR were emplaced within the same short period of a few million years as most late-Variscan granite intrusions of the Western and Central Erzgebirge (327-318 Ma), highlighting the broad regional significance of this magmatic event.

Keywords

altenbergtepliceschonfelderzgebirgekrusne horyu-pb agerhyolitegranitelate-variscan