Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Ivan Gnojek, Jiří Sedlák, Vladislav Rapprich, Zuzana Skácelová, Bedřich Mlčoch, Ottomar Krentz, Raymundo Casar-Garcia

Structure of the Carboniferous Altenberg-Teplice Caldera (Eastern part of the Krušné hory/Erzgebirge Mts.) revealed by combined airborne and ground gamma-ray spectrometry

Journal of Geosciences, volume 63 (2018), issue 1, 3 - 20

DOI: http://dx.doi.org/10.3190/jgeosci.251



The airborne gamma-ray spectrometry images from the Czech and German parts of the Carboniferous Altenberg-Teplice Volcanic Complex (ATVC) - both obtained during independent surveying campaigns - were merged to display the structure of the caldera fill (dominated by rhyolitic ignimbrites) and associated intrusive bodies. The airborne systematic measurements were supported by the ground- and laboratory gamma-ray spectrometry analyses (K, U, Th) of representative lithologies from outcrops and drill-cores.
Significant differences were identified between the younger and older (post- and pre-caldera respectively) intrusive complexes related to the ATVC. The younger Schellerhau granite displays 1.5-3.0× higher concentrations of radioactive elements than the older Fláje granite.
The ATVC was found to be split by the NW-SE trending Altenberg Fault into a southern and a northern segment that expose different stratigraphic levels of the caldera’s fill. The individual types of rhyolite ignimbrites defined in the Czech part of the ATVC are characterized by distinct concentrations of natural radioactive elements which enable identification of the individual types from the airborne gamma-spectrometry image. These characteristics were compared to data obtained from the German part, and several lithological types were unified to common units.
A single Th-rich unit (Pramenáč type in Czech part, Lugstein type in Germany and Teplice Rhyolite TR3a in Mi-4 borehole) can be traced across the entire caldera and may serve as the principal correlation member. Inclusion of the Vrchoslav type into this TR3a unit remains speculative due to lack of data, and further petrological research is required. On the other hand, Vlčí kámen and Medvědí vrch types from opposite sides of the caldera display identical properties allowing to merge them into a common unit TR3b overlain by the youngest unit TR4 (Přední Cínovec type) - restricted to the Czech territory. This result may suggest partly synclinal structure within the southern ATVC segment. The TR4 unit has a strong compositional tendency towards the post-ignimbrite granite porphyry intrusions.
Some lithotypes in the northern segment (e.g., Buschmühle) do not have counterparts on the Czech side and most likely represent an independent volcanic unit in the northern part of the caldera.
The uniform composition of the rhyolitic rocks observed in the entire profiles of the drillings located in the Town Teplice (TP-39 reaching 1170 m depth) may suggest that the main feeding conduit system for the TR4 ignimbrite was located within the Teplice-Lahošť horst area.

Journal of Geosciences, Published by © Czech Geological Society, with support from the Czech Geological Survey.
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Policy: Open Access

ISSN: 1802-6222

E-ISSN: 1803-1943