Jiří Adamovič

Nad Kačákem Cave, located in the Bohemian Karst (Czech Republic), has been investigated by archaeologists since the late 19th century. Archaeological finds are known only from a part of the cave, the Entrance Corridor. The oldest excavated archaeological horizon yielded a valuable collection of chipped stone industry. Published radiocarbon data indicate a calibrated radiocarbon age of c. 43–42.5 cal ka BP for this horizon. The assemblage is dominated by artefacts made of a dark grey to black fine-grained volcanic rock – andesite. A detailed petrographic comparison with volcanic rocks occurring within a 100 km radius from the cave identified two possible sources: Upper Cambrian andesite of the Křivoklát-Rokycany Volcanic Complex or, more probably, Upper Cambrian/lowermost Ordovician andesite of the Strašice Volcanic Complex. Lithics were knapped from pebbles rounded by transport in a stream. No suitable andesite pebbles were found in streams and fluvial sediments in the near vicinity of the cave. Nevertheless, they are abundant in streams within 20–30 km of the cave. This indicates that the cave dwellers were able to select suitable andesite pebbles at such a distance.

Post-Variscan lamprophyres of the Bohemian Massif hold the potential for the understanding of deep-mantle processes beneath the Bohemian Massif in association with mantle metasomatism as a consequence of Variscan subduction and Late Paleozoic extension in Central Europe, and tectonic processes between Variscan blocks. Two principal types of post-Variscan lamprophyres occur in the Bohemian Massif, contrasting in their age and composition: ultramafic lamprophyres of Late Cretaceous to Paleocene age and alkaline lamprophyres of Mid Eocene to Late Oligocene age. Combination of published and new whole-rock, isotope (Sr–Nd–Pb) and radiometric (K/Ar) data on lamprophyres of both types (including new data from samples from the deep boreholes) significantly contributes to the understanding of the changing tectonomagmatic position of post-Variscan volcanism in the Bohemian Massif. The striking shift in lamprophyre geochemistry is paralleled by a change in their structural position from the initial pre-rift period of volcanism to the developed syn-rift period and the related change in their mantle sources beneath the Bohemian Massif. The Late Cretaceous and Cenozoic volcanism is explained as related to lithospheric flexuring during the Alpine orogeny, resulting in an asthenospheric upwelling, or associated with the lithosphere deformation and perturbation of the thermal boundary layer.