Przejawy pleistoceńskiego wulkanizmu bazaltowego w Dębowcu koło Szklar na Dolnym Śląsku

Abstract

PHENOMENA OF PLEISTOCENE BASALTIC VOLCANISM AT DĘBOWIEC NEAR SZKLARY, LOWER SILESIASummaryIn the vicinity of Szklary, Lower Silesia area (Figs. 1 and 2), a small sheet of volcanic rocks crops out. This is one of numerous occurrences of young eruptive rocks that represent the (Middle-European petrographic province, called the Atlantic magmatic suite. In the group of volcanic rocks are found basalts and two generations of volcanic breccia. The volcanites belong here to shield eruption that has taken place along the line of young dislocation in the crystalline basement. The crystalline basement is built of granodiorites and of fine-grained granites. Lithological evidences prove two periods of volcanic activity here. In the first (pre-Pleistocene) period, basalt lava flowed out, accompanied by volcanic breccia. After this, a long period of erosional and denudational processes followed. As a result of these processes, the cover of the older volcanic rocks fell into several islands. This period was then followed by anew volcanic activity, at the time of which fissure eruption of volcanic breccia developed. The younger breccia consists of lava, of sintered clays, Tertiary in age, as well as of basaltic and granodiorite xenoliths. In the from of xenoliths are found also basalt pebbles, revealing weathered rims. This kind of volcanic breccia at the top, intertongues with the fluvioglacial sands of the Middle-Polish Glaciation (Fig. 3). The contact of the volcanic rocks with sands is an evidence of subglacial eruptions.