O pozycji tektonicznej wulkanitów trzeciorzędowych z południowo-zachodniego obrzeżenia niecki żytawskiej

Abstract

Trzeciorzędowe skały wulkaniczne z rejonu Opolna Zdroju powstały w dwóch etapach. Podczas dolnomioceńskicj fazy wulkanizmu, wzdłuż systemu uskoków o przebiegu z SW na NE, zachodziły wylewy law typu nefelinitów oliwinowych oraz bazanitów. Z fazą wulkanizmu młodszą od dolnego miocenu związane były erupcje law typu trachitów, które zachodziły wzdłuż systemu uskoków o kierunku SE–NW. ON TECTONIC SETTING OF TERTIARY VOLCANIC ROCKS AT SOUTH-WESTERN MARGIN OF THE ŻYTAWA BASIN The Żytawa Basin represents Tertiary tectonic depression formed in three tectonic phases. The Basin is infilled with Miocene brown-coal formation and clastic Cenozoic deposits. Rocks of Tertiary basalt formation crop out at south-eastern margin of the Basin, in the area of Opolno Zdrój. In that region, volcanic eruptions were related to two systems of tectonic discontinuity zones.Along an older system of SW – NE oriented faults, there are found volcanic lavas described as olivine nephelinites and basanites. Eruptions of these lavas were taking place in the Oligocene and Early Miocene.The volcanic phenomena and accompanying subsidence of floor of the Żytawa Basin were related to tectonic movements along the Erzgebirge-Ohre rift zone at these times. A younger system comprises SE – NW oriented faults. Eruptions of trachytes and, presumably, olivine nephelinites were related to that system. Subaerial flows of trachyte lavas have in places covered sandy deposits intercalated by Miocene coal clays. The system of SE – NW oriented faults was especially active in the Pliocene, in connection with reactivation of an old tectonic zone of the Lusatian overthrust.Trachyte lavas from Opolno Zdrój are presumably of the Pliocene age. Tectonic movements along the system of SE – NW oriented faults were related to the last, Pliocene phase in evolution of the Żytawa Basin.