Three age ranges of Cenozoic basaltic rocks from Lower Silesia (SW Poland) based on 40Ar/39Ar step-heating data

Abstract The precise ages of Cenozoic basaltic rocks from 20 localities (24 samples) in south-western Poland were studied by means the 40 Ar/ 39 Ar isotope method. Three phases volcanic activity identified this area. older, Ruphelian phase took place 31–29 Ma ago and younger, Aquitanian occurred 22–21 ago. Significantly younger (4.8–4.6 Ma: Zanclean phase) obtained for basalts cropping out vicinity Lądek Zdrój only. Most analyzed are classified as nephelinites. They occur area Lausitz Masif, south Sudetic Marginal Fault Opole Depression. crop wide north Fault. composed alkali basalts. youngest is represented basanites deep discontinuous tectonic structures intersecting areas SW Poland, parallel or oblique to stress directions previously reconstructed Oligocene Miocene Bohemian Massif, most probably reactivated an extension approximately slightly them, thus opening pathways migration magma Sudetes their foreland.