New age and petrological constraints on Lower Silesian basaltoids, SW Poland

Fifteen samples of basaltoid rocks were analysed from Lower Silesia, SW Poland, all of them situated close to the Sudetic Marginal Fault. K-Ar datings were made on whole rock samples, using the methodology applied by the Institute of Nuclear Research, Hungarian Academy of Sciences, Debrecen, Hungary. Most of the samples gave dates ranging between 21-38 Ma, whereas that derived from a borehole in the Mokrzeszów graben was dated to 44 Ma. Another borehole sample (Jeżów Sudecki B-5) is of 59 Ma age. On the other hand, the supposedly “Quaternary” basalts from the Dębowiec area fall into the interval of 29-30 Ma.The southeasternmost occurrences of the Lower Silesian basalts at Nowa Cerekiew display two generations of effusive activity: the older lava flows (26 Ma) are cut by plugs dated to 22 Ma. The Oligocene-Lower Miocene (26-33 Ma, 20-24 Ma) rocks represent alkali basalts and basanites. Most of the samples studied show properties typical of the two phases of volcanic activity, hitherto recorded in the Opole area by other authors.