RADIOMETRIC DATING OF THE TERTIARY VOLCANICS IN LOWER SILESIA, POLAND. V. K-Ar AND PALAEOMAGNETIC DATA FROM LATE OLIGOCENE TO EARLY MIOCENE BASALTIC ROCKS OF THE NORTH-SUDETIC DEPRESSION

Krzysztof BIRKENMAJER (1), Zoltán PÉCSKAY (2), Jacek GRABOWSKI (3), Marek W. LORENC (4) & Pawe³ P. ZAGO¯D¯ON (5)

1) Institute of Geological Sciences, Polish Academy of Sciences, Cracow Research Centre, Senacka 1, 31-002 Kraków, Poland, e-mail: ndbirken@cyf-kr.edu.pl
2) Institute of Nuclear Research, Hungarian Academy of Sciences, Bem tér. 18c, 4001 Debrecen, Hungary, e-mail: pecskay@namafia.atomki.hu
3) Polish Geological Institute, Rakowiecka 4, 00-975 Warszawa, Poland, e-mail: jgra@pgi.waw.pl
4) Institute of Building and Landscape Architecture, Agricultural University of Wroc³aw, pl. Grunwaldzki 24, 50-363 Wroc³aw, Poland, e-mail: mwlorenc@ozi.ar.wroc.pl
5) Institute of Mining, Wroc³aw University of Technology, pl. Teatralny 2, 50-051 Wroc³aw, Poland, e-mail: Pawel.Zagozdzon@pwr.wroc.pl

Birkenmajer, K., Pécskay, Z., Grabowski, J., Lorenc, M. W. & Zago¿d¿on, P. P., 2007. Radiometric dating of the Tertiary volcanics in Lower Silesia, Poland. V. K-Ar and palaeomagnetic data from Late Oligocene to Early Miocene basaltic volcanics of the North-Sudetic Depression. Annales Societatis Geologorum Poloniae, 77: 1-16.

Key words: K-Ar dating, basaltoid volcanics, palaeomagnetism, Late Oligocene, Early Miocene, Lower Silesia, Poland.
Abstract: This is the fifth contribution to geochronological, petrologic-geochemical and palaeomagnetic studies of the Tertiary basaltoids of Lower Silesia, Poland. It covers the area of the North-Sudetic Depression close to its contact with the Fore-Sudetic Block (6 new sites). The oldest K-Ar date was obtained from basanite plug at Sichów (BP-34: 27.80±1.27 Ma) located exactly on the Sudetic Marginal Fault. It determines the age of the fault as Late Oligocene. Five other sites (BP-35-39) yielded radiometric ages between 20.07±0.90 Ma and 18.72±0.81 Ma (Early Miocene). The volcanics investigated are typical within-plate basaltoids represented by ankaratrite and basanite. The Late Oligocene Sichów intrusion (BP-34) is normally magnetized, the Early Miocene basaltic rocks (ankaratrite BP-39 and basanites: BP-35-38) reveal reversed magnetization.

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Journal of the Geological
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