Radiometric dating of the Tertiary volcanics in Lower Silesia, Poland

• Autorzy: Birkenmajer K. , Pécskay Z. , Grabowski J. , Lorenc M. W. , Zagożdżon P. P.
• Języki publikacji: EN

Abstrakty

EN

The Tertiary volcanic rocks of the Fore-Sudetic Block (FSB), Lower Silesia (Poland), exposed between Strzelin in the east and Legnica in the west, typically represent within-plate basalts. Petrologically, they consist mainly of alkali basalts, basanites, tephrites and ankaratrites. 16 new K-Ar dates are recorded, spanning the Oligocene (31 Ma) through Early Miocene (Burdigalian c. 18 Ma) time. The majority of these K-Ar dates plot around two significantly different ages: 27š1.5 Ma, and 20š1.5 Ma. They indicate the presence in the FSB of two distinct separate phases of Tertiary vulcanicity: (i) the first phase, mainly Late Oligocene (Chattian), with a peak at c. 27; (ii) the second phase, Early Miocene (Aquitanian-Burdigalian), with a peak at about 20 Ma. These phases seem to be separated by a gap in vulcanicity about 3 Ma long at the Oligocene/Miocene boundary. Correlation of K-Ar-dated volcanic activity in the FSB with specific radiometrically-dated polarity intervals, poses some problems, and cannot be regarded definite at this stage of investigations. Considering the whole set of K-Ar and palaeomagnetic data from 40 sites, between the Opole area in the east and the Legnica area in the west, we suggest that volcanism of the first phase (Oligocene), although significantly spread out in time across multiple reversals, took place mostly during two well-defined, previously recognized events: (i) an older, reversed Odra event (within the C9r chron: 28.1š1.2 Ma); and (ii) a younger, normal Gracze event (within the C8n chron: 26.5š1.1 Ma). The second phase (Early Miocene) volcanism includes mainly a continuous set of reversely magnetized sites (mostly a single reversed C6r chron: 20.5š0.87 Ma).

Słowa kluczowe

EN

K-Ar dating; basaltic rocks; palaeomagnetism; Late Oligocene; Early Miocene; Lower Silesia; Poland

• Wydawca: Polskie Towarzystwo Geologiczne
• Czasopismo: Annales Societatis Geologorum Poloniae
• Rocznik: 2004
• Tom: Vol. 74, No 1
• Strony: 1--19
• Opis fizyczny: Bibliogr. 37 poz., rys., tab.

Twórcy

autor

Birkenmajer K.

• Institute of Geological Sciences, Polish Academy of Sciences, Cracow Research Centre, Senacka 1, 31-002 Kraków, Poland

autor

Pécskay Z.

• Institute of Nuclear Research, Hungarian Academy of Sciences, Bem tér. 18c, 4001 Debrecen, Hungary

autor

Grabowski J.

• Polish Geological Institute, Rakowiecka 4, 00-975 Warszawa, Poland

autor

Lorenc M. W.

• Institute of Geological Sciences, Polish Academy of Sciences, Sudetic Geology Department, Podwale 75, 50-449 Wrocław

autor

Zagożdżon P. P.

• Institute of Mining, Wroclaw University of Technology, pi. Teatralny 2, 50-051 Wrocław, Poland

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