Published: Feb 2004
Pages: 43 - 50
Abstract: Paleogene intrusive (tonalite, diorite) and volcanic (andesite, dacite) rocks have been identified in drilling cores from the Zala Basin, SW-Hungary. The age of these rocks has been considered to be Eocene on the basis of the observation that volcanic rocks are intimately interlayered with sedimentary rocks deposited during Nannoplankton Zone 15/16–18. However, new K/Ar data measured on mineral concentrates (amphibole, biotite, plagioclase) from intrusive and volcanic rocks yielded ages from 28.6±1.8 Ma to 33.9±1.4 Ma and from 26.0±1.2 Ma to 34.9±1.4 Ma, respectively. The Early Oligocene K/Ar age of the andesite and dacite studied contradicts the previous biostratigraphic interpretations. Furthermore, detailed petrographic study of the volcanic rocks and XRD analyses of the Eocene marl deposits are not consistent with simultaneous volcanic activity and sediment deposition. Alternatively, we propose that the volcanic rocks were emplaced as dykes into the Eocene marl during the Early Oligocene. However, an Eocene age of some explosive (mostly tuffaceous) rocks is not debated. The Early Oligocene K/Ar data of the intrusive bodies coincide with the age of other Paleogene tonalitic massives along the Periadriatic Lineament. The geochemical and radiometric age data clearly demonstrate the Alpine connection of the either intrusive or volcanic rocks studied. During the Paleogene the intrusive and volcanic rocks dislocated and as a result of the escape of the ALCAPA (Alpine-Carpathian-Pannonian) block from the Alpine realm they reached their present-day juxtaposed setting in the Early Miocene.
Keywords: Paleogene, Periadriatic Lineament, Zala Basin, geochemistry, radiometric age, calc-alkalineDownload PDF document