K/Ar geochronology of igneous amphibole phenocrysts in Miocene to Pliocene volcaniclastics, Styrian Basin, Austria

Abstract

We present fifteen new K/Ar ages on amphibole phenocrysts of Neogene volcaniclastic rocks from the Styrian Basin, Austria. The westernmost sub-basin of the Pannonian Basin is the Styrian Basin, which hosts a large number of phreatomagmatic tuff occurrences beside Middle Miocene shield volcanoes and Pliocene effusive alkaline volcanic rocks. The investigated tuffs contain the well-known mantle xenoliths and frequent amphibole and pyroxene phenocrysts. The new K/Ar ages indicate that the Late Miocene phreatomagmatic volcanism started in Pontian (7.51 Ma) and ended in Romanian (2.73 Ma) times. The complete interval of the youngest volcanism in the Styrian Basin covers 5.8 Ma, similar to the volcanism of the western part of the Pannonian Basin and the Nógrád/Novohrad area (West Carpathians). The dated volcanic occurrences display NNW–SSE oriented arrays which are approximately parallel to the Auersbach basinal high zone. The new data indicate that the Late Miocene to Pliocene volcanism of the Styrian Basin is synchronous with the onset of a regional compressional event and eastward tilting of the Styrian basin fill.