Mio-Pliocene Phreatomagmatic Volcanism in a Fluvio-Lacustrine Basin in Western Hungary

Late Miocene to Pliocene eroded maar complexes and tuff rings are preserved in the Pannonian Basin. They belong to the Bakony-Balaton Highland (BBHVF) and the Little Hungarian Plain Volcanic Field (LHPVF). The bulk of the volcanic fields are considered to have developed subaerially. Base surge and fallout deposits were formed around maars and tuff rings by phreatomagmatic explosions, caused by interactions between water-saturated sediments and alkali basalt magma locally carrying peridotite lherzolite xenoliths as well as pyroxene and olivine megacrysts. Particularly well exposed is a great variety of peperites, which commonly constitute the root of the volcanic vent as a result of non-explosive to very mildly explosive interaction of magma with wet, unconsolidated sediments. A slight time delay was found between the formation of initially phreatomagmatic landforms and lava effusion. The composition of the initial volcanic products is more evolved (tephrite, phonotephrite) in contrast to more basic composition of subsequent lavas. The time difference between phreatomagmatic explosive and effusive eruptions and the bimodality of melt involved in these eruptions suggests a dual melt involvement in volcanic eruptions in western Hungary.