International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

EVIDENCE FOR THE NEOGENE SMALL-VOLUME INTRACONTINENTAL VOLCANISM IN WESTERN HUNGARY: K/Ar GEOCHRONOLOGY OF THE TIHANY MAAR VOLCANIC COMPLEX

Pages: 91 - 99

Authors: KADOSA BALOGH, KAROLY NEMETH

Abstract: The Tihany Maar Volcanic Complex (TMVC) consists of several eruptive centres and is made up mostly of pyroclastic rocks. It belongs to the Bakony-Balaton Highland Volcanic Field (BBHVF), which is an extensive Late Miocene–Pliocene alkaline basaltic volcanic field in Western Hungary. The TMVC is the only known location in the BBHVF where volcanic rocks are in a stratigraphically fixed position near the boundary of the Congeria balatonica–Prosodacnomya Zones. Since 1985 this stratigraphic importance motivated repeated efforts to obtain unquestionable radiometric data with sufficient accuracy for the volcanic phases. Due to the difficulties of dating basaltic pyroclastic rocks (detrital contamination, excess argon, argon loss during hydrothermal alteration, high atmospheric argon content, etc.), this is for the first time a fully acceptable age of 7.92±0.22 Ma has been obtained for the onset of volcanic activity of the TMVC at the location Monk’s cave. This age is a key datum for the boundary of Congeria balatonica–Prosodacnomya Zones and it agrees well with the start of alkali basaltic volcanic activity in Central Slovakia. 7.35±0.45 Ma is obtained for Dióstető. The youngest ages, showing the greatest argon loss were measured for the location Gödrös. An analysis of the isochron diagrams suggests here an interval from 6.24±0.73 Ma to 5.92±0.41 Ma for the time of volcanic activity. This age sequence is in agreement with volcanological field observation and in spite of some uncertainty of the younger age limit, it is indicated that volcanism at Tihany was not a single event of the same volcano, but rather a result of longer lived eruptions from a closely spaced, nested volcanic system.

Keywords: Pannonian Basin, K/Ar geochronology, phreatomagmatic, scoria, monogenetic, maar, tuff ring, alkaline basalt

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