Lithofacies of magma and wet sediment interaction in the contact zone of Late Miocene andesite intrusions in the NE foreland of the Tardona settlement (NE Hungary)

Abstract

The 1.5 km-long Özvény Valley (with a strike about north-west–south-east) is situated on the left side of the Tardona
Stream, halfway between the settlements of Kazincbarcika and Tardona, among the Disznó, Körtvélyes and Eperjes
Crags. Detailed geological mapping was carried out using a scale of 1:1000 on the well-exposed rock surface of the valley.
Geological mapping carried out using scales of 1:10 000 and 1:25 000 is commonly practised. However, the maximum
diameter of the magmatic bodies near the Eperjes Crag and Özvény Valley do not exceed 30 m and thus the precise and
detailed mapping and presentation required the application of a 1:1000 scale during the field work. The results of the field
work made it possible to perform particular volcanological investigations of the Dubicsány Andesite Formation, this is
one of the most significant formation of the East Borsod Basin. More than one hundred andesite dykes, intrusions, vents
and diatremes of variable sizes (2-30 m in diameter) have been discovered in a model territory with a latitude of 500×350
m. Along the margin of the andesite intrusions well-developed contact lithofacies zones (autobrecciation, peperite,
hylaoclastite forming, welding) were revealed by careful description and interpretation of the textures of the outcrops.
This suggests intensive magma and wet sediment interaction. The host sediment of the intrusions was mainly andesite
lapilli-tuff. The andesitic magma intruded into the soft pyroclast shortly after its deposition or entered a bentonitic tuff
layer of the pre-volcanic basement. The physical and palaeohydrological condition of the host sediment favoured the
formation of blocky peperite. In the course of volcanological investigations it became clear that the size of the studied
intrusive magmatic bodies determines the method of their representation.