By analysing of spatial aspects of a monogenetic volcanic field, knowledge can be
acquired on the relationships between the basaltic magmatism and regional tectonics,
like impact of faults to the position of the volcanoes, vent propagation in the lithosphere,
age-dependent stress condition changes. Examination of the surface patterns of volcanoes
might help us understand better the process of magma generation, segregation, and
how magma travelled through a thin lithosphere. Moreover, by studying these processes,
we can get closer to understanding the evolution of a sedimentary basin in which we
can find the link between volcanism and a changing but essentially compressive stress
field, where basaltic volcanism is not evident. These spatial patterns of volcanoes
can be examined using GIS (geographic information systems). The study area was the
Mio-Pleistocene, monogenetic Bakony-Balaton Highland Volcanic Field (BBHVF, Carpathian-Pannonian
region, Central Europe), which is located in continental back-arc setting and compressive/transpressive
tectonic regime.
The methodological toolkit included creating heatmap based on the spatial distribution
of the volcanoes, measuring the orientation of the volcanic field comparing the orientation
of the faults in the region, and calculating distance to the nearest fault line from
each volcanic centre. Poisson nearest neighbour analysis was used to evaluate how
clustered or random the occurrence of the volcanoes across the volcanic field. All
volcanic lineaments (whether volcanic centres are situated along lines) were calculated,
and their orientation was measured to see any systematic directions.
The results suggest that the locations of the volcanoes in the BBHVF are most probably
tectonically determined. The orientation of volcanic lineaments is also the same as
the bounding geometries and the faults. Density of the volcanic centre distribution
is the largest in the central area of the BBHVF along a major inactive thrust fault.
We speculate that the NW dipping fault plane of this fault could be a ‘catchment area’
in the upper crust (just above the brittle-ductile transition zone), which channelized
the magmas and helped them reach the surface. Volcanoes in larger distance from any
faults have typically larger volume, and longer active period (several 100 ky), thus
their magmas needed to have larger buoyancy to reach the surface without the help
of any fault planes. Age pattern and spatial density suggest volcanism getting younger
and thicker towards the central part of the BBHVF. Thus, intracontinental monogenetic
volcanism in compressional regime is strongly influenced by lithospheric weaknesses
and the regional stress field.
