Subsurface structure of the volcanic centre of the ?eské St?edoho?í Mountains, North Bohemia, determined by geophysical surveys |
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| Authors: | J Mrlina V Cajz |
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| Institution: | (1) Geophysical Institute, Acad. Sci. Czech Republic, Boční II/1401, 141 31 Prague 4, Czech Republic;(2) Institute of Geology, Acad. Sci. Czech Republic, Rozvojová 135, 165 02 Prague 6, Czech Republic |
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| Abstract: | Former geophysical surveys performed in the region of the volcanic centre of the České Stř edohoří Mts. in North Bohemia (the
Ohře Rift zone) showed that anomalous volcanic bodies and features can be effectively identified within sedimentary environment.
For this reason we carried out new geophysical measurements in the area of the main mafic intrusion of essexitic character.
The target was the exact location and geometry of the intrusion and its relation to other components of the volcanic centre.
We used gravity, magnetic, shallow seismic and electromagnetic techniques. The new gravity and magnetic data were tied to
the old databases so that we could investigate the area as a whole complex. Electromagnetic measurements were applied in the
area of the expected extent of the intrusion, and the seismic measurements in the central part of the intrusion.
Based on all the data, mainly on gravity modelling, we delineated not only the surface and subsurface extent of the intrusion,
but we also defined the hidden relief of the intrusion. It was found that the intrusion is formed by a single body that has
a few protrusions, and not by a set of separate individual intrusions, as indicated by surface outcrops. However, the body
of the intrusion is affected by a major fault that caused lithological differences on both sides (essexite/monzodiorite).
In detail we show the depth of the debris cover and the thickness of the weathered zone in the central part of the essexite
body. We also derived indications of tectonic elements in the area of the intrusion in the main structural/tectonic direction
in the region. The results will be utilized to establish a 3D geological model of the whole volcanic centre.
This investigation may serve as an example of non-seismic geophysical exploration applied to the study of volcanic centres
surrounded by sedimentary rocks. |
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| Keywords: | geophysical survey gravimetry gravity modelling volcanics Č eské Stř edohoř í Mts Ohř e (Eger) Rift sedimentary basin |
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