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| Titel |
An Integrative Geoelectric, Sedimentologic and Soil Gas Investigation of a Magmatic CO2 Degassing Structure in the Cheb Basin/Czech Republic: A Natural Analogue Study to Understand Transport Processes in the Near Surface |
| VerfasserIn |
Christina Flechsig, Claudia Schütze, Robert Bussert, Horst Kämpf |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047729
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| Zusammenfassung |
| The mofette field of Hartoušov is located in the Cheb Basin, a shallow Neogene
intracontinental basin in Central Europe. The north-eastern part of the Cheb Basin is one of
the most seismically active regions of Central Europe. Seismic activity in the Cheb Basin has
mainly a swarm-like character. The numerous cold CO2 emanations (>99 Vol.% CO2) at the
surface of the basin are supposed to be generally connected to the seismic activity and to stem
from the upper mantle. The Hartoušov mofette field has been investigated by combining
geophysical measurements (geoelectrical resistivity tomography, self potential)
with sedimentological studies (grain size, Corg, mineralogy) and soil gas (CO2
flux and CO2 concentration) data. Key question of the research was to evaluate the
structural and sedimentological control at a CO2 degassing location. The investigations
reveal a positive correlation between areas of high soil gas (CO2) concentration and
flux with geophysical anomalies (negative self potential, positive structures of low
electrical resistivity) as well as with specific sediment properties (content of pyrite
and organic material, occurrence of dispersed pebbles, uplifted clay layer). These
features are thought to be directly or indirectly related to the magmatic caused
CO2 flow. Soil gas (CO2) measurements indicate areas of high CO2 content to
be marked by anomalous vegetation patterns. These anomalies spread out with a
linear trend, suggesting a fault control on gas ascent. Places of highest gas flow
form small hummocks, with minor depressions on top. Negative geoelectrical self
potentials at such locations were interpreted considering as having been caused by a
downward movement of the meteoric water balancing the upward CO2 flux. The
top of a pre-Quaternary clay-rich unit with a high content of smectite is highest
in the location nearest to the mofette showing the most intense CO2 emanation.
Most probably the clays form a domal feature below this mofette, as confirmed
by the 3-D geoelectric measurements by low electrical resistivities. The driving
force behind the updoming of the clays might be the pressure of uprising CO2.
Additionally, the more intense swelling of smectite due to higher rates of fluid flow at
these locations might also contribute to this phenomenon. Isolated quartz pebbles
dispersed in fine-grained sediments could have been transported upward by gas jets
bonded to vents during periods or events of intense gas emanation. The model of the
active mofettes has to consider its bonding to deep-seated faults, the presence of
sediment deformation structures due to gas pressure, upward transport of sediment
particles by gas jets and reducing conditions caused by the magmatic CO2 flux. |
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