Deformation structures in Plio- and Pleistocene sediments (NW Bohemia, Central Europe)

Abstract

The small intracratonic Cheb (Eger) Basin in NW Bohemia (Central Europe) is characterized by swarm earthquakes, many mineral springs and mofettes with upper mantle CO2 degassing and by neotectonic graben and basin structures. Especially in non-lithified Upper Pliocene clay formations of the basin, a variety of deformation patterns is exposed. They include non-tectonic and tectonic activity and comprise faulting and folding from µm- to km-scale. Previously unrecognized N-S- and ENE-striking faults are sites of mantle degassing and seismic activities. Confined-layer deformation and liquefaction structures hint to palaeoseismic events and gas escape activity. Cleavage-like arranged clay mineral plates represent the microfabric of clay within fault zones. For the first time the degassing channels of Upper Mantle fluids/gases through the Pliocene clay sediments can be documented: µm-scale micro-tubes were produced by the opening of Riedel shear planes induced by fault movements.

Active Magmatic Underplating in Western Eger Rift, Central Europe

“…It delineates the termination of the broad reflective zone and its change into a strong‐contrast interface. Its position is also in agreement with the surface manifestation of dextral shear fault zone Nová Ves of the same direction recognized by Bankwitz, Bankwitz, et al () at the northern edge of the Cheb Basin (see Figure a). Thus, the termination of reflectivity can be seen as a robust structural phenomenon manifested by several features at different crustal levels: (1) by the dextral shear zone detected by Bankwitz, Bankwitz, et al (), (2) by swarm seismicity at ~10 km depth, and (3) by the termination of reflectivity and change into the strong‐contrast interface at the lower crust.…”

“…These data show a strong reflector and absence of reflectivity toward the southeast in a prolongation of the northern shoulder of the Eger Rift (Figure ). Above, such termination of the lower crust reflectivity can be traced up to the surface where it is mapped by a shear fault zone detected by Bankwitz, Bankwitz, et al ().…”

“…Note the abrupt change of a thick lower crust in the northwest to a strong‐contrast interface in the southeast trending in the NE‐SW direction in a prolongation of the northern Eger Rift shoulder. The red line shows the position of the 9HR profile; the black cross marks the quarry with a detected dextral shear fault zone at the surface (after Bankwitz, Bankwitz, et al, ). (b) Reflection profile 9HR (after Mullick et al, ) with the projection of swarm earthquakes in the main NK focal zone (brown dots at ~10 km depth) above the termination of the lower crustal reflectivity.…”

Evidence for ascending upper mantle‐derived melt beneath the Cheb basin, central Europe

“…23, 24, 91) and the spring (no. 102, Table 1) with the highest 3 He/ 4 He ratios are positioned on previously unrecognized major fault zones within the unconsolidated sediments of the Cheb basin [ Bankwitz et al , 2003]. The presence of such high amounts of mantle‐derived 3 He may be an indication of still active geodynamics of the lithosphere.…”

Seismically triggered microbial methane production relating to the Vogtland NW Bohemia earthquake swarm period 2000, Central Europe

“…More than 10,000 micro-earthquakes in the Mahel et al (1984), Zoubek et al (1990) and Bankwitz et al (2003 Novy Kostel focal zone with magnitudes up to 3.3 were recorded by local seismic networks. Nine swarm phases were distinguished; five of them include event magnitudes greater than 3.0.…”