Magnetotelluric study of the eastern margin of the Bohemian Massif: relations between the Cadomian, Variscan, and Alpine orogeny
Abstrakt
Eastern margin of the Bohemian Massif is a geologically remarkable area, where three different orogenic cycles are meetingthe oldest, Cadomian, building a basement for younger cycles; a younger, Variscan; and the youngest, Alpine, covering the older units. In the past, this area was investigated by gravimetry and seismic methods.
Recently, we have supplemented broadband magnetotelluric measurements within the period range of 0.001-1000s, carried out on 29 stations distributed along a 140-km-long west-east regional profile. The profile direction was based on local geology and then confirmed by a dimensionality and directionality analysis.
Data showed moderate effects of cultural noise in the signals and could be successfully processed by robust methods. We carried out a 2D inversion of the data using the REBOCC approach.
The inversion results confirm the known near-surface geology and reveal deeper structures. On the west and in the central part of the profile, units of the Bohemian massif (the Moldanubian Zone, the Brunovistulicum) are interpreted.
In the east, the Western Carpathians units are encountered. Short-period data agree well with the known near-surface geology of all inner smaller units and bring new knowledge in particular on their thickness.
In the shallow structure, several conductive anomalies have been identified which are hypothesized to be related to graphitized layers in the Moldanubian Zone. From long-period data, a new image of the Moldanubian/Brunovistulicum contact and about the structure of the Brunovistulicum, especially the Brunovistulian Massifs, was obtained.