Charakterisierung der PIER-ICDP Bohrungen Mytina and Neualbenreuth Maar durch die Abbildung der elektrischen Leitfähigkeit auf lokaler und regionaler Skala (ConeEM)
Physik des Erdkörpers
Zusammenfassung der Projektergebnisse
The region of West Bohemia and Upper Palatinate at the German/Czech border is situated at the junction of three different tectonic Variscan units and hosts the Eger Rift as well as a multitude of different fault systems. The entire area is characterized by ongoing magmatic processes in the intra-continental lithospheric mantle expressed by a series of phenomena such as the occurrence of repeated earthquake swarms, massive degassing of mantle derived CO2 and Pleistocene volcanism represented by several scoria cones and maars. The Eger Rift is one of the few intra-continental regions in Europe where such deep seated, active processes take place. Therefore, this area is studied by the PIER-ICDP initiative involving an interdisciplinary drilling program advancing the field of earthquake-fluid-rock-biosphere interaction. With the Magnetotelluric (MT) method we image the electrical resistivity distribution of the subsurface on a crustal/lithospheric scale. Thereby, MT positively maps fluid pathways since a strong contrast is expected between conductive phases such as aqueous fluids or partial melts and the resistive crystalline basement. First MT experiments within the PIER-ICDP project were conducted in 2015/2016 along two regional 2D profiles across the Eger Rift and a dense areal grid centred on the Bublák and Hartoušov mofettes. 2D models by Muñoz et al. (2018) reveal a conductive channel in the vicinity of the earthquake swarm region that extends from the lower crust to the surface forming a fluid pathway into the mofette region. A second conductive channel is present in the south of their model. However, due to the 2D setup of stations, it was not possible to unambiguously explain this conductor. Therefore, a follow-up MT experiment was conducted in 2018 extending the study area. During this experiment, broad-band MT data were recorded along three 50 − 75 km long profiles with additional stations across volcanic structures. We processed the data using advanced processing techniques and also reprocessed the data from the previous field campaigns to increase the data quality. Finally, we were able to derive the following models: (i) a regional 3D model covering several volcanic structures and degassing centres (ii) a inner 3D model of the regional profiles from 2015, (iii) local 3D model of the Bublák and Hartoušov mofettes and (iv) 2D and 3D models across the Neualbenreuth and Mýtina maar as well as the newly discovered Ztracený Rybnik and Bažina maars. By means of these different MT studies, we could derive a comprehensive image of the subsurface in this region from the lower surface up to the surface on a regional as well as on a local scale. We were able to image following important structures: (i) Several spatially separated magma/fluid reservoirs at the lower crust, (ii) together with their ascent paths for fluids and gases from these reservoirs to several degassing centres at surface, (iii) the sedimentary Cheb Basin and (iv) the sedimentary infill of the maars, which allows an estimate of the dimensions of the maar diatremes and the depositional history. Furthermore, we were able to answer some questions which arose from the previous measurements. For instance, we figured out that the second conductor in the 2D model of Muñoz et al. (2018) is neither caused by the volcanic structures nor by a fault and suture zone. Instead, it is a projection into profile line of an off-profile conductive feature located several kilometres to the east. Moreover, we found that the hypo-centres of the swarm earthquakes are located around the fluid pathway indicating that the earthquakes are caused by fluid migration and pressure changes within the channel similar to the non-volcanic tremors that are observed at Cholame along the San Andreas Fault. In addition, we determined that the fluids and gases probably migrate horizontally into the Bublák and Hartoušov mofette fields originating from an ascent path several kilometres to the west.
Projektbezogene Publikationen (Auswahl)
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3D imaging of the subsurface electrical resistivity structure in West Bohemia/Upper Palatinate covering mofettes and Quaternary volcanic structures by using Magnetotellurics. Tectonophysics, 833(c(2022, 6)), 229353.
Platz, Anna; Weckmann, Ute; Pek, Josef; Kováčiková, Světlana; Klanica, Radek; Mair, Johannes & Aleid, Basel
