Site characterization of the PIER-ICDP drill holes by imaging the subsurface electrical conductivity structure: local and regional structure beneath Mytina and Neualbenreuth Maar (ConeEM)

点击翻译按钮获取中文摘要

The Bohemian Massif, the easternmost part of the Variscan orogenic belt, is one of the largest stable intra-continental units of pre-Permian rocks in Central and Western Europe. Even so the western part comprise ongoing geodynamic activity in terms of seismicity or enhanced CO2 flux and degassing suggesting deep magmatic processes, mantle-derived fluids and their migration. It seems to exist an underlying correlation between the occurrence of mid-crustal earthquake swarms, gas flux variations and changes of isotope composition at mofettes and springs. In addition, several Quaternary volcanoes have been discovered in the area; their feeding pathways and the interplay between deep magmatic processes, the general tectonic framework and their surface manifestation is not fully understood. Addressing open geo-scientific questions regarding this complex geodynamic system is central part of the funded PIER-ICDP Eger Rift project. Within the framework of a site characterization for possible drill locations, a Magnetotelluric (MT) experiment in the Eger Rift was conducted in 2015/2016. MT data sense the electrical resistivity of the Earth, a physical parameter that is particularly sensitive to the presence of low-resistivity phases such as aqueous fluids, partial melts or metallic compounds. This experiment revealed the first regional crustal conductivity model. Most prominent features are deep reaching channels providing pathways for mantle derived fluids. They are located beneath the Bublák and Hartoušov mofettes in the central part and beneath the Quaternary maars in the southern part of the profile. Since this experiment was focused on the mofettes and the earthquake swarms the site coverage is not sufficient to further interpret the anomaly beneath the maars unambiguously as a feeding channel or the imprint of the nearby suture zone between two major tectonic units.Therefore I propose a MT experiment centred on the location of the Quaternary volcanoes, since two of them are candidates of planned ICDP boreholes. The major objectives are (i) providing a site characterization and baseline study for drilling locations, (ii) imaging the electrical conductivity on shallow and crustal scale, including shallow maar structure as well as tectonic features such as fault and suture zones, (iii) imaging fluid pathways and their relation to a proposed deep seated lower crustal magmatic sources, (iv) investigate the spatial relation between the Quaternary volcanoes, the nearby Tachov fault zone and the suture zone between the Saxothuringian and Teplá-Barrandian units, (v) derive a consistent geological interpretation of different geophysical, petrophysical, geological and micro-biological observations.