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)

波希米亚地块，Variscan造山带的最东端，是中欧和西欧前二叠纪岩石最大的稳定大陆内单元之一。即便如此，从地震活动性或增强的二氧化碳通量和脱气方面来看，西部地区包括正在进行的地球动力学活动，这表明深部岩浆过程、地幔衍生流体及其迁移。地壳中地震群的发生、气体通量的变化与岩心和泉水同位素组成的变化之间似乎存在着潜在的相关性。此外，区内还发现了几座第四纪火山；它们的取食途径以及与深部岩浆作用的相互作用、总的构造格局和它们的地表表现还不完全清楚。解决关于这一复杂地球动力学系统的开放式地球科学问题是PIER-ICDP埃格裂谷项目的核心部分。2015/2016年，在对可能的钻孔位置进行现场表征的框架内，在Eger裂谷进行了大地电磁（MT）实验。MT数据检测地球的电阻率，这是一个对低电阻率相（如含水流体、部分熔体或金属化合物）的存在特别敏感的物理参数。该实验揭示了第一个区域地壳电导率模型。最突出的特征是为地幔流体提供通道的深层通道。它们位于剖面中部的Bublák和Hartoušov碎屑岩下方，以及剖面南部的第四纪泥岩下方。由于本实验的重点是岩纹和地震群，因此现场覆盖范围不足以进一步明确地将火星下的异常解释为一个补给通道或两个主要构造单元之间附近缝合带的印记。因此，我建议以第四纪火山的位置为中心进行MT实验，因为其中两个火山是计划的ICDP钻孔的候选者。主要目标是：(i)为钻探地点提供场地表征和基线研究；（ii）在浅层和地壳尺度上成像电导率，包括浅层马尔构造以及断层和缝合带等构造特征；（iii）成像流体通道及其与深部地壳岩浆源的关系；（iv）研究第四纪火山之间的空间关系。邻近的塔霍夫断裂带和萨克森图林根和Teplá-Barrandian单元之间的缝合带，(v)通过不同的地球物理、岩石物理、地质和微生物观测得出一致的地质解释。

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.