Active Magmatic Underplating in Western Eger Rift, Central Europe

Abstract

The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high‐velocity lower crust and relate them to the distribution and chemical status of mantle‐derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local‐scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high‐velocity lower crust with pronounced reflectivity and a high‐velocity reflection‐free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection‐free lower crust together with a strong reflector at its top at depths of ~28–30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

Mantle Degassing Through Continental Crust Triggered by Active Faults: The Case of the Baja California Peninsula, Mexico

“…The approach used in this work is general and can be applied to other continental areas where either magmatic or nonmagmatic gases are emitted. Indeed, Hrubcová et al () have used a similar approach for the case of the Western Eger Rift (central Europe).…”

Influence of CO2 Degassing on the Microbial Community in a Dry Mofette Field in Hartoušov, Czech Republic (Western Eger Rift)

“…Earthquake swarms usually occur in volcanic areas, geothermal fields, and ocean ridges, whereas intraplate earthquake swarms that are not connected to active volcanism are present in continental rifts, such as the Rio Grande Rift, the Kenya Rift, and the western Eger Rift ( Ibs-von Seht et al, 2008 ). Due to magmatic activity beneath the Cheb Basin, large-scale degassing of mantle-derived CO 2 (>99%) occurs, and traces of gases such as He, N 2 , Ar, and CH 4 are emitted ( Weinlich et al, 1999 ; Kämpf et al, 2013 ; Hrubcová et al, 2017 ; Bräuer et al, 2018 ). The gas migrates through the upper lithospheric mantle and the crust to the surface and mixes with water of deep thermal and shallow groundwater aquifers ( Bussert et al, 2017 ).…”

Large-scale electrical resistivity tomography in the Cheb Basin (Eger Rift) at an International Continental Drilling Program (ICDP) monitoring site to image fluid-related structures

“…The tectonic setting of the area has a great influence on the increased degassing of CO 2 at the surface. Since the early work of Irwin and Barnes (1980), it has become evident that a close relationship exists between the tectonic activity and anomalous crustal emissions of CO 2 . Due to their hydraulic permeability, faults can act as preferential pathways for the upward migration and release of deep fluids to the atmosphere in this area (Bankwitz et al, 2003a;Geissler et al, 2005).…”

“…The area is characterized by ongoing magmatic processes in the intracontinental lithospheric mantle. The most recent article on that topic by Hrubcová et al (2017) hypothesizes that this is caused by magmatic underplating. These processes take place in the absence of any currently active volcanism at the surface -the latest activity known is linked to the eruption of two scoria cones (Železná hůrka and Komorní hůrka) and two maar-diatreme volcanoes (Mýtina maar and Neualbenreuth maar, Mrlina et al, 2007Mrlina et al, , 2009Flechsig et al, 2015;Rohrmüller et al, 2018).…”