Nonvolcanic Carbon Dioxide Emission at Continental Rifts: The Bublak Mofette Area, Western Eger Rift, Czech Republic

Abstract

This study presents the results of gas flux measurements of cold, mantle-derived CO2 release at the Bublák mofette field (BMF), located inside of the N-S directed Počátky Plesná fault zone (PPFZ). The PPFZ is presently seismically active, located in the eastern part of the Cheb Basin, western Eger Rift, Central Europe. The goal of the work was to identify the linkage between tectonics and gas flux. The investigated area has a size of 0,43 km2 in which 1.115 locations have been measured. Besides classical soil CO2 gas flux measurements using the closed chamber method (West Systems), drone-based orthophotos were used in combination with knowledge of plant zonation to find zones of high degassing in the agriculturally unused part of the BMF. The highest observed soil CO2 gas flux is 177.926,17 g m-2 d-1, and the lowest is 0,28 g m-2 d-1. Three statistical methods were used for the calculation of the gas flux: arithmetic mean, kriging, and trans-Gaussian kriging. The average CO2 soil degassing of the BMF is 30 t d-1 for an area of 0,43 km2. Since the CO2 soil degassing of the Hartoušov mofette field (HMF) amounts to 23 t d-1 for an area of 0,35 km2, the average dry degassing values of the BMF and HMF are in the same magnitude of order. The amount of CO2 flux from wet mofettes is 3 t d-1 for the BMF and 0,6 t d-1 for the HMF. It was found that the degassing in the BMF and HMF is not in accordance with the pull-apart basin interpretation, based on the direction of degassing as well as topography and sediment fill of the suggested basins. En-echelon faults inside of the PPFZ act as fluid channels to depth (CO2 conduits). These structures inside the PPFZ show beginning faulting and act as tectonic control of CO2 degassing.

Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene Mýtina Maar (Czech Republic)

“…1, 2). The western part of the WSW-ENE-trending Eger Rift, particularly the Cheb Basin, which formed along NNW-SSEtrending faults (Špičáková et al 2000;Rojik et al 2014), is at present the most active geodynamic region in the European Cenozoic Rift System (ECRIS) with a high number of earthquake swarms at least in the last 40 years (Fischer et al 2014;Vavryčuk and Adamová 2018) as well as mantlederived CO 2 -degassing (Weinlich et al 1999;Bräuer et al 2009Bräuer et al , 2014Kämpf et al 2013Kämpf et al , 2019Nickschick et al 2015). The progressive increase of the He 3 /He 4 ratio at the eastern part of the Cheb Basin since about 2000 with shorttime peaks up to 6.3 R a in 2000 and 2006 at the Bublák mofette indicates an ascent of less degassed magma (dyke intrusion) from the lithospheric mantle reservoir into the crust (Bräuer et al 2009(Bräuer et al , 2018.…”

Microbial Signatures in Deep CO2-Saturated Miocene Sediments of the Active Hartoušov Mofette System (NW Czech Republic)

“…The CO 2 originates from active magma chambers at the crust-mantle boundary and from lithospheric mantle depths of about 65 km (Heuer et al, 2006 ; Bräuer et al, 2009 ). The CO 2 preferentially migrates to the surface as component of supercritical fluids in the lower crust or either dissolved in water or as a free gas phase along deep-seated faults in the upper crust (Weinlich et al, 1999 ; Weise et al, 2001 ; Bräuer et al, 2011 ; Kämpf et al, 2019 ). The PPZ started to develop at the boundary from Mid to Late Pleistocene (Bankwitz et al, 2003a , b ).…”

“…Previous investigations from sediments of the upper 9 m at the Hartoušov mofette system revealed that ascending CO 2 -containing fluids cause sediment fluidization, hydrofracturing, and geochemical alterations e.g., sediment bleaching, mobilization of metals and the preservation of organic matter (Flechsig et al, 2008 ; Rennert et al, 2011 ; Mehlhorn et al, 2016 , 2018 ; Rennert and Pfanz, 2016 ; Bussert et al, 2017 ; Liu et al, 2018 ). At the surface, CO 2 exhalation occurs in form of diffuse degassing structures (DDS, namely dry mofettes) and localized water filled, pool-like structures (wet mofettes) (Flechsig et al, 2008 ; Kämpf et al, 2013 , 2019 ; Nickschick et al, 2015 , 2017 ).…”

“…Dry mofette areas display high CO 2 soil gas concentrations, low soil pH, accelerated silicate weathering, leaching of base cations, anomalous vegetation patterns, low taxonomic, and functional biodiversity of soil biota and a limited microbial degradation of soil organic matter (SOM) (Rennert et al, 2011 ; Hohberg et al, 2015 ; Beulig et al, 2016 ; Rennert and Pfanz, 2016 ; Kämpf et al, 2019 ). In comparison to reference sites, the microbial community differs in composition and is dominated by anaerobic chemolithoautotrophic microorganisms, e.g., acidophilic, methanogenic, and sulfur-cycling organisms (Beulig et al, 2015 , 2016 ; Liu et al, 2018 ).…”

Insight Into Hartoušov Mofette, Czech Republic: Tales by the Fluids

“…In order to investigate relationships between geodynamic processes, CO 2 degassing, and the continental "deep biosphere, " three boreholes were drilled in the intensively degassing HMF (Dahm et al, 2013, 26 t/d of diffuse soil degassing; Kämpf et al, 2019). F1 [corresponding to 1H-031 in Bräuer et al (2018) andVP8303 in Fischer et al (2020)] was drilled in 2007 down to ∼28 m below ground and taps into a CO 2saturated, confined aquifer.…”