Seismically induced changes of the fluid signature detected by a multi‐isotope approach (He, CO₂, CH₄, N₂) at the Wettinquelle, Bad Brambach (central Europe)

Abstract

We present a study considering the systematics of gas and isotope compositions (3He/4He, δ13CCO2, δ13CCH4, δ15N) of a permanent magmatic CO2 flux in the hydrothermal system of the spring “Wettinquelle” in Bad Brambach and their relation to the seismic activity beneath the western Eger rift. The gas and isotope compositions were monitored for more than 3 years. The time series includes periods before, during, and after a 4‐month‐long seismically active period from the end of August to the end of December 2000. Shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period. In case of helium and nitrogen, isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period, contemporaneous with a water level anomaly of the well VL4 near the Wettinquelle. On the one hand, preseismic deformations may be responsible for the observed isotope anomalies; on the other hand, coseismic fracturing processes in the surroundings of the hypocenters may play a role. Both effects produce greater permeability and result in the release of crustal fluids. The migration and admixture of these crustal components to the “permanent” upper mantle‐derived fluid flux result in geochemical anomalies that persist for more than 2 years. The results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region Vogtland/NW Bohemia.

Construction of a Newly Designed Small-Size Mass Spectrometer for Helium Isotope Analysis: Toward the Continuous Monitoring Of 3He/4He Ratios In Natural Fluids

“…Moreover He can escape from the Earth's atmosphere to outer space because of its high velocity in the upper atmosphere, resulting in low concentrations of He in the atmosphere (5.2 ppm). ese features make the 3 He/ 4 He ratio a very sensitive tracer for the transportation of volatiles and identi cation of their source reservoirs. erefore, if we continuously monitor the isotopic ratio of He in uids derived from the interior of the Earth, it would be possible to detect a change of 3 He/ 4 He ratio resulting from He release with various 3 He/ 4 He ratios from di erent reservoirs as the result of seismic or volcanic activities occurring in the crust and/or mantle.…”

“…ese features make the 3 He/ 4 He ratio a very sensitive tracer for the transportation of volatiles and identi cation of their source reservoirs. erefore, if we continuously monitor the isotopic ratio of He in uids derived from the interior of the Earth, it would be possible to detect a change of 3 He/ 4 He ratio resulting from He release with various 3 He/ 4 He ratios from di erent reservoirs as the result of seismic or volcanic activities occurring in the crust and/or mantle. For example, variations in 3 He/ 4 He ratios in groundwater samples have been observed a er earthquakes, which were considered to be the result of changes in groundwater ow systems due to the destruction of brittle, crustal rocks associated with earthquakes.…”

“…Helium in several geochemical reservoirs of the Earth has characteristic isotopic ratios, i.e., 3 He/ 4 He= 1.4×10 −6 in air, 1.1×10 −5 in the upper mantle, and <10 −7 in the crust, resulting in a wide range of 3 He/ 4 He ratios of more than three orders of magnitude in geochemical/geological samples. 1,2) e di usivity of helium is very high compared to other geochemical tracers because of its low molecular weight and chemical inertness.…”

“…erefore, if we continuously monitor the isotopic ratio of He in uids derived from the interior of the Earth, it would be possible to detect a change of 3 He/ 4 He ratio resulting from He release with various 3 He/ 4 He ratios from di erent reservoirs as the result of seismic or volcanic activities occurring in the crust and/or mantle. For example, variations in 3 He/ 4 He ratios in groundwater samples have been observed a er earthquakes, which were considered to be the result of changes in groundwater ow systems due to the destruction of brittle, crustal rocks associated with earthquakes. [3][4][5] Sano et al 6) reported post-eruptive increase in 3 He/ 4 He ratios in steam wells from volcanic islands, possibly resulting from additional magmatic He discharges from activated magmas.…”

Drilling into an active mofette: pilot-hole study of the impact of CO&lt;sub&gt;2&lt;/sub&gt;-rich mantle-derived fluids on the geo–bio interaction in the western Eger Rift (Czech Republic)

“…The combination of intense CO 2 -rich mantle degassing, ongoing seismic activity including earthquakes swarms and microbiological activity that occurs in the Cheb Basin (western Eger Rift, Czech Republic; Fig. 1) is exceptional and allows the study of bio-geo interactions as part of active geodynamic processes in the lithosphere (Kämpf et al, 1989(Kämpf et al, , 2013Wagner et al, 2007;Bräuer et al, 2007Bräuer et al, , 2008Bräuer et al, , 2011Bräuer et al, , 2014Dahm et al, 2013;Fischer et al, 2014Fischer et al, , 2017Alawi et al, 2015;Schuessler et al, 2016).…”