Neogene and Quaternary dikes and related joints as conduits for recent juvenile degassing: case studies from the seismically active region of NW-Bohemia, Czech Republic

Abstract

The contemporary occurrence of juvenile gas emissions at springs or mofettes in active volcanic areas can be observed worldwide. This correlation is less frequent in areas with dormant or post-volcanic activity. The NW-Bohemia/Vogtland region located at the Eger rift zone (Czech Republic) provides an intriguing example of this correlation between numerous Neogene-aged post-volcanism locations and juvenile fluid emission sites. Newly discovered dikes and diatremes are located close to vents with the highest helium isotope ratios (3He/4He) of about 6 Ra. Our results lend support to the hypothesis that feeder dikes and their fractured wall rocks should be considered the predominant conduits for the continuous upwelling of juvenile fluids. Moreover, 77% of the CO2 gas emission sites are located close to dikes or diatremes, i.e., within a distance of 4 km. Our studies reveal a spatial dependence of the Ra values at the spring sites with the estimated distances to the basaltic bodies. The results confirm the negative trend known from the literature. That is, Ra values decrease with increasing distance from the feeder dikes.

Re-inventories at two study sites in the Oberpfalz (Bavaria, Germany): Increase in RWA nests, herb biodiversity and dead wood in sustainably managed forests

“…Furthermore, a shift of the nests hot spots towards the NW-SE trending Erbendorfer fault line in MG is suggested to be caused by stronger degassing of the tectonically and structurally controlled Erbendorfer fault line, which promotes RWA nests settlements [16,19]. It is hypothesized that this process is triggered by regional seismicity (Figure 1a) as an important driving force causing microfracturing [42,43,86,87]. These new fractures provide pathways for juvenile fluids with mantlederived CO2 and Helium to migrate over long distances, indicating hidden volcanic structures in the vicinity of these degassing sites [86,87].…”

“…It is hypothesized that this process is triggered by regional seismicity (Figure 1a) as an important driving force causing microfracturing [42,43,86,87]. These new fractures provide pathways for juvenile fluids with mantlederived CO2 and Helium to migrate over long distances, indicating hidden volcanic structures in the vicinity of these degassing sites [86,87]. Additionally, seismic events lead to the formation of new emanation surfaces and pathways and a significant increase in the radon signal, although the applied stress remains constant over time [88].…”

Re-Inventories at Two Study Sites in the Oberpfalz (Bavaria, Germany): Increase in RWA Nests, Herb Biodiversity and Dead Wood in Sustainably Managed Forests

“…During the period between the inventories (four to seven years), seismic activity has increased, creating faults and providing degassing pathways in this region [88,89]. Such structures are the most important prerequisite for nest settlements [14][15][16][17][18][19][20][21][22][23]30,31].…”

“…Furthermore, a shift of the nest hot spots towards the NW-SE-trending fault line "Erbendorfer Linie" in MG (Figure 9) is suggested to be caused by stronger degassing of the tectonically and structurally controlled "Erbendorfer Linie", which promotes RWA nest settlements [16,19] due to an increase in regional seismicity as an important driving force causing micro-fracturing (Figure 1a). These new fractures provide pathways for juvenile fluids with mantle-derived CO 2 and Helium to migrate over long distances, indicating hidden volcanic structures in the vicinity of these degassing sites [42,43,88,89]. In addition, seismic events lead to the formation of new emanation surfaces and pathways and a significant increase in the radon signal, even though the applied stress remains constant over time [93].…”