The current state of the hidden magmatic process beneath the western Eger Rift after the 2011 earthquake swarm traced by isotope studies

• Applicant: Dr. Karin Bräuer
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252970106

As a result of the detailed isotope-geochemical studies of the mantle-derived fluids related to the 2000 and 2008 earthquake swarms the temporal seismically induced release of crustal derived components could be identified at degassing locations along the Pocatky Plesna Fault Zone (PPZ) and at degassing sites along the Marianske Lazne Fault (MLF), but was also observed in the Vogtland area. Both, after the swarms 2000 and 2008, the admixture of crustal derived components to the steady mantle-derived fluid flow were repeatedly detected for about two years. Besides that a clear increase of mantle-derived helium (up to 6 Ra) was observed at locations in the Cheb basin at least since 2000. This increase indicates the existence of an active magmatic reservoir in the upper mantle beneath the Cheb basin. Superimposed to the progressive increase of mantle-derived helium further temporal increased portions of mantle-derived helium (to 6.3 Ra) were observed before the 2000 and 2008 earthquake swarms at locations close to the Novy Kostel focal zone (NKFZ). The recorded anomalies indicate that both, the 2000 and the 2008 swarm, seems to be linked with supply of fresh magma from a less degassed reservoir in the upper mantle. That means from the view of fluids both swarms seems to be triggered by hidden magma intrusions within the lithosphere. No fluid data could be recorded accompanying the earthquake swarm 2011. Thus, it is yet unknown whether the portion of mantle-derived gas has increased or decreased in the western Eger Rift area in relation to the latest earthquake swarm, and whether indications exist for a further spatial expansion of the area with increased portions of mantle-derived gas in the western Eger Rift, respectively?Therefore, the proposal is mainly focussed on two aims: (1) to evaluate and compare the geodynamic situation within the three degassing centres Cheb Basin (CB), Marianske Lazne and surroundings (ML) and Karlovy Vary (KV) after the earthquake swarm 2011, and (2) to evaluate the fluid signatures at the degassing locations close to the piece of the planned seismic and geoelectric profile together. As a result of the planned fluid studies an update of the distribution pattern of mantle-derived gas is to expect in comparison to situation about 20 years ago. The new fluid data, regional and close of the profiles of geophysical research, allow the evaluation the permeability of fluid migration paths supplying the respective sites by their gas characteristic at the surface and provide information on the current state of the magmatic reservoir. The final discussion of all data will assist the interpretation of spatial anomalies and indications of ascending fluid paths, respectively identified in geophysical studies and will supply essential information for a future ICDP drilling in the western Eger Rift.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1006: International Continental Scientific Drilling Program (ICDP)
• Participating Person: Dr. Horst Kämpf