More - Mofette Research

• Applicants: Professor Johannes Barth, Ph.D.; Dr. Heiko Woith
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2019 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419880416

• Final Report Year: 2021

Final Report Abstract

The mofette research project MoRe aimed to clarify physical links between fluid properties, their pathways and swarm earthquakes with special emphasis on possible influences of drilling activities on the local and regional fluid regime. At the Hartoušov mofette, a sophisticated online gas analytical system was set up to monitor flow, composition, and isotope signatures of the gases from different depth levels. This multi-level setup allows – for the first time – to monitor vertical gradients in the fluid regime. Gas migration velocities can thus be measured directly (from the arrival times of anomalies at different depth levels), and potential contaminations/dilutions of mantle fluids with crustal and/or meteoric fluids during their ascent to the Earth’s surface can be quantified. Due to lack of sufficiently large earthquakes within the funding period, the hypothesis that mofette gas emissions are modulated by seismic events could not yet be tested. Short-term pressure perturbations during the drilling of a new 239 m deep well led to a complex transient response of the local fluid system without any extreme reactions – likely because a heavy drillmud kept the borehole pressure under control and thus no gas eruptions occurred. No changes of fluid properties were observed outside the Hartoušov mofette field at the other mofettes within the Cheb basin. CO2 concentrations were above 99.1% in most samples, while O2 and N2 were below 0.6%. He ranged from 0.06 to 76.83 µmol/mol and CH4 was mostly below 12 µmol/mol. Isotope compositions of helium and carbon in CO2 ranged from 2.32 to 5.86 RA and from -3.2 to -1.3 ‰ versus V-PDB, respectively. Extraordinarily low CH4/3He ratios were observed at the Hartoušov mofette field, which need further research to understand the origin of CH4. Normally, a DIC increase corresponds to a decrease of δ13CDIC when the CO2 source is of biological origin. In the Cheb basin, a reverse trend of increasing DIC contents with increasing δ13CDIC values likely indicates varying degrees of CO2 addition, predominantly from the mantle. Stable isotope measurements revealed that some water isotope compositions do not fall on local meteoric water lines (LMWL). Shifts to the left are unusual and could have been caused by oxygen exchange during H2O-CO2 interactions. This opens the possibility to calculate relative proportions of H2O and mantle-derived CO2 via an isotope equilibrium model.

Publications

• (2020): Multi-Level Gas Monitoring: A New Approach in Earthquake Research, Frontiers in Earth Science, 8, 585733
  Woith, H., Daskalopoulou, K., Zimmer, M., Fischer, T., Vlček, J., Trubač, J., Rosberg, J.-E., Vylita, T. & Dahm, T.
  
• (2020): Variations of gas compositions during a drilling process: A key study on the Hartoušov Mofette, Czech Republic - Abstracts, EGU General Assembly 2020
  Daskalopoulou, K., Woith, H., Zimmer, M., Niedermann, S., Bag, C. D., Bauz, R., Trubac, J., Fischer, T.
  
• (2021): Insight into Hartoušov Mofette, Czech Republic: Tales by the fluids, Frontiers in Earth Science, 9, 615766
  Daskalopoulou, K., Woith, H., Zimmer, M., Niedermann, S., Barth, J.A.C., Frank, A.H., Vieth-Hillebrand, A., Vlcek, J., Bağ, C.D. & Bauz, R.