EGU25-15657, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-15657
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Unravelling cyclic fault healing in carbonates: A natural example for the interaction of mechanical and fluid-mediated processes
Berit Schwichtenberg1, Alfons Berger1, Marco Herwegh1, Christoph Schrank2,3, Michael W. Jones3,4,5, Stefano M. Bernasconi6, Dominik Fleitmann7, Cameron M. Kewish8,9, and Teo Neuenschwander1
Berit Schwichtenberg et al.
  • 1University of Bern, Institute of Geological Sciences, Bern, Switzerland (berit.schwichtenberg@unibe.ch)
  • 2Queensland University of Technology, School of Earth and Atmospheric Science, Brisbane, QLD, Australia
  • 3Queensland University of Technology, Planetary Surface Exploration, Brisbane, Australia
  • 4Queensland University of Technology, School of Chemistry and Physics, Brisbane, Australia
  • 5Queensland University of Technology, Central Analytical Research Facility, Brisbane, Australia
  • 6ETH Zürich, Geological Institute, Zürich, Switzerland
  • 7University of Basel, Department of Environmental Sciences, Basel, Switzerland
  • 8ANSTO Australian Synchrotron, Clayton, Australia
  • 9La Trobe University, Department of Mathematical & Physical Sciences, School of Computing, Engineering & Mathematical Sciences, Bundoora, Australia

During the interseismic phase, faults regain frictional strength through a process commonly referred to as fault healing. Key mechanisms include contact welding by dissolution-precipitation creep and cementation by mineral precipitation in fluid-rich environments. While much research has focused on experimental investigations of silicate systems, e.g. in slide-hold-slide experiments, the complex interaction between mechanical and chemical processes, as well as recurring fault healing over multiple earthquake cycles remain understudied. Particularly in the case of natural fault systems, the database is scarce as processes of interest occur at depth and show a low preservation potential during exhumation.

Here, we present a combination of microstructural and microchemical observations from a carbonate-hosted fault zone located within the Helvetic nappe stack of the south-western Swiss Alps which was recently exposed due to glacial retreat, creating excellent outcrop conditions. The microstructural record allows us to distinguish three major healing episodes within the principal slip zone. These episodes follow brittle deformation at sub-seismic to seismic rates, forming veins along sets of discrete fault-parallel fractures. Due to continuous brittle deformation, individual veins experienced subsequent mechanical overprinting which led to the modification of the vein texture, an increase in the local porosity and the formation of new fluid-rock interaction faces. Additionally, we use the unique geochemical fingerprint of each set of veins, documented and analysed by high-resolution X-ray fluorescence mapping of trace elements, to differentiate and characterize individual fluid pulses and dynamic changes in the physio-chemical conditions of the fluid-rock system over time. While we interpret the principal slip zone to represent the youngest deformation event in our study, adjacent vein-derived domains that are deformed by aseismic viscous processes represent relatively older structures. Comparison of the isotopic composition of newly formed calcite crystals with relict grains and the country rock provides insight into possible isotope fluid-rock equilibria during tectonic processes and therefore fluid sources. Measured stable oxygen isotopes (δ18O) show a significant influence of meteoric water while clumped isotope thermometry indicates temperatures of 65-120°C, which are at least 100°C lower than in the country rock and literature values of Tmax in the area.

Our results suggest that the observed microstructural record is representative of seismic deformation and associated fault healing caused by low-magnitude earthquakes at shallow crustal levels near the upper limit of the seismogenic zone. This interpretation is consistent with the depth distribution of current hypocenters within a seismically active structure that is located in the vicinity of our study area, the so-called Rawil Fault Zone. We, therefore, conclude that the processes identified in the exhumed tectonite samples can serve as proxies for active deformation and fluid flow at depth. In a wider context, this may offer valuable insights for geothermal exploration in southwest Switzerland.

How to cite: Schwichtenberg, B., Berger, A., Herwegh, M., Schrank, C., Jones, M. W., Bernasconi, S. M., Fleitmann, D., Kewish, C. M., and Neuenschwander, T.: Unravelling cyclic fault healing in carbonates: A natural example for the interaction of mechanical and fluid-mediated processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15657, https://doi.org/10.5194/egusphere-egu25-15657, 2025.