EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veins

Ismay Vénice Akker1, Christoph E. Schrank2, Michael W.M. Jones3, Cameron M. Kewish4,5, Alfons Berger1, and Marco Herwegh1
Ismay Vénice Akker et al.
  • 1Institute of Geological Sciences, University of Bern, Bern, Switzerland
  • 2School of Earth, Environmental, and Biological Sciences, Queensland University of Technology, Brisbane, Australia
  • 3Central Analytical Research Facility, Institute of Future Environments, Queensland University of Technology, Brisbane, Australia
  • 4Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Victoria, Australia
  • 5Australian Nuclear Science and Technology Organisation, Australian Synchrotron, Victoria, Australia

In plate-convergent settings, fluid-saturated sediments dehydrate during subduction. The sediments are subsequently accreted to the upper plate. Along their dehydration-deformation path, the initial unconsolidated soft marine sediments become thick, foliated, impermeable meta-sedimentary sequences. Fluid flow through such ‘non’-porous low-permeability rocks is concentrated in fracture networks, ranging from the mm- to the km-scale. We study the interplay between ductile and brittle deformation processes and fluid flow by investigating calcite veins in slates from the exhumed European Alpine accretionary wedge across scales (µm to km). These slates experienced peak metamorphic temperatures between 200°C and 330°C and represent the transition between the upper aseismic and seismic zone. With the use of Synchrotron X-ray Fluorescence Microscopy (SXFM), we investigate the slates by visualizing trace-element distributions. This technique shows that alternating cycles of slow pressure-dissolution processes and brittle fracturing persist over long time scales. At the micron-scale, pressure solution of the initial carbonate-rich slates is indicated by an enrichment of newly recrystallized phyllosilicates on cleavage planes and in pressure shadows. These ductile deformation features are mutually overprinted by calcite veins (aperture 10 µm), which are nicely visualized with Sr-SXFM maps. Increasing compaction and recrystallization in the slate-rich matrix leads to progressed dehydration resulting in an increased pore fluid pressure and subsequent hydrofracturing. The micron-sized fractures are immediately filled in with minerals, which are oversaturated at that time in the fluid, resulting in the formation of (i) micron-veinlets. Micron-veinlets collect (ii) into mm-cm sized veins, which themselves form (iii) vein arrays and (iv) mega-arrays, respectively at the 50-100 m and 300-400 m scale. This upscaling of fluid pathways indicates a localised fluid transport through the accretionary wedge, which has important implications for the understanding of the mechanical stability of the accretionary wedge and related seismic activity.

How to cite: Akker, I. V., Schrank, C. E., Jones, M. W. M., Kewish, C. M., Berger, A., and Herwegh, M.: The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6845,, 2020