GEOLOGICAL Research
Research interests and links to my peer-reviewed published papers
Outcrop overview of a dark purple anorthosite host rock at Nusfjord East cross-cut by bleached white shear zones of variable widths (hammer for scale). Between the shear zones, the purple anorthosite is decorated by pseudotachylytes.
ABOUT
I am interested in deformation processes and the causal links to fluid-rock interaction and metamorphism across a wide range of scales, stretching from the nanoscale to the tectonic scale. Of particular interest at the moment are deformation mechanisms occurring at the grain scale, which sheds light on the behaviour of geological materials under stress, and includes the diffusion of elements through minerals and pores. Fieldwork with a strong structural geology framework is the backbone of my research, coupled with lab techniques such as SEM (BSE, CL, EBSD), EMPA, and 3D micro-tomography (Avizo, Ilastik).
As of May 2025, I am a Postdoc Research Assistant in the project titled “Trigger”, funded by the German Ministry of Energy at the Johannes Gutenberg Universität Mainz. Within the project, I’ll be focusing on acquiring and processing 3D microtomography datasets of traditional geothermal reservoir rocks of the Upper Rhein Graben, characterizing porosity and permeability, and fluid-rock interactions before and after deformation and flow-through experiments.
EDUCATION
2025 PhD in Crustal Processes at the University of Oslo, Norway
2013 MSc in Geology at Lunds Universitet, Sweden
2011 BSc (Honours) in Geology and a minor in Geophysics at the University of Calgary, Canada
PUBLICATIONS
2025
Mechanisms of Aqueous Fluid Infiltration and Redistribution in a Lower-Crustal Pseudotachylyte-Bearing Fault
Stephen Paul Michalchuk, Mona Lueder, Nils B. Gies, Markus Ohl, Jörg Hermann, Luca Menegon
Plain Language Summary
Earthquakes are effective in fracturing rocks and creating pathways for fluids to flow and infiltrate deep within an otherwise dry and strong host rock. Fluids interacting with these dry and strong rocks, especially those in the lower crust at >25 km depth, may induce chemical reactions, produce new weaker minerals, and deteriorate the overall strength of the host rock. Areas that have become weaker will localize deformation and form ductile shear zones. The mechanistic processes that produce this transformation are poorly constrained and are the subject of this study. Using specialized microscopy techniques that measure the mineral's crystallographic orientation and the H2O content within plagioclase feldspar, we document that a single-event earthquake rupture in the lower crust can liberate and mobilize a small amount of locally sourced H2O over short distances along fractures. However, without a sustainable source of H2O, fractures will heal themselves and consume the free H2O. We determined that repeated earthquake events, which repeatedly fracture the dry host rock into increasingly smaller fragments and mobilize fluids after each event, will form volumetrically thicker sequences of wet fine-grained layers that can easily localize strain and form ductile shear zones.
Link to the open access article: Geochemistry, Geophysics, Geosystems
2023
Dynamic evolution of porosity in lower-crustal faults during the earthquake cycle
Stephen Paul Michalchuk, Sascha Zertani, François Renard, Florian Fusseis, Alireza Chogani, Oliver Plümper, Luca Menegon
Plain Language Summary
Earthquakes create fractures and increase the porosity in crustal rocks. These fractures can help transport fluids to newly accessible regions in the crust, which in turn may kickstart metamorphic reactions, and potentially alter the rheology. However, very little is known about the mechanisms, the microstructural context, and the morphology of this increased porosity. We analysed ancient earthquake-generated frictional melts (pseudotachylytes) and their immediate damage zone in the host rock, as well as plasticly deformed pseudotachylytes, that have since been exhumed from depth and are now exposed at the surface in Lofoten, Norway. We analysed these rocks to determine the processes that create porosity and how this porosity evolves with increasing plastic deformation. The pseudotachylyte hosts more porosity than the damage zone immediately flanking the vein, in particular there is a high concentration of porosity around garnets. We interpret this porosity to have formed as a result of the metamorphic growth of garnet. Much of the fracture-related porosity created during the initial earthquake has been efficiently sealed. Porosity is greatly reduced in the sheared pseudotachylytes because of solution-precipitation processes that operated during ductile. Porosity reduction may reflect fluid consumption, leading to shear zone hardening and possibly new pseudotachylyte formation.
Link to the open access article: Journal of Geophysical Research: Solid Earth
