Papers in Science Advances, Journal of Geophysical Research and Earth and Planetary Science Letters show that fluid introduction caused by earthquakes is key factor in initiating large-scale transformation of the Earth lower crust and upper mantle.
In a Nature paper, we show how shallow level Earthquake activity may trigger aftershocks that affect the lower crust and provide a top-down control on the structural and metamorphic evolution of the lower crust. Overpressured frictional melt may represent the strain weakening mechanism needed for deep earthquakes (Nature Geoscience, 2021).
Fluid introduction to dry lower crust of upper mantle follow in the wake of initial brittle deformation and trigger reactions with the wall rocks. Metamorphic reactions may lead to highly porous products, including a substantial amount of nanometer sized pores. In a Nature Geoscience paper, we demonstrate that nanoscale mass transport by ‘diffusio-osmosis’, is highly effective during replacement of feldspar minerals, the most abundant mineral group in the Earth crust. This transport mechanism was not previously considered in the geoscience literature.
Pressures exceeding the lithostatic may arise in any weak rock confined in a strong and highly stressed matrix. In a Scientific Reports paper, we demonstrate that this may explain the presence of high-pressure rocks at normal crustal depths. A new visco-elasto-plastic model was developed that describes the evolution of the lower crust from initial brittle fracturing, via subsequent fluid infiltration, to mechanical weakening and shear zone development (Communications Earth and Environment, 2022). I believe this is the most coherent, self-consistent, and accurate description of the mechanical and metamorphic evolution of the lower crust during orogeny described so far.
Interface effects control the progress of hydration reactions in systems subject to external stress. Novel experiments in a purpose-designed rig were carried out to study the effect of external stress on the hydration of periclase to brucite. This rig is attached to beamline#19 of the European Synchrotron Research Facility in Grenoble to enable direct observation of reaction progress by X-ray micro-tomography. In a G-cubed paper we report how the progress of this hydration reaction is halted if the mean stress exceeds ca. 30 MPa. At higher stress levels, the water layer between the reactant and product mineral is squeezed out. This is also demonstrated by a molecule-scale modelling study (Geochim Cosmochim Acta, 2021), and indicates that external tectonic stress may be essential for the progress of hydration reactions in the Earth crust and upper mantle. An atomic force microscopy (AFM) study indicates that surface forces may be very sensitive to fluid composition. Hence, it may be hard to draw general conclusions about interface forces for complex fluids (ACS Earth and Space Chemistry 2021).
ICDP drilling in Oman commenced in 2017/18. A DIME crew participated during the drilling in January and February 2018. Sampling and further studies took place on board the ODP drilling vessel Chikyu. Our studies demonstrate that the initial hydration of peridotites was associated with seismic deformation and introduction of sea-water derived fluids (Earth and Planetary Science Letters, 2021). Oxygen isotope and trace element data show that serpentinization occured at several kilometers depths in the oceanic lithosphere at temperatures around 200-250C.
