Periodic Reporting for period 2 - S-SIM (Sediments and Subduction Interface Mechanics: from micro-scale creep to global plate tectonics)
Okres sprawozdawczy: 2022-05-01 do 2023-10-31
This project seeks to test the hypothesis that sediment subduction strongly influences both the short-term (seismic) and long-term (million-year) mechanical behavior of the subduction interface. The underlying basis of this hypothesis is the possibility that sediments exhibit fundamentally different frictional and viscous properties than subducted mafic oceanic rocks— specifically that sediments are weaker at all conditions along the plate interface. To test this hypothesis, I have split my approach into three complementary and carefully linked tasks, including Task I. Observations from Exhumed rocks, Task II: Rock Deformation Experiments, and Task III: Numerical Modeling. Task I involves field geological campaigns in three sites representing different conditions of the plate interface, from shallow to deep. Task II involves three suites of experiments (closely linked to the field sites) aimed at quantifying the rheological properties of mafic rocks at different pressure-temperature conditions. Task III involves two types of numerical models: 1) seismo-thermomechanical modeling aimed at assessing the influence of heterogeneity on seismic slip behaviors, and 2) large-scale mantle convection modeling aimed at quantifying relationships and feedbacks between subduction interface rheology and plate speeds. This research has high potential to impact a number of Earth Science and related disciplines: establishing a lithological control on plate boundary strength, and hence on both subduction seismic behaviors and plate speeds, would establish a fundamental link between plate tectonics, climate, and life on planet Earth.
The work performed thus far includes the following:
1. Fieldwork in three focus areas, including southern Alaska (Figure 1), the Tauern Window in the Alps, and the Klamath Mountains in northern California. This work has highlighted distinctions between sediment- and basalt-dominated megathrust shear zones and has also allowed us to constrain the thicknesses, types of heterogeneities, and seismic properties of deep-seated subduction shear zones.
2. Several suites of numerical models have been developed, including 2D fully dynamic models of subduction interface dynamics, models of transient deformation frictional-viscous materials representing melange-type shear zones, and (in-progress) 3D models of subduction dynamics with incorporated surface processes (Figure 2). These models confirm the important role that interface rheology has on subduction dynamics as well as on transient deformation signals.
3. High temperature-pressure experiments on sodic amphibole have been conducted and thus far a diffusion creep flow law for blueschist is in press for publication (Figure 3). This flow law demonstrates that mafic oceanic crustal rocks at blueschist facies conditions are indeed more 'viscous' than metasedimentary protoliths at the same conditions.
1. Fieldwork in three focus areas, including southern Alaska (Figure 1), the Tauern Window in the Alps, and the Klamath Mountains in northern California. This work has highlighted distinctions between sediment- and basalt-dominated megathrust shear zones and has also allowed us to constrain the thicknesses, types of heterogeneities, and seismic properties of deep-seated subduction shear zones.
2. Several suites of numerical models have been developed, including 2D fully dynamic models of subduction interface dynamics, models of transient deformation frictional-viscous materials representing melange-type shear zones, and (in-progress) 3D models of subduction dynamics with incorporated surface processes (Figure 2). These models confirm the important role that interface rheology has on subduction dynamics as well as on transient deformation signals.
3. High temperature-pressure experiments on sodic amphibole have been conducted and thus far a diffusion creep flow law for blueschist is in press for publication (Figure 3). This flow law demonstrates that mafic oceanic crustal rocks at blueschist facies conditions are indeed more 'viscous' than metasedimentary protoliths at the same conditions.
We're providing a more advanced understanding of subduction dynamics through a multi-pronged approach combining numerical models, field observations, and rock deformation experiments. The impact of weak plate interfaces on slab sinking, rollback, and convergence rates offers a new framework for interpreting subduction dynamics.
The establishment of the first flow law for the creep of blueschists is a significant (and technologically challenging) milestone. This allows for a far more nuanced understanding of the strength variations among lithologies in subduction zones.
Our work is one of the first to link exhumed rock records to modern seismological observations. By correlating exhumed metasedimentary rocks with low-velocity layers observed in active subduction zones, our work provides important insights into the underlying geological factors affecting seismic behaviors.
Slow earthquakes are among the least understood phenomena in seismology. Our work through this project offers some of the first comprehensive overviews linking geophysical and geological records but also breaks new ground in elucidating the physical and mechanical processes at play. The insight that deep subduction interface deformation occurs in a widely distributed zone rather than along a discrete fault is important to seismic risk assessment. Additionally, the use of numerical models to explore the potential for finite-width brittle-viscous shear zones to produce slow slip opens a new frontier in our understanding of the complex interplay between stress, viscosity, and slip dynamics.
The establishment of the first flow law for the creep of blueschists is a significant (and technologically challenging) milestone. This allows for a far more nuanced understanding of the strength variations among lithologies in subduction zones.
Our work is one of the first to link exhumed rock records to modern seismological observations. By correlating exhumed metasedimentary rocks with low-velocity layers observed in active subduction zones, our work provides important insights into the underlying geological factors affecting seismic behaviors.
Slow earthquakes are among the least understood phenomena in seismology. Our work through this project offers some of the first comprehensive overviews linking geophysical and geological records but also breaks new ground in elucidating the physical and mechanical processes at play. The insight that deep subduction interface deformation occurs in a widely distributed zone rather than along a discrete fault is important to seismic risk assessment. Additionally, the use of numerical models to explore the potential for finite-width brittle-viscous shear zones to produce slow slip opens a new frontier in our understanding of the complex interplay between stress, viscosity, and slip dynamics.