Computing Rates and Distributions of Rock Recovery in Subduction Zones

Buchanan Kerswell1, Matthew Kohn1, Taras Gerya2,

1Department of Geology & Environmental Earth Science, Miami University, Ohio

2Department of Earth Sciences, ETH-Zürich

October 26 2022

Acknowledgments

High performance computing

  • Borah (Boise State University)
  • Euler (ETH Zürich).

Special thanks


Glossary

Term Description
markers numerical objects representing rock bodies in geodynamic simulations
rocks subduction-related rock samples w/ PT estimates and other metadata
recovery detachment of rock bodies from the subducting plate (max PT\(^*\))
recovery mode region in PT space with high sample density [high frequency]
PT pressure temperature
HP high pressure
OP oceanic plate
UP upper plate

Summary

Research questions

Where are rocks recovered along subduction interface shear zones?

How do recovery rates and distributions vary among subduction zones?

How do numerical and empirical PT distributions compare?




Main findings

Markers are overwhelmingly detached from ≤ 1 GPa

PT grads correlate w/ OP age & UP thickness, while depths correlate w/ velocity

Few markers detach from the highest-density regions of natural samples

Background  Where are rocks recovered from? How many?

Few rocks are recovered, but all come from the interface

Calvert et al. (2020)

The interface

Deformation styles

  • Stick-slip [discrete brittle]
  • Shear zone [mixed]
  • Coupled [distributed viscous]
  • Depends on dehydration rxns


Seismic properties

  • Low velocity zones (LVZs)
    • Few kms thick
    • High \(V_p/V_s\) ratio
    • High Poisson ratio

Background  Where are rocks recovered from? How many?

Geophysical images hint at shear zone structure…

Tewksbury-Christle & Behr (2021)

…and SZ rocks preserve exquisite detail