UMD: Boise State’s Kohn on Shear heating in subduction zones

2017 University of Maryland Geology Colloquium Series

Friday, November 17th 2017 at 3:00 pm
in PLS 1130, College Park campus

Matthew Kohn
Boise State University

Shear heating controls mineralogy, seismicity, and convection in subduction zones

Popular thermal-mechanical models of modern subduction systems are c. 300 °C colder at c. 50 km depth – the seismic-aseismic transition – than pressure-temperature conditions determined from exhumed metamorphic rocks, i.e. “Rocks are hotter than models” (Penniston-Dorland et al., 2015, EPSL). Subduction zone thermal structure is crucial for predicting depths of seismicity, fluid release, and sub-arc melting conditions. In this talk I will show that adding realistic shear stresses to thermal models quantitatively reproduces surface heat flow and the pressure-temperature conditions recorded by exhumed metamorphic rocks. A consistent seismic-aseismic transition depth of c. 50 km, however, is difficult to explain through mineralogical or thermal weakening mechanisms. Rather, I propose that mechanical removal of rheologically weak and buoyant rocks along the subduction interface leads to seismic decoupling and dynamic coupling bet! ween slab and mantle to drive mantle wedge convection and arc volcanism.

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