October 19 @ 4:00 pm - 5:00 pm CDT
EEPS Seminar: Whitney Behr, University of Texas
Abstract Title: Geologic heterogeneity and transient rheology of the deep subduction interface
The rheology of the deep subduction interface is fundamental to both large-scale and regional-scale plate dynamics, affecting plate velocities, styles and rates of exhumation of subducted material, and depths and style of seismicity. In this talk I will demonstrate how observations from the rock record can tell us fundamental information about the mechanical behavior of the deep roots of subduction megathrusts. I will focus on a spectacularly exposed exhumed analog of a warm subduction zone located on Syros Island in the Cyclades in Greece, which preserves blueschist- and eclogite-facies deformation fabrics within a wide range of protolith rock types (metabasalts, marbles, metavolcanics and metapelites). I will use these rocks to address two primary questions:
1) What controls the long-term viscosity of the deep subduction interface?
2) What processes may contribute to episodic tremor and slow slip (ETS) along the deep subduction interface?
I will make the case firstly that the viscosity of the plate interface is highly sensitive to subducted protolith rock type, and that switches from metamafic- to quartz-dominated protoliths with progressive subduction can result in plate velocity changes of up to several cm/yr and can substantially affect the exhumational style within the subduction channel. I will make the case secondly that smaller-scale heterogeneities within individual subducted protoliths may represent the rock record of ETS events similar to those observed along the deep interface in modern subduction zones (e.g. Cascadia).