Dr. Eirini Poulaki
University of Miami

Topic: Underplating and the effects of fluids on the subduction plate interface

Academic host: Barra Peak

Abstract: Subduction zones drive plate tectonics and host some of the most catastrophic natural disasters, including earthquakes and volcanic eruptions. The interplay between structural and chemical metamorphic processes operating along the plate interface in subduction zones remains elusive; however, using suites of rocks that have been subducted and exhumed to the surface can give us direct insights into these processes. In this talk, I will present insights from several subduction complexes in Greece, Spain, and California. In the first part of the talk, I will demonstrate how integrating field observations, zircon and apatite petrochronology, and microstructural analyses can resolve the pre-subduction stratigraphy, subsequent juxtaposition, and polymetamorphic history during subduction underplating and mélange formation.

The style of underplating is controlled by the shear zone thickness, lithologic heterogeneity, and pore pressure during metamorphic dehydration reactions. These conditions may modulate the transition to smaller thrust earthquakes & slow slip events along the megathrust.

In the second part of the talk, I will show a suite how geochronologic and petrologic techniques can be linked with slow slip and brittle failure. CO2-rich fluids during exhumation along the subduction interface are recorded in mineral trace elements at the depths of episodic slow slip and tremor. These fluids are derived from underplated marble layers, and evidence of epidote/quartz crack-seal veins indicate that this event likely led to brittle failure at conditions of ~450 ºC and 8 kbar.