Title: Exploring the impact of Plate Velocity Changes and Channel Rheology on Exhumation within Oceanic Subduction Models
Abstract: The mechanisms responsible for the exhumation of high-pressure (HP) rocks within oceanic subduction zones remain widely debated. Unlike in continental settings, where positive buoyancy aids exhumation, oceanic HP rocks like eclogites require additional forces due to their negative buoyancy. A driver for exhumation of dense eclogites has been proposed to be a drastic reduction in subduction velocity, which alters the stress state of the plate interface leading to the detachment and upward transport of crustal slivers. This hypothesis is based on simple analytical models that consider the interface as a uniform and parallel channel and thereby do not account for much of the complexity exhibited by plate interfaces in nature. To account for both this complexity and the frequent fluctuations of velocities over time exhibited by subduction zones on Earth, we develop time-dependent subduction models to examine the degree to which a time-dependent velocity influences HP rocks exhumation and underplating for different rheological parametrizations of the plate interface.
Our modeling results demonstrate that HP rock exhumation is a highly dynamic process that depends strongly on the phase (or velocity) of subduction, the depth of interest, and the rheology of the interface. For example, exhumation occurs episodically via corner flow in the shallow accretionary wedge only when the subduction velocity drops below 2.5 cm/yr. Stagnation of rocks, interpretable as underplanting within the channel, occurs deeper in the plate interface through episodic crustal slicing. A weaker rheology produces voluminous and continuous exhumation, while stronger interfaces produce scarce and discontinuous exhumation. As subduction velocity reduces further, exhumation then becomes more limited due to weakened corner flow, while stagnation increases overall. Dense eclogites, however, stop stagnating and instead start subducting, as a result of their negative buoyancy.
Overall, these results reveal complex interactions between plate velocity changes and deformation within the subduction channel, modulated by velocity changes, interface rheology, and the balance between exhumation and stagnation. The episodic nature of exhumation observed in our models aligns with the geological record, suggesting that transient changes in plate velocities impact the timing of this process within the lifetime of a subduction zone. As plate velocities are governed by large-scale tectonic and geodynamic forces, our results highlight the importance of large-scale subduction dynamics on the exhumation of HP rocks.
Biography: I am a PhD candidate in Marine Geosciences at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science. I hold a Bachelor’s degree in Physics from the University of Milan Statale and a Master’s degree in Physics of the Earth System from the University of Bologna (both are in Italy). My PhD research focuses on subduction zone Geodynamics, particularly the processes occurring at the plate interface, but I am generally interested in plate tectonics processes.
To join virtually: Zoom
Contact: valeria.turino@earth.miami.edu
U Miami Geodynamics Group Website: https://adamfholt.github.io
Recording: Zoom Recording (will be available within a week after the seminar)