Constraints on Juan De Fuca Plate Hydration From Controlled-Source Wide-Angle Seismic Studies

Date: 4/24/2019

Time: 04:15 PM

Room: Puget Sound

Quantifying hydration of oceanic lithosphere entering subduction zones is critical for understanding the range of subduction phenomena governed by dehydration of down-going slabs. Yet a comprehensive quantification of water content of incoming plate for any segment of the global subduction system is lacking, and how water is stored and distributed at depth within incoming plates, and how this hydration state is linked to various subduction zone processes, is debated. Here we use controlled-source wide-angle seismic reflection/refraction data collected in 2012 across the Juan de Fuca plate and along the central Cascadia margin seaward from the deformation front to estimate both pore and structurally bound water content and their distribution from the overlying sediments to the upper mantle of the Juan de Fuca plate entering the central Cascadia subduction zone. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting may dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab beneath this portion of the Cascadia margin.

Presenting Author: Juan Pablo Canales

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