Fig. 3

Potential location of high-salinity fluids in the forearc mantle and pathways of mixing with hotsprings and the volcanic arc. Magnetotelluric profiles in the Cascadia subduction (Wannamaker, et al. 2014) are shown on the right and are interpreted on the left. The southernmost section shows the highest conductivity in the forearc (green ellipse) that is interpreted as up to 1 m NaCl fluids using diagrams in Fig. 2. Lower forearc conductivities (green ellipses) on the other two sections indicate dilution by more than one order of magnitude by low-salinity dehydration fluids from the slab or a decrease by more than one order of magnitude of the fluid fraction. This is attributed drainage to shallow aquifers above the forearc region (e. g., the Willamette basin in Oregon, WB) or to the volcanic arc (VA) region (green arrows). High-conductivity regions further east are ascribed to melt-rich regions under the volcanic arc (red ellipses)