Fig. 1
From: Mantle hydration and Cl-rich fluids in the subduction forearc
Seismic velocities of rocks and minerals representative of the various lithologies in subduction zones. a Isotropic sound velocities showing that most rocks except quartzite lie close to VP/VS ratio of √3 or Poisson ratio of 0.25 (solid line). The effect of hydration is to reduce sound velocities (green arrow). A similar trend exists for the transformation of dry eclogite to hydrated gabbro. Lw and gl stand for lawsonite and glaucophane, respectively. b Effect of anisotropy in ultrabasic rocks and pore fluid overpressure (red arrow). Effects of anisotropy are especially marked in foliated serpentinites (Bezacier, et al. 2013; Bezacier, et al. 2010a) with the VS1 branch (full circles) and VS2 branch (crosses) covering a broad range of absolute velocities and VP/VS ratios. A foliated layer of serpentinite can explain the properties of anisotropic layers observed just above the subducting crust of Cascadia (N09, Nikulin, et al 2009). Ultra-low-velocity layers (A09-S09, Audet, et al. 2009, Song, et al. 2009) require pore fluid overpressure (Peacock, et al. 2011). Atg antigorite serpentinite, CPx clinopyroxene, OPx orthopyroxene, and Ol olivine. Olive symbols olivine aggregate and dark green symbols pyroxene-rich peridotite