Fig. 2
From: Mantle hydration and Cl-rich fluids in the subduction forearc
Relationships between fluid fraction, salinity, and electrical conductivity of the forearc mantle (modified from Reynard et al., 2011). Electrical conductivity increases from 10−3 to 10−4 S.m-1 (background of MT studies) up to ca. 1 S.m−1 from cold to hot subduction zones due to an increase in salinity of fluids at constant fluid fraction (dashed arrows) or an increase of fluid fraction at constant salinity (solid arrows). Inferred starting fluid composition match that expected for fluids issued by dehydration of altered oceanic crust (dark green shaded area) assuming Cl totally is dissolved in the fluid (Ito, et al. 1983). In Cascadia, the hottest subduction zone, extensive serpentinization is inferred from seismology. Modest values of conductivity around 2 10−2 S.m−1 are observed in Northern Cascadia. They are interpreted as dilution of saline fluids by “flooding” with additional low-salinity water from slab dehydration that are no longer consumed by serpentinization once it has reached completion (full red arrow), or by a decrease of fluid fraction due to fluid migration toward the arc (dashed red arrow, see Fig. 3). Cl content of serpentinites in equilibrium with fluid of a given salinity is calculated assuming a fluid/solid fractionation coefficient of 100 (Scambelluri, et al. 1997)