Apatite as an indicator of fluid salinity: An experimental study of chlorine and fluorine partitioning in subducted sediments

Apatites from representative eclogite facies metasediments were examined and found to have low Cl contents close to ∼100 ppm. Calculations using our experimentally determined KdCl-OHAp-aq of 0.004 at 2.5 GPa, 630 °C indicate a low salinity character (0.5-2 wt% NaCleq) for the fluid formed during dehydration of subducted oceanic sediment at ∼80 km depth.