Abstract. This study aims to experimentally constrain the water storage capacities of
olivine and wadsleyite at a depth near 410 km (12–14 GPa) under
water-saturated conditions, as a function of temperature, oxygen fugacity,
and the presence of carbon (molar H / C of 2). Experiments have been conducted
in the multi-anvil press, with sealed double capsules to preserve fluids, at
1200 to 1400 ∘C and three different oxygen fugacities fixed at the
rhenium–rhenium oxide buffer (RRO), nickel–nickel oxide buffer (NNO), and
iron-wüstite (IW) for oxidizing, intermediate, and reducing conditions,
respectively. The water contents of minerals were measured by Raman
spectroscopy that allows a very small beam size to be used and were
cross-checked on a few samples with NanoSIMS analyses. We observe an effect, although slight, of fO2 on the water storage
capacity of both wadsleyite and olivine and also on their solidus
temperatures. At 1200 ∘C, the storage capacity of the nominally anhydrous
minerals (NAMS)
increases with increasing oxygen fugacity (from the IW to the RRO buffer)
from 1 wt % to 1.5 wt % H2O in wadsleyite and from 0.1 wt % to 0.2 wt % in olivine, owing to the increase in H2O / H2 speciation in
the fluid, whereas at 1400 ∘C the storage capacity decreases from
1 wt % to 0.75 wt % H2O in wadsleyite and down to 0.03 wt % for
olivine. At high temperature, the water storage capacity is lowered due to
melting, and the more oxidized the conditions are the more the solidus is
depressed. Still, at 1400 ∘C and IW, wadsleyite can store
substantial amounts of water: 0.8 wt % to 1 wt % H2O. The effect of carbon is
to decrease water storage capacity in both wadsleyite and olivine by an
average factor 2 at 1300–1400 ∘C. The trends in water storage as a
function of fO2 and C presence are confirmed by NanoSIMS measurements.
The solidus at IW without C is located between 1300 and 1400 ∘C in
the wadsleyite stability field and drops to temperatures below 1300 ∘C in the olivine stability field. With the addition of C, the
solidus is found between 1200 and 1300 ∘C in both olivine and
wadsleyite stability fields.