Subduction fluxes of water, carbon dioxide, chlorine, and potassium

Abstract

[1] The alteration of upper oceanic crust entails growth of hydrous minerals and loss of macroporosity, with associated large-scale fluxes of H 2 O, CO 2 , Cl À , and K 2 O between seawater and crust. This agedependent alteration can be quantified by combining a conceptual alteration model with observed agedependent changes in crustal geophysical properties at DSDP/ODP sites, permitting estimation of crustal concentrations of H 2 O, CO 2 , Cl À , and K 2 O, given crustal age. Surprisingly, low-temperature alteration causes no net change in total water; pore water loss is nearly identical to bound water gain. Net change in total crustal K 2 O is also smaller than expected; the obvious low-temperature enrichment is partly offset by earlier high-temperature depletion, and most crustal K 2 O is primary rather than secondary. I calculate crustal concentrations of H 2 O, CO 2 , Cl À , and K 2 O for 41 modern subduction zones, thereby determining their modern mass fluxes both for individual subduction zones and globally. This data set is complemented by published flux determinations for subducting sediments at 26 of these subduction zones. Global mass fluxes among oceans, oceanic crust, continental crust, and mantle are calculated for H 2 O, Cl À , and K 2 O. Except for the present major imbalance between sedimentation and sediment subduction, most fluxes appear to be at or near steady state. I estimate that half to two thirds of subducted crustal water is later refluxed at the prism toe; most of the remaining water escapes at subarc depths, triggering partial melting. The flux of subducted volatiles, however, does not appear to correlate with either rate of arc magma generation or magnitude of interplate earthquakes.

Solubility of water in pyrope‐rich garnet at high pressures and temperature

“…Hence, the maximum amount of water transported by pyrope-rich garnet in the subducted oceanic crust is $3 Â 10 11 kg/year. This is roughly the half of the estimated water flux associated with the igneous components of subducted oceanic crust [Jarrard, 2003]. Substantially higher water solubility in pyrope-rich garnet might affect the relative strength of garnet with respect to other mineral phases such as olivine [Katayama and Karato, 2008].…”

The effects of deep water cycling on planetary thermal evolution

“…Our modeling supports this. Estimated fluxes range from 5.1 × 10 11 to 1.83 × 10 12 kg/yr for total water cycled back to the mantle and 2.1-2.3 × 10 11 for water currently degassed at MORs [Peacock, 1990;Maruyama, 1999;Bounama et al, 2001;Jarrard, 2003]. Some authors suggest values between 0.06 and 0.3 for the ratio of water that reaches deep mantle, with the specific values depending on the temperature or age of subducted slabs [Rupke et al, 2004].…”

Water, Life, and Planetary Geodynamical Evolution

“…Water is carried into the mantle in the form of sediment and igneous rock pore and structural water (Jarrard 2002 (Williams and Hemley 2001). Some of these minerals are stable down to great pressures (e.g.…”