5:15 PM - 6:30 PM
[SGC16-P04] Subduction of iodine-rich halogens and the I/Cl ratio in the mantle
Keywords:Subduction, Halogen, Mantle
Here, we use a box model to estimate the halogen subduction fluxes required to have maintained this I/Cl ratio in the mantle over the past 1.6 Gyr. These modeled halogen fluxes are compared with those estimated from (i) halogen/H2O ratios in natural serpentine in seafloor serpentinites  and the amount of water subducted within the hydrous slab mantle , and (ii) halogen/36Ar ratios in natural serpentine  and the subduction flux of 36Ar. The 36Ar subduction flux has been constrained from its concentration in the convecting mantle and its outgassing flux at mid-ocean ridge systems, which is estimated from the 36Ar/3He ratio in MORB source  and the 3He outgassing flux from mid-ocean ridges , respectively.
Our data show that the estimated subduction flux of iodine carried by the hydrous slab mantle is too high to keep the I/Cl ratio in the mantle constant over the investigated time period. The present-day DMM-like I/Cl ratio can only be preserved if halogens are not efficiently released from subducting slabs and consequently do not become incorporated into the convecting mantle. In contrast, subducted noble gases should be incorporated into the convecting mantle in order to account for its seawater-like noble gas signature . As such, we interpret that noble gases are readily expelled from subducting slabs at upper-mantle depths due to their high volatilities, whereas halogens are not, and so are transported to significantly greater depths in the Earth.
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