The Problem of CO2 Recycling in Subduction Zones

In connection with the imbalance between the carbon dioxide absorbed in the carbonate minerals in subduction zones and that emitted during island arc volcanism, the problem of redistribution the rest of the CO2 from the plate to the mantle arises. Experimental modeling of the interaction between model analogs of the oceanic crust and the mantle wedge was performed for two systems: glaucophane schist-olivine and glau-cophane schist-silicate marble-olivine under high pressure and varying temperature conditions that correspond to the oceanic crust-mantle transition zone in the subduction zone beneath the Cascade Mountains. The experiments carried out showed that there is a possibility that intensive CO2 degassing occurs from the plate in the forearc area, which is controlled by carbonate dissolution in an aqueous fluid. As a result of this process, carbonates can redeposit in the form of magnesite in the overlying mantle rocks according to the vertical temperature gradient. It is assumed that part of the carbon dioxide bonded in mantle rocks can be transported by viscous flow from the forearc area to the deep mantle horizons within the field of the thermodynamic stability of magnesite. In addition, the experiments we carried out showed that between marble and olivine in the ultrahigh pressure a metasomatic column consisting of four zones develops: Fe-Mg-Ca carbonate vertical bar dolomite vertical bar diopside vertical bar magnesite.