Metamorphic devolatilization in subduction zones: thermal, dynamic and thermodynamic modeling
Abstract
Significant quantities of mineralogically bound H2O and CO2 exist in the sediments, altered oceanic crust and (potentially) serpentinized upper most mantle of the oceanic lithosphere. Upon subduction the rocks undergo a progressive series of metamorphic dehydration reactions that are strongly dependent on rock composition, pressure, temperature and the presence of fluid phases. In earlier work (van Keken et al., JGR, 2011) we modeled the release of water from slabs worldwide by combining high resolution models of the global subduction system with Perple_X based thermodynamic calculations. We extend this work in two directions. First, we consider the consequences for CO2 devolatilization, which is particularly sensitive to the presence of fluids. The new mass balance computations provide an update to earlier work by Gorman et al. (EPSL, 2006) who considered a small number of end-member thermal models. The new set of models provide new constraints on the efficiency of subducting zones in transporting H2O and CO2 to the Earth's deep interior. Second, we use the predictions for fluid release as seed for fully coupled solid state and porous flow calculations, which allow us to self-consistently model the fluid pathways through the slab and overlying mantle wedge. The models suggest that fluid is sourced in relatively discrete depths (depending on the position within the stratified crust and upper mantle) but that fluids can efficiently be redistributed in the slab before they leave the slab and enter the mantle wedge. We also show the possibility of active rehydration of the fore-arc mantle by fluids released from the slab.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.U51D..07V
- Keywords:
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- 1031 GEOCHEMISTRY / Subduction zone processes