Mantle wedge serpentinization effects on slab dips

  • Author(s): Eh Tan
  • DOI: 10.3319/TAO.2016.09.21.01
  • Keywords: Subduction, Serpentinization, Mantle wedge
  • Citation: Tan, E., 2017: Mantle wedge serpentinization effects on slab dips. Terr. Atmos. Ocean. Sci., 28, 259-269, doi: 10.3319/TAO.2016.09.21.01
  • Slab dip unaffected by the thickness of shallow serpentinite
  • Slab dip increases with the thickness of deep serpentinite
  • Stable subduction requires at least a thin layer of serpentinite
Abstract

The mechanical coupling between a subducting slab and the overlying mantle wedge is an important factor in controlling the subduction dip angle and the flow in mantel wedge. This paper investigates the role of the amount of mantle serpentinization on the subduction zone evolution. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the mantle serpentinization thickness. A critical down-dip extent exists in mantle serpentinization, determined by the thickness of the overriding lithosphere. If the down-dip extent does not exceed the critical depth, the slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of the mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of the overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from the asthenosphere into the serpentinized mantle wedge. All of these results indicate that serpentinization is an important ingredient when studying the subduction dynamics in the mantle wedge.

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