A Weaker Asthenospheric Sub-Layer at Convergent Margins: Implication for the Evolution of a Congested Subduction Zone.
Abstract
Recent geophysical and geological regional observations have drawn considerable attention to the detailed structure of the asthenosphere at subduction zones. Some of these studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates in the proximity of different congested boundaries. This layer has been interpreted as being thin, weak and slightly buoyant and it has the potential to influence the dynamics of subducting plates. However, it is still not clear whether this layer represents a global or a regional feature. The ability to detect and distinguish narrow channels at the base of the subducting lithosphere has been hindered by the complicated nature of this boundary and by a trade-off that exists between resolving power and regional extent of seismic studies. We use 3D geodynamic numerical models of subduction to explore the implications of the regional asthenospheric structure on the evolution of a plate boundary geometry and deformation. In our models, we vary the physical properties and geometrical extent of the weak layer at the base of the oceanic lithosphere, showing that its presence alters plate and trench motions. This sub-asthenospheric heterogeneity may also affect the morphology of subducting slabs and the patterns of deformation flow into the upper mantle. We use these results to build a regime diagram that shows the effect of a weaker asthenospheric sub-layer on the dynamics of subducting plates. We also explore the possible implications given by the presence of this layer on the migration and rotation of plate boundaries at congested subduction zone.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMDI51B0011C
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRYDE: 8031 Rheology: crust and lithosphere;
- STRUCTURAL GEOLOGYDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8124 Earth's interior: composition and state;
- TECTONOPHYSICS