Lower Mantle Anisotropy Beneath Subduction Zones
Abstract
Seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet. While the presence of anisotropy in the uppermost mantle is well established, the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated. Here we use three-dimensional global seismic tomography images based on a large dataset that is sensitive to this region to show the presence of anisotropy in the lower mantle beneath subduction zones. Above the 660 km seismic discontinuity slabs are associated with fast SV anomalies up to about 3%, whilst in the lower mantle fast SH anomalies of about 2% persist near slabs down to about 1,000-1,200 km. In the Tonga-Kermadec region, our observations of anisotropy suggest that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. These various observations in different subduction settings are consistent with 3D numerical models of deformation from subducting slabs and the associated lattice-preferred orientation of bridgmanite produced in the dislocation creep regime in areas subjected to high stresses. Our work provides evidence that dislocation creep may be active in the Earth's lower mantle, providing new constraints on the debated nature of deformation in this key, but inaccessible, component of the deep Earth.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR24A..04S
- Keywords:
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- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS