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Internal deformation of the subducted Nazca slab inferred from seismic anisotropy

Internal deformation of the subducted Nazca slab inferred from seismic anisotropy
Internal deformation of the subducted Nazca slab inferred from seismic anisotropy

Within oceanic lithosphere a fossilized fabric is often preserved originating from the time of plate formation. Such fabric is thought to form at the mid-ocean ridge when olivine crystals align with the direction of plate spreading1, 2. It is unclear, however, whether this fossil fabric is preserved within slabs during subduction or overprinted by subduction-induced deformation. The alignment of olivine crystals, such as within fossil fabrics, can generate anisotropy that is sensed by passing seismic waves. Seismic anisotropy is therefore a useful tool for investigating the dynamics of subduction zones, but it has so far proved difficult to observe the anisotropic properties of the subducted slab itself. Here we analyse seismic anisotropy in the subducted Nazca slab beneath Peru and find that the fast direction of seismic wave propagation aligns with the contours of the slab. We use numerical modelling to simulate the olivine fabric created at the mid-ocean ridge, but find it is inconsistent with our observations of seismic anisotropy in the subducted Nazca slab. Instead we find that an orientation of the olivine crystal fast axes aligned parallel to the strike of the slab provides the best fit, consistent with along-strike extension induced by flattening of the slab during subduction (A. Kumar et al., manuscript in preparation). We conclude that the fossil fabric has been overprinted during subduction and that the Nazca slab must therefore be sufficiently weak to undergo internal deformation.
1752-0894
56-59
Eakin, Caroline M.
767ea10a-757b-4db5-8705-0c79368f8606
Long, Maureen D.
a17cb1ef-12be-49e4-9052-c6d4e7c5602f
Scire, Alissa
bf59c901-fb57-48d2-acc9-48f46aba2254
Beck, Susan L.
c96e19da-83d5-4af0-bc41-75efdfdb8062
Wagner, Lara S.
e517f9ff-a61d-4acc-858f-138546c6be6b
Zandt, George
98edfded-ee54-459e-9318-213ba9680026
Tavera, Hernando
e734dedd-0a1d-4510-b4b3-f5facd32e8e4
Eakin, Caroline M.
767ea10a-757b-4db5-8705-0c79368f8606
Long, Maureen D.
a17cb1ef-12be-49e4-9052-c6d4e7c5602f
Scire, Alissa
bf59c901-fb57-48d2-acc9-48f46aba2254
Beck, Susan L.
c96e19da-83d5-4af0-bc41-75efdfdb8062
Wagner, Lara S.
e517f9ff-a61d-4acc-858f-138546c6be6b
Zandt, George
98edfded-ee54-459e-9318-213ba9680026
Tavera, Hernando
e734dedd-0a1d-4510-b4b3-f5facd32e8e4

Eakin, Caroline M., Long, Maureen D., Scire, Alissa, Beck, Susan L., Wagner, Lara S., Zandt, George and Tavera, Hernando (2016) Internal deformation of the subducted Nazca slab inferred from seismic anisotropy. Nature Geoscience, 9, 56-59. (doi:10.1038/ngeo2592).

Record type: Article

Abstract


Within oceanic lithosphere a fossilized fabric is often preserved originating from the time of plate formation. Such fabric is thought to form at the mid-ocean ridge when olivine crystals align with the direction of plate spreading1, 2. It is unclear, however, whether this fossil fabric is preserved within slabs during subduction or overprinted by subduction-induced deformation. The alignment of olivine crystals, such as within fossil fabrics, can generate anisotropy that is sensed by passing seismic waves. Seismic anisotropy is therefore a useful tool for investigating the dynamics of subduction zones, but it has so far proved difficult to observe the anisotropic properties of the subducted slab itself. Here we analyse seismic anisotropy in the subducted Nazca slab beneath Peru and find that the fast direction of seismic wave propagation aligns with the contours of the slab. We use numerical modelling to simulate the olivine fabric created at the mid-ocean ridge, but find it is inconsistent with our observations of seismic anisotropy in the subducted Nazca slab. Instead we find that an orientation of the olivine crystal fast axes aligned parallel to the strike of the slab provides the best fit, consistent with along-strike extension induced by flattening of the slab during subduction (A. Kumar et al., manuscript in preparation). We conclude that the fossil fabric has been overprinted during subduction and that the Nazca slab must therefore be sufficiently weak to undergo internal deformation.

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e-pub ahead of print date: 23 November 2015
Published date: January 2016
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 384562
URI: http://eprints.soton.ac.uk/id/eprint/384562
ISSN: 1752-0894
PURE UUID: 91188239-c244-4613-9116-f3a13eb75938

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Date deposited: 01 Dec 2015 10:13
Last modified: 14 Mar 2024 22:01

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Contributors

Author: Caroline M. Eakin
Author: Maureen D. Long
Author: Alissa Scire
Author: Susan L. Beck
Author: Lara S. Wagner
Author: George Zandt
Author: Hernando Tavera

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