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The Role of Crustal Accretion Variations in Determining Slab Hydration at an Atlantic Subduction Zone

The Role of Crustal Accretion Variations in Determining Slab Hydration at an Atlantic Subduction Zone
The Role of Crustal Accretion Variations in Determining Slab Hydration at an Atlantic Subduction Zone
We present a 2D P-wave velocity model from the outer rise region of the Lesser Antilles island arc, the first wide-angle seismic study of outer rise processes at an Atlantic subduction zone. The survey consists of 46 OBS receivers over a 174 km profile with velocities resolved to 15 km below top basement. The final velocity model, produced through tomographic inversion, shows a clear decrease in the velocity of the lower crust and upper mantle of the incoming plate as it approaches the trench. We attribute this drop to outer rise bend-related hydration, similar to Pacific cases, but superimposed on spatial variations in hydration generated at the slow-spreading ridge axis. In thin, tectonically controlled crust formed under magma-poor spreading conditions the superposition of these sources of hydration results in compressional velocities as low as 6.5 km s−1 beneath the PmP reflector. In contrast, segments of crust interpreted as having formed under magma-rich conditions show velocity reductions and inferred hydrous alteration more like that observed in the Pacific. Hence, variations in the style of crustal accretion, which is observed on 50–100 km length scales both along and across isochrons, is a primary control over the distribution of water within the slab at Atlantic subduction systems. This heterogeneous pattern of water storage within the slab is likely further complicated by along strike variations in outer rise bending, subducting fracture zones and deformation at segment ends and may have important implications for our understanding of long-term patterns of hazard at Atlantic subduction systems.
2169-9356
Allen, Robert
faf7d3c0-7467-4ade-82e2-d36eaf73bef2
Collier, Jenny S.
04a0fcc8-caeb-4f08-a967-a19e57d1a5e1
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Allen, Robert
faf7d3c0-7467-4ade-82e2-d36eaf73bef2
Collier, Jenny S.
04a0fcc8-caeb-4f08-a967-a19e57d1a5e1
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb

Allen, Robert, Collier, Jenny S. and Henstock, Timothy (2022) The Role of Crustal Accretion Variations in Determining Slab Hydration at an Atlantic Subduction Zone. Journal of Geophysical Research: Solid Earth, 127 (8), [e2022JB024349]. (doi:10.1029/2022JB024349). (In Press)

Record type: Article

Abstract

We present a 2D P-wave velocity model from the outer rise region of the Lesser Antilles island arc, the first wide-angle seismic study of outer rise processes at an Atlantic subduction zone. The survey consists of 46 OBS receivers over a 174 km profile with velocities resolved to 15 km below top basement. The final velocity model, produced through tomographic inversion, shows a clear decrease in the velocity of the lower crust and upper mantle of the incoming plate as it approaches the trench. We attribute this drop to outer rise bend-related hydration, similar to Pacific cases, but superimposed on spatial variations in hydration generated at the slow-spreading ridge axis. In thin, tectonically controlled crust formed under magma-poor spreading conditions the superposition of these sources of hydration results in compressional velocities as low as 6.5 km s−1 beneath the PmP reflector. In contrast, segments of crust interpreted as having formed under magma-rich conditions show velocity reductions and inferred hydrous alteration more like that observed in the Pacific. Hence, variations in the style of crustal accretion, which is observed on 50–100 km length scales both along and across isochrons, is a primary control over the distribution of water within the slab at Atlantic subduction systems. This heterogeneous pattern of water storage within the slab is likely further complicated by along strike variations in outer rise bending, subducting fracture zones and deformation at segment ends and may have important implications for our understanding of long-term patterns of hazard at Atlantic subduction systems.

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Accepted/In Press date: 18 July 2022
Additional Information: Article is currently listed "in production" but the DOI has been assigned as above. Once published it will be open access (paid for from Imperial since they are lead institution)

Identifiers

Local EPrints ID: 468724
URI: http://eprints.soton.ac.uk/id/eprint/468724
ISSN: 2169-9356
PURE UUID: c3bee311-135d-4cae-847b-2644caeb1847
ORCID for Timothy Henstock: ORCID iD orcid.org/0000-0002-2132-2514

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Date deposited: 23 Aug 2022 16:59
Last modified: 24 Aug 2022 01:36

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Author: Robert Allen
Author: Jenny S. Collier

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