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.

Lesser Antilles, outer rise bend faults, serpentinization, structure of oceanic crust, subduction, wide-angle seismic survey

10.1029/2022JB024349

2169-9356

Allen, Robert

faf7d3c0-7467-4ade-82e2-d36eaf73bef2

Collier, Jenny S.

04a0fcc8-caeb-4f08-a967-a19e57d1a5e1

Henstock, Timothy

27c450a4-3e6b-41f8-97f9-4e0e181400bb

August 2022

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).

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Accepted/In Press date: 18 July 2022

Published date: August 2022

Additional Information: Funding Information: This work was funded under Natural Environment Research Council (NERC) grant NE/K010743/1 (VoiLA, Volatile Recycling in the Lesser Antilles). We thank the captain, John Leask, and the officers, crew, and science party members who sailed on RRS James Cook cruises JC149. We acknowledge Halliburton for providing access to SeisSpace/ProMax software via a grant to Imperial College London. We thank the UK Ocean-Bottom Instrumentation Facility (Minshull et al., 2005) and the German Instrument Pool for Amphibian Seismology (DEPAS), hosted by the Alfred Wegener Institute Bremerhaven, for providing the ocean-bottom seismometers. We thank the members of the VoiLA consortium for their contributions to this paper (for a full list of VoiLA consortium members, see Appendix A1). Allen was supported by a Ph.D. studentship funded by the NERC-Imperial Science and Solutions for a Changing Planet Doctoral Training Partnership (SSCP DTP) throughout much of this research. Funding Information: This work was funded under Natural Environment Research Council (NERC) grant NE/K010743/1 (VoiLA, Volatile Recycling in the Lesser Antilles). We thank the captain, John Leask, and the officers, crew, and science party members who sailed on RRS James Cook cruises JC149. We acknowledge Halliburton for providing access to SeisSpace/ProMax software via a grant to Imperial College London. We thank the UK Ocean‐Bottom Instrumentation Facility (Minshull et al., 2005 ) and the German Instrument Pool for Amphibian Seismology (DEPAS), hosted by the Alfred Wegener Institute Bremerhaven, for providing the ocean‐bottom seismometers. We thank the members of the VoiLA consortium for their contributions to this paper (for a full list of VoiLA consortium members, see Appendix A1 ). Allen was supported by a Ph.D. studentship funded by the NERC‐Imperial Science and Solutions for a Changing Planet Doctoral Training Partnership (SSCP DTP) throughout much of this research. Publisher Copyright: © 2022. The Authors.

Keywords: Lesser Antilles, outer rise bend faults, serpentinization, structure of oceanic crust, subduction, wide-angle seismic survey