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Wide-angle seismic imaging of two modes of crustal accretion in mature Atlantic Ocean crust

Wide-angle seismic imaging of two modes of crustal accretion in mature Atlantic Ocean crust
Wide-angle seismic imaging of two modes of crustal accretion in mature Atlantic Ocean crust
We present a high-resolution 2-D P-wave velocity model from a 225 km long active seismic profile, collected over ~60-75 Ma central Atlantic crust. The profile crosses five ridge segments separated by a transform and three non-transform offsets. All ridge discontinuities share similar primary characteristics, independent of the offset. We identify two types of crustal segment. The first displays a classic two-layer velocity structure with a high gradient layer 2 (~0.9 s-1) above a lower gradient layer 3 (0.2 s-1). Here PmP coincides with the 7.5 km s-1 contour and velocity increases to >7.8 km s-1 within 1 km below. We interpret these segments as magmatically-robust, with PmP representing a petrological boundary between crust and mantle. The second has a reduced contrast in velocity gradient between upper and lower crust, and PmP shallower than the 7.5 km s-1 contour. We interpret these segments as tectonically dominated, with PmP representing a serpentinized (alteration) front. Whilst velocity depth profiles fit within previous envelopes for slow-spreading crust, our results suggest that such generalizations give a misleading impression of uniformity. We estimate that the two crustal styles are present in equal proportions on the floor of the Atlantic. Within two tectonically dominated segments we make the first wide-angle seismic identifications of buried oceanic core complexes in mature (> 20 Ma) Atlantic Ocean crust. They have a ~20 km wide “domal” morphology with shallow basement and increased upper-crustal velocities. We interpret their mid-crustal seismic velocity inversions as alteration and rock-type assemblage contrasts across crustal-scale detachment faults.
active-source seismic, fracture zone, nontransform offset, oceanic core complexes, slow-spread oceanic crust, tomography
0148-0227
Davy, R.G.
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Collier, J.S.
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Henstock, T.J.
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Rietbrock, Andreas
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Goes, Saskia
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Blundy, J.
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Harmon, Nicholas
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Rychert, Catherine
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MacPherson, C.
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Van Hunen, Jeroen
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Kendall, Mike
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Wilkinson, Jamie
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Tait, Stephen
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Davidson, J
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Wilson, Marjorie
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Cooper, George
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Maunder, Ben
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Bie, Lidong
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Hicks, Stephen
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Allen, R.
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Chichester, Ben
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Robertson, Richie
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Latchman, Joan
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Krueger, Frank
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the E consortium
Davy, R.G.
1e7e9634-90ce-4023-a762-7f1529b7432d
Collier, J.S.
19dfa4bb-f743-4ca8-b15f-0f72f3f7263c
Henstock, T.J.
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Rietbrock, Andreas
e4656f22-06be-40fe-8f98-7f88c351c434
Goes, Saskia
8da1004a-3f5b-44c9-9889-046c5b6c537e
Blundy, J.
cada4533-3530-4c64-9530-e58500d1b37e
Harmon, Nicholas
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Rychert, Catherine
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MacPherson, C.
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Van Hunen, Jeroen
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Kendall, Mike
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Wilkinson, Jamie
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Tait, Stephen
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Davidson, J
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Wilson, Marjorie
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Cooper, George
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Maunder, Ben
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Bie, Lidong
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Hicks, Stephen
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Allen, R.
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Chichester, Ben
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Robertson, Richie
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Latchman, Joan
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Krueger, Frank
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Davy, R.G., Collier, J.S. and Henstock, T.J. , the E consortium (2020) Wide-angle seismic imaging of two modes of crustal accretion in mature Atlantic Ocean crust. Journal of Geophysical Research, 125 (6), [e2019JB019100]. (doi:10.1029/2019JB019100).

Record type: Article

Abstract

We present a high-resolution 2-D P-wave velocity model from a 225 km long active seismic profile, collected over ~60-75 Ma central Atlantic crust. The profile crosses five ridge segments separated by a transform and three non-transform offsets. All ridge discontinuities share similar primary characteristics, independent of the offset. We identify two types of crustal segment. The first displays a classic two-layer velocity structure with a high gradient layer 2 (~0.9 s-1) above a lower gradient layer 3 (0.2 s-1). Here PmP coincides with the 7.5 km s-1 contour and velocity increases to >7.8 km s-1 within 1 km below. We interpret these segments as magmatically-robust, with PmP representing a petrological boundary between crust and mantle. The second has a reduced contrast in velocity gradient between upper and lower crust, and PmP shallower than the 7.5 km s-1 contour. We interpret these segments as tectonically dominated, with PmP representing a serpentinized (alteration) front. Whilst velocity depth profiles fit within previous envelopes for slow-spreading crust, our results suggest that such generalizations give a misleading impression of uniformity. We estimate that the two crustal styles are present in equal proportions on the floor of the Atlantic. Within two tectonically dominated segments we make the first wide-angle seismic identifications of buried oceanic core complexes in mature (> 20 Ma) Atlantic Ocean crust. They have a ~20 km wide “domal” morphology with shallow basement and increased upper-crustal velocities. We interpret their mid-crustal seismic velocity inversions as alteration and rock-type assemblage contrasts across crustal-scale detachment faults.

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Accepted/In Press date: 16 April 2020
e-pub ahead of print date: 28 April 2020
Published date: 1 June 2020
Keywords: active-source seismic, fracture zone, nontransform offset, oceanic core complexes, slow-spread oceanic crust, tomography

Identifiers

Local EPrints ID: 439632
URI: http://eprints.soton.ac.uk/id/eprint/439632
ISSN: 0148-0227
PURE UUID: a20bb252-c423-4580-aee0-6d081e724367
ORCID for T.J. Henstock: ORCID iD orcid.org/0000-0002-2132-2514
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X

Catalogue record

Date deposited: 28 Apr 2020 16:35
Last modified: 22 Nov 2021 02:57

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Contributors

Author: R.G. Davy
Author: J.S. Collier
Author: T.J. Henstock ORCID iD
Author: Andreas Rietbrock
Author: Saskia Goes
Author: J. Blundy
Author: Nicholas Harmon ORCID iD
Author: C. MacPherson
Author: Jeroen Van Hunen
Author: Mike Kendall
Author: Jamie Wilkinson
Author: Stephen Tait
Author: J Davidson
Author: Marjorie Wilson
Author: George Cooper
Author: Ben Maunder
Author: Lidong Bie
Author: Stephen Hicks
Author: R. Allen
Author: Ben Chichester
Author: Richie Robertson
Author: Joan Latchman
Author: Frank Krueger
Corporate Author: the E consortium

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