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

Davy, R. G., Collier, J. S., Henstock, Tim, Rietbrock, Andreas, Goes, Saskia, Blundy, Jon, Harmon, Nick, Rychert, Catherine, Macpherson, Colin G., Van Hunen, Jeroen, Kendall, Mike, Wilkinson, Jamie, Davidson, Jon, Wilson, Marjorie, Cooper, George, Maunder, Benjamin, Bie, Lidong, Hicks, Stephen, Allen, Robert, Chichester, Ben, Tait, Stephen, Robertson, Richie, Latchman, Joan, Krüger, Frank, Collier, Jenny, Henstock, Tim, Allen, Robert, Butcher, Sophie, Castiello, Gabriella, Chen, Chen, Harkin, Caroline, Posse, Dan, Roche, Ben, Bird, Anna, Clegg, Andy, Pitcairn, Ben, Weeks, Martin, Kirk, Henning and Labahn, Erik (2020) Wide-angle seismic imaging of two modes of crustal accretion in mature Atlantic Ocean crust. Journal of Geophysical Research: Solid Earth, 125 (6). ISSN 2169-9313

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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 nontransform 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 the 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. While 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 midcrustal seismic velocity inversions as alteration and rock-type assemblage contrasts across crustal-scale detachment faults.

Item Type: Article
Additional Information: Funding Information: This work was funded under Natural Environment Research Council (NERC) Grants NE/K010743/1 and NE/K010654/1 (VoiLA). We thank the captain, John Leask, officers, crew, and science party members who sailed on RRS cruise JC149‐leg3 (science party members are listed in Appendix A2 ) (Collier, 2017 ). 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 ). This article was greatly improved by feedback from Matthias Delescluse and two anonymous reviewers. Swath bathymetry and wide‐angle seismic data from cruise JC149 are available from the Marine Geoscience Data System ( http://www.marine‐geo.org/tools/search/entry.php?id=JC149 , DOI: 10.26022/IEDA/327347 ). James Cook Funding Information: This work was funded under Natural Environment Research Council (NERC) Grants NE/K010743/1 and NE/K010654/1 (VoiLA). We thank the captain, John Leask, officers, crew, and science party members who sailed on RRS James Cook cruise JC149-leg3?(science party members are listed in Appendix A2) (Collier,?2017). 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). This article was greatly improved by feedback from Matthias Delescluse and two anonymous reviewers. Swath bathymetry and wide-angle seismic data from cruise JC149 are available from the Marine Geoscience Data System (http://www.marine-geo.org/tools/search/entry.php?id=JC149, DOI: 10.26022/IEDA/327347). Publisher Copyright: ©2020. The Authors.
Uncontrolled Keywords: active-source seismic,fracture zone,nontransform offset,oceanic core complexes,slow-spread oceanic crust,tomography,geophysics,geochemistry and petrology,earth and planetary sciences (miscellaneous),space and planetary science ,/dk/atira/pure/subjectarea/asjc/1900/1908
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Depositing User: LivePure Connector
Date Deposited: 22 Apr 2022 10:30
Last Modified: 25 Apr 2022 00:21
URI: https://ueaeprints.uea.ac.uk/id/eprint/84734
DOI: 10.1029/2019JB019100

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