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

Davy, R. G. and Collier, J. S. and Henstock, T. J. and Rietbrock, Andreas and Goes, Saskia and Blundy, Jon and Harmon, Nick and Rychert, Catherine and Macpherson, Colin G. and Van Hunen, Jeroen and Kendall, Mike and Wilkinson, Jamie and Davidson, Jon and Wilson, Marjorie and Cooper, George and Maunder, Benjamin and Bie, Lidong and Hicks, Stephen and Allen, Robert and Chichester, Ben and Tait, Stephen and Robertson, Richie and Latchman, Joan and Krüger, Frank and Collier, Jenny and Henstock, Tim and Allen, Robert and Butcher, Sophie and Castiello, Gabriella and Chen, Chen and Harkin, Caroline and Posse, Dan and Roche, Ben and Bird, Anna and Clegg, Andy and Pitcairn, Ben and Weeks, Martin and 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). e2019JB019100.

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
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1029/2019JB019100
Publisher statement:© 2020. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:16 April 2020
Date deposited:24 June 2020
Date of first online publication:20 June 2020
Date first made open access:24 June 2020

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