Wide‐Angle Seismic Imaging of Two Modes of Crustal Accretion in Mature Atlantic Ocean Crust

Davy, R.G.; Collier, J.S.; Henstock, T.J.; 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; Butcher, Sophie; Castiello, Gabriella; Chen, Chen; Harkin, Caroline; Posse, Dan; Roche, Ben; Bird, Anna; Clegg, Andy; Pitcairn, Ben; Weeks, Martin; Kirk, Henning; Labahn, Erik

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.

Citation

Davy, R., Collier, J., Henstock, T., Rietbrock, A., Goes, S., Blundy, J., …Labahn, E. (2020). Wide‐Angle Seismic Imaging of Two Modes of Crustal Accretion in Mature Atlantic Ocean Crust. Journal of Geophysical Research. Solid Earth, 125(6), Article e2019JB019100. https://doi.org/10.1029/2019jb019100

• Journal Article Type: Article
• Acceptance Date: Apr 16, 2020
• Online Publication Date: Jun 20, 2020
• Publication Date: 2020-06
• Deposit Date: Jun 24, 2020
• Publicly Available Date: Jun 24, 2020
• Journal: Journal of Geophysical Research. Solid Earth
• Print ISSN: 2169-9313
• Electronic ISSN: 2169-9356
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 125
• Issue: 6
• Article Number: e2019JB019100
• DOI: https://doi.org/10.1029/2019jb019100
• Public URL: https://durham-repository.worktribe.com/output/1261876