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Evolution of the oceanic lithosphere in the equatorial Atlantic From Rayleigh wave tomography, evidence for small‐scale convection From the PI‐LAB experiment

Evolution of the oceanic lithosphere in the equatorial Atlantic From Rayleigh wave tomography, evidence for small‐scale convection From the PI‐LAB experiment
Evolution of the oceanic lithosphere in the equatorial Atlantic From Rayleigh wave tomography, evidence for small‐scale convection From the PI‐LAB experiment
The oceanic lithosphere is a primary component of the plate tectonic system, yet its evolution and its asthenospheric interaction have rarely been quantified by in situ imaging at slow spreading systems. We use Rayleigh wave tomography from noise and teleseismic surface waves to image the shear wave velocity structure of the oceanic lithosphere‐asthenosphere system from 0 to 80 My at the equatorial Mid‐Atlantic Ridge using data from the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We observe fast lithosphere (VSV > 4.4 km/s) that thickens from 20–30 km near the ridge axis to ~70 km at seafloor >60 My. We observe several punctuated slow velocity anomalies (VSV < 4.1 km/s) in the asthenosphere between 50 and 150 km depth, not necessarily focused beneath the ridge axis. Some of the slow velocity regions are located within 100 km of the ridge axis, but other slow velocity regions are observed at distances > 400 km from the ridge. We observe a high velocity lithospheric downwelling drip beneath 30 My seafloor that extends to 80–130 km depth. The asthenospheric slow velocities likely require partial melt. Although melt is present off axis, the lack of off‐axis volcanism suggests the lithosphere acts as a permeability boundary for deeper melts. The punctuated and off‐axis character of the asthenospheric anomalies and lithospheric drip suggests small‐scale convection is active at a range of seafloor ages. Small‐scale convection and/or more complex mantle flow may be aided by the presence of large offset fracture zones and/or the presence of melt and its associated low‐viscosities and enhanced buoyancies.
Atlantic Ocean, PI-LAB, asthenosphere, oceanic lithosphere, shear velocity, surface wave tomography
1525-2027
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Kendall, Mike
49233af5-e888-4ab8-87b7-d97938f0ed27
Agius, Matthew
cb168c8d-0926-4c0d-951c-721fb4cf1ebf
Bogiatzis, Petros
8fc5767f-51a2-4d3f-aab9-1ee9cfa9272d
Tharimena, Saikiran
9e95dff0-7044-43d4-ac5e-51e72468b719
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Kendall, Mike
49233af5-e888-4ab8-87b7-d97938f0ed27
Agius, Matthew
cb168c8d-0926-4c0d-951c-721fb4cf1ebf
Bogiatzis, Petros
8fc5767f-51a2-4d3f-aab9-1ee9cfa9272d
Tharimena, Saikiran
9e95dff0-7044-43d4-ac5e-51e72468b719

Harmon, Nicholas, Rychert, Catherine, Kendall, Mike, Agius, Matthew, Bogiatzis, Petros and Tharimena, Saikiran (2020) Evolution of the oceanic lithosphere in the equatorial Atlantic From Rayleigh wave tomography, evidence for small‐scale convection From the PI‐LAB experiment. Geochemistry, Geophysics, Geosystems, 21 (9), [e2020GC009174]. (doi:10.1029/2020GC009174).

Record type: Article

Abstract

The oceanic lithosphere is a primary component of the plate tectonic system, yet its evolution and its asthenospheric interaction have rarely been quantified by in situ imaging at slow spreading systems. We use Rayleigh wave tomography from noise and teleseismic surface waves to image the shear wave velocity structure of the oceanic lithosphere‐asthenosphere system from 0 to 80 My at the equatorial Mid‐Atlantic Ridge using data from the Passive Imaging of the Lithosphere‐Asthenosphere Boundary (PI‐LAB) experiment. We observe fast lithosphere (VSV > 4.4 km/s) that thickens from 20–30 km near the ridge axis to ~70 km at seafloor >60 My. We observe several punctuated slow velocity anomalies (VSV < 4.1 km/s) in the asthenosphere between 50 and 150 km depth, not necessarily focused beneath the ridge axis. Some of the slow velocity regions are located within 100 km of the ridge axis, but other slow velocity regions are observed at distances > 400 km from the ridge. We observe a high velocity lithospheric downwelling drip beneath 30 My seafloor that extends to 80–130 km depth. The asthenospheric slow velocities likely require partial melt. Although melt is present off axis, the lack of off‐axis volcanism suggests the lithosphere acts as a permeability boundary for deeper melts. The punctuated and off‐axis character of the asthenospheric anomalies and lithospheric drip suggests small‐scale convection is active at a range of seafloor ages. Small‐scale convection and/or more complex mantle flow may be aided by the presence of large offset fracture zones and/or the presence of melt and its associated low‐viscosities and enhanced buoyancies.

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More information

Accepted/In Press date: 17 August 2020
e-pub ahead of print date: 29 August 2020
Published date: 1 September 2020
Keywords: Atlantic Ocean, PI-LAB, asthenosphere, oceanic lithosphere, shear velocity, surface wave tomography

Identifiers

Local EPrints ID: 444406
URI: http://eprints.soton.ac.uk/id/eprint/444406
ISSN: 1525-2027
PURE UUID: 3a2fcb19-797a-4107-bf70-9cf688527dc3
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X
ORCID for Petros Bogiatzis: ORCID iD orcid.org/0000-0003-1902-7476
ORCID for Saikiran Tharimena: ORCID iD orcid.org/0000-0002-1841-1911

Catalogue record

Date deposited: 16 Oct 2020 16:32
Last modified: 18 Feb 2021 17:31

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