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A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge

A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge
A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge
The location and degree of material transfer between the upper and lower mantle are key to the Earth’s thermal and chemical evolution. Sinking slabs and rising plumes are generally accepted as locations of transfer1,2, whereas mid-ocean ridges are not typically assumed to have a role3. However, tight constraints from in situ measurements at ridges have proved to be challenging. Here we use receiver functions that reveal the conversion of primary to secondary seismic waves to image the discontinuities that bound the mantle transition zone, using ocean bottom seismic data from the equatorial Mid-Atlantic Ridge. Our images show that the seismic discontinuity at depths of about 660 kilometres is broadly uplifted by 10 ± 4 kilometres over a swath about 600 kilometres wide and that the 410-kilometre discontinuity is depressed by 5 ± 4 kilometres. This thinning of the mantle transition zone is coincident with slow shear-wave velocities in the mantle, from global seismic tomography4–7. In addition, seismic velocities in the mantle transition zone beneath the Mid-Atlantic Ridge are on average slower than those beneath older Atlantic Ocean seafloor. The observations imply material transfer from the lower to the upper mantle—either continuous or punctuated—that is linked to the Mid-Atlantic Ridge. Given the length and longevity of the mid-ocean ridge system, this implies that whole-mantle convection may be more prevalent than previously thought, with ridge upwellings having a role in counterbalancing slab downwellings.
0028-0836
562-566
Agius, Matthew
cb168c8d-0926-4c0d-951c-721fb4cf1ebf
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Kendall, J.M.
efae6d05-97b1-4df8-8e69-66c3be807760
Agius, Matthew
cb168c8d-0926-4c0d-951c-721fb4cf1ebf
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Kendall, J.M.
efae6d05-97b1-4df8-8e69-66c3be807760

Agius, Matthew, Rychert, Catherine, Harmon, Nicholas and Kendall, J.M. (2021) A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge. Nature, 589 (7843), 562-566. (doi:10.1038/s41586-020-03139-x).

Record type: Article

Abstract

The location and degree of material transfer between the upper and lower mantle are key to the Earth’s thermal and chemical evolution. Sinking slabs and rising plumes are generally accepted as locations of transfer1,2, whereas mid-ocean ridges are not typically assumed to have a role3. However, tight constraints from in situ measurements at ridges have proved to be challenging. Here we use receiver functions that reveal the conversion of primary to secondary seismic waves to image the discontinuities that bound the mantle transition zone, using ocean bottom seismic data from the equatorial Mid-Atlantic Ridge. Our images show that the seismic discontinuity at depths of about 660 kilometres is broadly uplifted by 10 ± 4 kilometres over a swath about 600 kilometres wide and that the 410-kilometre discontinuity is depressed by 5 ± 4 kilometres. This thinning of the mantle transition zone is coincident with slow shear-wave velocities in the mantle, from global seismic tomography4–7. In addition, seismic velocities in the mantle transition zone beneath the Mid-Atlantic Ridge are on average slower than those beneath older Atlantic Ocean seafloor. The observations imply material transfer from the lower to the upper mantle—either continuous or punctuated—that is linked to the Mid-Atlantic Ridge. Given the length and longevity of the mid-ocean ridge system, this implies that whole-mantle convection may be more prevalent than previously thought, with ridge upwellings having a role in counterbalancing slab downwellings.

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Accepted/In Press date: 3 November 2020
e-pub ahead of print date: 27 January 2021
Published date: 28 January 2021

Identifiers

Local EPrints ID: 446695
URI: http://eprints.soton.ac.uk/id/eprint/446695
ISSN: 0028-0836
PURE UUID: 50586b66-9bef-46d2-b555-29c39fcdb783
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X

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Date deposited: 18 Feb 2021 17:30
Last modified: 27 Jul 2021 04:01

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Author: Matthew Agius
Author: Nicholas Harmon ORCID iD
Author: J.M. Kendall

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