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Crustal strain-dependent serpentinisation in the Porcupine Basin, offshore Ireland

Crustal strain-dependent serpentinisation in the Porcupine Basin, offshore Ireland
Crustal strain-dependent serpentinisation in the Porcupine Basin, offshore Ireland
Mantle hydration (serpentinisation) at magma-poor rifted margins is thought to play a key role in controlling the kinematics of low-angle faults and thus, hyperextension and crustal breakup. However, because geophysical data principally provide observations of the final structure of a margin, little is known about the evolution of serpentinisation and how this governs tectonics during hyperextension. Here we present new observational evidence on how crustal strain-dependent serpentinisation influences hyperextension from rifting to possible crustal breakup along the axis of the Porcupine Basin, offshore Ireland. We present three new P-wave seismic velocity models that show the seismic structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis. We use neighbouring seismic reflection lines to our tomographic models to estimate crustal stretching () of ∼2.5 in the north at 52.5° N and >10 in the south at 51.7° N. These values suggest that no crustal embrittlement occurred in the northernmost region, and that rifting may have progressed to crustal breakup in the southern part of the study area. We observed a decrease in mantle velocities across the basin axis from east to west. These variations occur in a region where is within the range at which crustal embrittlement and serpentinisation are possible ( 3–4). Across the basin axis, the lowest seismic velocity in the mantle spatially coincides with the maximum amount of crustal faulting, indicating fault-controlled mantle hydration. Mantle velocities also suggest that the degree of serpentinisation, together with the amount of crustal faulting, increases southwards along the basin axis. Seismic reflection lines show a major detachment fault surface that grows southwards along the basin axis and is only visible where the inferred degree of serpentinisation is >15%. This observation is consistent with laboratory measurements that show that at this degree of serpentinisation, mantle rocks are sufficiently weak to allow low-angle normal faulting. Based on these results, we propose two alternative formation models for the Porcupine Basin. The first involves a northward propagation of the hyperextension processes, while the second model suggests higher extension rates in the centre of the basin than in the north. Both scenarios postulate that the amount of crustal strain determines the extent and degree of serpentinisation, which eventually controls the development of detachments faults with advanced stretching.
Porcupine Basin, mantle serpentinisation , detachment faults, rifted margins, travel time tomography
0012-821X
148-159
Prada, Manel
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Watremez, Louise
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Chen, Chen
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O'Reilly, Brian M.
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Minshull, Tim A.
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Reston, Tim J.
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Shannon, Patrick M.
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Klaeschen, Dirk
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Wagner, Gerlind
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Gaw, Viola
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Prada, Manel
b69842a7-07db-4e82-a34d-6ff2b675837c
Watremez, Louise
bce54c70-b287-4c80-966b-5096a29bc93a
Chen, Chen
d12bd0bd-3a63-4aa5-bf03-4253e539cdbc
O'Reilly, Brian M.
a159a3c0-6c27-4532-b505-61afaacce3c3
Minshull, Tim A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Reston, Tim J.
0ba75307-667f-4f0e-b4fd-42f80a34b4f7
Shannon, Patrick M.
bc4ab42c-4b4b-4a12-9761-cc80f148cd03
Klaeschen, Dirk
6f4c994a-036e-44cc-b35e-c85e894f1bac
Wagner, Gerlind
5692e23d-4931-4cc1-b5a9-349898950f48
Gaw, Viola
01d99204-4534-4101-88f4-e38ad0cc5a29

Prada, Manel, Watremez, Louise, Chen, Chen, O'Reilly, Brian M., Minshull, Tim A., Reston, Tim J., Shannon, Patrick M., Klaeschen, Dirk, Wagner, Gerlind and Gaw, Viola (2017) Crustal strain-dependent serpentinisation in the Porcupine Basin, offshore Ireland. Earth and Planetary Science Letters, 474, 148-159. (doi:10.1016/j.epsl.2017.06.040).

Record type: Article

Abstract

Mantle hydration (serpentinisation) at magma-poor rifted margins is thought to play a key role in controlling the kinematics of low-angle faults and thus, hyperextension and crustal breakup. However, because geophysical data principally provide observations of the final structure of a margin, little is known about the evolution of serpentinisation and how this governs tectonics during hyperextension. Here we present new observational evidence on how crustal strain-dependent serpentinisation influences hyperextension from rifting to possible crustal breakup along the axis of the Porcupine Basin, offshore Ireland. We present three new P-wave seismic velocity models that show the seismic structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis. We use neighbouring seismic reflection lines to our tomographic models to estimate crustal stretching () of ∼2.5 in the north at 52.5° N and >10 in the south at 51.7° N. These values suggest that no crustal embrittlement occurred in the northernmost region, and that rifting may have progressed to crustal breakup in the southern part of the study area. We observed a decrease in mantle velocities across the basin axis from east to west. These variations occur in a region where is within the range at which crustal embrittlement and serpentinisation are possible ( 3–4). Across the basin axis, the lowest seismic velocity in the mantle spatially coincides with the maximum amount of crustal faulting, indicating fault-controlled mantle hydration. Mantle velocities also suggest that the degree of serpentinisation, together with the amount of crustal faulting, increases southwards along the basin axis. Seismic reflection lines show a major detachment fault surface that grows southwards along the basin axis and is only visible where the inferred degree of serpentinisation is >15%. This observation is consistent with laboratory measurements that show that at this degree of serpentinisation, mantle rocks are sufficiently weak to allow low-angle normal faulting. Based on these results, we propose two alternative formation models for the Porcupine Basin. The first involves a northward propagation of the hyperextension processes, while the second model suggests higher extension rates in the centre of the basin than in the north. Both scenarios postulate that the amount of crustal strain determines the extent and degree of serpentinisation, which eventually controls the development of detachments faults with advanced stretching.

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Prada-et-al-EPSL-final - Accepted Manuscript
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Accepted/In Press date: 30 June 2017
e-pub ahead of print date: 13 July 2017
Published date: 15 September 2017
Keywords: Porcupine Basin, mantle serpentinisation , detachment faults, rifted margins, travel time tomography
Organisations: Ocean and Earth Science, Geology & Geophysics, Southampton Marine & Maritime Institute

Identifiers

Local EPrints ID: 411946
URI: http://eprints.soton.ac.uk/id/eprint/411946
ISSN: 0012-821X
PURE UUID: 27a7767f-7943-4fed-ac28-8227be0a67a1
ORCID for Tim A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

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Date deposited: 03 Jul 2017 16:31
Last modified: 07 Oct 2020 05:33

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Contributors

Author: Manel Prada
Author: Louise Watremez
Author: Chen Chen
Author: Brian M. O'Reilly
Author: Tim A. Minshull ORCID iD
Author: Tim J. Reston
Author: Patrick M. Shannon
Author: Dirk Klaeschen
Author: Gerlind Wagner
Author: Viola Gaw

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