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3D development of detachment faulting during continental breakup

3D development of detachment faulting during continental breakup
3D development of detachment faulting during continental breakup
The developing asymmetry of rifting and continental breakup to form rifted margins has been much debated, as has the formation, mechanics and role of extensional detachments. Bespoke 3D seismic reflection data across the Galicia margin, west of Spain, image in unprecedented detail an asymmetric detachment (the S reflector). Mapping S in 3D reveals its surface is corrugated, proving that the overlying crustal blocks slipped on S surface during the rifting. Crucially, the 3D data show that the corrugations on S perfectly match the corrugations observed on the present-day block-bounding faults, demonstrating that S is a composite surface, comprising the juxtaposed rotated roots of block-bounding faults as in a rolling hinge system with each new fault propagation moving rifting oceanward; changes in the orientation of the corrugations record the same oceanward migration. However, in contrast to previous rolling hinge models, the slip of the crustal blocks on S occurred at angles as low as ∼20°, requiring that S was unusually weak, consistent with the hydration of the underlying mantle by seawater ingress following the embrittlement of the entire crust. As the crust only becomes entirely brittle once thinned to ∼10 km, the asymmetric S detachment and the hyper-extension of the continental crust only developed late in the rifting process, which is consistent with the observed development of asymmetry between conjugate magma poor margin pairs. The 3D volume allows analysis of the heaves and along strike architecture of the normal faults, whose planes laterally die or spatially link together, implying overlaps in faults activity during hyper-extension. Our results thus reveal for the first time the 3D mechanics and timing of detachment faulting growth, the relationship between the detachment and the network of block-bounding faults above it and the key processes controlling the asymmetrical development of conjugate rifted margins.
0012-821X
90-99
Lymer, Gaël
6f35819a-faab-42ad-b693-ba4ff26d2b9a
Cresswell, Derren J.f.
131a1e5e-6171-4408-bda8-c937eae5eec2
Reston, Tim J.
6a6f7b70-726a-4cda-b104-12296ac7318b
Bull, Jonathan M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Sawyer, Dale S.
9b2521e0-3bf5-425f-b057-995621975728
Morgan, Julia K.
af0f28ff-1eb0-4376-9e2d-341c548c35d2
Stevenson, Carl
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Causer, Annabel
237d9138-2961-48cb-bfd1-2ba2c0cc28ae
Minshull, Tim A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Shillington, Donna J.
7d553e6e-9f56-471a-88be-5736f7f9c826
Lymer, Gaël
6f35819a-faab-42ad-b693-ba4ff26d2b9a
Cresswell, Derren J.f.
131a1e5e-6171-4408-bda8-c937eae5eec2
Reston, Tim J.
6a6f7b70-726a-4cda-b104-12296ac7318b
Bull, Jonathan M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Sawyer, Dale S.
9b2521e0-3bf5-425f-b057-995621975728
Morgan, Julia K.
af0f28ff-1eb0-4376-9e2d-341c548c35d2
Stevenson, Carl
74bac4fe-7cf6-45a0-9d02-631fd856a641
Causer, Annabel
237d9138-2961-48cb-bfd1-2ba2c0cc28ae
Minshull, Tim A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Shillington, Donna J.
7d553e6e-9f56-471a-88be-5736f7f9c826

Lymer, Gaël, Cresswell, Derren J.f., Reston, Tim J., Bull, Jonathan M., Sawyer, Dale S., Morgan, Julia K., Stevenson, Carl, Causer, Annabel, Minshull, Tim A. and Shillington, Donna J. (2019) 3D development of detachment faulting during continental breakup. Earth and Planetary Science Letters, 515, 90-99. (doi:10.1016/j.epsl.2019.03.018).

Record type: Article

Abstract

The developing asymmetry of rifting and continental breakup to form rifted margins has been much debated, as has the formation, mechanics and role of extensional detachments. Bespoke 3D seismic reflection data across the Galicia margin, west of Spain, image in unprecedented detail an asymmetric detachment (the S reflector). Mapping S in 3D reveals its surface is corrugated, proving that the overlying crustal blocks slipped on S surface during the rifting. Crucially, the 3D data show that the corrugations on S perfectly match the corrugations observed on the present-day block-bounding faults, demonstrating that S is a composite surface, comprising the juxtaposed rotated roots of block-bounding faults as in a rolling hinge system with each new fault propagation moving rifting oceanward; changes in the orientation of the corrugations record the same oceanward migration. However, in contrast to previous rolling hinge models, the slip of the crustal blocks on S occurred at angles as low as ∼20°, requiring that S was unusually weak, consistent with the hydration of the underlying mantle by seawater ingress following the embrittlement of the entire crust. As the crust only becomes entirely brittle once thinned to ∼10 km, the asymmetric S detachment and the hyper-extension of the continental crust only developed late in the rifting process, which is consistent with the observed development of asymmetry between conjugate magma poor margin pairs. The 3D volume allows analysis of the heaves and along strike architecture of the normal faults, whose planes laterally die or spatially link together, implying overlaps in faults activity during hyper-extension. Our results thus reveal for the first time the 3D mechanics and timing of detachment faulting growth, the relationship between the detachment and the network of block-bounding faults above it and the key processes controlling the asymmetrical development of conjugate rifted margins.

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Lymer_et_al_2019_EPSL_Repository - Accepted Manuscript
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Accepted/In Press date: 12 March 2019
e-pub ahead of print date: 27 March 2019
Published date: 1 June 2019

Identifiers

Local EPrints ID: 430128
URI: https://eprints.soton.ac.uk/id/eprint/430128
ISSN: 0012-821X
PURE UUID: 406a50fd-7bc9-4b38-a423-f2944b812bfe
ORCID for Tim A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

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Date deposited: 12 Apr 2019 16:30
Last modified: 10 Dec 2019 01:49

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