TY - JOUR
T1 - 3D development of detachment faulting during continental breakup
AU - Lymer, Gaël
AU - Cresswell, Derren J.F.
AU - Reston, Tim J.
AU - Bull, Jonathan M.
AU - Sawyer, Dale S.
AU - Morgan, Julia K.
AU - Stevenson, Carl
AU - Causer, Annabel
AU - Minshull, Tim A.
AU - Shillington, Donna J.
N1 - Funding Information:
Data acquisition was funded by the National Science Foundation ( OCE-257 1031769 ) and UK Natural Environment Research Council (NERC) awards NE/E015883/1 and NE/E016502/1 . TAM was supported by a Wolfson Research Merit award. Data processing by Repsol was funded by NERC through grant NE/E015883/1 . We thank the crew of R / V Marcus G. Langseth . We are grateful to Nur Shuba for helpful discussion concerning Fig. 4 b. Reviews were by Marta Pérez-Gussinyé and an anonymous but helpful reviewer.
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/6/1
Y1 - 2019/6/1
N2 - 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.
AB - 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.
KW - 3D seismic reflection
KW - Galicia margin
KW - North Atlantic Ocean
KW - asymmetry
KW - detachment fault
KW - rifting processes
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U2 - 10.1016/j.epsl.2019.03.018
DO - 10.1016/j.epsl.2019.03.018
M3 - Article
AN - SCOPUS:85063377219
SN - 0012-821X
VL - 515
SP - 90
EP - 99
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -