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High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece

High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece
High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece

Low-angle normal faults (LANFs) accommodate extension during late-stage rifting and breakup, but what is more difficult to explain is the existence of LANFs in less-stretched continental rifts. A critical example is the <5 Ma Corinth Rift, central Greece, where microseismicity, the geometry of exposed fault planes, and deep seismically imaged faults have been used to argue for the presence of <30°-dipping normal faults. However, new and reinterpreted data call into question whether LANFs have been influential in controlling the observed rift geometry, which involves (1) exposed steep fault planes, (2) significant uplift of the southern rift margin, (3) time-averaged (tens of thousands to hundreds of thousands of years) uplift-to-subsidence ratios across south coast faults of 1:1–1:2, and (4) north margin subsidence. We test whether slip on a mature LANF can reproduce the long-term (tens of thousands of years) geometry and morphology of the Corinth Rift using a finite-element method, to model the uplift and subsidence fields associated with proposed fault geometries. Models involving LANFs at depth produce very minor coseismic uplift of the south margin, and post-seismic relaxation results in net subsidence. In contrast, models involving steep planar faults to the brittle-ductile transition produce displacement fields involving an uplifted south margin with uplift-to-subsidence ratios of ~1:2–3, compatible with geological observations. We therefore propose that LANFs cannot have controlled the geometry of the Corinth Rift over time scales of tens of thousands of years. We suggest that although LANFs may become important in the transition to breakup, in areas that have undergone mild stretching, do not have significant magmatic activity, and do not have optimally oriented preexisting low-angle structures, high-angle faulting would be the dominant strain accommodation mechanism in the upper crust during early rifting.

0091-7613
115-118
Bell, Rebecca E.
6ae1b7e9-eca2-4785-a40a-80b6ff58062a
Duclaux, Guillaume
02533f04-5aef-410e-b6af-430e9ac192e6
Nixon, Casey W.
18e290c7-3f4b-43d0-9118-0f3ac926aadd
Gawthorpe, Robert L.
a3c15d93-52d4-41a7-b51e-d8ed0adb4ee0
Mcneill, Lisa C.
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf
Bell, Rebecca E.
6ae1b7e9-eca2-4785-a40a-80b6ff58062a
Duclaux, Guillaume
02533f04-5aef-410e-b6af-430e9ac192e6
Nixon, Casey W.
18e290c7-3f4b-43d0-9118-0f3ac926aadd
Gawthorpe, Robert L.
a3c15d93-52d4-41a7-b51e-d8ed0adb4ee0
Mcneill, Lisa C.
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf

Bell, Rebecca E., Duclaux, Guillaume, Nixon, Casey W., Gawthorpe, Robert L. and Mcneill, Lisa C. (2017) High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece. Geology, 46 (2), 115-118. (doi:10.1130/G39560.1).

Record type: Article

Abstract

Low-angle normal faults (LANFs) accommodate extension during late-stage rifting and breakup, but what is more difficult to explain is the existence of LANFs in less-stretched continental rifts. A critical example is the <5 Ma Corinth Rift, central Greece, where microseismicity, the geometry of exposed fault planes, and deep seismically imaged faults have been used to argue for the presence of <30°-dipping normal faults. However, new and reinterpreted data call into question whether LANFs have been influential in controlling the observed rift geometry, which involves (1) exposed steep fault planes, (2) significant uplift of the southern rift margin, (3) time-averaged (tens of thousands to hundreds of thousands of years) uplift-to-subsidence ratios across south coast faults of 1:1–1:2, and (4) north margin subsidence. We test whether slip on a mature LANF can reproduce the long-term (tens of thousands of years) geometry and morphology of the Corinth Rift using a finite-element method, to model the uplift and subsidence fields associated with proposed fault geometries. Models involving LANFs at depth produce very minor coseismic uplift of the south margin, and post-seismic relaxation results in net subsidence. In contrast, models involving steep planar faults to the brittle-ductile transition produce displacement fields involving an uplifted south margin with uplift-to-subsidence ratios of ~1:2–3, compatible with geological observations. We therefore propose that LANFs cannot have controlled the geometry of the Corinth Rift over time scales of tens of thousands of years. We suggest that although LANFs may become important in the transition to breakup, in areas that have undergone mild stretching, do not have significant magmatic activity, and do not have optimally oriented preexisting low-angle structures, high-angle faulting would be the dominant strain accommodation mechanism in the upper crust during early rifting.

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Accepted/In Press date: 2 November 2017
e-pub ahead of print date: 8 December 2017
Published date: 8 December 2017

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Local EPrints ID: 417165
URI: https://eprints.soton.ac.uk/id/eprint/417165
ISSN: 0091-7613
PURE UUID: 36dd1940-149c-4c62-b035-bd1aa09f13da

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Date deposited: 23 Jan 2018 17:30
Last modified: 14 Mar 2019 05:18

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Contributors

Author: Rebecca E. Bell
Author: Guillaume Duclaux
Author: Casey W. Nixon
Author: Robert L. Gawthorpe
Author: Lisa C. Mcneill

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