Analogue modelling of marginal flexure in Afar, East Africa: Implications for passive margin formation
Analogue modelling of marginal flexure in Afar, East Africa: Implications for passive margin formation
The Afar region in East Africa is a key locality for studying continental break-up. Within Afar, passive margins are developing, of which the Southern Afar Margin (SAM) contains synthetic (basinward) faulting, whereas crustal flexure, antithetic faulting and marginal grabens occur along the Western Afar Margin (WAM). Numerous conflicting scenarios for the evolution of the WAM exist. In this analogue modelling study we test various factors that may affect the development of a WAM-style passive margin: brittle crustal thickness, (en echelon) rheological contrasts, sedimentation and oblique extension. Our experimental results illustrate how marginal flexure due to a weak lower crust below Afar can elegantly account for the structural features of the WAM. Brittle crustal thickness controls what structures occur: a thinner brittle crust accommodates flexure internally, whereas increasing brittle thicknesses lead to faulting. Large escarpment faults develop early on, followed by late-stage antithetic faulting and marginal grabens. A thicker brittle crust also causes enhanced subsidence, and increased strength contrasts between lower crustal domains leads to more localized deformation. Basin-wide sedimentation causes enhanced subsidence, as well as longer activity along large synthetic (escarpment) faults. Finally, oblique extension clearly prevents the development of marginal grabens, which only form in near-orthogonal extension. These results support a tectonic scenario involving initial oblique extension due to Arabian plate motion, creating echelon synthetic escarpment faults along the WAM. After the Danakil Block started its independent rotation, near-orthogonal extension conditions were established, allowing (enhanced) marginal flexure, antithetic faulting and marginal graben formation along the older en echelon escarpment. Differences in extension obliquity may also explain the differences in structural architectures between the WAM and SAM. The characteristics of the WAM are typical of magma-rich passive margins, and the margin has great potential for studying continental break-up and (magma-rich) passive margin formation.
Continental break-up, Crustal flexure, Magma-rich passive margin, Marginal graben, Passive margin, Rifting
Zwaan, Frank
25329ca2-014b-4cb9-9ef3-3b8a4259c675
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Sani, Federico
6c59b4c4-ecca-4ecc-ba2c-66efa5e5e3df
5 December 2020
Zwaan, Frank
25329ca2-014b-4cb9-9ef3-3b8a4259c675
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Sani, Federico
6c59b4c4-ecca-4ecc-ba2c-66efa5e5e3df
Zwaan, Frank, Corti, Giacomo, Keir, Derek and Sani, Federico
(2020)
Analogue modelling of marginal flexure in Afar, East Africa: Implications for passive margin formation.
Tectonophysics, 796, [228595].
(doi:10.1016/j.tecto.2020.228595).
Abstract
The Afar region in East Africa is a key locality for studying continental break-up. Within Afar, passive margins are developing, of which the Southern Afar Margin (SAM) contains synthetic (basinward) faulting, whereas crustal flexure, antithetic faulting and marginal grabens occur along the Western Afar Margin (WAM). Numerous conflicting scenarios for the evolution of the WAM exist. In this analogue modelling study we test various factors that may affect the development of a WAM-style passive margin: brittle crustal thickness, (en echelon) rheological contrasts, sedimentation and oblique extension. Our experimental results illustrate how marginal flexure due to a weak lower crust below Afar can elegantly account for the structural features of the WAM. Brittle crustal thickness controls what structures occur: a thinner brittle crust accommodates flexure internally, whereas increasing brittle thicknesses lead to faulting. Large escarpment faults develop early on, followed by late-stage antithetic faulting and marginal grabens. A thicker brittle crust also causes enhanced subsidence, and increased strength contrasts between lower crustal domains leads to more localized deformation. Basin-wide sedimentation causes enhanced subsidence, as well as longer activity along large synthetic (escarpment) faults. Finally, oblique extension clearly prevents the development of marginal grabens, which only form in near-orthogonal extension. These results support a tectonic scenario involving initial oblique extension due to Arabian plate motion, creating echelon synthetic escarpment faults along the WAM. After the Danakil Block started its independent rotation, near-orthogonal extension conditions were established, allowing (enhanced) marginal flexure, antithetic faulting and marginal graben formation along the older en echelon escarpment. Differences in extension obliquity may also explain the differences in structural architectures between the WAM and SAM. The characteristics of the WAM are typical of magma-rich passive margins, and the margin has great potential for studying continental break-up and (magma-rich) passive margin formation.
Text
1-s2.0-S004019512030278X-main
- Accepted Manuscript
More information
Accepted/In Press date: 18 August 2020
e-pub ahead of print date: 24 August 2020
Published date: 5 December 2020
Additional Information:
Funding Information:
We kindly thank Daniele Maestrelli for his support in the tectonic laboratory and introducing us to Photoscan, as well as Kirsten Elger and Matthias Rosenau for helping us publish our supplementary material in the form of three GFZ Data Publications ( Zwaan et al., 2020c-e ). Constructive feedback by Sandy Cruden and an anonymous reviewer are greatly appreciated. We also thank editor Zheng-Xiang Li. This project was funded by the Swiss National Science Foundation (Early Postdoc.Mobility grant P2BEP2_178523 ( http://p3.snf.ch/project-178523 ) awarded to FZ, and by PRIN2017 grant 2017P9AT72 .
Copyright © 1969, Elsevier
Keywords:
Continental break-up, Crustal flexure, Magma-rich passive margin, Marginal graben, Passive margin, Rifting
Identifiers
Local EPrints ID: 443890
URI: http://eprints.soton.ac.uk/id/eprint/443890
ISSN: 0040-1951
PURE UUID: 4d6a9669-5fd3-4afd-955c-3c1b738eaf45
Catalogue record
Date deposited: 16 Sep 2020 16:34
Last modified: 17 Mar 2024 03:24
Export record
Altmetrics
Contributors
Author:
Frank Zwaan
Author:
Giacomo Corti
Author:
Federico Sani
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics
