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Structural analysis of the Western Afar Margin, East Africa: evidence for multiphase rotational rifting

Structural analysis of the Western Afar Margin, East Africa: evidence for multiphase rotational rifting
Structural analysis of the Western Afar Margin, East Africa: evidence for multiphase rotational rifting

The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N-S striking WAM is still actively deforming and is characterized by NNW-SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first-ever borehole-calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large-scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.

Afar, East African rift, continental breakup, passive margin formation, rifting, rotational rifting
0278-7407
Zwaan, Frank
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Corti, Giacomo
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Sani, Federico
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Keir, Derek
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Muluneh, Ameha
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Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Papini, Mauro
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Zwaan, Frank
25329ca2-014b-4cb9-9ef3-3b8a4259c675
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Sani, Federico
6c59b4c4-ecca-4ecc-ba2c-66efa5e5e3df
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Muluneh, Ameha
9c48408f-650f-49ad-9133-bc201fa817ce
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Papini, Mauro
1f3c530a-7a26-435a-bc21-45b3bcb14d46

Zwaan, Frank, Corti, Giacomo, Sani, Federico, Keir, Derek, Muluneh, Ameha, Illsley-Kemp, Finnigan and Papini, Mauro (2020) Structural analysis of the Western Afar Margin, East Africa: evidence for multiphase rotational rifting. Tectonics, 39 (7), [e2019TC006043]. (doi:10.1029/2019TC006043).

Record type: Article

Abstract

The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N-S striking WAM is still actively deforming and is characterized by NNW-SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first-ever borehole-calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large-scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.

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Accepted/In Press date: 9 May 2020
e-pub ahead of print date: 9 May 2020
Published date: July 2020
Keywords: Afar, East African rift, continental breakup, passive margin formation, rifting, rotational rifting

Identifiers

Local EPrints ID: 441078
URI: http://eprints.soton.ac.uk/id/eprint/441078
ISSN: 0278-7407
PURE UUID: b8ee8122-a9c6-4847-8f48-1a2fcb02a028
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446
ORCID for Finnigan Illsley-Kemp: ORCID iD orcid.org/0000-0002-7114-033X

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Date deposited: 29 May 2020 16:30
Last modified: 26 Nov 2021 02:57

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Contributors

Author: Frank Zwaan
Author: Giacomo Corti
Author: Federico Sani
Author: Derek Keir ORCID iD
Author: Ameha Muluneh
Author: Finnigan Illsley-Kemp ORCID iD
Author: Mauro Papini

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