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Across and along-strike crustal structure variations of the western Afar margin and adjacent plateau: Insights from receiver functions analysis

Across and along-strike crustal structure variations of the western Afar margin and adjacent plateau: Insights from receiver functions analysis
Across and along-strike crustal structure variations of the western Afar margin and adjacent plateau: Insights from receiver functions analysis
We used teleseismic receiver function analysis to image the crustal structure beneath 24 broadband seismic stations densely deployed along two profiles traversing different structural units across the western Afar margin. Our high-resolution receiver function results image pronounced spatial variations in the crustal structure along the profiles and provide improved insights to understand how strain is partitioned in the crust during rifting. Beneath the western plateau next to northern Afar, the crust is likely felsic-to-intermediate in composition (average Vp/Vs 1.74), with a step like thinning of the crust from an average of 38 km beneath the western plateau to an average of 22 km beneath the marginal graben. Consistently thicker crust is observed beneath the southern profile (central Afar), showing four distinct regions of uniform crustal thickness: 1) an average crustal thickness of 42 km beneath the western plateau; 2) 34 km beneath the foothills area; 3) 28 km beneath the marginal graben and the wide extensional basin and 4) 21 km beneath the central rift axis. We use crustal thickness results to estimate a stretching factor β of 2.2 and 2.7 for central Afar and northern Afar respectively. Our estimated values are lower than β > 3.0 predicted from plate reconstructions, and we interpret that the variations are best explained by 2–5 km magmatic addition into the crust. The crustal composition beneath the southern profile is more complex with elevated Vp/Vs ratios ranging between 1.79 and 1.85 beneath the western plateau and marginal graben. This is consistent with a greater mafic component and best explained by crust altered by intrusions due to significant pre and syn-rift magmatic activity. Abnormally high Vp/Vs ratios of more than 1.90 are observed beneath the axial rift zone of central Afar, which most likely suggests the localization of partial melt within the crust.
Afar margin, Africa, Continental margin, Crustal structure, Receiver functions, Southern red sea rift
1464-343X
Ahmed, Abdulhakim
97c6ca5b-955e-4227-8b21-e13f225524f6
Doubre, Cecile
9f348925-f5b6-445c-8663-7f58f58b97f3
Leroy, Sylvie
627c503b-1036-41fc-a24c-3d09954fab0a
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0
Hammond, James O.S.
14123885-010a-42c1-820b-66f5c683abf1
Ayele, Atalay
730f62fb-c461-4a4e-b52d-b143a7936df6
et al.
Ahmed, Abdulhakim
97c6ca5b-955e-4227-8b21-e13f225524f6
Doubre, Cecile
9f348925-f5b6-445c-8663-7f58f58b97f3
Leroy, Sylvie
627c503b-1036-41fc-a24c-3d09954fab0a
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0
Hammond, James O.S.
14123885-010a-42c1-820b-66f5c683abf1
Ayele, Atalay
730f62fb-c461-4a4e-b52d-b143a7936df6

et al. (2022) Across and along-strike crustal structure variations of the western Afar margin and adjacent plateau: Insights from receiver functions analysis. Journal of African Earth Sciences, 192, [104570]. (doi:10.1016/j.jafrearsci.2022.104570).

Record type: Article

Abstract

We used teleseismic receiver function analysis to image the crustal structure beneath 24 broadband seismic stations densely deployed along two profiles traversing different structural units across the western Afar margin. Our high-resolution receiver function results image pronounced spatial variations in the crustal structure along the profiles and provide improved insights to understand how strain is partitioned in the crust during rifting. Beneath the western plateau next to northern Afar, the crust is likely felsic-to-intermediate in composition (average Vp/Vs 1.74), with a step like thinning of the crust from an average of 38 km beneath the western plateau to an average of 22 km beneath the marginal graben. Consistently thicker crust is observed beneath the southern profile (central Afar), showing four distinct regions of uniform crustal thickness: 1) an average crustal thickness of 42 km beneath the western plateau; 2) 34 km beneath the foothills area; 3) 28 km beneath the marginal graben and the wide extensional basin and 4) 21 km beneath the central rift axis. We use crustal thickness results to estimate a stretching factor β of 2.2 and 2.7 for central Afar and northern Afar respectively. Our estimated values are lower than β > 3.0 predicted from plate reconstructions, and we interpret that the variations are best explained by 2–5 km magmatic addition into the crust. The crustal composition beneath the southern profile is more complex with elevated Vp/Vs ratios ranging between 1.79 and 1.85 beneath the western plateau and marginal graben. This is consistent with a greater mafic component and best explained by crust altered by intrusions due to significant pre and syn-rift magmatic activity. Abnormally high Vp/Vs ratios of more than 1.90 are observed beneath the axial rift zone of central Afar, which most likely suggests the localization of partial melt within the crust.

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Accepted/In Press date: 21 April 2022
e-pub ahead of print date: 4 May 2022
Published date: 1 August 2022
Keywords: Afar margin, Africa, Continental margin, Crustal structure, Receiver functions, Southern red sea rift

Identifiers

Local EPrints ID: 457911
URI: http://eprints.soton.ac.uk/id/eprint/457911
ISSN: 1464-343X
PURE UUID: ddf0781c-bf97-4982-929e-c648e6dcaa6f
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 21 Jun 2022 18:26
Last modified: 09 Nov 2022 02:43

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Contributors

Author: Abdulhakim Ahmed
Author: Cecile Doubre
Author: Sylvie Leroy
Author: Derek Keir ORCID iD
Author: Carolina Pagli
Author: James O.S. Hammond
Author: Atalay Ayele
Corporate Author: et al.

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