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Subsurface structure of magmatic segments during continental breakup: Perspectives from a gravity data analysis along the Main Ethiopian Rift

Subsurface structure of magmatic segments during continental breakup: Perspectives from a gravity data analysis along the Main Ethiopian Rift
Subsurface structure of magmatic segments during continental breakup: Perspectives from a gravity data analysis along the Main Ethiopian Rift

In magma-rich continental rifts, extension is commonly localized as dike injection in discrete magmatic segments which appear from surface geology to mimic the along-axis segmentation of ocean ridges. However, the subsurface morphology of these zones of localized magma injection is unclear, and whether and at what depth range they remain with discrete subvolcanic plumbing systems is not fully understood. In addition, the relationship between zones of magma injection and tectonic faulting is also debated. The Main Ethiopian Rift (MER) provides a unique opportunity to examine the spatial scale, locus, and subsurface geometries of magmatic localization in active continental rifts. We examined spatial variations in the structure of the crust in the MER using gravity data to better understand the subsurface pattern of magma injection. Results of our study reveal discrete Bouguer gravity highs in the centers of the distinct right-stepping magmatic segments of the MER (Aluto, Gedemsa, and Boseti), and interpreted as the locus of mafic intrusions. The gravity data show that the boundary between each magmatic segment is observed down to depths of ∼20 km, suggesting that magmatic segments have discrete subvolcanic plumbing systems at least down to the mid-crust. Additionally, incorporating the fault network shows that the densest faulting occurs at the tips of the zones of densest magma injection shown by Bouguer gravity highs. This is similar to the axial segmentation observed at slow and ultra-slow spreading ridges and suggests strong along-axis variations in deformation mechanism, with magma injection accommodating extension at the segment centers and faulting dominating towards the segment ends. In addition, rift margin volcanic zones (Siltie Debrezeit, Yerer Tulu, and Galema) are also inferred from bandpass gravity anomaly maps, supported by petrologic evidence, which implies that extension by dike injection has also occurred near the rift flanks.

Main Ethiopian Rift, continental breakup, gravity anomaly, magmatic segment, rift-margin magmatism
Nigussie, Wubamlak
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Mickus, Kevin
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Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Alemu, Abera
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Muhabaw, Yoseph
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Muluneh, Ameha
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Yehualaw, Esubalew
e332fde1-b1bb-4ea2-8428-6b48c8d9e19c
Demissie, Zelalem
d9ae17ed-2aa6-4d9b-a1cb-73154142f893
Nigussie, Wubamlak
69c11fa3-ad0f-4a84-adef-e9f5efce3d78
Mickus, Kevin
1d2af94a-3c62-42be-8e34-c438f112cd32
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Alemu, Abera
e97a8b62-f02b-499c-aedd-4c00a34694e1
Muhabaw, Yoseph
cbe75ff0-6bec-4d9a-be90-55c3cd1754ac
Muluneh, Ameha
9c48408f-650f-49ad-9133-bc201fa817ce
Yehualaw, Esubalew
e332fde1-b1bb-4ea2-8428-6b48c8d9e19c
Demissie, Zelalem
d9ae17ed-2aa6-4d9b-a1cb-73154142f893

Nigussie, Wubamlak, Mickus, Kevin, Keir, Derek, Alemu, Abera, Muhabaw, Yoseph, Muluneh, Ameha, Yehualaw, Esubalew and Demissie, Zelalem (2023) Subsurface structure of magmatic segments during continental breakup: Perspectives from a gravity data analysis along the Main Ethiopian Rift. Frontiers in Earth Science, 10, [1092759]. (doi:10.3389/feart.2022.1092759).

Record type: Article

Abstract

In magma-rich continental rifts, extension is commonly localized as dike injection in discrete magmatic segments which appear from surface geology to mimic the along-axis segmentation of ocean ridges. However, the subsurface morphology of these zones of localized magma injection is unclear, and whether and at what depth range they remain with discrete subvolcanic plumbing systems is not fully understood. In addition, the relationship between zones of magma injection and tectonic faulting is also debated. The Main Ethiopian Rift (MER) provides a unique opportunity to examine the spatial scale, locus, and subsurface geometries of magmatic localization in active continental rifts. We examined spatial variations in the structure of the crust in the MER using gravity data to better understand the subsurface pattern of magma injection. Results of our study reveal discrete Bouguer gravity highs in the centers of the distinct right-stepping magmatic segments of the MER (Aluto, Gedemsa, and Boseti), and interpreted as the locus of mafic intrusions. The gravity data show that the boundary between each magmatic segment is observed down to depths of ∼20 km, suggesting that magmatic segments have discrete subvolcanic plumbing systems at least down to the mid-crust. Additionally, incorporating the fault network shows that the densest faulting occurs at the tips of the zones of densest magma injection shown by Bouguer gravity highs. This is similar to the axial segmentation observed at slow and ultra-slow spreading ridges and suggests strong along-axis variations in deformation mechanism, with magma injection accommodating extension at the segment centers and faulting dominating towards the segment ends. In addition, rift margin volcanic zones (Siltie Debrezeit, Yerer Tulu, and Galema) are also inferred from bandpass gravity anomaly maps, supported by petrologic evidence, which implies that extension by dike injection has also occurred near the rift flanks.

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Accepted/In Press date: 12 December 2022
Published date: 4 January 2023
Additional Information: Funding Information: We are thankful to the International Gravimetric Bureau for providing the gravity data which is freely available to the public (http://ddfe.curtin.edu.au/gravitymodels/GGMplus/data/). Publisher Copyright: Copyright © 2023 Nigussie, Mickus, Keir, Alemu, Muhabaw, Muluneh, Yehualaw and Demissie.
Keywords: Main Ethiopian Rift, continental breakup, gravity anomaly, magmatic segment, rift-margin magmatism

Identifiers

Local EPrints ID: 476858
URI: http://eprints.soton.ac.uk/id/eprint/476858
PURE UUID: 7458d27c-1467-4007-8d97-677009aca513
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 17 May 2023 17:08
Last modified: 06 Jun 2024 01:49

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Contributors

Author: Wubamlak Nigussie
Author: Kevin Mickus
Author: Derek Keir ORCID iD
Author: Abera Alemu
Author: Yoseph Muhabaw
Author: Ameha Muluneh
Author: Esubalew Yehualaw
Author: Zelalem Demissie

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