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Crustal structure of active deformation zones in Africa: Implications for global crustal processes

Crustal structure of active deformation zones in Africa: Implications for global crustal processes
Crustal structure of active deformation zones in Africa: Implications for global crustal processes
The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises ~20% new magmatic material ponded in the lower crust sills, and intruded as sills and dikes at shallower depths. In the Main Ethiopian rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward-dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km-thick crust. In the 30Ma-Recent CVL, which lacks a hotspot age-progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hotspot towards the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology and contributing significantly to global carbon and water fluxes.
0278-7407
Ebinger, C.B.
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Keir, D.
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Bastow, I.D.
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Whaler, K.
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Hammond, J.O.S.
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Ayele, A.
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Miller, M.S.
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Tiberi, C.
1ce11253-bdb2-4810-9536-962be2e24090
Hautot, S.
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Ebinger, C.B.
cf261414-c6ef-41b1-90f0-ac7371d44e72
Keir, D.
5616f81f-bf1b-4678-a167-3160b5647c65
Bastow, I.D.
7a2698d0-d535-4462-a9a9-0e3293d2d667
Whaler, K.
3e8d75e7-58b5-473d-bdb2-103bce91e04d
Hammond, J.O.S.
f376d740-07a8-47f7-a6cd-15cc7950a2d5
Ayele, A.
5b4eeb35-d229-4325-8940-d934dab7563d
Miller, M.S.
6991e721-6f92-4c95-b9c7-ef00a1fb0085
Tiberi, C.
1ce11253-bdb2-4810-9536-962be2e24090
Hautot, S.
9e6886a0-0d8b-41ed-8530-1dd5674ab043

Ebinger, C.B., Keir, D., Bastow, I.D., Whaler, K., Hammond, J.O.S., Ayele, A., Miller, M.S., Tiberi, C. and Hautot, S. (2017) Crustal structure of active deformation zones in Africa: Implications for global crustal processes. Tectonics. (doi:10.1002/2017TC004526).

Record type: Article

Abstract

The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises ~20% new magmatic material ponded in the lower crust sills, and intruded as sills and dikes at shallower depths. In the Main Ethiopian rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward-dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km-thick crust. In the 30Ma-Recent CVL, which lacks a hotspot age-progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hotspot towards the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology and contributing significantly to global carbon and water fluxes.

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Ebinger_et_al-2017-Tectonics - Accepted Manuscript
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Accepted/In Press date: 4 September 2017
e-pub ahead of print date: 13 November 2017

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Local EPrints ID: 415685
URI: http://eprints.soton.ac.uk/id/eprint/415685
ISSN: 0278-7407
PURE UUID: cfb0d55f-ddde-458b-9f1d-bdf7b763e05f
ORCID for D. Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 20 Nov 2017 17:30
Last modified: 28 Apr 2022 05:42

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Contributors

Author: C.B. Ebinger
Author: D. Keir ORCID iD
Author: I.D. Bastow
Author: K. Whaler
Author: J.O.S. Hammond
Author: A. Ayele
Author: M.S. Miller
Author: C. Tiberi
Author: S. Hautot

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