Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

C. J. Ebinger (1) , D. Keir (2, 3) , I. D. Bastow (4) , K. Whaler (5) , J. O. S. Hammond (6) , A. Ayele (7) , M. S. Miller (8) , Christel Tiberi (9) , S. Hautot

1 Tulane University
2 DST - Dipartimento di Scienze della Terra [Firenze]
3 Ocean and Earth Science [Southampton]
4 Department of Earth Science and Engineering [Imperial College London]
5 Edin. - University of Edinburgh
6 University of London [London]
7 AAU - Addis Ababa University
8 ANU - Australian National University
9 Géosciences Montpellier

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 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 30 Ma Recent CVL, which lacks a hot spot 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 hot spot toward 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.

Mots clés: magmatic rift; crustal structure; active deformation; Africa

Domaines: Tectonique

C. J. Ebinger, D. Keir, I. D. Bastow, K. Whaler, J. O. S. Hammond, et al.. Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes. Tectonics, 2017, 36 (12), pp.3298-3332. ⟨10.1002/2017TC004526⟩. ⟨hal-01738042⟩