Constraints on the magma source and rift evolution from geochemistry of the Stratoid Flood Basalts (Afar, Ethiopia)

The relationship between rifting and continental flood basalt eruptions is debated, and a control by mantle plume is commonly invoked for flood basalts production. In this work, we investigate the relationship between magmatism and rifting by studying the flood basalts erupted in Afar (4.5–0.6 Ma), known as the Stratoid and Gulf Series. We present new field observations and petrography, major and trace elements analyses and mineral chemistry of lavas collected during a regional campaign in Afar. The Series are characterized by E-MORB magmatism and residual amphibole in the mantle source, consistent with the contribution of metasomatized sub-continental lithospheric mantle during partial melting. Differences in garnet-compatible elements indicate a shallower melting column for the oldest and youngest products (4.5–2.6 Ma Lower Stratoid Series; 1.1–0.6 Ma Gulf Series), and deeper for the products erupted at 2.6–1.1 Ma (Upper Stratoid Series). Incompatible element ratios (Th/Nb, Th/Zr) indicate a higher degree of partial melting for the Gulf with respect to the Upper Stratoid Series. Accordingly with independent geophysical and stratigraphic evidence, we explain our results with rift re-localization: the Pliocene rift caused thinning of the lithosphere and the Lower Stratoid eruptions in Southern Afar, then the Pleistocene rift jumped to Central Afar under a less-extended lithosphere, producing the Upper Stratoid and, subsequently, as stretching of the lithosphere localized, the Gulf Series formed. Our findings suggest that rift migration and localization can exert a fundamental control on the spatial variability and character of flood basalts without requiring variations on the activity of the mantle plume.

Afar depression, Plio-Pleistocene magmatism, Stratoids Series, continental-ocean transition, metasomatized mantle source, rift jump

10.1029/2022GC010434

1525-2027

Tortelli, Gianmaria

cc85fd6a-8800-413d-8a4d-7d5be239dc28

Gioncada, Anna

498799a3-7cf3-469a-89cc-6bdf1c7deaac

Pagli, Carolina

290edb22-712b-4563-a868-af4c21fdb6b0

Braschi, Eleonora

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Gebru, Ermias F.

e7504b20-b499-4a5c-96b3-f562aed4ae0a

Keir, Derek

5616f81f-bf1b-4678-a167-3160b5647c65

19 August 2022

Tortelli, Gianmaria

cc85fd6a-8800-413d-8a4d-7d5be239dc28

Gioncada, Anna

498799a3-7cf3-469a-89cc-6bdf1c7deaac

Pagli, Carolina

290edb22-712b-4563-a868-af4c21fdb6b0

Braschi, Eleonora

c27793db-0d39-4eca-ac98-ead35b0c9a22

Gebru, Ermias F.

e7504b20-b499-4a5c-96b3-f562aed4ae0a

Keir, Derek

5616f81f-bf1b-4678-a167-3160b5647c65

Tortelli, Gianmaria, Gioncada, Anna, Pagli, Carolina, Braschi, Eleonora, Gebru, Ermias F. and Keir, Derek (2022) Constraints on the magma source and rift evolution from geochemistry of the Stratoid Flood Basalts (Afar, Ethiopia). Geochemistry, Geophysics, Geosystems, 23 (8), [e2022GC010434]. (doi:10.1029/2022GC010434).

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Accepted/In Press date: 7 July 2022

Published date: 19 August 2022

Additional Information: Funding Information: The research is part of the PhD of G.Tortelli and is funded by 2017 PRIN project-protocol MIUR: 2017P9AT72 PE10. G.Tortelli acknowledges support by the Tuscany Regional PhD Course in Earth Sciences. We thank R. Ishak and M. Gemelli (CISIM, University of Pisa), A. Orlando (EPMA lab., CNR-IGG of Firenze), and L. Ghezzi (ICP-MS lab., University of Pisa) for their support during analytical acquisition. We thank R. Santacroce (University of Pisa) for discussions and support. We thank the colleagues of the Addis Ababa University and the Ethiopian and Afar Regional Governments for their support and help in organizing the February 2020 campaign. We also thank the drivers of the rental agency Ethioder, and the local policeman and guides of the different woredas for their logistic support during the campaign. Open access funding provided by Università di Pisa within the CRUI-CARE Agreement. We would also like to thank Tanya Furman and one anonymous reviewer for their valuable comments and suggestions, which helped to improve the quality of our manuscript. Funding Information: The research is part of the PhD of G.Tortelli and is funded by 2017 PRIN project‐protocol MIUR: 2017P9AT72 PE10. G.Tortelli acknowledges support by the Tuscany Regional PhD Course in Earth Sciences. We thank R. Ishak and M. Gemelli (CISIM, University of Pisa), A. Orlando (EPMA lab., CNR‐IGG of Firenze), and L. Ghezzi (ICP‐MS lab., University of Pisa) for their support during analytical acquisition. We thank R. Santacroce (University of Pisa) for discussions and support. We thank the colleagues of the Addis Ababa University and the Ethiopian and Afar Regional Governments for their support and help in organizing the February 2020 campaign. We also thank the drivers of the rental agency Ethioder, and the local policeman and guides of the different woredas for their logistic support during the campaign. Open access funding provided by Università di Pisa within the CRUI‐CARE Agreement. We would also like to thank Tanya Furman and one anonymous reviewer for their valuable comments and suggestions, which helped to improve the quality of our manuscript. Publisher Copyright: © 2022. The Authors.

Keywords: Afar depression, Plio-Pleistocene magmatism, Stratoids Series, continental-ocean transition, metasomatized mantle source, rift jump