EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Stratoids flood basalt volcanism at the Afar rift: new insights from trace elements geochemistry 

Gianmaria Tortelli1,2, Anna Gioncada2, Carolina Pagli2, Eleonora Braschi3, Ermias Gebru4,5, and Derek Keir1,6
Gianmaria Tortelli et al.
  • 1University of Florence, Department of Earth Sciences, Via G. La Pira, 4, 50121 Florence, Italy (
  • 2University of Pisa, Department of Earth Sciences, Via Santa Maria, 53, 56126 Pisa, Italy
  • 3CNR, IGG, section of Florence, Via G. La Pira, 4, 50121 Firenze, Italy
  • 4University of Fribourg, Department of Geosciences, Chemin de Musée 6, 1700 Fribourg, Switzerland
  • 5Addis Ababa University, School of Earth Sciences, P. O. Box, 1176, Addis Ababa, Ethiopia
  • 6University of Southampton, School of Ocean and Earth Science, European Way, SO14 3ZH, Southampton, U.K.

In this work we investigate the genesis of widespread continental basaltic volcanism and the transition to localised magmatic segments at the Afar Rift-Rift-Rift triple junction. Basing on major and trace elements we investigated the thick (up to 1500m) and widespread (~55.000 km2) Lower (4.5-2.6 Ma) and Upper Stratoids (2.6-1.1 Ma) Series and the subsequent, less voluminous and focalised, Gulf Series (1.1-0.6 Ma). Our results, together with published geophysical and stratigraphical evidence, allow us to interpret the evolution of the Red Sea rift and the associated break-up process in Southern and Central Afar. The three Series are characterised by E-MORB magmatism and residual amphibole (K, Rb trough and Ba, Nb-Ta peak), with subordinately pyroxenite (Rb peak, Ba trough and MREE fractionation), in their mantle source, suggesting partial melting of the diffusely metasomatized sub-continental mantle. Marked differences in garnet-compatible trace elements reveal a deeper melting column for the Upper Stratoids (TbN/YbN > 1.7) with respect to the Lower Stratoids and the Gulf Series (TbN/YbN < 1.7), indicating distinct mantle sources for the three Series. Lower values of the incompatible element ratios Th/Nb, Th/Zr and LaN/SmN of the Gulf Series with respect to the Upper Stratoids indicate a higher degree of partial melting for the Gulf Series mantle source. The spatial variation in the volume and sources of Afar magmatism between 4.5-0.6 Ma correlates well with spatial changes in the locus of strain with two distinct episodes of rifting: (1) The late Miocene rifting episode (7-2.6 Ma), associated with thinned lithosphere and the Hadar Basin formation (3.8-2.9 Ma), erupted the Lower Stratoids in South Afar; (2) The Pleistocene rift (2.6-0.01 Ma), relocated in Central Afar, erupted the Upper Stratoids first (~2.6-1.1 Ma) and, subsequently, along with the stretching of the lithosphere and focalization of the rift, the Gulf Series (~1.1 Ma). Accordingly, our data supports the interpretation that the Afar strain localisation and associated magmatism migrated north-eastward from South to Central Afar through time, potentially in response to triple junction tectonics.

How to cite: Tortelli, G., Gioncada, A., Pagli, C., Braschi, E., Gebru, E., and Keir, D.: Stratoids flood basalt volcanism at the Afar rift: new insights from trace elements geochemistry , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11623,, 2022.


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