The Quaternary volcanic rocks of the northern Afar Depression (northern Ethiopia)

Author(s)

Miruts Hagos, Christian Koeberl, Benjamin van Wyk de Vries

Abstract

The northern Afar Depression is one of the most volcano-tectonically active parts of the East African Rift system, a place where oceanic rifting may be beginning to form an incipient oceanic crust. In its center, over an area that is ~80 km long and ~50 km wide, there are seven major NNW-SSE-aligned shield volcanoes/volcanic edifices surrounded by compositionally distinct fissure-fed basalts. The Quaternary lavas in this area range from transitional to tholeiitic basalts, with significant across-axis variation both in mineralogy and chemistry. The variation in the contents of the major elements (TiO

₂, Al

₂O

₃, and Fe

₂O

₃), incompatible trace elements (Nd, Hf, Th, Ta), and the contents and ratios of the rare earth elements (REE) (e.g., (La/Yb)n = 5.3-8.9) indicate some variation in the petrogenetic processes responsible for the formation of these basalts. However, the variation in isotopic compositions of the mafic lavas is minimal (

⁸⁷Sr/

⁸⁶Sr = 0.7036-0.7041,

¹⁴³Nd/

¹⁴⁴Nd = 0.51286-0.51289), which suggests only one source for all the Danakil Depression basalts. These basalts have isotope and incompatible trace element ratios that overlap with those of the Oligocene High-Ti2 flood basalts from the Ethiopian Plateau, interpreted as being derived from the last phase/tail of the Afar mantle plume source. Moreover, the Ce/Pb, Ba/U ratios indicate that the involvement of continental crust in the petrogenesis of the basaltic rocks is minimal; instead, both depth and degree of melting of the source reservoir underneath the northern Afar Depression played a major role for the production of incompatible element-enriched basalts (e.g., AleBagu Shield basalts) and the incompatible element-depleted tholeiitic basalts (e.g., Erta'Ale and Alu Shield basalts).

Organisation(s)

Department of Lithospheric Research

External organisation(s)

Mekelle University, Naturhistorisches Museum Wien (NHM), Université Blaise Pascal, Clermont-Ferrand II

Journal

Journal of African Earth Sciences

Volume

117

Pages

29-47

No. of pages

19

ISSN

1464-343X

DOI

https://doi.org/10.1016/j.jafrearsci.2015.11.022

Publication date

05-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

105105 Geochemistry, 105124 Tectonics, 105120 Petrology

Keywords

ASJC Scopus subject areas

Earth-Surface Processes, Geology

Portal url

https://ucrisportal.univie.ac.at/en/publications/the-quaternary-volcanic-rocks-of-the-northern-afar-depression-northern-ethiopia(816841dd-a8a1-4359-b0bf-f2170186b894).html