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Geochemical Journal Vol. 58 No. 3 (2024) pp. 109–126 DOI: 10.2343/geochemj.GJ24010
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Citation
Mengesha, H., Hiluf, H., Meshesha, D., Chekol, T. and Asimow, P. D. (2024) Geochemical characteristics of flood basalts from Adigrat area, northwestern Ethiopian
Plateau: Implication for mantle source heterogeneity.
Geochem. J.
,
58
, 109–126.
Copyright © 2024 The Geochemical Society of Japan. This is an open access article distributed under the terms of the Creative Commons BY (Attribution) License
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A R T I C L E
Geochemical characteristics of
flood
basalts
from Adigrat area, northwestern Ethiopian
Plateau: Implication for mantle source
heterogeneity
Hayelom Mengesha
1,2,3
, Hagos Hiluf
1
, Daniel Meshesha
2,3
*
, Takele Chekol
2,3
, and
Paul D. Asimow
4
1
Department of Geology, College of Natural and Computational Sciences, Adigrat University, P.O. Box 50, Adigrat, Ethiopia
2
Department of Geology, College of Applied Sciences, Addis Ababa Science and Technology University, P.O. Box 16417, Addis
Ababa, Ethiopia
3
Mineral Exploration, Extraction and Processing Center of Excellence, Addis Ababa Science and Technology University, P.O. Box
16417, Addis Ababa, Ethiopia
4
California Institute of Technology, 1200 E. California Blvd. M/C170-25 Pasadena, CA 91125, USA
*Corresponding author E-mail: daniel.meshesha@aastu.edu.et
Abstract
Geochemical data are presented for flood basalts from the Adigrat area in the northwestern Ethiopian Plateau to
determine their genesis and mantle source compositions. Stratigraphically, Adigrat flood basalts can be subdivided
into upper and lower basalts that are both sub-alkaline in composition. The lower basalts show a wider range of
MgO content (6.41–11 wt. %) relative to the upper basalts (4.77–4.9 wt. %). The geochemical variations between
the upper and lower basalts cannot be explained by crystal fractionation from a common magma source but might
reflect either the involvement of variable mantle sources or different depths and degrees of partial melting. The
trace element patterns of the upper basalts resemble those of ocean island basalt (OIB), whereas those of the lower
basalts are more akin to enriched asthenospheric mantle (E-MORB). Trace elements and their ratios show the
involvement of at least three mantle components (OIB, E-MORB, and N-MORB) in the genesis of the Adigrat
flood basalts. We envisage a scenario wherein the Oligocene continental flood basalts of the northwestern
Ethiopia plateau were triggered by the arrival of the Afar mantle plume. Low-degree melts of the plume
metasomatized the depleted asthenosphere (N-MORB component) and subsequently the thermal effect of the hot
mantle plume triggered melting of the metasomatized asthenosphere (E-MORB component) in the garnet-spinel
transition zone. The mixing of these E-MORB and N-MORB mantle components generated the lower basalts.
decompression melting of the mantle plume generated an OIB component in garnet stability field, which mixed
with the E-MORB component to produce the upper basalts.
Keywords
Adigrat, flood basalt, Afar plume, mantle source, Ethiopian Plateau
Dates
Received: July 17, 2023 Accepted: April 23, 2024 Advance publication: May 16, 2024
Introduction
The widespread volcanic activity in Ethiopia is related to
the impingement of the Afar mantle plume beneath the
lithosphere (Ebinger and Sleep, 1998; Pik
et al.
, 1998
,
1999; Rogers
et al.
, 2000; Tommasini
et al.
, 2005
;
Furman
et al.
, 2006; Beccaluva
et al.
, 2009; Rooney
et
al.
, 2012; Hiluf and Asrat, 2021; Tamirat
et al.
, 2021
;
Meshesha
et al.
, 2021). Currently, Ethiopian volcanism
forms the Ethiopian Plateau, Main Ethiopian Rift, and
Afar Depression (Rochette
et al.
, 1998; Pik
et al.
, 1998
;
Ayalew
et al.
, 2002,
2006; Peccerillo
et al.
, 2003
;
Beccaluva
et al.
, 2009). Magmatism began at 45 Ma in
southern Ethiopia (Davidson and Rex, 1980; Ebinger
et
al.
, 1993; George
et al.
, 1998); however, voluminous
continental flood basalts (CFB) erupted in the Ethiopian
plateau within a short period of time between 31 and 29
Ma, prior to the onset of rifting (Hofmann
et al.
, 1997
;
Ukstins
et al.
, 2002; Coulié
et al.
, 2003
; Ayalew and
Yirgu, 2003). Later, the flood basalts were covered by
the eruptives from several large shield volcanoes (e.g.,
Simen shield ~29.1 Ma, Gunguftu ~22.3 Ma, Mt. Choke
~22.4 Ma, Mt. Uorra and Mt. Guna ~10.7 Ma; Kieffer
et
al.
, 2004 and references therein). This feature makes the
Ethiopian continental flood basalt province different
from other continental flood basalt provinces (e.g.,
Parana and Deccan provinces,
Hawkesworth
et al.
, 1986,
1988; Macdougall, 1988; Piccirillo and Melfi, 1988
).
These shield volcanoes have alkaline to transitional geo‐
chemical affinity (Kieffer
et al.
, 2004; Tamirat
et al.
,
2021; Girum
et al.
, 2023).
The sources of the Ethiopian flood and shield volca‐
noes have been assigned, by various authors, to a hetero‐
geneous Afar mantle plume and to asthenospheric and
lithospheric mantle components (e.g., Hart
et al.
, 1989
;
Feyissa
et al.
, 2017; Pik
et al.
, 1998, 1999; Kieffer
et al.
,
2004; Meshesha and Shinjo, 2007,
2008; Beccaluva
et
al.
, 2009,
2011 ; Nelson
et al.
, 2019; Natali
et al.
, 2016
,
Tamirat
et al.
, 2021; Meshesha
et al.
, 2021; Girum
et al.
,
2023). Isotopic studies have suggested contributions of
nearly all of the commonly recognized oceanic mantle
end-members [Depleted MORB Mantle (DMM),
Enriched Mantle (EM I and II), high-μ (HIMU), and
Primitive Mantle (PRIMA)] in different proportions and
also indicated mixing of these components with distinc‐
tively continental components including both subconti‐
nental lithospheric mantle and crustal materials.
However, the relative involvement of lithospheric mantle
components (Pik
et al.
, 1998,
1999; Shinjo
et al.
, 2011
;
Feyissa
et al.
, 2017) and continental crust (Baker
et al.
,
2000; Meshesha and Shinjo, 2007,
2010) remains debat‐
able. Most studies on Ethiopian plateau magmatism have
been conducted on a regional scale (Hofmann
et al.
,
1997; Pik
et al.
, 1998, 1999; Ayalew
et al.
, 2002; Kieffer
et al.
, 2004; Beccaluva
et al.
, 2009
). Although a few spe‐
cific sections in some parts of the northwestern plateau
have been well studied (Tamirat
et al.
, 2021;
Meshesha
et al.
, 2021; Hiluf and Asrat, 2021; Girum
et al.
, 2023
),
detailed geological and geochemical investigations of
stratigraphically-controlled sections of the plateau,
including the current study area, are still scarce. Hence, it
remains difficult to correlate much of the existing geo‐
logical and geochemical data from various parts of the
Ethiopian flood basalt province.
In this study, we present an integrated study of the
Adigrat section of the Ethiopian flood basalt province.
We combine detailed field, petrographic, and major and
trace element geochemical results to evaluate the petro‐
genetic evolution and compositional variation of the
flood basalt sequence. These studies contribute addi‐
tional constraints on the regional origin of the northwest‐
ern Ethiopian plateau and reveal the involvement of
mantle plume, asthenosphere mantle and lithospheric
mantle in forming the Ethiopian flood basalts.
Geological Setting
The East African Rift System (EARS), formed in the
Cenozoic, is approximately 4,000 km long and along
much of its length is divided into Western and Eastern
branches (Chorowicz, 2005) (
Fig. 1
). The Eastern branch
includes the 1,000 km long Main Ethiopian (MER) and
1,300 km long Kenya rift systems, which cut across the
uplifted Ethiopian and Kenyan plateaus (Baker
et al.
,
1972, 1996; Merla
et al.
, 1979; George
et al.
, 1998
;
Ebinger and Sleep, 1998
; Rogers
et al.
, 2000; Wolfenden
et al.
, 2004). The Ethiopian Plateau, in turn, largely con‐
sists of a continental flood basalt province that covers a
Fig. 1.
NASA STRM image showing the distribution of
Ethiopian Continental Flood Basalt, volcanic features and
classification of the flood basalts into LT, HT-1, and HT-2 (Pik
et
al.
, 1998; Kieffer
et al.
, 2004; Beccaluva
et al.
, 2009;
Corti,
2009), (Red Rectangle represent the study area).
110
Geochemical Journal Vol. 58 No. 3 (2024)
Mengesha, H.
et al.