For Peer Review
Draft Manuscript for Review
Transition from plume-driven to plate-driven magmatism in
the evolution of Main Ethiopian Rift
Journal:
Journal of Petrology
Manuscript ID
JPET-Sep-18-0118.R2
Manuscript Type:
Original Manuscript
Date Submitted by the
Author:
28-Jun-2019
Complete List of Authors:
Feyissa, Dejene; Institute for Planetary Materials, Okayama University
Kitagawa, Hiroshi; Institute for Planetary Matetials, Okayama University,
Bizuneh, Tesfaye; Ethiopian Space Science and Technology Institute
Tanaka, Ryoji; Okayama University, Institute for Study of the Earth's
Interior
Kabeto, Kurkura; Addis Ababa Science and Technology University
Nakamura, Eizo; Okayama University, Institute for Study of the Earth's
Interior
Keyword:
Ethiopian Plateau, Ethiopian Rift, Afar Depression, mantle source, mantle
melting
http://www.petrology.oupjournals.org/
Manuscript submitted to Journal of Petrology
1 Transition from plume-driven to plate-driven magmatism in the
2 evolution of the Main Ethiopian Rift
3
4 Dejene Hailemariam Feyissa
1
, Hiroshi Kitagawa
1*
, Tesfaye Demissie
5 Bizuneh
1, 2
, Ryoji Tanaka
1
,
Kurkura Kabeto
1, 3†
and Eizo Nakamura
1
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7
1
Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University,
8 Yamada 827, Misasa, Tottori 682-0193, Japan
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Ethiopian Space Science and Technology Institute, Addis Ababa (5 kilo)
10
3
Addis Ababa Science and Technology University, Addis Ababa, Ethiopia, P.O Box 1647
11
†
Deceased
12
13 *Corresponding author. Email: kitaga-h@okayama-u.ac.jp
14
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16 ABSTRACT
17 New K-Ar ages, major and trace element concentrations, and Sr-Nd-Pb isotope data are
18 presented for Oligocene to recent mafic volcanic rocks from the Ethiopian Plateau, the Main
19 Ethiopian Rift (MER), and the Afar depression. Chronological and geochemical data from
20 this study are combined with previously published data sets to reveal secular variations in
21 magmatism throughout the entire Ethiopian volcanic region. The mafic lavas in these regions
22 show variability in terms of silica-saturation (i.e., alkaline and sub-alkaline series) and extent
23 of differentiation (mafic through intermediate to felsic). The P-T conditions of melting,
24 estimated using the least differentiated basalts, reveal a secular decrease in the mantle
25 potential temperature, from when the flood basalt magmas erupted (up to 1550 ˚C) to the time
26 of the rift-related magmatism (<1500 ˚C). Variations in the Sr-Nd-Pb isotopic compositions
27 of the mafic lavas can account for the involvement of multiple end-member components. The
28 relative contributions of these end-member components vary in space and time owing to
29 changes in the thermal condition of the asthenosphere and the thickness of the lithosphere.
30 The evolution of the Ethiopian rift is caused by a transition from plume-driven to plate-driven
31 mantle upwelling, although the present-day mantle beneath the MER and the Afar depression
32 is still warmer than normal asthenosphere.
33 KEY WORDS: Ethiopian Plateau, Ethiopian Rift; Afar Depression; mantle source; mantle
34 melting
35
36 INTRODUCTION
37 Understanding of the genesis of basaltic magmas in relation to tectonic setting is fundamental
38 in the petrologic and geochemical disciplines. It is generally accepted that basaltic magmas
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39 are derived, to a first order, by melting of asthenospheric mantle that adiabatically upwells to
40 the base of the lithosphere (McKenzie, 1984). Magma productivity is primarily controlled by
41 the temperature of the melting region; thus voluminous emplacement of basalt, as in Large
42 Igneous Provinces (LIPs), is generally attributed to melting of anomalously hot mantle
43 (White & McKenzie, 1989; White et al., 2008). Compositional heterogeneity is also
44 considered to be an important factor in enhancing magma productivity and diminishing the
45 need for extremely high temperatures in the mantle (Korenaga, 2004; Kitagawa et al., 2008).
46 The LIP basalts in intra-continental plate settings show geochemical evidence for interaction
47 with sub-continental lithosphere, which could result in high magma production through
48 enrichment of volatiles in the melting regions (Arndt & Christensen, 1992; Furman et al.,
49 2016).
50 The Afar province in eastern Africa and adjacent regions is one example of a recent
51 terrestrial LIP (Fig. 1; White & McKenzie, 1989). Magmatism in the region began with
52 Oligocene trap formation at about 30 Ma (Jones & Rex, 1974; Hofmann et al., 1997;
53 Rochette et al., 1998; Ukstins et al., 2002; Coulié et al., 2003; Kieffer et al., 2004; Prave et
54 al., 2016). The ensuing rift-related magmatism has been active over the last c. 27–24 Myr in
55 the Main Ethiopian Rift (MER) and Afar (WoldeGabriel et al., 1990; Chernet et al., 1998;
56 Ukistins et al., 2002; Bonini et al., 2005; Wolfenden et al., 2005; Feyissa et al., 2017). Trap-
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57 phase magmatism is thought to be the surface manifestation of melting of actively upwelling
58 mantle (i.e., a plume; Hart et al., 1989; Marty et al., 1996; Pik et al., 1998, 1999; Furman et
59 al., 2006a; Beccaluva et al., 2009; Natali et al., 2016). The present-day rift magmatism is also
60 considered to be influenced by the mantle plume (Afar mantle plume), and its
61 thermochemical effect has been intensively discussed in petrologic, geochemical, and
62 geophysical studies. For example, the excess temperature in the mantle has been estimated to
63 be 100–200 ˚C by petrologic models (Ayalew & Gibson, 2009; Rooney et al., 2012a;
64 Ferguson et al., 2013a; Pinzuti et al., 2013; Armitage et al., 2015), which are consistent with
65 the estimates based upon seismic tomography and receiver function analysis, if the
66 uncertainty of compositional effects is taken into account (e.g., Nyblade et al., 2000; Rychert
67 et al., 2012; Hammond et al., 2013). Persistent upwelling of a buoyant mantle plume is also
68 suggested by the geochemistry of Oligocene to Recent mafic volcanic rocks, such as the
69 occurrence of high
3
He/
4
He or high-T magmas throughout this period (Marty et al., 1996;
70 Scarsi & Craig, 1996; Pik et al., 2006; Furman et al., 2006a; Ayalew & Gibson, 2009;
71 Rooney et al., 2012a; Rogers et al., 2010).
72 Magmatism related to rifting in Ethiopia is still ongoing, and young volcanic activity
73 (early Pleistocene, <2 Ma) occurs in the axial sectors of the MER and Afar. Numerous
74 studies have addressed the petrogenesis of mafic magmas in these sectors in conjunction with
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