TY - JOUR
T1 - Tertiary mafic lavas of Turkana, Kenya
T2 - Constraints on East African plume structure and the occurrence of high-μ volcanism in Africa
AU - Furman, Tanya
AU - Kaleta, Kelly M.
AU - Bryce, Julia G.
AU - Hanan, Barry B.
N1 - Funding Information:
This paper grew out of the M.S. thesis of K.M.K., who gratefully acknowledges fellowship support from the Department of Geosciences at Penn State. We are very grateful for He isotope analyses performed by D. Graham, and for Ar dates obtained by R. Duncan. Major and trace element analyses at Duke University were performed by M. Rudnicki and G. Dwyer, and we thank E. Klein for making her facility available to us. We thank Haibo Zou for conducting the TIMS analyses. T.F. supported this work through NSF EAR-0207764 and a George H. Deike, Jr grant from the College of Earth and Mineral Sciences at Penn State. J.G.B. is appreciative of support during the preparation of this manuscript from NSF EAR-0338385, as well as funds from the UNH College of Engineering and Physical Sciences. Thoughtful comments from S. Gibson, J. Mahoney and D. Geist have served to clarify our thinking and improve the manuscript.
PY - 2006/6
Y1 - 2006/6
N2 - The East African Rift System is important to understanding plume-initiated rifting as manifest in the geochemistry of mafic lavas erupted along the rift throughout its evolution. We present new data from high-MgO Tertiary lavas from Turkana, northern Kenya, to investigate regional melt source components, to identify the depths and degrees of melting, and to characterize spatially and temporally the chemical structure of the underlying mantle. The Turkana area is a region of high lithospheric extension that sits between two topographic uplifts thought to be surface expressions of one or more upwelling mantle plumes. Thinning of local crust is believed to be accompanied by widespread removal of the mantle lithosphere, causing the asthenosphere to be in close contact with the overlying crust. New geochemical data on basanites, picrites and basalts (MgO >7 wt %) tightly constrain the primary melt source regions of Tertiary volcanism. Initial isotopic signatures (143Nd/144 Nd = 0·51267-0·51283, 87Sr/86Sr = 0·7031-0·7036) and trace element abundances (Ce/Pb ∼30, La/Nb = 0·6-0·8 and Ba/Nb = 3-10) in these lavas are consistent with derivation from sub-lithospheric sources. Basalts and picrites erupted between ∼23 and 20 Ma have Sr-Nd-Pb-He isotopic characteristics indicative of high-μ influence, record high depths and degrees of partial melting, and are associated with rift propagation to the north and south. Accordingly, these lavas sample a source region that is geochemically distinct from that reflected both in Oligocene Ethiopian flood basalts and in the modern Afar region. The geochemical data support numerical and theoretical models as well as tomographic results providing for a complex thermal structure in the mantle beneath East Africa and are interpreted to reflect isotopically distinct plume heads beneath Tanzania and Afar that are derived from the chemically heterogeneous South African superplume.
AB - The East African Rift System is important to understanding plume-initiated rifting as manifest in the geochemistry of mafic lavas erupted along the rift throughout its evolution. We present new data from high-MgO Tertiary lavas from Turkana, northern Kenya, to investigate regional melt source components, to identify the depths and degrees of melting, and to characterize spatially and temporally the chemical structure of the underlying mantle. The Turkana area is a region of high lithospheric extension that sits between two topographic uplifts thought to be surface expressions of one or more upwelling mantle plumes. Thinning of local crust is believed to be accompanied by widespread removal of the mantle lithosphere, causing the asthenosphere to be in close contact with the overlying crust. New geochemical data on basanites, picrites and basalts (MgO >7 wt %) tightly constrain the primary melt source regions of Tertiary volcanism. Initial isotopic signatures (143Nd/144 Nd = 0·51267-0·51283, 87Sr/86Sr = 0·7031-0·7036) and trace element abundances (Ce/Pb ∼30, La/Nb = 0·6-0·8 and Ba/Nb = 3-10) in these lavas are consistent with derivation from sub-lithospheric sources. Basalts and picrites erupted between ∼23 and 20 Ma have Sr-Nd-Pb-He isotopic characteristics indicative of high-μ influence, record high depths and degrees of partial melting, and are associated with rift propagation to the north and south. Accordingly, these lavas sample a source region that is geochemically distinct from that reflected both in Oligocene Ethiopian flood basalts and in the modern Afar region. The geochemical data support numerical and theoretical models as well as tomographic results providing for a complex thermal structure in the mantle beneath East Africa and are interpreted to reflect isotopically distinct plume heads beneath Tanzania and Afar that are derived from the chemically heterogeneous South African superplume.
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U2 - 10.1093/petrology/egl009
DO - 10.1093/petrology/egl009
M3 - Article
AN - SCOPUS:33646872239
SN - 0022-3530
VL - 47
SP - 1221
EP - 1244
JO - Journal of Petrology
JF - Journal of Petrology
IS - 6
ER -