Implications of widespread high-A volcanism on the Arabian Plate for Afar mantle plume and lithosphere composition Herve ´ Bertrand a, * , Gilles Chazot b , Janne Blichert-Toft a , Sophie Thoral a a Ecole Normale Supe ´rieure de Lyon et UCBL, Laboratoire des Sciences de la Terre, CNRS UMR 5570, 46 Alle ´e d’Italie, 69364 Lyon Cedex 07, France b Universite ´ Blaise Pascal et OPGC, Laboratoire de Ge ´ologie, CNRS UMR 6524, 5 rue Kessler, 63038 Clermont-Ferrand, France Received 6 August 2001; accepted 21 November 2002 Abstract We report on 55 Nd – Sr – Pb and 23 Hf isotopic compositions for late Miocene to Plio – Quaternary basalts from the Arabian Plate. The sampling profile represents a 2500 km N –S transect along the Red Sea margin from Syria to Yemen. 206 Pb/ 204 Pb displays a wide range (from 18.60 to 19.55) from south to north, indicating a pervasive high-A distribution that questions the previous attribution of this component to the Afar plume. We rather suggest that the high-A signature resides within the Arabian lithospheric mantle. Compared to basalts from northern and central Arabia (Saudi Arabia to Syria), basalts from southern Arabia (Yemen) display similar ranges for 143 Nd/ 144 Nd, 176 Hf/ 177 Hf, and 206 Pb/ 204 Pb, but are shifted towards compositions more radiogenic in Sr and 208 Pb. These distinct time-integrated Rb/Sr and Th/U ratios between north and south are believed to reflect heterogeneous development of the Arabian lithosphere through time and/or result from the thermal effect of the Afar plume on the southern part of the lithosphere. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Arabian plate; Afar; Isotope geochemistry; Lithosphere; Mantle plume 1. Introduction It is widely accepted that most Large Igneous Provinces (LIP) represent the surface expression of the arrival of mantle plume heads beneath the litho- sphere. As an example, the Afar mantle plume is believed to be responsible for the eruption of more than 2000-m-thick Oligocene flood basalts and sub- sequent volcanism over the last 30 Ma in Ethiopia, Djibouti, and Yemen. Over the past decade, a num- ber of studies have focused on the chemical and isotopic compositions of recent lavas in this area and along the Red Sea and Gulf of Aden in order to assess the composition of the Afar plume and its spatial and temporal contribution to this volcanism (Hart et al., 1989; Barrat et al., 1990; Vidal et al., 1991; Schilling et al., 1992; Chazot and Bertrand, 1993; Rogers, 1993; Volker et al., 1993; Marty et al., 0009-2541/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2541(02)00418-7 * Corresponding author. Fax: +33-472-728677. E-mail addresses: Herve.Bertrand@ens-lyon.fr (H. Bertrand), g.chazot@opgc.univ-bpclermont.fr (G. Chazot), jblicher@ens-lyon.fr (J. Blichert-Toft). www.elsevier.com/locate/chemgeo Chemical Geology 198 (2003) 47 – 61