The Geochemistry of the Arabian Lithospheric Mantle-a Source for Intraplate Volcanism?

We present trace element and Sr-Nd-Hf-Pb isotope compositions for clinopyroxenes from anhydrous spinel peridotite and garnet ± spinel pyroxenite xenoliths of Pan-African lithospheric mantle from Jordan, including the first high-precision double-spike Pb isotope measurements of mantle clinopyroxene. Clinopyroxenes from the peridotites are variably Th-U-LILE-LREE enriched and display prominent negative Nb, Zr and Ti anomalies. MREE-HREE abundances can generally be modelled as partial melting residues of spinel lherzolite with primitive-mantle-like composition after extraction of 5-10% melt, whereas the enrichments in Th-U-LILE-LREE require a Pan-African or later metasomatic event. The large range of Nd, Sr, Pb and Hf isotope ratios in both peridotites and pyroxenites (e.g. εNd ∼ 1·4-17·5; 206Pb/204Pb ∼ 17·2-20·4; εHf ∼ 0·6-164·6) encompasses compositions more radiogenic than mid-ocean ridge basalt (MORB), and Pb isotopes cover almost the entire range of oceanic basalt values. εHf values are some of the highest ever recorded in mantle samples and are decoupled from εNd in the same samples. Marked correlations between Sr-Nd-Pb isotopes, LILE-LREE enrichments and HFSE depletion suggest that the metasomatizing agent was a carbonatitic-rich melt and isotopic data suggest that metasomatism may have been related to Pan-African subduction. The metasomatic melt permeated depleted upper mantle (