Sr-Nd-Pb isotope and trace-element geochemistry evidence for a young HIMU source and assimilation at Tenerife (Canary Island)

Late Miocene-Pliocene volcanism on the Tenerife island consists of three di fferent series (Teno, Rogue del Conde and Anaga). These three series have d istinct differences in isotopic compositions. Teno, the western massif, has the most radiogenic Nd and Pb isotopes and least radiogenic Sr ratios. Ana ga, the easternmost massif, has the least radiogenic Nd and Ph, and most ra diogenic Sr found in the island. Rogue del Conde in the south has isotopic compositions between that of Teno and Anaga, similar to the younger volcani c series. All of the three late Miocene-Pliocene massifs have trace-element characteristics resembling those found in HIMU basalts. and there are only small variations between the different massifs. Variations in isotopic cha racteristics are attributed to two distinct mantle sources. One source appe ars to be a young HIMU source. The other source is an "enriched mantle sour ce" with isotopic ratios broadly similar to an EM I source, but with lower Pb-207/Pb-204 to given Pb-206/Pb-204. Assimilation during fractional crysta llisation also seems evident. The younger basalts (Las: Canadas. Dorsal and Historic) exhibit relatively homogeneous Nd and Pb isotopic compositions, but show considerable diversit y in incompatible tract-element ratios. Fractional crystallisation in perio dically refilled magma chambers and assimilation of syenite may have fracti onated incompatible trace-element ratios to some degree, but the variations could also be caused by a different degree of partial melting, with the yo unger basalt generally derived from smaller degrees of partial melt than th e older massifs. (C) 2000 Elsevier Science B.V. All rights reserved.