Crustal versus source processes recorded in dykes from the Northeast volcanic rift zone of Tenerife, Canary Islands

The Miocene-Pliocene Northeast Rift Zone (NERZ) on Tenerife is a well exposed example of a feeder system to a major ocean island volcanic rift. We present elemental and O-Sr-Nd-Pb isotope data for dykes of the NERZ with the aim of unravelling the petrological evolution of the rift and ultimately defining the mantle source contributions. Fractional crystallisation is found to be the principal control on major and trace element variability in the dykes. Differing degrees of low temperature alteration and assimilation of hydrothermally altered island edifice and pre-island siliciclastic sediment elevated the delta O-18 and the Sr-87/Sr-86 ratio of many of the dykes, but had little to no discernible effect on Nd and Pb isotopes. Once the data are screened for alteration and shallow level contamination, the underlying source variations of the NERZ essentially reflect derivation from a young High-mu (HIMU, where mu=U-238/Pb-204)-type mantle component mixed with depleted mid-ocean ridge-type mantle (DMM). The Pb isotope data of the NERZ rocks (Pb-206/Pb-204 and Pb-207/Pb-204 range from 19.591 to 19.838 and 15.603 to 15.635, respectively) support a model of initiation and growth of the rift from the Central Shield volcano (Roque del Conde), consistent with latest geochronology results. The similar isotope signature of the NERZ to both the Miocene Central Shield and the Pliocene Las Canadas central volcano suggests that the central part of Tenerife Island was supplied from a mantle source that remained of similar composition through the Miocene to the Pliocene. This can be explained by the presence of a discrete column of young HIMU-like plume material, <= 100 km in vertical extent occupying the melting zone beneath central Tenerife throughout this period. The most recent central magmatism on Tenerife appears to reflect greater entrainment of DMM material, perhaps due to waning of the HIMU-like "blob" with time. (C) 2012 Elsevier B.V. All rights reserved.