H, O, Sr, Nd, and Pb isotopic evidence for recycled oceanic crust in the Transitional Volcanic Group of Fuerteventura, Canary Islands, Spain

The origin of low delta(18)O values for ocean island basalts (OIBs) is debated as such low values have been taken as evidence for melt contamination by altered oceanic crust with low delta(18)O values or for the involvement of altered and subducted oceanic crust during melting at mantle depths. For the submarine-subaerial Transitional Volcanic Group of Fuerteventura (Canary Islands, Spain) low delta(18)O values (4.8 +/- 0.3 parts per thousand) measured for phlogopite and amphibole megacrysts with close-to-HIMU Sr-Nd-Pb isotope characteristics are interpreted to be primary and, on the basis of hydrogen isotope compositions, exclude the influence of crustal assimilation. The model that best describes the chemical and H-O-Sr-Nd-Pb isotope compositions of these minerals favours melting of subducted ocean crust in the OIB source as a cause of low delta(18)O values. Low deltaD values of -115 +/- 4 parts per thousand have been measured for amphibole megacrysts and are attributed to preceding phlogopite crystallization from a fluid-rich magma. However, phlogopites with close-to-HIM Sr-Nd-Pb isotope ratios are also depleted in deuterium relative to upper mantle compositions with deltaD values of -96 +/- 1 parts per thousand, which may be regarded as the pristine H isotope composition characteristic for plume material. (C) 2004 Elsevier B.V. All rights reserved.