Origin and implications of mafic xenoliths associated with Cenozoic extension-related volcanism in the Valencia Trough, NE Spain

The Valencia Trough of northeastern Spain represents a poorly understood re gion of Cenozoic extension-related magmatism in western Europe. We present chemical data on mafic xenoliths and their host basalt from the Roca Negra cinder cone in the Catalan Volcanic Zone in the Valencia Trough. The xenoli ths consist of augite+hornblende+ oxides+/-plagioclase+/-apatite+/-olivine/-biotite+/-orthopyroxene, and range from clinopyroxenites and hornblendite s to gabbroic rocks. The major and trace element compositions of the xenoli ths are compatible with formation as cumulates from a range of olivine thol eiitic to strongly alkaline magmas, and show a strong affinity to the Middl e Miocene to Recent rift-related magmatism in the Catalan Volcanic Zone. Th e xenoliths formed at temperatures of 1110-1180 degrees C, pressures of 2-7 kb (with 10 kb as the upper limit), and oxygen fugacities corresponding to 1-2 log units above the NNO oxygen buffer. The estimated pressure range im plies formation in magma chambers within the crust, possibly also near the crust/mantle boundary (underplating). The presence of crustal cumulates ind icates that the total volume of magmas emplaced into the crust in the Catal an Volcanic Zone may be significantly larger than indicated by surface expo sures. Isotopic compositions of the xenoliths are Sr-87/Sr-86: 0.703537-0.7 03647, Nd-143/Nd-144: 0.512732-0.512766, Pb-206/Pb-204: 18.097-19.106, Pb-2 07/Pb-204: 15.522-15.579, and Pb-208/Pb-204: 37.850-38.794. This range sugg ests the involvement of two mantle source components. One of these may be t he low-velocity component recognized in Cenozoic magmatism in the eastern A tlantic Ocean to central Europe and western Mediterranean. The other compon ent, which differs from those involved in other domains of Cenozoic volcani sm in Europe and adjacent areas, may be located in the lithospheric mantle underlying NE Spain, which was metasomatized during late Variscan to early Alpine deformation.