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

摘要

The Valencia Trough of northeastern Spainrepresents a poorly understood region of Cenozoic extension-related magmatism in western Europe. We present chemical dataon mafic xenoliths and their host basalt from the Roca Negracinder cone in the Catalan Volcanic Zone in the Valencia Trough.The xenoliths consist ofaugite+hornblende+oxides±plagioclase±apatite±olivine±biotite±orthopyroxene, and range from clinopyroxenites and hornblenditesto gabbroic rocks. The major and trace element compositions ofthe xenoliths are compatible with formation as cumulates from arange of olivine tholeiitic to strongly alkaline magmas, and show astrong affinity to the Middle Miocene to Recent rift-relatedmagmatism in the Catalan Volcanic Zone. The xenoliths formed attemperatures of 1110-1180℃, pressures of 2-7kb (with10kb as the upper limit), and oxygen fugacitiescorresponding to 1-2 log units above the NNO oxygenbuffer. The estimated pressure range impliesformation in magma chambers within the crust, possiblyalso near the crust/mantle boundary (underplating).The presence of crustal cumulates indicates that thetotal volume of magmas emplaced into the crust in theCatalan Volcanic Zone may be significantly larger thanindicated by surface exposures. Isotopic compositionsof the xenoliths are 87Sr/86Sr: 0.703537-0.703647,143Nd/144Nd: 0.512732-0.512766, 206Pb/204Pb: 18.097-19.106, 207Pb/204Pb: 15.522-15.579, and 208Pb/204Pb:37.850-38.794. This range suggests the involvement oftwo mantle source components. One of these may be thelow-velocity component recognized in Cenozoicmagmatism in the eastern Atlantic Ocean to centralEurope and western Mediterranean. The other component,which differs from those involved in other domains ofCenozoic volcanism in Europe and adjacent areas, maybe located in the lithospheric mantle underlying NESpain, which was metasomatized during late Variscan to early Alpine deformation.