Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain

The Neogene volcanic province of SE Spain (NVPS) is characterized by calc-a lkaline (CA), high-K calc-alkaline (KCA), shoshonitic (SH), ultrapotassic ( UP), and alkaline basaltic (AB) volcanic series. All these series, except t he AB, have high LILE/LREE, LILE/HFSE and B/Be ratios and high but variable Sr, Pb and O isotope compositions. The KCA and SH lavas contain metapeliti c xenoliths whose mineralogical and chemical composition are typical of ana tectic restites. The geochemical characteristics of CA, KCA, SH and UP seri es suggest that they originated from the lithospheric mantle, previously co ntaminated by fluids derived from pelagic sediments. Additionally, the pres ence of restite xenoliths in the KCA and SH lavas indicates some sort of in teraction between the mantle-derived magmas and the continental crust. Trac e element and isotope modeling for the KCA and SH lavas and the restites, p oint towards the existence of two mixing stages. During the first stage, th e lithospheric mantle was contaminated by 1-5% of fluids derived from pelag ic sediments, which produced a fertile source heterogeneously enriched in i ncompatible elements (particularly LILE and LREE), as well as in Sr-87/Sr-8 6, without significant modifications of the delta(18)O values. In the secon d stage, the primary melts derived from this metasomatized mantle, which in herited the enrichment in LILE, LREE and Sr-87/Sr-86, interacted with crust al liquids from the Betic Paleozoic basement during their ascent towards th e surface. This mixing process caused an increase in delta(18)O values and, to a lesser extent, in Sr-87/Sr-86 ratios. However, the incompatible trace elements abundances only change slightly, even for high mixing rates, due to their similar concentrations in both components. We suggest the followin g geodynamic scenario to account for the global evolution of this area: (1) a Late Cretaceous to Oligocene subduction scheme during which mantle metas omatism took place, shortly followed by Upper Oligocene to Lower Miocene co ntinental collision, and (2) a Middle to Upper Miocene extensional event tr iggering partial melting of the previously metasomatized mantle and the ext rusion of the CA and associated magmas. (C) 1999 Elsevier Science B.V. All rights reserved.