Metasedimentary and igneous xenoliths from the volcano of Tallante (Betic Cordillera, Spain): a reappraisal based on isotopic analyses

Deep seated xenoliths entrained by volcanics provide information on the composition, thermal regime and physical properties of deep inaccessible lithologies. Unfortunately, the approach of study is somewhat limited because: i) xenoliths are rare and not ubiquitous in all volcanic centers; ii) in each volcanic center the xenolith population is often monotonous, i.e. mainly represented by a prevalent lithology. The homogeneity of xenolith suites from distinct volcanic sites is ascribed to the uptake mechanism, mainly related to fluid release and bubble nucleation, which trigger discrete event of crack formation and breaking of the surrounding deep rocks. The specific depth of xenolith formation is distinctive of each magma type, and usually Cenozoic alkaline basalts of the Mediterranean region entrain xenoliths from either the uppermost lithospheric mantle (30-50 Km depth) or the lower crust, and sampling from different depths is rare. In this view, the volcano of Tallante (Pliocene) in the Betic Cordillera (Spain) represents a peculiar occurrence, where alkaline basalts uprising from mantle sources exhumed an extremely heterogeneous xenolith association, including protogranular peridotites, felsic metasedimentary rocks, as well as diverse cumulitic igneous rocks such as amphibole-clinopyroxenites and norite-gabbros. Noteworthy, the numerous studies available in the literature mainly focused on the peridotite xenoliths and failed to consider in a coherent framework the total xenolith suite of Tallante and to explain its extreme variability. Only recently, Bianchini et al. (2013) proposed that the extreme xenoliths heterogeneity recorded at Tallante could be related to the specific geodynamic setting, located along a collisioned belt, where the crust-mantle boundary is possibly characterized by an intimate association of crustal and subcrustal lithologies, interlayered as result of orogenic processes. This contribution presents new Sr-Nd isotopic analyses carried out on metasedimentary and igneous xenoliths, as well as in-situ U-Pb dating of a zircon grain from a gabbroic xenolith. The new data, discussed taking into account the most recent geophysical evidence (Thurner et al., 2014) give insights to refine the pre-existing petrological hypotheses, in the general geological framework of the Betic orogenic belt. References - Bianchini G., Braga R. & Langone A., 2013. Crustal xenoliths from Tallante (Betic Cordillera, Spain): insights into the crust–mantle boundary. Geol. Magaz. 150, 952-958. - Thurner S., Palomeras I., Levander A., Carbonell R., & Lee C.-T. Ongoing lithospheric removal in the western Mediterranean: Evidence from Ps receiver functions and thermobarometry of Neogene basalts (PICASSO project). Geochem. Geophy. Geosyst. 10.1002/2013GC005124.