Multi-stage evolution of the lithospheric mantle beneath the westernmost Mediterranean: Geochemical constraints from peridotite xenoliths in the eastern Betic Cordillera (SE Spain) Claudio Marchesi a,b, ⁎, Zoltán Konc b , Carlos J. Garrido b , Delphine Bosch c , Károly Hidas b , María Isabel Varas-Reus b , Antonio Acosta-Vigil b,d a Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18002 Granada, Spain b Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC-Universidad de Granada, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain c Géosciences Montpellier, CNRS-Université de Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France d Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, 35131 Padua, Italy abstract article info Article history: Received 31 March 2016 Accepted 16 December 2016 Available online 23 December 2016 Spinel (±plagioclase) peridotite xenoliths from the Tallante and Los Perez volcanic centres in the eastern Betics (SE Spain) range from depleted (clinopyroxene-poor) harzburgites to fertile (clinopyroxene-rich) lherzolites and orthopyroxene-free wehrlites. Significantly, only one harzburgite, which is depleted in heavy rare earth elements (HREE), retains the imprint of ca. 20% ancient melting of an original garnet lherzolite source. In contrast, REE abundances of other harzburgites and lherzolites from the eastern Betics have been increased by melt-rock reac- tion. The whole-rock and mineral compositions of these mantle rocks are largely controlled by three types of modal metasomatism: 1) common clinopyroxene-orthopyroxene addition and olivine consumption which in- creased FeOt, SiO 2 and Al 2 O 3 , and decreased MgO compared to the refractory melting products; 2) subordinate orthopyroxene dissolution and precipitation of clinopyroxene and olivine, which led to higher FeOt and MgO and lower SiO 2 than in common (orthopyroxene-rich) lherzolites; and 3) rare orthopyroxene consumption and olivine addition that caused higher FeOt and lower SiO 2 compared to the original melting residues. These mineral modal and major element variations have been produced mostly by interactions with relatively FeOt-rich/SiO 2 -poor melts, likely derived from a peridotite-pyroxenite lithospheric mantle with a highly hetero- geneous isotopic composition. Melting of the lithospheric mantle in the western Mediterranean was triggered by upwelling of the asthenosphere induced by back-arc extension in the Late Oligocene-Early Miocene. Trapping of small fractions of exotic melts in whole-rocks — likely the parental magmas of Miocene back-arc dykes that intruded the Betic crust — caused local disequilibrium between the trace element signatures and Pb isotopic compositions of clinopyroxene and whole-rock. Subsequent interaction with SiO 2 -undersaturated magmas, similar to the parental melts of the Pliocene alkali basalts that host the xenoliths, promoted orthopyroxene con- sumption and clinopyroxene-olivine enrichment at locations close to magma conduits, and finally generated orthopyroxene-free wehrlites. This event constitutes the last episode of the Cenozoic magmatic evolution of the westernmost Mediterranean which is recorded in the mantle xenoliths from the eastern Betics. © 2016 Elsevier B.V. All rights reserved. Keywords: Alkaline basalts Mantle metasomatism Pyroxenite melts Sr-Nd-Pb radiogenic isotopes Westernmost Mediterranean 1. Introduction Tectonically-emplaced orogenic peridotite massifs and mantle xeno- liths in basalts provide key pieces of information that aid the under- standing of the composition, structure, and geodynamic evolution of the lithospheric upper mantle (e.g., Bodinier and Godard, 2014; Downes, 2001; Pearson et al., 2014, and references therein). In orogens with a convoluted tectonic history, upper mantle xenoliths in post- orogenic basalts may provide invaluable help in deciphering the tectono-magmatic processes recorded in deep lithospheric mantle roots. In the Alpine Betic-Rif arched belt in the westernmost Mediterra- nean (Fig. 1a), post-orogenic Pliocene alkali basalts in the eastern Betic Cordillera entrained numerous mantle xenoliths after a complex geodynamic evolution that shaped the Gibraltar arc (Bianchini et al., 2011; Duggen et al., 2004, 2005; Rampone et al., 2010; Shimizu et al., 2008). This arc formed during N-S to NW-SE convergence between the African and European plates and contemporaneous Tertiary exten- sion that led to the opening of the Alboran sea basin. The geodynamic Lithos 276 (2017) 75–89 ⁎ Corresponding author at: Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18002 Granada, Spain. E-mail address: claudio@ugr.es (C. Marchesi). http://dx.doi.org/10.1016/j.lithos.2016.12.011 0024-4937/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos