Helium and argon isotopic compositions of mantle xenoliths from Tallante and Calatrava, Spain M. Martelli a, ⁎, G. Bianchini b,c , L. Beccaluva c , A. Rizzo a a Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Italy b Istituto di Geoscienze e Georisorse, Consiglio Nazionale delle Ricerche, Pisa, Italy c Dipartimento di Scienze della Terra, Università di Ferrara, Italy abstract article info Article history: Received 12 April 2010 Accepted 15 November 2010 Available online 24 November 2010 Keywords: noble gas mantle xenoliths volcanism Spain We have analyzed by single-step crushing helium and argon isotopes in olivine and orthopyroxene from mantle xenoliths of Calatrava (CLV) in central Spain and Tallante (TL) in southeast Spain. The investigation focused on carefully selected samples previously characterized in terms of major and trace elements on both bulk rock and constituent minerals, and Sr and Nd isotopes on clinopyroxene separates. Six analyses were performed on protogranular spinel lherzolites from CLV, and 17 were performed on spinel harzburgites, lherzolites, and orthopyroxenites from TL. The 40 Ar/ 36 Ar ratio was between 296 and 622, indicating atmospheric contamination, which probably occurred during exposure to the surface. The helium-isotope ratio ( 3 He/ 4 He) ranged between 3.6 and 6.5 Ra in CLV samples and between 1.4 and 5.7 Ra in TL samples. There was a positive correlation between the 3 He/ 4 He and 4 He/ 40 Ar* ratios, possibly reflecting diffusive fractionation between 3 He, 4 He, and 40 Ar within mantle sections interacting with ascending melts. However, the difference between the maximum 3 He/ 4 He ratios measured in CLV and TL appears to be related to significant differences in the metasomatic melts that affected the two sectors of the lithospheric mantle. In agreement with the findings of previous studies, the helium isotopes at CLV are compatible with metasomatism due to ascending HIMU-type asthenospheric melts. In contrast, the lower 3 He/ 4 He values recorded at TL suggest subduction-related metasomatic components that are possibly related to the Cenozoic subduction of the Betic system. Such event plausibly introduced crust-derived fluids that metasomatized the mantle wedge, slightly decreasing its 3 He/ 4 He value. Noble gases appear decoupled from other elements during these mantle processes, since comparatively low 3 He/ 4 He values have been recorded also in samples that are relatively unmetasomatized in terms of incompatible lithophile elements. We hypothesize a role for volatile-dominated, CO 2 -rich fluids progressively decoupling from the ascending metasomatic melts and migrating in the surrounding peridotite matrix to form a diffuse aureola enriched in noble gases. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The constituent minerals of mantle xenoliths often retain noble gases (mainly He, Ne, and Ar) within fluid inclusions (e.g., Dunai and Porcelli, 2002), which provides unique information on the evolution of mantle sources. Variation in the isotopic composition of He originates from the isotopic difference between (a) the pristine He trapped in the mantle at the time of formation of the Earth ( 3 He/ 4 He ~ 120 Ra, where Ra is the atmospheric 3 He/ 4 He=1.40×10 -6 ; Porcelli and Ballentine, 2002) and (b) the radiogenic He continuously produced by U and Th decay (0.03 Ra; O'Nions and Oxburgh, 1988). Mixing of these components produces a homogeneous upper asthenospheric mantle, as sampled by MORBs, of 7–9 Ra (e.g., Farley and Neroda, 1998). Therefore, He isotopes and other noble gases are a sensitive proxy of the balance between primitive and differentiated Earth reservoirs and can be used to discern the ultimate origin of fluids and their relations with subduction processes, plume ascent, and related processes. The subcontinental lithospheric mantle (SCLM) is a reservoir isolated from the convective mantle that has developed its own geochemical signature distinct from the MORB source. In this case, the peculiar affinity of noble gases for the volatile phase in a melt–volatile system (Jambon et al., 1986) means that He isotopes are often decoupled from the Sr, Nd, and Pb isotopes in subcontinental mantle xenoliths (Porcelli et al., 1986; Dunai and Porcelli, 2002), providing further information for revealing the complex petrological history of the SCLM (Graham et al., 2009 and references therein). Mantle xenoliths from the SCLM, although characterized by a low content of noble gases (e.g., Gautheron et al., 2005) that makes analysis difficult, have the advantage that they ascend very rapidly to the surface (~ 10 m/s; Yamamoto et al., 2002; Buikin et al., 2005; Kim et al., 2005), thus avoiding the crustal contamination that may affect Journal of Volcanology and Geothermal Research 200 (2011) 18–26 ⁎ Corresponding author. Via Ugo La Malfa 153, Palermo, 90146, Italy. Tel.: + 39 0916809403; fax: + 39 0916809449. E-mail address: m.martelli@pa.ingv.it (M. Martelli). 0377-0273/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2010.11.015 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores