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作者:
edited by M. Coltorti ... [et al.].
ISBN:
9781862393042
出版年代:
2010
出版社:
Geological Society
文件大小:
0 KB

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PERIDOTITE XENOLITHS FROM CENTRAL SPAIN147mantle source (asthenospheric component) and a deeply recycled enriched component, as recently suggested in some French Massif Central mantle xenoliths (Touron et al. 2008), making arguable the involvement of a HIMU component. In this sense, mantle xenoliths from the northernmost El Palo volcano indicate a long-term recycling of oceanic subducted components (Bianchini et al. 2010) that is not recorded in our studied lherzolite xenolith suite. Thus, additional sampling and new isotope data (Pb, O, etc.) are required to solve this problem.On the origin of Calatrava wehrlite xenolithsThe presence of ultrama rock types, which are not likely to be partial melting residues from fertile mantle in peridotite xenolith suites, poses the problem of their origin and signiance. Wehrlites are common in many lherzolite and harzburgite xenoliths suites. Their origin has been discussed in terms of cumulates from ma melts trapped in mantle depths or by reaction of residual wall-rock peridotites with migrating magmatic liquids, either carbonate-rich or subsaturated Fe�Ti-rich silicate melts (e.g. Hauri et al. 1993; Coltorti et al. 1999; Ionov et al. 2005; Beard et al. 2007). Wehrlite 75674, from the Calatrava xenoliths, has no cumulate textures, contains some olivine grains showing strain and deformation twins, and the majority of crystals have smooth curvilinear boundaries. Moreover, this wehrlite shows similar geochemical signatures to those of lherzolite 65294 and the other Cerro Pelado xenoliths (Figs 9�1). Thus, our petrographical observations and whole-rock composition rule out a cumulate origin for the Calatrava wehrlite studied. The similar Al content in the orthopyroxenes from the lherzolites and wehrlites (Fig. 4a) suggest that the original rock was lherzolitic. Moreover, major element trends shown by the Cerro Pelado xenoliths are similar to those described for the Fe-rich lherzolite 搘ehrlite (LW) series formed by reactive melt percolation in associated lherzolites (Ionov et al. 2005). The overlapping of trace element patterns (wehrlite and Cerro Pelado lherzolites have almost identical REE patterns, Fig. 10b) also indicates that wehrlite might have been originated by the transformation of associated slightly residual lherzolites, by percolation of metasomatic melts. Accordingly, associated lherzolites must be the protolith of the wehrlite. The lack of a marked LREE enrichment, in addition to a strong Ti�Fe enrichment of the wehrlite, suggest that the metasomatic agent was not a carbonate-rich silicate melt (Hauri et al. 1993; Coltorti et al. 1999). This is also in agreement with the lack of carbonatite metasomatism in the Calatrava peridotites, togetherFig. 14. Trace element composition of melts in equilibrium with (a) clinopyroxenes and (b) amphiboles from Calatrava lherzolites. (a) Data calculated using cpxasaltic melt partition coefients (Hart & Dunn 1993), except for Rb (Foley et al. 1996) and Ta (Adam & Green 2003). (b) Data calculated using amph�melt partition coefients of La Tourrette et al. (1995). The average composition of Calatrava host volcanics is from Cebria & Lopez-Ruiz (1995). Normalizing values for primitive mantle from McDonough & Sun (1995).xenolith compared to those from El Aprisco, and the coincidence in isotopic composition with the host basaltic magmas (Table 5 and Fig. 11). It is also in agreement with the composition of associated interstitial glasses, which involves a Na-rich alkaline melt. Thus, different silicate metasomatic agents are involved in the genesis of the wide range of Calatrava peridotite xenoliths. Cenozoic Calatrava volcanics record a HIMU component in their lithospheric�asthenospheric mantle sources based on their Sr揘d b isotopic composition (Lopez-Ruiz et al. 2002). The Sr揘d isotopic composition of mantle xenoliths from central Spain also plot close to the HIMU compositional ld (Fig. 11). Nevertheless, studied mantle xenoliths rect a previous subduction-related metasomatic imprint. Isotopic composition of mantle xenoliths from central Spain could be the result of the mixing between a more depleted
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