Mantle metasomatism by melts of HIMU piclogite components: new insights from Fe-lherzolite xenoliths (Calatrava Volcanic District, central Spain)
Published:January 01, 2010
Gianluca Bianchini, Luigi Beccaluva, Costanza Bonadiman, Geoff M. Nowell, D. Graham Pearson, Franca Siena, Marjorie Wilson, 2010. "Mantle metasomatism by melts of HIMU piclogite components: new insights from Fe-lherzolite xenoliths (Calatrava Volcanic District, central Spain)", Petrological Evolution of the European Lithospheric Mantle, M. Coltorti, H. Downes, M. Grégoire, S. Y. O’Reilly
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Supplementary material: An extended dataset for calatrava xenoliths is available at: http://geolsoc.org.uk/sup18410.
Mantle xenoliths from the Calatrava Volcanic District (CLV), central Spain, are characterized by a wide compositional range that includes lherzolites (prevalent), as well as minor amounts of wehrlite, olivine (ol)-websterite and rare dunites. They generally have a bulk-rock Mg# of less than 89, lower than any primordial mantle estimates. Intra-suite variations in modal proportions are inconsistent with those predicted by melting models irrespective of the starting composition; mineral and bulk-rock variation diagrams show inconsistencies between the CLV compositions (anomalously enriched in Fe–Ti) and those predicted from the partial melting of primordial mantle material. Processes other than pure melt extraction are confirmed by the whole-rock REE (rare earth element) budget, typically characterized by LREE enrichments, with LaN/YbN (up to 6.7), probably related to pervasive metasomatism. CLV mantle clinopyroxenes (cpx) generally display fractionated REE patterns with upwards-convex shapes, characterized by low HREE (Tm–Lu) concentrations (typically <6× chondrite) and enrichments in middle–light REE (MREE–LREE) (NdN/YbN up to 7, LaN/YbN up to 5). These ‘enriched’ cpx compositions either result from re-equilibration of primary mantle cpx with an incoming melt, or represent cpx crystallization directly from the metasomatic agent. The latter was plausibly generated at greater depths in the presence of residual garnet (from peridotite or eclogite starting materials). Separated cpx have homogeneous 87Sr/86Sr compositions between 0.7031 and 0.7032; 143Nd/144Nd ranges from 0.51288 to 0.51295 (ɛNd 4.74–6.07) and 176Hf/177Hf is in the range 0.28302–0.28265 (ɛHf −3.6 to 9.0). Unlike mantle xenoliths and alpine-type peridotites from other Iberian occurrences, which range in composition from the depleted mantle (DM) to the enriched mantle (EM), the CLV mantle cpx approach the composition of the HIMU mantle end member, the genesis of which is generally interpreted as the result of long-term recycling of oceanic basalts/gabbros (or their eclogitic equivalent) via ancient subduction. A model is proposed for the mantle evolution under central Iberia, where sublithospheric convective instabilities – possibly triggered by the neighbouring subduction along the Betic collisional belt – could have remobilized deep domains from the mantle ‘transition zone’ (410–660 km), which may include relicts of older subducted slabs. Within these remobilized domains, characterized by the coexistence of peridotite and eclogite and referred to as a ‘piclogite’ association, the eclogites melt preferentially generating Fe–Ti rich melts characterized by a HIMU isotopic signature that infiltrates and metasomatizes the shallower lithospheric mantle.
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Petrological Evolution of the European Lithospheric Mantle
Several different databases and models have been developed over many years of petrological study carried out by several European and non-European groups on mantle xenoliths, peridotite massifs, ophiolites and mafic magmas spanning in age from Archaean to Recent times. This volume aims to bring together these different approaches and to integrate the geochemical perceptions of the European upper mantle. The papers include regional petrological studies of the European lithospheric mantle, from Spain to the Pannonian Basin, from Corsica and Serbia as far north as Svalbard. Six contributions are based on studies of mantle xenoliths, while the remaining three deal with ophiolitic and peridotitic complexes. A further article provides an update on the textural classification of mantle rocks using a computer-aided approach and there is an introductory overview.