Abstract This volume, together with its companion volume in Journal of Petrology (Volume 50, No. 7), is the result of the EMAW (European MAntle Workshop: Petrological evolution of the European Lithospheric Mantle: from Archean to Present Day) held in Ferrara from 29 to 31 August 2007. The meeting was organized by M. Coltorti (Earth Sciences Department, University of Ferrara), H. Downes (Birkbeck College, London University), M. Grégoire (Observatoire Midi Pyrénées, CNRS, Toulouse) and S. Y. O'Reilly (ARC National Key Centre, GEMOC, Macquarie University), and was sponsored by the University of Ferrara, the Istituto Universitario di Studi Superiori (IUSS) of the same university, the Gruppo Nazionale di Petrografia (GNP) and the Federazione Italiana di Scienze della Terra (FIST). The organizers would like to express their deep satisfaction with the success of the meeting and the enthusiasm it provoked, as well as a sincere thanks to all participants for their contributions. Almost 100 researchers participated in the meeting, coming from most European countries, China, Japan and Australia. The meeting was an attempt to homogenize the different databases and models that have been developed from many years of study on European mantle xenoliths, peridotite massifs, ophiolites and mafic magmas spanning in age from Archaen to Recent times. Xenoliths from Europe are mostly entrained in Cenozoic mafic magmas, and the imprints of older events may be difficult to recognize in these materials. On the other hand, ophiolites and peridotite massifs record events confined to the Mesozoic history of the upper mantle, while the mafic magmas

Abstract The Monte Maggiore peridotite represents subcontinental mantle that underwent tectonic and magmatic evolution during the rifting stage of the Jurassic Ligurian Tethys oceanic basin. Pristine garnet peridotites were first equilibrated under spinel-facies conditions. During continental extension they were diffusely infiltrated by asthenospheric melts that consisted of single fractional melt increments (6% melting degree) showing depleted MORB (mid-ocean ridge basalt) signature. Diffuse melt migration of undersaturated melts at spinel-facies conditions formed reactive spinel peridotites, and melt impregnation at plagioclase-facies conditions formed impregnated plagioclase peridotites. Further focused melt migration occurred within high-porosity dunite channels. Subsequently, the single melt fractions underwent coalescence to form aggregate MORB melts that were intruded into shallow magma chambers. They underwent fractional crystallization and formation of variably evolved Mg-rich and Fe–Ti-rich magmas. Mg- and Fe–Ti-gabbroic dykes were formed by intrusion along fractures of these magmas. Melt-percolated peridotites and gabbroic rocks are isotopically homogeneous, suggesting that melts which percolated and intruded the mantle lithosphere derived from isotopically homogeneous asthenospheric mantle sources. The magmatic cycle, that is, asthenosphere partial melting, lithosphere diffuse melt percolation and dyke intrusion, occurred during Late Jurassic times (163–150 Ma) and represents the youngest events of lithosphere–asthenosphere interaction so far documented in ophiolitic peridotites from the Ligurian Tethys. The Ligurian Tethys basin never reached a mature oceanic stage, that is, the genetic link between exposed oceanic crustal rocks and refractory mantle peridotites.

Abstract The Lanzo Massif in the Western Alps consists of three bodies (North, Central and South) of mantle peridotites that were exhumed from the subcontinental mantle lithosphere to the sea floor during lithosphere extension related to the formation of the Jurassic Ligurian Tethys oceanic basin. The North Lanzo protoliths were located at shallower lithospheric levels than the South Lanzo protoliths. During exhumation, early MORB-type fractional melts from the asthenosphere infiltrated and modified the South Lanzo protoliths. Later on, aggregate MORB melts passed through the South Lanzo peridotites, migrating within replacive peridotite channels, and impregnated the North Lanzo peridotites. Ongoing lithosphere extension and stretching caused break-up of the continental crust and sea-floor exposure of the Lanzo peridotites. The North Lanzo peridotites, deriving from shallower lithospheric levels, were exhumed and exposed at more external ocean–continent transition (OCT) zones of the basin, whereas the South Lanzo peridotites, deriving from deeper lithospheric levels, were exhumed and exposed at more internal oceanic (MIO) settings of the basin. Field, petrographical–structural and petrological–geochemical studies on the Lanzo mantle peridotites provide mantle constraints regarding the geodynamic evolution of the Europe–Adria extensional system during the rifting and opening of the Ligurian Tethys basin.

Abstract The Sverrefjell Quaternary volcano in Spitsbergen contains composite xenoliths showing lherzolite rocks cross-cut by websterite veins. These two rock types are characterized by similar major element compositions of olivines, orthopyroxenes, clinopyroxenes and spinels, as well as similar trace element composition for clinopyroxene. The clinopyroxenes of both rock types mostly display upwards convex or spoon-shaped REE (rare earth elements) patterns with a systematic enrichment in La over Ce (Ce N /Yb N 0.72–1.32; Sm N /Yb N 0.86–1.93 and La N /Ce N 1.27–1.93), except for one sample (SV-69) in which clinopyroxenes show a pattern characterized by low LREE compare to HREE (Ce N /Yb N 0.33–0.35). Metasomatic processes appear to be the most reasonable origin to form the lherzolite–websterite associations. We therefore propose that the Spitsbergen mantle has undergone at least two events: (1) a sub-alkaline (tholeiitic) metasomatism followed by (2) an alkaline metasomatic event.

Abstract This paper describes a rare occurrence of graphite in non-cratonic mantle rocks. Graphite has been found in garnet clinopyroxenite layers from the External Liguride peridotites that represent slices of subcontinental lithospheric mantle exhumed at the ocean floor in Mesozoic times. The high-pressure assemblage of the pyroxenites is characterized by garnet+Al–Na-rich clinopyroxene, and testifies to an early stage of equilibration at approximately 2.8 GPa and 1100 °C. Graphite occurs as small dispersed euhedral flakes and stacks of flakes. Structural characterization by microRaman spectrometry indicates a highly ordered structure, compatible with a high-temperature mantle origin. C isotope composition of graphite has a typical mantle signature. Fe–Ni–Cu sulphides occur as accessory phases, both as blebs enclosed in silicates (E-Type) and interstitial grains (I-Type). The sulphide assemblage (Ni-free pyrrhotite, pentlandite, Cu–Fe sulphides) mainly reflects subsolidus exsolution from high-temperature Fe–Ni–Cu monosulphide solid solutions with variable Ni (up to 18 wt%) and Cu content (up to 7 wt%). The origin of E- and I-Type sulphides requires the existence of an immiscible Fe–Ni–Cu sulphide liquid, which segregated from the partial melt of the garnet pyroxenite. Graphite precipitation in the pyroxenite was presumably related to the reduction of a more oxidized carbon species interacting with the sulphide liquid as a reducing agent.

Abstract 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 La N /Yb N (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) (Nd N /Yb N up to 7, La N /Yb N 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 87 Sr/ 86 Sr compositions between 0.7031 and 0.7032; 143 Nd/ 144 Nd ranges from 0.51288 to 0.51295 (ɛNd 4.74–6.07) and 176 Hf/ 177 Hf 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.

Abstract Spinel lherzolite xenoliths from the Cenozoic Calatrava volcanic field provide a sampling of the lithospheric mantle of central Spain. The xenoliths are estimated to originate from depths of 35–50 km. Trace element content of clinopyroxene and Cr-number in spinel indicate low degrees of partial melting (≤ 5%) of the xenoliths. Although a major element whole-rock model suggests wider degrees of melting, the Calatrava peridotite chemistry indicates a moderately fertile mantle beneath central Spain. Calatrava peridotite xenoliths bear evidence for interaction with two different metasomatic agents. The enrichment in LREE(light rare earth element), Th, U and Pb, and the negative anomalies in Nb–Ta in clinopyroxene and amphibole from xenoliths of El Aprisco, indicate that the metasomatic agent was probably a subduction-related melt, whereas the enrichment in MREE in clinopyroxene from xenoliths of the Cerro Pelado centre suggests an alkaline melt similar to the host undersaturated magmas. These metasomatic agents are also consistent with the chemistry of interstitial glasses found in xenoliths of the two volcanic centres. Differences in metasomatism but also in mantle composition is supported by Sr–Nd whole-rock data which show a more radiogenic nature for Sr isotopes of samples from the El Aprisco centre ( 87 Sr/ 86 Sr ratios of 0.7035–0.7044 instead of 0.7032–0.7037 for samples from Cerro Pelado). The timing of the subduction-related metasomatic stage is unconstrained, although the Calatrava intraplate volcanism intrudes an old Variscan lithospheric section reworked during the converging plate system affecting SE Iberia in the Tertiary. The presence of wehrlite types within the Calatrava peridotite xenoliths is here interpreted as a reaction of host lherzolites with silica-undersaturated silicate melts that could be related to the Calatrava alkaline magmatism. The Sr–Nd isotopic composition of Calatrava peridotites plot within the European athenospheric reservoir(EAR) mantle, these values represent more enriched signatures than those found in the other Spanish Cenozoic alkaline province of Olot.

Abstract Ultramafic xenoliths from Mont Briançon, Ray Pic and Puy Beaunit in the French Massif Central show variable mineral compositions that indicate a residual origin after various degrees of partial melting of a fertile peridotite. Furthermore, trace element and Sr–Nd isotopic variations of clinopyroxenes indicate mixing processes between depleted mantle and enriched components such as asthenospheric melt and silicate carbonatite melt. Pyroxene geothermometer and CO 2 geobarometer estimates are 860–1060 °C at 0.92–1.10 GPa for Mont Briançon, 930–980 °C at 0.89–1.04 GPa for Ray Pic and 840–940 °C at 0.59–0.71 GPa for Puy Beaunit. From south to north, the xenoliths show the following trends: (1) deeper to shallower origin; (2) more depleted mineral compositions, suggesting higher degrees of partial melting; and (3) more enriched isotopes and trace elements, indicating a mixing process with a silicate-rich carbonatite melt characterized by high H 2 O and K 2 O, possibly during Variscan subduction.

Abstract Clino- and orthopyroxenes in anhydrous spinel peridotite xenoliths from Pliocene alkali basalts of the western Pannonian Basin have been analysed for trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Clinopyroxenes show highly variable mantle normalized REE (rare earth elements) patterns but basically can be classified into three major groups: LREE-depleted, LREE-enriched and U-shaped patterns. As the REE patterns of clinopyroxenes usually reflect the REE patterns of the host peridotite, the three major REE patterns define three geochemically different groups of xenoliths. LREE-depleted xenoliths generally have undeformed protogranular textures, while the more deformed xenoliths with porphyroclastic and equigranular textures have LREE-enriched trace element patterns. The U-shaped pattern is very distinctive and is generally associated with poikilitic textures. The HREE content of the clinopyroxenes suggest that most of the xenoliths experienced less than15% partial melting, with the lowest degree occurring in the LREE-depleted xenoliths, and the highest degree in LREE-enriched xenoliths. Cryptic metasomatism frequently accompanies deformation. Metasomatic enrichment of incompatible trace elements can be observed not only in clinopyroxenes but also in coexisting orthopyroxenes. The metasomatic agents were probably alkaline mafic melts of asthenospheric origin and some may relate to upper Cretaceous alkali lamprophyre magmatism. Geochemical signatures of subduction-related melts or fluids have not been found in the anhydrous LREE-enriched xenoliths, although poikilitic xenoliths with U-shaped normalized REE patterns may indicate the influence of subduction-related melts.

Abstract A method for quantitative characterization of grain size in thin sections has been established for mantle spinel peridotite xenoliths, using optical scanning of large areas of thin sections, skeletonization of grain-section outlines and computerized measurement of individual grain-section areas. Measurements range from 218 for the coarsest example to more than 3000 in the finest grained. Variability of the samples has been examined in relation to size and number of grain-section areas measured by using multiple and orthogonal sections from several xenoliths. The results show a linear relationship of arithmetic mean against additive standard deviation, including data from coarse-grained protogranular, through porphyroclastic to the finer-grained equigranular examples. This suggests that peridotite textures form a continuous series rather than discrete groups, as suggested by qualitative (subjective) assessment. The observed distributions of grain-section areas have been explored in relation to their description and possible mechanistic origin. By direct measurement and comparison of cumulative number and area distribution curves, we show that qualitatively assessed ‘typical grain sizes’ are influenced by a small number of larger grain sections. Although the arithmetic mean and standard deviation provide a convenient method for comparison, in practice grain-section area distributions show marked positive skewness more consistent with log-normal or power-law functions. Linear log-probability curves also support the existence of a continuous series of peridotite textures, suggesting that the shallow lithospheric mantle has been subject to processes of comminution and/or grain growth dependent on the Law of Proportionate Effect. Supplementary material: Details of resolution and boundary recognition can be found at http://www.geolsoc.org.uk/SUP18398 .

Abstract Effects of mafic alkaline metasomatism have been investigated by a combined study of the East Serbian mantle xenoliths and their host alkaline rocks. Fertile xenoliths and tiny mineral assemblages found in depleted xenoliths have been investigated. Fertile lithologies are represented by clinopyroxene (cpx)-rich lherzolite and spinel (sp)-rich olivine websterite containing Ti–Al-rich Cr-augite, Fe-rich olivine, Fe–Al-rich orthopyroxene and Al-rich spinel. Depleted xenoliths, which are the predominant lithology in the suite of East Serbian xenoliths, are harzburgite, cpx-poor lherzolite and rare Mg-rich dunite. They contain small-scale assemblages occurring as pocket-like, symplectitic or irregular, deformation-assisted accumulations of metasomatic phases, generally composed of Ti–Al- and incompatible element-rich Cr-diopside, Cr–Fe–Ti-rich spinel, altered glass, olivine, apatite, ilmenite, carbonate, feldspar, and a high-TiO 2 ( c . 11 wt%) phlogopite. The fertile xenoliths are too rich in Al, Ca and Fe to simply represent undepleted mantle. By contrast, their composition can be reproduced by the addition of 5–20 wt% of a basanitic melt to refractory mantle. However, textural relationships found in tiny mineral assemblages inside depleted xenoliths imply the following reaction: opx+sp1 (primary mantle Cr-spinel) ±phlogopite+Si-poor alkaline melt=Ti–Al-cpx+sp2 (metasomatic Ti-rich spinel)±ol±other minor phases. Inversion modelling, performed on the least contaminated and most isotopically uniform host basanites ( 87 Sr/ 86 Sr= c . 0.7031; 143 Nd/ 144 Nd= c . 0.5129), implies a source that was enriched in highly and moderately incompatible elements ( c . 35–40× chondrite for U–Th–Nb–Ta, 2× chondrite for heavy rare earth elements (HREE), made up of clinopyroxene, carbonate ( c . 5%), and traces of ilmenite ( c . 1%) and apatite ( c . 0.05%). A schematic model involves: first, percolation of CO 2 - and H 2 O-rich fluids and precipitation of metasomatic hydrous minerals; and, second, the subsequent breakdown of these hydrous minerals due to the further uplift of hot asthenospheric mantle. This model links intraplate alkaline magmatism to lithospheric mantle sources enriched by sublithospheric melts at some time in the past.

Abstract 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.

Abstract Spinel lherzolites and harzburgites from Mont-Briançon and Marais de Limagne in the Devès volcanic district display coarse-grained to porphyroclastic microstructures and the modal content of volatile-bearing phases increases with the degree of deformation. Clinopyroxene and/or spinel are partly or totally reacted to amphibole. The coupled interpretations of trace-element, rare earth element (REE) and O–Sr–Nd data for clinopyroxene and amphibole indicate that the metasomatized mantle beneath Devès is a mixture of depleted and enriched mantle associated with an alkaline, high field strength element poor, and light rare earth element, U- and Th-rich carbonate-rich silicate fluid–melt metasomatic agent. Oxygen isotope and REE data for clinopyroxene–amphibole pairs indicate a (La/Yb) N enrichment related to an increasing metasomatic agent/rock ratio.

Geochemical tomography sections based on mantle-derived pyrope garnet xenocrysts have been constructed for different tectonic domains along a southern transect crossing the Tasman Line. At the regional scale, these sections reveal thicker lithosphere and lower geothermal gradients with increasing tectonothermal age of the lithosphere domains. In a transect from the easternmost locality (Jugiong) in Phanerozoic eastern Australia to the Eyre Peninsula (Gawler Craton) in Proterozoic South Australia, the palaeogeotherm decreases from greater than 50 mW/m 2 at Jugiong to around 40 mW/m 2 In South Australia and the depth to the lithosphere-asthenosphere boundary changes from ∼100 to 180 km. Geochemical tomography sections for the Gawler Craton region sampled in the Permian and the Jurassic, indicate lithosphere thinning by about 10–15 km, attributed to the effect of Pangean rifting. These physical changes are paralleled by higher MgO and lower CaO and AI 2 O 3 contents in progressively older lithospheric mantle, consistent with the global secular variation in mantle composition previously documented. Olivine is the most abundant mantle mineral in all sections and the Fe/Mg ratio of olivine is important in controlling the physical properties of lithospheric regions (density, Vp, Vs). Because olivine is rarely preserved, an inversion of the garnet-olivine Fe-Mg-exchange geothermometer has been used to calculate the Fe/Mg of olivine coexisting with each garnet grain. Application of this inversion to the southern Australian transect shows high Mg# (Mg/(Mg+Fe)) for olivine in the shallow parts of the Proterozoic western sections and more Fe-rich olivine in the Phanerozoic eastern sections. There also is an overall trend to lower Mg# with increasing depth in each section, which may reflect infiltration by asthenospherlc melts near the lithosphere-asthenosphere boundary. Olivine density varies inversely with Mg#, and the Proterozoic lithosphere in this traverse therefore is more buoyant, relative to the asthenosphere, than the Phanerozoic sections despite the lower geotherm beneath the craton. Vp and Vs vary directly with Mg# (the higher the Mg#, the higher the Vp and Vs) and thus these compositional differences are important in the interpretation of seismic tomography.