The volcanic rocks from Cenozoic Trans-Khamar-Daban volcanic zone (TKDVZ) in Russia and their xenocrysts and crust-mantle xenoliths were investigated by electron microprobe (EPMA) and laser-ablation inductively coupled mass-spectrometry (LA ICP MS) and other methods. They were used to show the composition and reconstructions of structure of the crust and mantle. Volcanism started from Central Part of ridge at 23 Ma and distributed to the shoulders (18–16 Ma) rift margins (13–16 Ma) and top of volcanoes (12–10 Ma), followed by rift valleys (5–2 Ma) and culminated in cinder cones volcanoes (0.8–0.15 Ma). Lavas evolved from sub-alkali to alkaline basalts and tephrites. Lherzolitic xenoliths are nearly primitive, having relics of garnets and simplectites which represent the material of mantle diapirs. The volcanics from Tunka and Dzhida valleys carry abundant cumulate xenoliths related to 2.0–1.0 GPa. The geothermal regimes reconstructed using electron probe (EPMA) mineral analyses and mineral thermobarometry is close to the South-Eastern Australian Geotherm (SEA). At the first stage, it shows heating to 1350 ◦C near Baikal Lake (Sukhoy volcano). The trace elements in the lherzolites are close to primitive mantle being more depleted near Tunka valley and showing ancient subduction related depletion and hydration in Dzhida. The cumulates show fractionation trends for pyroxenes, garnets amphiboles. The megacrysts show high La/Yb ratios increasing with Fe# for clinopyroxenes and garnets and LILE enrichments for amphiboles and Ti-biotites. The volcanism was caused by deep plume generated with the influence of the subduction from the Pacific and correlated with the events of India- Eurasia collision.

Amphibole in peridotite xenoliths in Cenozoic volcanic rocks of the Massif Central, France, is generally sparse but widely distributed. Here, we discuss its origin in the xenolith suite of Marais de Limagne (Devès volcanic field) and its bearing on evolution of lithospheric mantle in the southern part of the Massif Central. The xenoliths are lherzolites containing (1) no amphibole, (2) 2–5 vol.

The study area is located within the Bohemian Massif, a major component of the European Variscan orogenic belt. A characteristic unit within the Bohemian Massif is the multiphase South Bohemian Pluton. This work focuses on two granitic bodies within the latter, referred to as the Gutau and Kefermarkt granites. Geochemically, they display a weakly peraluminous bulk chemistry with a granitic to granodioritic composition. Gutau and Kefermarkt granites are geochemically indistinguishable and are characterized by high Th concentrations varying between 80 ppm and 100 ppm (max.120 ppm), attributed to monazite inclusions in biotite. The main characteristic of these granites is their elevated Th/U ratio, which ranges from approximately 15 to 22, significantly higher than the average continental crust value of about 4. No comparable high Th/U ratios have been reported within the South Bohemian Pluton so far. The Gutau and Kefermarkt granites are classified as A-type granites. Monazite dating from the Gutau granite yields an intrusion age of ~ 306 Ma, relating it to the youngest intrusive event within the South Bohemian Pluton. The estimated Zr-saturation temperatures are high, ranging from 820–900°C. This suggests emplacement during late post-orogenic to anorogenic tectonic relaxation. Fibrolitic sillimanite preserved as inclusions within Kfsp indicates that the granitic melts were derived from metamorphic rocks of the Monotonous Unit within the South Bohemian Pluton.

Serpentinites in fore-arc settings provide critical constraints on mantle depletion, redox evolution, and slab-mantle fluid transfer during subduction initiation. In the northern Semail Ophiolite of the United Arab Emirates, serpentinites of the Jabal Mundassah-Malaqet (JMM) are studied using mineral chemistry, whole-rock geochemitry, and platinum-group element (PGEs) compositions to constrain protolith characteristics, melting history, and tectono-magmatic evolution. The rocks comprise massive and foliated serpentinites dominated by intergrown lizardite and antigorite with relict Cr-spinel and altered olivine. The JMM serpentinites are characterized by high MgO (34.9-39.2 wt.%), extremely low Al2O3 (0.21-0.92 wt.%) and TiO2 (0.01-0.03 wt.%), elevated Ni (up to 2462 ppm) and Cr (up to 3143 ppm), and very low high-field-strength element (HFSE) and Th-U contents. These features indicate a highly refractory dunite-harzburgite protolith formed by extensive melt extraction. This interpretation is reinforced by Cr-spinel compositions (Cr# = 0.42-0.48; Mg# = 0.58-0.61) and low total PGE abundances (Sigma PGE approximate to 15-35 ppb), which are diagnostic of a strongly depleted, sulfide-exhausted mantle residue. Pronounced depletion in HFSE coupled with diagnostic Nb-Th systematics definitively fingerprints a supra-subduction zone (SSZ) fore-arc tectonic setting. PGE systematics (Sigma PGE approximate to 8-26 ppb; modest Pt-Pd enrichment over Os-Ir-Ru; low Pd/Ir=1.18-1.61) record moderate partial melting followed by selective mobilization of PPGEs during serpentinization, preserving a dominantly magmatic signature with a limited metasomatic overprint. We propose the JMM serpentinites originated as a highly depleted mantle residue during intra-oceanic subduction initiation. It was subsequently serpentinized by slab-derived fluids under fore-arc conditions before being tectonically emplaced onto the Arabian margin during Late Cretaceous ophiolite obduction. Relative to the main Semail mantle section, the JMM captures an earlier, less-evolved snapshot of fore-arc development during Late Cretaceous obduction, refining models for Neo-Tethyan subduction initiation and ophiolite assembly.

An unusual phlogopite-amphibole-plagioclase-bearing websterite xenolith has been sampled in an alkali basaltic pyrolastite from Guinadji volcano, SE Ngaoundéré, Adamawa plateau, northern Cameroon, eastern extension of the continental sector of the Cameroon volcanic line. This olivine-free websterite exhibits cumulative texture with diopside (En43.88–45.13Wo45.90–46.91Fs8.92–9.28; Mg#: 0.83–0.85) and enstatite (En75.98–76.65Wo1.21–1.76Fs21.74–22.45; Mg#: 0.77–0.79) as cumulus phases while plagioclase, a labradorite (An58.30–An61.47), represents the intercumulus phase. Amphibole is an edenite and has a Mg# varying between 0.82 and 0.83 while phlogopite has a Mg# of 0.86. Using clinopyroxene geothermobarometer, the estimated mineral equilibration temperature ranges from 1195°C to 1208°C, at pressure between 4.7 and 5.9 kbar. The metasomatic minerals filling small spaces among these pyroxenes have high potassium (K2O ∼10 wt% for phlogopite and ∼2 wt% for amphibole), high titanium (TiO2 ∼4 wt% for phlogopite and ∼2 wt% for amphibole) and high fluorine (F > 1.20 wt%) contents. This websterite would thus be of cumulative origin, formed from tholeiitic magma and metasomatized by a K–F rich crustal-derived fluids/melts with relatively high contents of Ti. The estimated high temperature at low pressure suggests a steep geothermal gradient which could be attributed to the existing plume underneath this region. Upwelling of tholeiitic magma, which represents the parental melt of the cumulate, was emplaced at the crust–mantle boundary, where the cumulate crystallized. Continued plume upwelling subsequently led to the uplift and re-equilibration of this cumulate at depths of approximately 20 km, where it underwent metasomatic modification.

The granitoids in St. Martin Island, Lesser Antilles - Caribbean, consist of granodiorites (Type-I low REE; Type-II high REE), leucotonalites, melatonalites and Qz-monzodiorites. These are I-type calc-alkaline granitoids, although classification of the newly identified melatonalites remains enigmatic, likely reflecting magma mixing between different sources for their formation. Geothermometry applications yield high formation temperatures for the melatonalites and the Type-II granodiorites exceeding by 100 degrees C those calculated for the other granitoids. Pressure conditions were relatively high for the melatonalites and granodiorites ( 4.2 and 4.0 kbar respectively), with the lowest assigned to the leucotonalites ( 1.8 kbar). Magnesiohornblende crystallized at the final crystallization stages ( 740 degrees C; 2.5 km depth), under hydrous (H2O = 3.5 wt%) and highly oxidizing conditions (Delta NNO up to +2.7). Fractional crystallization significantly contributed to the compositional variability of the evolved granitoid lithotypes, with plagioclase being preferably fractionated in the Type-I granodiorites, relative to the Type-II granodiorites that mostly involved K-feldspar removal. Additionally, fluctuation of the hydrous and slabderived fluid fluxes further promoted granitoid differentiation. Geochemical and Sr-Nd isotopic data reveal restricted sediment contamination of the mantle wedge. Melatonalites and Type-II granodiorites appear to have been formed during the early evolution stages of subduction initiation, whereas leucotonalites represent the latestage shallow crystallization granitoid phase.

The Middle Triassic magmatic event in the Southern Alps (Italy) is characterised by the emplacement and eruption of multiple magma batches with different geochemical affinities in a short time span. In this work, we present the first geochemical and geochronological data on highly differentiated alkaline dykes (phonolites) exposed in and near the Middle Triassic Predazzo magmatic complex (Southern Alps, Italy) and a first complete geochronological survey of the Predazzo pluton. The phonolites, cutting the Middle Triassic volcanic sequences, are sodalite- and aegirine-bearing and have titanite, apatite and magnetite as accessory phases. Their trace element concentration reflects a geochemical signature similar to the orogenic-like signature typical of the Middle Triassic magmatic rocks of the Predazzo complex. New in situ U-Pb dating on titanite from the phonolite dykes and U-Pb dating on zircon separates from all the magmatic units of the Predazzo pluton show that the phonolite dykes were emplaced between 233.8 f 3.1 Ma and 238.1 f 4.5 Ma, i.e., overlapping to and postdating the emplacement and crystallisation of plutonic rocks, which yield ages ranging from 237.97 f 0.15 Ma to 238.31 f 0.13 Ma. The ages obtained for the diverse suites of the pluton are in good agreement with previous dating and show that silica-saturated to -undersaturated rocks were placed within the same context in a short time span. Thermometry and hygrometry on titanite, clinopyroxene and K-feldspar revealed that phonolites represent volatile- and REE-rich (H2O = 8 f 0.6 wt%) highly differentiated alkaline melts intruding at relatively low T (752-868 degrees C), which easily caused the spatially related Cu-W mineralisation. Comparisons with subvolcanic rocks exposed in the Central (Edolo) and Western Alps (Finero mafic complex) indicate that the phonolites still preserve the orogenic signature of the Middle Triassic event in the Southalpine, that characterise all magmas emplaced before the opening of the Alpine Tethys in the Late Triassic. These new geochronological constraints on the Predazzo pluton and phonolite dykes enable us to outline the complete sequence of magmatic events associated with the emplacement of the Predazzo volcano-plutonic complex during Mid-Triassic and to speculate about the genesis of Cu-W mineralisation.

Extensional processes related to subduction initiation stages often result in the formation of back-arc basins. In central Anatolia and the northern-central Aegean, the main lithotypes geochemically correspond to high-K calk-alkaline rocks that formed during the Early Miocene, while volcanism in the Middle Miocene was predominantly Na-rich. The latter lithotypes were in most cases significantly affected by differentiation processes. On the island of Chios, volcanism is comprised of lithotypes that vary significantly from alkali basalts to rhyolites. In particular, the Pyrgi lavas are fine-grained with typical porphyritic and seriate textures, which are classified as alkali basalts according to the AFM ternary plot. These lavas also exhibit positive anomalies in PM-normalized P, Sr, and Pb elements and significant enrichments in LILE (i.e., Cs, Rb, Ba), presenting a probable interaction with subduction melts. The negative correlation between SiO2 contents and the Nb/Yb ratio indicates that crustal contamination did not play a significant role during differentiation. Crystallization appears to be under extremely dry conditions due to the absence of hydrous phases (e.g., amphibole). The presence of MORB signature spinel crystals suggests the implication of a MORB-type source. In the case of Chios, the high Nb tholeiites can be associated with petrogenetic processes in which OIB-related melts interacted with the previously metasomatized mantle wedge, confirming the back-arc extension of the Northern Aegean during the Miocene and possibly to mantle delamination in the western Anatolia region. Acknowledgments This work is part of the first author's MSc. research, which is financially supported by the «Andreas Mentzelopoulos Foundation».

The Hessian Depression in Germany is the northern continuation of the Upper Rhine Graben, from which it is separated by the Vogelsberg volcanic region. Abundant Cenozoic basaltic eruptions locally brought mantle xenoliths to the surface. The legacy suite of 15 ultramafic xenoliths from the St & ouml;pfling quarry has been studied in detail to decipher nature and evolution of this fragment of European mantle lithosphere. The xenolith suite comprises harzburgites, clinopyroxene-poor lherzolites and clinopyroxene-rich lherzolites. One of the xenoliths is a harzburgite hosting a centimetric olivine websterite layer. Olivine contains 90.1-91.5 % forsterite, 0.39-0.43 wt%. NiO, 120-500 mu g/g Ca. Orthopyroxene (0.10-0.18 atoms of Al per formula unit, pfu), has Mg/(Mg + Fe), Mg#, of 0.90-0.92, similar to that of olivine. Clinopyroxene (0.12-0.25 atoms Al pfu; Mg# 0.90-0.95). Rare Earth Elements (REE) and trace-element patterns are highly variable, but all are enriched in light REE relative to medium/heavy REE. Spinel Cr/(Cr + Al) varies from 17 to 46. The Sr-87/Sr-86 ratios measured in situ in clinopyroxene vary from 0.703969(+/- 37 1 sigma) to 0.708615(+/- 149 1 sigma) and are in part heterogenous at the scale of individual samples and grains. The peridotites typically have well defined olivine-orthopyroxene or olivine-only crystal preferred orientation, whereas clinopyroxene (or clinopyroxene and orthopyroxene) is oriented independently in most of the rocks. This is taken to reflect secondary clinopyroxene addition to an originally refractory harzburgite protolith. The latter is still preserved in two harzburgites with highly depleted compositions and low clinopyroxene modal abundances. Melt depletion recorded in the most depleted harzburgites was followed by carbonatitic metasomatism, whereas other harzburgites and clinopyroxene-poor lherzolites were metasomatized by carbonated silicate or alkaline silicate melts. The clinopyroxene-rich lherzolites preserved relics of MORB-like refertilization, overprinted by alkaline metasomatism analogous to that affecting the rest of the rocks. The two-pyroxene equilibration temperatures (940-1050 degrees C) mostly show excellent agreement between FeMg and REE-based thermometers. This suggests chemical and thermal equilibration after clinopyroxene addition and shows that Stopfling xenoliths sample a rather narrow similar to 8 km depth interval of the mantle lithosphere. The St & ouml;pfling mantle profile probably records two-stage tectono-metasomatic evolution, comprising (1) mantle lithosphere upwelling and melting during flattening of the Variscan orogen root due to late orogenic collapse followed by thermal re-equilibration, and (2) further local lithosphere thinning during Alpine rifting, accompanied by multiple local chromatographic-style metasomatic episodes that culminated in volcanism as well as xenolith entrainment and transport to the surface.

The Jurassic western-type ophiolites of the Tethyan Pindos oceanic basin are part of an ophiolite belt that extends within the Apulian and Pelagonian subcontinents in the Balkan Peninsula. These ophiolites tend to display MORB geochemical affinities, in contrast to the adjacent eastern-type ophiolites with SSZ affinities. The Orliakas locality in Pindos (Greece) and Krrabi in the Mirdita ophiolite (Albania) are two characteristic localities, representative of the south and north branches respectively of the Pindos western-type ophiolitic belt. Both localities include rodingitized gabbroic dykes hosted in highly serpentinized peridotites.We report the occurrence of gabbronorite and olivine gabbro dykes of comparable thickness (0.5- 1.0 m) that were partly affected by rodingitization processes. In some cases, the gabbroic protoliths were found almost intact at the central parts of the dykes. Protoliths from the two localities exhibit highly comparable whole-rock geochemical properties: SiO2: 48.1-49.3 wt.%, TiO2: 0.08-0.11 wt.%, Al2O3: 16.7-18.0 wt.%, MgO: 12.2-13.5 wt.%; analogous REE patterns [(La/Yb)CN=0.2-0.4; EuCN/Eu*= 1.65-1.82]. PM-normalized multi-element patterns are also evidently comparable: noticeable LILE enrichments (e.g. Cs, Ba), higher ThPM-N and UPM-N compared to NbPM-N and TaPM-N, striking positive Pb and Sr anomalies, negative Zr and Ti anomalies.Within the same dykes from the two localities, rodingites are also highly comparable in terms of: i) participating minerals and modal composition; ii) presence of hydrogarnets of similar composition (Avg. Adr4.0Grs94.3Prp1.6Sps0.1Uv0.1); iii) subparallel whole-rock PM-normalized multi-element patterns. In addition, the REE patterns obtained from LA-ICP-MS of the garnets, vesuvianites and clinopyroxenes display similar profiles. These features signify that similarities between the south and north branches of the Pindos ophiolitic belt are likely not limited to their magmatic lithotypes but may have also experienced comparable post-magmatic rodingitization processes, assigned to extensive infiltration of alkaline, Ca-rich, and Si-poor fluids.

The middle Late Bronze Age Pre-Gava/Cruceni-Belegis II Phase (cca. 1350-1100 BCE) fortified settlement of Csanadpalota - Foldvar is located on the Hungarian-Romanian border in South-East-Hungary. The ground stone tool assemblage of the megasite has a large variety of raw materials, e.g. different types of sandstones, volcanites, metamorphic rocks etc. In this work, we are focusing on the detailed petrographic and geochemical investigation of the basalt raw material, and the comparison with the various types of Neogene-Quaternary alkaline basaltic rocks in the Carpathian-Pannonian Region. Based on the similar mineral composition and texture, bulk rock chemical composition and the composition of the olivine and spinel minerals the most probable source of this raw material is the Lucaret, - S,anovit,a (Lukacsko-Sziklas) volcano (Banat Region, Romania).

The presence of mafic enclaves within volcanic rocks, which present an evolved geochemical character, tends to be related to magma mixing. In the Hellenic Volcanic Arc, mafic enclaves are regularly encountered within the volcanics. There are a few reports regarding the islands of Santorini and Nisyros as well as in the peninsula of Methana. The petrographic and mineral chemistry data we present here concern enclaves only from the Methana peninsula. Enclaves in Methana vary in size (from a few cm up to hand-sized samples) and color (reddish to black) depending on their host lava. The typical mineral assemblage is amphibole + clinopyroxene + olivine + plagioclase ± spinel ± mica. Mineral phases of amphibole, olivine, and clinopyroxene form the major phenocrysts that are embedded within a matrix mostly of fine-grained plagioclase laths and fine-grained needle-shaped amphibole. Textural features of plagioclase reveal the predominance of wet conditions during their crystallization since their cores and/or intermediate growth zones are usually dissolved suggesting a hydrous and volatile enriched magma related to the mafic enclaves. The aforementioned mineral assemblage along with the latter petrographic features match with lamprophyric rocks and their typical porphyritic and panidiomorphic textures. This counterpart is further ascertained by the mineral chemistry of Mg-rich amphibole varieties, and primary forsterite-rich olivine as well as by the lamprophyre-related trends of clinopyroxene and mica. These preliminary results provide new insights regarding magma mixing processes that occurred at the western margin of the Hellenic Subduction Zone. Acknowledgments This work is part of the first author's Ph.D. research, which is financially supported by the «Andreas Mentzelopoulos Foundation».

Cenozoic volcanic rocks occurring in Devès volcanic field (3.5 – 0.5 Ma) in the southern mantle domain of the French Massif Central (FMC) carry abundant peridotite xenoliths sampling Continental Lithospheric Mantle (CLM) [1, 2]. CLM in this area is fertile and might have formed due to 1) extraction of small amounts of partial melt(s) from mantle, and/or 2) refertilization of depleted mantle by asthenosphere-derived melts [1, 2]. We present mineral data for peridotites from several xenolith localities at Devès, in order to shed new light on the problem and document regional-scale CLM variability. Here, we complement the existing set of mineral chemical data from Allègre [2], Mt. Coupet [3] and Mt. Briançon [4] with a new data set on peridotitic xenoliths from Allègre volcano.Peridotite xenoliths from Allègre (n = 16) are represented mostly by fine- to medium-granular lherzolites. Forsterite in olivine varies from 89.34 to 91.42%. The Mg# and Al content in orthopyroxene are: 0.89 – 0.92 and 0.06 – 0.22 apfu, respectively. In clinopyroxene, Mg# is 0.88 – 0.93 and Al content is 0.03 – 0.32 apfu. In spinel, Cr# and Mg# are: 0.09 – 0.50 and 0.63 – 0.76, respectively. Three major groups are recognized based on clinopyroxene REE patterns: (A) LREE-depleted, (B) LREE-enriched and (C) moderately LREE-enriched (spoon-shaped). However, two samples are characterized by significantly higher Cr# (0.38 – 0.50), lower Mg# (0.63 – 0.68) in spinel and lower Al in Opx and Cpx (0.06 – 0.13 and 0.03 – 0.20 apfu, respectively), along with strong LREE-enrichment and were classified as group D.The mineral major element compositions for peridotite xenoliths from Allègre resemble those from other xenolith suites at Devès [2, 3, 4]. The only difference is recognized in the composition of spinel, which in peridotites from Allègre has higher Cr# (higher by up to ~0.20) and lower Mg# (~0.05) than that from other Devès localities (including previous data from Allègre [2]). Moreover, the trace element composition of pyroxenes is very similar in all three localities. Therefore, we assume that Allègre peridotites share an evolution with peridotites from other Devès localities. They record multi-stage metasomatism, including reaction with MORB-like melt (group A) and overprint by percolating alkaline melts (group B), additionally documented by transitional lithologies (group C). On the other hand, the chemical composition of group D peridotites, which are more refractory but more strongly incompatible element-enriched, suggests the existence of mantle domains, which were not affected by MORB-like metasomatism observed in group A. Thus, despite the generally fertile composition of peridotites typical for the southern FMC mantle domain [1, 2], isolated relic pockets of more refractory material persist in the CLM, offering the rare opportunity to unravel regional CLM evolution prior to pervasive refertilization. Funding. We gratefully acknowledge funding by the project of Polish National Centre of Research 2021/41/B/ST10/00900 to JP. [1] Lenoir et al. (2000). EPSL 181, 359-375.[2] Puziewicz et al. (2020). Lithos 362–363, 105467.[3] Mazurek et al. (2024). Abstract EGU24-8658[4] Ziobro-Mikrut et al. (2024). Lithos 482-483, 107670.

The preservation of volcanic and plutonic records holds the potential to improve our comprehension of plumbing systems. It is widely accepted that numerous magmatic complexes are fed by crystal-rich magma ponding at mid to shallow crustal depth, which is periodically remobilized by the intrusion of hotter melts over extended periods. However, these mechanisms are rarely recorded in plutons. The Dolomites (Southern Alps; Italy) host large volumes of Middle Triassic volcanic and plutonic outcrops, characterized by an excellent state of preservation. This condition enables us to deeply investigate the plumbing system dynamics and connect the effusive and intrusive components of the Middle-Triassic magmatism in the Southalpine domain. In this study, a detailed textural and compositional investigation of clinopyroxene crystals in shallow crustal pyroxenites and gabbros has been done to link plutonic features to the already investigated volcanic counterparts (Nardini et al. 2022). Augitic clinopyroxene is the dominant mineral phase, with euhedral to subhedral crystals up to cm-sized dimensions. Its compositions show Mg# [MgO/(MgO+FeOtot) mol%] from 62 to 75 coupled with low Cr2O3 concentration (< 0.1 wt.%) and 0.5-1 wt.% of TiO2. The crystals occasionally show step zoning patterns towards diopsidic domains having high-Mg# (80-90), higher Cr2O3 and lower TiO2 (both from 0.1 to 0.5 wt.%) organised as outer rims, intermediate bands or as resorbed cores. These preliminary data confirm what recorded by the volcanic counterparts, suggesting a periodical mixing between trachyandesitic and trachybasaltic melts (see Nardini et al. 2022). The remarkable preservation of zoning patterns in the plutonic rocks, coupled with the consistency of clinopyroxene composition and zoning in alignment with the lavas and dykes, provides a powerful volcano-plutonic link. The analyses of exposed plutonic rocks, chemically associated with the erupted materials, provide concrete evidence of the magmatic processes that are inferred through petrogenetic modelling in volcanic rocks, with the potential to deepen our understanding of the plumbing system dynamics. ReferencesNardini, N., Casetta, F., Ickert, R. B., Mark, D. F., Ntaflos, T., Zanetti, A., & Coltorti, M. (2022). From the Middle Triassic Cima Pape complex (Dolomites; Southern Alps) to the feeding systems beneath active volcanoes: Clues from clinopyroxene textural and compositional zoning. Journal of Volcanology and Geothermal Research, 422, 107459.

Two types of mare basalt have been previously reported in the Luna-16 returned soil samples: dominant Intermediate-Ti basalts and minor Very-Low-Ti (VLT) basalts. The crystallization age of the main group of Intermediate-Ti basalts determined for 14 fragments by the Pb-Pb isochron approach is 3590.3 +/- 9.4 Ma. Intermediate-Ti basalts are likely to represent the late episode of volcanism that occupies the largest part of the Mare Fecunditatis surface. The VLT group Pb-Pb isochron obtained from 3 fragments corresponds to an age 3919 +/- 27 Ma. The VLT basalts may represent an initial underlying basaltic filling of Mare Fecunditatis, at least in some parts of the basin.

The Marais de Limagne (MdL) site is located at the Devès volcanic field in the French Massif Central. MdL is known for abundant peridotite xenoliths, which come from the “southern domain” of lithospheric mantle underlying Variscan crust of the Massif Central. The MdL xenolith suite consists of spinel lherzolites and harzburgites which contain from 0 to 21 vol. % of amphibole (Touron et al. 2008). We studied in detail 13 xenoliths in order to understand better the mechanisms of amphibole formation by modal metasomatism. The suite studied by us contains from 0 to ca. 20 vol. % of amphibole, the textural context and volume of which varies from thin rims of the mineral on spinel to rocks containing thick mantles of amphibole on subordinate or relict spinel. Exceptionally (one xenolith), amphibole occurs as interstitial grains independent of spinel. Amphibole is pargasite sensu IMA 2012 classification. Peridotites consist of olivine Fo 89.4-90.5, orthopyroxene Al 0.11-0.19 atoms per formula unit (apfu), clinopyroxene Al 0.13-0.28 apfu and spinel Cr# 0.09-0.39. The exception is harzburgite with olivine Fo 87.0 (orthopyroxene Al 0.11, clinopyroxene Al 0.15 apfu, spinel Cr# 0.15). Clinopyroxene REE patterns vary from LREE-depleted to LREE-enriched. The abundance of amphibole in many xenoliths and equal participation of peridotites with LREE-depleted and LREE-enriched clinopyroxene distinguishes the MdL suite from other xenolith suites from the Devès volcanic field, dominated by lherzolites which contain no or only traces of amphibole and mostly contain aluminous clinopyroxene with LREE-depleted REE patterns. Clinopyroxene occurring in rocks containing no or little amphibole has < 100 ppm of Sr, whereas that coexisting with abundant amphibole has 230-370 ppm of Sr. The content of Ba in amphibole varies from 2.6 ppm in rocks with only thin rims of mineral on spinel to 467.0 ppm in those which contain high volumes of amphibole. The REE patterns of amphibole are similar to those of coexisting clinopyroxene. Because both Sr and Ba are fluid-mobile elements, we assume that amphibole has originated by reaction of hydrous fluid with spinel, in which clinopyroxene has also participated as a source of elements not present in a fluid or spinel. By analogy with a similar mechanism described by Puziewicz et al. (2023), we speculate that hydrous fluid migration through the peridotite host might have induced its recrystallization. Puziewicz et al. 2023, Journal of Petrology 64: https://doi.org./10.1093/petrology/egad049 Touron et al. (2008), In: Metasomatism in Oceanic and Continental Lithospheric Mantle, Geological Society Special Publ. 293, 177-196.

Peridotite xenoliths from Scania (S Sweden), brought to the surface by Mesozoic basanitic magmas, provide insights into the lithospheric mantle underlying the East European Craton. During their ascent, some of the entrained xenoliths were infiltrated by a Si-undersaturated melt. The infiltration triggered orthopyroxene dissolution and the formation of fine-grained olivine, clinopyroxene and Si-rich glasses (trachytic/trachydacitic and dacitic). The latter interacted with clinopyroxene and/or spinel creating spongy rims of various thicknesses (from few to hundreds of μm). The reactions varied in intensity and effect depending on the distance from the xenolith margin and the duration of the reaction time. At the outer parts of xenoliths, intense reactions dissolved orthopyroxene entirely, forming spongy rims on spinel and clinopyroxene, while inner sections showed limited reactions, primarily between mafic melts and orthopyroxene. The local reheating and melting of fine-grained aggregates during the ascent of xenoliths resulted in the formation of a hydrous, high-Mg, glass-like phase.

This study investigates the mineral chemistry of olivine, orthopyroxene, clinopyroxene, and chromite phases from the Wadi Zikt high Al-chromitite within the Khor Fakkan massif of the UAE ophiolites. The ophiolites, part of the well-preserved Semail ophiolite complex, represent mantle sections formed in a supra-subduction zone (SSZ) environment. Detailed analyses reveal that the olivine exhibits high forsterite contents (Fo > 90), elevated NiO concentrations (up to 0.6 wt%), and low MnO (< 0.2 wt%), indicating significant partial melting under hydrous conditions. Orthopyroxenes display high Mg# (> 90), low Al₂O₃ (< 1.2 wt%), and elevated Cr₂O₃ (up to 0.62 wt%) contents, consistent with residues of extensive melt extraction. Clinopyroxenes are characterized by high Mg# and low TiO₂, Al₂O₃, Dy, and Yb contents suggesting a forearc setting. Chromite analyses show high Cr# (51–67), low TiO₂ (< 0.8 wt%), and low Ga/Fe3# ratio, reinforcing a fore-arc origin. The studied chromites are analogues to those of the fore-arc peridotite, indicating high degrees of partial melting (25–35%). The geochemical signatures of the studied phases, including low Ti, high Cr#, and high Mg#, suggest that the Wadi Zikt chromitite formed in a depleted mantle wedge influenced by subduction-derived fluids and boninitic melts during the early stages of subduction initiation. These findings provide critical insights into mantle wedge processes, arc magma genesis, and ophiolite formation in SSZ settings. This study underscores the significance of the Wadi Zikt chromitite as a key example of SSZ mantle dynamics and melt evolution, contributing to the broader understanding of ophiolite complexes worldwide.

Studies on mantle xenoliths evidence heterogeneities occurring in scale from single localities to large geological units. Variations of chemical composition (exceeding analytical uncertainty) occur also within single crystals, as well-defined zoning or as patchy zones. Whereas mantle-derived melts average out such micro-heterogeneities, in-situ study of mantle xenoliths allows to probe their extent and thereby unveil processes affecting the mineralogical and compositional evolution of the mantle lithosphere. Here, we present different types of micro-heterogeneities recorded by clinopyroxene and associated phases from xenolithic mantle peridotites from Sweden (Scania) and the French Massif Central (Mt. Briançon).Micro-heterogeneities in clinopyroxene occur in only one out of five types of peridotites from Scania and are mirrored by contents of major and trace elements which in general vary between cores and rims of grains, however the composition of cores may also be not homogenous. Cores of clinopyroxene crystals containing oriented lamellae of spinel are enriched in Cr (0.033-0.035 vs. 0.028-0.02 afpu in Cr-poor parts of cores) in 10-100 µm thick layers parallel to the elongation of the spinel crystals. Variations in Cr content are not reflected in trace element compositions. Furthermore, margins and areas along cracks in some clinopyroxene grains (both, lamellae-bearing and lamellae-free), are enriched in Al (0.195-0.206 vs. 0.159-0.196 afpu in unaffected rims), Cr (0.026-0.032 vs. 0.018-0.031 afpu in unaffected rims) as well as in LREE, Zr, Hf, and Ti, the latter recorded also in orthopyroxene.In Mt. Briançon mantle lherzolites, chemically heterogeneous clinopyroxene occurs in ~14% of the studied xenoliths. In some samples, the Mg# of pyroxenes and olivine Fo change gradually across a petrographic section from 0.87 to 0.89 and from 86.5 to 89.0%, respectively. The REE patterns of clinopyroxene are homogeneous at the grain scale and vary among the grains from spoon-shaped to LREE-enriched, but with no correlation to Mg# values. Another type of heterogeneity is evidenced by higher (by 0.01-0.03) values of Mg# (0.89-0.91) and contents of Al (0.245-0.252 vs 0.226-0.232 apfu in rims) and Cr (0.037-0.038 vs 0.028-0.033 apfu in rims) in cores than in rims of the same clinopyroxene grain. In those samples, clinopyroxene rims are LREE-enriched, whereas REE patterns in cores vary from spoon-shaped to LREE-enriched. The heterogeneities in cores of lamellae-bearing crystals of clinopyroxene from Sweden result from incomplete exsolution of Cr-rich spinel from the structure of clinopyroxene, while the enrichment in Al, Cr and trace elements evidences infiltration of silicate melts along margins and cracks in grains. The section-scale heterogeneities in xenoliths from Mt. Briançon document chromatographic effects of alkaline silicate metasomatism that modifies spoon-shaped REE clinopyroxene patterns to LREE-enriched ones. The LREE-enrichment of clinopyroxene rims is a record of the early stage of this process. The data unveil the dynamic nature of lithospheric mantle in terms of chemical composition and texture (e.g., exsolution) due to varying degrees of metasomatism and emphasize that detailed in-situ studies of mantle phases are necessary to fully understand Earth’s evolution. Funded by Polish National Science Centre grants no. UMO-2016/23/B/ST10/01905, UMO-2018/29/N/ST10/00259 and 2021/41/B/ST10/00900.