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Southern Sweden (Scania region) is located in the peripherical parts of the East European Craton (EEC). In the Mesozoic, up to three pulses of volcanic activity took place between 191 and 110 Ma (Bergelin et al., 2006, IJES; Tappe et al., 2016, GCA). Some of the alkali basaltoids carry ultramafic, mafic and felsic xenoliths (Rehfeldt et al, 2007, IJES). In this study, we focused on the evolution of the lithospheric mantle sampled by anhydrous, spinel-facies lherzolites, harzburgites, and subordinate dunites.Based on the Fo content in olivine, the peridotites were classified into three groups. Group X peridotites are characterized by Ca-rich olivine (890-1470 ppm) with Fo=91.1-91.7. Enstatite has Mg#=91.5-91.9 and Al=0.16-0.22 atoms per formula unit (apfu), while the Cr-augite has Mg#= 90.8-91.2 and Al=0.21-0.28 apfu. Clinopyroxene is chemically homogenous in terms of trace elements and is LREE-enriched with positive Eu-anomaly. The Nd and Sr isotopic ratios in clinopyroxene are 143Nd/144Nd=0.512548 (εNd=2.63) and 87Sr/86Sr=0.704237, respectively. Olivine in group Y peridotites is Ca-poor (143Nd/144Nd=0.512624–0.512644 (εNd=4.13-4.52) and 87Sr/86Sr=0.703027–0.703100, therefore significantly more depleted than group X. In group Z peridotite the Fo content in olivine is 88.1-89.1, the Mg# in enstatite is 89.1-89.5 and its Al content is 0.19-0.20 apfu. The Mg# of Cr-diopside is 88.5-89.4 and the Al content is 0.24-0.25 apfu. The trace elements contents in clinopyroxene is homogenous and the REE pattern is flat at values double that in the primitive mantle. The highest equilibration temperatures were estimated for the group X xenoliths, where TWES=1101-1110 °C (Witt-Eickschen and Seck, 1991, CMP) and TBK=1214-1241 °C (Brey and Köhler, 1990, JoP). The temperatures calculated for group Y xenoliths are TWES=875-1033 °C and TBK=872-1027 °C and do not significantly differ between subgroups. Temperatures recorded by the group Z sample are TWES=1040-1056 °C and TBK=1065-1081 °C.The composition of group X peridotites suggests their metasomatism by a high-temperature mafic melt resembling the basaltoids from Scania. Alternatively, they may represent high-pressure cumulates, as suggested by their coarse-grained texture. The group Y peridotites record cryptic metasomatism of a significantly depleted peridotite (melt extraction ranging typically between 25 and 30%) by a carbonatitic melt. The carbonatitic metasomatic agent was fractionating chromatographically from REE-, Th- and U-rich in subgroup Y2 to -poor in those elements in subgroup Y2. The group Z peridotite possibly represents depleted peridotite which was further metasomatized by a mafic melt. The lithospheric mantle beneath the marginal part of EEC has a complex composition, which is however different from a typical cratonic mantle. Founded by Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905 and WTZ PL 08/2018.

The Wum maar is located in the Oku Volcanic group, part of continental sector of the Cameroon Volcanic Line (CVL) in west Africa, which consists of volcanoes active from Eocene to recent. The continental part of the CVL is located on the metamorphic-igneous basement of the Neoproterozoic Central African Orogenic Belt (CAOB), which originated during Gondwana assembly. Some of the CVL lavas contain spinel-facies peridotite and pyroxenite xenoliths giving insight into the mantle lithosphere underlying the CAOB.We studied xenolith suite (19 xenoliths) from the Wum maar, comprising 14 lherzolites and 5 websterites. The half of lherzolites (7) consist of minerals with fertile composition (olivine Fo89, orthopyroxene Al 0.16-0.19 atoms per formula unit, clinopyroxene Al 0.28-0.31 a pfu, spinel Cr# 0.08-0.13). Clinopyroxene is REE-depleted and has 87Sr/86Sr ratios of 0.7017-0.7021. A reconnaissance study of crystal preferred orientation (CPO) by EBSD shows that at least in part of the rocks the clinopyroxene fabric is very weak, suggesting that its crystallization post-dates the primary deformation event recorded by the olivine-orthopyroxene framework. A smaller part of lherzolites (5) contains clinopyroxene the CPO of which fits that of the olivine-orthopyroxene framework, is LREE-enriched and has 87Sr/86Sr ratios of 0.7027-0.7028. One of these lherzolites contains amphibole (pargasite), which forms aggregates and schlieren and texturally is later than olivine-pyroxene host. CPO of amphibole, ortho- and clinopyroxene is decoupled from that of olivine in that rock. Two lherzolites have slightly depleted mineral compositions (olivine Fo90-91, orthopyroxene Al 0.15 apfu, clinopyroxene Al 0.25 a pfu, spinel Cr# 0.18).Websterites are dominated by orthopyroxene (Al 0.20-0.21 a pfu) whereas clinopyroxene (Al 0.30-0.31) is subordinate, and is characterized by LREE-depletion and 87Sr/86Sr ratios of 0.7019-0.7020. Spinel occurring in websterites is aluminous (Cr# 0.04-0.06), in some samples subordinate olivine (Fo90) occurs. One of the xenoliths consists of millimetric monomineral layers of pyroxenes and olivine chemically identical to those occurring in websterites. The mineral chemical data coupled with mineral fabrics suggest that lherzolites with LREE-depleted clinopyroxene could have originated by late crystallization caused by melt metasomatism. The metasomatic agent is probably best represented by websterites, which contain LREE-depleted clinopyroxene with similar, depleted 87Sr/86Sr of 0.7019-0.7020 (compare to DM value of 0.7026, Workman and Hart 2005), confirming earlier findings of refertilization of the regional lithospheric mantle by highly depleted melts (Tedonkenfack et al. 2021). The addition of amphibole was connected with recrystallization of ortho- and clinopyroxene and with significant change of its 87Sr/86Sr signature to more radiogenic values.Funding. This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.References:Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Contributions to Mineralogy and Petrology 176: 37.Workman RK, Hart SR (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231: 53-72.

Late Carboniferous/early Permian mafic volcanic rocks occurring in Scotland carry a broad spectrum of peridotitic and pyroxenitic xenoliths. The latter provide evidence of magmatic processes in the lower crust and the lithospheric mantle. In this study we present textural and compositional data on twenty-eight pyroxenitic xenoliths from six localities from southern Scotland (Midland Valley and Southern Uplands Terranes).Most are interpreted as adcumulates (varying in grain size from fine to coarse) although some others are mesocumulates. They include both clinopyroxenites and websterites with variable amounts of olivine; phlogopite is present in only one sample. Cores of greenish clinopyroxene in three of the olivine clinopyroxenites are enveloped by brownish clinopyroxene, while one composite xenolith comprising coarse-grained olivine clinopyroxenite in sharp contact with harzburgite. Five groups, based on textural and mineralogical features were distinguished. Representatives of more than one group can be present in a single locality.Most of the samples from the same textural group share similar chemical composition. In general, the clinopyroxenes are Ti,Al-diopside/augite with Mg#=0.74-0.86; where clinopyroxenes are zoned the rims have lower Mg# and higher Al content. The orthopyroxene is an Al (±Cr)-enstatite with Mg#=0.78-0.89, olivine (Fo76-77) is relatively NiO-rich (0.16-0.29 wt.%). In clinopyroxenites the pyroxenes are LREE-enriched (LaN/LuN=1.31-3.17) with convex-upward REE patterns (SmN/LuN=2.48-7.37).The temperatures and pressures of clinopyroxene crystallization in most of the clinopyroxenites are 1220-1300°C and 1.08–1.30 GPa (Putirka, 2008), respectively. Only the composite xenolith and the coarse-grained clinopyroxenites recorded higher pressures (1.42 and 1.65-2.03 GPa, respectively). As the Moho beneath S Scotland is located at ~35 km (corresponding to ~1 GPa; Davis et al., 2012), most of the clinopyroxenites are considered to come from the uppermost portions of lithospheric mantle or lowermost continental crust; the coarse-grained clinopyroxenites and the composite xenolith sample lithospheric mantle.Clinopyroxenites from the southern Scotland crystallized from alkaline basaltic magmas similar to those that entrained them. Whilst Downes et al. (2007, 2001) had previously suggested this for clinopyroxenites from Midland Valley localities, our studies show that crystallization of mafic melts was more widespread. Strong chemical and textural variations in the pyroxenites together with relatively constant PT conditions of crystallization suggest that they formed either from melts of slightly different composition, perhaps in response to magma chamber processes such as magma replenishment and/ or mixing. While, the presence of mafic cumulates points to possible crustal underplating beneath S Scotland, the presence of a high-pressure clinopyroxenites and composite clinopyroxenitic-peridotitic xenolith imply that some of the pyroxenites originated in the lithospheric mantle.Davis et al. (2012). Geoph.J. Int., 190, 705-725.Downes et al., (2007). J. Geol. Soc., 164, 1217-1231.Downes et al. (2001). Lithos, 58, 105-124.Putirka et al. (2008). Rev. Min. Petr., 69, 61-120.This study was funded by Polish National Science Centre to MMM no. DEC-2016/23/B/ST10/01905. EPMA analyses were done within the frame of the Polish-Austrian project WTZ PL/16 and WTZ PL 08/2018.

Cameroon Volcanic Line (CVL) is located in the western part of equatorial Africa and consists of volcanoes which were active from Eocene to recent, stretching ca. 1700 km from the Atlantic in the SW into the African continent in the NE. The continental part of the CVL is located on the Neoproterozoic Central African Orogenic Belt and is situated between the Congo craton and Sahara/Western Africa craton. Mantle peridotite xenoliths which occur locally in lavas of the CVL come from the spinel facies only, suggesting a relatively shallow lithosphere-asthenosphere boundary (LAB). This is supported by seismic studies, showing the LAB at 90-100 km.In order to understand better the evolution of the lithospheric mantle beneath the CVL, we studied xenolith suite (16 xenoliths) from Befang in the Oku Massif (Tedonkenfack et al., submitted). The Befang xenoliths are almost entirely lherzolites which have cataclastic to weakly porphyroclastic texture. Harzburgites and websterites occur subordinately. Spinel is interstitial and has amoeboidal shape. The studied peridotites (14 lherzolites, 1 harzburgite) consist of minerals with almost constant composition (olivine Fo88.7-90.3, orthopyroxene Al 0.17-0.19 atoms per formula unit (a pfu), clinopyroxene Al 0.28-0.30 a pfu, spinel Cr# dominantly 0.09-0.11). Spinel of Cr# 0.15 occurs in one of the lherzolites, whereas that occurring in harzburgite has Cr# 0.19. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the EBSD-studied subset of 8 samples (one harzburgite and 7 lherzolites). Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of the fabric of host rock.These data, thermometry, phase relationships and phase equilibria diagrams suggest that the Befang mantle section was refertilised by MORB-like melt at pressures 1.0-1.4 GPa and temperatures slightly above 1200 – 1275 ºC. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the fabric of protolith. On the other hand, the LREE-depleted clinopyroxene shows discordant orientation relative to olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the melt. The major element and REEs composition of pyroxenes occurring in the Befang peridotites indicate chemical reequilibration at temperatures 930 – 1000 ºC. Trace element modeling shows that websterites can be linked to Cenozoic volcanism. We speculate that they form veins in the lithospheric mantle. Our study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process, which contrasts with the incompatible element-enriched melts typically invoked in within-plate settings.This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.References:Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Submitted.

The origin and evolution of subcontinental lithospheric mantle (SCLM) are important issues of Earth’s chemical and physical evolution. Here, we report detailed textural and chemical analyses on a mantle xenolith suite from Befang (Oku Volcanic Group, Cameroon Volcanic Line), which represents a major tectono-magmatic structure of the African plate. The samples are sourced from spinel-facies mantle and are dominated by lherzolites. Their texture is cataclastic to porphyroclastic, and foliation defined by grain-size variation and alignment of spinel occurs in part of peridotites. Spinel is interstitial and has amoeboidal shape. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the subset of one harzburgite and 7 lherzolites studied by EBSD. Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of host rock fabric. The textural, chemical and thermobarometric constraints indicate that the Befang mantle section was refertilised by MORB-like melt at pressures of 1.0–1.4 GPa and temperatures slightly above 1200–1275 °C. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the protolith fabric. In contrast, the LREE-depleted clinopyroxene, showing discordant deformation relative to the olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the infiltrating melt. The major element and REEs composition of minerals forming the Befang peridotites indicate subsequent reequilibration at temperatures 930–1000 °C. This was followed by the formation of websterite veins in the lithospheric mantle, which can be linked to Cenozoic volcanism in the Cameroon Volcanic Line that also brought the xenoliths to the surface. This study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process.

Petrographic observations as well as new and published mineral major and trace element compositions, in part complemented by electron backscatter diffraction, evidence that representative mantle xenolith suites from several Cenozoic basalt locations in the European Variscan orogen can be grouped into three main types. Each type is derived from parts of the sub-continental lithospheric mantle which have experienced a different geological history. The oldest type, referred to as orogenic mantle, is dominated by strongly depleted harzburgites, which represent a fossil Variscan mantle wedge with slices of mantle of continental and oceanic plates attached to it during collision. This mantle lithosphere has been overprinted by Cenozoic carbonated alkali basalt melts, and clinopyroxene, if present, is LREE-enriched and re-introduced. This type of mantle is exemplified by xenoliths from Lower Silesia (Poland) and the northern Massif Central (France). The second type of lithospheric mantle lies beneath parts of the Variscan orogen which experienced Cenozoic rifting. This mantle is dominated by harzburgites and lherzolites formed by multiple episodes of reactive percolation of basaltic melts generated at various stages of continental rifting. The clinopyroxene REE patterns range from flat to LREE-enriched. The xenoliths from Vogelsberg (Germany) are an example of such a lithospheric mantle. The third mantle type consists of lherzolites which originated by refertilization of a harzburgitic protolith by melts derived from upwelled asthenosphere. Lherzolites contain primary clinopyroxene characterized by LREE-depleted-patterns. The xenoliths from south Massif Central (France) are an example of that third type. The xenoliths in Cenozoic basalts considered so far show that the mantle root of the Variscan orogen in Central Europe consists of various domains which in part conserve their characteristics from the time of the Variscan collision, and in part are overprinted by metasomatism caused by late-orogenic asthenosphere upwelling or by Cenozoic rifting. The metasomatically affected domains are decoupled from the Variscan structure of the orogen.

Cameroon Volcanic Line (CVL) is a ca. 1600 km long Cenozoic volcanic chain which crosses the boundary between ocean and continent in West Africa. Its origin, as well as the nature and age of the underlying continental lithospheric mantle (CLM), is still a matter of debate. Some of the CVL lavas contain peridotite xenoliths that can provide data elucidating the role of the CLM in the sustained magma generation along the line. In this abstract we describe xenolith suite from the Befang pyroclastic cone (< 1Ma) in the Oku Massif in the continental part of CVL, consisting of 14 spinel lherzolites, one spinel harzburgite and one websterite. The xenoliths are between 3 and 21 cm in diameter and have porphyroclastic to serial or equigranular texture, with porphyroclasts of olivine or orthopyroxene up to 9 mm in diameter. Some are weakly foliated. Olivine is Fo 88.6-90.4, contains 0.36 to 0.42 wt.% NiO and 180-750 ppm of Ca. Orthopyroxene (Mg# 0.89-0.91) contains 0.14 – 0.19 atoms of Al pfu, and clinopyroxene (Mg# 0.90-0.92) contains 0.24 – 0.31 atoms of Al pfu. The Cr# of lherzolite spinel is 0.09-0.15, in the harzburgitic one it is 0.18-0.19. Pyroxenes in all studied peridotites record a temperature range of 910 – 1010°C (Brey and Köhler 1990). Clinopyroxenes’ REE patterns are flat at HREE-MREE and make a spectrum from slightly LREE-depleted to slightly LREE-enriched (LaN/LuN from 0.08 to 2.65). The trace-element patterns are flat except well-defined negative Nb-Ta and positive Th-U anomalies. Orthopyroxenes’ REE patterns are variably depleted from HREE to LREE (LaN/LuN from 0.001 to 0.037). The REE pattern of clinopyroxene occurring in websterite exhibits enrichment from HREE towards LREE with hump in Sm/Nd, typical of silicate melt crystallization. The REE pattern of clinopyroxene The Befang lherzolites represent CLM metasomatised by melts produced by various, but generally low degrees of melting of DMM-like (Depleted MORB Mantle) source. Conversely, the harzburgite was formed by low degrees (few percent) of melting of DMM.Acknowledgements. The study was funded by Polish National Centre for Science project UMO-2017/27/B/ST10/00365 to JP. EPMA analyses were done thanks to the Polish-Austrian project WTZ PL 08/2018.References:Brey, G.P. & Köhler, T. (1990). Geothermobarometry in four-phase lherzolites II. New thermobarometers and practical assessment of existing thermobarometers. Journal of Petrology 31, 1353-1378.

Mantle xenoliths in the 20 Ma Wilcza Gora basanite (Lower Silesia, NE Bohemian Massif) are mostly harzburgites, some with amphibole which is exceptional in the region. Forsterite content in olivine defines two Groups of peridotites: Group A (Fo89.1–91.5) and Group B (Fo84.2–89.2). Hornblende-clinopyroxenite, websterite and one composite xenolith consisting of dunite, olivine-hornblendite and pyroxene-hornblende-peridotite contain olivine with Fo77.3–82.5 and are classified as Group C. Group A xenoliths contain Al-poor orthopyroxene and some contain LREE-enriched clinopyroxene with negative Ti, Zr–Hf and Nb–Ta anomalies. Spinel (Cr# 0.57–0.68) is scarce in Group A, and Cr-rich pargasite occurs in only two xenoliths. Group B xenoliths contain less magnesian orthopyroxene and clinopyroxene. The REE patterns of Group B clinopyroxene are convex downward, less enriched in LREE and have smaller negative Ti, Zr–Hf and Nb–Ta anomalies than those in Group A. The Cr# in Group B spinel is 0.26–0.56, while pargasite is Ti-rich and Cr-poor. Clinopyroxene from Group C is low magnesian, slightly enriched in LREE and has no negative Ti, Zr–Hf and Nb–Ta anomalies. Group C pargasite is rich in Ti and poor in Cr. Equilibration temperatures recorded in all groups vary within the range of 905–970 °C. Xenoliths from Wilcza Gora record a polyphase lithospheric mantle evolution, starting with melting which extracted ca. 30% melt from the protolith and left a harzburgite residuum depleted in Al, lacking clinopyroxene and containing rare Cr-rich spinel. This residuum was later overprinted by chromatographic metasomatism by carbonated hydrous silicate melt related to Cenozoic volcanism. The metasomatic agent was locally hydrous enough to enable amphibole to crystallize. The Group C pyroxenites formed directly from the metasomatic melt or during peridotite–melt reactions at high melt–rock ratio. The melt is inferred to have percolated through the wall-rock peridotite, decreasing its amount and changing composition (and that of the crystallizing clinopyroxene and amphibole) as it differentiated chromatographically from Groups B to A. Enrichment in carbonatite component occurred in the further parts of a chromatographic column. Group B peridotites closest to the source of the metasomatic agent were percolated by an iron-rich melt. The latter, aside from crystallizing clinopyroxene and amphibole, caused Fe-enrichment in the host harzburgite. Such a metasomatic history is typical for the lithospheric mantle located beneath the northern margin of the Bohemian Massif, but Wilcza Gora is the only locality, where activity of a hydrous metasomatic agent is recorded. Thus, the lithospheric mantle in this area was affected by mafic silicate metasomatic agents of variable compositions.

Mantle xenoliths in Oligocene-Miocene alka- line lavas in Lower Silesia (SW Poland) and adjacent part of Upper Lusatia (SE Germany) are samples of the subcon- tinental lithospheric mantle at the time of culmination of rifting in the Eger Rift (Bohemian Massif, Central Europe). The xenoliths come from the spinel mantle facies and show that two major lithologies occur in the area: A—highly magnesian (olivine Fo 90.5-92.0) harzburgites, and B— less magnesian (olivine Fo 84.0-90.0) harzburgites. The protolith of group A was clinopyroxene-free harzburgite being the residue after extensive melting. It was affected by chromatographic carbonatite/silicate melt metasomatism, with the carbonatite metasomatism only recorded in distal parts of the chromatographic systems. The B harzburgites were penetratively metasomatised by percolating alkaline silicate melts at the time of volcanism. That metasomatism was mostly anhydrous and typically cryptic; it lowered the Mg/(Mg + Fe) ratio of olivine and orthopyroxene in the peridotites subjected to melt percolation and led in places to dissolution of clinopyroxene. The mostly harzburgitic subcontinental mantle lithospheric domain beneath Lower Silesia and Upper Lusatia differs from the lherzolitic/

A small (280 x 140 m) outcrop of peridotite occurs on Popiel Hill (Sudetes, SW Poland) within the low-grade metabasic rocks of the Rudawy Janowickie Complex, which form the eastern and north-eastern cover of the Variscan Karkonosze granite. The peridotite is situated on the Intra-Sudetic Fault, one of the major Variscan dislocations in the region. The rock consists of strongly tectonised olivine (Fo 84-88 ) and orthopyroxene (Mg# 0.84–0.88) aggregates, overgrown by tremolite-magnesiohornblende, locally forming large crystals, embedded in serpentine. Spinel and magnetite are subordinate; ilmenite, Fe-sulfide, and apatite are accessories. The bulk-rock chemical composition suggests a lherzolitic composition and the occurrence of primary clinopyroxene, now completely replaced by tremolite and magnesiohornblende. Rare Earth Element patterns are flat, slightly enriched relatively to primitive mantle, as is typical of island arc tholeiites. Olivine, orthopyroxene, and spinel were the first to crystallize, and they represent relics of a primary igneous assemblage. They were followed by tremolite and serpentine, formed during uplift and related metamorphism. The last mineral to crystallize was magnesiohornblende, which originated due to contact metamorphism by the Karkonosze granite magma. The Popiel peridotite probably represents a small slice of lherzolitic cumulate, which originated in a tholeiitic magma chamber at the roots of a supra-subduction volcanic arc.