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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 part...
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/ Abstract.
The 156–138 Ma Chidliak kimberlites on the Eastern Hall peninsula (EHP) of Baffin Island entrained mantle xenoliths interpreted to have been a part of the Archean North Atlantic Craton (NAC) lithospheri...
The Jhalida porphyritic granitoid pluton is exposed in a regional shear zone belonging to the Chhotanagpur Gneissic Complex of the Satpura Orogen (c. 1.0 Ga), regarded as the collisional suture between the South and North Indian blocks. The pluton intruded the migmatitic gneisses, metapelites, calc-silicate rocks and amphibolites belonging to the a...
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... Franke et al., 2017;Schulmann et al., 2022), the underlying continental lithospheric mantle (CLM) has been seldom studied in relation to the crust-based division (e.g. Puziewicz et al., 2020). The CLM of the Variscan orogen in Europe has been sampled indirectly by alkaline lavas of the Central European Volcanic Province, which mark Cenozoic rifting in the foreland of the Alps (Dèzes et al., 2004), and more directly by mantle xenoliths contained therein. ...
... Briançon consists mostly of lherzolites resembling the depleted MORB mantle (DMM), and which contain LREE-depleted clinopyroxene. We show that these lherzolites originated by refertilization by MORB-like basaltic melts, consistent with the model suggested by Lenoir et al. (2000) and documented by Puziewicz et al. (2020) in xenolith suites from the nearby Allègre and Alleyras sites. ...
... Uenver-Thiele et al. (2017 and references therein) showed that the main metasomatic agents operating in the Massif Central lithospheric mantle were subduction related fluids (only in the northern domain), silicate and locally carbonatite and carbonated-silicate melts. Puziewicz et al. (2020) combined geochemical and microstructural studies on xenoliths from the southern domain. They concluded that LREE-depleted clinopyroxene is texturally later than the olivineorthopyroxene fabric and thus it is of metasomatic origin. ...
Mantle xenoliths from the Cenozoic Mt. Briançon cinder cone in the Massif Central (France) were studied in order to test previously proposed hypotheses on the structure and chemical evolution of the lithospheric mantle in the region. Mineral major and trace element compositions coupled with characterization of crystal preferred orientation (CPO) of grains allow to recognize the compositional evolution and deformation history of peridotites and show which minerals constitute the primary vs. later fabric of the rock. The Mt. Briançon xenolith suite (n = 21) consists of spinel lherzolites, except one spinel harzburgite and one olivine clinopyroxenite. Lherzolites (olivine Fo 88.5-90.4) form three major groups. Those of Group I (51-65 vol.% olivine and 10-16 vol.% clinopyroxene) contain pyroxenes of variable Al content (orthopyroxene 0.142-0.217 apfu; clinopyroxene 0.244-0.316 apfu) and aluminous spinel (Cr# 0.09-0.12). Clinopyroxene is LREE-depleted and exhibits CPO indicating that it is a newly crystallized/recrystallized phase added to the rock framework consisting of olivine and orthopyroxene. Group II lherzolites (67-83 vol.% olivine, 5-9 vol.% clinopyroxene) contain Al-poor clinopyroxene (0.208-0.245 apfu) and spinel of Cr# 0.16-0.28. Clinopyroxene is LREE-enriched and its CPO is coherent with the fabric defined by olivine and orthopyroxene, indicating a joint deformation history. The lherzolites of Group Ia (46-66 vol.% olivine, 11-26 vol.% clinopyroxene) are transitional between those of Group I and II, and the majority contain pyroxenes with Al contents similar to those of Group I, and spinel of Cr# 0.11-0.15. Clinopyroxene REE patterns are spoon-shaped. Three lherzolites cannot be classified into the mentioned groups because they exhibit REE contents in clinopyroxene that change gradually from LREE-depleted to LREE-enriched on the scale of a petrographic section. In one of them, this change is observed at the grain scale, with spoon-shaped REE patterns in the cores and LREE-enriched ones at the margins. The harzburgite is rich in Mg (olivine Fo 91.1, pyroxenes Mg# 0.92) and impoverished in Al (spinel Cr# 0.43). Clinopyroxene is enriched in LREE, the contents of which are significantly lower than those of lherzolitic clinopyroxene. It forms nearly undeformed grains in an olivine-orthopyroxene framework. The lherzolites of Group I were formed by reactive percolation of MORB-like melts under suprasolidus conditions, which enabled replacement and/or addition of clinopyroxene to the solid olivine-orthopyroxene framework. Zonal REE distribution in clinopyroxene from one of the lherzolites documents alkaline melt percolation overprinting the Group I, which ultimately formed the Group II lherzolites. The lherzolites of Group Ia document transition between those of Group I and Group II. Hypothetical melt in equilibrium with clinopyroxene in olivine clinopyroxenite has a composition similar to that of the host lava. This rock likely represents a cumulate from the same melt that infiltrated the lithosphere during the Cenozoic volcanic activity of the Massif Central.
... Mantle metasomatism by a silicate melt with crustal origin has been investigated extensively (e.g., Zanetti et al., 1999;Malaspina et al., 2006Malaspina et al., , 2009Vrijmoed et al., 2013;Zhao et al., 2021), but the composition of the metasomatizing agent has often been estimated indirectly, either because of the lack of inclusions or because the inclusions found in the targeted rocks do not represent the pristine agent (Malaspina et al., 2006(Malaspina et al., , 2009. Many studies on metasomatizing agents were conducted in mantle xenoliths (e.g., Andersen et al., 1984;Wulff-Pedersen et al., 1996;Sajona et al., 2000;Bali et al., 2002;Matusiak-Małek et al., 2010;Puziewicz et al., 2020;Liptai et al., 2021), which however mostly record processes entirely mantle related; i.e., the metasomatizing agent is originated in the mantle without any crustal contribution. In recent years, the study of MI in metamorphic rocks originally developed in partially melted rocks (e.g., Cesare et al., 2015;Nicoli and Ferrero, 2021;Nicoli et al., 2022a) has expanded to include rocks affected by external melts, thus allowing us to describe and directly characterize the nature of metasomatizing agents, especially when the metasomatism takes place in the absence of phases which are clearly metasomatic products. ...
Primary granitic melt inclusions are trapped in garnets of eclogites in the garnet peridotite body of Pfaffenberg, Granulitgebirge (Bohemian Massif, Germany). These polycrystalline inclusions, based on their nature and composition, can be called nanogranitoids and contain mainly phlogopite/biotite, kumdykolite, quartz/rare cristobalite, a phase with the main Raman peak at 412 cm−1, a phase with the main Raman peak at 430 cm−1, osumilite and plagioclase. The melt is hydrous, peraluminous and granitic and significantly enriched in large ion lithophile elements (LILE), Th, U, Li, B and Pb. The melt major element composition resembles that of melts produced by the partial melting of metasediments, as also supported by its trace element signature characterized by elements (LILE, Pb, Li and B) typical of the continental crust. These microstructural and geochemical features suggest that the investigated melt originated in the subducted continental crust and interacted with the mantle to produce the Pfaffenberg eclogite. Moreover, in situ analyses and calculations based on partition coefficients between apatite and melt show that the melt was also enriched in Cl and F, pointing toward the presence of a brine during melting. The melt preserved in inclusions can thus be regarded as an example of a metasomatizing agent present at depth and responsible for the interaction between the crust and the mantle. Chemical similarities between this melt and other metasomatizing melts measured in other eclogites from the Granulitgebirge and Erzgebirge, in addition to the overall similar enrichment in trace elements observed in other metasomatized mantle rocks from central Europe, suggest an extended crustal contamination of the mantle beneath the Bohemian Massif during the Variscan orogeny.
... In the CVF, there are two different inherited mantle domains, and the oldest may be a DMM that was probably formed during seafloor and oceanic subduction in mantle wedges of arc settings when the peri-Gondwanan Iberian microplate occupied a Cadomian margin [10,34]. The second inherited SCLM component is the Variscan orogenic mantle that is common in many other European Cenozoic volcanic fields (e.g., Silesia [72] and the French Massif Central [33,49]). The coincidence in Re-Os model ages from some CVF mantle xenoliths with the Cadomian and Variscan orogenic times reinforce the idea of a substantial crustal-mantle interaction at those periods in Central Iberia [73]. ...
... The coincidence in Re-Os model ages from some CVF mantle xenoliths with the Cadomian and Variscan orogenic times reinforce the idea of a substantial crustal-mantle interaction at those periods in Central Iberia [73]. Finally, the refertilized SCLM domain is dominant in the CiMACI, as successive inputs of Cenozoic alkaline magmatism widely overprinted the shallow mantle lithosphere levels in all the CiMACI, from where the xenoliths were extracted [72], as described in the here-studied Cerro Pelado and El Palo xenolith suites. ...
Much of the lithospheric subcontinental mantle (SCLM) sampled in the Calatrava Volcanic Field (CVF) shows refertilization by alkaline metasomatic agents. The Cerro Pelado and El Palo ultramafic xenolith suites record the best evidence of this type of metasomatism in this volcanic field. Several groups of peridotite (lherzolite, wehrlite, and dunite) and pyroxenite (clinopyroxenite and websterite) xenoliths have been distinguished. Despite having scarce phlogopites and amphiboles as modal metasomatic phases, all studied xenoliths present a variable cryptic metasomatism, highlighted by the strong Fe-Ti enrichment and fractionated REE patterns in the most evolved wehrlite and pyroxenite varieties. They show a common trend of an Fe-Ti-Ca increase, whereas the pyroxenites are more depleted in Fe compared to the lherzolites and wehrlites. Trace-element (REE and multi-trace) patterns are roughly similar among them, suggesting different interactions and refertilization degrees by alkaline silicate melts. The same Sr–Nd isotopic EAR composition, combined with trace-element chemistry of metasomatic xenolith phases and phenocrysts from the Calatrava volcanics, highlights the main role of this magmatism in percolation processes beneath Central Iberia. These mantle xenoliths also show variable amounts of interstitial glass that originated by in situ partial melting, favored by the enriched chemical nature of cryptically metasomatized clinopyroxene during their volcanic transport. This alkaline-refertilized mantle type represents the main domain within the SCLM beneath Central Iberia, as was also recorded in other Western European Cenozoic volcanic fields.
... With respect to geochemical 'evidences' on formation of basaltic melts that display 'garnet signature', most often interpreted to have formed at deep mantle levels by melting within the garnet-lherzolite stability field, recent research suggests that pooled and near-fractionated melts of compositionally and thermally variable peridotites in the spinel-lherzolite and plagioclase-lherzolite stability fields commonly display similar highly variable trace element and isotope garnet signatures [64]. Mantle sources from a number of central European localities, which underwent previous rifting/extension events, commonly contain compositionally variable sub-continental lithospheric mantle (SCLM) xenoliths that in turn are intensely metasomatised by alkali or silica-saturated/oversaturated basaltic melts, which formed by low-percentage melting within the underlying asthenospheric mantle [65,66]. ...
Abstract: In this contribution we present novel radiometric 40Ar/39Ar ages representing a number of basaltic sills/lavas of the Faroe Islands, which themselves form part of the North Atlantic Igneous Province. Measured ages are utilised in an attempt to assess the local igneous history, where the new ages are contrasted against those of other local rocks of known ages as well as against those of comparable/neighbouring North Atlantic igneous regions. The novel ages presented in this contribution allow us to put new constraints on the timing of late stage magmatic activity and associated crustal extension of this part of the North Atlantic area. In this research we present new ages as young as ~50.5 Ma for some of the smallest Faroese sills and demonstrate that the larger and oldest local sills, grouped into the low-TiO2 Streymoy/Kvívík sills and the high-TiO2 Eysturoy/Sundini sills respectively (~55.5 Ma), likely formed immediately subsequent to the formation of the uppermost parts of the Enni Formation, which itself represent the latest stages of local surface magmatism at ~55.8 Ma. Gradually decreasing sill volumes coupled with successively younger ages point to systematic decrease of local igneous activity with increasing distances to active contemporaneous local rifting zones. Comparable scenarios recorded for other parts of the North Atlantic Igneous Province support our inferences regarding the nature of late-stage magmatic activity at some distances from zones of active seafloor-spreading. Comparisons between ages of Faroese igneous products versus those of e. g. central E Greenland point to a somewhat diachronous evolution pattern within this part of the North Atlantic Igneous Province subsequent to ~57.5 Ma. The lithosphere-asthenosphere boundary is commonly thought to be critical for the formation of basaltic magmas. Accordingly, the close spatial and temporal associations between many high-TiO2 and low-TiO2 Faroese rock suites are interpreted in the context of a regional version of this boundary.
... With respect to geochemical 'evidences' on formation of basaltic melts that display 'garnet signature', most often interpreted to have formed at deep mantle levels by melting within the garnet-lherzolite stability field, recent research suggests that pooled and near-fractionated melts of PRIVATE COPY Earth Sciences 2023; X(X): XX-XX 13 compositionally and thermally variable peridotites in the spinel-lherzolite and plagioclase-lherzolite stability fields commonly display similar highly variable trace element and isotope garnet signatures [64]. Mantle sources from a number of central European localities, which underwent previous rifting/extension events, commonly contain compositionally variable sub-continental lithospheric mantle (SCLM) xenoliths that in turn are intensely metasomatised by alkali or silica-saturated/oversaturated basaltic melts, which formed by low-percentage melting within the underlying asthenospheric mantle [65,66]. ...
In this contribution we present novel radiometric 40 Ar/ 39 Ar ages representing a number of basaltic sills/lavas of the Faroe Islands, which themselves form part of the North Atlantic Igneous Province. Measured ages are utilised in an attempt to assess the local igneous history, where the new ages are contrasted against those of other local rocks of known ages as well as against those of comparable/neighbouring North Atlantic igneous regions. The novel ages presented in this contribution allow us to put new constraints on the timing of late stage magmatic activity and associated crustal extension of this part of the North Atlantic area. In this research we present new ages as young as ~50.5 Ma for some of the smallest Faroese sills and demonstrate that the larger and oldest local sills, grouped into the low-TiO 2 Streymoy/Kvívík sills and the high-TiO 2 Eysturoy/Sundini sills respectively (~55.5 Ma), likely formed immediately subsequent to the formation of the uppermost parts of the Enni Formation, which itself represent the latest stages of local surface magmatism at ~55.8 Ma. Gradually decreasing sill volumes coupled with successively younger ages point to systematic decrease of local igneous activity with increasing distances to active contemporaneous local rifting zones. Comparable scenarios recorded for other parts of the North Atlantic Igneous Province support our inferences regarding the nature of late-stage magmatic activity at some distances from zones of active seafloor-spreading. Comparisons between ages of Faroese igneous products versus those of e. g. central E Greenland point to a somewhat diachronous evolution pattern within this part of the North Atlantic Igneous Province subsequent to ~57.5 Ma. The lithosphere-asthenosphere boundary is commonly thought to be critical for the formation of basaltic magmas. Accordingly, the close spatial and temporal associations between many high-TiO 2 and low-TiO 2 Faroese rock suites are interpreted in the context of a regional version of this boundary.
... These relationships suggest a record of intergranular melt percolation in the peridotite protolith, which enabled crystallization and/or recrystallization of spinel, clinopyroxene and locally orthopyroxene in a solid framework consisting of olivine ± orthopyroxene. Similar fabric relationships were described and analogously interpreted in peridotite xenoliths by Kaczmarek et al. (2016); Morales & Tommasi (2011);Puziewicz et al. (2020);, Tedonkenfack et al. (2021); Tommasi et al. (2008) and Zaffarana et al. (2014). ...
The lithospheric mantle as sampled by peridotite xenoliths in some continental settings resembles the source of mid-ocean ridge basalts (MORB). Whether this resemblance is a primary feature or the result of post-formation secondary processes remains controversial. Here, the age, origin and thermochemical evolution of fertile continental mantle are constrained based on the chemical composition of minerals in spinel-facies lherzolite and websterite xenoliths from the Wum maar and Befang cinder cone of the Oku Volcanic Group (Cameroon Volcanic Line, West Africa), combined with in-situ Sr isotope compositions of clinopyroxene and fabric investigation by Electron Backscatter Diffraction (EBSD).
The majority of lherzolites (here assigned to Group I) consist of minerals with fertile composition (olivine Fo89, Al-rich pyroxenes, spinel Cr# 0.08-0.10). Clinopyroxene is LREE-depleted and has depleted ⁸⁷Sr/⁸⁶Sr (0.7017-0.7020). Crystal-preferred orientation determined by EBSD reveals that clinopyroxene, and sporadically both clino- and orthopyroxene, post-date the olivine framework. Subordinate Group II lherzolites also contain secondary clinopyroxene which is LREE-enriched and has higher ⁸⁷Sr/⁸⁶Sr (0.7033). In contrast, the scarce lherzolites of Group III are more refractory: they contain 72-78 vol. % olivine, Al-poor pyroxenes, and spinel with Cr# 0.18. Clinopyroxene (⁸⁷Sr/⁸⁶Sr 0.7021) is texturally coeval with olivine and orthopyroxene. Few lherzolites contain amphibole (⁸⁷Sr/⁸⁶Sr 0.7031) which post-dates the nominally anhydrous minerals. Most of the websterites (Group A) are aluminous (spinel Cr# 0.04-0.06) with LREE-depleted clinopyroxene having depleted ⁸⁷Sr/⁸⁶Sr ratios (0.7017-0.7020) similar to Group I lherzolites.
Chemical characteristics of minerals coupled with the crystal-preferred orientation data suggests that Group I lherzolites originated in the spinel stability field by reactive intergranular percolation of an incompatible element-depleted MORB-like melt. Group A websterites likely formed as cumulates from that melt. The Group II lherzolites supposedly occur close to lithosphere-asthenosphere boundary and record interaction with lavas of the Cameroon Volcanic Line, whereas Group III lherzolites occur in the shallow part of the mantle profile and represent the protolith from which the Group I lherzolites were formed. Local crystallization of amphibole and concomitant recrystallization of the host lherzolite were driven by supply of water in an event post-dating the formation of LREE-depleted rejuvenated rocks.
Migration of alkaline melts of the CVL apparently did not significantly affect the mineral and chemical composition of the lithospheric mantle, which allowed Group I lherzolites and Group A websterites to retain very low ⁸⁷Rb/⁸⁶Sr (average 0.002) and depleted ⁸⁷Sr/⁸⁶Sr ratios in clinopyroxene. This not only indicates their formation in the Paleoproterozoic (~2.0-2.25 Ga), possibly during the Eburnean orogeny at the margin of the Congo craton, but also indicates surprisingly little influence of the regionally-recognized Pan-African event.
... According to studies on mantle rocks from Western and Central Europe the inherited signature may be due to the Variscan collisional event (Puziewicz et al., 2020) and/or the Permian extensional event (Manatschal et al., 2023, and references therein). The determined mineralogical composition suggest serpentinization during the exhumation of the sub-lithospheric mantle as the most likely scenario. ...
The Neo-Tethys margin evolution is preserved in the Northern Calcareous Alps (Eastern Alps), from Late Permian crustal stretching to Late Triassic oceanization. The Northern Calcareous Alps represent the salt-floored fold-and-thrust developed from the salt-influenced Triassic carbonate sedimentary cover of the ancestral European margin of the Neo-Tethys Ocean. A crustal scale model for the margin has been obtained by restoration of regional cross-sections of the Northern Calcareous Alps carbonate platforms. Lithospheric break-up was investigated from remnants of exhumed mantle found within an evaporitic melange, suggesting hyperextended crust underneath the distal Triassic platforms of the Northern Calcareous Alps preceding breakup. By modelling the thermal evolution of the margin in combination with excellent stratigraphic control, a detailed timeline has been established for the evolution of the Neo-Tethys margin, especially around the period of rapid mantle exhumation. Our study indicates that salt-floored carbonate shelfs can be used as a proxy to characterize the margins evolution, from crustal stretching to continental breakup. Diagnostic stratigraphic records are preserved in the carbonate platforms: pre- mantle exhumation carbonates are represented by aggrading isolated carbonate platforms first, followed by expanding and margin wide prograding carbonate shelfs once thermal subsidence dominates. In addition, a distinct clastic sequence is deposited as an immediate response to mantle exhumation, in between the pre- and post-mantle exhumation carbonate factory. Our study proposes a new refined model for the formation of the Neo-Tethys margin and provides new insights for the dynamic coupling of salt-controlled carbonate shelfs and the underlying lithosphere during continental breakup
... Conversely, several authors have stated that refertilization processes in the SCLM can be represented by clinopyroxenes fertile in terms of major element compositions but depleted in terms of incompatible trace elements (e.g., LREE), being similar to depleted MORB-mantle (Carlson and Ionov, 2019;Downes et al., 2003;Le Roux et al., 2007;Tedonkenfack et al., 2021). Le Roux et al. (2007) and Puziewicz et al. (2020) argue that LREE-depleted lherzolites are formed by the refertilization of strongly depleted harzburgite by MORB-like melts. Similarly, our clinopyroxenes from the type II spinel lherzolites have fertile major element composition (e.g., high Al 2 O 3 , CaO, Na 2 O, TiO 2 ) but are depleted in incompatible elements (e.g., LREE), suggesting a refertilization by silicate melts in the shallower SCLM beneath Catalão. ...
A suite of kimberlite-hosted mantle xenoliths from the Catalão region, southwestern margin of the São Francisco Craton (SFC), Brazil, consists of spinel lherzolites (type I and II) and garnet-phlogopite wehrlites. The chemical composition of these xenoliths provides evidence of chemical enrichment and refertilization of the SFC lithosphere which were caused by distinct metasomatic agents. Garnet-phlogopite wehrlites have porphyroclastic textures and were equilibrated between 1005 and 1010 °C and 2.9–3.0 GPa (~99 km). They record metasomatism caused by carbonatite and proto-kimberlite melts. Type I spinel lherzolite contain spinel-pyroxene symplectites indicating garnet destabilization due to variations of the P-T conditions. The minerals in this rock were equilibrated between 975 and 990 °C and their chemical compositions contain evidence for carbonatite metasomatism. High-Cr and low-Al clinopyroxene of garnet-phlogopite wehrlites and type I spinel lherzolite have high Mg#, Ca/Al, La/YbN, Zr/Hf ratios, and high Sr contents, coupled with low to intermediate Ti/Eu and Ti/Nb, which also suggests that they were formed by carbonatite melt. These geochemical features, together with the presence of carbonate inclusions in the olivines, corroborate the interaction with carbonatite melt. The low-Ti-Cr phlogopite (Phl1), which is restricted to only the garnet-phlogopite wehrlites, was probably produced through the release of volatiles components from the carbonatite melt that reacted with garnet porphyroclasts. Furthermore, metasomatic reactions involving garnet-phlogopite wehrlites and a proto-kimberlite melt formed high-Ti-Cr phlogopite (Phl2), consuming the original phlogopite (Phl1). Phl2 occurs as rims around Phl1, as isolated flakes around garnets, and in the matrix of wehrlites. Therefore, we assume that the proto-kimberlite metasomatism responsible for generation of Phl2 occurred prior to the eruption of the host kimberlite magma.
Conversely, type II spinel lherzolites (876–915 °C; ~1.5 GPa) contain evidence for metasomatic reactions with silicate melts. These samples have high cpx/opx ratios (1.10–2.93) with low-Cr and high-Al clinopyroxene, and depleted incompatible trace element compositions. Some clinopyroxene crystals, however, show some enrichment in light rare earth elements (LREE), large ion lithophile elements (LILE), and Ti. Their low Ca/Al, La/YbN, and Zr/Hf, low Sr contents, high Ti/Eu and Ti/Nb, and a strong positive correlation of Ti with the other high field strength elements (HFSE) and LREE, may indicate that these clinopyroxene crystals were formed by refertilization caused by a silicate melt that was depleted in incompatible elements. Overall, these metasomatic processes suggest a pervasive refertilization of the cratonic lithosphere where the typically depleted peridotites of cratonic regions were replaced by a pyroxene-rich lithology.
... Considering the variable composition, the different ages and magma volumes, and the occasional lack of spatial correlation between volcanism, graben structures, and thinned lithosphere for CEVP volcanic activity (Dunworth and Wilson 1998;Goes et al. 1999;Pfänder et al. 2018), it seems likely that a single general model alone cannot explain the petrogenesis of all the occurrences (Eynatten et al. 2021;Lustrino and Wilson 2007;Mertz et al. 2015). Rather, the spatial chemical heterogeneity of the lower lithospheric mantle, the formation depth and origin of the magmas, and the varying position of the lithosphere-asthenosphere boundary must be integrated into a comprehensive geodynamic scenario (Lustrino and Carminati 2007;Lustrino and Wilson 2007;Puziewicz et al. 2020). ...
... Other models, however, locate the melt generation of melilite-bearing rocks in the CEVP at the base of the lithosphere (Blusztajn and Hegner 2002), possibly in the thermal boundary layer (TBL; Heldburg region; Pfänder et al. 2018). Despite the timing, origin, and processes of metasomatic overprint are not yet well constrained, previous modifications to ancient subduction processes are widely accepted as the major forces for metasomatic overprinting of the mantle (e.g., Blusztajn and Hegner 2002;Hegner and Vennemann 1997;Lustrino and Wilson 2007;Puziewicz et al. 2020;Ulrych et al. 2011;Witt-Eickschen and Kramm 1998). According to Pfänder et al. (2018), prolonged subduction of oceanic and continental lithosphere with successive dehydration during Variscan Orogeny generates aqueous to supercritical fluids enriched in volatiles and other trace elements, causing metasomatism at great depths (> 125 km) in the thickened lithosphere. ...
... Such compositional sequences have been attributed to pre-, syn-, and post-rift stages (e.g., Eger Graben; Ulrych et al. 2011), differentiation due to magmatic plumbing systems (e.g., Siebengebirge; Przybyla et al. 2018), and/or different sources and depths of melt generation (e.g., Heldburg region, Kaiserstuhl, Eger Graben; Braunger et al. 2018;Ghobadi et al. 2021;Pfänder et al. 2018;Ulrych et al. 2016). Likewise in the southern CEVP, the high temporal, spatial, and compositional variability of the individual regions on the one hand, and the compositional similarities of coeval occurrences on the other hand, refer to heterogeneities in the sub-lithospheric mantle beneath Central Europe (Puziewicz et al. 2020). The temporal trend for primitive rocks in the southern CEVP from melilite-free nephelinitic-basanitic rocks to melilitebearing olivine nephelinites and olivine melilitites may indicate decreasing partial melting degrees, greater formation depths, a thicker lithosphere, a more carbonate-accentuated source, and/or a reduced influence of assimilation and fractional crystallization for the latter (e.g., Bogaard and Wörner Fig. 8 Age distribution of igneous rocks in the Central European Volcanic Province. ...
Petrographic observations and in situ U–Pb ages of melilitites, foidites, basanites, phonolites, and trachytes from the southern part of the Central European Volcanic Province (CEVP) and related plutonic inclusions therein reveal two distinct age groups separated by a gap of ~ 20 Myr. A late Cretaceous to early Eocene group (~ 73–47 Ma; Taunus, Lower Main plain, Odenwald and Kraichgau area, Bonndorfer Graben and Freiburger Bucht area, Vosges and Pfälzerwald) is characterized by nephelinites and basanites mostly devoid of melilite and perovskite, and by rare haüynites, and trachytes. In contrast, a late Oligocene to late Miocene group (~ 27–9 Ma; Lorraine, southern Upper Rhine Graben, Urach, Hegau area) is dominated by melilitites, melilite-bearing nephelinites (both carrying perovskite), and phonolites. Both magmatic episodes are related to domal topographic uplift, erosion, and formation of major angular unconformities in the Upper Rhine Graben, suggesting an association with dynamic topography interrupted by phases of subsidence (or abatements of uplift). The investigated rocks in the southern CEVP (south of a line Eifel–Vogelsberg–Rhön–Heldburg), except for the Kaiserstuhl volcanic complex, mostly comprise small and isolated occurrences or monogenetic volcanic fields, whereas the northern CEVP is dominated by large volcanic complexes and dyke swarms, which are mostly SiO2-saturated to weakly SiO2-undersaturated. In the northern CEVP, evidence of spatially varying but recurrent volcanic activity exists since the Eocene, lacking the distinct 20 Myr gap as documented from the southern CEVP. While the temporal and spatial distribution of volcanism are a result of the Cretaceous to Miocene tectonic evolution in Central Europe, further studies are needed to explain the petrographic differences between the two age groups in the south.
... The xenoliths contain abundant olivine and orthopyroxene (Table 1) -6). This reference frame is the same as that chosen for work on East Otago xenoliths and represents the most common orthopyroxene CPO (Gan et al., 2011;Puziewicz et al., 2020;Yu et al., 2019). The reference frame choice is arbitrary and will be discussed further later in the paper (Section 5.4). ...
Mantle xenoliths from the Southern Alps, New Zealand, provide insight into the origin of mantle seismic anisotropy related to the Australian‐Pacific plate boundary. Most xenoliths from within 100 km lateral distance of the Alpine Fault are coarse grained, but a small number are finer grained protomylonites. The protomylonites contain connected networks of fine grains with a different crystallographic preferred orientation (CPO) to coarse porphyroclasts in the same xenolith, suggesting that protomylonites and coarse‐grained samples record different deformation kinematics. The CPOs of fine grains in protomylonites have monoclinic symmetry, with the 2‐fold rotation axis normal to a plane that contains olivine [010] and orthopyroxene [100] maxima, suggesting that the protomylonite deformation involved significant simple shear. Some coarse‐grained samples contain unconnected lenses and layers of fine grains with the same CPO as the coarse grains. Microstructures suggest that these fine grains formed by subgrain rotation recrystallization and that protomylonites may represent an up‐strain progression of this microstructure, where the connectivity of fine grains has allowed them to localize shear and develop a new Alpine Fault CPO. The samples tell us about the state of the mantle at 25 Ma, in the early history of the plate boundary. If this suite of samples is representative of the mantle beneath the Alpine Fault in the present day, then we can interpret the complex seismic anisotropy patterns in the lithospheric mantle as representative of blocks containing variably rotated older CPOs juxtaposed by narrow shear zones associated with Alpine Fault deformation.
