The Serra de Monchique Complex in southern Portugal is comprised of an inner core of rather homogeneous nepheline syenites that are occasionally intercalated with amphibole malignites, surrounded by an outer roof zone of sodalite-and nepheline-bearing alkali feldspar syenites. The rocks contain titanite, +/- zircon and Na-Ca-HFSE-F-disilicates of the wo & uml;hlerite and rinkite groups that formed during orthomagmatic and late-magmatic stages, which allows studying the transition from miaskitic to agpaitic assemblages. The two main rock units are interpreted as products of two variably evolved alkaline magma batches that mingled during emplacement in the shallow crust. Initially, basanitic magma fractionated mainly forsterite, diopside, kaersutite and plagioclase, which formed base cumulates of amphibole malignite, while alkali feldspar accumulated largely in the roof region. Sufficient enrichment of REE, HFSE and retention of halogens in the residual melt fractions caused transition to agpaitic conditions, during which Na-Ca-HFSE-F-disilicates crystallized as in the roof zone rocks. Stemming from a more evolved basanite, nepheline syenites represent a later magma, that crystallized mainly alkali feldspar, nepheline and sodalite as cumulus phases. Coeval crystallization of biotite and sodalite served as halogen sink, buffering halogen content in the melt during differentiation, limiting crystallization of Na-Ca-HFSE-F-disilicates to interstitial assemblages. Locally variable fabric of the nepheline syenites suggest reworking of crystal mushes and filter pressing is invoked to explain late-stage melts and deuteric fluids percolating through settled crystal mush, resulting in breakdown of Na-Ca-HFSE-F-disilicates to secondary phases. The present juxtaposition of the main rock units is attributed to post-emplacement normal faulting.

Unconformity-related hydrothermal vein-type deposits are key sources of high-purity fluorite, baryte, and base metals, with occurrences in Nigeria, particularly along the Benue Trough. However, the genesis of the Nigerian deposits is not well understood. This study examines fluid inclusion systematics from mineralized veins at Enyigba, Ameta, Ikwo, Otim Land, and Uburu-Abakaliki, using microthermometry, crush-leach analysis, and Raman spectroscopy. Fluid inclusion microthermometry reveals homogenization temperatures between 99 and 190 degrees C and salinities of 18.3-22 wt%NaCl + CaCl2, typical of unconformity-related hydrothermal vein systems. Geochemical data indicate the mineralizing fluids resulted from mixing of bittern brines (low Cl/Br), halite-dissolution brines (high Cl/Br), and oilfield brines, as shown by Cl/Br ratios and Rb/Cs values. Microraman spectroscopy suggests the presence of hydrocarbons, supporting the involvement of reduced oilfield brines. These findings point to a complex fluid mixing process, likely driven by crustal-scale faulting during the rifting of the Benue Trough in the context of Pangaea break-up. This research suggests a common ore-forming process for the Nigerian deposits.

Explosive eruptions of low viscosity lava, such as basalts and basanites, are widespread and are a dominant form of volcanism on Earth. They commonly display Hawaiian and Strombolian eruption styles and are relatively well documented. Carbonatite, another magma composition distinguished by a high volume fraction of carbonate minerals, is also characterised by low melt viscosities. However, documented examples of explosive carbonatite eruptions are very rare. We examined the composition and textural features of carbonatite pyroclasts from the Miocene Kaiserstuhl Volcanic Complex, Germany. Three pyroclastic rock samples from the Kirchberg and Henkenberg regions of the complex were studied using optical petrography, scanning electron microscopy, and image analysis techniques. Our observations indicate that after primary fragmentation, the pyroclasts underwent in-flight relaxation and experienced pyroclast-pyroclast collisions to form complex, agglutinated pyroclasts. The vesicles within the pyroclasts are well preserved by secondary mineralisation of carbonates. Comprehensive image analysis enabled the reconstruction of both the primary and secondary (agglutinated) grain size and shape distributions, which represent the initial, primary formation of pyroclasts and their textural features after agglutination. Finally, these data are used interpret the potential fragmentation processes and eruption conditions for the extrusive carbonatites of the Kaiserstuhl volcanic complex.

The Eocene Dicker Willem carbonatite complex (southern Namibia) primarily comprises fine-grained calcite carbonatites hosting xenoliths and irregular inclusions of calcite ijolites, calcite syenites, nepheline silicocarbonatites, and coarse-grained calcite carbonatites. A 7 by 6 m xenolith within the complex exhibits zonal lithological transitions, evolving from calcite-bearing ijolite via calcite syenite and silicocarbonatite to coarse-grained calcite carbonatite. This succession reflects initial carbohydrothermal alteration (fenitization), followed by interaction with carbonatitic melt, as evidenced by textures, mineralogy and element transport. In the central ijolitic zone, primary nepheline is replaced by orthoclase, while the outer margins show intense resorption of original silicate minerals, replaced by coarse calcite, biotite +/- aegirine-rich clinopyroxene and magnetite, ultimately forming coarse calcite carbonatite. Mass transfer reveals enrichment in Ca, Sr, and REE, alongside depletion in Na, Mg, Al, Si, and K. Sample sets from other parts of Dicker Willem, transitioning from ijolite to nepheline silicocarbonatite, exhibit increasing replacement of nepheline by cancrinite, driven by magmatic interaction as well. These findings indicate that nepheline silicocarbonatite is a transitional lithology, not an orthomagmatic rock, formed through in-situ dissolution-reprecipitation of silicates and replacement by calcite, with significant silica introduction into the carbonatitic magma. Scaling this process up to the entire Dicker Willem Complex suggests that even silicate-bearing coarse-grained calcite carbonatites could result from carbonatite magma-induced transformation, consistent with published isotopic and mineral data.

Co-mobilizing fluoride (F-) and uranium (U) into groundwater poses a drinking water quality problem globally. Competitive ion exchange with aquifer sediments has been hypothesized to cause their co-mobilization. However, this hypothesis has been postulated merely based on correlations of F- and U with other groundwater parameters without characterizing that F- and U were present as exchangeable in the aquifer sediments. The present study, therefore, tested this hypothesis by determining the abundance and association of F- and U in the aquifer sediments and correlating these data with the groundwater composition in the alluvial aquifers of southern Punjab, India, where the groundwater contamination by F- and U is severe. Our results support the hypothesis that competitive ion exchange can co-mobilize F- and U into groundwater. However, the specific ion exchange reaction involved in the F- and U mobilization can differ. In the study area, the U mobilization into groundwater was linked to increased ionic strength due to the increase in concentration of any ionic species. However, the mobilization of F- was explicitly linked to the changes in OH- and HCO3- concentrations rather than the overall ionic strength. Bicarbonate was the most critical ionic species that could cause F- and U co-mobilization.

A regional assessment of the halogens distribution across the Sn-W mineralised Cornubian batholith is presented in this study, including a comprehensive dataset of the halogen chemistry of whole rocks, minerals and fluids. Overall, the F content in most halogen-bearing minerals increases with progressive differentiation of the granite. On the other hand, Cl only increases during early stages of magmatic fractionation, in correspondence to the second regional pulse of magma across the region (forming G3 granite), and the successive exsolution of fluid from the melt resulted in a rapid drop in Cl content, observed in both whole rock content and halogen-bearing minerals (in particular micas and apatite). The fluid inclusion record, covering the entire evolution from magmatic to hydrothermal conditions, shows no evident differences in terms of halogen ratios between intermediate density fluids, brines and diluted fluids. However, a significant decrease in Br/Cl and I/Cl for late magmatic and late hydrothermal samples is observed. This shift can be attributed to mixing with an external fluid relatively poor in Br and I, or to the effect of progressive fractionation, causing a decrease in both ratios according to existing experimental studies, with the latter hypothesis being preferred. The overlap in Br/I across all samples suggest that Br and I do not significantly fractionate from each other during the magmatic-hydrothermal evolution of such granites, and behave similarly to Cl. This represents further evidence that the external fluids mixing with magmatic fluids giving rise to the Sn-W and polymetallic mineralisation across the Cornubian batholith are halogen-free and therefore have a meteoric origin. Whole-rock leaching experiments demonstrate that Cl, Br and possibly I are for the most part not tightly-bound to minerals, but rather hosted in fluid inclusions or forming weak bonds on mineral surfaces, whereas F is obviously strongly bound in micas, apatite and tourmaline, and in very evolved granites (G5 and Gx) in fluorite and topaz. This study shows the potential of triple halogens analysis (Cl-Br-I) in recognising fluid sources and as tracer of fluid mixing even at large scale, independently from other tracers more commonly used in the literature to discern these processes.

Three occurrences of primitive, alkaline, SiO2-undersaturated, volcanic rocks from SW Germany show coarse-grained, mm-to cm-thin veinlets and pockets of differentiated lithologies that are a missing link in an evolutionary trend towards phonolites. (1) In the Hegau region (Hohenstoffeln), melilite-bearing olivine nephelinite contains ijolite pockets with skeletal perovskite, titanomagnetite, and euhedral fluorapatite. (2) Compositionally similar olivine melilitite at Urach (Sternberg) is crosscut by ijolite veinlets with late-magmatic lileyite and wadeite, in which subhedral-euhedral titanomagnetite and perovskite lack a skeletal shape. (3) Nepheline syenitic domains in a phlogopite-nepheline basanite from the Kraichgau region (Steinsberg) contain less clinopyroxene, titanomagnetite, and apatite, but accessory titanite. Differences between the fractionation products partly result from variable host magma compositions. However, the exact starting point of residual melt separation was the key factor explaining the trace element evolution of late mineral phases. Under conditions of advanced clinopyroxene crystallization and perovskite saturation (Urach), massive trace element fractionation led to high Nb/Ta and Zr/Nb, but low LREE/HREE and Zr/Hf ratios in clinopyroxene and perovskite. High F contents contributed to the stabilization of LILE, Zr, and Hf in the enriched residual melt which finally caused crystallization of an agpaitic assemblage. In contrast, melt separation before perovskite saturation (Hegau) resulted in strong, uniform enrichment of LILE, HFSE, and REE in clinopyroxene and perovskite. The nepheline syenite (Kraichgau) underwent a similar evolution with incompatible element enrichment in clinopyroxene and titanite, although its mineral assemblage differs from the ijolites due to higher SiO2 and H2O but lower F and P concentrations in the melt.

Intraplate magmatism has traditionally been linked to anomalously hot mantle (hotspots) transported upwards from deep-sourced mantle plumes. However, many intraplate magmatic provinces lack convincing evidence for a mantle-plume origin, and the Cameroon Volcanic Line (CVL) located on the West African continental margin is one such province. Despite being active for ca. 65 million years, it lacks the time-progressive volcanic activity that would suggest the presence of a fixed mantle hotspot or plume; instead CVL magmatism has been linked to a shallow, enriched asthenospheric source. Etinde, a relatively young (<1 Ma) volcano located at the centre of the CVL on the continent-ocean boundary, is the most silica-undersaturated and incompatible element-enriched volcano in the region and forms the focus of this study. It is constructed almost entirely of feldspar-free nephelinite lava flows, with compositions ranging from olivine nephelinite to felsic leucite nephelinite. We report new sulfide-, sulfate- and bulk-delta S-34 data for a suite of Etinde rock samples; the first sulfur-isotope data for the CVL. Strong (similar to 8 parts per thousand) S-isotope fractionation between sulfide and sulfate (ha & uuml;yne, nosean) phases suggest equilibration temperatures of similar to 600 degrees C, well below the magma solidus temperature and likely due to sub-solidus exsolution of nanoscale sulfide particles from the sulfate phenocryst phases. The most mafic samples from Etinde have been extensively degassed, containing less than 60 ppm sulfur, and therefore cannot be used to constrain the primary delta S-34. Instead, we use the intermediate and felsic volcanic rocks, where sulfur is locked in phenocrysts of ha & uuml;yne and nosean, respectively. Bulk delta S-34 of these rocks, which best represents the primary magmatic values, ranges from +3.7 parts per thousand to +6.3 parts per thousand, a heavier signature than previously reported in alkaline igneous rocks. We propose that the heavy sulfur isotope values, together with the extreme silica undersaturation and incompatible element concentrations, reflect enrichment of the mantle source and fingerprint carbonate metasomatism in the mantle beneath the CVL. The heavy sulfur isotopic signature requires low-temperature fractionation and therefore implies the addition of sulfur through subduction processes. Our study has broad geochemical significance in contributing to a growing understanding of sulfur-isotope compositional variability in geochemically enriched mantle globally.

The four spatially associated igneous complexes of Kalkfeld, Ondurakorume, Osongombo and Etaneno are situated within the Damaraland Igneous Province (northwestern Namibia), which formed in response to the rifting of the South Atlantic during the early Cretaceous. Spatially-resolved LA-ICP MS U-Pb age dating on zircon and titanite confirms the Cretaceous age for Etaneno (mean of 139.2 f 6.7 Ma), while Triassic and Permian emplacement ages are indicated for nepheline syenites from Kalkfeld (249.6 f 3.2 and 249.4 f 2.9 Ma) and Ondurakorume (272.1 f 1.5 Ma). Furthermore, apatite ages for nepheline syenites from Etaneno (mean of 122.8 f 3.8 Ma) and Kalkfeld (217.4 f 24.5 Ma), and for carbonatites of Ondurakorume (248.1 f 4.8 Ma) broadly agree with the zircon and titanite ages, while apatite from basement marbles yields a presumably metamorphic age of 479.6 f 2.6 Ma and 465.1 f 7.0 Ma. Detailed petrographic analysis of syenites, nepheline syenites, carbonatites, silicocarbonatites and fenites from Ondurakorume reveals variable interaction processes between alkaline-silicate rocks and carbonatites. Syenites and nepheline syenites contain interstitial calcite with burbankite or carbocernaite inclusions (as commonly found in calcite carbonatites) and baddeleyite-zircon replacement textures. In some carbonatites and in silicocarbonatites, local contamination with (nepheline) syenites and granitic basement caused elevated Si activity, triggering enhanced formation of clinopyroxene, amphibole and mica. Compositional variations in the released fenitizing fluids are indicated by clinopyroxene compositions that vary from nearly end-member aegirine (Aeg69-91Di0-10Hed0-7) in proximal fenites to less sodic aegirine-augite (Aeg54-96Di0-17Hed0-16) in more distal fenite samples, with the latter containing additional sodic amphibole. Compared to clinopyroxene in nepheline syenites and carbonatites, clinopyroxene in fenites shows elevated Ti contents (mostly >0.05 apfu Ti) that are highest in distal fenites (up to 0.22 apfu Ti), suggesting Ti mobility. These changes suggest either a compositional evolution during fluid-rock interaction or two different fluid sources (carbonatites and (nepheline) syenites, respectively).

Carbonatite metasomatism at crustal pressures can significantly modify igneous and sedimentary rocks and understanding these processes is critical for interpreting mantle-derived magmas and their associated carbonatebearing fluids. The Blue Hill complex in Namibia, located within the carbonatitic Gross Brukkaros volcanic field, represents an ideal natural laboratory to study the interaction between ultramafic lamprophyres (damtjernites) and carbonatitic fluids. In this setting, the damtjernites occur in direct spatial association with numerous carbonatite dykes, enabling detailed investigation of alteration processes. Evidence from olivine, spinel and wholerock chemistry supports a mantle-derived UML parental melt that experienced post-emplacement COQ degassing, contributing to monticellite formation and possibly the adjacent fenitization of the country rock. Three distinct alteration types are identified: textures A (serpentine-magnetite-phlogopite-chlorite) and B (pectolite-apatite-hydrogarnet-calcite), which occur concentrically within the main complex, whereas C (phlogopiteserpentine-apatite-hydrogarnet-calcite) forms crosscutting veins. This study aims to explore to what extent the alteration of the damtjernite reflects carbonatitic activity within the Gibeon province. Texture A records mainly deuteric (late-magmatic) alteration with minor meteoric input, while texture C shows a clear carbonatitic signature with Ba-Al-rich phlogopite, Mg-calcite and abundant apatite. Texture B remains more complex and might represent either a separate COQ-rich fluid, possibly related to texture C, or the evolved residue of the fluid responsible for texture A. Geochronological data is in accordance with a multi-stage history of magmatism and fluid interaction, with emplacement of the Blue Hill at 84 +/- 4 Ma and later resetting at 60 +/- 14 Ma. Notably, the first reported age for the nearby Gross Brukkaros carbonatite (66 +/- 8 Ma) appears to be younger than the Blue Hill emplacement. These constrains provide one of the few documented examples of carbonatitic liquids modifying pre-existing ultramafic rocks, expanding our understanding of metasomatism in carbonatite-bearing provinces.

Nepheline syenites from the X 1.2 Ga Il & iacute;maussaq Complex of southern Greenland are examined to assess the utility of anisotropy of magnetic susceptibility (AMS) fabrics as proxies for silicate petrofabrics. Mineral lamination is a relatively common structural feature in cumulate rocks, including in the Il & iacute;maussaq intrusion, but there is little consensus on the process (or processes) responsible for its formation. The Il & iacute;maussaq AMS data are combined with rock magnetic experiments and electron backscatter diffraction (EBSD) measurements to characterize the magnetic mineralogy and compare the magnetic fabrics obtained to the silicate petrofabric. The data show that Na-amphibole (arfvedsonite) is most likely the dominant control on the AMS fabrics in the coarse-grained nepheline syenites (referred to as kakortokites), and that the AMS fabric is inverse relative to the observed silicate fabric. The EBSD data for a kakortokite sample suggests that the petrofabric is defned by arfvedsonite and is wholly planar, with evidence of only weak cross-lineation of c axes. The f ne-grained nepheline syenites (lujavrites), two of which have a well-developed lamination carried by Na-pyroxene (aegirine), appear to have composite AMS fabrics that are considered to be a consequence of a mixed aegirine (normal) and arfvedsonite (inverse) response. The combined datasets shed light on the mechanisms of fabric acquisition in both lithologies. In the kakortokites, the AMS fabrics and silicate crystallographic preferred orientations, as well as the lack of observed microstructural evidence for subsolidus intra-crystal deformation, support models invoking gravitationally controlled crystal mats in the development of the macro-rhythmic layering of these rocks. In the lujavrites, the strong planar fabrics revealed by both the AMS and EBSD datasets, with some evidence of subsolidus deformation, point to fabric formation and perhaps even aegirine crystallization at the postcumulus stage. The combination of EBSD and AMS fabric datasets is a powerful means of deciphering the processes responsible for mineral alignment in igneous cumulates.

Halogen (F, Cl, Br, and I) concentrations for 129 loess samples from worldwide localities yield geometric means of 517 +/- 53 mu g/g F, 150 +/- 20 mu g/g Cl, 1.58 +/- 0.16 mu g/g Br, 1.16 +/- 0.11 mu g/g I (2 standard errors). These concentrations, notably for Br and I, are substantially higher than previous estimates for the average upper continental crystalline bedrocks, with enrichment factors of 1.3(-0.4)(+0.7) (F), 1.8(-0.8)(+2.4) (Cl), 3.8(-1.0)(+1.3) (Br), and 39(-16)(+71) (I) (95 % confidence), documenting enrichment of halogens on the continental surface. These surface halogens are likely sourced from the oceans and may be influenced by climate fluctuations. Halogen ratios (Br/Cl, I/Cl, and Br/I) in loess are similar to those of organic-rich soils/sediments from both terrigenous and marine settings, suggesting that terrigenous and marine organic matter have indistinguishable halogen ratios. The Br/I ratios differ from those in the fine grained matrix of glacial diamictites, indicating that another process (beyond biological influence) is responsible for fractionating halogens in the upper continental crust. Using a mixing model, we calculate that over 80-90 % of loess originates from crystalline bedrocks, while the remainder (<10-20 %) derives from the halogen- and organic-rich sedimentary cover or other sources (e.g., marine aerosols).

Globally, groundwater contamination by fluoride (F-) is a threat to the safe drinking water supply. Nevertheless, our understanding of the geochemical processes of F- mobilization to the groundwater by linking groundwater and aquifer material chemistry is limited. We therefore characterized that in the hard-rock aquifers of Central India, an area that has not been investigated thoroughly despite the known severity of the problem. Exploratory drilling of boreholes (n=45) and lithostratigraphic modeling identified weathered basalt, vesicular basalt, fractured basalt, sandstone of Lameta, and fractured granite as major aquifers in the study area. The groundwater contamination by F- (concentration >1.5 mg/L) mainly occurred at depths >35 m bgl (at elevations <500 m amsl) of the fractured basalt and fractured granite aquifers, while samples collected from the shallow basalt, sandstone of Lameta, and shallow granite were mostly safe. The F- contamination of groundwater was primarily governed by the chemical evolution of groundwater along the flow path. Solute mass balance in groundwater, in conjunction with the mineralogical characterization of the aquifer materials, suggests that weathering of silicate and carbonate minerals was the dominant form of mineral dissolution in aquifers, which consumed dissolved CO2 along the flow path and resulted in an alkaline pH (>8) in groundwater of the deeper aquifers. The mobilization of F- in the groundwater could primarily be attributed to the ion exchange between OH- in water and structural F- in fluorapatite and F-bearing mica/amphibole. By assessing water quality and aquifer properties, this study suggests that primarily, the sandstone of Lameta and weathered and vesicular basalts can be targeted for F-safe drinking water supply in the study area. Targeting shallow aquifers can be an option for F-safe drinking water supply in other affected areas with similar geological and environmental settings.

Nephelinitic rocks from Burko volcano in the Northern Tanzanian Divergence Zone of the East African Rift System represent transitional compositions between primitive and evolved nephelinites which exhibit two distinct phase assemblages, allowing to constrain the magmatic history of such particular rock types. Detailed petrography, mineral compositions and whole rock geochemistry were used to reconstruct the crystallization conditions and the petrological evolution of the Burko rocks and to compare them to the nearby volcanoes of Oldoinyo Lengai and Sadiman. Burko samples report a characteristic mineralogy of intermediate nephelinites (Mg# of 60-40) which comprise nepheline-diopside-magnetite-perovskite assemblages. They evolved mainly via fractionation of clinopyroxene, apatite, magnetite, and perovskite/titanite to peralkaline nephelinites (Mg# of 40-25) comprising nepheline-aegirine-augite-titanite-andradite +/- K-feldspar assemblages. The presence of unexposed primitive olivine nephelinites is, however, indicated by rare forsterite antecrysts. Reworking of crystal mushes and/or magma mixing are evident from different xenocrysts, antecrysts and pyroxenitic-ijolitic inclusions, precluding simple fractional crystallization modelling. The evolution from diopside-bearing nephelinites towards aegirine-augite-bearing ones was accompanied by a decrease in temperature (from 1100 to 900 degrees C) and an increase of log(aSiO2) towards -0.5 and of fO2 (Delta FMQ 2.5 to 3). Especially in the peralkaline nephelinites, late-stage enrichment of Sr, Ba and halogens is documented by Sr-and F-rich apatite, barytolamprophyllite, celsian, gotzenite, and eudialyte. In comparison, evolved and mostly peralkaline nephelinites from the nearby Oldoinyo Lengai and Sadiman volcanoes contain similar mineral assemblages, indicating comparable formation processes, but slightly different melt evolution trajectories. The variations in nephelinite composition and phase assemblages are linked to a) slightly different parental melt compositions related to variable amounts of amphibole, mica and carbonate in the molten mantle veins and b) different crystallization conditions, especially redox conditions, during cooling.

Upper Cretaceous-Miocene alkaline SiO2-undersaturated volcanic rocks in the southern Central European Volcanic Province (CEVP) comprise two distinct rock series: (i) Upper Cretaceous-Eocene (similar to 73-47 Ma) olivine nephelinites, basanitic nephelinites, and nepheline basanites have moderate to high MgO (8-16 wt. %), CaO, Ni, Co, Cr, Nb, and Ba, coupled with low F and SiO2 concentrations. These rocks contain abundant clinopyroxene and variable amounts of olivine macrocrysts as well as nepheline, K-dominated F-poor mica, and hydroxyapatite. Evolved and less common apatite-rich (phonolitic) hauynites/noseanites and hauyne nephelinites (similar to 68-62 Ma) represent differentiated counterparts within this older group, showing higher alkali, Al2O3, P2O5, Nb, Zn, REE, and SO3 concentrations at low MgO (4-6 wt. %), CaO, Ni, Co, and Cr contents. (ii) Oligocene-Miocene (similar to 27-9 Ma) olivine melilitites and melilite-bearing olivine nephelinites are characterized by even higher MgO (10-22 wt. %), CaO, Ni, Co, Cr, Nb, Ba, and high F contents at lower SiO2 concentrations, as reflected by the presence of abundant olivine macrocrysts, melilite, perovskite, Cr-rich spinel, F- and Ba-rich mica, and fluorapatite in addition to clinopyroxene and nepheline. Distinct mineral assemblages, crystallization trends, and various xenocrysts indicate different melt sources, a varying extent of enrichment, retention, and loss of volatiles (including timing of H2O and CO2 saturation), and limited wall rock interaction for the two rock groups. Partly resorbed, Fo-depleted olivine cores in the younger rocks and green-core pyroxenes in the older ones suggest early magma mixing. The nephelinitic-basanitic magmas derived from up to 6% partial melting of amphibole-bearing garnet/spinel lherzolite at or just above the lithosphere-asthenosphere boundary. This source was metasomatized involving hydrous melts or fluids. On the other hand, the melilite-bearing rocks probably originated in the upper asthenosphere by less than 3.5% partial melting of amphibole +/- phlogopite-bearing garnet wehrlite, previously generated by subduction-related metasomatism with high CaO/MgO and CO2/(CO2 + H2O) ratios. Infiltration and storage of the metasomatic agents occurred in the former lower lithosphere, following continuous recycling of oceanic crust, comprising the release of Ca, CO2, H2O, further volatiles, and incompatible elements. Both volcanic episodes coincide with topographic uplift, erosion, rifting, and reactivation of lithosphere-scale faults, probably related to phases of strong mechanical coupling between Alpine orogen and European foreland. The first period overlapped with an era of prolonged N-directed intraplate compressional stress due to the Adriatic-Eurasian collision, provoking large-scale deformation, isostatic compensation, erosion, and consequent lithosphere thinning in the future CEVP. The second period is associated with the Oligocene-Miocene main stage of the European Cenozoic Rift System. Onset of volcanism was accompanied by a change in deformation in the Upper Rhine Graben from (W)NW extension to (E)NE extension and transtension by a complex interplay of evasive movements responding to shortening in Alps and Jura. Magma compositions, barely magmatic graben structures, volcanic activity outside rifts, and extensive exhumation suggest that in response to rifting, passive asthenospheric doming also contributed to magmatism by causing strong lithosphere-asthenosphere interaction and providing heat.

The compositional evolution of magmatic-hydrothermal fluids from the Sn - W mineralized Cornubian batholith was investigated via in situ fluid inclusion LA-ICP-MS microanalysis and reveals a large degree of variation between intrusive stages and at the sample scale, with complexities due to superposition of several mechanisms affecting fluids chemistry during the protracted evolution of the batholith. Despite large ranges of salinities (from <1 wt% to 48 wt% NaCl (eq.) ), the effects of individual processes such as magmatic differentiation, fluid saturation and boiling, fluid mixing and dilution can all be discerned on the basis of fluid inclusion trace element geochemistry combined with detailed petrography and microthermometry. In all samples, different fluid types (aqueous liquid-rich, vapor-rich and brine inclusions) were identified in variable proportions and microthermometry revealed complex temporal trends. Granite-related samples from the G5 intrusive stage are characterized by intermediate density fluids undergoing magmatic fractionation under pressure conditions above 1.5 kbar, indicated by successively decreasing fluid salinities with concomitant increases in Li, B, Rb and Cs concentrations. The latter two elements later strongly partitioned in the brine phase upon boiling, together with most of the other Cl-complexing elements (e.g., Fe, Mn, Pb, Zn). Those brines subsequently underwent progressive dilution with meteoric waters that caused a decrease in the concentration of all elements (besides B) and homogenization temperatures. In G3 granite from Dartmoor, on the other hand, brine inclusions represent the earliest fluid type while intermediate density fluids are absent, and a large salinity range in the fluid inclusion record associated with a decrease in homogenization temperatures represents their progressive dilution with meteoric fluid. The lack of intermediate density fluids at Dartmoor indicates fluid exsolution at relatively low pressures resulting in immediate phase separation into brine and vapor. All studied samples associated with ore mineralization display only the trend of dilution of high-salinity magmatic fluids. Their transition metal contents (e.g. Fe, Mn, Pb and Zn) show the expected positive correlation with salinity of the fluids. Conversely, the compositional trends observed for Sn and particularly W are more enigmatic, as they do not appear to significantly fractionate during most of the physicochemical processes outlined above and appear to be unrelated to fluid salinity, opposite of what would be expected for Sn as it is dominantly transported in Cl-complexes. This study highlights the key advantages of high-resolution geochemical fluid inclusion studies in discerning a variety of magmatic and post-magmatic processes in fluids in comparison to bulk fluid inclusion techniques or more simplistic fluid inclusions studies which might overlook important aspects of the typically complex history of fluids evolution in magmatic-hydrothermal systems.

Primitive olivine melilitites and melilite-bearing olivine nephelinites (12-9 Ma) are characterized by high MgO, CaO, Fe2O3, TiO2, Ni, V, F, moderate alkalis, Al2O3, P2O5, Ba, Nb, Zr, and low SiO2, Rb, Pb, and U concentrations. The rocks are composed of forsteritic olivine, diopsidic clinopyroxene, melilite, perovskite, Cr-bearing oxyspinel, F- and Ba-rich mica, and fluorapatite. In rare cases, they contain coeval coarse-grained ijolite patches generated by rapid in-situ fractionation in small melt pockets. Evolved nosean phonolites (14-11 Ma) comprise high alkalis, Al2O3, SiO2, Rb, Nb, Zr, U, Pb, S, and low MgO, CaO, Fe2O3, TiO2, P2O5, Ba, Ni, and V concentrations, and contain abundant Ba-bearing alkali feldspar and nosean-ha & uuml;yne-sodalite(ss) macrocrysts, aegirine-augitic clinopyroxene, as well as accessory apatite, titanite, zircon, and pyrochlore. The melilititic-nephelinitic rocks formed by low degrees of partial melting of a carbonated amphibole +/- phlogopite-bearing garnet wehrlite in the uppermost asthenosphere or in the thermal boundary layer and occur also in neighbouring regions. However, their coexistence with evolved nosean phonolites is a unique and so far, unexplained feature in the southern Central European Volcanic Province. Thermodynamic modelling implies that removal of 11-19% oxyspinel, 4-10% olivine, 42-57% clinopyroxene, <3% mica, <9% feldspathoids, <8% feldspar from melilititic-nephelinitic parental melts at upper crustal conditions (similar to 200 MPa) results in significant amounts of phonolitic residues that are compositionally similar to the exposed nosean phonolites. Strongly negative P and Ti anomalies and a trough of MREE in primitive mantle-normalized trace element patterns of phonolites indicate additional fractionation of titanite and apatite, consistent with the mineralogy of coarse-grained (nepheline) syenitic cumulates, which are present as enclaves in both rock suites. The modelling results suggest crystallization of the (nepheline) syenite cumulates between 1050 and 800 degrees C and ascent and eruption of the phonolite residues at no less than similar to 900 degrees C with complete solidification of the observed assemblage at >750 degrees C. Significant crustal assimilation during fractionation appears unnecessary to explain the mineralogical, mineral chemical, and geochemical characteristics of the phonolites. Prolonged upper crustal differentiation of the magmas in one case (nosean phonolites) and fast ascent of primitive melts in the other (olivine melilitites and melilite-bearing olivine nephelinites) can be explained by stress field changes from an extensional to a more compressive regime, the magma ascent becoming thereby increasingly structurally controlled and supported by brittle deformation.

&lt;p&gt;The recent need of a green-energy transition has sparked even more interest on critical elements such as tungsten and tin, whose genesis in ore deposits is linked to fluids exsolving from granitic plutons, but some mechanisms of formation remain unclear. Most authors in the past have proposed the mixing with meteoric, metamorphic or basinal fluids to be critical, while others believe that these deposits can form by simple cooling of magmatic fluids.&lt;/p&gt; &lt;p&gt;Given the modern advances in analytical techniques, it is nowadays possible to characterize fluid inclusions in-situ also for trace elements such as bromine and especially iodine with the LA-ICP-MS. This study aims to apply a novel technique of measuring Br/Cl and I/Cl in individual fluid inclusions and bring some new insights on the Sn-W ore deposits genesis from a different perspective. In fact, halogens are well known to be highly incompatible in most minerals, retaining the fluid source reservoir signature, and to behave conservatively in fluid-rock interaction, therefore they can be regarded as suitable tracers for fluid evolution. These characteristics make heavy halogen studies particularly suitable for tackling the open question on the formation of Sn-W mineralized systems.&lt;/p&gt; &lt;p&gt;The study area is the well-studied Cornubian batholith, in south-west England, which has been extensively mined in the past mostly for tin, copper and tungsten. It consists of 5 types of granites, divided into two main fractionation series, and cross-cut by mineralized veins rich in cassiterite, Cu-sulphides and W-oxides (among others), outcropping mainly in proximity of the contacts with the country rock.&lt;/p&gt; &lt;p&gt;Despite significant mineralogical variation across the samples, representing different stages of the transition from magmatic to hydrothermal environments, halogen ratios are relatively homogeneous, especially under the hydrothermal regime, with magmatic fractionation as the only candidate process for a shift to higher Br/Cl and I/Cl values. On the other hand, alkalis and metals in fluid inclusions display variations of several orders of magnitude, with Li and B peaking in pegmatites and base metals being particularly abundant in the magmatic stage.&lt;/p&gt; &lt;p&gt;These results suggest that even moderate changes in P-T conditions (from granitic stage to low-T mineralisation) do not affect significantly the halogen signature of the evolving fluids in the Cornubian batholith. Additionally, given the linear relation between fluid salinity and alkali/metal content, it can be postulated that meteoric water is the main diluting agent throughout the evolution of the system, as mixing with metamorphic fluids or basinal brines would also significantly change the halogen signatures.&amp;#160;&lt;/p&gt;

In many alkaline complexes, large amounts of ultramafic rocks occur together with carbonatites, melilitolites and other alkaline silicate rocks. There is an ongoing debate if and how these contrasting lithologies were formed by differentiation of a common, mantle-derived silicate magma or rather by metasomatic processes between carbonatite and country rocks. In order to find petrological evidence for one or the other, two key examples, the Gardiner (E Greenland) and Kovdor (Russia) complexes are compared in this study. Despite their similar tectonic setting and succession of rock types, they show significant differences in the texture and mineral composition of ultramafic rocks. Ultramafic rocks from Kovdor include calcite- and biotite-rich dunites and pyroxenites without typical cumulate textures. They consist of Ni-poor forsterite, Cr-poor diopside and Ni-Cr-poor spinel and are possibly metasomatic reaction products between mantle-derived carbonatite melts and silicic host rocks. Similar ultramafic rocks are associated with carbonatites e. g. at Palabora (South Africa), Afrikanda (Russia), and Salitre (Brazil). In contrast, the ultramafic rocks from Gardiner show well-preserved cumulate textures and consist of Ni-rich forsterite, Cr-rich diopside as well as Cr-Ni-Ti-rich spinel and also contain F-Cl-rich apatite. They record an increase in aSiO2 from dunite to pyroxenite at similar fO2 (ΔFMQ ~ +1.2, with FMQ = fayalite-magnetite-quartz buffer), indicating that these rocks represent cumulates of an evolving, moderately oxidized mafic melt derived from a Ti-rich mantle source, similar to other rocks of the North Atlantic igneous province. In contrast to systems like Kovdor where carbonatite metasomatism is likely dominant, Ti-rich parental silicate magmas can abundantly crystallize Ti phases, as recorded by massive perovskite cumulates in Gardiner melilitolites. This can effectively scavenge HFSE from the magmatic system early in its evolution and likely explains HFSE-barren carbonatites at Gardiner, while those from Kovdor are highly HFSE-enriched. In summary, the results of our study provide strong textural and mineral chemical evidence that ultramafic rocks in alkaline complexes can be of both cumulate and metasomatic origin; the specific type has an important bearing on their HFSE enrichment and on the types of ores present in such complexes.

The continental crust is an important reservoir for incompatible elements, including the halogen elements (F, Cl, Br, and I), but their concentrations remain poorly known, thus hindering better understanding of the role of the crust in Earth's halogen cycle. We present halogen data (F, Cl, Br, and I) for twentyfour well-characterized glacial diamictite composites that derive from the upper continental crust (UCC) and were deposited during discrete glacial events at similar to 2.9 Ga, similar to 2.4-2.2 Ga, 0.75-0.58 Ga, and similar to 0.30 Ga. A good correlation between Cl and the highly soluble Na (R-2 = 0.70), together with low and scattered Cl concentrations in the diamictites (2-279 ppm), indicates significant Cl loss during chemical weathering of the continents. The other halogens (F, Br, and I), however, are not strongly affected by chemical weathering as revealed by their correlations with less soluble elements like K, P, Nd, and Lu, which may be due to their retention in secondary minerals and/or organic matter. Increasing concentrations of F in the composites through time may reflect the evolving composition of the UCC. Using the median values of the Neoproterozoic and Paleozoic diamictite composites, halogen concentrations of the present-day weathered UCC are estimated to be: 575 +/- 87 ppm F, 29 +/- 20 ppm Cl, 0.65 +/- 0.14 ppm Br, and 0.05 +/- 0.01 pp m I (errors quoted at the median absolute deviation). Linear correlations between halogens and other elements provide estimates for minimum halogen concentrations of the present-day crystalline UCC: 394 +/- 67 ppm F, 83 +/- 24 ppm Cl, 0.41 +/- 0.04 ppm Br, and 0.03 +/- 0.01 ppm I (with 2 sigma uncertainties). These estimates are all lower than normalized concentrations of elements of similar incompatibility during igneous differentiation, which may reflect loss of halogens via magmatic degassing/exsolution and/or chemical weathering during the formation of the continental crust. The distinct behavior of Cl compared to Br and I during continental weathering leads to a wide range of Br/Cl (2-265 * 10(-3)) and I/Cl (122-197,952 * 10(-6)) ratios, and Br/I ratios that are distinctly higher than those of pelagic sediments and marine pore fluids. Similar halogen signals have been reported from the lithospheric mantle and may reflect recycling of terrigenous sediments. The calculated weathering flux of Cl from the continents is quite small compared to the total Cl content of seawater (< 8-34 %), suggesting that Cl in seawater is mainly derived from outgassing of the mantle and/or late volatile accretion. On the other hand, the significantly higher Br and I contents in terrigenous organic-rich sediments compared to those of crystalline bedrocks suggest that significant amounts of Br and I were transported from the oceans to the continents. (c) 2022 The Authors. Published by Elsevier Ltd.