The Arcuentu Volcanic Complex, expression of the Cenozoic subduction-related magmatic cycle in Sardinia (Italy), consists of abundant calcalkaline and tholeiitic effusive rocks and minor intrusive products. Although its effusive products have been extensively investigated, mainly due to their wide isotopic variability, intrusive counterparts remain poorly constrained. We present new petrographic, mineral chemical, whole-rock geochemical, isotopic and 40Ar/39Ar geochronological data for Monte Nureci intrusive rocks. They comprise coarse-grained orthopyroxene-bearing olivine gabbro and olivine-bearing gabbronorite, and fine-grained diorite with zoned plagioclase and pyroxene crystals. Plagioclase from olivine-bearing gabbronorite provided a 40Ar/39Ar age of 19.2 Å} 0.07 Ma. The chemical composition of mineral phases and bulk-rock isotopic composition (87Sr/86Sri = 0.70881–0.70958 and 143Nd/144Ndi = 0.51226–0.51228) closely match those of the Arcuentu basaltic andesites pointing to a genetic relationship. The three rock types have cumulitic texture, reflecting fractional crystallization from basaltic andesite to dacite magmas of the Arcuentu, at different stages of magma evolution, in open-system conditions. This is supported by mass balance calculations and Assimilation + Fractional Crystallization modelling. These results explain also the wide isotopic variation (87Sr/86Sr = 0.705–0.711) observed in the Arcuentu rocks, affected by a calculated moderate degree of crustal assimilation (r ≈ 0.2–0.3) of the Palaeozoic basement, starting from primitive magmas with variable isotopic composition (87Sr/86Sri = 0.7054-0.7063), derived from a heterogeneous mantle source.The Monte Nureci intrusive rocks, that follow the trend of crustal contamination defined by the Arcuentu effusive rocks, likely crystallized by distinct magma batches with different isotopic compositions, that had undergone varying degrees of crustal assimilation. They likely represent different magma chamber apophyses, emplaced at varying depths within the Arcuentu Volcanic Complex, later uplifted during the opening of the Campidano Graben in SW Sardinia. The main magmatic activity of the Arcuentu district was concentrated in 3-4 My, with multiple magma recharge events, generating the oscillatory and reverse zoning patterns observed in the plagioclase and pyroxene crystals of the diorite. In this rock, the minerals continued to interact with evolving magmas during their crystallization, in contrast to the unzoned crystals of the coarse- grained samples, crystallized from less compositionally variable magmas.

The Cretaceous-Paleogene (K-Pg) mass extinction was a pivotal event in Earth's history and is attributed to the interplay of two major events—the Deccan Traps volcanism and the Chicxulub asteroid impact. We contribute to refine of our understanding of the volcanic stressor for this extinction by investigating the sulfur and fluorine budgets of Deccan lavas from the Western Ghats (India), spanning the K-Pg boundary [1].Sulfur and fluorine concentrations were analyzed in clinopyroxene phenocrysts from Deccan Traps lavas, by Synchrotron-light X-ray fluorescence (beamline I18, Diamond Light Source, U.K.), and ion probe (CAMECA IMS 1280 at Nordsim Laboratory, Swedish Museum of Natural History, Stockholm, SE), respectively. The results were divided by experimentally determined partition coefficients to calculate melt concentrations.Our analyses reveal variable magmatic volcanic fluorine concentrations ranging from 400 to 3000 parts per million, suggesting the potential for regional environmental impact. The highest sulfur concentrations, reaching up to 1800 parts per million, are observed in Deccan lavas emplaced just prior to the extinction interval, within a timeframe of 0.1 million years. In contrast, later basalts generally exhibit lower sulfur concentrations, only up to 750 parts per million.Independent evidence [2] supports that eruption of the Deccan flood basalts occurred in multiple voluminous eruptive pulses each lasting on the order of centuries, as typical of continental flood basalts. Our findings propose that the volcanic sulfur degassing associated with such activity may have led to repeated, short-lived global temperature drops, too short to be recorded by global paleotemperature record, albeit coupled with a global cooling trend. Sulfur-induced cold snaps likely imposed stress on ecosystems long before the decisive impact of the Chicxulub bolide at the end of the Cretaceous. [1] Sara Callegaro, et al., (2023) Recurring volcanic winters during the latest Cretaceous: Sulfur and fluorine budgets of Deccan Traps lavas. Sci. Adv. 9, eadg8284 doi:10.1126/sciadv.adg8284. [2] I. M. Fendley, et al., 2019. Constraints on the volume and rate of Deccan Traps flood basalt eruptions using a combination of high-resolution terrestrial mercury records and geochemical box models. Earth Planet Sci Lett. (524) 115721.

Melilitites are ultramafic magmas characterized by normative Ca2SiO4, larnite, high FeO* and TiO2. Liquids compositionally close to melilitites were experimentally reproduced from carbonated lherzolites in alkali, Fe and Ti-free model systems at 3.2-3.3 GPa, approx. 1500 °C (Gudfinnsson & Presnall, 2005), at relatively high melt proportions. In complex compositions, MORB-eclogite derived, carbonated, partial melts reacted with a fertile peridotite were proposed at the origin of melilitites (Mallik & Dasgupta, 2013, 2014). The experimental reconstruction of phase relationships along a join olivine melilitite - carbonate revealed that at 3 GPa, clinopyroxene and olivine or garnet are stable on the liquidus (Brey & Ryabchikov, 1994), suggesting that carbonated wehrlites are potential sources for the genesis of melilitites.Here, we explore phase relationships on the high pressure melting of a model wehrlite, initially composed of a mechanical mixture of San Carlos olivine, diopside, aegirine, dolomite, rutile and kyanite. Starting materials were loaded in graphite capsules, inserted in sealed platinum capsules. Vitreous carbon spheres and synthetic diamond grains were adopted for liquid traps. Preliminary experimental results show that at 3 GPa the solidus is located at temperatures lower than 1200 °C. A thick, orthopyroxene-rich layer, with polygonal microstructure, forms at contact with aggregates resulting from quenched liquids, both at 1200 °C and 1400 °C. Estimates of liquid composition are melilititic, with TiO2 approx. 2.5 wt.% on a volatile free basis.Currently available experiments suggest that the solidus is controlled by the reaction dolomite + olivine + clinopyroxene = orthopyroxene + liquid, as suggested in Eggler (1976). This is feasible only if the liquid composition is located on the CaO-rich side of the plane diopside-forsterite-dolomite in the model system CaO-MgO-SiO2-CO2, i.e. on the normative larnite (akermanite) portion of the tetrahedron. Brey G.P. & Ryabchikov I.D. (1994). Carbon-dioxide in strongly silica undersaturated melts and origin of kimberlite magmas. Neues Jahrbuch Fur Mineralogie-Monatshefte, (10), 449-463.Eggler D.H. (1976). Does CO2 cause partial melting in the low-velocity layer of the mantle?. Geology, 4(2), 69-72Gudfinnsson G.H. & Presnall D.C. (2005). Continuous gradations among primary carbonatitic, kimberlitic, melilititic, basaltic, picritic, and komatiitic melts in equilibrium with garnet lherzolite at 3–8 GPa. Journal of Petrology, 46(8), 1645-1659.Mallik A. & Dasgupta R. (2013). Reactive infiltration of MORB-eclogite-derived carbonated silicate melt into fertile peridotite at 3 GPa and genesis of alkalic magmas. Journal of Petrology, 54(11), 2267-23

Cenozoic (>= 43 Ma) silica undersaturated (potassic) trachybasalts and trachyandesites in southwestern Madagascar (Tsianihy-Manja, southern Morondava Basin) form a small monogenetic volcanic field emplaced above Paleogene detritic sedimentary rocks, along a NE-SW-trending fault system. These olivine-chromite +/- clinopyroxene-phyric primitive lavas (Mg# = 69; MgO = 10-11 wt%; Cr = 450 ppm, Ni = 200 ppm; K2O = 3-4 wt%) have highly peculiar trace element and isotopic composition (e.g., Ba/Nb = 18.4; 87Sr/86Sri = 0.70529-0.70555, 143Nd/144Ndi = 0.51262-0.51263, 206Pb/204Pbm = 18.415-18.424, 207Pb/204Pbm = 15.576-15.579, 208Pb/204Pbm = 38.799-38.813). A hitherto undescribed plug of primitive (sodic) basanite of the 11-12 Ma-old Ankililoaka district south of Tsianihy-Manja (hosting spinel lherzolite mantle xenoliths) has noticeable different geochemistry (Ba/Nb = 8-9.2; 87Sr/86Sri = 0.70346-0.7036, 143Nd/144Ndi = 0.51281-0.51282, 206Pb/204Pbm = 19.079-19.374, 207Pb/204Pbm = 15.621-15.645, 208Pb/204Pbm = 39.115-39.424). The relatively low CaO, Sc, V, Fe2O3t, MnO at high MgO, Cr and Ni, and the potassic affinity of the TsianihyManja trachybasalts, all indicate that the mantle source is relatively clinopyroxene-poor (i.e., depleted by previous melt extractions), in the same way as the source of lamproitic (or boninitic) magmas, but the primitive nature, the concentration of high field strength elements, the incompatible element patterns and their isotopic ratios indicate their unequivocal within-plate setting and indicate a derivation by low-degree partial melting of an incompatible element-enriched mantle and insignificant role for crustal contamination. In terms of incompatible element concentrations, and thus also Sr-Nd-Pb-isotopic composition, we find no evidence in favour of a mid-ocean ridge basalt (MORB)-mantle component, or for a MORB-mantle strongly enriched by ocean island basalt-like components, to form the mantle source regions of the Tsianihy-Manja and Ankililoaka mafic alkaline rocks. The significant isotopic change from the northernmost Cenozoic volcanic rocks of Madagascar and those in the central and southern part of the island (which range in composition from sodic to potassic, and from tholeiitic basalt to olivine melilitite) implicates a distinct source heterogeneity, and ultimately assess the role of the old continental lithospheric mantle as source region.

The lavas of the Mt. Somma volcanic epoch were erupted during the early stage of the Somma-Vesuvius volcanic complex. These lavas are mildly differentiated with the presence of plagioclase-clinopyroxene-olivine- +/- leucitebearing rocks ( leucite tephrites, leucite-bearing shoshonites , latites ), also characterized by low in MgO, Cr and Ni, with a Sr-Nd-isotope range ( 87 Sr/ 86 Sr = 0.706865-0.707861; 143 Nd/ 144 Nd = 0.51244-0.51258) that overlaps with lavas of the late stage Vesuvius erupted after 1631 CE (late stage of the Somma-Vesuvius volcanic complex). Differentiation is dominated by closed -system processes, with fractional crystallization of clinopyroxene, calcic plagioclase, olivine, magnetite, and leucite. Open -system differentiation processes are subordinate and associated with limited interaction with crustal rocks. Oxygen isotopes on clinopyroxene and olivine phenocrysts (delta 18 O = 6.5-7.9 parts per thousand) are higher than typical uncontaminated mantle magmas, suggesting a crustal contribution to the melt. Although open -system assimilation + fractional crystallization certainly took place, this process alone does not adequately reproduce the chemical and isotopic composition of the Mt. Somma ultrapotassic magmas. Therefore, a contribution from a recycled crustal component in the mantle source is required, but probably dominated by sediment -derived fluids and melts. The Mt. Somma lavas are characterized by distinctly different geochemical features compared to the mafic products of the neighboring volcanic areas (i.e., Phlegrean, Procida and Ischia volcanic fields), where the recycled crustal component is less pronounced.

Two events share the stage as main drivers of the Cretaceous-Paleogene mass extinction-Deccan Traps volcanism, and an asteroid impact recorded by the Chicxulub crater. We contribute to refining knowledge of the volcanic stressor by providing sulfur and fluorine budgets of Deccan lavas from the Western Ghats (India), which straddle the Cretaceous-Paleogene boundary. Volcanic fluorine budgets were variable (400 to 3000 parts per million) and probably sufficient to affect the environment, albeit only regionally. The highest sulfur budgets (up to 1800 parts per million) are recorded in Deccan lavas emplaced just prior (within 0.1 million years) to the extinction interval, whereas later basalts are generally sulfur-poor (up to 750 parts per million). Independent evidence suggests the Deccan flood basalts erupted in high-flux pulses. Our data suggest that volcanic sulfur degassing from such activity could have caused repeated short-lived global drops in temperature, stressing the ecosystems long before the bolide impact delivered its final blow at the end of the Cretaceous.

The lava domes of the Cixerri half-graben (SW Sardinia) are part of the subduction-related igneous activity that developed in Sardinia during the Upper Eocene-Middle Miocene (38-12 Ma), with calcalkaline and high-K calcalkaline affinity. The investigated rocks are porphyritic basaltic andesites and andesites, with amphibole, plagioclase and minor clinopyroxene phenocrysts included in a groundmass composed of the same phases together with feldspar, quartz and opaque oxides. Ar-40/Ar-39 analyses of plagioclase and amphibole separates from an andesite indicate a crystallization age of 21.31 +/- 0.05 Ma. The high abundance of amphibole in the Cixerri rocks, unlike andesites from the neighboring Sardinian districts, could be explained with the high calculated oxygen fugacity (NNO+1-NNO+2) and H2O content (up to 9 wt%) in the Cixerri magmas. Bulk-rock major and trace element variations, and mass balance calculations are consistent with a magma evolution mainly driven by fractional crystallization of amphibole and plagioclase, which occurred in a polybaric plumbing sys-tem, as highlighted by the calculated pressure of amphibole crystallization (2-4 kbar and 6-9 kbar). Bulk rock isotope variations (Sr-87/Sr-86(i) = 0.70701-0.70786 and Nd-143/Nd-144(i) = 0.512328-0.512436) indicate that the magma evolution took place in open-system conditions with a low degree of crustal assimilation. The HREE flat patterns point to a magma source in the spinel stability field located in a mantle wedge depleted in incompatible elements and metasomatized by slab and sediment derived fluids and melts.

The flood basalts of Cretaceous age in southwestern Madagascar range from moderately incompatible-element-enriched, tholeiitic, high-Ti ferrobasalt/basaltic andesite lavas (MgO = 4-5 wt%, Fe2O3t = 14-16 wt%; TiO2 = 3-3.6 wt%, Nb =16-22 ppm, Zr = 236-269 ppm; Lan/Ybn = 7-8) in the southernmost outcrops (Lavanono, Tulear), to incompatible element-poor basaltic dikes (MgO = 4.2-4.9 wt%, Fe2O3t = 12-13 wt%; TiO2 = 1.6 wt %, Nb = 8-9 ppm, Zr = 90-100 ppm; Lan/Ybn = 2.3) around Morondava. The two magma types, at the same degree of magmatic evolution, have markedly different Sr-Nd-Pb isotopic composition (e.g., 87Sr/86Sri = 0.7121-0.7123, 208Pb/204Pb = 40.9-41.3 for the Tulear-Lavanono lavas vs 87Sr/86Sri = 0.7033-0.7040, 208Pb/204Pb = 38.7 for the Morondava dikes), that suggest markedly different sources, magmatic history, and variable interplay between Madagascan Precambrian crust and mantle-derived melts, some with a marked enriched mid-ocean ridge basalt-like composition. The geochemical and isotopic data show no involvement of ancient basement crust in the genesis of the Morondava dikes. The Tulear-Lavanono lavas have high Ba/Nb and La/Nb ratios and Sr-Nd-Pb isotopic characteristic of magmas that have assimilated crustal material. The chemical and isotopic composition of the contaminated tholeiites of southern Madagascar matches some Late Cretaceous group B1 basalts of the Androy volcanic complex and tholeiites of the Ejeda-Bekily dike swarm, and therefore they could derive from the same feeding system or were fed by similar parental magmas. Basalts from the Southwest Indian Ridge between 39 and 41 degrees E section (anomalous magmatic sectors) with low 206Pb/204Pb and 143Nd/144Nd have been interpreted to contain a component of either recycled lower continental crust and/or subcontinental lithospheric mantle. A detailed review of the isotopic and geochemical compositions of the Mesozoic-and Cenozoic-magmatism in Madagascar, and of the lower and upper crustal domains point out that the sources of the anomalous magmatic sectors of the Southwest Indian Ridge do not contain lower crustal (or lithospheric mantle) components of Madagascan origin.Comparison between the samples from the northern and southern parts of the Madagascar flood basalts province indicates that several different parental magmas and mantle sources were involved in the petrogenesis of the Madagascan basalts, and that chemical contributions from a "Marion" hotspot (as a magma source or source component) to the Madagascar primary magmas is not identifiable.

The Bobaomby volcanic field (10–11 Ma) is the northernmost volcanic area of Madagascar, and is a monogenetic volcanic field comprising outcrops of lava flows, dykes, scoria cones, tuff rings and plugs, widely scattered over an area of roughly 500 km 2 . The volcanic rocks range in composition from nephelinite, basanite and tephrite, through tephritic phonolite, to F- and Cl-rich peralkaline phonolite (MgO from 13 to 0.01 wt%), and the serial affinity varies from sodic to potassic. A few mica-amphibole-rich lamprophyric dykes have tephritic composition and ultrapotassic affinity. The mafic lavas host intrusive xenoliths with evident cumulate features (wehrlites, composite olivine gabbros s.l., amphibole clinopyroxenites and “ kaersutitites ”), as well as various types of mantle-derived xenoliths and xenocrysts in the most primitive rocks. The very wide compositional variations of the observed phases (olivine, clinopyroxene, amphibole, oxides, feldspars, feldspathoids, apatite, titanite, aenigmatite and other accessories) in lavas, dykes and cognate xenoliths are fully consistent with the variable degree of differentiation of the host lavas/dykes, and pointing out to limited open-system or polybaric crystallization. The mafic lavas have marked enrichment in incompatible elements and light rare-earth element (LREE) (e.g., La n /Yb n = 19–27), whereas concave REE patterns are found in the peralkaline phonolites, as a result of removal of accessory titanite starting from tephritic phonolite magmas. The gabbroic/ultramafic xenoliths are interpreted as crustal cumulates of basanitic and tephritic magmas. Several liquid lines of descent in the basanites and tephrites are evident from the trace-element distribution, and from the differing geochemistry of the evolved rocks. The isotopic compositions reach extreme values (e.g., 206 Pb/ 204 Pb = 20.065 in the ultrapotassic lamprophyre) when compared to the rest of the Cenozoic/Recent Madagascan volcanic rocks, but similar to those of the Comoros archipelago, suggesting analogies of mantle sources and enrichment processes in the lithosphere of this volcanic archipelago. The origin of the Bobaomby mafic rocks is compatible from a derivation from low degree partial melting of an incompatible element-enriched peridotite source (possibly located in the lowermost lithospheric mantle) rich in volatile-rich phases (pargasite, locally also phlogopite and possibly carbonates), matching the sources of other Cenozoic volcanic areas throughout Madagascar, and perhaps Comoros.

We here investigate the geochemical and isotopic variability of primitive and evolved magmas of the Nyamulagira and Nyiragongo volcanic complexes (Virunga Volcanic Province, western branch of the east African Rift), including the very last products of the Nyiragongo's May 22, 2021 eruptive event and the Nyamulagira lava lake in February 2020. The different degree of silica undersaturation (i.e., potassic basanites/tephrites at Nyamulagira vs. potassic olivine melilitites/melilite nephelinites at Nyiragongo) and distinct incompatible element enrichment between the two volcanoes (e.g., Zr/Nb = 3.3-4 at Nyamulagira vs. Zr/Nb = 1.2-2.1 at Nyiragongo) are remarkable. Concentration of volatile elements (especially F and S) increases with the degree of magmatic evolution, and is also markedly different at the same level of magma evolution for the products of the two volcanic complexes, suggesting distinct volatile concentration of the primary magmas. The Sr-Nd-Pb isotopic range (e.g., 87Sr/86Sr = 0.7052-0.7059 at Nyamulagira vs. 87Sr/86Sr = 0.7045-0.7047 at Nyiragongo; 206Pb/204Pb = 19.19-19.31 at Nyamulagira vs. 206Pb/204Pb = 19.41-19.75 at Nyiragongo) overlaps with previous analyses obtained in the Virunga Volcanic Province (VVP), and is discussed with respect to other potassic/ ultrapotassic rocks from different tectonic settings. The Ba/Nb and La/Nb ratios and Cs concentration of Nyamulagira and Nyiragongo indicate a negligible role for subducted sediments as a mantle-added geochemical component, as instead took place in the source of other primitive potassic/ ultrapotassic rocks such as those of the Roman Volcanic Province. The genesis of the primitive lavas of Nyamulagira and Nyiragongo is related to partial melting of a heterogeneous lithospheric peridotite hosting phlogopite and variable amounts of carbonates, which was moderately to highly enriched in incompatible elements, particularly Nb, Ta, LREE, (K), Ba and Sr. No high-temperature (plume), asthenospheric components or pyroxenites are evident or unambiguously detectable.

Abstract The Late Cretaceous magmatism in Madagascar is correlated with the break-up between Madagascar and Greater India, with a presumed track of a hotspot from Madagascar towards the Marion Island and with an anoxic event in the Late Cretaceous. The lava succession and associated dyke swarms and sills of western Madagascar (Mailaka area) represent a volumetrically important area of the igneous province, where dykes with random orientation, several igneous intrusions and a flood basalt to rhyodacite sequence do occur. The magmas have a tholeiitic and weakly alkaline affinity. Using plagioclase separates, we obtained two plateau 40 Ar/ 39 Ar ages, and an inverse isochron age statistically indistinguishable, ranging from 92.9 ± 3.8 to 91.2 ± 1.3 Ma (2 σ ). These ages indicate that tholeiitic and alkaline rocks were erupted in the same age span. In addition, these ages are close to the Cenomanian–Turonian (C–T; 93.9 ± 0.2 Ma) boundary and are indistinguishable from the U–Pb ages available for the capping rhyodacitic unit of the Mailaka lava succession. A filtered compilation of eight ages for northern and central-western Madagascar rocks suggests a duration for the magmatic activity in this part of Madagascar province of the order of c. 3 Ma. If the western Madagascar magmatism is plume related, the plume head would need to have been located near the Mailaka area at c. 93 Ma. The geochemistry of the mafic lavas and dykes of western Madagascar is barely distinguishable from mid-ocean ridge basalt (MORB), with an increasing crustal contamination towards the evolved rocks, and does not constrain input of typical components derived by plume magmatism.

A comprehensive mineralogical, geochemical and isotopic review of six ultramafic-alkaline-carbonatite magmatic intrusions of the Shillong Plateau (Sung Valley, Jasra, Swangkre-Rongjeng, and Mawpyut) and Mikir Hills (Samchampi-Samteran and Barpung) is presented here, using the published data. These intrusions emplaced ca. 115–102 Ma ago, thus are significantly younger than the tholeiitic flood basalts erupted in Rajmahal-Sylhet province (ca. 118–115 Ma). The intrusive lithologies vary from ultramafic (dunites, clinopyroxenites, melilitolites) to mafic (ijolites, gabbros sensu lato, shonkinites), to felsic (syenites, nepheline syenites) and carbonatites (mostly calcite-rich varieties). The volcanic-subvolcanic facies (lamprophyres, phonolites) are not abundant. The range of chemical compositions of the magmatic phases in the various assemblages is notable; the intrusive rocks are thus the result of crystallization of magmas from variably evolved, independent liquid-lines-of descent, generally of alkaline/strongly alkaline lineages and sodic-to-potassic in affinity. The large variations of the Sr–Nd isotopic ratios of the silicate intrusive rocks (sensu lato) suggest a role of shallow-level crustal contamination during their formation. The carbonatites of the Sung Valley and Samchampi-Samteran have different isotope ratios than the associated silicate rocks, have some isotopic affinity with the Group I tholeiitic basalts of Rajmahal Traps and have an ultimate genesis in a carbonate-bearing lithospheric mantle.

A mineralogical, major, LA-ICP-MS trace element mineral chemistry and bulk-rock geochemical study of juvenile samples of the Mercato, Avellino, Pompeii and Pollena eruptions, collected in stratigraphically and volcano -logically well-characterized sections of the Somma-Vesuvius stratovolcano (Roman Magmatic Province), along with reference data on the 1944 CE and the Pomici di Base eruptions, highlights the compositional variability of bulk-rock and glass from leucite phonotephrite to garnet-bearing phonolite. The latter products have extreme fractionation of trace elements (e.g., La/Yb-n = 126, Zr/Y = 89, Zr/Hf =78, Nb/Ta = 40; Th/U = 2.3), very low Sc, V, Y, HREE and very high As, Tl, Cs, Pb, Th and U. The Pomici di Base products, older than the eruptions described above, range from leucite-bearing shoshonites to trachytes, are devoid of garnet and belong to an independent liquid-line-of-descent, having also different fractionation between trace elements (e.g., La/Yb-n = 15; Zr/Y = 12.4, Zr/Hf = 50, Nb/Ta = 15.6; Th/U = 3 in the Pomici di Base trachytes). A marked chemical variability of the observed phases is found. The geochemistry of garnet, amphibole, clinopyroxene and other phases shows wide variations of concentrations and elemental ratios (e.g., La/Ybn up to 520 in the sadanagaite coexisting with garnet). The magmatic evolution is dominated by low-pressure, oxidized, nearly closed-system fractional crystallization of clinopyroxene, plagioclase, leucite, +/- magnetite, +/- biotite, +/- olivine and apatite in the transition tephrite-phonotephrite, and of potassic sanidine (+/- hyalophane), Fe-clinopyroxene, melanite garnet +/- Fe-amphibole in the transition tephriphonolite-phonolite. Mineralogic and geochemical evidence and model-ling points out the existence of independent, zoned magma batches throughout the activity of the stratovolcano, which possibly started to crystallize at similar depths. The Somma-Vesuvius magmas thus evolved in shallow independent reservoirs with respect to those of the neighbouring volcanic complexes (Campi Flegrei, Ischia) as shown, for instance, by the contrasting compositional trends of clinopyroxene and amphibole, and have very limited evidence of crustal contamination (and/or carbonate assimilation).

The olivine melilitites from the southern part of the 6.8 Ma-old Takarindiona volcanic field (Eastern Madagascar) are olivine + chmmite -phyric lavas, with zoned titanaugite, perovskite, melilite, nepheline, monticellite, Ba Timica and Fe Ti oxides as micmphenocrysts and groundmass phases. The rocks are very primitive, rich in incompatible trace elements (e.g., Ba = 1049 + 153 ppm, Sr = 1050 + 167 ppm, Nb = 98 + 13 ppm; La/Yb = 41 + 5; La/Nb = 0.88 + 0.05), and have restricted ranges of initial Sr-87/Sr-86 (0.70391-0.70410) and Nd-143/Nd-144 (0.51272-0.51282). The rocks follow a differentiation trend controlled by ab. 20% removal/ addition of phenocryst olivine + chromite. The olivine melilititic magmas are the product of small degrees of partial melting (1-3%) of a peridotitic source, enriched in highly incompatible trace elements by CO2-, F-, and H20-rich melts, located within the garnet stability field (3-3.5 GPa and 100 km depth) of sub-continental lithospheric mantle, where carbonates (dolomite) and possibly phlogopite were stable phases. Mantle xenoliths within the volcanics are mostly spinel harzburgites having mineral modes and chemical compositions suggesting variable degrees of "basalt" melt extraction. Based on textural and chemical evidence, and quantitative thermobarometric estimates, the xenoliths were incorporated at a pressure of 1.1 GPa (-35-40 km depth), far shallower than the source of the melilititic magmas, and along a predictably cool geotherm beneath Archean continental lithosphere. Highly resorbed orthopyroxene xenocrysts mantled by augite indicate that the melilitites may have also entrained lower crustal materials or underplated subalkaline rocks. The mantle sources of the lavas and mantle xenoliths of the Takarindiona district indicate stratification of the lithospheric mantle, and help constraining the lithospheric features and the magmatic history of the Eastern Madagascar craton.

The Deccan-Traps-related "ijolite" intrusion of Rajpuri, Murud, south of Mumbai, is formed by dominant diopside +/- forsteritic olivine, set in a holocrystalline, fine-grained matrix rich in nepheline, opaque oxides, perovskite, phlogopite and other phases, grading a more felsic facies rich in phenocrysts of altered nepheline and less clinopyroxene (i.e., a "nephelinite"). The holocrystalline samples have clinopyroxene crystals hosting rounded microcrystals of melilite close to the rims. The presence of melilite is unique among the Deccan Trap-related alkaline intrusions in India, and implies that a batch of larnite-nonnative, extremely silica undersaturated silicate magma filled the Murud intrusion, and that crystallization took place in a low-pressure environment. Interstitial Mg-rich alkali amphibole (potassic richterite), growing poikilitically around nepheline, oxides and tetraferriphlogopite also suggest that many clinopyroxene phenocrysts of the Rajpuri intrusion, and their host melilite grains, crystallized in magmas different from the last they were entrained. Melilite and potassic richterite are not phases that can crystallize together in sodic-alkaline magmas. The unusual geochemical and isotopic composition of the Rajpuri intrusion, indicating magmas derived from old, enriched lithospheric mantle, and the presence of melilite, are strong indication that this is one of the most peculiar alkaline intrusions related to the Deccan Traps.

The Late Cretaceous (similar to 78 Ma) Pocos de Caldas massif is the largest alkaline complex in Brazil and the second in the world by extension (>800 km(2)). It is considered the westernmost outcrop of the Cabo Frio magmatic lineament, in the northern sector of Serra do Mar potassic-ultrapotassic igneous province, central-eastern Brazil. The outcropping rocks are peralkaline phonolites (similar to 80%) and nepheline syenites (similar to 15%) with rarer (<5%) basic-ultrabasic rocks (leucite basanites, basanites, basalts and lamprophyres). The phonolites have different levels of volatile (F and Cl) and other trace elements, which tend to decrease with increasing evolution, due to removal of F-, Mn-, HFSE- and REE-rich accessory phases accompanying cotectic alkali feldspar and nepheline. The geochemical variability of titanite, eudialyte, F-disilicates, aenigmatite, lamprophyllite, clinopyroxene, amphibole and other phases indicate the effects of removal of accessory phases and the presence of independent liquid lines of descent in the various intrusive pulses. The initial Sr-Nd isotopic ratios of the basic-ultrabasic lavas [Sr-87/(86)Sri = 0.70440-0.70498; epsilon(Ndi) = -3.7 to -1.2] are within the range of the other Late Cretaceous-Paleogene rocks of the northern sector of Serra do Mar, indicating a highly metasomatized K-rich lithospheric source. Nepheline syenites and phonolites have Srsingle bondNd isotopes largely overlapping with that of the basic-ultrabasic lavas (Sr-87/(86)Sri = 0.70503-0.70540 and epsilon(Ndi) =-3.9 to -2.5 for nepheline syenites; Sr-87/(86)Sri = 0.70511-0.70527 and epsilon(Ndi) = -3.4 to-3.2 for phonolites). Prolonged fractional crystallization processes dominated by clinopyroxene removal from melts with compositions resembling those of the basic-ultrabasic compositions can produce residual liquids qualitatively comparable with those represented by the phonolites and nepheline syenites.

The Nyiragongo lava of 2002, and the new one flowing from the spatter cone grown up in 2016 close to the lava lake, are melilitites (melilite-nephelinites). They have low MgO (4 wt%), are chemically almost indistinguishable from the lavas of 1977 and from that erupted in 2017, are multiply saturated in melilite, nepheline, leucite, clinopyroxene, olivine, apatite and magnetite, and are rich in fresh glass having significant concentration of SO3, F and Cl. Glasses and bulk-rocks plot close to one atmosphere cotectics in pertinent phase diagrams. The LA-ICP-MS analyses of the observed phases and mineral/glass partition coefficients indicate that REE and Y are moderately incompatible in melilite (e.g., DLa = 0.46–0.48, DEu = 0.56–0.57; DLu = 0.18–0.25; DY = 0.25–0.27), whereas Sr is compatible (DSr = 1.6–1.8); clinopyroxene/melt partition coefficients are similar to melilite for LREE (e.g., DLa = 0.36), and significantly higher for HREE (DLu = 0.74), Y (DY = 0.7), Zr (≈1) and Hf (DHf = 1.6), while lower for Sr (DSr = 0.38). Apatites have high concentration ratios for REE, particularly MREE (DLa = 4.6–6.4, DNd = 5.8–7.7; DEu = 4.9–6.9; DLu = 1.3–1.6; DY = 3.1–4.4), and high DSr (1.8–2.2). Nepheline and leucite are highly and differently selective for Rb, Cs, Ba and Sr; both phases show negligible concentration of REE (hence Eu, +Y), Th, U and first row transition elements. Olivine and magnetite have the expected high concentration of transition elements, with small preference of olivine for divalent cations and magnetite for trivalent cations. The distribution of trace elements in melilite compared with clinopyroxene, nepheline -or even feldspar- clearly indicate that melilite is not an equivalent of any of these phases, and that melilite removal cannot be considered the main cause of Eu troughs or of decreasing fractionation between light and heavy REE in more evolved melts, being these elements still significantly incompatible. At the same time, removal of the observed phenocrysts at this stage of crystallization cannot be the cause of anomalous fractionation of elements with similar geochemical behaviour found in the Nyiragongo lavas. These new data indicate that the magmatic system of the Nyiragongo is in a roughly steady state at least since the eruption of 1977 to the activity of 2017, with periodic eruptions, withdrawal or feeding from the uppermost magma reservoir by broadly the same “cotectic” magma compositions, from which phases of the same composition nucleated in a very low-pressure regime.

The Passa Quatro alkaline complex is one of the main intrusions in the Serra do Mar Cretaceous to Paleogene Igneous Province of southeastern Brazil. It is composed mainly of nepheline syenites and alkali syenites, with minor phonolitic dikes. The dominant felsic phases are potassic feldspar and nepheline, with minor sodic plagioclase in less silica-undersaturated rocks. The main mafic phases are clinopyroxene, amphibole, biotite, and oxides. The wealth of accessory phases includes titanite, eudialyte, astrophyllite-kupletskite, F-disilicates, phosphates, phosphosilicates, and F-REE-carbonates, with their specific ranges of composition. These accessory minerals often mantle zircon and fluorite corroded crystals, evidence of (1) the petrographic transition from miaskitic to agpaitic in the same rock, and (2) a decrease in the activity of fluorine in the coexisting residual magmas, from the stability range of fluorite to that of F-poorer disilicates. There is also a major role, as yet undervalued, for manganese in the phase stability of the various accessory phases in rocks/magmas devoid of magnesium. The three neighboring complexes of Itatiaia, Passa Quatro, and Po cos de Caldas have significant differences in the types and amounts of agpaitic minerals in their peralkaline rocks. The Passa Quatro intrusion (with aegirine, titanite, and minor eudialyte) can be considered slightly more silica undersaturated and peralkaline than the nearby Itatiaia complex and has transitional features towards the highly agpaitic nepheline syenites of Po cos de Caldas (with aegirine, titanite, eudialyte, and aenigmatite). Eudialyte and titanite represent accessory phases that influence the incompatible element behavior in the residual magmatic compositions (mostly phonolites and peralkaline phonolites) of the Serra do Mar potassic province.