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In this experimental study, we documented the formation of strongly ultrabasic and ultracalcic melts through the interaction of melilititic and basanitic melts with calcite. Three strongly to moderately SiO2-undersaturated volcanic rocks from the Bohemian Massif (central Europe) were mixed with 10, 30, and 50 wt% CaCO3 and melted at 1100, 1200, and 1300 °C at 2 kbar to evaluate the maximum amount of carbonate that can be assimilated by natural ultrabasic melts at shallow depths. Experiments revealed a surprisingly complete dissolution of the CaCO3, only rarely reaching carbonate saturation, with typical liquidus phases represented by olivine, spinel, melilite, and clinopyroxene. Only in the runs with the most SiO2-undersaturated compositions did abundant monticellite form instead of clinopyroxene. For all starting mixtures, strongly ultrabasic (SiO2 down to 15.6 wt%), lime-rich (CaO up to 43.6 wt%), ultracalcic (CaO/Al2O3 up to ~27) melt compositions were produced at 1200 and 1300 °C, with up to ~25 wt% dissolved CO2. When present, quenched olivine showed much higher forsterite content (Fo95-97) than olivine in the natural samples (Fo79-85). The two major results of this study are (1) silicate-carbonatite melt compositions do not necessarily imply the existence of carbonatitic components in the mantle, because they are also produced during limestone assimilation, and (2) Fo-rich olivines cannot be used to infer any primitive character of the melt nor high potential temperature (Tp). [ABSTRACT FROM AUTHOR]

The small Quaternary volcanic district of Nowbaran (NW Iran) belongs to the Urumieh-Dokhtar Magmatic Arc, a ∼1800-km long NW–SE striking Cenozoic belt characterized by the irregular but abundant presence of subduction-related igneous products. Nowbaran rocks are characterized by absence of feldspars coupled with abundance of clinopyroxene and olivine plus nepheline, melilite and other rarer phases. All the rocks show extremely low SiO2 (35.4–41.4 wt%), very high CaO (13.1–18.3 wt%) and low Al2O3 (8.6–11.6 wt%), leading to ultracalcic compositions (i.e. CaO/Al2O3 > 1). Other less peculiar, but still noteworthy, characteristics are the high MgO (8.7–13.3 wt%) and Mg# (0.70–0.75), coupled with a variable alkali content with sodic affinity (Na2O = 1.8–5.4 wt%; K2O = 0.2–2.3 wt%) and variably high LOI (1.9–10.4 wt%; average 4.4 wt%). Measured isotopic ratios (87Sr/86Sr = 0.7052–0.7056; 143Nd/144Nd = 0.51263–0.51266; 206Pb/204Pb = 18.54–18.66; 207Pb/204Pb = 15.66–15.68; 208Pb/204Pb = 38.66–38.79) show small variations and plot within the literature field for the Cenozoic volcanic rocks of western Iran but tend to be displaced towards slightly higher 207Pb/204Pb. Primitive mantle-normalized multielemental patterns are intermediate between typical subduction-related melts and nephelinitic/melilititic melts emplaced in intraplate tectonic settings. The enrichment in Th, coupled with high Ba/Nb and La/Nb, troughs at Ti in primitive mantle-normalized patterns, radiogenic 87Sr/86Sr and positive Δ7/4 anomalies (from +15.2 to +17.0) are consistent with the presence of (old) recycled crustal lithologies in the sources. The origin of Nowbaran magmas cannot be related to partial melting of C–H-free peridotitic mantle, nor to digestion of limestones and marls by 'normal' basaltic melts. Rather, we favour an origin from carbonated lithologies. Carbonated eclogite-derived melts or supercritical fluids, derived from a subducted slab, reacting with peridotite matrix, could have produced peritectic orthopyroxene- and garnet-rich metasomes at the expenses of mantle olivine and clinopyroxene. The residual melt compositions could evolve towards SiO2-undersaturated, CaO- and MgO-rich and Al2O3-poor alkaline melts. During their percolation upwards, these melts can partially freeze reacting chromatographically with portions of the upper mantle wedge, but can also mix with melts from shallower carbonated peridotite. The T – P equilibration estimates for Nowbaran magmas based on recent models on ultrabasic melt compositions are compatible with provenance from the lithosphere-asthenosphere boundary at average temperature (∼1200°C ± 50°C). Mixing of melts derived from subduction-modified mantle sources with liquids devoid of any subduction imprint, passively upwelling from slab break-off tears could generate magmas with compositions recorded in Nowbaran. [ABSTRACT FROM AUTHOR]

The Miocene Galatian Volcanic Province (GVP) is one of the largest volcanic provinces in central-western Anatolia, with an extent of ~ 8,900 km2. The volcanic activity is extended from 22.5 to 7.5 Ma. The volcanic compositions straddle the alkaline-subalkaline fields, from basic to acid compositions and mostly transitional to sodic affinity. Major oxides show good correlation with SiO2 indicating prolonged effects of fractional crystallization. Primitive mantle-normalized multi-element patterns indicate overall similarities among the different samples of the three geographic sectors, sharing strong negative anomalies in Nb–Ta–Ti, strong positive peaks at Cs and K, coupled with a common, albeit not always present, positive anomaly at Pb. Mineral-melt geothermobarometric estimates indicates ~1070–1235°C and ~7–19 kbar for melting conditions of basaltic compositions and ~1000–1150°C and ~3–12 kbar for andesitic-dacitic rocks. The absence of correlation between radiogenic isotopes and SiO2 and MgO is here interpreted as consequence of assimilation-fractional-crystalization processes involving lower continental crust as contaminant. The GVP parental magmas are generated from ~2% to 10% partial melting of a lherzolitic mantle with high spinel/garnet ratio based on intra-REE fractionation constraints. The subduction-related metasomatism inferred for the GVP mantle sources based on their chemistry is interpreted to be linked to the northward subduction of the northern branch of the Neo-Tethys slab. Successive slab retreat resulted in extension for the critical stress distribution through the Cyprus slab, favouring magma propagation for the GVP volcanic region. The eventual break-off of the slab after the continent-continent collision of Arabian and Eurasian plates could have caused a toroidal mantle flow, favouring the widely distributed 15–16 Ma alkaline magmatism in the eastern GVP, associated with passive hot asthenospheric upwelling imaged by teleseismic P-wave tomography. [ABSTRACT FROM AUTHOR]

We present a comprehensive geochronological, mineralogical, and geochemical study on previously unknown olivine leucitites occurring in the Maiga area of southern Tibet to examine the possibility of carbonate recycling during continental subduction. The Miocene (∼16 Ma) Maiga olivine leucitites are characterized by low SiO 2 (44.6–46.3 wt%), high MgO (14.0–15.7 wt%), and ultra-calcic (CaO/Al 2 O 3 = 1.1–1.2) compositions, along with arc-like incompatible element patterns (e.g., enrichment in large-ion lithophile and light rare earth elements, and depletion in high-field-strength elements). These rocks also have extremely radiogenic 87Sr/86Sr (i) (0.715647–0.715844), unradiogenic εNd (i) (−11.6 to −11.2) and εHf (i) (−10.5 to −10.0), and moderately radiogenic 206Pb/204Pb (i) (18.44–18.46) isotopic compositions. The studied samples are also characterized by slightly heavy O isotope ratios (clinopyroxene δ18O = +6.7‰ to +8.7‰) and relatively low water contents (0.75–1.75 wt%). The geochemical features of the Maiga olivine leucitites are compatible with an origin from a carbonated peridotite mantle source. Additionally, based on the regional tectonic evolution and mid-ocean-ridge-basalt-like Zn isotopic compositions (δ66Zn = +0.26‰ to +0.30‰), we hypothesize these magmas formed from interactions between ambient mantle peridotite and recycled Ca-rich carbonate sediments during Indian continental subduction. The transition from the neighboring Miocene lamproite-like rocks in southern Tibet to olivine leucititic magmas in Maiga is assumed to reflect the tapping of two different mantle sources. The first was modified by silicate-rich sediments, which generated lamproite-like rocks, whereas the Maiga mantle source was modified by carbonate-rich sediments. This study and previous research on other K 2 O-rich subduction-related magmas indicate that non-negligible amounts of carbonates can be recycled deep into the mantle during continental subduction, which may play an important role in global carbon recycling. • Maiga olivine leucitites have low water contents and MORB-like Zn isotope. • Maiga olivine leucitites originated from mantle peridotite containing recycled carbonates. • Carbonated mantle source was generated during the Indian continental subduction. [ABSTRACT FROM AUTHOR]

Abstract Leucite-bearing volcanic rocks are commonly found within and around the Mediterranean area. A specific type of this rock group are leucitites. They are found both in a hinterland position of active and fossil subduction systems as well as in foreland tectonic settings, but none have been found in the Maghreb (N Africa) and Mashreq (Middle East) areas. Here a review of the main leucitite occurrences in the circum-Mediterranean area is presented, with new whole-rock, mineral chemical and Sr-Nd-Pb isotopic ratios on key districts, with the aim of clarifying the classification and genesis of this rock type. Many of the rocks classified in literature as leucitites do not conform to the IUGS definition of leucitite (i.e., rocks with >10 vol% modal leucite and with foids/(foids + feldspars) ratio > 0.9, with leucite being the most abundant foid). Among circum-Mediterranean rocks classified as leucitites in the literature, we distinguish two types: clinopyroxene-olivine-phyric (COP) and leucite- phyric (LP) types. Only the second group can be truly classified as leucitite, being characterized by the absence or the very rare presence of feldspars, as well as by ultrapotassic composition. The COP group can be distinguished from the LP group on the basis of lower SiO 2 , Na 2 O + K 2 O, K 2 O/Na 2 O, Al 2 O 3 , Rb and Ba, and higher MgO, TiO 2 , Nb, Cr and Ni. The LP group shows multi-elemental patterns resembling magmas emplaced in subduction-related settings, while COP rocks are much more variable, showing HIMU-OIB-like to subduction-related-like incompatible element patterns. COP rocks are also characterized generally by more homogeneous isotopic compositions clustering towards low Sr and high Nd isotopic ratios, while LP leucitites plot all in the enriched Sr-Nd isotopic quadrant. LP rocks usually have lower 206Pb/204Pb and higher 207Pb/204Pb. This study shows that the geochemical signal of mantle melts does not always reflect the tectonic setting of magma emplacement, suggesting paying extreme attention in proposing geodynamic reconstructions on the basis of chemical data only. Graphical abstract Unlabelled Image Highlights • Leucitites are reported in several localities within and around the Mediterranean area. • Literature data for 179 "leucititic" rocks plus new data for 23 samples are presented here and reported in a MS Excel file. • We distinguish two "leucitite" rocks on the basis of petrography, mineral chemistry, whole-rock chemistry and Sr-Nd-Pb isotopic compositions. • These two rock groups (clinopyroxene-olivine-phyric – COP – and leucite-phyric – LP) seem to be confined to different geodynamic settings. • The main result of our contribution is that true leucitites are extremely rare compositions and confined to subduction-related settings only. [ABSTRACT FROM AUTHOR]

Provence (SE France) was affected by two main phases of sporadic igneous activity during the Cenozoic. New 40 Ar/ 39 Ar laser step-heating data constrain the beginning of the oldest phase to late Eocene (40.82 ± 0.73 Ma), with activity present until early Miocene (~ 20 Ma). The products are mainly andesites, microdiorites, dacites and basaltic andesites mostly emplaced in the Agay-Estérel area. Major- and trace-element constraints, together with Sr Nd Pb isotopic ratios suggest derivation from a sub-continental lithosphere mantle source variably modified by subduction-related metasomatic processes. The compositions of these rocks overlap those of nearly coeval (emplaced ~ 38–15 Ma) late Eocene-middle Miocene magmatism of Sardinia. The genesis of dacitic rocks cannot be accounted for by simple fractional crystallization alone, and may require interaction of evolved melts with lower crustal lithologies. The youngest phase of igneous activity comprises basaltic volcanic rocks with mildly sodic alkaline affinity emplaced in the Toulon area ~ 10 Myr after the end of the previous subduction-related phase. These rocks show geochemical and isotopic characteristics akin to magmas emplaced in intraplate tectonic settings, indicating a sub-lithospheric HiMu + EM-II mantle source for the magmas, melting approximately in the spinel/garnet-lherzolite transition zone. New 40 Ar/ 39 Ar laser step-heating ages place the beginning of the volcanic activity in the late Miocene–Pliocene (5.57 ± 0.09 Ma). The emplacement of “anorogenic” igneous rocks a few Myr after rocks of orogenic character is a common feature in the Cenozoic districts of the Central-Western Mediterranean area. The origin of such “anorogenic” rocks can be explained with the activation of different mantle sources not directly modified by subduction-related metasomatic processes, possibly located in the sub-lithospheric mantle, and thus unrelated to the shallower lithospheric mantle source of the “orogenic” magmatism. [ABSTRACT FROM AUTHOR]

The late Miocene (11–9 Ma) volcanic rocks of Kef Hahouner, ~ 40 km NE of Constantine (NE Algeria), are commonly classified as lamproites in literature. However, these rocks are characterized by an anhydrous paragenesis with plagioclase and Mg-rich olivine phenocrysts, set in a groundmass made up of feldspars, pyroxenes and opaque minerals. Thus, we classify the Kef Hahouner rocks as ultrapotassic shoshonites and latites, having K 2 O > 3 wt.%, K 2 O/Na 2 O > 2.5, MgO > 3–4 wt.%, SiO 2 < 55–57 wt.% and SiO 2 /K 2 O < 15. All the investigated samples show primitive mantle-normalized multi-element patterns typical of orogenic (arc-type) magmas, i.e. enriched in LILE (e.g. Cs, Rb and Ba) and LREE (e.g. La/Yb = 37–59) with respect to the HFSE, peaks at Pb and troughs at Nb and Ta. Initial isotopic ratios are in the range of 87 Sr/ 86 Sr = 0.70874–0.70961, 143 Nd/ 144 Nd = 0.51222–0.51223, 206 Pb/ 204 Pb = 18.54–18.60, 207 Pb/ 204 Pb = 15.62–15.70 and 208 Pb/ 204 Pb = 38.88–39.16. The Kef Hahouner volcanic rocks show multi-element patterns similar to the other circum-Mediterranean lamproites and extreme Sr, Nd and Pb isotopic compositions. Nevertheless, the abundant plagioclase, the presence of Al-rich augite coupled with high Al 2 O 3 whole rock compositions (9.6–21.4 wt.%), and the absence of phlogopite are all at inconsistent with the definition of lamproite. We reviewed the rocks classified as lamproites worldwide, and found that many of these rocks, as for the Kef Hahouner samples, should be actually defined as “normal” potassic to ultrapotassic volcanic rocks. Even the grouping of lamproites into “orogenic” and “anorogenic” types appears questionable. [ABSTRACT FROM AUTHOR]

The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks. Groundmass and macrocryst olivines range from δ 18 O VSMOW of +4.8‰, typical of mantle olivine values, to +7.4‰, indicating contamination by sedimentary carbonate. Carbonates are characterized by heavy oxygen isotope compositions (δ 18 O VSMOW >+24‰), and relatively light carbon isotopes (δ 13 C PDB <−11‰), resembling skarn values, and distinct from typical mantle carbonatite compositions. Petrography, mineral compositions such as low Mg# of clinopyroxene and biotite, low Ca# and low incompatible element abundance of the carbonate, and isotopic ratios of O and C, do not support a mantle origin for the carbonate. Rather, the carbonate inclusions found in the olivine macrocrysts are interpreted as basement limestone fragments entrapped by the rising crystallizing magma. Comparison with experimental carbonatitic and silicate-carbonatitic melts indicates that low-degree partial melts of a carbonated peridotite must have a dolomitic rather than the aragonitic/calcitic composition as those found trapped in the Morron de Villamayor olivine macrocrysts. [ABSTRACT FROM AUTHOR]

This work discusses and interprets the factors responsible for the Oligocene-Miocene drowning of the Central Apennine platform deposits, based on facies and stable-isotope analyses of two representative stratigraphic sections. The Mediterranean carbonate platforms were affected during the Oligocene-Miocene boundary by a carbonate production crisis that was induced by global factors and amplified by regional events, such as volcanic activity. The positive δ13C shift observed in the studied sections corresponds to vertical facies changes reflecting the evolution from middle carbonate ramp to outer ramp-hemipelagic depositional environments. This drowning event is recorded not only in the Apennine platforms, but also in other Mediterranean platforms such as in southern Apulia, Sicily and Malta, and outside the Mediterranean Basin. The ~24-23.5 Ma Mi-1 glacial maximum may have had a significant influence on this drowning event because it was associated with high rates of accumulation of continent-derived sediments. The increased continental weathering and runoff sustained high trophic conditions. These probably were a consequence of the Aquitanian-Burdigalian volcanic activity in the Central-Western Mediterranean, that may have led to an increase in nutrient content in seawater and an increase in atmospheric and marine CO2 concentrations. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Partition coefficients (Min/LD) for a series of geochemically relevant elements have been calculated from combined EMP/LA-ICP-HRMS analyses of plagioclase, alkali feldspar, Ti-magnetite, biotite, apatite, and trachytic/trachyphonolitic melt pairs in selected Campi Flegrei rocks. Pl/LD and Kfs/LD values are generally very low for most of the trace-elements but Sr, Ba, and Eu. Kfs/LD for the latter elements record a systematic increase as the melt composition changes from trachyte to trachyphonolite, likely due to increasing structural compliance of the sanidine in the trachyphonolites related to larger Na/K values. Conversely, Kfs/LD values for transitional, highly charged incompatible elements (e.g., LREE) decrease from trachyte to trachyphonolite, possibly in response to the decrease of melt polymerization. Min/LD values for titanomagnetite generally decrease with the increasing melt evolution, the highest values being those measured for Ti, V, and Sc. Ti, Ba, Sc, Rb, Nb, Ta, and V are compatible in biotite in equilibrium with trachytic melt, whereas Cs, Sr, and Pb are incompatible and REE are strongly incompatible, as supported by the extremely low Bt/LDY (0.003-0.008). Partition coefficients for apatite and trachyphonolitic glass pairs are high for Sr, REE (particularly MREE), and Y, large for Th, U, and V, generally low for HFSE, and variable for other LILE. The comparison of measured Min/LD values for Campi Flegrei trachytes/trachyphonolites with other sets of partition coefficients reported in literature for evolved systems suggests that a reliable data set for magma evolution modeling requires: (1) a thorough preliminary selection of natural samples; (2) the adoption of accurate microanalytical techniques; (3) the direct measurement of Min/LD values for each specific melt composition. [ABSTRACT FROM AUTHOR]

Abstract: The Cenozoic igneous activity of Sardinia is essentially concentrated in the 38–0.1Myr time range. On the basis of volcanological, petrographic, mineralogical, geochemical and isotopic considerations, two main rock types can be defined. The first group, here defined SR (subduction-related) comprises Late Eocene–Middle Miocene (~38–15Ma) igneous rocks, essentially developed along the Sardinian Trough, a N–S oriented graben developed during the Late Oligocene–Middle Miocene. The climax of magmatism is recorded during the Early Miocene (~23–18Ma) with minor activity before and after this time range. Major and trace element indicators, as well as Sr–Nd–Pb–Hf–Os–O isotope systematic indicate complex petrogenetic processes including subduction-related metasomatism, variable degrees of crustal contamination at shallow depths, fractional crystallization and basic rock partial melting. Hybridization processes between mantle and crustal melts and between pure mantle and crustally contaminated mantle melts increased the isotopic and elemental variability of the composition of the evolved (intermediate to acid) melts. The earliest igneous activity, pre-dating the Early Miocene magmatic climax, is related to the pushing effects exerted by the Alpine Tethys over the Hercynian or older lower crust, rather than to dehydration processes of the oceanic plate itself. The second group comprises volcanic rocks emplaced from ~12 to ~0.1Ma. The major and, partially, trace element content of these rocks roughly resemble magmas emplaced in within-plate tectonic settings. From a Sr–Nd–Pb–Hf–Os isotopic point of view, it is possible to subdivide these rocks into two subgroups. The first, defined RPV (Radiogenic Pb Volcanic) group comprises the oldest and very rare products (~12–4.4Ma) occurring only in the southern sectors of Sardinia. The second group, defined UPV (Unradiogenic Pb Volcanic), comprises rocks emplaced in the remaining central and northern sectors during the ~4.8–0.1Ma time range. The origin of the RPV rocks remains quite enigmatic, since they formed just a few Myr after the end of a subduction-related igneous activity but do not show any evidence of slab-derived metasomatic effects. In contrast, the complex origin of the mafic UPV rocks, characterized by low 206Pb/204Pb (17.4–18.1), low 143Nd/144Nd (0.51232–0.51264), low 176Hf/177Hf (0.28258–0.28280), mildly radiogenic 87Sr/86Sr (~0.7044) and radiogenic 187Os/188Os ratios (0.125–0.160) can be explained with a mantle source modified after interaction with ancient delaminated lower crustal lithologies. The strong isotopic difference between the RPV and UPV magmas and the absence of lower crustal-related features in the SR and RPV remain aspects to be solved. [Copyright &y& Elsevier]

Niu (2021) reviews fundamental topics of basaltic magma generation in the oceans and continents, including passive and active margins as well as intraplate regions. In his approach, Niu (2021) focuses on the role exerted by lithospheric ("LID") thickness in controlling basalt compositions and volumes, proposing only a minor role, if any, for the thermal state of the mantle. A consequence of this is rejection of mantle plumes in controlling the compositions of MORB and OIB, albeit not excluding completely their existence to explain basalt petrogenesis. Although the fundamental role of the lithospheric mantle on continental breakup, deformation and volcanism was recognized over 50 years ago, this region has only rarely been considered a candidate source for basaltic rocks, being thought to be too cold, stiff and sterile to produce significant amounts of partial melt. However, the stability of C-H-bearing mineral phases such as carbonates, phlogopite and pargasitic amphibole at lithospheric mantle depths indicates relatively low solidus temperature, and the possibility to produce partial melts even under relatively cold thermal regimes. We contribute to this debate by proposing that a wide range of variables explain igneous activity on Earth and, likely, the other rocky planets. The "lid effect" is certainly important but there is evidence that other factors and variables also influence the compositions and volumes of melts produced in the upper mantle. Among these, bulk- and trace-element chemical heterogeneities, the distribution and speciation of volatiles, and large-wavelength variations in temperature caused by radiogenic decay, are the most relevant. [ABSTRACT FROM AUTHOR]

Abstract: Late Miocene basanites of Nosy Be and Nosy Sakatia islands (Nosy Be Archipelago, northern Madagascar) carry spinel-facies anhydrous ultramafic xenoliths (lherzolites, harzburgites and wehrlites). Geothermobarometric estimates indicate that these xenoliths derive from shallow mantle depths of 35–40 km, with those from Nosy Be island showing equilibration T (averages in the range of 945–985 °C) lower than the Nosy Sakatia analogues (averages ranging from 1010 to 1110 °C). One Nosy Sakatia mantle xenolith exhibits relatively fertile lherzolite composition, with trace and major element mineral chemistry consistent with a residual character after low degrees (1–2%) of mafic melt extraction. We interpret this composition as that resembling a depleted mantle (DM)-like lithospheric composition before metasomatic overprints. The other lherzolites and harzburgites display petrochemical characters consistent with variable extent of partial melting (up to 18%), associated with pronounced metasomatic overprints caused by migrating melts, as highlighted by enrichments in highly incompatible trace elements (e.g. light rare earth elements, LREE and Sr), together with the abundant occurrence of wehrlitic lithologies. The variability of petrochemical features points to different styles of metasomatism and metasomatic agents. The estimated composition of the parental melts of wehrlites matches that of host basanites. The combination of this evidence with the petrographic features, characterized by coarse-granular to porphyroclastic textures and by the presence of olivine without kink-banding, suggests that wehrlites are veins or pockets of high pressure cumulates within the mantle peridotite. The same melts also metasomatized via porous-flow percolation some lherzolites and harzburgites. Distinctly, a group of lherzolites and harzburgites was metasomatized by a different alkaline melt having markedly lower incompatible trace element contents. Late infiltration of metasomatic fluids is responsible for the spongy texture of some clinopyroxenes of lherzolites, harzburgites and wehrlites. [Copyright &y& Elsevier]

Abstract: The north-western sector of the Gharyan volcanic field (northern Libya) consists of trachytic-phonolitic domes emplaced between ~41 and 38Ma, and small-volume mafic alkaline volcanic centres (basanites, tephrites, alkali basalts, hawaiites and rare benmoreites) of Middle Miocene-Pliocene age (~12–2Ma). Two types of trachytes and phonolites have been recognized on the basis of petrography, mineralogy and geochemistry. Type-1 trachytes and phonolites display a smooth spoon-shaped REE pattern without negative Europium anomalies. Type-2 trachytes and phonolites show a remarkable Eu negative anomaly, higher concentration in HFSE (Nbph name="sbnd" />Zrand Ti than Type-1 rocks. The origin of Type-1 trachytes and phonolites is compatible with removal of clinopyroxene, plagioclase, alkali feldspar, amphibole, magnetite and titanite starting from benmoreitic magmas, found in the same outcrops. Type-2 trachytes and phonolites could be the result of extensive fractional crystallization starting from mafic alkaline magma, without removal of titanite. In primitive mantle-normalized diagrams, the mafic rocks (Mg#=62–68, Cr up to 514ppm, Ni up to 425ppm) show peaks at Nb and Ta and troughs at K. These characteristics, coupled with low 87Sr/86Sr(i) (0.7033-0.7038) and positive εNd (from +4.2 to +5.3) features typical of the mafic anorogenic magmas of the northern African plate and of HIMU-OIB-like magma in general. The origin of the mafic rocks is compatible from a derivation from low degree partial melting (3–9%) shallow mantle sources in the spinel/garnet facies, placed just below the rigid plate in the uppermost low-velocity zone. The origin of the igneous activity is considered linked to passive lithospheric thinning related to the development of continental rifts like those of Sicily Channel (e.g., Pantelleria and Linosa) and Sardinia (e.g., Campidano Graben) in the Central-Western Mediterranean Sea. [Copyright &y& Elsevier]

Abstract: We present a geodynamic reconstruction of the Central–Western Mediterranean and neighboring areas during the last 50Myr, including magmatological and tectonic observations. This area was interested by different styles of evolution and polarity of subduction zones influenced by the fragmented Mesozoic and Early Cenozoic paleogeography between Africa and Eurasia. Both oceanic and continental lithospheric plates were diachronously consumed along plate boundaries. The hinge of subducting slabs converged toward the upper plate in the double-vergent thick-skinned Alps–Betics and Dinarides, characterized by two slowly-subsiding foredeeps. The hinge diverged from the upper plate in the single-vergent thin-skinned Apennines–Maghrebides and Carpathians orogens, characterized by a single fast-subsiding foredeep. The retreating lithosphere deficit was compensated by asthenosphere upwelling and by the opening of several back-arc basins (the Ligurian–Provençal, Valencia Trough, Northern Algerian, Tyrrhenian and Pannonian basins). In our reconstruction, the W-directed Apennines–Maghrebides and Carpathians subductions nucleated along the retro-belt of the Alps and the Dinarides, respectively. The wide chemical composition of the igneous rocks emplaced during this tectonic evolution confirms a strong heterogeneity of the Mediterranean upper mantle and of the subducting plates. In the Apennine–Maghrebide and Carpathian systems the subduction-related igneous activity (mostly medium- to high-K calcalkaline melts) is commonly followed in time by mildly sodic alkaline and tholeiitic melts. The magmatic evolution of the Mediterranean area cannot be easily reconciled with simple magmatological models proposed for the Pacific subductions. This is most probably due to synchronous occurrence of several subduction zones that strongly perturbed the chemical composition of the upper mantle in the Mediterranean region and, above all, to the presence of ancient modifications related to past orogeneses. The classical approach of using the geochemical composition of igneous rocks to infer the coeval tectonic setting characteristics cannot be used in geologically complex systems like the Mediterranean area. [Copyright &y& Elsevier]

Mantle xenoliths hosted in Miocene-Quaternary mafic alkaline volcanic rocks from Sardinia have been investigated with electron microprobe, laser ablation microprobe-inductively coupled plasma-mass spectrometry and thermal ionization mass spectrometry techniques. The xenoliths are anhydrous clinopyroxene-poor lherzolites and harzburgites, plus very rare websterites and olivine-websterites. Glassy pods having thin subhedral to euhedral microlites of olivine, clinopyroxene and spinel have been found in harzburgites and websterites. Clinopyroxene shows trace element variability, with values of (La/Yb) ranging from sub-chondritic (0.01) to supra-chondritic (8.6). The Sr-Nd isotopic ratios of the clinopyroxenes fall mostly in the field of the European lithospheric mantle xenoliths (Sr/Sr from 0.70385 to 0.70568 and Nd/Nd ranging from 0.512557 to 0.512953). The geochemical characteristics of the Sardinian xenoliths testify to the variable degrees of earlier partial melt extraction, followed by metasomatic modification by alkaline melts or fluids. Websterites are considered to represent small lenses or veins of cumulitic (i.e. magmatic) origin within the mantle peridotite. [ABSTRACT FROM AUTHOR]

Abstract: The volcanic activity of Mt. Karacadağ (SE Anatolia) is divided into three major stages: Siverek Stage (∼11–2.7Ma), Karacadağ Stage (∼1.9–1.0Ma) and Ovabağ Stage (0.4–0.01Ma). The magmas are mildly alkaline mafic rocks, mostly basanites, hawaiites and alkali basalts. Detailed geochemical investigation indicates a continuous variation of composition with time, with the oldest products (Siverek Stage) being characterized by average lowest HFSE (Ti, Hf, Zr, Nb, Ta), 143Nd/144Nd, Nb/U, Ta/Yb, Nb/Nb* and the highest ΔQ, La/Nb, Ti/Nb, Zr/Nb, Ba/Nb, Th/Ta, K/La, and the youngest products (Ovabağ Stage) at the opposite end of the trend. The overall incompatible element content of the Karacadağ volcanic rocks resembles closely average HIMU-OIB compositions, with the oldest samples deviating more strongly from typical compositions of “anorogenic” magmas. We interpret these geochemical variations with a process of partial melting of a chemically and mineralogically heterogeneous mantle source rather than with process of variable crustal contamination at shallow depths. During the first stages of mantle melting the volumes with lowest solidus temperature (e.g., the amphibole and phlogopite-rich metasomes, particularly abundant in the Arabia mantle xenolith suite) contributed significantly to the partial melts. “Average” peridotitic matrix is involved in partial melting processes only when these metasomatic volumes start to be exhausted, producing mantle melts with geochemical composition resembling average “anorogenic” mildly alkaline sodic rocks, common in the circum-Mediterranean area. [Copyright &y& Elsevier]

Abstract: The present-day northern Apennines represent an area where two different orogenic cycles took place. The most ancient is the Alpine Orogeny, initiated with a south- to south-eastward subduction of oceanic lithosphere (Early Cretaceous to Late Eocene phase), followed by continental collision. The younger is referred to the Apennines Orogeny, characterized by a west- to north-westward oceanic lithosphere subduction started from Late Eocene and still active in the southernmost sectors of Italy (Calabrian Arc). In this framework, during the Early Oligocene, an ~800m thick conglomeratic succession extremely rich in volcanic material (up to ~90% in volume) was deposited in the Northern Apennines, forming the Aveto-Petrignacola Formation (APF). The volcanic fraction of this succession is made up of basaltic andesites, andesites and dacites, with minor rhyolites, basalts and gabbros found as pebbles ~0.001–0.5m3 in size. Petrographic, mineral chemical, major and trace element analyses, as well as Sr–Nd–Pb isotopic ratios are compatible with calc-alkaline magmatism generated as a consequence of metasomatic modifications related to the subduction of oceanic lithosphere. The large spectrum of lithologies is compatible with processes of fractional crystallization of the main phases observed in thin sections. However, the large range of isotopic ratios (87Sr/86Sr=0.7044–0.71013; 143Nd/144Nd=0.51278–0.51223; 206Pb/204Pb=18.44–18.83; 207Pb/204Pb=15.55–15.67; 208Pb/204Pb=38.05–38.85) suggests the presence of heterogeneous mantle sources, possibly coupled with interaction of melts with crustal rocks at shallow depth. On the basis of field geology constraints, we propose that the subduction-related geochemical and mineralogical characteristics of the APF volcanic rocks reflect ancient modifications of their mantle sources, lacking any evidence for a genetic link with the Apennine subduction system. Subduction-related metasomatism of APF mantle sources likely occurred during the older south-east dipping subduction of the Alpine Tethys under Northern Adria (present day Northern Italy). [Copyright &y& Elsevier]

The composition of the upper mantle bounded by the Canaries, Eastern Anatolia, Libya and Poland is indirectly investigated by means of the chemical composition of igneous rocks with ‘anorogenic’ geochemical characteristics emplaced during the Cenozoic. The relatively homogeneous composition of these products in terms of incompatible trace-element content and Sr–Nd–Pb isotopic composition is unexpected, considering the variable lithospheric structure of this large area and the different tectono-thermal histories of the various districts. In order to reconcile the geochemical characteristics with a statistical sampling model, it would be necessary to propose volumes of the enriched regions much lower than the sampling volumes for each volcano (that is, less than 10 cubic metres), or alternatively, efficient magma blending from larger areas. The data are consistent with a relatively well-stirred and mixed sub-lithospheric upper mantle, in the solid state, which is also hard to understand. This contrasts with the situation under oceans where magma blending from diverse sources and sampling theory can explain the compositional statistics. [ABSTRACT FROM AUTHOR]

Abstract: The central-western Mediterranean area is a key region for understanding the complex interaction between igneous activity and tectonics. In this review, the specific geochemical character of several ‘subduction-related’ Cenozoic igneous provinces are described with a view to identifying the processes responsible for the modifications of their sources. Different petrogenetic models are reviewed in the light of competing geological and geodynamic scenarios proposed in the literature. Plutonic rocks occur almost exclusively in the Eocene–Oligocene Periadriatic Province of the Alps while relatively minor plutonic bodies (mostly Miocene in age) crop out in N Morocco, S Spain and N Algeria. Igneous activity is otherwise confined to lava flows and dykes accompanied by relatively greater volumes of pyroclastic (often ignimbritic) products. Overall, the igneous activity spanned a wide temporal range, from middle Eocene (such as the Periadriatic Province) to the present (as in the Neapolitan of southern Italy). The magmatic products are mostly SiO2-oversaturated, showing calcalkaline to high-K calcalcaline affinity, except in some areas (as in peninsular Italy) where potassic to ultrapotassic compositions prevail. The ultrapotassic magmas (which include leucitites to leucite-phonolites) are dominantly SiO2-undersaturated, although rare, SiO2-saturated (i.e., leucite-free lamproites) appear over much of this region, examples being in the Betics (southeast Spain), the northwest Alps, northeast Corsica (France), Tuscany (northwest Italy), southeast Tyrrhenian Sea (Cornacya Seamount) and possibly in the Tell region (northeast Algeria). Excepted for the Alpine case, subduction-related igneous activity is strictly linked to the formation of the Mediterranean Sea. This Sea, at least in its central and western sectors, is made up of several young (<30Ma) V-shaped back-arc basins plus several dispersed continental fragments, originally in crustal continuity with the European plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle ‘wedge’ regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO2 and H2O in the fluid phase released by the subducting plates are the most important. Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) centrifugal wave of both compressive and extensional tectonics starting from a ‘pivotal’ region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction ‘inversion’ events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subduction-related magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related ‘exotic’ (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the hanging-wall of the Late Cretaceous–Eocene Adria–Europe subduction system in the Alps); i) voluminous production of subduction-related magmas coeval with extensional tectonic régimes (e.g., during Oligo-Miocene Sardinian Trough formation). To summarize, these salient central-western Mediterranean features, characterizing a late-stage of the classic ‘Wilson Cycle’ offer a ‘template’ for interpreting magmatic compositions in analogous settings elsewhere. [Copyright &y& Elsevier]

Petrological and geochemical data for basic (alkali basalts and hawaiites) and silicic peralkaline rocks, plus rare intermediate products (mugearites and benmoreites) from the Pleistocene Boseti volcanic complex (Main Ethiopian Rift, East Africa) are reported in this work. The basalts are slightly alkaline or transitional, have peaks at Ba and Nb in the mantle-normalized diagrams and relatively low 87Sr/86Sr (0.7039–0.7044). The silicic rocks (pantellerites and comendites) are rich in sanidine and anorthoclase, with mafic phases being represented by fayalite-rich olivine, opaque oxides, aenigmatite and slightly Na-rich ferroaugite (ferrohedenbergite). These rocks were generated after prolonged fractional crystallization process (up to 90–95 %) starting from basaltic parent magmas at shallow depths and fO2 conditions near the QFM buffer. The apparent Daly Gap between mafic and evolved Boseti rocks is explained with a model involving the silicic products filling upper crustal magma chambers and erupted preferentially with respect to basic and intermediate products. Evolved liquids could have been the only magmas which filled the uppermost magma reservoirs in the crust, thus giving time to evolve towards Rb-, Zr- and Nb-rich peralkaline rhyolites in broadly closed systems. [ABSTRACT FROM AUTHOR]

Abstract: The central-western Mediterranean is one of the most important areas on Earth for studying subduction-related potassic and ultrapotassic magmatism. In the circum-Tyrrhenian area leucite-free (i.e., lamproite) and leucite-bearing (i.e., kamafugite, leucitite, and plagioleucitite) ultrapotassic rocks have been emplaced and are associated with shoshonites and high-K calc-alkaline volcanic rocks. Four different magmatic provinces are recognised from this area. Eastward and then south-eastward migration of magmatism with time occurred following roll-back of the subducting plate. Leucite-free silica-rich lamproites are restricted to the early stages of magmatism, associated with shoshonites and high-K calc-alkaline volcanic rocks. Present day volcanic activity is restricted to the Neapolitan district where ultrapotassic rocks with variable geochemical and isotopic characteristics occur. Ultrapotassic rocks are strongly enriched in incompatible trace elements with variable fractionation of Ta, Nb, and Ti with respect to Th and large ion lithophile elements. Mafic ultrapotassic rocks are also variably enriched in radiogenic Sr and Pb and unradiogenic Nd. The main geochemical and isotopic signatures result from sediment recycling within the upper mantle via subduction. Selected trace element ratios suggest that high temperatures are required to generate sediment-derived melts. Recycling of carbonated pelites play an important role in the Roman province controlling the genesis of leucite-bearing magmas. Large volumes of metasomatic components are predicted to be accommodated within a vein network in the sub-continental lithospheric mantle. Partial melting of the pure vein mineralogy is likely to generate ultrapotassic magmas of either lamproitic or kamafugitic nature. Over time, increased interaction between the metasomatic vein lithology and the surrounding mantle dilutes the alkaline component producing shoshonites and high-K calc–alkaline rocks. The addition of a further subduction-related component shortly before magma generation is required to explain the isotopic composition of rocks from the Neapolitan district. In the last phases of circum-Tyrrhenian evolution, a within-plate component appears within south-eastern Italy. This component is evident at Vulture volcano, in the Lucanian Magmatic province (SE Italy). [Copyright &y& Elsevier]

The Isola del Toro is a small island (∼1 km2) about 5 nautical miles SW of Sardinia entirely made up of mildly alkaline sodic evolved rocks (benmoreites and trachytes) related to each other by fractionation processes. 40Ar/39Ar dating of an anorthoclase mineral separate from a trachyte gave an age of 11.83 ± 0.10 Ma. This age estimate falls within an interval previously considered a-magmatic in Sardinia. The results of this study shift the beginning of the Middle Miocene–Quaternary anorogenic volcanism of Sardinia back to the Late Serravalian. The transition between orogenic and anorogenic activity in Sardinia is markedly different from that recorded in the rest of the circum-Mediterranean area, where this transition is much more gradual, both in time and in terms of magma composition. On the other hand, the transition between orogenic and anorogenic magmatism in Sardinia is rather sharp and lacks hybrid compositions. The Isola del Toro volcanic rocks represent the first anorogenic products produced during the opening of the western Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Abstract: During the Cenozoic widespread anorogenic magmatism, unrelated to recent supra-subduction zone modification of its mantle source, developed within the Mediterranean and surrounding regions; this is referred to collectively as the CiMACI (Circum-Mediterranean Anorogenic Cenozoic Igneous) province. On the basis of a comprehensive review of published and new major and trace element and Sr–Nd–Pb isotopic data (more than 7800 samples) for the magmatic rocks, a common sub-lithospheric mantle source component is identified for most of the region. This has geochemical affinities to the source of HIMU oceanic island basalts and to the European Asthenospheric Reservoir (EAR) and the Low Velocity Component (LVC) of previous workers; we refer to this as the Common Mantle Reservoir (CMR). Global and local seismic tomography studies of the mantle beneath the CiMACI province have revealed a range of P- and S-wave velocity anomalies, some of which have been related to the presence of mantle plumes. Detailed local tomography experiments in the Massif Central of France and the Eifel region of central Germany suggest that, locally, there are diapiric upwellings rooted within the upper mantle which induce adiabatic decompression melting and magma generation. These velocity anomalies can be interpreted as evidence of mantle temperatures up to 150 °C hotter than the ambient mantle. However, the seismic attenuation could also be attributable to the presence of fluid or partial melt and significant thermal anomalies are not necessary to explain the petrogenesis of the magmas. A model is proposed in which the geochemical and isotopic characteristics of the sub-lithospheric mantle beneath the CiMACI province reflect the introduction of recycled crustal components (derived from both oceanic and continental lithosphere) into the ambient depleted upper mantle. This sub-lithospheric mantle is subsequently partially melted in a variety of geodynamic settings related to lithospheric extension, continental collision and orogenic collapse, and contemporaneous subduction, slab roll-back and slab-window formation. On the basis of this in-depth geochemical and petrological study of the CiMACI province, we consider that there is no need to invoke the involvement of anomalously hot mantle (i.e., the presence of a single or multiple deep mantle plumes) in the petrogenesis of the magmas. If, however, we adopt a more permissive definition of “mantle plume”, allowing it to encompass passive, diapiric upwellings of the upper mantle, then we can relate the CiMACI province magmatism to multiple upper mantle plumes upwelling at various times during the Cenozoic. To avoid confusion we recommend that such upper mantle plumes are referred to as diapiric instabilities. [Copyright &y& Elsevier]

Abstract: The Cenozoic (mostly Neogene) volcanic activity in Syria is part of the extensive magmatism that took place in the Mashrek Region, Middle East, from upper Eocene to Holocene (∼40–0.0005Ma). Samples in western Syria are mostly high TiO2 (TiO2 ∼1.8–3.7wt.%) alkaline mafic rocks (basanites, hawaiites and alkali basalts) plus rare transitional/tholeiitic basalts and basaltic andesites) with within-plate-like trace element signature. On the basis of incompatible trace element content, the volcanic activity in Syria has been divided into two stages: the first lasting from ∼25 to ∼5Ma and the second from ∼5 to recent times. Indeed, the Syrian lavas show incompatible trace element content increasing with decreasing age from ∼25 to ∼5Ma, followed by an abrupt decrease to low values roughly at the Miocene–Pliocene boundary. This temporal shift in composition is related to major tectonic re-organization occurred during upper Miocene. The proposed petrogenetic model invokes three steps: (a) passive upwelling of the shallow asthenosphere during the development of the Dead Sea transform fault system. Different degrees of partial melting were followed by variable extents of fractional crystallization and limited upper crustal contamination; (b) the Miocene–Pliocene boundary tectonic change enhanced passive decompression of the same sources and a consequent increase in degree of partial melting resulting in low incompatible trace element content of the relatively high-volume liquids; (c) after this phase, the incompatible trace element content in the basaltic magmas increased as consequence of fractional crystallization processes. Major and trace element content similarities with the rest of the circum-Mediterranean igneous rocks are consistent with a common relatively shallow origin for the Cenozoic anorogenic magmatism of the entire circum-Mediterranean area (the so-called Common Magmatic Reservoir). Because much of the igneous activity in the studied area is concentrated near the Dead Sea fault, the origin of Cenozoic magmatism in Syria (and in the rest of the circum-Mediterranean area) reflects a strong lithospheric control on the loci of partial melting. Mantle plumes from lower mantle and/or north-westward channelling of the Afar mantle plume is not needed to explain volcanic activity in Syria and the Mashrek area. [Copyright &y& Elsevier]

Abstract: The Earth''s lithosphere can focus basaltic magmatism along pre-existing weakness zones or discontinuities. However, apart from the influence on the geochemistry of magmas emplaced in subduction tectonic settings (mantle wedge metasomatism related to dehydration of the subducting plates) the role of lithosphere as a magma source for intra-plate (both oceanic and continental), continental margin, and mid-ocean ridge magmatism is not yet fully understood. In many cases intra-plate magmatism has been explained with the existence of deep thermal anomalies (mantle plumes) whose origin has been placed near the upper–lower mantle transition zone (660 km discontinuity) or even deeper, near the mantle–core boundary (∼2900 km). Also in many continental flood basalt provinces (mostly initiated at craton margins) an active role for mantle plumes has been invoked to explain the high melt productivity. In these cases, no active role for melt production has been attributed to the lithospheric mantle. Potential contaminations of asthenospheric or even deeper mantle melts are often considered the only influence of the lithosphere (both crust and mantle) in basalt petrogenesis. In other cases, an active role of the lithospheric mantle has been proposed: the thermal anomalies related to the presence of mantle plumes would trigger partial melting in the lithospheric mantle. At present there is no unequivocal geochemical tracer that reflects the relative role of lithosphere and upper/lower mantle as magma sources. In this paper another role of the lithosphere is proposed. The new model presented here is based on the role of lower crustal and lithospheric mantle recycling by delamination and detachment. This process can explain at least some geochemical peculiarities of basaltic rocks found in large and small volume igneous provinces, as well as in mid-ocean ridge basalts. Metamorphic reactions occurring in the lower continental crust as a consequence of continent–continent can lead to a density increase (up to 3.8 g/cm3) with the appearance of garnet in the metamorphic assemblage (basalt→amphibolite→garnet clinopyroxenite/eclogite) leading to gravitative instability of the overthickened lithospheric keel (lower crust+lithospheric mantle). This may detach from the uppermost lithosphere and sink into the upper mantle. Accordingly, metasomatic reactions between SiO2-rich lower crust partial melts and the uprising asthenospheric mantle (replacing the volume formerly occupied by the sunken lithospheric mantle and the lower crust) lead to formation of orthopyroxene-rich layers with strong crustal signatures. Such metasomatized mantle volumes may remain untapped also for several Ma before being reactivated by geological processes. Partial melts of such sources would bear strong lower crustal signatures giving rise to Enriched Mantle type 1 (EMI)-like basaltic magmatism. Basaltic magmatism with such a geochemical signature is relatively scarce but in some cases (e.g., Indian Ocean) it can be a geographically widespread and long-lasting phenomenon. [Copyright &y& Elsevier]

Abstract: The early Cretaceous (∼130 Ma) igneous complex of Valle Chico (SE Uruguay) is made up of felsic plutonic and subordinate volcanic rocks and dykes cropping out over an area of about 250 km2. This complex is strictly linked with the formation of the Paraná–Etendeka Igneous Province and the first stages of the South Atlantic Ocean rifting. The plutonic rocks range from quartz-monzonite to syenite, quartz-syenite and granite. The volcanic rocks and the dykes range from quartz-latite to trachyte and rhyolite; no substantial differences in term of chemical composition have been found between plutonic and volcanic rocks. Only a sample of basaltic composition (with tholeiitic affinity) has been sampled associated with the felsic rocks. The Agpaitic Index of the Valle Chico felsic rocks range from 0.72 to 1.34, with the peralkaline terms confined in the most evolved samples (SiO2>65 wt.%). Initial 87Sr/86Sr(130) of the felsic rocks range from 0.7046 to 0.7201, but the range of 87Sr/86Sr of low-Rb/Sr samples cluster at 0.7083; 143Nd/144Nd(130) ratios range from 0.5121 (syenite) to 0.5117 (granite). The tholeiitic basalt show more depleted isotopic compositions (87Sr/86Sr(130)=0.7061; 143Nd/144Nd(130)=0.5122), and plots in the field of other early Cretaceous low-Ti basaltic rocks of SE Uruguay. The radiogenic Sr and unradiogenic Nd of the Valle Chico felsic rocks require involvement of lower crustal material in their genesis either as melt contaminant or as protolith (crustal anatexis). In particular, most of the Valle Chico (VC) felsic rocks define a near-vertical array in Sr–Nd isotopic spaces, pointing toward classical EMI-type composition; this feature is considered to reflect a lower crust involvement as observed for other mafic and felsic rocks of the Paraná–Etendeka Igneous Province. Decompression melting of the lower crust related to Gondwana continental rifting before the opening of the South Atlantic Ocean or the presence of thermal anomalies related to the Tristan plume may have induced the lower crust to partially melt. Alternative hypothesis considers contamination of upper mantle by a mafic/ultramafic keel composed of lower crust and uppermost mantle after delamination and detachment processes. This interaction may have occurred after the continent–continent collision during the last stages of the Panafrican Orogeny. This “lower crust” model does not exclude active involvement of upper crust as contaminant, necessary to explain the strongly radiogenic 87Sr/86Sr(130) isotopic composition of some VC SiO2-rich rocks. Mineralogical (sporadic presence of pigeonite, Ca–Na and Na clinopyroxene, calcic- and calco-sodic amphibole) and geochemical evidences (major and trace element as well as Sr–Nd isotopic similarities with the felsic early Cretaceous volcanic rocks of the Arequita Formation in SE Uruguay) allow us to propose for the VC rocks a transitional rock series (the most abundant rock types are of syenitic/trachytic composition) preferentially evolving towards SiO2-oversaturated compositions (granite/rhyolite) also with a strong upper crustal contribution as melt contaminant. This conclusion is in contrast with previous studies according which the VC complex had clear alkaline affinity. Many similarities between VC and the coeval Paresis granitoids (Etendeka, Namibia) are evidenced in this paper. The genetic similarities between VC and the rhyolites (s.l.) of SE Uruguay may find counterparts with the genetic link existing between the early Cretaceous tholeiitic-alkaline Messum complex and the quartz latites (s.l.) of the Awahab Formation (Etendeka region, Namibia). [Copyright &y& Elsevier]

During the Pliocene, simultaneously with the opening of the Tyrrhenian Sea, mafic magmas were erupted in NE Sardinia (Orosei-Dorgali area). These range from mildly alkaline with sodic affinity (about 80% of exposure) to tholeiitic (about 20%). The tholeiitic rocks (basaltic andesite) are slightly more evolved than the alkaline ones and show geochemical features (e.g., Mg#<63; Ni<150 ppm and Cr<270 ppm) different from typical primitive mantle liquids, suggesting low pressure fractional crystallization processes. Alkaline lavas (mainly hawaiite plus rare alkali basalt and mugearite) are commonly characterized by the presence of mantle xenoliths and have higher Mg# (up to 71), Ni (up to 340 ppm) and Cr (up to 420 ppm) than the tholeiitic rocks. Both alkaline and tholeiitic lavas show sub-parallel patterns in primitive mantle-normalized diagrams, with peaks at Ba, Pb and Sr and relatively low abundances of Nb and Ta, resulting in high Ba/Nb ratios (generally >20). Similar incompatible element ratios for both alkaline and tholeiitic rocks suggest different degrees of melting of a single mantle source. Mathematical modeling indicates ∼4–6% and ∼10–15% partial melting for alkaline and tholeiitic lavas, respectively. Trace element abundances of the Orosei-Dorgali volcanic rocks are typical of Plio-Pleistocene volcanic rocks of Sardinia but differ strongly from other Cenozoic anorogenic volcanic rocks of Europe. Similarly, Sr (87Sr/86Sr=0.70442–0.70455), Nd (143Nd/144Nd=0.512465–0.512558) and Pb (206Pb/204Pb=17.74–17.86; 207Pb/204Pb=15.53–15.60; 208Pb/204Pb=37.89–38.02) isotopic ratios are very unusual when compared with other Cenozoic European volcanic rocks. Trace element abundances and isotopic composition of the Orosei-Dorgali volcanic rocks suggest a lithospheric mantle origin. [Copyright &y& Elsevier]

The Late Cretaceous (~78 Ma) Poços de Caldas massif is the largest alkaline complex in Brazil and the second in the world by extension (>800 km2). 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 (~80%) and nepheline syenites (~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 [87Sr/86Sr i = 0.70440–0.70498; ε 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 Sr Nd isotopes largely overlapping with that of the basic-ultrabasic lavas (87Sr/86Sr i = 0.70503–0.70540 and ε Ndi = −3.9 to −2.5 for nepheline syenites; 87Sr/86Sr i = 0.70511–0.70527 and ε 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. • Different pulses of magmas generated nepheline syenites and phonolites. • The rare basic rocks may represent the parental liquid of the evolved compositions. • Titanite, eudialyte, and F-disilicates dominate the REE concentration budget. • Different REE patterns suggest the different stages of crystallization. [ABSTRACT FROM AUTHOR]

The Pleistocene (~460–265 ka) San Venanzo volcanic complex belongs to the IAP (Intra-Apennine Province) in central Italy, which comprises at least four small Pleistocene monogenetic volcanoes plus several unrooted pyroclastic deposits with peculiar mineralogical and whole-rock chemical compositions. San Venanzo products are strongly SiO 2 -undersaturated, CaO- and MgO-rich and show ultrapotassic serial character. The relatively common occurrence of calcite in the pyroclastic rocks and the overall high CaO content are interpreted in literature as primary mineral. The main rock facies at San Venanzo are calcite-rich scoria and lapilli tuffs, with minor massive lava flows, and a rare pegmatoid variant (melilitolitic pockets). All the San Venanzo rocks are feldspar-free, with a typical paragenesis of forsteritic olivine, non-stoichiometric Ca-rich diopside, melilite, leucite, kalsilite, opaque minerals, nepheline, phlogopite, calcite, apatite, cuspidine, wollastonite, kirschsteinite-monticellite s.s. ± glass and other minor and very rare minerals typical of agpaitic melts. Based on petrographic analyses, the studied rocks can be classified as olivine melilitites, olivine leucite melilitites, venanzites (a local variant of kamafugites), calcite leucite melilitolites and Ca-rich olivine leucite melilitite tuffs. Mass balance calculations indicate a direct genetic link between the lava bodies and the pegmatoid melilitolitic pocket through a fractional crystallization process characterized by the removal of ~74% of a melilite-bearing uganditic cumulate made up of melilite, leucite, olivine, kalsilite and chromite. Primitive mantle-normalized patterns of the lavas and tuffs are rather spiked and share negative anomalies for Ba, Nb, Ta, P and Ti resembling typical magmas generated by supra-subduction mantle wedge. These compositions are very different from the only two other kamafugite localities outside Italy (Toro Ankole and Virunga in the East Africa Rift and Alto Paranaiba Igneous Province in SE Brazil). The melilitolite sample is more incompatible element-enriched than the other San Venanzo volcanic rocks, coherently with its evolved liquid composition proposed here. Major and trace element contents indicate a general depletion proportional to the amount of CaO content. The negative trends in Harker-type diagrams with CaO as abscissa are compatible with a process of variable interaction between a silicate magma with sedimentary marly carbonates/limestones. The presence of Mg-rich (Fo 97 – 92) and rim-ward CaO-enriched (up to 1.72 wt%) euhedral olivine, as well as the presence of thin kirschsteinite rim around olivine crystals agree with a process of crustal carbonate assimilation by an originally strongly SiO 2 -undersaturated silicate magma. On the other hand, the lack of feldspars even in the rocks with the highest SiO 2 , the high CaO content, and the extreme SiO 2 -undersaturation of San Venanzo rocks exclude their derivation from a simple peridotitic source. In order to generate these peculiar compositions, the presence of a SiO 2 -K 2 O-CaO-rich H 2 O-bearing component, identified in a carbonated phlogopite peridotite is required. The results of different isotopic systematics (Sr-Nd-Pb-He-Ne-Ar) presented here are compatible with a process of crustal contamination both at mantle source levels (to explain the general N-S isotopic trends recorded in Quaternary volcanic rocks of Italian peninsula and Sicily) and with interaction of ultrabasic melts with limestones at shallow crustal depths. Unlabelled Image [ABSTRACT FROM AUTHOR]

The small upper Pleistocene diatreme of Polino (central Italy) is known in literature as one of the few monticellite alvikites (volcanic Ca-carbonatite) worldwide. This outcrop belongs to the Umbria-Latium Ultra-alkaline District (ULUD), an area characterized by scattered and small-volume strongly SiO2-undersaturated ultrabasic igneous rocks located in the axial sector of the Apennine Mts. in central Italy. Petrographic and mineralogical evidences indicate that Polino olivine and phlogopite are liquidus phases rather than mantle xenocrysts as instead reported in literature. The presence of monticellite as rim of olivine phenocrysts and as groundmass phase indicates its late appearance in magma chambers at shallow depths, as demonstrated by experimental studies too. The absence of plagioclase and clinopyroxene along with the extremely MgO-rich composition of olivine (Fo92–94) and phlogopite (average Mg# ~93) suggest for Polino magmas an origin from a carbonated H2O-bearing mantle source at depths at least of 90–100 km, in the magnesite stability field. In contrast with what reported in literature, the ultimate strongly ultrabasic Ca-rich whole-rock composition (~15–25 wt% SiO2, ~31–40 wt% CaO) and the abundant modal groundmass calcite are not pristine features of Polino magma. We propose that the observed mineral assemblage and whole-rock compositions result mostly from the assimilation of limestones by an ultrabasic melt at a depth of ~5 km. A reaction involving liquidus olivine + limestone producing monticellite + CO2 vapour + calcite is at the base of the origin of the Polino pseudocarbonatitic igneous rocks. [ABSTRACT FROM AUTHOR]

Miocene (ca. 18 Ma) subduction-related basalts and basaltic andesites from Monte Arcuentu, southern Sardinia, Italy, show a remarkable correlation between 87Sr/86Sr (from ~0.705 to ~0.711) over a small range of SiO2 (~51- 58 wt%) that contrasts with most other orogenic volcanic suites worldwide. New high-precision Pb and Hf isotope data help to constrain the petrogenesis of these rocks. The most primitive Monte Arcuentu rocks (MgO >8.5 wt%) were sourced from a mantle wedge metasomatized by melts derived from terrigenous sediment, likely derived from Archean terranes of northern Africa. This gave rise to magmas with high 87Sr/86Sr (0.705-0.709) and 207Pb/204Pb (15.65-15.67) with moderate εHf (-1 to +8) and εNd (-6 to +1), but it does not account for the full range of compositions observed. More evolved rocks (MgO <8.5 wt%) have higher 87Sr/86Sr (up to 0.711) and 207Pb/204Pb (up to 15.68), with εHf and εNd as low as -8 and -9, respectively. Mixing calculations suggest that evolved rocks with low Rb/Ba and low 206Pb/204Pb interacted with lower crust similar compositionally to that exposed today in Calabria, Italy, which was formerly in crustal continuity with Sardinia. High Rb/Ba and high 206Pb/204Pb magmas interacted with lithospheric mantle similar to that sampled by Italian lamproites. Partial melting of lower crustal and upper mantle lithologies was facilitated by the rapid extension, and subsequent passive mantle upwelling, that occurred as Sardinia drifted away from the European plate during the Oligo-Miocene (ca. 32-15 Ma). Fractional crystallization under these PT conditions involved olivine + clinopyroxene with little or no plagioclase, such that differentiation proceeded without significant increase in SiO2. The Monte Arcuentu rocks provide insights into assimilation process in the lower crust and lithospheric mantle that may be obscured by upper crustal assimilation--fractional crystallization (AFC) processes in other orogenic suites. [ABSTRACT FROM AUTHOR]

We report the results of a study on early Miocene to Pleistocene volcanic rocks cropping out west of the Karlıova Triple Junction in Eastern Anatolia (Elazığ, Tunceli, and Bingöl provinces). Here the Eurasia-Arabia convergence resulted in collision, marked by the Bitlis-Zagros suture (~13 Ma), followed by activation of the dextral transform North Anatolian Fault (NAF). At ~6 Ma the formation of the sinistral transform East Anatolian Fault (EAF) marked the separation of the Anatolian block, which became a kinematically independent plate. On the basis of petrographic, geochemical and Sr-Nd-Pb isotopic characteristics, as well as new 40Ar-39Ar age determinations, we distinguish three phases of activity: (1) early-middle Miocene (16·3-15·5 Ma) production of calc-alkaline basaltic trachyandesite to dacites in the Pertek and Mazgirt districts; (2) emplacement of late Miocene (11·4-11·0 Ma) transitional basalts in the Tunceli area; (3) emplacement of Plio-Pleistocene Na-alkali basalts in Karakoçan (4·1 Ma) and Elazığ (1·7 Ma). The oldest samples are characterized by large ion lithophile element (LILE) enrichment (e.g. Ba/Nb = 32-76) with high 87Sr/86Sr (0·7052-0·7065) and low 143Nd/144Nd isotopic ratios (0·51246-0·51262). The late Miocene basalts display variable geochemical characteristics, including large variations in 87Sr/86Sr (0·7039-0·7068) and LILE/HFSE (high field strength element) ratios (e.g. Ba/Nb = 13-36). The Plio-Pleistocene alkali basalts have higher LILE and HFSE contents and lower LILE/HFSE ratios (Ba/Nb = 8-21) compared with the two previous groups, low 87Sr/86Sr (0·7033-0·7038) and high 143Nd/144Nd (0·51270-0·51290), with compositions similar to those of oceanic intraplate magmas. Pb isotopes vary slightly: 206Pb/204Pb ranges from 18·66 to 19·11, 207Pb/204Pb from 15·64 to 15·72 and 208Pb/204Pb from 38·67 to 39·24, with the calc-alkaline early-middle Miocene rocks characterized by higher 207Pb/204Pb and 208Pb/204Pb at a given 206Pb/204Pb. The evolution of volcanic activity is strictly linked to the geodynamic scenario. The early-middle Miocene magmas, emplaced in a convergent setting, indicate derivation from mantle sources modified by subduction components, whereas the late Miocene Tunceli transitional basalts mark the change from compressional to strike-slip tectonics. During the development of the NAF and EAF, passive upwelling of the sub-slab mantle, favoured by the formation of small pull-apart basins, led to the onset of Na-alkali basaltic activity. [ABSTRACT FROM AUTHOR]

The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- and trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondritenormalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/ trachytic/ phonolitic complexes of the Serra do Mar and elsewhere. [ABSTRACT FROM AUTHOR]

During the dismembering of the Pangea supercontinent, middle-late Triassic sub-volcanic alkaline rocks were emplaced in central Sicily. These rocks have an alkali basaltic composition and show OIB-like incompatible element patterns in primitive mantle-normalized diagrams (e.g., enrichments in HFSE and LREE coupled with high HFSE/LILE ratios), as well as slightly positive $$ \varepsilon_{{{\text{Nd}} }} $$ values. Only subtle effects of crustal contamination at shallow depths emerge from geochemical data. These characteristics are very different compared with the Permian calcalkaline magmas from elsewhere in SW Europe still carrying the geochemical signature of modifications related to the Variscan orogeny. The mineralogical, geochemical and isotopic compositions of the investigated samples from central Sicily are also different from the coeval shoshonitic volcano-plutonic formations of Southern Alps (Dolomites). The incompatible element composition and Nd isotopic ratios are consistent with low-degree partial melting of a moderately depleted asthenospheric mantle source, with a negligible involvement of the thinned continental crust. The studied alkaline basalts represent the only known evidence of a segment of the Triassic rift system associated with early Pangea breakup in central Sicily. The close similarity of the central Sicily Triassic alkali basalts with coeval basalts emplaced along former orogenic sutures across the peri-Mediterranean area suggests a common origin related, at least partly, to asthenospheric passive upwelling following the tectonic collapse of the Variscan Belt. These rocks provide new constraints on the spatial-temporal distribution, magma source evolution and geodynamic meaning of the widespread Permo-Triassic basic magmatism developed after the end of the Variscan Orogeny in southwestern Europe. [ABSTRACT FROM AUTHOR]

The Montefiascone Volcanic Complex belongs to the Vulsini Mts. volcanic district, one of the several leucite-bearing ultrapotassic Pleistocene volcanoes of the Roman Province (Central Italy). It is characterized by abundant pyroclastic successions and minor lava flows emplaced during a caldera formation phase occurred ∼0.3–0.2 Ma. The volcanic products span from leucite-basanites and leucite-tephrites to rarer leucitites and melilitites, occasionally associated with very rare kalsilite melilitolite ejecta. Here we report for the first time the presence of primary kalsilite in two lava flows in Forcinella and Feltricci localities, identifying a kamafugitic component among the Montefiascone volcanics. Detailed petrographic, SEM and EPMA studies on ten samples from the two localities revealed, in addition to kalsilite, variable amounts of clinopyroxene, melilite, leucite and nepheline plus rarer olivine coupled with carbonate-bearing segregation pockets in the groundmass. Geochemical and isotopic data confirm the exotic nature of the analysed rocks, showing ultrabasic/basic (SiO 2 = 42.15–45.94 wt%) and ultrapotassic (K 2 O = 6.17–8.48 wt%; K 2 O/Na 2 O = 5.3–8.7) compositions, as well as strongly radiogenic 87Sr/86Sr (0.71038–0.711068), poorly radiogenic 143Nd/144Nd (0.512057.512091) and uniform middle radiogenic 206Pb/204Pb (18.76–18.78). Boron isotopes (δ11B ranges from 7.36 to 8.82‰) almost overlaps the typical MORB-OIB range values. These geochemical features recall those of the nearby kamafugite rocks from the Intra-Apennine Province. Major oxide and trace element modelling support fractionation links among the Italian kamafugite types. The overall geochemical and isotopic signatures speak for a common strongly subduction-metasomatized and orthopyroxene-free lithospheric mantle source. As already proposed for some nearby kamafugite centres in central Italy, limestone assimilation during magma ascent is a viable option to explain the mineralogical and whole-rock composition of Montefiascone lavas (i.e., the presence of carbonate plagues in the lava groundmass). This is particularly relevant considering the thick sedimentary sequence pierced by the limited volume of the upwelling magma. On the other hand, many other key features (such as the general lack of crustal xenoliths, the overall incompatible element fractionation and the radiogenic Sr isotopic ratios) clearly require also derivation from subduction-modified mantle sources. • New kamafugite occurrence in Pleistocene leucite-rich ultrapotassic volcanics, Italy. • Whole-rock data point to a mantle source rich in phlogopite, clinopyroxene, carbonate. • Mass balance models support fractional crystallization links among kamafugite melts. [ABSTRACT FROM AUTHOR]

The Cenozoic Arabia–Iran continental collision was associated with emplacement of a large variety of magmatic rock types. This aspect is particularly evident in the Bijar-Qorveh area of NW Iran, where Miocene andesitic to rhyolitic rocks and Quaternary basic alkaline rocks crop out. The Miocene intermediate to acid products show radiogenic Sr and Pb isotopic compositions (87Sr/86Sri 0.70531–0.71109, 206Pb/204Pb 18.71–19.01, 207Pb/204Pb 15.66–15.73, 208Pb/204Pb 38.76–39.14), coupled with unradiogenic Nd isotopic ratios (143Nd/144Ndi 0.51223–0.51265). These characteristics, together with primitive mantle-normalised multielemental patterns resembling 'subduction-related' geochemical fingerprints, are considered ultimately derived from the Iranian plate mantle wedge, metasomatised during previous NE-directed Neothetyan Ocean subduction. The alkali-rich andesitic and dacitic rocks evidence both closed- and open-system differentiation, as typically observed for collisional settings in general. Both rock types display a high Sr/Y (37–100) and La/Yb (29–74) 'adakitic' signature that it is interpreted here with plagioclase (± amphibole) accumulation or melting of local mafic crustal rocks. Open-system processes involve recycling of crustal cumulates for pyroxene-rich andesite and biotite-rich dacite varieties and low-degree partial melting of the local crust for rhyolites. A radical change occurred during the Quaternary, when SiO2-understaturated to SiO2-saturated poorly evolved rocks (basanites, tephrites, alkaline and subalkaline basalts) were emplaced. The complete change of mantle sources suggests a phase of local extensional tectonics related with WNW-ESE right-transcurrent faults. The major oxide, as well as incompatible trace element and Sr-Nd-Pb isotopic fingerprint of these younger rocks is more akin to that of intraplate magmas, but still bearing some evidences for a variable contribution from a 'subduction-modified' mantle source. The NW-trend of increasing involvement of this subduction component is indicative of the strong tectonic control on magmatism. Additional lithotypes indicate the presence of open-system differentiation and remelting processes in the youngest phase of magmatic activity. [ABSTRACT FROM AUTHOR]

The kimberlites, kamafugites and phlogopite-picrites of Alto Paranaíba Igneous Province (APIP), southern Brazil, span a range between ~91 and 78Ma with new in-situ, more tightly constrained U–Pb ages. The kimberlites show porphyritic texture with olivine xeno- and phenocrysts plus phlogopite, Fe-Ti-Cr oxides and perovskite microcrysts set in a carbonate-rich matrix. The kamafugites are feldspar-free rocks represented by ugandites and mafurites. Ugandites and mafurites are porphyritic and contain olivine and clinopyroxene phenocrysts in a fine-grained groundmass composed by clinopyroxene, perovskite, apatite, magnetite, phlogopite, leucite and/or analcime in ugandites, and by olivine, clinopyroxene, amphibole, phlogopite, perovskite, magnetite, kalsilite and Ba-zeolites in mafurites. Phlogopite-picrites have a pseudo-fluidal porphyritic texture with olivine phenocrysts and abundant phlogopite microcrysts in a groundmass composed by olivine, spinel, apatite, perovskite, calcite and rare garnet. New in‐situ Sr and Nd isotopic data on perovskites (87Sr/86Sri =0.70467–0.70565 and 143Nd/144Ndi =0.51222–0.51233) fall within the known ranges of APIP rocks (87Sr/86Sri =0.70431–0.70686; 143Nd/144Ndi =0.51205–0.51280). The APIP magmas derived from a source assemblage made up of an old metasomatized mica-carbonate garnet lherzolite, that did not suffer interaction with convective mantle, nor with any hypothetical melts derived from a Trindade mantle plume. Geochemical modelling show that low degree melting (f =0.5–2%) of such a source can produce compositions resembling the APIP rocks. The geochemical and isotopic composition of the magmas, the calculated degrees of partial melting, the composition of the calculated source and the absence of a hot spot track from Goias to Alto Paranaíba igneous provinces can be explained with the presence of chemically and mineralogically heterogeneous mantle sources that melted at different pressures. [ABSTRACT FROM AUTHOR]

The Eslamieh Peninsula in NW Iran exposes Miocene potassic to ultrapotassic volcanic rocks that are often associated with a variety of ultramafic xenoliths. Based on geochemical features, the rocks investigated in this study can be subdivided into two main groups: 1) MgO-rich (8.0–13.9 wt%) basic (SiO 2 = 46.1–50.9 wt%) rocks, which comprise mafic lamprophyres and pyroxenite xenoliths, and 2) MgO-poor (1.5–6.4 wt%) basic to intermediate (SiO 2 = 48.2–61.2 wt%) rocks, mainly consisting of trachytes, felsic lamprophyres, and analcime-bearing tephriphonolites and phonotephrites. Rocks in both groups have variable but generally low Ni (10–115 ppm; mostly <60 ppm) and Cr (6–628 ppm; mostly <200 ppm), and display enrichment in LREE over HREE (e.g., La/Yb = 17–55), with a large overlap between the MgO-rich and MgO-poor types. These features are coupled with enriched LILE/HFSE ratios (e.g., Ba/Nb mostly 16–116), negative Nb-Ta-Ti anomalies and positive Pb peaks in primitive mantle-normalised diagrams (e.g., Nb/Nb* mostly <0.7). Both high-and poor-MgO samples have strongly radiogenic (87Sr/86Sr) i ratios (0.7078–0.7086), (143Nd/144Nd) i below the Chondritic Uniform Reservoir (CHUR) = 0.51235–0.51244, and ɛHf i ranging from −3.1 to −11.1‰, suggesting involvement of a lower continental crust component in their genesis. The major oxide and trace element contents the high-MgO and high-CaO rocks indicate derivation from a subcontinental lithospheric mantle source, variably metasomatised by fluids and melts released by a subducted slab in a mantle wedge. Primitive melts evolved via mafic mineral fractionation and possible assimilation of lower crust, generating the SiO 2 higher and CaO-MgO-poorer group. We suggest that small degree partial melting of the enriched mantle sources could have been triggered by Neo-Tethys slab roll-back during the Arabian-Iranian collision. • Mantle peridotite played a role in the genesis of potassic to ultrapotassic magmas • High-MgO and low-MgO magmas are derived from peridotite and peridotite-melt reactions • Pyroxenite and glimmerite xenoliths were genetically related with mantle sources [ABSTRACT FROM AUTHOR]

The Sahand volcano in NW Iran is characterised by voluminous Late Miocene to Quaternary magmatic activity. Petrographic, mineral chemical, whole-rock geochemical and Sr-Nd-Pb isotope data allowed to identify two rock groups, continuously emplaced from the ancient Paleo-Sahand to the later Neo-Sahand stages. These are represented by abundant evolved rocks, with dacitic to rhyolitic compositions and less common intermediate (andesitic) rocks. Both rock types have the typical LILE-enriched and HFSE-depleted fingerprints of magmas originated from subduction-modified mantle sources, as well as radiogenic Sr- and Pb- (18.8–18.9 206Pb/204Pb, 15.6–15.7 207Pb/204Pb and 38.8–39.2 208Pb/204Pb) isotope compositions. Nevertheless, the evolved rocks have lower 87Sr/86Sr (0.70437–0.70491 vs 0.70494–0.70585) and display an evident high Sr/Y vs Y and high La/Yb vs Yb "adakitic" signature, suggesting derivation from the partial melting of lower continental crust rocks, rather than from the differentiation of the non-adakitic intermediate rocks. The latter would be the derivative melts of magmas generated by the partial melting of lithospheric mantle sources modified by metasomatic fluids released by the subducted Neotethyan oceanic lithosphere. During their ascent and differentiation, these magmas likely provided the heat necessary to induce partial melting of the lower continental crust, eventually producing adakitic evolved magmas. Quantitative models and geothermobarometric calculations suggest that differentiation processes for both rock groups occurred mainly by polybaric fractional crystallisation (in the 29–4 km depth range), possibly coupled with minor assimilation of local crustal rocks. The peculiar style of the Sahand magmatic activity (with both adakitic and non-adakitic products) and its temporal evolution (with an overall increase of the degree of evolution and a decrease of the non-adakitic melts) are somewhat different with respect to those of the coeval neighbouring districts of Saray, Sabalan and Bijar-Qorveh. These can be reconciled within a general model for NW Iran where magmatism is triggered by upwelling of the sub-lithospheric mantle as a consequence of slab break-off (or the opening of a slab tear). The progressive propagation (and subsequent exhaustion) of the thermal pulse and the increasing thickness of the continental crust played a main role in determining both the progressively later inception of active magmatism (from ∼11 to 4.5 Ma) and the change in magma types (from largely variable to adakitic only) at increasing distance from the Iran-Arabia suture. • Adakitic and non-adakitic magmas were continuously emplaced at the Sahand volcano. • Non-adakitic magmas were sourced in the metasomatised lithospheric mantle. • Adakitic magmas originated from the partial melting of the lower crust. • The two different parental melts evolved independently from each other. • Peculiar spatial and temporal trends are recognised in the magmatism of NW Iran. [ABSTRACT FROM AUTHOR]

In the Dolomites (Eastern Southern Alps, Italy), a diffuse Middle Triassic igneous activity is now present mostly as lava flow and pyroclastic successions, with rare shallow-depth intrusive bodies cropping out at Predazzo, Monzoni and Cima Pape areas. In this work, the emplacement modes of the Predazzo and Monzoni bodies were investigated by means of petrographic and anisotropy of magnetic susceptibility (AMS) data coupled with a field geological study. The presence of intrusive rocks in between these two bodies and the continuity of the metamorphic aureola from west of the Predazzo to east of the Monzoni body suggest that they are parts of a ∼20 km wide SW-NE oriented continuous pluton, sub-parallel to Ladinian strike-slip faults. AMS and petrographic data from the Predazzo body are consistent with a multistage ring-dyke emplacement mode, with areas of upward flow of the magma located in the NW and ESE part of the intrusion, whereas in the southern sector of the pluton our data suggest prevalently horizontal flows. In general, the Predazzo sheets indicate either upward magma flow or along-strike lateral magma transport, and the round shape suggests no influence of Ladinian tectonic structures. On the contrary, the ENE-WSW elongated shape of the Monzoni body was controlled by the occurrence of strike-slip faults associated with Ladinian-tectonics, the feeder being likely located at the NE edge of the body. However, the absence of deformation at the field- and micro-scale is consistent with a post Ladinian-tectonics timing of emplacement, as for the Predazzo pluton. [ABSTRACT FROM AUTHOR]

Post-collisional magmatism in the Late Miocene Rodna-Bârgău subvolcanic district (East Carpathians) gave rise to a wide variety of rock compositions, allowing recognition of four groups of calcalkaline rocks with distinctive petrography, mineral chemistry, whole-rock geochemistry and Sr-Nd-Hf isotope features. New U-Pb zircon datings, together with literature data, indicate that the emplacement of the four rock groups was basically contemporaneous in the 11.5–8 Ma time span. The low potassium group (LKG) includes the most abundant lithotypes of the area, ranging from basaltic andesite to dacite, characterized by K-poor tschermakitic amphibole, weak enrichment in LILE and LREE, relatively low 87 Sr/ 86 Sr, coupled with relatively high 143 Nd/ 144 Nd and 176 Hf/ 177 Hf. The high potassium group (HKG) includes amphibole-bearing microgabbro, amphibole andesite and amphibole- and biotite dacite, with K-richer magnesio-hastingsite to hastingsite amphibole, more marked enrichments in incompatible elements, higher 87 Sr/ 86 Sr and lower 143 Nd/ 144 Nd and 176 Hf/ 177 Hf. These two main rock groups seem to have originated from similar juxtaposed mantle sources, with the HKG possibly related to slightly more enriched domains (with higher H 2 O reflected by the higher modal amphibole) with respect to LKG (with higher plagioclase/amphibole ratios). The evolution of the two rock series involved also open-system processes, taking place mainly in the upper crust for the HKG, in the lower crust for LKG magmas. In addition, limited occurrences of generally younger strongly evolved peraluminous rhyolites and microgranites (Acid group) and sialic-dominated “leucocratic” andesites and dacites (LAD group) were also recognized to the opposite outermost areas of the district. These two latter rock groups were generated by the melting of a basic metamorphic crustal source (respectively in hydrous and anhydrous conditions), favored by the heat released by mantle melts from the adjoining central area. The peculiar distribution of the products of the four rock groups in well defined sectors argues for a strong control of the local crustal tectonic regime on magmatism, influenced by the change from a transpressional to trastensional stage. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the space and time distribution of the Cenozoic magmatism and the associated porphyry Cu-Mo ± Au and other hydrothermal (mostly epithermal) ore deposits along the south Caucasus-west Iranian tectono-magmatic belt. We use a comprehensive georeferenced database containing whole-rock and geochronological analyses of 3150 samples from the igneous rocks distributed in the study area. Overall, the timing of the ore deposits overlaps with the timing of the Eocene to Miocene diachronous collision between the Arabia and Eurasia plates. This is associated with a change in the geochemical fingerprints of the magmas during and after collisional thickening, with a marked increase in Sr/Y values associated with a general transition towards adakitic signatures. This is interpreted with a change towards an amphibole- (±garnet) rich residue at the arc roots. Clusters of ore mineralization are observed within areas of long-lived magmatism (lasting >10 Myr), usually located at the intersections of basement fault zones, parallel and orthogonal to the collisional boundaries and likely formed along inherited zones of crustal/lithospheric weakness. The isotopic data of the ore-forming magmas show a pronounced correlation with young (<0.7 Ga) Nd depleted mantle model ages (TDM Nd) and (87Sr/86Sr) i isotopic ratios ranging from ∼0.704 to ∼0.706. This evidence attests to post-Cadomian metal- and volatile-rich sources at crust roots, during incremental magmatic underplating. We suggest that optimum conditions to form clusters of ore deposits along the collisional zone are achieved when passive asthenosphere upwelling along slab windows (or induced by lithosphere delamination and/or slab break-off) causes the partial melting of the fertile arc roots in the amphibole ± garnet stability field. The end of mineralization along the west Iran magmatic belt is associated with crust overthickening (as evidenced by the inferred presence of a garnet-dominated residue), either as a consequence of consumption of the fertile metal-enriched sources or after the total removal/foundering of the arc roots. [Display omitted] • We present a database of magmatism and linked deposits for Armenia and west Iran. • Ore deposits mainly occur in areas of long-lived and stationary magmatism. • The diachronous collision-related crustal thickening controls timing of deposits. • Productive melts are derived from partial melting of the fertile lower crust roots. • Inherited block boundaries host prolonged magmatism, leading to ore deposition. [ABSTRACT FROM AUTHOR]

Quantitative provenance analysis based on high-resolution bulk-petrography and heavy-mineral data on beach and dune sands, integrated with detrital-zircon geochronology and chemical analyses of pyroxene, garnet and staurolite, demonstrates that sand derived from the Orange River is carried by powerful and persistent longshore currents as far as northern Namibia and southern Angola, 1750 km north of its mouth. This is the longest cell of littoral sand transport documented so far. Compositional forward modeling indicates that ≥ 80% of dune sand in the Skeleton Coast is Orange-derived, the remaining ≤ 20% being supplied by slow erosion of the Damara Orogen chiefly via the Swakop River. A decrease in basaltic rock fragments and pyroxene with relative enrichment in garnet, staurolite, tourmaline and other metamorphic minerals north of Walvis Bay indicates that only one-third of beach sand in the 350 km dune-free gap between the Namib and Skeleton Coast Ergs is Orange-derived, the remaining two-thirds being supplied largely by the Swakop River draining the Damara Orogen. Although volcanic gravel becomes dominant in beaches of the Skeleton Coast north of the Uniab mouth, detritus from Cretaceous Etendeka lavas accounts for only 4% of beach sand, reflecting limited sand generation in the arid catchment. Contributions from the Kunene River to either dune or beach sands is ruled out, indicating that gem diamonds found in placer deposits along the coast of Namibia are all derived from the Orange River. [ABSTRACT FROM AUTHOR]

A ~ 400 m thick Middle-Late Triassic volcano-sedimentary succession crops out in a relatively narrow corridor ~75 km long and ~ 25 km wide close to Antalya Gulf, SW Turkey. The volcanic and subvolcanic rocks represent the majority of the succession and are associated with epiclastic breccia, turbiditic sediments as well as chert and limestone layers. The igneous rocks are alkali basalts, with incompatible element content matching the classical HiMU-OIB types. These are considered as the precursors of a rift system that would have later evolved into a mature Neotethyan oceanic system, with emplacement of massive tholeiitic basalt sequences, not recorded in the investigated area. Clinopyroxene-melt thermobarometric constraints indicate the presence of two main magma chambers, one equilibrated at ~7–10 km depth and ~ 1070 °C and the other at ~15–21 km depth and ~ 1300 °C. Based on these estimates, a 3-D finite element modelling has been applied, simulating the presence of ellipsoidal magma chambers at different depths and with variable sizes, applying different boundary loading conditions. The scenario that best fits the distribution of the volcanic rocks assumes the contemporaneous presence of two magma reservoirs. One is shallow, with a size of ~17 × 1.5 × 1.5 km, and the second is deeper, with a size of ~37 × 3 × 3 km. Numerical simulations show maximum 6 m opening and dilation through horizontal plane at the surface during the Permian/Triassic intracontinental rift phases. Morphological constraints of this rift zone, with the presence of massive lava eruptions also as pillow facies, have been simulated with the existence of a slowly opening rift system. In order to produce the voluminous magma batches in the Antalya region, pure extensional tectonic regimes seem insufficient, and the presence of a transtensional regime must have accompanied the tectonic forces during the Triassic intracontinental rifting stage. • Thermobarometric shows the presence of two magma chambers at ~15–21 km and at ~7–10 km depth. • We suggest that in this OIB system two magma chambers, ~17 × 1.5 × 1.5 km- and ~37 × 3 × 3 km sizes, feed the volcanism • Numerical simulations indicate dilation, reaching 6 m, above the central magma chamber compartment. • The models show similarities with a slow-opening of the intracontinental rifting during the Triassic. [ABSTRACT FROM AUTHOR]

Geological and geodynamic models of the mantle often rely on joint interpretations of published seismic tomography images and petrological/geochemical data. This approach tends to neglect the fundamental limitations of, and uncertainties in, seismic tomography results. These limitations and uncertainties involve theory, correcting for the crust, the lack of rays throughout much of the mantle, the difficulty in obtaining the true strength of anomalies, choice of what background model to subtract to reveal anomalies, and what cross-sections to select for publication. The aim of this review is to provide a relatively non-technical summary of the most important of these problems, collected together in a single paper, and presented in a form accessible to non-seismologists. Appreciation of these issues is essential if final geodynamic models are to be robust, and required by the scientific observations. [ABSTRACT FROM AUTHOR]

Abstract: Sourced as the Nile in distant basaltic rift highlands, the Orange River is the predominant ultimate source of sand for the Namib Desert dunes, as proved independently by bulk-petrography, heavy-mineral, pyroxene-chemistry, and U/Pb zircon-age datasets. Additional local entry points of sand do exist at the edges of the desert, and were quantified by comparison with detrital modes and heavy-mineral suites of hinterland-river sediments. After long-distance fluvial transport, Orange sand is washed by ocean waves and dragged northwards by vigorous longshore currents. Under the incessant action of southerly winds, sand is blown inland and carried farther north to accumulate in the Namib erg, a peculiar wind-dominated sediment sink displaced hundreds of kilometres away from the river mouth. And yet changes in sand mineralogy along the way are minor. After a multistep journey of cumulative 3000km from their source in Lesotho, volcanic rock fragments and pyroxene are found in unchanged abundance as far as the northern edge of the desert. Only locally is volcanic detritus slightly depleted and minor but regular enrichment in quartz and garnet is observed, the sole potential effect of prolonged transport or recycling of Tertiary aeolianites. Selective comminution of fragile minerals is thus proved unable to substantially modify sand composition in fluvial, coastal, or aeolian settings. Mechanical processes have a much greater effect on the morphology of detrital grains, which in Namib dunes appear commonly shaped into nearly perfect spheres. Aeolian sorting concentrates denser minerals locally in placer lags, but such effects can be identified and compensated for. This study demonstrates that mechanical breakdown is unable to markedly affect provenance signatures even during long-distance and prolonged multistep transport in high-energy settings. In arid climates, where chemical processes are negligible, high-resolution bulk-petrography and heavy-mineral analyses are thus powerful techniques to quantitatively reconstruct provenance, and to trace sediment sources and dispersal paths over distances up to thousands of kilometres. [Copyright &y& Elsevier]