Journal articles on the topic 'Éléments traces Magmatisme'

Abstract In contrast to the widespread occurrence of mafic arc magmatism during oceanic subduction, there is a general lack of such magmatism during continental subduction. This paradigm is challenged by the discovery of Early-Middle Triassic mafic igneous rocks from the southeastern margin of the North China Block (NCB), which was subducted by the South China Block (SCB) during the Triassic. Zircon U-Pb dating for these mafic rocks yields 247 ± 2–244 ± 5 Ma for their emplacement, coeval with the initial collision between the two continental blocks. These Triassic mafic rocks generally exhibit ocean island basalt (OIB)-like trace element distribution patterns, intermediate (87Sr/86Sr)i ratios of 0.7057–0.7091, weakly negative εNd(t) values of –1.2 to –3.8, and εHf(t) values of –1.3 to –3.2. Such geochemical features indicate origination from a metasomatic mantle source with involvement of felsic melts derived from dehydration melting of the previously subducting Paleo-Tethyan oceanic crust. The syn-magmatic zircons of Triassic age show variable Hf-O isotopic compositions, indicating that the crustal component was composed of both altered basaltic oceanic crust and terrigenous sediment. High Fe/Mn and Zn/Fe ratios suggest that the mantle source would mainly consist of ultramafic pyroxenites. The melt-mobile incompatible trace elements were further fractionated relative to melt-immobile trace elements during partial melting of these pyroxenites, giving rise to basaltic melts with OIB-like geochemical signatures. The mafic magmatism may be caused by tectonic extension due to rollback of the subducting Paleo-Tethyan oceanic slab in response to the initial collision of the NCB and SCB in the Early Triassic. Therefore, the syn-subduction mafic magmatism provides new geochemical evidence for tectonic transition from oceanic subduction to continental collision in east-central China.

Magmatism that accompanied the 1.1 Ga Midcontinent rift system (MRS) is attributed to the upwelling and decompression melting of a mantle plume beneath North America. Five distinctive flood-basalt compositions are recognized in the rift-related basalt succession along the south shore of western Lake Superior, based on stratigraphically correlated major element, trace element, and Nd isotopic analyses. These distinctive compositions can be correlated with equivalent basalt types in comparable stratigraphic positions in other MRS localities around western Lake Superior. Four of these compositions are also recognized at Mamainse Point more than 200 km away in eastern Lake Superior. These regionally correlative basalt compositions provide the basis for determining the sequential contribution of various mantle sources to flood-basalt magmatism during rift development, extending a model originally developed for eastern Lake Superior. In this refined model, the earliest basalts were derived from small degrees of partial melting at great depth of an enriched, ocean-island-type plume mantle source (εNd(1100) value of about 0), followed by magmas representing melts from this plume source and interaction with another mantle source, most likely continental lithospheric mantle (εNd(1100) < 0). The relative contribution of this second mantle source diminished with time as larger degree partial melts of the plume became the dominant source for the voluminous younger basalts (εNd(1100) value of about 0). Towards the end of magmatism, mixtures of melts from the plume and a depleted asthenospheric mantle source became dominant (εNd(1100) = 0 to +3).

New England and Maritime Canada host two major suites of Mesozoic diabase dykes. The oldest is the Coastal New England dykes that were emplaced between 225 and 230 Ma. These rocks are dominantly alkaline with trace element and isotopic compositions indicative of a high-238U/204Pb mantle (HIMU) source. The oldest of the ~200 Ma Mesozoic rift magmas is represented by the Talcott basalt of the Hartford basin and its feeder dykes. External to the basin is the compositionally equivalent Higganum dyke. The extension of the Higganum, the Onway dyke in New Hampshire, is identical in major and trace element and isotopic compositions indicating that the dyke system represented a feeder to flows of flood basalt proportions. The Talcott system rocks have some trace element similarities with arc basalts and have been interpreted as representing melts of a subduction zone modified mantle beneath the Laurentian- Gondwanan suture. Incompatible trace element ratios and Ba, Th, and U values are, however, unlike arc basalts and are more indicative of crustal contamination of the primary magma. The coastal New England magmas have oceanic island basalt signatures that are generally thought to represent plume-tail magmatism, which is antithetic to a plume-head origin for the younger eastern North America magmas. However, coastal New England rocks have the same trace element signatures as the alkaline rocks of the Loihi seamount, which represent the pre-shield stage to the voluminous tholeiitic magmatism in Hawaii.

As a result of mineralogical and thermobarogeochemical researches of different-age basaltic complexes of Archipelago Franz Josef Land (FJL) regular changes in time of compositions of plagioclases, clinopyroxenes and melt inclusions are established. Chemical compositions of inclusions directly testify to prevalence in Early Jurassic of plateau basaltic melts similar (according to the content of the basic components, and also trace and rare-earth elements) to typical basalt tholeiitic magma of the Siberian platform. In Early Cretaceous melts already had the enriched subalkaline character. Calculations of conditions of magma generation, spent on the basis of the data on melt inclusions, have shown evolution from Early Jurassic to Early Cretaceous (with allocation of three peaks of magmatic activity: 192.2±2.8, 157.4±3.5 and 131.5±0.8 million years) depths and temperatures (accordingly: 70-110 km and to 120 km, 1430-1580°С; 60-110 km, 1390-1580°С; 50-140 km, 1350-1690°С) of mantle melting with formation of deep sources of the FJL magmas.

AbstractSr and Nd isotope ratios, together with lithophile trace elements, have been measured in a representative set of igneous rocks and Lewisian gneisses from the Isle of Rum in order to unravel the petrogenesis of the felsic rocks that erupted in the early stages of Palaeogene magmatism in the North Atlantic Igneous Province (NAIP). The Rum rhyodacites appear to be the products of large amounts of melting of Lewisian amphibolite gneiss. The Sr and Nd isotopic composition of the magmas can be explained without invoking an additional granulitic crustal component. Concentrations of the trace element Cs in the rhyodacites strongly suggests that the gneiss parent rock had experienced Cs and Rb loss prior to Palaeogene times, possibly during a Caledonian event. This depletion caused heterogeneity with respect to87Sr/86Sr in the crustal source of silicic melts. Other igneous rock types on Rum (dacites, early gabbros) are mixtures of crustal melts and and primary mantle melts. Forward Rare Earth Element modelling shows that late stage picritic melts on Rum are close analogues for the parent melts of the Rum Layered Suite, and for the mantle melts that caused crustal anatexis of the Lewisian gneiss. These primary mantle melts have close affinities to Mid-Oceanic Ridge Basalts (MORB), whose trace element content varies from slightly depleted to slightly enriched. Crustal anatexis is a common process in the rift-to-drift evolution during continental break-up and the formation of Volcanic Rifted Margins systems. The ‘early felsic–later mafic’ volcanic rock associations from Rum are compared to similar associations recovered from the now-drowned seaward-dipping wedges on the shelf of SE Greenland and on the Vøring Plateau (Norwegian Sea). These three regions show geochemical differences that result from variations in the regional crustal composition and the depth at which crustal anatexis took place.

ABSTRACTA specific type of granitoid, referred to as sanukitoid (Shirey & Hanson 1984), was emplaced mainly across the Archaean–Proterozoic transition. The major and trace element composition of sanukitoids is intermediate between typical Archaean TTG and modern arc granitoids. However, among sanukitoids, two groups can be distinguished on the basis of the Ti content of the less differentiated rocks of the suite: high- and low-Ti sanukitoids. Melting experiments and petrogenetic modelling show that they may have formed by either (1) melting of mantle peridotite previously metasomatised by felsic melts of TTG composition, or (2) by reaction between TTG melts and mantle peridotite (assimilation). Rocks of the sanukitoid suite were emplaced at the Archaean–Proterozoic boundary, possibly marking the time when TTG-dominated granitoid magmatism changed to a more modern-style, arc-dominated magmatism. Consequently, the intermediate character of sanukitoids is not only compositional but chronological. The succession of granitoid magmatism with time is integrated in a plate tectonic model where it is linked to the thermal evolution of subduction zones, reflecting the progressive cooling of Earth: (1) the Archaean Earth’s heat production was high enough to allow the production of large amounts of TTG granitoids formed by partial melting of recycled basaltic crust (‘slab melting’); (2) at the end of the Archaean, due to the progressive cooling of the Earth, the extent of slab melting was reduced, resulting in lower melt:rock ratios. In such conditions the slab melts can be strongly contaminated by assimilation of mantle peridotite, thus giving rise to low-Ti sanukitoids. It is also possible that the slab melts were totally consumed in reactions with mantle peridotite, subsequent melting of this ‘melt-metasomatised mantle’ producing the high-Ti sanukitoid magmas; (3) after 2·5 Ga, Earth heat production was too low to allow slab melting, except in relatively rare geodynamic circumstances, and most modern arc magmas are produced by melting of the mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab. Of course, such changes did not take place exactly at the same time all over the world. The Archaean mechanisms coexisted with new processes over a relatively long time period, even if they were subordinate to the more modern processes.

The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1–3 GPa have not successfully produced melts with K2O >5 wt%–6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%–8.5 wt% K2O and K/Na of 6–7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting.

Abstract The petrogenesis of calc-alkaline magmatism in the Eocene Absaroka Volcanic Province (AVP) is investigated at Washburn volcano, a major eruptive center in the low-K western belt of the AVP. New 40Ar/39Ar age determinations indicate that magmatism at the volcano commenced as early as 55 Ma and continued until at least 52 Ma. Although mineral and whole-rock compositional data reflect near equilibrium crystallization of modal phenocrysts, petrogenetic modeling demonstrates that intermediate composition magmas are hybrids formed by mixing variably fractionated and contaminated mantle-derived melts and heterogeneous silicic crustal melts. Nd and Sr isotopic compositions along with trace element data indicate that silicic melts in the Washburn system are derived from deep-crustal rocks broadly similar in composition to granulite-facies xenoliths in the Wyoming Province. Our preferred explanation for these features is that mantle-derived basaltic magma intruded repeatedly in the deep continental crust leading to fractional crystallization, silicic melt production, and homogenization of magmas, followed by ascent to shallow reservoirs and crystallization of new plagioclase-rich mineral assemblages in equilibrium with the intermediate hybrid liquids. The implications of this process are that (1) some calc-alkaline magmas may only be recognized as hybrids on purely chemical grounds, particularly in systems where mixing precedes and is widely separated from crystallization in space and time, and (2) given the role ascribed to crustal processes at Washburn volcano, the variation between rocks that follow calc-alkaline trends in the western AVP and those that follow shoshonitic trends in the east cannot simply reflect higher pressures of fractionation to the east in Moho-level magma chambers in the absence of crustal interaction.

Abstract Arc volcanism and trace-element recycling are controlled by the devolatilization of oceanic crust during subduction. The type of fluid—either aqueous fluids or hydrous melts—released during subduction is controlled by the thermal structure of the subduction zone. Recent thermomechanical models and results from experimental petrology argue that slab melting occurs in almost all subduction zones, although this is not completely supported by the rock record. Here we show via phase equilibrium modeling that melting of either fresh or hydrothermally altered basalt rarely occurs during subduction, even at water-saturated conditions. Melting occurs only along the hottest slab-top geotherms, with aqueous fluids being released in the forearc region and anatexis restricted to subarc depths, leading to high-SiO2 adakitic magmatism. We posit that aqueous fluids and hydrous melts preferentially enhance chemical recycling in “hot” subduction zones. Our models show that subducted hydrothermally altered basalt is more fertile than pristine basaltic crust, enhancing fluid and melt production during subduction and leading to a greater degree of chemical recycling. In this contribution, we put forward a petrological model to explain (the lack of) melting during the subduction of oceanic crust and suggest that many large-scale models of mass transfer between Earth’s surface and interior may require revision.

AbstractLarge-volume rhyolitic volcanism along the proto-Pacific margin of Gondwana consists of three major episodes of magmatism or ‘flare-ups’. The initial episode (V1) overlaps with the Karoo–Ferrar large igneous provinces atc.183 Ma. A second (V2) episode was erupted in the interval 171–167 Ma, and a third episode (V3) was emplaced in the interval 157–153 Ma. The magmatic events of the V1 and V2 episodes of the Antarctic Peninsula are reviewed here describing major and trace elements, and isotopic (Sr, Nd, O) data from rhyolitic volcanic rocks and more minor basaltic magmatism. An isotopically uniform intermediate magma developed as a result of anatexis of hydrous mafic lower crust, which can be linked to earlier, arc-related underplating. The subsequent lower-crust partial melts mixed with fractionated mafic underplate, followed by mid-crust storage and homogenization. Early Jurassic (V1) volcanic rocks of the southern Antarctic Peninsula are derived from the isotopically uniform magma, but they have mixed with melts of upper-crustal paragneiss in high-level magma chambers. The V2 rhyolites from the northern Antarctic Peninsula are the result of assimilation and fractional crystallization of the isotopically uniform magma. This process took place in upper-crust magma reservoirs involving crustal assimilants with an isotopic composition akin to that of the magma. A continental margin-arc setting was critical in allowing the development of an hydrous, fusible lower crust. Lower-crustal anatexis was in response to mafic underplating associated with the mantle plume thought to be responsible for the contemporaneous Karoo magmatic province and rifting associated with the initial break-up of Gondwana.

Abstract The Kuntabin Sn-W deposit, located in southern Myanmar, is characterized by abundant greisen-type and quartz vein-type cassiterite and wolframite mineralization. We have conducted multiple geochronological methods and isotope and trace element analyses to reveal the age and evolution of the Kuntabin magmatichydrothermal system. Zircon U-Pb dating of the two-mica granite yielded a weighted mean 206Pb/238U age of 90.1 ± 0.7 Ma. Cassiterite U-Pb dating provided a lower intercept age of 88.1 ± 1.9 Ma in the Tera-Wasserburg U-Pb concordia diagram. Molybdenite Re-Os dating returned a weighted mean model age of 87.7 ± 0.5 Ma and an isochron age of 88.7 ± 2.7 Ma. These ages indicate a genetic relationship between granite and Sn-W mineralization in the Kuntabin deposit and record the earliest magmatism and Sn-W mineralization in the Sibumasu and Tengchong terranes related to subduction of the Neo-Tethys oceanic slab. Three generations of cassiterite have been identified with distinctive cathodoluminescence textures and trace element patterns, indicating the episodic input of ore-forming fluids and distinctive changes in the physical-chemical conditions of the Kuntabin magmatichydrothermal system. Sudden changes of fluid pressure, temperature, pH, etc., may have facilitated the deposition of Sn and W. Rhenium contents of molybdenite from the Kuntabin deposit and many other Sn-W deposits in Myanmar are characteristically low compared to porphyry Cu-Mo-(Au) deposits worldwide. In combination with zircon Hf isotope signatures, we infer that granites associated with Sn-W deposits in Myanmar were predominantly derived by melting of ancient continental crust and contain minimal mantle contribution. Subduction of the Neo-Tethys oceanic slab from west of the West Burma terrane reached beneath the Sibumasu terrane and led to magmatism and Sn-W mineralization at ~90 Ma when the Kuntabin deposit was formed. The Paleoproterozoic Sibumasu crust was activated during the subduction-related magmatism to form predominantly crust derived melts. After a high degree of fractional crystallization and fluid exsolution, physical-chemical changes of the hydrothermal fluid resulted in Sn and W precipitation to form the Kuntabin Sn-W deposit.

AbstractMost continental flood basalt (CFB) provinces of the world contain silicic (granitic and rhyolitic) rocks, which are of significant petrogenetic interest. These rocks can form by advanced fractional crystallization of basaltic magmas, crustal assimilation with fractional crystallization, partial melting of hydrothermally altered basaltic lava flows or intrusions, anatexis of old basement crust, or hybridization between basaltic and crustal melts. In the Deccan Traps CFB province of India, the Barda and Alech Hills, dominated by granophyre and rhyolite, respectively, form the largest silicic complexes. We present petrographic, mineral chemical, and whole-rock geochemical (major and trace element and Sr–Nd isotopic) data on rocks of both complexes, along with 40Ar–39Ar ages of 69.5–68.5 Ma on three Barda granophyres. Whereas silicic magmatism in the Deccan Traps typically postdates flood basalt eruptions, the Barda granophyre intrusions (and the Deccan basalt flows they intrude) significantly pre-date (by 3–4 My) the intense 66–65 Ma flood basalt phase forming the bulk of the province. A tholeiitic dyke cutting the Barda granophyres contains quartzite xenoliths, the first being reported from Saurashtra and probably representing Precambrian basement crust. However, geochemical–isotopic data show little involvement of ancient basement crust in the genesis of the Barda–Alech silicic rocks. We conclude that these rocks formed by advanced (70–75 %), nearly-closed system fractional crystallization of basaltic magmas in crustal magma chambers. The sheer size of each complex (tens of kilometres in diameter) indicates a very large mafic magma chamber, and a wide, pronounced, circular-shaped gravity high and magnetic anomaly mapped over these complexes is arguably the geophysical signature of this solidified magma chamber. The Barda and Alech complexes are important for understanding CFB-associated silicic magmatism, and anorogenic, intraplate silicic magmatism in general.

Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing trace element partitioning schemes to calculate the compositions of amphibole equilibrium melts (AEMs). The AEM compositions show that Mt Lamington andesites and plutonic enclaves are dominated by fractionation of amphibole + plagioclase + biotite, with assimilation of plagioclase and zircon. Magnesiohastingsite crystals in the andesite and diktytaxitic mafic enclaves reflect multiple episodes of recharge by more primitive, geochemically variable melts. The andesite also contains clots with rounded grains and melt on grain boundaries. These features indicate slow crystallization, and the retention of melt films could significantly enhance the potential for remobilization of crystals by infiltrating melts or during magma mixing. Variations in crystallization conditions could thus significantly affect the mush microstructure. We suggest that this could result in a significant bias of the volcanic record towards the preferential incorporation of more slowly cooled plutonic material from the lower crust or from more thermally mature plumbing systems. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.

Abstract Postcollisional magmatism in the eastern Sakarya zone was recorded by voluminous basic volcanism and repeated plutonism during the early Cenozoic. The temporal and geochemical evolution of these magmatic rocks is important for understanding the possible geodynamic history of the Sakarya zone. Here, we investigated three representative plutons lying between the towns of Çamlıhemşin (Rize) and İspir (Erzurum), Turkey. These are largely composed of medium-K gabbroic diorites (Marselavat Pluton), shoshonitic monzonites (Güllübağ Pluton), and high-K granites (Ayder Pluton). We present whole-rock geochemistry, 40Ar/39Ar geochronology, and Sr, Nd, and Pb isotope analyses from the plutons to constrain the timing of variations in magmatism and source characteristics, and we provide a new approach to the proposed geodynamic models, which are still heavily debated. The 40Ar/39Ar geochronology reveals a cooling sequence from ca. 45 Ma for the Marselavat Pluton through ca. 41 Ma for the Güllübağ Pluton to ca. 40 Ma for the Ayder Pluton. Whole-rock geochemistry and Sr, Nd, Pb isotopes suggest that crustal contamination was not an important factor affecting magma compositions. Although there was no arc-related tectonic setting in the region during the middle Eocene, the Marselavat Pluton shows some subduction affinities, such as moderately negative Nb and Ta anomalies, and slightly positive Pb anomalies. These signatures were possibly inherited from a depleted mantle source that was modified by hydrous fluids released from the oceanic slab during Late Cretaceous subduction. Geochemical traces of the earlier subduction become uncertain in the Güllübağ samples. They display ocean-island basalt–like multi-element profiles and Nb/Ta, Ce/Pb, and La/Ba ratios. All these point to a mantle source in which earlier subduction signatures were hybridized by the addition of asthenospheric melts. Melting of calc-alkaline crustal material, probably emplaced during the first phase of middle Eocene magmatism (Marselavat), led to the formation of granitic plutonism (Ayder Pluton). Our data in conjunction with early Eocene adakite-like rocks show that melt generation, as in the given sequence, was most probably triggered by breakoff of the northern Neotethyan oceanic slab, ∼13 m.y. after the early Maastrichtian collision between the Sakarya zone and Anatolide-Tauride block, and continued until the end of the middle Eocene. A shallow-marine transgression occurred contemporaneously with the middle Eocene magmatism throughout the Sakarya zone. An extension in this magnitude seems unlikely to be the result of orogenic collapse processes only. The main cause of this extension was most probably related to the northward subduction of the southern Neotethys Ocean beneath the Anatolide-Tauride block. The result is a volumetrically larger amount of middle Eocene magmatism than that expected in response to slab breakoff.

ABSTRACTTrace element inversion modelling of Grenvillean anorthosite massifs and associated rocks yield NMORB-normalised trace element profiles enriched in highly incompatible elements; commonly with negative Nb and Th anomalies. Model melts can be divided into subtypes that cannot be linked through fractional crystallisation processes. Most model melts are depleted in the heavy rare-earth elements and can be explained by partial melting of arc basaltic sources (5–60 melting ) with garnet-bearing residues. Some of the model melts have flat NMORB-normalised profiles (for rare-earth elements), have high compatible element contents, and might have been derived from mantle fertilised by arc magmatism, followed by low-pressure fractional crystallisation. Intermediate Ce/Yb types may represent mixtures of these end-members, or less probably, variations in the crustal source composition and residual assemblage. The active tectonic context now favoured for the Grenville Province appears to be inconsistent with plume or thermal insulation models. The heat source for crustal and mantle melting could record either post-orogenic thermal relaxation of a tectonically-thickened arc crust, or basaltic underplating caused by delamination of a mantle root or subduction slab beneath this arc crust. In this context, pre-Proterozoic anorthosites may be lacking, because prior to ca. 2·5 Ga, the crust may have been too weak to be thickened tectonically. The absence of post-Proterozoic anorthosites may be due to the secular decrease in radiogenic heating and cooling of the mantle and crust.

AbstractMafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.

We present new in situ geochronological data of controversial silicic metavolcanic rocks from the lower terrigenous-metavolcanic sequence of the São Roque Group, Ribeira Belt, confirming that they are older than the rocks of higher-metamorphic grade sequences of the Serra do Itaberaba Group. The age of the Polvilho meta-trachydacite was established at 1760 ± 17 Ma, furthermore the results suggest that the bi-modal volcanism of the Boturuna Formation has parent melts from an old (Archean to Paleoproterozoic) continental crust that was melted in a within-plate environment. Trace-element chemistry of zircon, suggests similarities with high-temperature melts (T Zrsat = 900–915ºC) similar to A-type granites (high negative EuN/EuN* and moderate positive CeN/CeN*) from continental sources under reducing conditions.

AbstractThe late Lower to Middle Permian Panjal Traps (NW Himalaya, India-Pakistan) represent the greatest magmatic province erupted on the northern Indian platform during the Neotethys opening. New geochemical and isotopic analyses were performed on basalts from the eastern borders of the traps (SE Zanskar-NW Spiti area) in order to characterize this volcanism, to discuss its compositional variations in comparison to Panjal counterparts and its relationships with the opening of Neotethys. Lavas show features of tholeiitic low-Ti (&lt; 1.6%) continental flood basalts with LREE, Th enrichments and Nb-Ta negative anomalies. Trace element ratios combined with εNdi values (−3.6 to +0.9) and high Pb isotopic ratios suggest that these tholeiitic basalts were derived from an OIB-like mantle contaminated at various degrees by a continental crust component. Previous geochemical features are broadly similar to those of the coeval Panjal volcanic sequences identified westwards (Ladakh, Kashmir and Pakistan). Present geochemical constraints obtained for the Panjal Traps basalts suggest they originated from rapid effusion of tholeiitic melts during opening of the Neotethys Ocean. Similar magmatism implying an OIB-type reservoir is contemporaneously recognized on and along the adjacent Arabian platform. Both Indian and Arabian Permian volcanics were emplaced during coeval syn-rift to post rift transition. These Lower to Middle Permian south Neotethyan continental flood magmatism are regarded as associated to a passive rifting. In this scheme, OIB-type isotopic signature would be related either to a melting episode of syn-rift up-welling mantle plumes or to a melting of a regional abnormally hot and enriched mantle.

Foreland magmatism occurs in the lower plate during arc–continent or continent–continent collision, although it is uncommon. Ancient examples are recognized by a stratigraphic section into which mafic lavas and/or shallow sills are emplaced at a level at the top of a passive margin cover sequence, or within the overlying deeper water deposits that include mudrocks and flysch-type turbidites. Extensional structures associated with the emplacement of the volcanic rocks may develop slightly prior to or contemporaneous with the arrival of the approaching thrust front. We have selected twelve examples of magmatism in collisional forelands, modern and ancient, and have compared the tectonic associations of the magmatism with the magmatic geochemistry. Foreland magmatic settings fall into two strikingly distinct geochemical groups: a more enriched alkaline group (Rhine-type) and a more heterogeneous tholeiitic group (Maine-type) that may show traces of prior subduction processes. In the examples where the contemporaneous extensional structures are known, faults and basins develop parallel to the thrust front for the tholeiitic group and have oblique orientations, in several cases at a high angle to the thrust front, for the alkaline group. The geochemical results are quite sufficiently distinct to permit discrimination of these two foreland magmatic rock suites from each other in ancient examples where the foreland setting is clear from geological evidence. However, magmatic products of the same range of compositions can be generated in other tectonic environments (rifts, back-arc basins), so the geochemical characteristics alone are insufficient to identify a foreland basin setting. The alkaline Rhine-type group formed primarily in response to localized upwelling convective activity from the sub-asthenospheric mantle beneath the lower plate during collision while the tholeiitic Maine-type group formed primarily in response to melting of subcontinental asthenospheric mantle during extension of the lower plate by slab pull, and resulting lithospheric detachment. It is possible that there has been a long-term secular decrease in the occurrence of the Maine-type foreland magmatism since the early Proterozoic.RÉSUMÉBien que peu fréquent, il arrive qu’un magmatisme d’avantpays se produise dans la plaque inférieure durant une collision arc-continent ou continent-continent. Des exemples anciens ont été décrits dans une coupe stratigraphique renfermant des laves mafiques et/ou des filons-couches au haut d’une séquence de couverture de marge passive, ou au sein de dépôts de plus grandes profondeurs comme des boues ou des turbidites de type flysch. Des structures d’étirement associées à la mise en place des roches volcaniques peuvent se développer un peu avant ou en même temps que l’arrivée du front de chevauchement. Nous avons choisi douze exemples de magmatisme au sein d’avant-pays de collision, modernes et anciens, et nous avons comparé les associations tectoniques du magmatisme avec la géochimie magmatique. Les configurations magmatiques d’avant-pays se divisent en deux groupes géochimiques très différents : un groupe alcalin plus enrichi (type-Rhin), et un groupe tholéiitique plus hétérogène (type-Maine) et qui peut montrer des traces de précédentes activités de subduction. Dans les exemples où les structures d’étirement contemporaines sont connues, les failles et les bassins se développent parallèlement au front de chevauchement pour le groupe tholéiitique, alors que leurs orientations sont obliques, voire à angles aigus au front de chevauchement pour le groupe alcalin. Les résultats géochimiques sont suffisamment distincts pour permettre de distinguer ces deux suites de roches magmatiques dans les exemples anciens où la configuration d’avant-pays est évidente de par sa géologie. Cependant, des produits magmatiques de même type compositionnel peuvent advenir dans d’autres environnements tectoniques (fosses, bassins d’arrière-arc), et donc, la caractérisation géochimique seule ne permet pas de distinguer une configuration de bassin d’avant-pays. Le groupe alcalin de type-Rhin s’est principalement formé en réponse à une activité d’éruption de convection issue du manteau sous-asthénosphérique sous la plaque inférieure durant la collision, alors que le groupe tholéiitique de type-Maine s’est formé principalement en réaction à la fusion du manteau sous-continental asthénosphérique durant l’extension de la plaque inférieure par étirement de la plaque, et le détachement lithosphérique qui en découle. Depuis le Protérozoïque, est possible qu’il y ait eu une décroissance progressive à long terme des événements magmatiques de type-Maine.

New bedrock mapping completed as part of the Nechako NATMAP Project indicates that the area between Babine and Takla lakes in central British Columbia is underlain by rocks of the Early Permian Asitka, Late Triassic Takla, and Early to Middle Jurassic Hazelton volcanic-arc assemblages of the Stikine Terrane. These are cut by large composite stocks of quartz diorite, granodiorite, and quartz monzonite previously mapped as the Late Triassic to Early Jurassic Topley intrusions. New U/Pb (n = 6) and laser 40Ar/39Ar (n = 10) isotopic age dates reported in this paper suggest there are two distinct ages of plutons: the Topley intrusive suite with isotopic ages between 218 and 193 Ma; and, east of Babine Lake, the new Spike Peak intrusive suite with isotopic ages ranging from 179 to 166 Ma. West of the main plutonic belt is a thick volcanic succession of subaerial, porphyritic andesite flows, volcanic breccias, and rhyolitic ash-flow tuffs that have isotopic ages between 185 and 174 Ma. These rocks are assigned to the Saddle Hill Formation of the Hazelton Group. The plutonic roots of this proximal arc assemblage are most likely the coeval and compositionally similar plutons of the Spike Peak intrusive suite that have been unroofed in the area east of the Takla Fault. Major oxide and trace element data support the interpretation that the Topley and Spike Peak granitic rocks formed in a juvenile volcanic-arc environment and that magmatism is related to melts generated above a long-lived subduction zone of unknown orientation.

Abstract The ca. 2.97 to 2.80 Ga Witwatersrand Supergroup, South Africa, represents the oldest intracontinental sedimentary basin of the Kaapvaal craton. Two volcanic units occur in this supergroup: the widespread Crown Formation lavas in the marine shale-dominated West Rand Group and the more geographically restricted Bird Member lavas, intercalated with fluvial to fluvio-deltaic sandstone and conglomerate of the Central Rand Group. These units remain poorly studied as they are rarely exposed and generally deeply weathered when cropping out. We report whole-rock major and trace elements, Hf and Nd-isotope whole-rock analyses of the lavas from core samples drilled in the south of the Witwatersrand basin and underground samples from the Evander Goldfield in the northeast. In the studied areas, both the Crown Formation and Bird Member are composed of two units of lava separated by sandstone. Whereas all the Crown Formation samples show a similar geochemical composition, the upper and lower volcanic units of the Bird Member present clear differences. However, the primitive mantle-normalized incompatible trace element concentrations of all Crown Formation and Bird Member samples show variously enriched patterns and marked negative Nb and Ta anomalies relative to Th and La. Despite the convergent geodynamic setting of the Witwatersrand Supergroup suggested by the literature, the Crown Formation and Bird Member are probably not related to subduction-related magmatism but more to decompression melting. Overall, the combined trace element and Sm-Nd isotopic data indicate melts from slightly to moderately depleted sources that were variably contaminated with crustal material. Greater contamination, followed by differentiation in different magma chambers, can explain the difference between the two signatures of the Bird Member. Finally, despite previous proposals for stratigraphically correlating the Witwatersrand Supergroup to the Mozaan Group of the Pongola Supergroup, their volcanic units are overall geochemically distinct.

A combination of methods is applied in the present study to define the exact age of the Petrohan and Mezdreya plutons and trace their magma evolution. Field, petrological, and geochemical studies of the Petrohan pluton revealed its complex evolution and emphasized the role of magma mingling and mixing, complementary to the normal assimilation and fractional crystallization (AFC) processes. Using high-precision conventional U-Pb (CA)-ID-TIMS zircon and titanite dating in combination with CA-LA-ICP-MS zircon dating and tracing, we suggest an incremental growth of a common Petrohan-Mezdreya pluton. It was assembled over minimum 4.5 Ma from 311.14±0.48 Ma to 307.54±0.54 Ma. The younger age of the gabbro (308.12±0.33 Ma), compared with the age of granodiorites (311.14±0.48 Ma), provides numerical proofs for magma replenishment during the assembling of the Petrohan pluton. Whole-rock strontium-neodymium (initial 87Sr/86Sr ratios of 0.70521–0.70527 to 0.70462 and 143Nd/144Nd of 0.51221 to 0.51210) and Hf-zircon isotope data (ε-Hf from –5.8 to +3.6) argue for interaction of mantle derived magma with crustal melts but also mixing and mingling and transfer of zircon grains between the gabbroic and granitic melts. Possible petrogenetic scenario includes melting of subcontinental mantle lithosphere and crust and evolution trough AFC, FC and mingling/mixing processes. Considering the Petrohan-Mezdreya pluton as part of the Variscan orogeny in SE Europe, our new data support the accretion/collision of both the Balkan and Sredna Gora/Getic units with Moesia in the Early Carboniferous followed by syn- and post-collisional Carboniferous and Permian magmatism.

This paper presents the preliminary results regarding the lithostratigraphy, petrography and petrology of James Ross Island Volcanic Group dominating the Lachman Crags and Cape Lachman lava-fed deltas in the Ulu Peninsula, James Ross Island north-eastern Antarctic Peninsula. Studied lava-fed deltas were produced via Late Miocene to Pleistocene sub-marine and sub-glacial volcanism and made up four main lithofacies: a- bottomset pillow lavas, peperites and associated volcanoclastic/siliciclastic deposits; b- foreset-bedded hyaloclastite breccias; c- intrusions (feeder dykes, sills, and plugs) and d- topset subaerial lavas. Collectively these lithofacies record the transition from an effusive subaqueous to an effusive subaerial eruption environment. All lava samples and dykes from bottomset, foreset and topset lava-fed delta associations are olivine-phyric alkali basalts and are mineralogically and geochemically homogeneous. These eruptive products display significant enrichments in alkali contents and have ocean island basalt (OIB)-type, intra-plate geochemical signatures characterized by enrichments in all highly to moderately incompatible trace elements relative to basaltic rocks from ocean ridge settings. Volcanic products from a number of different eruptive periods display limited variations in major and trace element relative abundances, indicating derivation from a relatively homogeneous mantle source. The results of quantitative modelling of geochemical data is consistent with the view that the primary melts from which these mafic alkaline rocks were originated are the products of relatively small degrees (~3-7%) of partial melting of a volatile-bearing, metasomatized mantle source. The magmatism is likely the result of extension-driven mantle upwelling.

The Piedade Granite (~600 Ma) was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit) and core (metaluminous titanite-bearing biotite monzogranite BmgT unit) and felsic pink inequigranular granite (Bmg unit) between them. Bmg has high LaN/YbN (up to 100), Th/U (>10) and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (~45), Ba and Sr, fractionated REE patterns (LaN/YbN= 45), 87Sr/86Sr(t)~ 0.710, epsilonNd(t) ~ -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta). The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t) = 0.713-0.714; epsilonNd(t)= -14 to -16), similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

Laser ablation MC-ICP-MS was used to measure the Os-isotope compositions of single sulfide grains, including laurite (RuS2) and pentlandite [(Fe,Ni)9S8], from two chromitite bodies and host lherzolites from ophiolites of North Andaman (Indo-Burma-Sumatra subduction zone). The results show isotopic heterogeneity in both laurite (n = 24) and pentlandite (n = 37), similar to that observed in other chromitites and peridotites from the mantle sections of ophiolites. Rhenium-depletion model ages (TRD) of laurite and pentlandite reveal episodes of mantle magmatism and/or metasomatism in the Andaman mantle predating the formation of the ophiolite (and the host chromitites), mainly at ≈0.5, 1.2, 1.8, 2.1 and 2.5 Ga. These ages match well with the main tectonothermal events that are documented in the continental crustal rocks of South India, suggesting that the Andaman mantle (or its protolith) had a volume of lithospheric mantle once underlaying this southern Indian continental crust. As observed in other oceanic lithospheres, blocks of ancient subcontinental lithospheric mantle (SCLM) could have contributed to the development of the subduction-related Andaman–Java volcanic arc. Major- and trace-element compositions of chromite indicate crystallization from melts akin to high-Mg IAT and boninites during the initial stages of development of this intra-oceanic subduction system.

AbstractPeraluminous granites and trondhjemites make up small plutonic bodies intruded into high-grade paragneisses in the Peloritani Mountains, marking the beginning of late Variscan granitoid magmatism in southernmost Italy. The granites range from low-Ca monzogranites to alkali feldspar granites, while the trondhjemites vary from trondhjemites s.s. to low-Ca trondhjemites. Relatively high radiogenic (87Sr/86Sr)i ratios (mostly from 0.7073 to 0.7125) and negative εNd values (mostly from −5.66 to −8.73) point to crustal sources for all the granitoids. Major and trace element compositions indicate an absence of genetic relationships between the trondhjemites s.s. and the low-Ca granitoids, but possible relationships between the low-Ca trondhjemites and the granites. All of the studied granitoids have near-pure melts compositions, consistent with H2O-fluxed and dehydration melting of metasediments for the trondhjemites and the granites, respectively. However, the unusual compositions of the low-Ca trondhjemites and microstructural evidence in these rocks for pervasive subsolidus replacement of magmatic feldspars by secondary sodic plagioclase indicate that they were derived instead from metasomatic alteration of the granites. Thus, water may be involved in the production of trondhjemites in two different ways, driving water-fluxed melting in the magma source and driving alkali metasomatism at the sites of granite emplacement in the upper crust.

Abstract Magmatism in the East African Rift System (EARS) contains a spatial and temporal record of changing contributions from the Afar mantle plume, anciently metasomatized lithosphere, the upper mantle and the continental crust. A full understanding of this record requires characterizing volcanic products both within the rift valley and on its flanks. In this study, three suites of mafic, transitional to alkaline lavas, were collected over a northeast-southwest distance of ∼150 km along the southeastern Ethiopian Plateau, adjacent to the Main Ethiopian Rift. Specifically, late Oligocene to Quaternary mafic lavas were collected from Chiro, Debre Sahil and the Bale Mountains. New major element, trace element, 40Ar/39Ar ages and isotopic results (Sr, Nd, Pb, Hf, Os, He) show spatial and temporal variation in the lavas caused by dynamical changes in the source of volcanism during the evolution of the EARS. The trace element compositions of Oligocene and Miocene Chiro lavas indicate derivation from mildly depleted and nominally anhydrous lithospheric mantle, with variable inputs from the crust. Further south, Miocene Debre Sahil and alkaline Bale Mountains lavas have enriched incompatible trace element ratios (e.g. Ba/Nb = 12–43, La/SmN = 3·1–4·9, Tb/YbN = 1·6–2·4). Additionally, their 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf and 206Pb/204Pb values trend toward a radiogenic Pb (HIMU) component. Radiogenic 187Os/188Os in these lavas correlates positively with 206Pb/204Pb and trace element indicators consistent with ancient metasomatic enrichment of their mantle source. In contrast, transitional Miocene Bale Mountains lavas have lower incompatible trace element abundances, less enriched trace element ratios (Ba/Nb ∼7, La/SmN = 2·3–2·5) and less radiogenic isotopic signatures that originate from melting garnet-bearing, anhydrous lithospheric mantle (Tb/YbN = 2·5–2·9). Pliocene and Quaternary Bale Mountains basaltic lavas are chemically and isotopically similar to Main Ethiopian Rift lavas. Trace element and isotopic indicators in both of these suites denote an amphibole-bearing source distinct from that sampled by the older Bale Mountains lavas. Isotopically, Pliocene and Quaternary Bale lavas have notably less radiogenic Sr–Nd–Pb–Hf isotopic ratios. Quaternary Bale Mountains lavas have the strongest mantle plume contribution (3He/4He = 12·1–12·5 RA), while other Bale Mountains, Debre Sahil and Chiro lavas were derived dominantly by melting of lithospheric or upper mantle sources (3He/4He = 5·1–9·1 RA). A multi-stage, regional-scale model of metasomatism and partial melting accounts for the spatial and temporal variations on the southeastern Ethiopian Plateau. Early Debre Sahil and alkaline Bale Mountains mafic lavas are melts derived from Pan-African lithosphere containing amphibole-bearing metasomes, while later transitional Bale basalts are melts of lithosphere containing anhydrous, clinopyroxene-rich veins. These ancient metasomatized domains were eventually removed through preferential melting, potentially during thermal erosion of the lithosphere or lithospheric foundering. Pliocene and Quaternary Bale Mountains lavas erupted after tectonic extension progressed throughout Ethiopia and was accompanied by increased plume influence on the volcanic products.

Two syenite sills intrude the local Paleozoic strata of eastern New York State and are exposed along the western shore of Lake Champlain. The sills are fine-grained, alkali feldspar syenites and quartz syenites, with phenocrysts of sanidine and albite. The two sills are compositionally distinct, with crossing rare earth element profiles and different incompatible element ratios, which eliminates the possibility of a simple petrogenetic relationship. Zircon extracted from the upper sill yields a U–Pb age of 131.1 ± 1.7 Ma, making the sills the youngest known igneous rocks in New York State. This age is similar to that of the earliest intrusions in the Monteregian Hills of Quebec, >100 km to the north. Sr and Nd radiogenic isotope ratios are also similar to those observed in some of the syenitic rocks of the eastern Monteregian Hills. The Cannon Point syenites have compositions typical of A-type, within-plate granitoids. They exhibit unusually high Ta and Nb concentrations, resulting in distinct trace element signatures that are similar to those of the silicic rocks of the Valles Caldera, a large, rift-related magmatic system. We suggest that the Cannon Point syenites were melts derived primarily by anatexis of old, primitive, lower crustal material in response to Mesozoic rifting and to the intrusion of mantle-derived magmas. The sills indicate that the effects of continental rifting were spatially and temporally extensive, resulting in the reactivation of basement faults in the Lake Champlain Valley hundreds of kilometers west of the active rift boundary, and crustal melting >50 Ma after the initiation of rifting.

ABSTRACT The Indaiá-I and Indaiá-II intrusions are hypabyssal, small-sized ultrabasic bodies belonging to the Cretaceous magmatism of the Alto Paranaiba Alkaline Province (southeast-central western Brazil). While Indaiá-I is classified as an archetypal group-I kimberlite, Indaiá-II (its satellite intrusion) presents several petrographic and chemical distinctions: (1) an ultrapotassic composition (similar to kamafugites), (2) lower volumes of olivine macrocrysts, (3) diopside as the main matrix phase (in contrast with the presence of monticellite in Indaiá-I), (4) high amounts of phlogopite, and (5) abundant felsic boudinaged and stretched microenclaves and crustal xenoliths. Disequilibrium features, such as embayment and sieve textures in olivine and clinopyroxene grains, are indicative of open-system processes in Indaiá-II. Mineral reactions observed in Indaiá-II (e.g., diopside formed at the expense of monticellite and olivine; phlogopite nearby crustal enclaves and close to olivine macrocrysts) point to an increase in the silica activity of the kimberlite magma; otherwise partially melted crustal xenoliths present kalsilite, generated by desilification reactions. The high Contamination Index (2.12–2.25) and the large amounts of crustal xenoliths (most of them totally transformed or with evidence of partial melting) indicate a high degree of crustal assimilation in the Indaiá-II intrusion. Calculated melts (after removal of olivine xenocrysts) of Indaiá-II have higher amounts of SiO2, Al2O3, K2O, slightly higher Rb/Sr ratios, lower Ce/Pb and Gd/Lu ratios, higher 87Sr/86Sr, and lower 143Nd/144Nd than those calculated for Indaiá-I. Crustal contamination models were developed considering mixing between the calculated melts of Indaiá-I and partial melts modeled from the granitoid country rocks. Mixing-model curves using major and trace elements and isotopic compositions are consistent with crustal assimilation processes with amounts of crustal contribution of ca. 30%. We conclude that (1) Indaiá-II is representative of a highly contaminated kimberlitic intrusion, (2) this contamination occurred by the assimilation of anatectic melts from the main crustal country rocks of this area, and (3) Indaiá-I and Indaiá-II could have had the same parent melt, but with different degrees of crustal contamination. Our petrological model also indicates that Indaiá-II is a satellite blind pipe linked to the main occurrence of Indaiá-I.

Abstract —We present the results of study of the influence of trap magmatism on the geochemical composition of brines and on the geothermal regime of the Earth’s interior in the western areas of the Kureika syneclise. The Siberian trap province, which unites all cutting and layered tholeiite–basic magmatic intrusions and erupted basaltic lava, is the world’s largest Phanerozoic continental basalt province. Brines, hydrocarbon deposits, and organic matter of the sedimentary cover were subjected to a significant thermal impact as a result of the Permo-Triassic trap magmatism. During the trap intrusion, the maximum paleotemperatures in major Silurian (D’yavolskii), Ordovician (Baikit), and Cambrian (Deltula–Tanachi, Abakun, and Moktakon) productive horizons reached 650 °C. The Paleozoic and Proterozoic deposits of the study area contain brines with TDS = 50–470 g/dm3. By chemical composition, they are of Na, Na–Ca, Ca–Na, Ca–Mg, and Ca chloride types (according to the classification by S.A. Shchukarev), with mixed Ca–Na and Na–Ca chloride brines dominating. The studied brines can be divided into three groups according to the degree of metamorphism: low (S1), medium (S2), and high (S3). The first group includes mainly sodium chloride brines with TDS = 50–370 g/dm3 (rNa/rCl = 0.60–0.95; S ≤ 100). The second (dominating) group comprises Na–Ca, Ca–Na, Ca, and Ca–Mg chloride brines with TDS = 150–470 g/dm3 (rNa/rCl = 0.10–0.87; 100 ≤ S ≤ 300). The third group is Ca–Na and Ca chloride brines with TDS = 223–381 g/dm3 (rNa/rCl = 0.12–0.45; S ≥ 300). We have first established changes in the hydrogeochemical field (major- and trace-component and gas compositions) with distance from the contacts of intruded dolerite sills and dikes. Hydrocarbons (CH4, C2H6, C3H8, i-C4H10, n-C4H10, i-C5H12, n-C5H12, and C6H14) and water-soluble components I, B, and NH4 were most actively subjected to destruction. For example, at a distance of 100 m from the intrusion zone, the water-dissolved gases are dominated by CO2 (&gt;90 vol.%), and CH4 amounts to 5 vol.%, whereas at a distance of 250 m, the concentration of CO2 decreases to 30 vol.%, and that of CH4 increases to 60–70 vol.%. In addition to the negative effect on the hydrocarbon preservation in the contact zone (≤400 m), the intrusive trap magmatism favored the formation of hydrocarbons in remote horizons. The reaction of intruding traps with brines of the sedimentary cover led to the saturation of the latter with iron, aluminum, and silica, which suggests extraction of metals in the form of salts from magmatic melts into an ore-bearing fluid.

Abstract Abundant zoned olivine xenocrysts from Early Cretaceous basalts of the Yixian Formation in western Liaoning Province, China, contain critical information about the nature and evolution of the lithospheric mantle of the northern North China Craton. These olivine xenocrysts are large (600–1600 µm), usually rounded and embayed, with well-developed cracks. Their cores have high and uniform forsterite (Fo) contents (88–91), similar to the peridotitic olivine entrained by regional Cenozoic basalts. Their rims have much lower Fo contents (74–82), comparable to phenocrysts (72–81) in the host basalts. These characteristics reveal that the zoned olivine has been disaggregated from mantle xenoliths and thus can be used to trace the underlying lithospheric mantle at the time of basaltic magmatism. The olivine cores have high oxygen isotope compositions (δ18OSMOW = 5.9–7.0‰) relative to the normal mantle value, suggesting that the Early Cretaceous lithospheric mantle was enriched and metasomatized mainly by melts/fluids released from subducted oceanic crust that had experienced low-temperature hydrothermal alteration. Preservation of zoned olivine xenocrysts in the Early Cretaceous basalts indicates that olivine-melt/fluid reaction could have been prevalent in the lithospheric mantle as an important mechanism for the transformation from old refractory (high-Mg) peridotitic mantle to young, fertile (low-Mg), and enriched lithospheric mantle during the early Mesozoic.

Research on two strata-like intrusions from Slatina-Timiş (STG) and Buchin (BG) at West Getic Domain of the South Carpathians (Semenic Mountains) identified granitoids with adakitic signature in a continental collision environment. Whole-rock geochemical composition with high Na2O, Al2O3 and Sr, depleted Y (18ppm) and HREE (Yb 1.8ppm) contents, high Sr/Y (40), (La/Yb)N (10) ratios and no Eu anomalies overlaps the High-Silica Adakites (HSA) main characteristics, though there are differences related to lower Mg#, heavy metal contents and slightly increased 87Sr/86Sr ratios. Comparison with HSA, Tonalite-Trondhjemite-Granodiorite (TTG) rocks and melts from experiments on basaltic sources suggests partial melting at pressures exceeding 1.25GPa and temperatures of 800-900ºC (confirmed by calculated Ti-in zircon temperatures) as the main genetic process, leaving residues of garnet amphibolite, garnet granulite or eclogite type. The adakitic signature along with geochemical variations observed in the STG-BG rocks indicate oceanic source melts affected by increasing mantle influence and decreasing crustal input that may restrict the tectonic setting to slab melting during a subduction at low angle conditions. An alternative model relates the STG-BG magma genesis to garnet-amphibolite and eclogite partial melting due to decompression and heating at crustal depth of 60-50km during syn-subduction exhumation of eclogitized slab fragments and mantle cumulates. The granitoids were entrained into a buoyant mélange during collision and placed randomly between two continental units. U-Pb zircon ages obtained by LA-ICP-MS and interpreted as Ordovician igneous crystallization time and Variscan recrystallization imprint are confirmed by trace-element characteristics of the dated zircon zones, connecting the STG-BG magmatism to a pre-Variscan subduction-collision event. The rich zircon inheritance reveals Neoproterozoic juvenile source and older crustal components represented by Neoarchean to Paleoproterozoic zircons.

Introduction: The study compares two banking systems that have marked and mark the current system in Europe and the Middle East. The Monti di Pietà of 1500 and the Islamic banks which have developed several key features of the past, present the pillars of the Neo-Aristotelian concept of common good. Aim of the work: The study aims to identify the historical, cultural, and accounting factors, similarities, and ethical principles of the two models to identify key ele-ments supporting the common good concept. Methodological approach: This study adopts a historiographical approach that delves into the relationship between narrative, interpretive, and explanatory history, in which it argues that the historical narrative involves elements of interpretation and explanation. Furthermore, a considerable importance is given to the banking environment's political, religious, and regulatory aspects. Main findings: The analysis conducted traces ethical, cultural, and religious components, highlighting many aspects that confirm the starting theory and enrich its conception through financial models that are apparently distant from each other. The study highlights how reciprocity, solidarity, and support for the social fabric of growth have joint agreements and aspects characterizing the two models. Originality: The study provides and integrates significant elements on which the concept of the common good is based.

The metamorphic sole rocks observed between the Pozantı–Karsantı ophiolite and the melange unit are located on the eastern part of the Tauride carbonate platform. They consist of ortho-amphibolites at the top and metasedimentary lithologies at the base. Amphibolites from the metamorphic sole rocks are represented by OIB, MORB and IAT based on their major, trace and REE compositions. The isolated dolerite dykes intrude both the metamorphic sole rocks and the ophiolitic unit at different structural levels. The dolerite dykes cutting the metamorphic sole rocks are enriched in LILE and depleted in HFSE. Enrichment in LILE such as Th, relative to HFSE, is indicative of the presence of a subduction component. Flat-lying REE patterns of the dolerite dykes also confirm an IAT source. Pyroxenite and albitite dykes also cut the metamorphic sole rocks. REE patterns of pyroxenite dykes show prominent LREE enrichment, similar to that observed in within-plate alkaline basalts. The alkaline isolated pyroxenite dykes were probably the result of late-stage magmatism fed by melts that originated from an OIB source, shortly before the emplacement of the Pozantı–Karsantı ophiolite onto the Tauride carbonate platform. A hydrothermal alteration stage is characterized by albitite formation in the joints of the metamorphic sole rocks and by secondary mineralization along the contact zones of dolerite dykes. Mineral parageneses in the metamorphic sole rocks exhibit amphibolite and greenschist-facies assemblages. Geothermobarometric studies based on a newly recognized mineral assemblage (e.g. kyanite) and chemical compositions of minerals in the metamorphic sole rocks indicate that the metamorphic temperature during the metamorphism was 570–580°C and the pressure was around 5–6 kbar.

AbstractCarbonatite magmas are considered to be ultimately derived from mantle sources, which may include lithospheric and asthenospheric reservoirs. Isotopic studies of carbonatite magmatism around the globe have typically suggested that more than one source needs to be invoked for generation of the parental melts to carbonatites, often involving the interaction of asthenosphere and lithosphere.In the rift-related, Proterozoic Gardar Igneous Province of SW Greenland, carbonatite occurs as dykes within the Igaliko Nepheline Syenite Complex, as eruptive rocks and diatremes at Qassiarsuk, as a late plug associated with nepheline syenite at Grønnedal-Íka, and as small bodies associated with ultramafic lamprophyre dykes. The well-known cryolite deposit at Ivittuut was also rich in magmatic carbonate. The carbonatites are derived from the mantle with relatively little crustal contamination, and therefore should provide important information about the mantle sources of Gardar magmas. In particular, they are found intruded both into Archaean and Proterozoic crust, and hence provide a test for the involvement of lithospheric mantle.A synthesis of new and previously published major and trace element, Sr, Nd, C and O isotope data for carbonatites and associated lamprophyres from the Gardar Province is presented. The majority of Gardar carbonatites and lamprophyres have consistent geochemical and isotopic signatures that are similar to those typically found in ocean island basalts. The geochemical characteristics of the two suites of magmas are similar enough to suggest that they were derived from the same mantle source. C and O isotope data are also consistent with a mantle derivation for the carbonatite magmas, and support the theory of a cogenetic origin for the carbonatites and the lamprophyres. The differences between the carbonatites and lamprophyres are considered to represent differing degrees of partial melting of a similar source.We suggest that the ultimate source of these magmas is the asthenospheric mantle, since there is no geochemical or isotopic evidence for their having been derived directly from ancient, enriched sub-continental lithospheric mantle. However, it is likely that the magmas actually formed through a two-stage process, with small-degree volatile-rich partial melts rising from the asthenospheric mantle and being ‘frozen in’ as metasomites, which were then rapidly remobilized during Gardar rifting.

A batholith of around 10,000 km2 was formed during the Hercynian orogeny in the Spanish Central System (SCS). Geochronological data indicate concentrated magmatic activity during the period 325-284 Ma. This late-orogenic magmatism is essentially granitic with only minor associated basic rocks (< 2% in outcrop). The SCS is a remarkably homogeneous batholith showing a restricted range of geochemical granite types without any evolutionary pattern related to time. These peraluminous granites show a limited variation in Na2O/K2O) (0·60-0·95), K/Rb (140-240), (La/Yb)n (6-13), and Eu/Eu* (0·34-0·62) ratios. This constancy in chemical characteristics is also reflected in their isotopic signatures: most monzogranites have initial 87Sr/86Sr ratios in the range of 0·7073-0·71229, initial εNd values vary between —5·4 and —6·6 and δ 18O values group in the restricted range of 8·9-9·6‰. The lack of significant differences among SCS granitoids, maintained during a long geological period, suggests constancy in the nature of their source regions and conditions of magma generation. (1) Limited range of crustal sources: an essentially magmatic recycling during Hercynian orogen is suggested. Mantle-derived components are very limited and restricted to a minor role in the origin of the batholith. Geochemical and isotopic features of SCS granitoids are compatible with felsic lower crustal sources. (2) Constraints in melt conditions: uniformity in residual mineral assemblages (feldspars and garnet are always present in the granulitic residua) combined with a lack of attainment of equilibrium conditions during accessory phase dissolution in the crustal melting process is suggested. Granitic melts never reach saturation in some trace elements (REE, Th, Y, Zr), restricting their chemical variability. (3) Homogenisation in magma chambers: long-lived magmatic systems whose successive pulses accumulate into large magma chambers have the opportunity to mingle, thus reducing source differences.

Calc-alkaline andesitic rocks are a major product of subduction-related magmatism at convergent margins. Where these melts are originated, how long they are stored in the magma chambers, and how they evolved is still a matter of debate. In this study, we present new data of whole-rock elemental and Sr-Nd-Pb isotope compositions, and zircon U-Pb-Th isotopes and trace element contents of Nageng (basaltic-)andesites in the East Kunlun Orogen (NW China). The similar age and whole-rock elemental and Sr-Nd-Pb isotope contents suggest that the Nageng andesite and basaltic andesite are co-magmatic. Their low initial 87Sr/86Sr (0.7084–0.7086) but negative εNd(t) values (−10.61 to −9.49) are consistent with a magma source from the juvenile mafic lower crust, possibly related to the mantle wedge with recycled sediment input. The U-Pb age gap between the zircon core (ca. 248 Ma) and rim (ca. 240 Ma) reveals a protracted magma storage (~8 Myr) prior to the volcanic eruption. When compared to the zircon rims, the zircon cores have higher Ti content and Zr/Hf and Nb/Ta ratios, but lower Hf content and light/heavy rare earth element ratios, which suggests that the parental magma was hotter and less evolved than the basaltic andesite. The plagioclase accumulation likely resulted in Al2O3-enrichment and Fe-depletion, forming the calc-alkaline signature of the Nageng (basaltic-)andesites. The magma temperature, as indicated by the zircon saturation and Ti-in-zircon thermometry, remained low (725–828 °C), and allowed for the magma chamber to survive over ~8 Myr. The decreasing εHf(t) values from zircon core (avg. 0.21, range: −1.28 to 1.32) to rim (avg. −3.68, range: −7.30 to −1.13), together with the presence of some very old xenocrystic zircons (268–856 Ma), suggest that the magma chamber had undergone extensive crustal contamination.

The article traces the process of forming the planning structure of the historical core in the general structure of Moroccan cities. The sequence of development the Medina of Marrakech, the main ele-ments of its planning structure and development by periods is revealed. This study examines the Islamic period with the alternation of ruling dynasties. The general features of the planning of Morocco cities and characteristics of the planning structure of Marrakesh are reflected. There are five identified stages in the development of functional-planning structure of Marrakech, each is characterized by change and addition of the planning structure elements, the increase in perimeter buildings of the Medina, with the inclusion of new elements. The history of construction and transformation of key monuments of architectural heritage and their impact on the general structure of the Medina is considered. The development of the territory and construction of residential areas along the perimeter of the existing Medina led to the emergence of a new contour of the enclosing wall with trade and craft sectors. This is typical for the second and the third period. Further development of the city takes place in the fourth and fifth period through the construction of residential areas outside the Medina (stone walls) and the resettlement of new population. Analysis of the Medina of Marrakesh development allows to reveal its architectural and planning structure, relating it to the type of formation of medieval cities. The considered data can assist to predict the further direction of development the planning structure of the Medina and to prevent its loss and "dissolution" in the city.

SUMMARYThe Repulse Bay block (RBb) of the southern Melville Peninsula, Nunavut, lies within the Rae craton and exposes a large (50,000 km2) area of middle to lower crust. The block is composed of ca. 2.86 Ga and 2.73–2.71 Ga tonalite-trondhjemite-granodiorite (TTG) and granitic gneiss that was derived from an older 3.25 and 3.10 Ga crustal substrate. This period of crustal generation was followed by the emplacement of ca. 2.69–2.66 Ga enderbite, charnockite, and granitoid intrusions with entrained websterite xenoliths. These voluminous batholith-scale bodies (dehydrated and hydrated intrusions), and the associated websterite xenoliths, have similar whole rock geochemical properties, including fractionated light rare earth element (LREE)–heavy (H)REE whole rock patterns and negative Nb, Ti, and Ta anomalies. Dehydrated intrusions and websterite xenoliths also contain similar mineralogy (two pyroxene, biotite, interstitial amphibole) and similar pyroxene trace element compositions. Based on geochemical and mineralogical properties, the two lithologies are interpreted to be related by fractional crystallization, and to be the product of a magmatic cumulate processes. Reworking of the crust in a ca. 2.72 Ga subduction zone setting was followed by ca. 2.69 Ga upwelling of the asthenospheric mantle and the intrusion of massif-type granitoid plutons. Based on a dramatic increase in FeO, Zr, Hf, and LREE content of the most evolved granitoid components from the 2.69–2.66 Ga cumulate intrusion, we propose that those granitoid plutons were in part derived from a metasomatized mantle source enriched by fluids from the subducting oceanic slab that underwent further hybridization (via assimilation) with the crust. Large-scale, mantle-derived Neoarchean sanukitoid-type magmatism played a role in the development of a depleted lower crust and residual sub-continental lithospheric mantle, a crucial element in the preservation of the RBb.RÉSUMÉLe bloc de Repulse Bay (RBb) dans le sud de la péninsule de Melville, au Nunavut, est situé dans le craton de Rae et expose une large zone (50 000 km2) de croûte moyenne à inférieur. Ce bloc est composé de tonalite-trondhjémite-granodiorite (TTG) daté à ca. 2,86 Ga et 2,73–2,71 Ga, et de gneiss granitique dérivé d’un substrat crustal plus ancien daté à 3,25 Ga et 3,10 Ga. Cette période de croissance crustale a été suivie par la mise en place entre ca. 2,69 et 2,66 Ga d’intrusions d’enderbite, charnockite et de granitoïde incluant des xénolites d’entraînement de websterite. Ces intrusions de taille batholitique (intrusions déshydratées et hydratées) ainsi que les xénolites d’entraînement de websterite associés, ont des propriétés géochimiques sur roche totale semblables notamment leurs profils de fractionnement des terres rares légers (LREE) et des terres rares lourds (HREE) ainsi que leurs anomalies négatives en Nb, Ti et Ta. Les intrusions déshydratées et les xénolites de websterite ont aussi des minéralogies similaires (deux pyroxènes, biotite, amphibole interstitielle) ainsi que des compositions semblables en éléments traces de leurs pyroxènes. Étant donné leurs propriétés géochimiques et minéralogiques, ces deux lithologies sont interprétées comme provenant d’une cristallisation fractionnée, et comme étant le produit de processus d'accumulations magmatiques. Le remaniement de la croûte dans un contexte de subduction vers ca. 2,72 Ga, a été suivi vers ca. 2,69 Ga d’une remontée du manteau asthénosphérique et de l’intrusion de granitoïdes de type massif. D'après l’importante augmentation en FeO, Zr, Hf et LREE dans les granitoïdes les plus évolués du magmatisme ayant pris place entre ca. 2,69 Ga et 2,66 Ga, nous proposons que ces plutons aient été en partie dérivés d’une source mantélique métasomatisée enrichies par des fluides d’une plaque océanique en subduction et qui a subi une hybridation supplémentaire (par assimilation) avec la croûte. Le magmatisme néo-archéen de type sanukitoïde, dérivé du manteau et de grande échelle, a joué un rôle dans le développement d’une croûte inférieure et d’un manteau lithosphérique continental résiduel appauvri, un élément déterminant pour la préservation du RBb.

Abstract The 2·08 Ma, ∼2500 km3 Huckleberry Ridge Tuff (HRT) eruption, Yellowstone, generated two fall deposits and three ignimbrite members (A, B, C), accompanying a ∼95 x 65 km caldera collapse. Field data imply that the pre-A fall deposits took weeks to be erupted, then breaks of weeks to months occurred between members A and B, and years to decades between B and C. We present compositional and isotopic data from single silicic clasts (pumice or fiamme) in the three ignimbrite members, plus new data from co-eruptive mafic components to reconstruct the nature and evacuation history of the HRT crustal magmatic complex. Geochemical data, building on field characteristics, are used to group nine silicic clast types into seven compositional suites (A1-A3; B1; C1-C3) within their respective members A, B and C. Isotopic data are then added to define four magmatic systems that were tapped simultaneously and/or sequentially during the eruption. Systems 1 and 2 fed the initial fall deposits and then vented throughout member A, accompanied by trace amounts of mafic magma. In member A, volumetrically dominant system 1 is represented by a rhyolite suite (A1: 73·0–77·7 wt % SiO2, 450–1680 ppm Ba) plus a distinct low-silica rhyolite suite (A2: 69·2–71·6 wt % SiO2, >2500 ppm Ba). System 2 yielded only a low-Ba, high-silica rhyolite suite (A3: 76·7–77·4 wt % SiO2, ≤250 ppm Ba). Glass compositions in pumices from systems 1 and 2 show clustering, indicative of the same multiple melt-dominant bodies identified in the initial fall deposits and earliest ignimbrite. Member B samples define suite B1 (70·7–77·4 wt % SiO2, 540–3040 ppm Ba) derived from magmatic system 1 (but not 2) that had undergone mixing and reorganisation during the A: B time break, accompanying mafic magma inputs. Mafic scoriae erupted in upper member B cover similar compositions to the member A clasts, but extend over a much broader compositional range. Member C clast compositions reflect major changes during the B: C time break, including rejuvenation of magmatic system 2 (last seen in member A) as suite C3 (75·3–77·2 wt % SiO2, 100–410 ppm Ba), plus the appearance of two new suites with strong crustal signatures. Suite C2 is another rhyolite (74·7–77·6 wt % SiO2, with Ba decreasing with silica from 2840 to 470 ppm) that defines magmatic system 3. Suite C2 also shows clustered glass compositions, suggesting that multiple melt-dominant bodies were a repetitive feature of the HRT magmatic complex. Suite C1, in contrast, is dacite to rhyolite (65·6–75·0 wt % SiO2, with Ba increasing with silica from 750 to 1710 ppm) that defines magmatic system 4. Compositions from magmatic systems 1 and 2 dominantly reflect fractional crystallization, but include partial melting of cumulates related to earlier intrusions of the same mafic magmas as those syn-eruptively vented. Country rock assimilation was limited to minor amounts of a more radiogenic (with respect to Sr) evolved contaminant. In contrast, systems 3 and 4 show similar strongly crustal isotopic compositions (despite their differences in elemental composition) consistent with assimilation of Archean rocks via partial melts derived from cumulates associated with contrasting mafic lineages. System 3 links to the same HRT mafic compositions co-erupted in members A and B. In contrast, system 4 links to olivine tholeiite compositions erupted in the Yellowstone area before, sparsely during, and following the HRT itself. All four magmatic systems were housed beneath the HRT caldera area. Systems 1 and 2 were hosted in Archean crust that had been modified by Cretaceous/Eocene magmatism, whereas systems 3 and 4 were hosted within crust that retained Archean isotopic characteristics. The extreme compositional diversity in the HRT highlights the spatial and temporal complexities that can be associated with large-volume silicic magmatism.

Study of petrological and geochemical characteristics of mantle peridotite xenoliths in Pliocene alkaline basalt in Nghia Dan (West Nghe An) was carried out. Rock-forming clinopyroxenes, the major trace element containers, were separated from the xenoliths to analyze for major, trace element and Sr-Nd isotopic compositions. The data were interpreted for source geochemical characteristics and geodynamic processes of the lithospheric mantle beneath the region. The peridotite xenoliths being mostly spinel-lherzolites in composition, are residual entities having been produced following partial melting events of ultramafic rocks in the asthenosphere. They are depleted in trace element abundance and Sr-Nd isotopic composition. Some are even more depleted as compared to mid-ocean ridge mantle xenoliths. Modelled calculation based on trace element abundances and their corresponding solid/liquid distribution coefficients showed that the Nghia Dan mantle xenoliths may be produced of melting degrees from 8 to 12%. Applying various methods for two-pyroxene temperature- pressure estimates, the Nghia Dan mantle xenoliths show ranges of crystallization temperature and pressure, respectively, of 1010-1044°C and 13-14.2 kbar, roughly about 43km. A geotherm constructed for the mantle xenoliths showed a higher geothermal gradient as compared to that of in the western Highlands (Vietnam) and a conductive model, implying a thermal perturbation under the region. The calculated Sm-Nd model ages for the clinopyroxenes yielded 127 and 122 Ma. 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Abstract The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components.

This paper reviews the geological setting and reports new geochemical trace element data from the Ordovician Lawrence Head Volcanics (LHV) and the underlying gabbro sills in the Exploits Group. In combination with existing published analyses and ages of these rocks, the volcanic rocks and sills are indistinguishable in composition and age, and the data are consistent with the hypothesis that they represent the same (mostly E-MORB composition) magmatic event in the early–mid Darriwilian (~465 ± 2 Ma). The LHV and their enclosing strata show regional evidence for: 1) upward decline of volume and grain size of arc-derived volcaniclastic materials over the uppermost interval of turbidite sedimentary strata below the LHV; 2) change to shallow marine conditions locally by the end of the LHV event, followed immediately by significant subsidence, and 3) no evidence of coarse-grained clastic input, nor of normal faulting, during or immediately after LHV magmatism. Ridge–trench interaction (ridge subduction) at a subduction system is consistent with all of these features and spatial distribution of related elements, but a rift (back-arc) origin over a subduction zone can only accommodate the compositions, and is inconsistent with the geological evidence. The Dunnage Mélange (DM) has been interpreted either as olistostromal in a developing back-arc rift basin, or as a subduction accretionary prism. Peraluminous intrusions in the mélange (Coaker Porphyry ― CP) are more readily explained by ridge subduction, and a previously reported zircon age (469 ± 4 Ma) is consistent with the age of the LHV and gabbro sills, also interpreted as products of ridge subduction. Localization of the CP in the eastern area of DM, and of most of the large LHV-derived volcanic blocks in the western DM, suggests a slightly younger age, and perhaps a different mechanism, for the origin of the western DM.SOMMAIRECet article passe en revue le contexte géologique et présente de nouvelles données géochimiques d’éléments traces des roches volcaniques ordoviciennes de Lawrence Head (LHV) et des filons-couches de gabbro sous-jacents du Groupe Exploits. Considérant la combinaison des données d’analyse publiées et des datations de ces roches, les roches volcaniques et les filons-couches sont indiscernables tant en composition qu’en âge, et les données sont compatibles avec l’hypothèse selon laquelle ils représentent le même événement magmatique (principalement E-MORB) du Darriwilien précoce à moyen (~465 ± 2 Ma). Les LHV ainsi que les strates de l’encaissant renferment des indices régionaux qui montrent : 1) que le volume et la granulométrie des matériaux volcanoclastiques d’arc diminuent vers le haut dans l’intervalle supérieur des strates de turbidites sédimentaires sous les LHV; 2) que le changement vers des milieux marins peu profonds localement vers la fin de l’événement des LHV a été suivi immédiatement par une subsidence importante, et 3) qu’il n’existe pas d’indices d’apports clastiques à gros grains, non plus que de formation de failles normales, durant ou immédiatement après le magmatisme des LHV. L’interaction crête-fosse (subduction de la crête) au lieu d’un système de subduction concorde avec toutes ces caractéristiques et la répartition spatiale des éléments reliés, alors qu’une origine de crête (arrière-arc) au-dessus d’une zone de subduction ne peut expliquer que les compositions et qu’elle est incompatible avec l’évidence géologique. Le Dunnage Mélange (DM) a été interprété soit comme un olistostome dans un bassin d’arrière-arc en développement, ou comme un prisme d’accrétion de subduction. Les intrusions hyperalumineuses dans le mélange (Porphyre Coaker — CP), s’explique plus facilement par une subduction de crête, et un âge de datation sur zircon de (469 ± 4 Ma) correspond à l’âge des LHV et des filons-couche de gabbro, aussi interprétés comme produits d’une subduction de crête. La localisation du CP dans la portion orientale du DM, et de la majeure partie des grands blocs volcaniques dérivés des LHV de la portion ouest du DM, suggère un âge légèrement plus jeune, et peut-être un mécanisme différent, pour l’origine de la portion ouest du DM.

(francuski) Le d?veloppement et le renforcement de l'Etat serbe se sont traduits par l'?tablissement de contacts intenses, et sur un vaste plan, tant avec les ?tats voisins qu'avec des contr?es plus ?loign?es, ouvrant ainsi la voie ? de fortes influences originaires du monde byzantin et des pays d'Europe centrale et occidentale. L'id?ologie imp?riale, d'une part, et la culture aulique ainsi que celle fond?e sur les id?aux de la chevalerie, d'autre part, se sont rencontr?es sur le territoire serbe o? leurs traces s'entrem?lent dans la diplomatique, les monnayages mais aussi dans la vie quotidienne. Une de ces traces particuli?res est assur?ment constitu?e par l'apparition et l'emploi de l'h?raldique. De nombreux exemples de blasons repr?sent?s sur des sceaux, des monnaies, des monuments fun?raires, des parures, des v?tements et de la vaisselle r?v?lent l'importance conf?r?e ? l'h?raldique en Serbie m?di?vale o? cet art re?oit une place ? part enti?re sous le r?gne de Stefan Dusan. Cette p?n?tration de l'h?raldique est parfaitement attest?e par le sceau et les monnaies de ce souverain sur lesquels l'image du blason ainsi que les repr?sentations simplifi?es de divers attributs rev?tent un r?le de tout premier plan. Il convient ?galement de mentionner ici la place importante de l'h?raldique parmi les seigneurs de Stefan Dusan, laquelle est attest?e, entre autres monuments, par la dalle fun?raire du vo?vode Nikola Stanjevic ? Konca, la repr?sentation du casque avec lambrequins d'Orest, un des puissants vassaux de l'empereur, visible sur une tour ? Serr?s, une ceinture du s?bastocrator (?) Branko, etc. Tous ces exemples t?moignent de l'instauration d'une culture fond?e sur les id?aux de la chevalerie et aulique ? l'?poque de Stefan Dusan, qui ?tait assur?ment li?e au r?le important jou? par les puissants et l'arm?e. Les changements r?els et profonds alors survenus sont ?galement parfaitement attest?s par l'apposition de symboles h?raldiques sur les monuments fun?raires. Cette pratique a trouv? sa pleine expression sur le monument fun?raire de l'empereur Dusan qui a ?t? rehauss? d'un gisant ? personnification du d?funt rev?tu de tous les attributs du pouvoir corporels et t?moignage de sa puissance, o? cette statue mortuaire est un emprunt propre ? l'Europe occidentale. La p?n?tration des symboles h?raldiques s'est effectu?e sous l'influence importante, voire capitale, des chevaliers et mercenaires allemands recrut?s par la cour de Stefan Dusan, avec ? leur t?te le chevalier Palman. Cette th?se trouve en sa faveur les symboles h?raldiques m?mes relev?s en Serbie, qui, par leur caract?re, appartiennent ? l'h?ritage de l'h?raldique germanique ? teutonique, ainsi que les nombreuses analogies avec les insignes repr?sent?s dans Le r?le d'armes de Zurich dat? vers 1340. Sur la base du mat?riel disponible il reste difficile de dire dans quelle mesure l'h?raldique et l'esprit inspir? de l'id?al de la chevalerie ont p?n?tr? dans les strates inf?rieures de la soci?t?. De nombreux documents, avant tout ?crits, attestent assur?ment toute l'importance alors conf?r?e au blason. Sur la base des monuments conserv?s il est d?j? possible de conclure ? l'existence de certaines r?gles et principes h?raldiques: le blason compos? d'un ?cu orn? d'une ?roue?, d'un casque avec cimier repr?sente par un cousin, une rosette et un plumet, apparaissant sur une monnaie de Stefan Dusan, respectivement la repr?sentation de ces m?mes ?l?ments sans ?cu sur d'autres monnaies mais aussi sur le sceau de ce m?me souverain r?v?lent clairement que les repr?sentations h?raldiques avaient trouv? place dans la symbolique du pouvoir royal, respectivement imp?rial en Serbie m?di?vale. Par ailleurs, l'utilisation d'une symbolique h?raldique reprenant les m?mes embl?mes sur les monnaies de l'empereur Uros, du serviteur Branko, du joupan Nikola Altomanovic, Djuradj 1er Balsic, Vuk Brankovic et Jakov ne fait que confirmer l'importance des repr? sentations h?raldiques chez les dynastes serbes. L'?tape suivante dans le d?veloppement de l'h?raldique est constitu?e par l'apparition de nouveaux symboles h?raldiques li?s ? certaines familles et r?gions, tel que le symbole compos? d'un casque cimier associ? ? une repr?sentation de l'imp?ratrice apparaissant sur des monnaies de l'empereur Uros, de l'imp?ratrice Jelena, du roi Vukasin et de la reine Jelena, symbole que nous trouvons ?galement sur un sceau du roi Vukasin. C'est sous une m?me lumi?re qu'il convient ?galement de voir la marque familiale des Balsic qui sera reprise parmi les seigneurs et petits seigneurs, tout particuli?rement sur le territoire de Kosovo, ? en juger par les nombreuses trouvailles de bagues sceaux sur ce territoire. Une place particuli?re revient aux blasons familiales des Lazarevic ayant pour motif principal un casque avec cornes de veau qui appara?t sur des sceaux et des monnaies du prince Lazar, et qui ? l'?poque de Stefan Lazarevic formera un symbole h?raldique complet associ? ? l'image d'un aigle bic?phale aux ailes d?ploy?es repr?sent? sur un ?cu, des monnaies ou sous forme de cimier sur un casque, sur un sceau. Ce m?me embl?me a ?t? un bref temps gard? par Djuradj Brankovic sur un rare dinar, avant de le remplacer par un ?cu orn? d'une bande diagonale et d'un lys dans chaque champ libre, associ? ?galement ? un casque avec cimier en forme de lion sur un sceau conserv?. D'apr?s ce sceau exceptionnel Lazar Brankovic a adopt? le lion ? embl?me familial ? qui orne l'?cu et le cimier. Durant cette p?riode le r?le de la culture fond?e sur les id?aux de la chevalerie et aulique jouait un r?le significatif comme l'atteste le fait que le despote Stefan ?tait membre de l'ordre de chevalerie du Dragon cr?? par le roi de Hongrie Sigismond et que c'est en cette qualit? et en qualit? de souverain qu'il adoubait des chevaliers. D'apr?s les dires de Konstantin Filozof des ?occidentaux? venaient ? la cour de Serbie pour que le despote les ?couronne? en tant que chevalier. On note dans l'h?raldique serbe m?di?vale le m?lange de deux symboles ? le blason des chevaliers allemands et l'embl?me imp?rial. Le blason repr?sentait un symbole des armes au sens originel de cette notion alors que l'aigle bic?phale ?tait consid?r? comme le symbole du souverain, ?national?. Ce symbole a eu, dans une premi?re p?riode, une signification id?ologique et symbolique ? la base de laquelle se trouvait le rattachement de la dynastie serbe ? la famille byzantine r?gnante. L'aigle bic?phale, ? en juger par ses mod?les iconographiques, a ?volu? en marque du souverain, pour, dans une derni?re phase de son ?volution, ? l'?poque des despotes, recevoir la signification d'un symbole h?raldique. Celui-ci impliquait le droit ? h?riter du tr?ne et de l'empire serbes repr?sent?s par l'image de l'aigle bic?phale embl?me reconnaissable sur la carte d'Angelin Dulcert de 1339 et sur le sceau de Tvrtko 1er. La manifestation parall?le de fortes influences originaires d'Occident et de Byzance se refl?te ?galement dans le mausol?e de Stefan Dusan o? le monument fun?raire de ce souverain, en forme de gisant, c?toyait des fresques ex?cut?es selon le programme et l'iconographie byzantines. Nous retrouvons ?galement cette symbiose sur de nombreuses ?missions mon?taires ? commencer par celles du r?gne de l'empereur Uros avec repr?sentations de symboles h?raldiques d'un c?t? et de l'empereur ? cheval tenant un sceptre de l'autre c?t?, repr?sentation qui peut ind?niablement ?tre li?e ? l'id?ologie imp?riale byzantine. La question se pose de savoir si la Serbie m?di?vale a vu se d?velopper des symboles nationaux ayant pu conduire ? la cr?ation de son propre blason. Les diff?rentes repr?sentations de blasons enregistr?es ? partir du r?gne du roi Dusan, en passant par les dynastes serbes, jusqu'? l'?poque du despote Lazar Brankovic semblent ?tre en faveur du d?veloppement d'une h?raldique familiale, alors que l'id?e d'un symbole national n'a m?ri que progressivement pour recevoir sa pleine forme apr?s la chute du despotat, assur?ment en tant qu'expression d'une aspiration ? la r?alisation du renouveau de l'Etat serbe. Cette id?e ?tait li?e ? l'embl?me de l'aigle bic?phale ? symbole national ? et aux symboles h?raldiques ? embl?mes de l'h?ritage byzantin, europ?en mais aussi serbe.

(francuski) Le but du pr?sent ouvrage est de pr?senter la structure ethnique de la Mac?doine de l'Est dans la p?riode entre 1300 et 1341, et cela en se basant sur les donn?es anthroponymiques. Cette limitation dans le temps et l'espace a ?t? impos?e par les sources elles-m?me, qui sont les praktika (une sorte de registre des cadastres) des monast?res d'Athos, car ils sont les seuls ? avoir ?t? conserv?s. Les monast?res en question avaient eu des propri?t?s dans cette r?gion-l? et c'est uniquement pour cette p?riode qu'ils permettent de suivre continuellement la population dans certains villages. Il faudrait prendre en consid?ration le fait que dans les praktika ?taient recens?s uniquement les par?ques (paysans d?pendants) des monast?res d'Athos dans 65 villages, et non pas la population enti?re de cette r?gion. Parfois un monast?re dans un certain village n'avait qu'un ou deux m?nages de par?ques. Cela signifie que les r?sultats que nous avons obtenus ?taient relatifs. Deuxi?mement, toutes les agglom?rations ne sont pas couvertes par les sources pour toute la p?riode mentionn?e. Rares sont les cas o? pour un village il existe 3-4 praktika ce qui nous permet de suivre sa population dans 2-3 g?n?rations. Le cas le plus fr?quent est lorsqu'il n'existe qu'un seul praktika ce qui nous permet uniquement de constater dans quelle circonstance avait apparu le praktika, mais pas de suivre les changements ?ventuels dans la structure de la population. ?galement, il faudrait tenir compte du fait que c'est uniquement la population paysanne qui a ?t? recens?e. Dans la majorit? des praktika, les m?nages de par?ques sont d?crit en d?tail, quant aux par?ques eux-m?me, ils sont identifi?s de mani?re diff?rente, le plus souvent d'apr?s leur nom individuel ou d'apr?s une autre caract?ristique comme par exemple un surnom, une profession compl?mentaire une origine ethnique, lieu d'o? la personne ?tait venue, relation familiale par rapport ? une autre personne. Ces moyens d'identification nous pr?sentent des donn?es pr?cieuses sur la soci?t? rurale et sur les professions compl?mentaires exerc?es par les paysans (il s'agit le plus souvent de m?tiers et plus exactement le m?tier de cordonnier, de forgeron et de potelier), sur les rapports entre les gens, les conditions mat?rielles, les migrations, la langue utilis?e par la population... Afin d'?tudier la structure ethnique d'apr?s l'anthroponymie, il fallait avant tout classifier les pr?noms. En effectuant cela, nous nous sommes confront?s ? plusieurs probl?mes. Il arrive parfois que dans la litt?rature scientifique que nous avons consult?e, on donne des interpr?tations compl?tement diff?rentes des pr?noms que nous avons rencontr?s, c'est pourquoi, nous avons d? juger de nous-m?me assez souvent. Tout en nous basant avant tout sur l'?tymologie mais ?galement sur l'observation de la situation sur le terrain. Par exemple si pour un pr?nom ou un mot on suppose qu'il est d'origine slave, nous nous sommes efforc?s de d?finir si ce nom apparaissait plus souvent dans un milieu o? il y a des Slaves. Les listes des noms et surnoms sont aussi donn?es afin que nos conclusions puissent ?tre contr?l?es. Certains des probl?mes sont originaires des recenseurs eux-m?mes. Ils ?taient Grecs et certains d'entre-eux ne savaient pas transcrire correctement les pr?noms et les surnoms non-grecs. Cela est particuli?rement valable pour les sons qui n'existent pas dans la langue grecque. Parfois ils hell?nisent les pr?noms non-grecs et leur donnent un sens qu'ils n'avaient pas. Par exemple: le surnom slave Stur (St?nr?z) est transcris d'une mani?re incorrecte en tant que surnom grec Zgur (Sgsyr?z). Derri?re ces formes aussi modifi?es il est impossible de reconna?tre la forme v?ritable sauf s'il existe des s?ries praktika qui permettent que les donn?es soient compar?es. Pourtant, la classification m?me des pr?noms ne suffit pas pour aboutir ? des conclusions fiables sur l'appartenance ethnique de leur porteurs. N?anmoins, le plus grand nombre repr?sentent les pr?noms du calendrier qui n'indiquent rien sur l'appartenance ethnique, ? moins que des variations populaires de ces pr?noms ne soient utilis?es (par ex. Joanakis ou Joanikije au lieu de Jovan chez les Grecs ou Ivan, Ivanko Janko chez les Slaves) et ceci est extr?mement rare. Les plus pr?cieux sont les pr?noms populaires. Mais, l? aussi il faut ?tre tr?s vigilant. En g?n?ral, si quelqu'un porte un pr?nom slave, il est Slave. Cependant, il arrivait souvent que ce pr?nom devienne un nom patronymique et soit ainsi transmis ? travers les g?n?rations, quant ? la famille, elle s'hell?nisait entre-temps. Nous sommes arriv?s ? la conclusion que l? o? les noms individuels apparaissent au moins dans deux g?n?rations, il s'agissait s?rement des Slaves pop-hell?nis?s (qui parlent le slave). Au cas o? les descendants des Slaves portent des noms individuels grecs, nous avons de bonnes raisons ? douter qu'il s'agisse d'une hell?nisation (qui est du moins entam?e, ce qui ne veut pas dire qu'elle ait aboutit ? une fin). Les surnoms sont nombreux et vari?s. Ils peuvent nous ?tre d'une grande utilit? dans la d?termination de l'appartenance ethnique de quelqu'un. Vu que la majorit? de par?ques porte des pr?noms eccl?siastiques c'est-?-dire neutres, comme nous les avons nomm?s pour les besoins de notre ouvrage, les surnoms sont particuli?rement pr?cieux lorsque nous rencontrons ce genre de situations. N?anmoins, l'existence de surnoms slaves nous montre que dans le milieu o? ils apparaissent, la langue slave est comprise et parl?e, alors que le grec nous indique que le grec est compris et parl?. En principe, celui qui porte un surnom slave est le plus souvent Slave. Cependant, l'existence de ce genre de surnom n'exclut pas Fhell?nisation. Il existe une autre difficult? qui est que les membres d'un groupe ethnique peuvent avoir un surnom dans la langue de l'autre peuple avec lequel le plus souvent ils cohabitent. Il existe plusieurs cas o? les Slaves pour lesquels nous sommes certains qu'ils sont Slaves, car les membres de leur famille portent des noms individuels slaves ont un surnom grec. L'analyse a montr? que ce genre de cas se rencontrent dans les r?gions bilingues o? ce surnom avait ?t? compr?hensible aux membres des deux ethnies. C'est pourquoi, les surnoms, en tant qu'indices de l'appartenance ethnique ne peuvent en aucun cas ?tre utilis?s individuellement, mais uniquement en combinaison avec d'autres donn?es. Les r?sultats auquels nous sommes parvenus sont les suivants. La Mac?doine de l'est ?tait au XIVe si?cle une r?gion encore ethniquement h?t?rog?ne ce qui ne fait que confirmer les r?sultats des autres chercheurs. Pourtant, la question de la structure ethnique est r?duite ? la question des relations entre Grecs et Slaves. Les autres peuples qui se rencontrent, et qui sont les Latins, les Valaches, divers peuples turcs, les Albanais, les Arm?niens les Rom et m?me un Juif et une famille hongroise, ils forment tous une minorit? g?n?ralement d?j? assimil?e. Dans la moyenne, les pr?noms et surnoms slaves se manifestent dans un peu plus d'un quart de familles recens?es. Cela ne veut pas dire que les Slaves pop-hell?nis?s repr?sentaient r?ellement une partie si importante de la population de l'est de la Mac?doine, car leur pr?noms et surnoms se transformaient parfois en nom de famille et ?taient ainsi conserv?s m?me apr?s que la famille se soit hell?nis?e. D'autre part il faut prendre en consid?ration qu'un certain nombre de Slaves se dissimulait derri?re des pr?noms eccl?siastiques et c'est pourquoi il est rest? pour nous imperceptible. Donc, les donn?es statistiques pr?sentent uniquement une image relative de la r?alit?, mais elles sont donn?es dans l'ouvrage car il a ?t? n?cessaire de donner un certain rapport num?rique de la pr?sence des Grecs et des Slaves. La pr?sence de la population slave dans la Mac?doine de l'Est n'est pas proportionn?e. On observe plusieurs r?gions qui se distinguent par la pr?sence des Slaves ? leur sein, c'est pourquoi nous les avons analys?s individuellement. La Chalcidique est une r?gion o? le nombre de Slaves, dans la p?riode depuis le d?but du XIVe si?cle jusqu'en 1341 ?tait consid?rable. En moyenne, leurs pr?noms et surnoms se manifestent dans environ 25% de m?nages ce qui, statistiquement parlant, nous indique que les Slaves repr?sentait un quart de la Chalcidique, qu'il s'agisse des Slaves qui avait encore gard? leurs caract?ristiques ethniques, ou qu'il s'agisse de ceux qui se sont hell?nis?s mais qui ont gard? leur noms individuels ou leurs surnoms slaves en tant que noms de famille. Lorsque l'on effectue une coupe dans le temps de la pr?sence des pr?noms et surnoms slaves, il est ?vident que le nombre de Slaves en Chalcidiques diminue sans cesse. De 35,98% combien il y en avait au d?but du XIVe si?cle, leur nombre jusqu'aux ann?es vingt avait diminu? et repr?sentait 20,81% et le d?croissement continuait jusqu'? 1341 lorsqu'ils apparaissent dans uniquement 13,69% de m?nages. Dans cette m?me p?riode, on distingue une hausse du nombre de m?nages portant des pr?noms grecs, ainsi qu'une baisse de m?nages portant des pr?noms mixtes c'est-?-dire avec des pr?noms populaires d'au moins deux peuples, dans ce cas-l?, le plus souvent grec et slave. Nous pensons que dans ce ph?nom?ne se cache l'explication de la diminution du nombre de familles portant des pr?noms slaves. N?anmoins, comme les mariages mixtes ?tait une chose fr?quente, avec le temps, dans ces couples dominait l'influence grecque ce qui est tout ? fait compr?hensible, ?tant donn? que les Grecs, comme on peut le remarquer sur le tableau 3, d?j? au d?but du si?cle ?taient dominants. En plus du fait que l'on remarque que le nombre de Slaves est en baisse continue, on remarque que leur pr?sence n'?tait pas partout la m?me. En relation avec cela, il existe de nombreuses diff?rences entre la Chalcidique de l'Ouest et de l'Est. En g?n?ral, pour la Chalcidique de l'Ouest on pourrait dire que le nombre de Slaves, plus exactement, les familles portant des pr?noms et surnoms slaves est petit. Statistiquement observant, ce nombre s'?l?ve ? environ 13% et reste stable pour toute la p?riode de 1301 jusqu'? 1341. Cependant, dans certains endroits comme par exemple Epan?-Bolbos Skyloch?rion, N?akitou ainsi que d'autres endroits, ils n'apparaissent pas du tout. M?me dans les endroits o? il y en avait dans un nombre consid?rablement plus grand que la moyenne, comme c'est le cas avec Sainte-Euph?mie, nous sommes les t?moins de leur disparition ? la suite de l'hell?nisation compl?t?e. Deux autres faits t?moignent de la fin du processus d'hell?nisation des Slaves dans la Chalcidique de l'Ouest. Le premier fait est que dans la majorit? des cas o? nous rencontrons des pr?noms ou surnoms slaves, ils apparaissent en fonction de noms fig?s et sont port?s par des personnes aux pr?noms eccl?siastiques voire m?me grecs alors qu'il y a tr?s peu de noms individuels slaves. Deuxi?mement, l? o? les pr?noms slaves apparaissent comme noms individuels, ils sont le plus souvent port?s par des immigrants, dont certains d'entre eux sont devenus les gendres dans certaines familles grecques autochtones. En Chalcidique de l'Est il y avait consid?rablemet plus de Slaves que dans la partie ouest de la p?ninsule. En moyenne, les pr?noms slaves apparaissent dans un tiers de m?nages. Pourtant si nous observons chronologiquement les sources, nous nous apercevons que le nombre de Slaves est en baisse continue. De 38,29% combien ils ?taient au d?but du si?cle, leur nombre baisse ? environ 30% dans les ann?es vingt du XIVe si?cle pour ensuite baisser ? seulement 14,49% en 1338-1341. Ce dernier r?sultat est ? prendre avec r?serve. N?anmoins pour les ?tapes pr?c?dentes nous disposons de dix fois plus de donn?es que pour la derni?re ?tape. C'est pourquoi nous estimons que le r?sultat obtenu est, au moins partiellement, la cons?quence de la nature fragmentaire des sources, et qu'il y aurait pu ?tre beaucoup plus de Slaves. Ici, les Slaves ?taient encore rest?s en tant que groupe ethnique solide. L'hell?nisation ?tait ici aussi entam?e, mais elle n'a pas ?t? compl?t?e. Ce qui caract?rise en g?n?ral cette r?gion, c'est l'importante mixit? ethnique de la population, la coexistence et le bilinguisme. Cependant, la situation varie d'un village ? un autre. Il y en a de ceux o? les pr?noms et les surnoms slaves se manifestent uniquement en fonction de patronymes, alors qu'aucun membre de la communaut? ne porte un pr?nom slave en tant que nom individuel ce qui t?moigne du fait que les Slaves, autrefois, dans un pass? pas si lointain, ?taient pr?sents, l?, mais qu'une hell?nisation a ?t? effectu?e comme c'est le cas avec Hi?rissos et Gomatou. Il y en a aussi o? le nombre de Slaves est important mais qui dimunue avec le temps ce qui indique que l'hell?nisation est en cours comme ? Kozla. Certains villages indiquent un haut pourcentage de population slave comme Gradista, Simeon et S?lada, mais on y rencontre pourtant des traces d'hell?nisation. Dans d'autre, n?anmoins le nombre de Slaves augmente: ? Kontogrikon et ? M?tallin.Ce qui peut aussi ?tre observ? c'est qu'une si grande pr?sence de Slaves pourrait ?tre expliqu?e non seulement par leur r?sistance vis-?-vis de l'hell?nisation mais aussi par leur migrations r?centes dans ces r?gions-l?, ce qui signifie qu'ici nous ne rencontrons pas uniquement les descendants des Anciens Slaves, c'est-?-dire ceux qui ?taient venus dans ces r?gions d?j? au septi?me si?cle, mais aussi que la communaut? ethnique slave ?tait renforc?e avec l'arriv?e des nouveaux Slaves. Dans la r?gion de Strymon, on distingue plusieurs r?gions caract?ristiques. La premi?re r?gion est la vall?e de Strimona pour laquelle on pourrait dire la m?me chose que pour la Chalcidique de l'Ouest, c'est pour cela que nous ne r?p?terons pas les r?sultats ? cet endroit-l?. La deuxi?me est la r?gion montagneuse de Kerdylion et Bolb?. Malheureusement, pour cette r?gion nous disposons uniquement de donn?es pour les dix premi?res ann?es du XIVe si?cle. En g?n?ral, on pourrait dire pour elle que le nombre de Slaves est ?lev?. Leur pr?sence correspond ? celle de la Chalcidique de l'Est, elle est m?me quelque peu plus importante. Malgr? l'hell?nisation qui s'?coule en toute ?vidence, leur nombre est relativement stable. Le fait qu'en 1318-1321, les pr?noms populaires slaves se rencontrent seuls dans plus de 20% de m?nages nous indique qu'au moins un cinqui?me de la population devait ?tre slave et pop-hell?nis?e. Le nombre de mariages mixtes est important. On parle les deux langues, le slave et le grec. Cependant, ceci est valable uniquement pour une p?riode de vingt ans, de 1301 jusqu'? 1321. Malheureusement, les sources ne nous permettent pas de suivre ce qui se passait plus tard avec la population de ces villages-l?. La troisi?me province est la r?gion du mont de Pang?e qui est caract?ris?e par une forte pr?sence de Slaves. Ils repr?sentaient presque la moiti? de la population de cette r?gion. Dans certains villages il y en avait m?me beaucoup plus par exemple ? Boriskos en 1316, dans certains villages ils ?taient plus nombreux que les pr?noms purement grecs comme dans le m?toque de Saint-Pent?l??im?n et Ob?los. Les pr?noms slaves se rencontrent comme noms individuels, c'est-?-dire pr?noms vivants, et non pas comme des mots slaves fig?s en fonction des noms patronymiques. Sur l'existence de l'?l?ment slave nous parlent non seulement les nombreux cas que les descendants des Slaves portent des pr?noms slaves mais il y a aussi de nombreux cas o? les enfants issus de mariages mixtes gr?co-slave portent ?galement des pr?noms slaves. Ceci d?montre que dans ces mariages-l? il n'y avait pas la domination de l'?l?ment grec, ou du moins pas tout de suite. Nous sommes les t?moins que les enfants de parents aux pr?noms grecs portent parfois des pr?noms slaves. Ceci pourrait signifier que m?me l? o? l'on donnait des pr?noms grecs aux Slaves, ces derniers n'ont pas ?t? automatiquement hell?nis?s, mais vu qu'entour?s d'une importante population slave, ils r?ussissaient ? conserver encore leurs caract?ristiques ethniques ainsi que le fait qu'ils ?taient hell?nis?s tr?s difficilement et lentement. Ils s'?taient maintenus ici en tant qu'?l?ment ethnique extr?mement fort et ils n'ont pas ?t? hell?nis?s jusqu'? l'arriv?e des Turques. Les exemples de villages de Dobrobikeia et Ob?los le montrent tr?s bien, ces villages ?taient d?plac?s ? la suite d'attaques turques dans la p?riode entre 1316 jusqu'? 1341. En g?n?ral, on pourrait y ajouter encore que la population slave s'est beaucoup mieux maintenue dans les r?gions montagneuses que dans les r?gions maritimes et dans les plaines. On pourrait dire que la Mac?doine de l'Est ?tait une r?gion interm?diaire entre les provinces slaves du nord et les provinces grecques du sud. Il est imp?ratif d'ajouter que la mixit? de la population est grande et que tout partage en population purement grecque ou purement slave pourrait ?tre artificiel. On peut facilement remarquer dans les sources que les habitants de certaines r?gions et agglom?rations comprenaient les deux langues et que le nombre de mariages mixtes ?tait consid?rable. Il y avait des familles qui contenaient voire m?me trois ?l?ments ethniques. Le bilinguisme et la coexistence ?taient chose commune c'est pourquoi nous pensons qu'ils repr?sentent m?me le principal facteur d'hell?nisation ?tant donn? qu'avec le temps, il y a eu une domination de l'?l?ment ethnique grec m?me dans les milieux caract?ris?s par une forte pr?sence des Slaves.

Abstract Besides standard thermo-mechanical conservation laws, a general description of mantle magmatism requires the simultaneous consideration of phase changes (e.g. from solid to liquid), chemical reactions (i.e. exchange of chemical components) and multiple dynamic phases (e.g. liquid percolating through a deforming matrix). Typically, these processes evolve at different rates, over multiple spatial scales and exhibit complex feedback loops and disequilibrium features. Partially as a result of these complexities, integrated descriptions of the thermal, mechanical and chemical evolution of mantle magmatism have been challenging for numerical models. Here we present a conceptual and numerical model that provides a versatile platform to study the dynamics and nonlinear feedbacks inherent in mantle magmatism and to make quantitative comparisons between petrological and geochemical datasets. Our model is based on the combination of three main modules: (1) a Two-Phase, Multi-Component, Reactive Transport module that describes how liquids and solids evolve in space and time; (2) a melting formalism, called Dynamic Disequilibirum Melting, based on thermodynamic grounds and capable of describing the chemical exchange of major elements between phases in disequilibrium; (3) a grain-scale model for diffusion-controlled trace-element mass transfer. We illustrate some of the benefits of the model by analyzing both major and trace elements during mantle magmatism in a mid-ocean ridge-like context. We systematically explore the effects of mantle potential temperature, upwelling velocity, degree of equilibrium and hetererogeneous sources on the compositional variability of melts and residual peridotites. Our model not only reproduces the main thermo-chemical features of decompression melting but also predicts counter-intuitive differentiation trends as a consequence of phase changes and transport occurring in disequilibrium. These include a negative correlation between Na2O and FeO in melts generated at the same Tp and the continued increase of the melt’s CaO/Al2O3 after Cpx exhaustion. Our model results also emphasize the role of disequilibrium arising from diffusion for the interpretation of trace-element signatures. The latter is shown to be able to reconcile the major- and trace-element compositions of abyssal peridotites with field evidence indicating extensive reaction between peridotites and melts. The combination of chemical disequilibrium of major elements and sluggish diffusion of trace elements may also result in weakened middle rare earth to heavy rare earth depletion comparable with the effect of residual garnet in mid-ocean ridge basalt, despite its absence in the modelled melts source. We also find that the crystallization of basalts ascending in disequilibrium through the asthenospheric mantle could be responsible for the formation of olivine gabbros and wehrlites that are observed in the deep sections of ophiolites. The presented framework is general and readily extendable to accommodate additional processes of geological relevance (e.g. melting in the presence of volatiles and/or of complex heterogeneous sources, refertilization of the lithospheric mantle, magma channelization and shallow processes) and the implementation of other geochemical and isotopic proxies. Here we illustrate the effect of heterogeneous sources on the thermo-mechanical-chemical evolution of melts and residues using a mixed peridotite–pyroxenite source.

The bimodal Wichita igneous province (WIP) represents the only exposed Ediacaran to Cambrian anorogenic magmatic assemblage present along the buried southern margin of Laurentia and was emplaced during rifting in the Southern Oklahoma Aulacogen prior to Cambrian opening of the southern Iapetus Ocean. Here, we establish the first high-precision U-Pb zircon geochronological framework for the province. Weighted mean 206Pb/238U dates from mafic and felsic rocks in the Wichita Mountains indicate emplacement in a narrow time frame from 532.49 ± 0.12 Ma to 530.23 ± 0.14 Ma. Rhyolite lavas in the Arbuckle Mountains farther east yield weighted mean 206Pb/238U dates of 539.20 ± 0.15 Ma and 539.46 ± 0.13 Ma. These dates for the WIP indicate that magmatism in the Southern Oklahoma Aulacogen postdated the ca. 540 Ma rift-drift transition along the Appalachian margin to the east. Wholerock trace-element and isotopic geochemistry, supplemented by trace elements in zircon, tracks the evolution of magma sources during WIP petrogenesis. These data indicate that initial melting and assimilation of subcontinental mantle lithosphere by an uprising mantle plume were followed by increasing involvement of asthenospheric melts with time. We suggest that upwelling of this plume in the area of the Southern Oklahoma Aulacogen triggered an inboard jump of the spreading center active along the eastern margin of Laurentia, which led to separation of the Precordillera terrane (now located in Argentina) from the Ouachita embayment present in the southern Laurentian margin.