Articles de revues : « Calc-alkaline magmatism »

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Hernandez, Jean, Francois Dominique de Larouziere, Jean Bolze et Pierre Bordet. « Le magmatisme neogene betico-rifain et le couloir de decrochement trans-Alboran ». Bulletin de la Société Géologique de France III, n^o 2 (1 mars 1987) : 257–67. http://dx.doi.org/10.2113/gssgfbull.iii.2.257.

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Abstract The Miocene basin evolution of southeastern Spain and eastern Morocco is linked to a "shear zone" elongated from SW across the Alboran Sea. In Spain the magmatism is mostly calc-alkaline (or K-rich calc-alkaline). Most of the products are locatred on strike-slip faults (Almeria-Cabo de Gata). Lavas of dacitic compositions are interpreted as products of crustal anatexis. During Messinian time, lamproites are erupted over an extended area. Later (Plio-Quaternary), alkali basalts are located near Cartagena. In Morocco, calc-alkaline magmatism is not as developed as in Spain; late Tortonian-Messinian volcanoes (Gourougou, Guilliz) have erupted of shoshonitic lavas. Alkali basalts are abundant and appear from the end of Messinian to Quaternary all over northwestern Africa. In the studied area, there are no chronological nor geochemical polarity of the magmatism according to the existence of a Miocene subduction. The association of the magmatism with tectonics and basin evolution shows that it is linked with their aperture. The structure of the lithosphere, as it appears from the geophysical data, shows the existence of two different crusts, separated by the western part of the "shear zone". Trans-Alboran calc-alkaline magmatism is clearly correlated with the activity of this "shear zone", from Miocene to present time.

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Homonnay, Emmanuelle, Jean-Marc Lardeaux, Michel Corsini, Asmae El Bakili, Delphine Bosch, Olivier Bruguier et Mohamed Ouazzani-Touhami. « Arc-related high-K magmatism in the Ceuta Peninsula (Internal Rif, Spain) : discovery and consequences ». Geological Magazine 156, n^o 08 (30 octobre 2018) : 1385–99. http://dx.doi.org/10.1017/s0016756818000717.

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AbstractWe document the occurrence of micro-diorite magmatic sills, with magmatic enclaves, in the Ceuta Peninsula within metapelites from the Lower Sebtides units (Internal Rif). All magmatic rocks show a primary magmatic mineralogy and geochemical signature diagnostic for high-K calc-alkaline to shoshonitic island arc magmatism. Moreover, these rocks are significantly affected by secondary metamorphic transformations under greenschist- to amphibolite-facies conditions, regionally dated atc. 21 Ma. Geometric relationships between the sills and the main regional foliation, developed under intermediate-pressure granulite-facies conditions atc. 28 Ma, demonstrate that the sills emplaced during the late stage of this main tectonic event. New U–Pbin situanalyses of monazite performed on the micro-diorite sills provide an age of 20.64 ± 0.19 Ma, coherent with this chronological framework and interpreted as the age of greenschist-facies re-equilibration. The discovery of pre-Miocene high-K calc-alkaline to shoshonitic arc-related magmatism is clearly consistent with the subduction context proposed for the Alboran Basin evolution, according to geophysical investigations. In this framework, the Lower Sebtides units could be considered as part of the upper plate of the subduction system, while the Upper Sebtides must be regarded as the lower subducted plate.

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Goulart, Luís Emanoel Alexandre, et Mauricio Antonio Carneiro. « Evolution of arc magmatism in the Carmópolis de Minas Layered Suite, Minas Gerais, Brazil : Sm-Nd and Rb-Sr isotope geochemistry ». Rem : Revista Escola de Minas 66, n^o 4 (décembre 2013) : 447–54. http://dx.doi.org/10.1590/s0370-44672013000400007.

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The Carmópolis de Minas Layered Suite (CMLS) is a Neoarchean Unit metamorphosed at amphibolite- to granulite-facies conditions, comprised of metaultramafic rocks, amphibolites and metarhyolites. The CMLS is marked by two distinct phases of tholeiitic and calc-alkaline magmatism. Previous geochemical data and regional constraints suggest that the CMLS is possibly a metamorphosed arc-tholeiitic suite of the type boninite-basalt-andesite-rhyolite, interpreted in this study as a dismembered remnant of the juvenile oceanic arc. The rocks of tholeiitic affinity record a signature of depleted to enriched mantle with positive to weakly negative εNd(t) and predominantly positive εSr(t) values, indicating some degree of crustal assimilation. The rocks of calc-alkaline affinity present a signature of juvenile crust with εNd(t) close to the CHUR and weakly positive εSr(t) values. The Sm-Nd isochron age of 2736 ± 300 Ma obtained with εNd(i) = +0.4, suggests the edification of an intra-oceanic arc during the late phases of the Rio das Velhas Tectonothermal Event. The arc evolution involved tholeiitic magmatism in the early stages in association with calc-alkaline magmatism, of probably anatectic character, in the tardy-orogenic stages.

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Widana, Kurnia Setiawan, et Bambang Priadi. « Karakteristik Unsur Jejak Dalam Diskriminasi Magmatisme Granitoid Pulau Bangka ». EKSPLORIUM 36, n^o 1 (30 mai 2015) : 1. http://dx.doi.org/10.17146/eksplorium.2015.36.1.2766.

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Geologi Pulau Bangka disusun oleh variasi granit sebagai Granitoid Klabat yang tersebar di berbagai lokasi. Unsur jejak dapat diaplikasikan dalam diskriminasi magmatisme dalam pembentukan granitoid tersebut. Tujuan penelitian ini adalah mengetahui karakteristik granitoid yang tersebar di Pulau Bangka berdasarkan geokimia unsur jejak untuk diaplikasikan dalam mempelajari magmatisme, sumber dan situasi tektoniknya.Metode analisis geokimia yang diaplikasikan dengan menggunakan Analisis Aktivasi Neutron (AAN) dan portableX-Ray Fluorescence (pXRF) untuk analisis kualitatif dan kuantitatif pada 27 sampel dari Granitoid Klabat di Pulau Bangka.Hasil penelitian ini menyimpulkan Granitoid Bangka Utara (Belinyu) dan Bangka Tengah sebagai percampuran kerak-mantel dengan afinitas Calc-Alkaline, karakteristik Tipe I sedangkan Granitoid Bangka Selatan dan Barat asal kerak dengan afinitas High-KCalc-Alkaline sebagai Tipe S. Diharapkan diskrimasi magmatisme granitoid bermanfaat dalam memberikan panduan eksplorasi bahan galian nuklir di Pulau Bangka. Geology of Bangka Island consists by variation of granite as Klabat Granitoid scattered in various locations. Trace elements can be applied in magmatism discrimination of granitoid.The purpose of this study was to determine the characteristics Bangka Island granitoid based on trace element geochemistry to be applied in the study of magmatism, source and tectonic situation. Geochemical analyses method used are the Neutron Activation Analysis (NAA) and portableX-Ray Fluorescence (pXRF) for qualitative and quantitative analyses on 27 samples of Klabat granitoid on Bangka Island. This study concluded granitoid East Bangka (Belinyu) and Central Bangka as crust-mantle mixing with affinityCalc-Alkaline, characteristic of I Type while South and West Bangka granitoid crust origin with affinity high K Calc-Alkaline as S Type. Expectedmagmatismdiscrimination ofgranitoidhelpfulin providingradioactive mineral explorationguidein BangkaIsland.

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Cambeses, Aitor, José F. Molina, Irene Morales, Concepción Lázaro, Juan A. Moreno, Pilar Montero et Fernando Bea. « Compositional Evolution of the Variscan Intra-Orogenic Extensional Magmatism in the Valencia del Ventoso Plutonic Complex, Ossa-Morena Zone (SW Iberia) : A View from Amphibole Compositional Relationships ». Minerals 11, n^o 4 (18 avril 2021) : 431. http://dx.doi.org/10.3390/min11040431.

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The Ossa-Morena Zone (OMZ), SW Iberia, has numerous Lower Carboniferous compositionally zoned plutons that formed in a Variscan intra-orogenic extensional setting. This magmatism shows a wide compositional variation comprising alkaline, transitional, and calc-alkaline suites. The calc-alkaline suite was produced by hybridization of alkaline magmas with felsic melts generated by crustal anatexis related to the intrusion of mafic magmas in the middle crust. In this work, we present a textural and mineralogical study of the Variscan Valencia del Ventoso main pluton from the OMZ to track the compositional evolution of magmas during hybridization using constraints from amphibole compositions and to determine the P-T conditions of emplacement using amphibole-based thermobarometry. This pluton exhibits reverse zoning with an inner facies containing alkaline dolerites, gabbros, and quartz diorites, an intermediate facies with transitional diorites, and an outer facies with calc-alkaline quartz diorites to monzogranites. Magmas from the intermediate and border facies crystallized under oxidizing conditions at relatively low temperatures (range: 640–760 °C) and ca. 280–300 MPa, implying near H2O-saturated conditions. These rock facies show mineralogical evidence of hybridization between alkaline to mildly alkalic and calc-alkaline magmas. The former is inferred from the occurrence of antecrysts of labradorite-andesine, high-Ti pargasite-hastingsite, and biotite with deficiency in tetrahedral-site occupancy, a distinctive feature of biotite from the inner facies alkaline dolerites. This contrasts with later crystallization from the calc-alkaline magma of andesine-oligoclase, low-Ti magnesiohornblende-edenite, and biotite with full tetrahedral-site occupancy. Constraints from amphibole-melt compositional relationships in antecrystic high-Ti amphibole suggest that the alkaline magmatic component could have a high- to ultra-K affinity.

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İLBEYLİ, N. « Mineralogical–geochemical constraints on intrusives in central Anatolia, Turkey : tectono-magmatic evolution and characteristics of mantle source ». Geological Magazine 142, n^o 2 (mars 2005) : 187–207. http://dx.doi.org/10.1017/s0016756805000476.

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Collision-related rocks intrude metamorphic rocks overthrust by ophiolitic units to make up the Central Anatolian Crystalline Complex. A wide variety of rock types were produced by the latest Cretaceous magmatism in the complex. These rocks can be divided into three distinct units: (1) calc-alkaline (Ağaçören, Behrekdağ, Cefalıkdağ, Çelebi, Ekecikdağ, Halaçlı, Karamadazı, Kösefakılı, Terlemez, Üçkapılı, Yozgat); (2) sub-alkaline (Baranadağ); and (3) alkaline (Atdere, Davulalan, Eğrialan, Hamit, İdişdağı, Karaçayır). The calc-alkaline rocks are metaluminous/peraluminous I- to S-type plutons ranging from monzodiorite to granite. The sub-alkaline rocks are metaluminous I-type plutons ranging from monzonite to granite. The alkaline rocks are metaluminous to peralkaline plutons, predominantly A-type, ranging from foid-bearing monzosyenite to granite. These plutons crystallized under varying pressures (5.3–2.6 kbar) and a wide range of temperatures (858–698 °C) from highly oxidized magmas (log fO2 −17 to −12). All intrusive rocks display enrichment in LILE and LREE compare to HFSE and have high 87Sr/86Sr and low 143Nd/144Nd ratios. These characteristics indicate that these rocks are derived from a mantle source containing large subduction components, and have experienced assimilation coupled with fractional crystallization (AFC) during uprise through crust. The coexistence of calc-alkaline and alkaline magmatism in the complex may be ascribed to mantle source heterogeneity before collision. Either thermal perturbation of the metasomatized lithosphere by delamination of the thermal boundary layer or removal of a subducted plate (slab breakoff) are the likely mechanisms for the initiation of the collision-related magmatism in the complex.

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Aarons, Sarah M., Jesse R. Reimink, Nicolas D. Greber, Andy W. Heard, Zhe Zhang et Nicolas Dauphas. « Titanium isotopes constrain a magmatic transition at the Hadean-Archean boundary in the Acasta Gneiss Complex ». Science Advances 6, n^o 50 (décembre 2020) : eabc9959. http://dx.doi.org/10.1126/sciadv.abc9959.

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Plate subduction greatly influences the physical and chemical characteristics of Earth’s surface and deep interior, yet the timing of its initiation is debated because of the paucity of exposed rocks from Earth’s early history. We show that the titanium isotopic composition of orthogneisses from the Acasta Gneiss Complex spanning the Hadean to Eoarchean transition falls on two distinct magmatic differentiation trends. Hadean tonalitic gneisses show titanium isotopic compositions comparable to modern evolved tholeiitic magmas, formed by differentiation of dry parental magmas in plume settings. Younger Eoarchean granitoid gneisses have titanium isotopic compositions comparable to modern calc-alkaline magmas produced in convergent arcs. Our data therefore document a shift from tholeiitic- to calc-alkaline–style magmatism between 4.02 and 3.75 billion years (Ga) in the Slave craton.

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AGHAZADEH, MEHRAJ, ANTONIO CASTRO, ZAHRA BADRZADEH et KATHARINA VOGT. « Post-collisional polycyclic plutonism from the Zagros hinterland : the Shaivar Dagh plutonic complex, Alborz belt, Iran ». Geological Magazine 148, n^o 5-6 (24 juin 2011) : 980–1008. http://dx.doi.org/10.1017/s0016756811000380.

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AbstractThe petrological and geochronological study of the Cenozoic Shaivar Dagh composite intrusion in the Alborz Mountain belt (NW Iran) reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the Tethyan (Alpine–Himalayan) orogenic belt. This pluton is formed by intrusion at different times of two main magmatic cycles. The older (Cycle 1) is formed by calc-alkaline silicic rocks, which range in composition from diorites to granodiorites and biotite granites, with abundant mafic microgranular enclaves. The younger cycle (Cycle 2) is formed by K-rich monzodiorite and monzonite of marked shoshonitic affinity. The latter form the larger volumes of the exposed plutonic rocks in the studied complex. Zircon geochronology (laser ablation ICP-MS analyses) gives a concordia age of 30.8 ± 2.1 Ma for the calc-alkaline rocks (Cycle 1) and a range from 23.3 ± 0.5 to 25.1 ± 0.9 Ma for the shoshonitic association (Cycle 2). Major and trace element relations strongly support distinct origins for each magmatic cycle. Rocks of Cycle 1 have all the characteristic features of active continental margins. Shoshonitic rocks (Cycle 2) define two continuous fractionation trends: one departing from a K-rich basaltic composition and the other from an intermediate, K-rich composition. A metasomatized-mantle origin for the two shoshonitic series of Cycle 2 is proposed on the basis of comparisons with experimental data. The origin of the calc-alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted mélanges in the form of silicic cold plumes. A time sequence can be established for the processes responsible of the generation of the two magmatic cycles: first a calc-alkaline cycle typical of active continental margins, and second a K-rich cycle formed by monzonites and monzodiorites. This sequence precludes the younger potassic magmas as precursors of the older calc-alkaline series. By contrast, the older calc-alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision.

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Petrov, G. A., N. I. Tristan, G. N. Borozdina et A. V. Maslov. « The final stage of the Acid Island Arc magmatism in the Northern Urals ». Доклады Академии наук 489, n^o 2 (20 novembre 2019) : 166–69. http://dx.doi.org/10.31857/s0869-56524892166-169.

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For the first time, the time of completion of the formation of calc-alkaline volcanic complexes of the Devonian Island Arc (Franian) in the Northern Urals was determined. It is shown that the late Devonian volcanic rocks of the Limka series have geochemical characteristics that bring them closer to the rocks of developed island arcs and active continental margins. The detected delay of the final episode of calc-alkaline volcanism in the Northern Urals in comparison with the similar event in the southern Urals may be due to the oblique nature of the subduction.

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Chandra, Rakesh, Rajeev Upadhyay et Anshu K. Sinha. « Subduction and collision related magmatism in the Shyok Suture and eastern Karakoram ». Journal of Palaeosciences 48, n^o (1-3) (31 décembre 1999) : 183–209. http://dx.doi.org/10.54991/jop.1999.1303.

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The Shyok Suture is represented by distinct sets of volcano-plutonic rock assemblages. The high-Mg tholeiitic basalt and calc-alkaline andesites of the Shyok Volcanics have a subduction zone chemical signature. The REE data on tholeiitic basalt suggest a chemical affinity between primitive N-MORB to E-MORB. The calc-alkaline andesites, however, resembles to transitional nature of basalt between E-MORB to OIB. The geochemical data and regional tectonic setting suggest a close similarity between the Shyok Volcanics of northern Ladakh and the Chalt Volcanics of Kohistan. The mildly deformed trondhjemite-tonalite-granodiorite of the Tirit Granitoids are composite plutons located south of the Shyok Suture melange. These granitoids are subalkaline, I-type and represented by volcanic arc chemical signatures. The regional tectonic setting, the nature of occurrence and the composition of Tirit Granitoids are similar to the plutonic suites of northern Kohistan (Gindai, Matum Das and Nomal plutons). The eastern Karakoram Batholith is dominated by quartz monzonite-tonalite-granodiorite and granite. The subalkaline to calc-alkaline Karakoram Batholith is constituted by both I-and S-type granitoids with volcanic arc and syn-collision chemical signatures. REE data suggest that the I-type granitoids of eastern Karakoram are calc-alkaline magmatism of a subduction zone environment. In contrast, most of the S-type granitoids are crust-derived peraluminous granitoids. New Rb/Sr isotopic whole rock age data indicates that an S-type intrusive phase was active in the eastern Karakoram region during 83±9 Ma. The syn-collision nature of these granitoids are similar to those of north Sost pluton and Karambar pluton of northern Kohistan. This indicates that the collision between Kohistan-Ladakh arc and Karakoram block was active during 83±9 Ma.

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Berkelhammer, Samuel E., Matthew E. Brueseke, Jeffrey A. Benowitz, Jeffrey M. Trop, Kailyn Davis, Paul W. Layer et Maridee Weber. « Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction : Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska ». Geosphere 15, n^o 5 (10 septembre 2019) : 1508–38. http://dx.doi.org/10.1130/ges02114.1.

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Abstract The Sonya Creek volcanic field (SCVF) contains the oldest in situ volcanic products in the ca. 30 Ma–modern Wrangell Arc (WA) in south-central Alaska, which commenced due to Yakutat microplate subduction initiation. The WA occurs within a transition zone between Aleutian subduction to the west and dextral strike-slip tectonics along the Queen Charlotte–Fairweather and Denali–Duke River fault systems to the east. New 40Ar/39Ar geochronology of bedrock shows that SCVF magmatism occurred from ca. 30–19 Ma. New field mapping, physical volcanology, and major- and trace-element geochemistry, coupled with the 40Ar/39Ar ages and prior reconnaissance work, allows for the reconstruction of SCVF magmatic evolution. Initial SCVF magmatism that commenced at ca. 30 Ma records hydrous, subduction-related, calc-alkaline magmatism and also an adakite-like component that we interpret to represent slab-edge melting of the Yakutat slab. A minor westward shift of volcanism within the SCVF at ca. 25 Ma was accompanied by continued subduction-related magmatism without the adakite-like component (i.e., mantle-wedge melting), represented by ca. 25–20 Ma basaltic-andesite to dacite domes and associated diorites. These eruptions were coeval with another westward shift to anhydrous, transitional-tholeiitic, basaltic-andesite to rhyolite lavas and tuffs of the ca. 23–19 Ma Sonya Creek shield volcano; we attribute these eruptions to intra-arc extension. SCVF activity was also marked by a small southward shift in volcanism at ca. 21 Ma, characterized by hydrous calc-alkaline lavas. SCVF geochemical compositions closely overlap those from the <13 Ma WA, and no alkaline lavas that characterize the ca. 18–10 Ma eastern Wrangell volcanic belt exposed in Yukon Territory are observed. Calc-alkaline, transitional-tholeiitic, and adakite-like SCVF volcanism from ca. 30–19 Ma reflects subduction of oceanic lithosphere of the Yakutat microplate beneath North America. We suggest that the increase in magmatic flux and adakitic eruptions at ca. 25 Ma, align with a recently documented change in Pacific plate direction and velocity at this time and regional deformation events in southern Alaska. By ca. 18 Ma, SCVF activity ceased, and the locus of WA magmatism shifted to the south and east. The change in relative plate motions would be expected to transfer stress to strike-slip faults above the inboard margin of the subducting Yakutat slab, a scenario consistent with increased transtensional-related melting recorded by the ca. 23–19 Ma transitional-tholeiitic Sonya Creek shield volcano between the Denali and Totschunda faults. Moreover, we infer the Totschunda fault accommodated more than ∼85 km of horizontal offset since ca. 18 Ma, based on reconstructing the initial alignment of the early WA (i.e., 30–18 Ma SCVF) and temporally and chemically similar intrusions that crop out to the west on the opposite side of the Totschunda fault. Our results from the SCVF quantify spatial-temporal changes in deformation and magmatism that may typify arc-transform junctions over similar time scales (>10 m.y.).

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Pharaoh, T. C., T. S. Brewer et P. C. Webb. « Subduction-related magmatism of late Ordovician age in eastern England ». Geological Magazine 130, n^o 5 (septembre 1993) : 647–56. http://dx.doi.org/10.1017/s0016756800020951.

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AbstractDeep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.

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Mytrokhyn, O. V., L. I. Gavryliv et V. G. Bakhmutov. « PETROLOGY OF CENOZOIC DYKES ON THE ARGENTINE ISLANDS (WILHELM ARCHIPELAGO, WEST ANTARCTICA) ». Mineralogical Journal 44, n^o 3 (2022) : 67–82. http://dx.doi.org/10.15407/mineraljournal.44.03.067.

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Dyke swarms that intrude Paleogene granitoids of the Argentine Islands near the Ukrainian Antarctic Station "Akademik Vernadsky" were studied. The field relations and mineralogical, petrographical and geochemical properties of the dykes allow their relative geological age and the geodynamic conditions to be clarified. The magmatic activity in the study area did not cease, at least until the end of the Miocene when the processes of orogenic uplift led to the erosive exposure of the Paleogene granitoids of the Barchans-Forge Massif. Tectonic exhumation of the latter was accompanied by the intrusion of dykes of different compositions at different depths. Cenozoic basalt and diabase dykes are the most common. Most are subvolcanic fractured intrusions formed after the complete exhumation of the host granitoids, which ended by the Miocene (11 Ma). The basaltic dykes are probably one of the youngest representatives of magmatism in the region. They have an intermediate position between high-LILE tholeiites and the calc-alkaline series. However, the nature of contamination of the basaltic dykes by crustal rocks requires additional research. Cenozoic microdiorites dykes are rarer than basaltic ones. They are hypabyssal fractured intrusions formed during the tectonic exhumation of the Barchans-Forge granitoids between the beginning of the Paleocene and the end of the Miocene (61-11 Ma). The microdiorites belong to the orogenic calc-alkaline series and they could be related to subduction processes. The discovery of only one dacite dyke indicates the rarity of acid magmatism during the Cenozoic period. It occurs as a fractured intrusion and formed after the exhumation of the host granitoids. The dacite dyke belongs to the calc-alkaline series, which, along with other compositional properties, suggests that dacite and microdiorite dykes are comagmatic.

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Frezzotti, Maria Luce, Gianfilippo De Astis, Luigi Dallai et Claudio Ghezzo. « Coexisting calc-alkaline and ultrapotassic magmatism at Monti Ernici, Mid Latina Valley (Latium, central Italy) ». European Journal of Mineralogy 19, n^o 4 (13 septembre 2007) : 479–97. http://dx.doi.org/10.1127/0935-1221/2007/0019-1754.

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Birkenmajer, K., L. Francalanci et A. Peccerillo. « Petrological and geochemical constraints on the genesis of Mesozoic–Cenozoic magmatism of King George Island, South Shetland Islands, Antarctica ». Antarctic Science 3, n^o 3 (septembre 1991) : 293–308. http://dx.doi.org/10.1017/s0954102091000354.

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Petrological and geochemical data are reported for a series of Late Cretaceous-Middle Miocene volcanic, hypabyssal and intrusive rocks from King George Island (KGI) and from nearby Ridley Island, South Shetland Islands. Major element data indicate a calc-alkaline, basic to intermediate composition for the analysed samples. Although emplaced on a continental margin, the KGI rocks generally display low abundances of incompatible trace elements, close to those typically observed in calc-alkaline suites erupted in intraoceanic island arcs. A few samples have a significant negative Ce anomaly. Many incompatible elements define smooth positive trends on interelemental variation diagrams which suggests that magmas erupted at different times on KGI maintained a rather constant composition in terms of incompatible element ratios. Geochemical modelling, based on Sr isotope ratios and incompatible element ratios, suggests that the primary calc-alkaline magmas of KGI were all generated in an upper mantle modified by addition of small amounts of pelagic sediments dragged down by subduction processes.

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Ernst, W. G. « Subduction-zone metamorphism, calc-alkaline magmatism, and convergent-margin crustal evolution ». Gondwana Research 18, n^o 1 (juillet 2010) : 8–16. http://dx.doi.org/10.1016/j.gr.2009.05.010.

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Casetta, Federico, Ryan B. Ickert, Darren F. Mark, Costanza Bonadiman, Pier Paolo Giacomoni, Theodoros Ntaflos et Massimo Coltorti. « The Alkaline Lamprophyres of the Dolomitic Area (Southern Alps, Italy) : Markers of the Late Triassic Change from Orogenic-like to Anorogenic Magmatism ». Journal of Petrology 60, n^o 6 (1 juin 2019) : 1263–98. http://dx.doi.org/10.1093/petrology/egz031.

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AbstractWe present the first complete petrological, geochemical and geochronological characterization of the oldest lamprophyric rocks in Italy, which crop out around Predazzo (Dolomitic Area), with the aim of deciphering their relationship with Triassic magmatic events across the whole of the Southern Alps. Their Mg# of between 37 and 70, together with their trace element contents, suggests that fractional crystallization was the main process responsible for their differentiation, together with small-scale mixing, as evidenced by some complex amphibole textures. Moreover, the occurrence of primary carbonate ocelli suggests an intimate association between the alkaline lamprophyric magmas and a carbonatitic melt. 40Ar/39Ar data show that the lamprophyres were emplaced at 219·22 ± 0·73 Ma (2σ; full systematic uncertainties), around 20 Myr after the high-K calc-alkaline to shoshonitic, short-lived, Ladinian (237–238 Ma) magmatic event of the Dolomitic Area. Their trace element and Sr–Nd isotopic signatures (87Sr/86Sri = 0·7033–0·7040; 143Nd/144Ndi = 0·51260–0·51265) are probably related to a garnet–amphibole-bearing lithosphere interacting with an asthenospheric component, significantly more depleted than the mantle source of the high-K calc-alkaline to shoshonitic magmas. These features suggest that the Predazzo lamprophyres belong to the same alkaline–carbonatitic magmatic event that intruded the mantle beneath the Southern Alps (e.g. Finero peridotite) between 190 and 225 Ma. In this scenario, the Predazzo lamprophyres cannot be considered as a late-stage pulse of the orogenic-like Ladinian magmatism of the Dolomitic Area, but most probably represent a petrological bridge to the opening of the Alpine Tethys.

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Leat, P. T., et R. S. Thorpe. « Ordovician volcanism in the Welsh Borderland ». Geological Magazine 123, n^o 6 (novembre 1986) : 629–40. http://dx.doi.org/10.1017/s0016756800024146.

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AbstractBasaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.

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Pipera, K., A. Koroneos, T. Soldatos, G. Poli et G. Christofides. « Origin of the High-K Tertiary magmatism in Northern Greece : Implications for mantle geochemistry and geotectonic setting. » Bulletin of the Geological Society of Greece 47, n^o 1 (5 septembre 2013) : 416. http://dx.doi.org/10.12681/bgsg.11017.

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Tertiary plutonic and volcanic rocks cropping out in the Rhodope Massif (N. Greece) are studied using existing and new geochemical and isotopic data. Most of these rocks belong to the post-collisional magmatism formed as part of the prolonged extensional tectonics of the Rhodope region in Late Cretaceous– Paleogene time. This magmatism is considered to be of mantle origin; however, the character of the mantle source is controversial. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and shoshonitic features associated with magmatism at convergent margins. Initial 87Sr/86Sr, 143Nd/144Nd ratios, Pb isotopes and REE composition of the mafic rocks indicate mainly an enriched mantle source, even if some rocks indicate a depleted mantle source. Low- and High-K mafic members of these rocks coexist indicating a strongly heterogeneous mantle source. The High-K character of some of the mafic rocks is primarily strongly related to mantle enrichment by subduction-related components, rather than crustal contamination. The geochemical characteristics of the studied rocks (e.g Ba/Th,Th/Yb,Ba/La, U/Th, Ce/Pb) indicate that primarily sediments and/or sediment melts, rather than fluid released by the subducted oceanic crust controlled the source enrichment under the Rhodope Massif.

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Schaltegger, Urs. « The Central Aar Granite : Highly differentiated calc-alkaline magmatism in the Aar Massif (Central Alps, Switzerland) ». European Journal of Mineralogy 2, n^o 2 (17 avril 1990) : 245–60. http://dx.doi.org/10.1127/ejm/2/2/0245.

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Isachsen, Clark E. « Geology, geochemistry, and cooling history of the Westcoast Crystalline Complex and related rocks, Meares Island and vicinity, Vancouver Island, British Columbia ». Canadian Journal of Earth Sciences 24, n^o 10 (1 octobre 1987) : 2047–64. http://dx.doi.org/10.1139/e87-194.

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The Westcoast Crystalline Complex is a belt of plutonic rocks along the west coast of Vancouver Island. It is composed mainly of heterogeneous amphibolitic country rock (Westcoast amphibolite), granitoids of trondhjemitic to gabbroic composition (Westcoast diorite), and variable mixtures of these two components (Westcoast migmatite).Although the protolith of some deformed enclaves may be Paleozoic, most of these rocks were generated in a magmatic-arc setting and intruded in Jurassic time. Major- and trace-element chemistry of the Westcoast Crystalline Complex shows a sub-alkaline tholeiitic to calc-alkaline trend.The exponential cooling curves derived for Westcoast diorites are not consistent with in situ crustal magma genesis but instead indicate that these rocks intruded relatively cool country rock.Based on age and chemistry, the Westcoast Crystalline Complex can be interpreted as the deeper crustal equivalent of the more differentiated Island Intrusions and Bonanza Volcanics. Taken together, these rocks provide a disrupted and perhaps incomplete cross section of the magmatic arc of Vancouver Island.Reconnaissance of the Wark–Colquitz Complex of southern Vancouver Island shows it to be essentially indistinguishable in petrography, chemistry, and age from the Westcoast Crystalline Complex, and a similar history is inferred.A calc-alkaline chemistry and rapid initial cooling also characterize a Catface Intrusion dated at 41 Ma. This is again compatible with arc magmatism, but its proximity to the coeval trench is enigmatic.

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El Aouli, El Hassan, Dominique Gasquet et Moha Ikenne. « Le magmatisme basique de la boutonniere d'Igherm (Anti-Atlas occidental, Maroc) ; un jalon des distensions neoproterozoiques sur la bordure nord du craton ouest-africain ». Bulletin de la Société Géologique de France 172, n^o 3 (1 mai 2001) : 309–17. http://dx.doi.org/10.2113/172.3.309.

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Abstract In the Igherm inlier (western Anti-Atlas, Morocco) doleritic dyke swarms with various directions and gabbroic intrusive bodies were emplaced during Neoproterozoic times, cutting across either Eburnean micaschists and granites or Panafrican limestones and quartzites. All these rocks were deformed by the main Panafrican schistosity and covered by molassic and volcanic Upper Neoproterozoic series. The primary mineralogical assemblages (plagioclase, augite, olivine...) of the mafic rocks are nearly completely replaced by secondary assemblages (albite, actinolite, chlorite, epidote, calcite, quartz, leucoxene, magnetite, hematite...). However, three main groups have been recognized by the means of relative chronology and petrography. The group 1 is earlier, as shown by the intrusive character of the dykes of the other two groups into its gabbroic bodies. Using incompatible trace elements and rare earth elements it appears that this magmatism is truly heterogeneous and that the three groups have different magmatic affinities. The group 1 corresponds to tholeiitic dolerites and gabbros characterized by intersertal and ophitic textures and by high contents in Fe 2 O 3 (12.16 to 16.64%), TiO 2 (1.46 to 2.5%), Zr (90 to 174 ppm), Nb (7 to 13 ppm), Y (21.68 to 38.74 ppm) and V (264 to 419 ppm). The REE contents are low (Sigma REE = 49 to 137 ppm) and the REE patterns are flat [1.99<(La/Yb) N <4.56] showing a relative slight enrichment in LREE and no anomaly in Eu (0.89>Eu/Eu (super *) <1.11). These features as the TiO 2 vs FeO (super *) /MgO and V vs Ti/1000 diagrams are characteristic of anorogenic intraplate magmas. The group 2 corresponds to calc-alkaline dolerites and gabbros showing fine-grained intersertal textures and high contents of Al 2 O 3 (14.10 to 20.64%) and low contents of Fe 2 O 3 (8.35 to 12.91%), TiO 2 (0.68 to 1.41%), Zr (66 to 106 ppm), Nb (5 to 7 ppm), Y (16.41 to 20.75 ppm) and V (144 to 264 ppm). The REE contents vary from 67 to 155 ppm and the REE patterns are fractionated (2.78<(La/Yb) N <6.62) with a strong enrichment in LREE. The slight positive Eu anomaly (0.91<Eu/Eu (super *) <1.37) is related to the wealth of plagioclases frequently observed in these rocks. The TiO 2 contents of these rocks and their low FeO (super *) /MgO ratios give them a calc-alkaline affinity similar to that of calc-alkaline orogenic basalts related to an oceanic subduction. The group 3 corresponds to alkaline dolerites characterized by fine-grained intersertal textures with high contents of TiO 2 (3.85 to 3.97%), P 2 O 5 (0.66 to 0.77%), Nb (33 to 39 ppm), Zr (262 to 287 ppm), Y (39.6 to 47.7 ppm) and REE (Sigma REE = 205 to 218 ppm). The REE patterns are fractionated (7.77<La/Yb) N <6.65) without no Eu anomaly (0.99<Eu/Eu (super *) <1.02). The Ti/V and Y/Nb ratios (65.26 to 74.95 and 1.19 to 1.22, respectively) are those of alkaline rocks found in intraplate environments. The detailed petrographical, geochemical and field studies of the Igherm inlier show that the mafic magmatism is more complex than previously described. The mafic tholeiitic and alkaline magmatism occurring in the Igherm inlier is also present in the other inliers of the Moroccan Anti-Atlas during Neoproterozoic times. On the other hand the calc-alkaline Neoproterozoic mafic magmatism is very rare elsewhere in the Anti-Atlas except in the Siroua Massif and locally in the Bas Draa and Tagragra d'Akka inliers (western Anti-Atlas). The geodynamical environment of this mafic magmatism is linked to a strong extensional tectonic regime occurring at the northern border of the West African craton during Neoproterozoic times. This regime is related to the oceanic opening described in Central Anti-Atlas and to the emplacement of the ophiolites of Bou Azzer and Siroua or occurs immediately after the oceanic opening. The chemical heterogeneities observed in the three defined groups can be related to heterogeneities of mantellic sources and/or various partial melting ratios of the sub-continental mantle. We can assume that this major fissural magmatic event, not precisely dated, is equivalent to that observed in the other Neoproterozoic provinces in Hoggar, Cameroon, north America and Brazil.

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Chen, Cheng-Hong, Wayne Lin, Ching-Ying Lan et Chi-Yu Lee. « Geochemical, Sr and Nd isotopic characteristics and tectonic implications for three stages of igneous rock in the Late Yanshanian (Cretaceous) orogeny, SE China ». Earth and Environmental Science Transactions of the Royal Society of Edinburgh 95, n^o 1-2 (mars 2004) : 237–48. http://dx.doi.org/10.1017/s0263593300001048.

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ABSTRACTLate Yanshanian magmatism in SE China includes three stages of thermal event induced by the interaction between the continental margin of Eurasia and the paleo-Pacific plate during the Cretaceous period. Products of syn-orogenic magmatism (130–110 Ma) include high-Al gabbros (HAG), and gneissic tonalite, trondhjemite and granodiorite (TTG), which intruded into the deep basement (18–24 km). Rocks of the post- and an-orogenic magmatism are shallow-level (6–8 km) I-type granitoids (110–99 Ma), and miarolitic A-type granites plus rhyolite-dominate bimodal volcanics (94–81 Ma), respectively. Geochemically, HAG and TTG belong to the medium-K calc-alkaline affinity with high Sr/Y, whereas other granitoids are mainly high-K calc-alkaline to shoshonitic rocks with low Sr/Y. Sr and Nd isotope compositions suggest different sources of HAG and TTG from other rocks. Progressive depletions of Ba, Sr, Eu and P from I- to A-type granites reflect partial melting of felsic granulites from hydrous to dry conditions, whereas high Sr/Y in HAG and TTG are compatible with dehydration melting of amphibolites. Tectonic models which accommodate HAG and TTG may involve thickening of the lithosphere to convert the pre-existing lower-crust basic rocks into amphibolites. It was followed by basaltic underplating which is attributed to delamination of the thickened lithosphere and led to triggering of crust melting under exten

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Hawkesworth, Chris, Simon Turner, Kerry Gallagher, Arlëne Hunter, Tim Bradshaw et Nick Rogers. « Calc-alkaline magmatism, lithospheric thinning and extension in the Basin and Range ». Journal of Geophysical Research : Solid Earth 100, B6 (10 juin 1995) : 10271–86. http://dx.doi.org/10.1029/94jb02508.

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Hooper, P. R., D. G. Bailey et G. A. McCarley Holder. « Tertiary calc-alkaline magmatism associated with lithospheric extension in the Pacific Northwest ». Journal of Geophysical Research : Solid Earth 100, B6 (10 juin 1995) : 10303–19. http://dx.doi.org/10.1029/94jb03328.

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Delibaş, Okan, Robert Moritz, David Selby, Deniz Göç et Mustafa Kemal Revan. « Multiple Porphyry Cu-Mo Events in the Eastern Pontides Metallogenic Belt, Turkey : From Early Cretaceous Subduction to Eocene Postcollision Evolution ». Economic Geology 114, n^o 7 (1 novembre 2019) : 1285–300. http://dx.doi.org/10.5382/econgeo.4663.

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Abstract Four porphyry Cu-Mo systems were investigated by Re-Os molybdenite geochronology to constrain their timing with respect to the geodynamic and magmatic evolution of the eastern Pontides, Turkey. Molybdenite from the Ispir-Ulutaş deposit yielded an Re-Os age of 131.0 ± 0.7 Ma, which is consistent with Early Cretaceous U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon ages of local calc-alkaline intrusions. It demonstrates that porphyry deposits were already formed during Early Cretaceous subduction of the Neotethys along the eastern Pontides, and that they can be correlated with porphyry Cu events in the adjacent Lesser Caucasus. Molybdenite Re-Os ages of 76.0 ± 0.4 and 75.7 ± 0.4 Ma at the Elbeyli prospect and 77.2 ± 1.0 Ma at the Emeksen prospect overlap with U-Pb LA-ICP-MS zircon ages of shoshonitic to high-K calc-alkaline intrusions in the region, which were emplaced during Late Cretaceous Neotethys subduction. A 50.7 ± 0.3 Ma molybdenite Re-Os age at the Güzelyayla deposit confirms porphyry Cu-Mo emplacement coeval with Eocene postcollisional, calc-alkaline adakitic magmatism of the eastern Pontides. An electron microprobe study of molybdenite samples, supplemented by data obtained during Re-Os dating, shows that the Eocene Güzelyayla deposit and the Late Cretaceous Emeksen prospect have the highest Re enrichment. Postcollisional melting of a thickened mafic lower continental crust and melting of a metasomatized lithospheric mantle with little to no interaction with upper crustal rocks may explain the Re enrichment at Güzelyayla and Emeksen, respectively.

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FEELEY, T. C., M. A. COSCA et C. R. LINDSAY. « Petrogenesis and Implications of Calc-Alkaline Cryptic Hybrid Magmas from Washburn Volcano, Absaroka Volcanic Province, USA ». Journal of Petrology 43, n^o 4 (1 avril 2002) : 663–703. http://dx.doi.org/10.1093/petrology/43.4.663.

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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.

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Αρίκας, Κ., Π. Βουδούρης, M. R. Kloos et Ch Tesch. « PETROLOGY - GEOCHEMISTRY AND METALLOGENESIS OF VOLCANIC ROCKS IN THE PETROTA GRABEN/MARONIA, W.THRACE ». Bulletin of the Geological Society of Greece 36, n^o 1 (1 janvier 2004) : 482. http://dx.doi.org/10.12681/bgsg.16740.

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The penological, mineralogical and geochemical study of tertiary volcanic rocks from Petrota Graben/Maronia, resulted in the distinction of the following pétrographie groups: a) a high-K calcalkaline group (andesites-dacites), b) a shoshonitic group (shoshonitic andésites, trachytic lavas, c) rhyodacitic ignimbrites and ignimbritic tuffs with high-K calc-alkaline to shoshonitic affinity, and d) rhyolites. The shoshonitic volcanic rocks and the rhyolites are probably originated from the neighbouring Maronia plutonio complex. In addition the calc-alkaline group is related to similar volcanics outcroping in the Mesti-Kassiteres area (the northeastern extension of the Graben). The petrogenesis of the volcanic rocks of the Petrota gragen is attibuted to fractional crystallization and/or magma mixing processes. Epithermal style mineralizations in Mavrokoryfi, Perama Hill and Odontoto are believed to be genetically related to the rhyolitic magmatism in the area.

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Pedersen, Rolf B., et Jan Hertogen. « Magmatic evolution of the Karm�y Ophiolite Complex, SW Norway : relationships between MORB-IAT-boninitic-calc-alkaline and alkaline magmatism ». Contributions to Mineralogy and Petrology 104, n^o 3 (1990) : 277–93. http://dx.doi.org/10.1007/bf00321485.

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Sepidbar, Fatemeh, Ghasem Ghorbani, Basem Zoheir, Richard M. Palin, Seyed Masoud Homam, Tehseen Zafar, Jinlong Ma et Li He. « Coeval calc-alkaline and alkaline Cadomian magmatism in the Bafq, central Iran : Insights into their petrogenesis ». Lithos 406-407 (décembre 2021) : 106535. http://dx.doi.org/10.1016/j.lithos.2021.106535.

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Xu, Nan, Cai-lai Wu, Yuan-Hong Gao, Min Lei, Kun Zheng et Dong Gao. « Tectonic evolution of the South Altyn, NW China : constraints by geochemical, zircon U–Pb and Lu–Hf isotopic analysis of the Palaeozoic granitic plutons in the Mangya area ». Geological Magazine 157, n^o 7 (14 mai 2020) : 1121–43. http://dx.doi.org/10.1017/s0016756820000126.

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AbstractThe South Altyn Orogenic Belt (SAOB) is one of the most important orogenic belts in NW China, consisting of the South Altyn Continental Block and the Apa–Mangya Ophiolitic Mélange Belt. However, its Palaeozoic tectonic evolution is still controversial. Here, we present petrological, geochemical, zircon U–Pb and Lu–Hf isotopic data for the Mangya plutons with the aim of establishing the Palaeozoic tectonic evolution. We divide the Early Palaeozoic magmatism in the Apa–Mangya Ophiolitic Mélange Belt into four episodes and propose a plate tectonic model for the formation of these rocks. During 511–494 Ma, the South Altyn Ocean (SAO) was in a spreading stage, and some shoshonite series, I-type granitic rocks were generated. From 484 to 458 Ma, the oceanic crust of the SAO subducted northward, accompanied by large-scale magmatic events resulting in the generation of vast high-K calc-alkaline series, I-type granitic rocks. During 450–433 Ma, the SAO closed, and break-off of the subducted oceanic slab occurred, with the generation of some high-K calc-alkaline series, I–S transitional type granites. The SAOB was in post-orogenic extensional environment from 419 to 404 Ma, and many A-type granites were generated.

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Wu, Cailai, Shuwen Dong, Di Wu, Xin Zhang et W. G. Ernst. « Late Mesozoic high-K calc-alkaline magmatism in Southeast China : the Tongling example ». International Geology Review 60, n^o 11-14 (10 avril 2017) : 1326–60. http://dx.doi.org/10.1080/00206814.2017.1313137.

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DAVIS, J., et C. J. HAWKESWORTH. « Early calc-alkaline magmatism in the Mogollon-Data Volcanic Field, New Mexico, USA ». Journal of the Geological Society 151, n^o 5 (septembre 1994) : 825–43. http://dx.doi.org/10.1144/gsjgs.151.5.0825.

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Boyet, Maud, Henriette Lapierre, Marc Tardy, Delphine Bosch et Rene Maury. « Nature des sources des composants andesitiques des Gres du Champsaur et des Gres de Taveyannaz ; implications dans l'evolution des Alpes occidentales au Paleogene ». Bulletin de la Société Géologique de France 172, n^o 4 (1 juillet 2001) : 487–501. http://dx.doi.org/10.2113/172.4.487.

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Abstract Paleogene magmatism is widespread in the western Alps and its origin is still a matter of debate. It consists of calc-alkaline and shoshonitic suites with mainly granodioritic intrusions in the Internal Zone (northern Italy), andesitic volcanism in the Delphino-Helvetic Zone (French-Swiss domain) and the Esterellite intrusions in Provence. In the External Alpine Zone, the Taveyannaz Sandstones and the Champsaur Sandstones preserve andesitic pebbles and mineral fragments dated at 32 Ma. On the basis of trace-element and isotopic geochemistry (Sr, Nd, Pb and O) of mineral separates (amphibole, pyroxene and plagioclase) and andesitic clasts, we characterise the nature of magmatic source(s) and compare the isotopic compositions of the andesites with those of well known Paleogene igneous suites.

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Pécskay, Zoltán, Ioan Seghedi, Marinel Kovacs, Alexandru Szakács et Alexandrina Fülöp. « Geochronology of the Neogene calc-alkaline intrusive magmatism in the "Subvolcanic Zone" of the Eastern Carpathians (Romania) ». Geologica Carpathica 60, n^o 2 (1 avril 2009) : 181–90. http://dx.doi.org/10.2478/v10096-009-0012-5.

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Geochronology of the Neogene calc-alkaline intrusive magmatism in the "Subvolcanic Zone" of the Eastern Carpathians (Romania)The Poiana Botizei-Ţibleş-Toroiaga-Rodna-Bârgâu intrusive area (PBTTRB), northwest Romania, known as the "Subvolcanic Zone", is located between the Gutâi (NW) and Câlimani (SE) volcanic massifs. It consists of rocks displaying a wide range of compositions and textures: equigranular or porphyritic with holocrystalline groundmass (gabbro-diorites, diorites, monzodiorites and granodiorites), and/or porphyritic with fine holocrystalline or glassycryptocrystalline groundmass, similar with effusive rocks: basalts, basaltic andesites, andesites, dacites and rhyolites. The time-span of intrusive rocks emplacement is similar with the nearest calc-alkaline volcanic rocks from Gutâi (NW) and Câlimani (SE) massifs. They are represented by stocks, laccoliths, dykes and sills typical for an upper crustal intrusive environment. In the absence of biostratigraphic evidence, a comprehensive K-Ar study of intrusive rocks using whole rock samples, groundmass and monomineral fractions (biotite, hornblende) has been carried out in order to understand the magmatic evolution of the area. The oldest K-Ar ages recorded in the analysed rocks are close to 11.5 Ma and magmatism continued to develop until about 8.0 Ma. The inception of intrusion emplacement in the PBTTRB is coeval with intrusive activity spatially related to volcanism within the neighbouring Gutâi and Câlimani massifs. However, its culmination at ca. 8 Ma ago is younger than the interruption of this activity at ca. 9.2 Ma in Gutâi and Câlimani Mts where intrusive activity resumed for ca. 1 Myr. These circumstances strongly suggest that the geodynamic evolution of the area controlled the development of both volcanic and intrusive activity and their reciprocal relationships. The overall geological data suggest that in the PBTTRB intra-lithospheric transpressional-transtensional tectonic processes controlled the generation and emplacement of intrusive bodies between ca. 12-8 Ma.

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Blein, Olivier, Henriette Lapierre, Richard A. Schweickert, Arnaud Pecher et Cedric Reynaud. « Volcanisme triasique calco-alcalin a shoshonitique du Nevada occidental ». Bulletin de la Société Géologique de France 172, n^o 2 (1 mars 2001) : 189–200. http://dx.doi.org/10.2113/172.2.189.

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Abstract Two types of island-arc occur in the North American Cordillera during the Permian-Triassic times. The first type is exposed in the eastern Klamath and Blue Mountains (fig. 1). Its stratigraphy is continuous from Permian to Triassic, and is composed of arc-tholeiites with minor calc-alkaline lavas. This suite shows high epsilon Nd (sub (T)) values similar to the range of intra-oceanic island-arc [Lapierre et al., 1987; Brouxel et al., 1987, 1988; Charvet et al., 1990; Lapierre et al., 1990, 1994]. In contrast, the second type, exposed in northern Sierra Nevada and central-western Nevada (Black Dyke) (fig. 1), is characterized by an early Permian calc-alkaline suite, with positive to negative epsilon Nd (sub (T)) values. Its basement is inferred to present continental affinities [Rouer et Lapierre, 1989; Rouer et al., 1989; Blein et al., 1996, 2000]. In western Nevada, volcanic rocks of early Triassic age are present in few localities: (1) the Triassic Koipato Group in central Nevada (fig. 1); (2) the Pablo Formation in the Shoshone mountains and the Paradise Range (figs. 1 and 2); and (3) the Garfield Flat formation in the Excelsior mountains (figs. 1 and 2). Silberling [1959] has subdivided the Pablo formation into three members: clastic, limestone, and greenstone (fig. 3). The clastic member consists of andesites, interbedded with volcaniclastic turbidites. The contact between the clastic and the limestone members is gradational and interlensing. The limestones are locally bioclastic with shell fragments, indicating a shallow-water deposition. They yielded a reworked late Permian fauna which suggests a late Permian or younger age. The clastic and limestone members could represent the recurrent rapid deposition in a shallow marine basin of volcanic flows, reworked material from a nearby terrane of volcanic, granitic, and sedimentary rocks. The greenstone member is composed of andesites, volcanic breccias and tuffs. The middle Triassic Granstville formation rests conformably on the Pablo formation. Both formations are affected by Mesozoic polyphase deformations [Oldow, 1985]. The Permian and/or Triassic Garfield Flat formation is composed of ignimbrites and pyroclastic breccia interlayered with conglomerates, sandstones, calcareous and red pelites (fig. 4). The Jurassic-Triassic Gabbs-Sunrise formation rests unconformably on the Garfield Flat formation. Both formations are affected by Mesozoic polyphase deformations [Oldow, 1985]. In the Pablo formation, lavas are shoshonitic basalts and calc-alkaline andesites, while calc-alkaline andesites and rhyolites predominate in the Garfield Flat formation. Basalts and andesites exhibit enriched LREE patterns (fig. 6) with slight negative anomalies in TiO 2 , Nb and Ta typical of subducted-related magmas in the primitive mantle-normalized spidergrams (fig. 7). The lavas show epsilon Sr (sub (T)) and epsilon Nd (sub (T)) values which range between -0.4 to +19.6, and -1.4 to +0.8 respectively (fig. 8). Most of the samples are displaced from the mantle array toward higher epsilon Sr (sub (T)) values, due to the alteration. The epsilon Nd (sub (T)) values, close to the Bulk Earth composition, record an interaction between material from a juvenile pole (mantle or young crust) and from an old crust. The Pablo and Garfield Flat formations differ from the Permian Black Dyke formation. This latter is characterized by calc-alkaline basalts and mafic andesites enriched in LREE, and a mantle source contaminated by subducted sediments or arc-basement [Blein et al., 2000]. The Pablo and Garfield Flat formations show many similarities with the Koipato Group. In central Nevada, the Koipato Group is a sequence of andesites, dacites and rhyolites interbedded with tuffs and volcaniclastic sediments. It rests with a marked angular unconformity on folded Upper Paleozoic oceanic rocks [Silberling and Roberts, 1962]. Fission-track dating on zircon [McKee and Burke, 1972] indicate an age of 225+ or -30 Ma for the Koipato Group. Ammonites, near the top, are considered to be upper early Triassic [Silberling, 1973]. The Pablo and Garfield Flat lavas share in common with the Koipato Group: (1) late Permian to middle Triassic ages; (2) abundant andesites and rhyolites with minor basalts, associated with felsic pyroclastic breccias; (3) LILE and LREE enrichement; (4) low epsilon Nd (sub (T)) values suggesting a juvenile source with slight contamination by a crustal component; (5) La/Nb ratios close to the lower limit of orogenic andesites [Gill, 1981]; and (6) high Nb/Zr ratios suggesting a generation far from a subduction zone [Thieblemont and Tegyey, 1994]. This Triassic high-K calc-alkaline to shoshonitic magmatism is enriched in K, Rb, Th, Nb and Ta relative to the calc-alkaline Black Dyke lavas, and is mainly juvenile judging from Nd isotopic ratios. The source may correspond either to a juvenile crust composed of high-K andesites [Roberts and Clemens, 1993], which could be the Black Dyke lavas, or to phlogopite-K-richterite enriched lithospheric mantle. In both cases, the generation of the high-K calc-alkaline magmatism needs the former existence of an important subduction phase to generate its source. The lavas of the Pablo and Garfield Flat formations are similar to calc-alkaline and shoshonitic lavas emitted in post-collisional setting. Post-collisional arc/continent magmatism is varied from intermediate to felsic, calc-alkaline to shoshonitic, low to high-K and meta-aluminous to hyper-aluminous. The studied lavas may be compared to the arc/passive margin collision of Papua-New Guinea, where a post-collisional magmatism characterized by high-K basalts, andesites and shoshonites [McKenzie, 1976]. In Nevada, this post-collisional event develops after the accretion of the Permian Black Dyke island-arc (Type 2), and before the accretion of the intra-oceanic Permo-Triassic arc (Type 1).

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King, J. E., W. J. Davis et C. Relf. « Late Archean tectono-magmatic evolution of the central Slave Province, Northwest Territories ». Canadian Journal of Earth Sciences 29, n^o 10 (1 octobre 1992) : 2156–70. http://dx.doi.org/10.1139/e92-171.

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An early tectono-stratigraphic and late plutonic assemblage are distinguished in the central part of the Archean Slave Province (Contwoyto Lake area) on the basis of their relationship to deformation and metamorphic episodes, and by geochemical characteristics. The older assemblage, which predates the onset of intense deformation and the thermal peak of metamorphism, comprises 2.68–2.65 Ga calc-alkaline volcanic and plutonic rocks, as well as extensive turbidites. The younger assemblage comprises ca. 2.61–2.58 Ga plutonic units that were emplaced during and after deformation (D,–D3) and the thermal peak of metamorphism. Compositions of the late plutonic units vary systematically with time of intrusion from an early, calc-alkaline, diorite – tonalite suite to late peraluminous granites. The early assemblage is interpreted to represent remnants of an island arc (or arcs) overlain by turbidites and accreted during D1 and D2. The later assemblage is interpreted as a product of late- to post-accretion, suprasubduction-zone magmatism and associated crustal melting.

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Sommer, Carlos A., Evandro F. Lima, Lauro V. S. Nardi, Joaquim D. Liz et Breno L. Waichel. « The evolution of Neoproterozoic magmatism in Southernmost Brazil : shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins ». Anais da Academia Brasileira de Ciências 78, n^o 3 (septembre 2006) : 573–89. http://dx.doi.org/10.1590/s0001-37652006000300015.

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The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

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Wang, Bo, Dominique Cluzel, Liangshu Shu, Michel Faure, Jacques Charvet, Yan Chen, Sebastien Meffre et Koen de Jong. « Evolution of calc-alkaline to alkaline magmatism through Carboniferous convergence to Permian transcurrent tectonics, western Chinese Tianshan ». International Journal of Earth Sciences 98, n^o 6 (8 janvier 2009) : 1275–98. http://dx.doi.org/10.1007/s00531-008-0408-y.

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Corfu, F., et H. Wallace. « U–Pb zircon ages for magmatism in the Red Lake greenstone belt, northwestern Ontario ». Canadian Journal of Earth Sciences 23, n^o 1 (1 janvier 1986) : 27–42. http://dx.doi.org/10.1139/e86-004.

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U–Pb dating was carried out on nine volcanic rocks and two felsic intrusions from the Red Lake greenstone belt in order to establish an absolute time framework for the magmatic evolution of the area and yield first indications on the time of deformation and gold mineralization.The data indicate a protracted period of igneous activity spanning at least 270 Ma. Felsic volcanic rocks near the top of the tholeiitic to komatiitic sequence in the eastern part of the belt yield ages of [Formula: see text] and [Formula: see text]. A third unit, dated at [Formula: see text], contains inherited zircons older than 2982 Ma, which casts some uncertainty on the validity of the inferred intercept age. Rocks in the western part of the belt, previously believed to form a relatively young calc-alkalic sequence but now known to be dominantly tholeiitic, are shown to be relatively old, with ages of [Formula: see text] and [Formula: see text]. These two dates also bracket the age of stromatolites occurring in chemical sediments that are under and overlain by the dated units.Another volcanic horizon in the centre of the belt is dated at 2830 ± 15 Ma, and calc-alkaline volcanic sequences on the southern and northern flanks of the belt yield ages of 2739.0 ± 3.0 and [Formula: see text], respectively. An age of [Formula: see text] was determined for tholeiitic pyroclastic rocks near the base of the predominantly calc-alkaline Heyson sequence.The major gold deposits of the Red Lake belt appear to be present dominantly within older supracrustal sequences. On the other hand, they are also associated with late deformation zones that postdate the intrusion of the Dome Stock dated at 2718.2 ± 1.1 Ma ago. The time of an earlier folding event is bracketed by this age and by the age of [Formula: see text] for an isoclinally folded felsic dike.

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Whalen, Joseph B. « The Topsails igneous suite, western Newfoundland : an Early Silurian subduction-related magmatic suite ? » Canadian Journal of Earth Sciences 26, n^o 12 (1 décembre 1989) : 2421–34. http://dx.doi.org/10.1139/e89-207.

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The Topsails igneous suite contains several Late Ordovician to Early Silurian volcanic and intrusive sequences, which overlie and intrude Early to Middle Ordovician oceanic and arc rocks. The oldest components of this suite may represent calc-alkaline, continental-arc magmatism. The younger components are bimodal, with felsic compositions vastly predominating, and include a major (> 2200 km2) alkaline (A-type) granite complex. These felsic components have similarities to peralkaline suites formed in unusual subduction-related settings. Younger mafic components resemble within-plate basalts emplaced in a continental setting.Silurian magmatic activity in the Canadian Appalachians is widespread, includes diverse magmatic types, and has contrasting metamorphic and tectonic overprinting, even in contiguous areas. These features and the probability of major post-Silurian displacements in the orogen render correlation and interpretation difficult. Tectonic models that consider basin closure and major plate movements to be complete by Middle Ordovician time fail to adequately explain the Silurian activity. Available data best fit a model that relates Late Ordovician to Silurian magmatic activity to the opening and closing of small, discontinuous basins, portions of which may have been floored by oceanic crust.

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Di Giuseppe, Paolo, Samuele Agostini, Gianfranco Di Vincenzo, Piero Manetti, Mehmet Yilmaz Savaşçın et Sandro Conticelli. « From subduction to strike slip-related volcanism : insights from Sr, Nd, and Pb isotopes and geochronology of lavas from Sivas–Malatya region, Central Eastern Anatolia ». International Journal of Earth Sciences 110, n^o 3 (10 mars 2021) : 849–74. http://dx.doi.org/10.1007/s00531-021-01995-0.

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AbstractAnatolia is characterised by a complex geodynamic evolution, mirrored by a wide spectrum of magmatism. Here, we investigated the timing and the geochemical/isotopic characters of the Miocene to Pliocene volcanism of Sivas–Malatya Region (Central Eastern Anatolia), and its relationships with local and regional tectonics. Na-alkaline basaltic lavas were emplaced during middle Miocene at Sivas (16.7–13.1 Ma), in the North, whilst transition from calc-alkaline to Na-alkaline rocks is observed at Yamadağ and Kepez Dağ volcanic complexes. Calc-alkaline products erupted during early to middle Miocene, and more precisely from 19.5 to 13.6 Ma at Yamadağ and from 16.4 to 13.5 Ma at Kepez Dağ, with final Na-alkaline activity of the Arguvan volcanic field lasting till late Miocene (15.7–10.6 Ma). Volcanism renewed during the Pliocene in the Kangal (5.9–4.0 Ma) volcanic field with the emission of K-alkaline igneous rocks. Mafic calc-alkaline and Na-alkaline rocks partially overlap in age but can be easily distinguished by their petrochemical characters. Mafic calc-alkaline igneous rocks show typical subduction-related petrological and geochemical affinities. They are both two-pyroxene or clinopyroxene and amphibole-bearing rocks, characterised by high LILE/HFSE values, with variable 87Sr/86Sri (0.70396–0.70539) and 143Nd/144Ndi (0.51260–0.51287). Mafic Na-alkaline igneous rocks are characterised by big olivine phenocrysts and show intraplate geochemical flavours, although some LILE depletion with respect to HFSE as well as variable 87Sr/86Sri (0.70347–0.70553) and 143Nd/144Ndi (0.51261–0.51291) isotopic compositions are present. These characteristics are suggestive for the occurrence, at some stage of their genesis, of a possible interaction with subduction-related reservoirs. The Kangal K-alkali basalts still show intraplate-like petrological and geochemical affinities with LILE/HFSE ratios similar to those of the Miocene Na-alkaline rocks, and largely variable 87Sr/86Sri (0.70425–0.70520) and 143Nd/144Ndi (0.51262–0.51277) isotopic compositions, overlapping the arrays observed in the earlier stages of volcanism. A general transition from calc-alkaline to Na-alkaline volcanic rocks is observed with time, according to the evolution of the geodynamics of the Anatolia region. Early to middle Miocene calc-alkaline magmas were derived by partial melting of the mantle wedge delimited by the subduction of the last oceanic branch of Neotethys. The Na-alkaline magmas, on the other hand, were generated within the asthenospheric mantle beneath the slab and migrated through slab tears into the mantle wedge where they mixed with subduction-related components. The subduction-related component decreased with time and transitional magmas are found in the youngest activity of Yamadağ and Kepez Dağ, shortly followed by clear within-plate lavas formed in the Arguvan volcanic field. The appearance of the youngest K-alkaline volcanic rocks in the Kangal basin represents an abrupt change in the magma supply at depth, although continental crustal contamination en-route to the surface played an important role in their genesis.

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De Souza, Zorano Sérgio, Hervé Martin, Jean-Jacques Peucat, Emanuel Ferraz Jardim De Sá et Maria Helena De Freitas Macedo. « Calc-Alkaline Magmatism at the Archean–Proterozoic Transition : the Caicó Complex Basement (NE Brazil) ». Journal of Petrology 48, n^o 11 (9 octobre 2007) : 2149–85. http://dx.doi.org/10.1093/petrology/egm055.

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Rawlings-Hinchey, Alana M., Paul J. Sylvester, John S. Myers, Greg R. Dunning et Jan Kosler. « Paleoproterozoic crustal genesis : calc-alkaline magmatism of the Torngat Orogen, Voisey’s Bay area, Labrador ». Precambrian Research 125, n^o 1-2 (juillet 2003) : 55–85. http://dx.doi.org/10.1016/s0301-9268(03)00077-9.

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Machado, A., E. F. Lima, F. Chemale, D. Morata, O. Oteiza, D. P. M. Almeida, A. M. G. Figueiredo, F. M. Alexandre et J. L. Urrutia. « Geochemistry constraints of Mesozoic–Cenozoic calc-alkaline magmatism in the South Shetland arc, Antarctica ». Journal of South American Earth Sciences 18, n^o 3-4 (mars 2005) : 407–25. http://dx.doi.org/10.1016/j.jsames.2004.11.011.

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Deniel, Catherine, Erkan Aydar et Alain Gourgaud. « The Hasan Dagi stratovolcano (Central Anatolia, Turkey) : evolution from calc-alkaline to alkaline magmatism in a collision zone ». Journal of Volcanology and Geothermal Research 87, n^o 1-4 (décembre 1998) : 275–302. http://dx.doi.org/10.1016/s0377-0273(98)00097-3.

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Schiano, Pierre, Robert Clocchiatti, Luisa Ottolini et Alessandro Sbrana. « The relationship between potassic, calc-alkaline and Na-alkaline magmatism in South Italy volcanoes : A melt inclusion approach ». Earth and Planetary Science Letters 220, n^o 1-2 (mars 2004) : 121–37. http://dx.doi.org/10.1016/s0012-821x(04)00048-2.

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Eyal, M., B. Litvinovsky, B. M. Jahn, A. Zanvilevich et Y. Katzir. « Origin and evolution of post-collisional magmatism : Coeval Neoproterozoic calc-alkaline and alkaline suites of the Sinai Peninsula ». Chemical Geology 269, n^o 3-4 (janvier 2010) : 153–79. http://dx.doi.org/10.1016/j.chemgeo.2009.09.010.

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Goodenough, K. M., B. N. Young et I. Parsons. « The minor intrusions of Assynt, NW Scotland : early development of magmatism along the Caledonian Front ». Mineralogical Magazine 68, n^o 4 (août 2004) : 541–59. http://dx.doi.org/10.1180/0026461046840207.

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AbstractThe Assynt Culmination of the Moine Thrust Belt, in the northwest Scottish Highlands, contains a variety of Caledonian alkaline and calc-alkaline intrusions that are mostly of Silurian age. These include a significant but little-studied suite of dykes and sills, the Northwest Highlands Minor Intrusion Suite. We describe the structural relationships of these minor intrusions and suggest a classification into seven swarms. The majority of the minor intrusions can be shown to pre-date movement in the Moine Thrust Belt, but some appear to have been intruded during the period of thrusting. A complex history of magmatism is thus recorded within this part of the Moine Thrust Belt. New geochemical data provide evidence of a subduction-related component in the mantle source of the minor intrusions.

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KHALATBARI JAFARI, MORTEZA, HADI SEPEHR et KATAYOUN MOBASHER. « Tectonomagmatic evolution of the South Dehshir Ophiolite, Central Iran ». Geological Magazine 153, n^o 4 (7 octobre 2015) : 557–77. http://dx.doi.org/10.1017/s0016756815000618.

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AbstractThe South Dehshir Ophiolite, exposed along the southwestern margin of the Central Iranian microcontinent, comprises a mantle and a crustal sequence. This massif contains serpentinized peridotites, gabbros and diabase sheeted dykes cutting across wherlite, pegmatitic gabbro and plagiogranite, and is tectonically covered by radiolarites, pelagic limestones with Late Cretaceous microfauna and lavas. Under a microscope, the gabbros exhibit mesocumulate, adcumulate and hetradcumulate textures presumably formed in open magma chambers. Hypabyssal and lava samples show tholeiitic to calc-alkaline affinities, and their compositions cluster in the fields of arc or supra-subduction zone magmatism. Binary diagrams display compositional trends of magmatic differentiation, plotting away from the mid-ocean-ridge basalt (MORB) (tholeiitic) trend and following the arc (calc-alkaline) trend. Rare Earth element (REE) and spider diagrams display various enrichments at different levels. Moderate enrichment of the large-ion lithophile elements (LILE; Rb, Ba, Th, U, La, Sr) relative to the high-field-strength elements (HFSE; Nb, Ta) and slight depletion of Ti and Zr in some patterns may be attributed to variable influences of subduction components over the depleted mantle wedge. Elemental ratios display evidence for the contribution of both fluids and melt released from the subducted slab. Few patterns display ocean-island basalt (OIB) characteristics, possibly attributed to the involvement of local mantle plumes on the partial melting of the mantle wedge. This evidence indicates that the crustal rocks of the South Dehshir Ophiolite formed in a supra-subduction zone.

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