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金沢大学大学院自然科学研究科, 丹後半島中央部に分布する八鹿累層は前期中新世の日本海拡大時に噴出した玄武岩～安山岩質溶岩および火砕岩からなる.それらの斑晶組み合わせばType1がOl-Cpx-Pl,Type2がOl-Opx-Pl,Type3がOl-Pl,そしてType4がPlであり,FeO^*/MgOはこの順に増加するがSiO_2はほぼ一定のソレアイト的分化傾向を示す.これらはLILEおよびLREEに富み,ZrやZr/Yが高く,Nbに涸渇し,大陸性島弧火山岩の特徴を示す.新発見のType1ピクライト質玄武岩はMgO(12wt.%),Ni(300ppm),Cr(1,100ppm)に富み,スピネルのCr/(Al+Cr)が0.64-0.84で他のType1玄武岩(0.49-0.59)より高いが,液相濃集元素組成や他の鉱物化学組成はそれらと同様である.このピクライト質玄武岩は,他の八鹿累層火山岩類と同じ給源マントルから,若干含水条件下で,温度上昇による高い部分溶融程度で形成されたと考えられる.同様なピクライトは活動的背弧海盆の沖縄トラフ周辺にもあり,日本海拡大初期の高温マントルの上昇を示唆する. The Yoka Formation in the central part of the Tango Peninsula consists of early Miocene lavas and pyroclastic rocks of basaltic and andesitic composition, which extruded during the Japan Sea opening. These volcanic rocks are grouped into five types on the basis of phenocryst assemblages; Type 1 is olivine (Ol)-clinopyroxene (Cpx)-plagioclase (Pl), Type 2 is Ol- orthopyro-xene (Opx)-Pl, Type 3 is Ol-Pl, Type 4 is only Pl (large phenocrysts), and Type 5 is Cpx-Opx-Pl±Ol. The bulk-rock FeO^*/MgO (^*total iron as FeO) increases from Type 1 to Type 4 with almost constant SiO_2, indicating a tholeiitic fractionation trend, al-though Type 5 shows relatively high SiO_2. All these rocks are characterized by enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), high Zr and Zr/Y, and depletion of Nb, indicating continental island-arc basalt signature. The newly found picritic basalt is classified into Type 1, and has more MgO (12 wt.%), Ni (300 ppm) and Cr (1100 ppm) than other Type 1 basalts. It is depleted in HFSEs but is slightly enriched in LILEs compared to other Type 1 basalts, al-though they are chemically very close (e.g. equal in SiO_2). It also shows the same mineral chemistry as other Type 1 basalts except for its chromian spinel, which shows distinctly higher Cr/(Cr±Al) (0.64-0.84) than that of other Type 1 basalts (0.49-0.59). These facts suggest that the picritic basalt was formed through a higher degree of partial melting under slightly hydrous condition from almost the same source mantle as for other Type 1 basalts. A closely resembling picrite has been reported from the Okinawa Trough area, where active back-arc rifting is taking place, suggesting upheaval of the high-temperature mantle in the early stage of the Japan Sea opening.

Mumbai City, situated on the western Indian coast, is well known for exposures of late-stage Deccan pillow basalts and spilites, pyroclastic rocks, rhyolite lavas, and trachyte intrusions. These rock units, and a little-studied sequence of tholeiitic flows and dykes in the eastern part of Mumbai City, constitute the west-dipping limb of a regional tectonic structure called the Panvel flexure. Here we present field, petrographic, major and trace element and Sr-Nd isotopic data on these tholeiitic flows and dykes, best exposed in the Ghatkopar-Powai area. The flows closely resemble the Mahabaleshwar Formation of the thick Western Ghats sequence to the east, in Sr-Nd isotopic ratios and multielement patterns, but have other geochemical characteristics (e.g., incompatible trace element ratios) unlike the Mahabaleshwar or any other Formation. The flows may have originated from a nearby eruptive center, possibly offshore of Mumbai. Two dykes resemble the Ambenali Formation of the Western Ghats in all geochemical characteristics, though they may not represent feeders of the Ambenali Formation lavas. Most dykes are distinct from any of the Western Ghats stratigraphic units. Some show partial (e.g., Sr-Nd isotopic) similarities to the Mahabaleshwar Formation, and these include several dykes with unusual, concave-downward REE patterns suggesting residual amphibole and thus a lithospheric source. The flows and dykes are inferred to have undergone little or no contamination, by lower continental crust. Most dykes are almost vertical, suggesting emplacement after the formation of the Panvel flexure, and indicate considerable east-west lithospheric extension during this late but magmatically vigorous stage of Deccan volcanism. (C) 2013 Elsevier Ltd. All rights reserved.

TEZ7742 Tez (Yüksek Lisans) -- Çukurova Üniversitesi, Adana, 2010. Kaynakça (s. 58-64 ) var. viii, 65 s. : rnk. res. ; 29 cm. The study area, situated in Üzümlü-Çayırlı (Erzincan) region, is characterized by pre-Permian Yoncayolu formation, Permian Çayderesi limestone, Jurassic-Cretaceous Hozbirikyayla formation, tectonically overlying Refahiye ophiolitic melange and unconformably overlying cover sediments, namely Lower-Middle Eocene Gülandere formation and Miocene Kemah formation. Except volcanics, the Refahiye ophiolite in the study area displays an intact ophiolite stratigraphy from bottom to top. Whereas the volcanics are found in melange unit. The base of the Refahiye ophiolite is represented by variably serpentinized harzburgite and dunite. Well preserved ultramafic (dunite, wehrlite, clinopyroxenite) to mafic (gabbro) cumulate rocks rest tectonically on the tectonites. Isotropic gabbros (gabbro, diorite), sheeted dikes (diabase) and plagiogranites constitute the upper part of the Refahiye ophiolite. The volcanic rocks are basaltic in composition and variably altered. On the basis of geochemical analysis, the isotropic gabbros and sheeted dikes were derived from both tholeiitic and boninitic magmas whereas the volcanic were derived from tholeiitic and alkaline magmas. The rocks, derived from tholeiitic and boninitic magmas, were formed in a fore-arc (suprasubduction zone) setting as a result of north deeping intraoceanic subduction zone in the northern branch of Neotethys since late Cretaceous. The alkaline volcanic rocks are not related to the ophiolite formation. But they are more seamount type in origin. Üzümlü-Çayırlı (Erzincan) bölgesinde yer alan inceleme alanı; Permiyen öncesi bir yaşa sahip Yoncayolu Formasyonu, Permiyen yaşlı Çayderesi Kireçtaşı, Jura-Kretase yaşlı Hozbirikyayla Formasyonu, bu birimleri tektonik olarak üzerleyen Refahiye Ofiyolitli Karışığı, tüm birimleri uyumsuz olarak örten Alt-Orta Eosen yaşlı Gülandere Formasyonu ve Miyosen yaşlı Kemah Formasyonu ile temsil edilmektedir. İnceleme alanında yer alan Refahiye ofiyoliti tabandan tavana doğru volkanikler hariç tam bir ofiyolit dizisi sunar. Volkanik kayaçlar ise daha ziyade melanj birimi içinde yer alırlar. Refahiye ofiyolitinin tabanı değişik oranlarda serpantinleşmiş harzburjit ve dunitler ile temsil edilmektedirler. Bunların üzerine iyi gelişmiş ultramafik (dunit, verlit, klinopiroksenit) ve mafik (gabro) kümülat kayaçları yer alırlar. İzotrop gabrolar (gabro, diyorit), levha daykları (diyabaz) ve plajiyogranitler ise istifin üst kesimlerini meydana getirmektedirler. Volkanikler ise bazalt bileşimli olup, değişik oranlarda alterasyona maruz kalmışlardır. Yapılan jeokimyasal çalışmalar sonucunda; izotrop gabro ve levha dayklarına ait kayaçların toleyitik ve boninitik magmadan itibaren oluştukları ve volkaniklerin ise hem toleyitik hem de alkalen magmadan itibaren oluştukları ortaya çıkmaktadır. Toleyitik ve boninitik magmadan türeyen Refahiye ofiyolitine ait kayaçların Neotetis'in kuzey kolunun Üst Kretase'den itibaren kuzeye doğru dalmaya başlaması ile okyanus içi yitim zonu üzerinde yay-önü ortamda oluştuğu sonucu ortaya çıkmaktadır. Alkalen magmadan türeyen volkaniklerin ise ofiyolit oluşumu ile ilgili olmadığı ve okyanus adası volkanikleri olduğu düşünülmektedir. Bu çalışma Ç.Ü. Bilimsel Araştırma Projeleri Birimi Tarafından Desteklenmiştir. Proje No: MMF2008YL13

The SW Antalya Complex is an assemblage of Mesozoic carbonate platform, margin and ophiolitic rocks which record the formation and tectonic emplacement of a small Mesozoic ocean basin. The late Cretaceous ophiolitic rocks are located at two localities, namely the relatively intact Tekirova ophiolite to the east of Kemer zone and the dismembered Gödene ophiolite to the west of Kemer zone. The Tekirova (Antalya) ophiolite comprises harzburgitic tectonites, ultramafic to mafic cumulates, isotropic gabbros and sheeted dikes. Numerous isolated dikes, ranging in thickness from 5 cm to 10 m, intruded the crustal rocks at different structural levels. The isotropic gabbros are represented by gabbro, diorite and quartz diorite rocks with granular to ophitic-subophitic textures. The isolated dikes are characterized by dolerite, diabase and microdiorite with ophitic, intersertal and microgranular textures. These rocks exhibit tholeiitic to alkaline compositions. New geochemical data presented in this paper from the isolated dikes and isotropic gabbros suggest that there are three main types of parental basic magmas that form the oceanic crustal rocks of the Tekirova (Antalya) ophiolite. These are (1) IAT series which can be referred to the Group I isolated dikes and isotropic gabbros; (2) low-Ti boninitic series characterized by the Group II isolated dike and isotropic gabbros; and (3) OIB-type including the Group III isotropic gabbros. The geochemical evidence suggests that the crustal rocks of the Tekirova (Antalya) ophiolite were generated from a progressive source depletion from island arc tholeiites (IAT) to boninites. Therefore, a fore-arc tectonic setting seems likely for the generation of the crustal rocks from the Tekirova (Antalya) ophiolite in the southern branch of Neotethys during the Late Cretaceous. The OIB-type alkaline isotropic gabbros are thought to have resulted from either (1) a late-stage magmatic activity fed by melts that originated within an asthenospheric window due to slab break-off or (2) subduction of a ridge system which generated OIB source across the asthenospheric window that has been no influence of fluids from the subducted slab into the overlying mantle wedge, shortly before the emplacement of the Tekirova (Antalya) ophiolite onto the Tauride platform. © Springer-Verlag 2007. FBE2000D12 TÜBA-GEBİP/2003-111 Acknowledgments This work is a part of PhD study of Utku Bag^cı. Financial support from the C¸ ukurova University Research Foundation (Project No: FBE2000D12) is gratefully acknowledged. We would like to thank Fabio Capponi for performing major and trace element analyses. We are grateful to Prof Michel Delaloye for thoughtful discussions on evolution of the eastern Mediterranean ophiolites. Osman Parlak gratefully acknowledges the financial support of TÜBA (Turkish Academy of Sciences) in the framework of the Young Scientist Award Program (TÜBA-GEBİP/2003-111). We are grateful to Profs Alastair Robertson for the valuable scientific comments that improved the quality of the present manuscript and Wolf-Christian Dullo for editorial handling.

Early geophysical studies hypothesized a continental rift structure beneath the Wilkes Subglacial Basin. Recent models favour a flexural origin for the basin linked to Transantarctic Mountains uplift and to East Antarctic Craton lithospheric rigidity. Flexural modelling predicts crustal thickening beneath the basin. Gravity modelling along the International Trans-Antarctic Scientific Expedition traverse (1998/99), however, reveals crustal thinning beneath the basin. At 75°S the crust thins from 37 km beneath the Transantarctic Mountains to 31 ± 2 km beneath the Wilkes Basin. The western flank of the basin features a sharp magnetic break. This signature may arise from a fault separating highly magnetic Precambrian craton crust from weakly magnetic Neoproterozoic(?) crust. Much later crustal extension may have focussed along the craton margin. The eastern flank of the Wilkes Basin exhibits a prominent aeromagnetic signature. Potential field modelling predicts 1-4 km thick sedimentary infill within the Wilkes extended terrane, interpreted mainly as Beacon Supergroup intruded by Jurassic Ferrar tholeiites. The adjacent Adventure Subglacial Trench is a narrow rift basin with 25±5 km thick crust and a 10±4 km sedimentary infill. © 2001 Elsevier Science B.V. All rights reserved.

This is a comparative study of the siliceous and basicrocks occuring in two ophiolitic massifs. The petrographie study (including typological study of the zircons from albitites) and geochemistry of the major elements, both support a tholeiitic nature for the magmas. The behaviour of the trace elements (Zr, Y, Nb, Th, Cr, REE) brings out among the basic rocks of the Montgenèvre massif, a trend leading from LREE-enriched basalts located at the bottom of the series, to late LREE-depleted basalts (typical N-MORB) belonging to the uppermost aphyric unit, and also to some doleritic and basaltic dykes. Such an evolution seems to arise from a dynamic partial melting, the only mechanism that could provide a good explanation for the La/Sm ratio's variations. In the Haute- Ubaye massif the basic rocks exhibit a better geochemical homogeneity than those of the Montgenèvre massif, the latter showing a majority of humped REE patterns. Variations of the degree of partial melting (Montgenèvre), and in the features of fractional crystallization (Montgenèvre and Haute- Ubaye) are also detailed. The trace element distribution of albitites in both massifs brings out the geochemical diversity of such rocks and the probable existence of many parental magmas. In the Montgenèvre massif, only the massive albitites of the Replatte du Gondran (Chenaillet) can be regarded as cogenetic with pillow basalts. The Punta Rascia (Italy) albitites are presumably older than the Chenaillet albitites, but later than the first magmatic stage which gave birth to the main Montgenèvre gabbroic mass. In the Haute- Ubaye massif, there is no geochemical relationship between basic and siliceous rocks. Both field obserations and geochemical data suggest a complex time-related evolution, and the lavas seem to have been emplaced, on the flank of the ridge, after the main on-ridge magmatism. Typological study of zircons from acidic clements of a polygenic breccia located at the ophiolite-sediments interface, in the eastern part of the Montgenèvre massif, points out the calco-alcaline nature of some elements. Compared with similar breccias studied in Queyras area, such elements might originate from the dismembering of the surronding continental crust. Consequently, with regards to both its structural location and geochemical features, the Montgenèvre ophiolite is probably related to the earliest event of the tethyan oceanic magmatism., Les termes acides et basiques des massifs ophiolitiques du Montgenèvre et de Haute- Ubaye sont étudiés en parallèle dans ce travail. L'étude pétrographique (notamment l'étude typologique des zircons pour les albitites) et la géochimie des éléments majeurs confirment la nature tholéilique des magmasétudiés. L'étude du comportement des éléments traces (Zr, Y, Nb,Th, Cr, REE) permet de mettre en évidence, pour le Montgenèvre,une évolution continue des roches basiques conduisant de basaltes enrichis en LREE, situés à la base de la série, à des basaltes appauvris en LREE (N -MORB typiques) tardifs et représenlés par les coulées aphyriques supérieures et certains filons doléritobasaltiques. Une telle évolution paraît refléter une fusion partielle dynamique, seule capable d'expliquer les variations importantes du rapport La/Sm. Les roches basiques de Haute- Ubaye montrent une plus grande homogénéité géochimique que celles du Montgenèvre avec une majorité de spectres de terres rares bombés. Les variations du taux de fusion partielle (Montgenèvre) et les caractères de la cristallisation fractionnée (Montgenèvre el Haute Ubaye) sont précisés. L'étude des éléments-lraces des albitites des deux ensembles révèle également la diversité géochimique de ces roches et vraissemblablement l'existence de plusieurs souches parentales. Au Montgenèvre, seules les albitites massives de la Replatte du Gondran (Chenaillet) peuvent être considérées comme cogénétiques des basaltes en coussins. Les albitites de la Punta Rascia (Italie) seraient plus anciennes, postérieures au premier épisode magmatique à l'origine de la grande masse gabbroïque du Montgenèvre. En Haute- Ubaye, il n'existe aucune filiation géochimique nette entre les roches basiques et les roches acides. Les observations de terrain et les données géochimiques permettent d'envisager une évolution temporelle complexe où les termes effusifs paraissent s'être mis en place tardivement et latéralement par rapport au rift océanique. L'étude typologique des zircons des éléments acides d'une brèche polygénique située à l'interface ophiolite-sédiments dans la partie orientale du massif a montré la nature calco-alcaline de certains de ces éléments. Par comparaison avec des brèches semblables étudiées dans le Queyras, ces éléments pourraient provenir du démantèlement de la croûte continentale voisine. Ainsi, les ophiolites du Montgenèvre sont, par leur position structurale et leurs caractéristiques géochimiques, à rapporter vraissemblablement aux premiers termes du magmatisme océanique téthysien.

The Middle Jurassic Ferrar Magmatic Province extends along the proto-Pacific margin of Gondwana from Antarctica to Tasmania, Australia and New Zealand. This magmatism is part of the Mesozoic low-Ti Gondwana Province (Cox, 1988), but differs from the other Mesozoic Large Igneous Provinces, related to the break-up of Gondwana, by having high SiO2 content, LILE/HFSE ratios and Sr isotopic compositions (87Sr/86Sr > 0.708). In Antarctica, the Ferrar magmatism is represented by the mafic layered intrusions of Dufek, the sills and dikes of the Ferrar Dolerite and by the lava flows of the Kirkpatrick Basalt. Geochemical and isotopic studies on the Kirkpatrick basalts from the Mesa Range (Victoria Land) revealed the occurrence of two geochemical types: the Mount Fazio (low-Fe; MFCT) and the overlying Scarab Peak (high-Fe; SPCT; Fleming et al., 1995). Ferrar sills and lavas from Prince Albert Mountains have been investigated for major and trace elements and Sr-Nd isotopic compositions. The studied rocks mainly belong to the low-Fe tholeiites (MFCT) and consist of tholeiitic-andesitic basalts and andesites, while the high-Fe tholeiites (SPCT) have been found only at Brimstone Peak. High-Fe (SPCT) rocks are represented by evolved (rag# 23-18) andesites characterized by relatively high FeOt (>I3.0 wt.%) and TiO2 (>1.8 wt.%) and low SiO2 (56-59) contents. Relative to the high-Fe (SPCT) rocks, the low-Fe (MFCT) rocks cover a wider range of mg# (54-23) showing lower FeOt (

A part of a layered intrusion involving pyriclasites, garnet bearing pyriclasites and anorthosites has been discovered in the granulitic basement from Saleix. Field evidences as well as petrological and mineralogical studies supported by experimental data indicate conditions of primary crystallization from tholeiitic melt towards the base of the crust followed by a recrystallization in the granulite facies near 7-9 kbar and 750-800 °C. This outcrop related to basic granulites associated with the surrounding « kinzigites », could be considered as the upper part of a magmatic complex after the example of Balmuccia (Western Alps, where dunites, harzburgites and pyroxenites complete down the magmatic sequence). Occurrence of the same kind of petrological association at Castillon authorizes a close comparison between the latter area and the outcropping basement at Saleix and suggests a period of intense magmatic activity towards the base of the crust., Un fragment de complexe basique stratifié comportant pyriclasites, pyriclasites à grenat et anorthosites, a été mis en évidence au sein des formations granulitiques de Saleix. Les relations spatiales sur le terrain, les études pétrographiques et minéralogiques appuyées sur les données expérimentales, indiquent que cette intrusion a cristallisé à la base de la croûte, à partir d'un liquide tholéiitique, et a recristallisé dans les conditions du faciès des granulites vers 7-9 kbar et 750-800 °C. Cet affleurement, qui paraît être en relation avec les granulites basiques étroitement associées aux « kinzigites », pourrait représenter la partie supérieure d'un ensemble magmatique comparable à celui de Balmuccia (où dunites, harzburgites et pyroxénites complètent vers le bas la série magmatique). L'existence d'une association similaire dans le Castillon justifie une comparaison étroite entre ce dernier massif et l'écaille de Saleix et indique, pour l'unité structurale ainsi définie, une période d'intense activité magmatique à la base de la croûte., Vielzeuf Daniel. Existence d'un fragment de « complexe stratifié » (pyriclasites et anorthosites) associé à la série granulitique du port de Saleix (Pyrénées ariégeoises). In: Bulletin de Minéralogie, volume 103, 2, 1980. pp. 287-296.

Clinopyroxene–liquid geothermobarometry is a widely used tool for estimating the conditions under which mafic magmas are stored before they erupt. However, redox variability, sector zoning and disequilibrium crystallization present major challenges to the robust estimation of magma storage conditions. Moreover, most recent studies seeking to address these challenges have focused on clinopyroxenes from alkalic systems and are thus of limited use for understanding clinopyroxenes from the tholeiitic systems that dominate global magma budgets. Here we combine observations on natural clinopyroxenes from the 2014–2015 Holuhraun lava in Iceland with observations on experimental clinopyroxenes synthesized during high-pressure, high-temperature experiments on the same lava in order to investigate clinopyroxene–liquid equilibria in tholeiitic systems and optimize of geothermobarometric strategies. Natural clinopyroxenes from the 2014–2015 Holuhraun lava are sector zoned, with {1-11} hourglass sectors being enriched in the enstatite–ferrosillite component at the expense of all other components with respect to {hk0} prism sectors. In contrast with observations on clinopyroxenes from alkalic systems, sector zoning in clinopyroxenes from the 2014–2015 Holuhraun lava is characterized by differences in Ca and Na contents as well as in Ti and Al contents. The products of crystallization experiments performed at 100–600 MPa and 1140–1220 °C on a powdered starting glass at two sets of melt H2O content–oxygen fugacity conditions (∼0·1 wt % H2O and close to the graphite-oxygen redox buffer, and 0·5–1·0 wt % H2O and approximately one and half log units above the quartz–fayalite–magnetite redox buffer) demonstrate that clinopyroxene crystals from nominally equilibrium experiments can preserve strongly disequilibrium compositions. The compositional systematics of experimental clinopyroxenes are consistent with the presence of sector zoning. Furthermore, the magnitude of compositional variability increases with decreasing melt H2O content and increasing deviations of experimental temperatures below clinopyroxene liquidus temperatures (i.e. degrees of undercooling sensu lato), indicating that kinetic processes play a key role in controlling clinopyroxene compositions, even under notionally equilibrium conditions. Few published analyses of experimental clinopyroxene crystals may thus represent truly equilibrium compositions. Stoichiometric calculations on natural and experimental clinopyroxenes show that Fe3+ is a major constituent of clinopyroxenes from tholeiitic magmas under naturally relevant oxygen fugacity conditions. They also show that Fe3+ is most likely incorporated as Ca- and Al- bearing Ca–Fe-Tschermak’s component rather than Na-bearing aegirine component at oxygen fugacities up to one and a half log units above the quartz–fayalite–magnetite buffer. Elevated oxygen fugacities are thus less likely to compromise clinopyroxene–liquid geothermobarometry than previously thought. Guided by our experimental results, we combined published descriptions of clinopyroxene–liquid equilibria with geothermobarometric equations to develop an internally consistent and widely applicable method for performing geothermobarometry on tholeiitic magmas that does not require equilibrium zones to be selected a priori. Applying this method to natural clinopyroxene crystals from the 2014–2015 Holuhraun lava that formed under low but variable degrees of undercooling (perhaps 25 °C or less) returns values in excellent agreement with those from independent methods (232 ± 86 MPa, 1161 ± 11 °C). Robust estimates of magma storage conditions can thus be obtained by performing clinopyroxene–liquid geothermobarometry on tholeiitic magmas when disequilibrium is suitably accounted for.

L'étude de nombreuses coupes, complétée par une étude des caractères pétrologiques, minéralogiques et géochimiques a permis: de mettre en évidence un volcanisme permien d'affinité tholéiitique ; de préciser les caractères géodynamiques du volcanisme fini-triasique; d'envisager leur évolution dans le cadre général de l'ouverture de l'Atlantique . Le Volcanisme permien: Situé à la base de la série permienne continentale, ce volcanisme affleure de manière très locale à Annrar (Vallée de l'Ourika) et à Aguergour (Amizmizi). Il correspond à un empilement de 2 à 5 coulées peu épaisses (5 à 10 m chacune). Ce volcanisme d'affinité tholéiitique (continental), est marqué localement par un caractère hyperpotassique que masque parfois une spilitisation (paragenèse albite - chlorite - carbonates). Si la spilitisation, n'affectant que le sommet de certaines coulées, semble correspondre à une transformation hydrothermale au moment de l'épanchement, le caractère hyperpotassique affectant l'ensemble de certaines coulées, pourrait avoir une origine précoce par contamination du socle sous-jacent (Précambrien et Paléozoïque). Le Volcanisme Fini-Triasique: Situé au sommet de la série gréseuse triasique, ce volcanisme affleure de manière continue sur tout le' secteur considéré et s'intègre au sein d'un vaste trapp signant un épisode important, l'ouverture de l'Atlantique. Des observations de terrain complétées par une étude minéralogique (composition des pyroxènes) et géochimique (traces) ont montré que ce volcanisme est caractérisé par quatre formations (100 à 200 m) (Formations Inférieure, Intermédiaire, Supérieure et Récurrente). Celles-ci renferment chacune plusieurs coulées (parfois prismées) et sont séparées par des horizons sédimentaires. Une phase hydrothermale (silicieuse) est contemporaine de la mise en place de chaque épanchement où une zonalité de faciès (depuis des microdolérites porphyriques jusqu'à des dolérites intersertales microgrenues), a pu être mise en évidence. Des centres d'émission (Col du Tizi Ouzla), s'alignent selon une direction N 1100 et témoignent ainsi du rejeu d'an- ciens accidents tardi-hercyniens lors de la tectonique distensive triasique. A proximité des centres éruptifs, des formations transformées, correspondent à des lessivages à caractère deutérique de certains sommets de coulées (préhnite-calcite-silice) et ainsi qu'au piégeage du fluide hydrothermal au sein d'épanchements se succédant très rapidement dans le temps . La nature tholéiitique de ce volcanisme montre une évolution depuis des tholéiites continentales (Formation Inférieure), jusqu'à des tholéiites à caractère légèrement plus océanique (Formations Supérieure et Récurrente). Il proviendrait d'un processus normal de fusion partielle du manteau supérieur montrant une évolution en relation avec l'ouverture océanique. Le volcanisme permien et fini-triasique du Haut-Atlas occidental, présente un modèle géodynamique cohérent avec ceux évoqués actuellement dans le cas d'une zone de rift . Le volcanisme permien serait le témoin d'un stade de pré-rifting ; Le volcanisme fini-triasique serait contemporain du rifting., Pas de résumé

The Bellecôte massif ("département de Savoie") has a Permian and Triassic cover. Locally allochthonous because of Alpine age décollements, this Briançonnais-type cover may also have remained stratigraphically tied to its basement, on which it rests unconfomably with frequently reduced thicknesses : “Werfenian” (Lower Triassic) and Permian sandstones are often missing between the pre-Permian basement and the carbonate Triassic cover.The pre-Permian terranes remain undated, but might be of pre-Upper Carboniferous age. 1/10,000-scale mappings have allowed to recognize a 2 km-thick series. Chemical data, petrologically controlled, have revealed a chemical-stratigraphic zoning, which concerns mainly the abundant metamorphosed greenstones, of magmatic origin, and magmatic related, hydrothermally altered levels.The Pre-Permian series (overlaying an hypothetical, polymetamorphic basement, made of garnet micaschists) includes :- 1 km of banded greenstones, previously spilitic basalts, with thinner beds of soda-rich quartz-keratophyrs. Their spilitization took place early, but later than their magmatic cooling. The last felsic-mafic alternances include gabbro-diorite laccoliths, and soda-poor, mainly siliceous levels (SiO2 > 90% ; long-lasting hydrothermal silicifications ?). Most greenstones have revealed a low-TiO2 (0.5-1.5 %) tholeiite composition. Taking into account their probably submarine spilitization, those chemical features could indicate a marginal basin context.- 1 km of black slates (thin-grained, organic matter and pyrite-rich metasediments). Albite is abundant (Na2O > 4 %, K2O < 1.5 %) and attests prevailing volcanic influences, beside a low proportion of sialic detritals . The black slates contain many dark-green sills, again having a tholeiite chemical composition but TiO2-rich (2-2.5 %). Those last greenstones are therefore chemically similar to mid-oceanic tholeiites.Since its main characters suggest an oceanic setting, the Bellecôte pre-Permian series radically differs from the neighboring Upper Carboniferous (paleontologically dated as Namurian to Stephanian) and from the Stephano-Permian formations, both typically continental. Moreover, it could have been folded before the Permian. Hence, the northern Vanoise would display a pre-Namurian basement, without Upper Carboniferous deposits, locally unreached by sedimentation until the Triassic times. Such pre-Namurian series do exist in the contiguous massifs (Mont Pourri, Grand Bec), and in the External Crystalline Massifs (located 50-100 km to the W). All those similar series might be of Ordovician to Silurian age.Following a presumed pre-Permian folding, three major Alpine tectonic events have been separated. During the FIRST EVENT, a great, kilometric-scale, flat - lying Penninic fold have been generated, N- to NE-verging, the core of which includes metamylonites. The SECOND EVENT would have been the so-called backfolding, E- to SSE- verging. The THIRD EVENT has been characterized by a moderate lithostatic overburden, and by high fluid pressures along the thrusts and faults, creating tectonic, mineralized breccias (among which the so-called cargneules, issued from dolomitic Triassic formations). During that third event, northern Vanoise has been thrust over the "zone houillère” to the North ; its displacement may be related to a greater scale, senestral, N-S strike-slip fault, which runs along the frontier between Internal Briançonnais zone (the Vanoise, to the E) and external Briançonnais zone (the "zone houllière", to the W)., Centré sur le haut massif de Bellecôte, en Savoie, ce terrain (8 km x l2 km) possède une couverture permienne et triasique à faciès brianconnais, parfois décollée tectoniquement. Elle peut aussi être adhérente, discordante stratigraphiquement sur l'Antépermien, et est alors souvent réduite: le Werfénien (Scythien) et le Permien peuvent manquer totalement.L'Antépermien est d'âge inconnu. La cartographie à 1/10 000 permet d'y reconnaître une série de deux kilomètres environ de puissance. En liaison avec l'étude pétrologique, les analyses chimiques montrent une zonation chimiostratigraphique, du moins pour les nombreuses formations d'origine magmatique ou volcanique, y compris les produits de l'altération hydrothermale précoce.Sur un possible socle polymétamorphique (micaschistes à grenats), la série antépermienne comporte 1 km de métabasites rubanées, anciens basaltes spilitiques, à niveaux subordonnés de quartz-kératophyres sodiques. La spilitisation est précoce, mais postmagmatique. Les dernières alternances acide-basique consistent en laccolites gabbro-dioritiques, et en barres de quartz-kératophyres non sodiques, très siliceux (SiO2 > 90%; silicification hydrothermale prolongée ?). Jusqu'à ce niveau, les "roches vertes" paléozoïques ont un chimisme de tholéiites pauvres en TiO2 (moins de 1,5%). Ceci, avec la spilitisation probablement sous-marine, permet de proposer un contexte de bassin marginal.Puis viennent 1 000 m de schistes noirs (métasédiments fins riches en matière organique et en pyrite). L'albite y est abondante (4% de Na2O contre 1% de K2O) et témoigne d'influences volcaniques dominantes, avec une faible proportion d'apports sialiques. Les nombreux sills vert sombre dans ces schistes noirs ont une composition de tholéiites riches en TiO2 (2% à 2,5%), et sont ainsi analogues aux tholéiites médioocéaniques.Par ses caractères, évoquant un contexte océanique, l'Antépermien de Bellecôte diffère du Houiller, daté et situé à l'Ouest, et du Stéphano- Permien, tous deux continentaux. Ce matériel pourrait de plus avoir été plissé avant le Permien. On peut donc voir dans la Vanoise septentrionale un socle antéhouiller, émergé au Carbonifère supérieur et parfois jusqu'au Trias. Des séries analogues existent dans les massifs voisins (Mont Pourri, Grand Bec), et dans les massifs cristallins externes. L'hypothèse d'un âge siluro-ordovicien est envisageable.Outre un possible plissement antépermien, trois phases tectoniques alpines majeures sont distinguées. La phase 1 aurait créé un vaste pli couché à vergence N ou NE, dont le cœur est jalonné de métamylonites. La phase 2 serait celle dite de rétrocharriage, à vergence E à SSE selon les lieux. La phase 3 est caractérisée par une faible charge lithostatique, et les fortes pressions de fluides le long des accidents ont engendré des roches broyées et minéralisées (entre autres cargneules). Lors de cette dernière phase se produit le chevauchement vers le N de la Vanoise septentrionale sur la zone houillère, mouvement qui peut être relié à un vaste décrochement senestre orienté N-S, à la frontière entre le Briançonnais interne (Vanoise, à l'E) et le Briançonnais externe (zone houillère, à l'W).

National audience

The Bellecôte massif ("département de Savoie") has a Permian and Triassic cover. Locally allochthonous because of Alpine age décollements, this Briançonnais-type cover may also have remained stratigraphically tied to its basement, on which it rests unconfomably with frequently reduced thicknesses : “Werfenian” (Lower Triassic) and Permian sandstones are often missing between the pre-Permian basement and the carbonate Triassic cover.The pre-Permian terranes remain undated, but might be of pre-Upper Carboniferous age. 1/10,000-scale mappings have allowed to recognize a 2 km-thick series. Chemical data, petrologically controlled, have revealed a chemical-stratigraphic zoning, which concerns mainly the abundant metamorphosed greenstones, of magmatic origin, and magmatic related, hydrothermally altered levels.The Pre-Permian series (overlaying an hypothetical, polymetamorphic basement, made of garnet micaschists) includes :- 1 km of banded greenstones, previously spilitic basalts, with thinner beds of soda-rich quartz-keratophyrs. Their spilitization took place early, but later than their magmatic cooling. The last felsic-mafic alternances include gabbro-diorite laccoliths, and soda-poor, mainly siliceous levels (SiO2 > 90% ; long-lasting hydrothermal silicifications ?). Most greenstones have revealed a low-TiO2 (0.5-1.5 %) tholeiite composition. Taking into account their probably submarine spilitization, those chemical features could indicate a marginal basin context.- 1 km of black slates (thin-grained, organic matter and pyrite-rich metasediments). Albite is abundant (Na2O > 4 %, K2O < 1.5 %) and attests prevailing volcanic influences, beside a low proportion of sialic detritals . The black slates contain many dark-green sills, again having a tholeiite chemical composition but TiO2-rich (2-2.5 %). Those last greenstones are therefore chemically similar to mid-oceanic tholeiites.Since its main characters suggest an oceanic setting, the Bellecôte pre-Permian series radically differs from the neighboring Upper Carboniferous (paleontologically dated as Namurian to Stephanian) and from the Stephano-Permian formations, both typically continental. Moreover, it could have been folded before the Permian. Hence, the northern Vanoise would display a pre-Namurian basement, without Upper Carboniferous deposits, locally unreached by sedimentation until the Triassic times. Such pre-Namurian series do exist in the contiguous massifs (Mont Pourri, Grand Bec), and in the External Crystalline Massifs (located 50-100 km to the W). All those similar series might be of Ordovician to Silurian age.Following a presumed pre-Permian folding, three major Alpine tectonic events have been separated. During the FIRST EVENT, a great, kilometric-scale, flat - lying Penninic fold have been generated, N- to NE-verging, the core of which includes metamylonites. The SECOND EVENT would have been the so-called backfolding, E- to SSE- verging. The THIRD EVENT has been characterized by a moderate lithostatic overburden, and by high fluid pressures along the thrusts and faults, creating tectonic, mineralized breccias (among which the so-called cargneules, issued from dolomitic Triassic formations). During that third event, northern Vanoise has been thrust over the "zone houillère” to the North ; its displacement may be related to a greater scale, senestral, N-S strike-slip fault, which runs along the frontier between Internal Briançonnais zone (the Vanoise, to the E) and external Briançonnais zone (the "zone houllière", to the W)., Centré sur le haut massif de Bellecôte, en Savoie, ce terrain (8 km x l2 km) possède une couverture permienne et triasique à faciès brianconnais, parfois décollée tectoniquement. Elle peut aussi être adhérente, discordante stratigraphiquement sur l'Antépermien, et est alors souvent réduite: le Werfénien (Scythien) et le Permien peuvent manquer totalement.L'Antépermien est d'âge inconnu. La cartographie à 1/10 000 permet d'y reconnaître une série de deux kilomètres environ de puissance. En liaison avec l'étude pétrologique, les analyses chimiques montrent une zonation chimiostratigraphique, du moins pour les nombreuses formations d'origine magmatique ou volcanique, y compris les produits de l'altération hydrothermale précoce.Sur un possible socle polymétamorphique (micaschistes à grenats), la série antépermienne comporte 1 km de métabasites rubanées, anciens basaltes spilitiques, à niveaux subordonnés de quartz-kératophyres sodiques. La spilitisation est précoce, mais postmagmatique. Les dernières alternances acide-basique consistent en laccolites gabbro-dioritiques, et en barres de quartz-kératophyres non sodiques, très siliceux (SiO2 > 90%; silicification hydrothermale prolongée ?). Jusqu'à ce niveau, les "roches vertes" paléozoïques ont un chimisme de tholéiites pauvres en TiO2 (moins de 1,5%). Ceci, avec la spilitisation probablement sous-marine, permet de proposer un contexte de bassin marginal.Puis viennent 1 000 m de schistes noirs (métasédiments fins riches en matière organique et en pyrite). L'albite y est abondante (4% de Na2O contre 1% de K2O) et témoigne d'influences volcaniques dominantes, avec une faible proportion d'apports sialiques. Les nombreux sills vert sombre dans ces schistes noirs ont une composition de tholéiites riches en TiO2 (2% à 2,5%), et sont ainsi analogues aux tholéiites médioocéaniques.Par ses caractères, évoquant un contexte océanique, l'Antépermien de Bellecôte diffère du Houiller, daté et situé à l'Ouest, et du Stéphano- Permien, tous deux continentaux. Ce matériel pourrait de plus avoir été plissé avant le Permien. On peut donc voir dans la Vanoise septentrionale un socle antéhouiller, émergé au Carbonifère supérieur et parfois jusqu'au Trias. Des séries analogues existent dans les massifs voisins (Mont Pourri, Grand Bec), et dans les massifs cristallins externes. L'hypothèse d'un âge siluro-ordovicien est envisageable.Outre un possible plissement antépermien, trois phases tectoniques alpines majeures sont distinguées. La phase 1 aurait créé un vaste pli couché à vergence N ou NE, dont le cœur est jalonné de métamylonites. La phase 2 serait celle dite de rétrocharriage, à vergence E à SSE selon les lieux. La phase 3 est caractérisée par une faible charge lithostatique, et les fortes pressions de fluides le long des accidents ont engendré des roches broyées et minéralisées (entre autres cargneules). Lors de cette dernière phase se produit le chevauchement vers le N de la Vanoise septentrionale sur la zone houillère, mouvement qui peut être relié à un vaste décrochement senestre orienté N-S, à la frontière entre le Briançonnais interne (Vanoise, à l'E) et le Briançonnais externe (zone houillère, à l'W).