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International audience; We describe a case of S-type alkali-feldspar granite (quartz/K-feldspar/plagioclase/ biotite/garnet ∼ 30/35/20/13/2 vol%) showing skeletal and dendritic textures. It consists of three nested units distinguishable by the size of biotite crystals: a first-emplaced unit characterized by small biotite flakes (0.4–9 mm); a second unit with cm-sized biotite platelets (0.3–28 mm) outlining a syn-magmatic foliation; and a third unit formed of large biotite plates (0.7–850 mm) showing dendritic and radial growth patterns.Quartz occurs mostly as rounded to euhedral grains, but also shows complex shapes (serrated outline, re-entrants, etc.). Cathodoluminescence imaging reveals that grains consist of both rounded and skeletal bluish cores (quartz-1) rimmed by reddish overgrowths (quartz-2) that lead locally to the coalescence of neighbouring grains and equilibrated texture. Biotite is poikilitic enclosing dominantly quartz grains but also in lesser amount plagioclase and garnet. In the third unit, biotite shows textures typical of dendritic growth (bifurcating, radiating or branching structures, skeletal core). Plagioclase (An≤25) occurs as small euhedral to subhedral grains scattered in the matrix or forming glomerophyric aggregates. K-feldspar (Or74–100) mostly forms an almost equilibrated mosaic of anhedral perthitic crystals; it also appears in association with albite as a secondary phase replacing plagioclase. The crystallization sequence started with garnet, then proceeded with quartz, plagioclase, biotite and K-feldspar, ended with cordierite, and was followed by subsolidus reequilibration.The variability in size and morphology of quartz and biotite is interpreted in terms of variable undercooling depending on temperature of the host-rocks and on more or less intense degassing of magma batches with variable melt water content. Here, rapid crystallization prevented significant textural reequilibration and allowed the initial crystallization textures of quartz to be preserved. Overall, this study shows that behind the common “coarse-grained” texture of quartz in granite, subsist primary disequilibrium crystallization textures.

International audience

We present structural, petrological, geochemical and geochronological data compiled in a new geological map on the high-grade metamorphic rocks exposed in the Mbe – Sassa-Mbersi region located along the Tchollire-Banyo Shear Zone, at the northern edge of the Central Cameroon domain. The region exposes a complex assemblage of metabasic (hornblendite, metagabbro, amphibolite) and metasedimentary (garnet paragneiss, calc-silicate gneiss) rocks alternating with ubiquitous migmatitic intermediate to felsic gneisses. U-Pb ages on detrital zircon in paragneiss point to the contribution of Archean, Paleoproterozoic and Neoproterozoic sources, and suggest a maximum deposition age of 725 ± 12 Ma for their sedimentary protolith. The protolith of some amphibolites was emplaced during the Neoproterozoic as indicated by U–Pb ages on magmatic zircon at 600 ± 4 and 599 ± 6 Ma. Plutonic rocks with I-type chemical signatures were emplaced discontinuously over a period of ca. 80 Ma. The magmatic evolution started with the intrusion of magnesian medium-K tonalites and trondhjemites at 651 ± 3 Ma, followed by magnesian high-K hornblende-biotite granites and ferroan shoshonitic biotite granites until 599 ± 2 Ma. Finally, pegmatite dykes were emplaced along dextral shear zones at 573 ± 2 Ma. The metamorphic rocks show a penetrative shallow-dipping foliation partially to totally transposed in a NE–SW trending steep-dipping foliation bearing a shallow-dipping lineation. These ductile syn-migmatitic fabrics, developed under high-grade metamorphic conditions in the presence of melt, between the metamorphic peak at ca. 1.3 GPa–770 °C, and the following isothermal decompression down to ca. 0.8 GPa. In situ U–Pb dating of metamorphic zircon rims from a garnet migmatitic paragneiss yields an age of 582 ± 4 Ma. Localization of high-grade deformation is indicated by the development of the Tchollire-Banyo Shear Zone, characterized by mutually crosscutting subvertical and shallow-dipping mylonitic to ultramylonitic shear zones associated with sinistral and top-to-the SW kinematic criteria, respectively. These data indicate that the Central Cameroon domain exposed in the Mbe – Sassa-Mbersi region, represents the exhumed mid-to lower part of the former orogenic root of the Pan-African Central Africa Orogenic Belt that has undergone partial melting, lateral flow and intrusion of mafic to felsic calc-alkaline magmas between 650 and 580 Ma. The waning stage of the Pan-African orogeny is marked by the emplacement of syntectonic pegmatitic granite at ca. 575 Ma in subvertical E-W trending retrogressive dextral shear zones.

This study presents new U–Pb zircon ages for three granitoid bodies in the Imiter inlier at the eastern part of the Moroccan Anti-Atlas chain, which is located in the northwestern edge of the West African Craton (WAC). Analyzes of zircon grains yield the following ages: 538 ± 6 and 575 ± 10 Ma for the Igoudrane massif , 567 ± 6 Ma for the nearby Bou Teglimt granodiorite , and 582 ± 6 Ma for the Bou Fliou granite . These new data reveal that the Igoudrane massif is younger than previously thought (677 Ma), and that all the granitoids in the Imiter area are Ediacaran in age and are related to the Ouarzazate Group. Sm-Nd isotopic data yield negative eNd(t) values (−4.5 to −0.2) and T DM model ages of 1.04–1.82 Ga. These data indicate the presence of an inherited Paleoproterozoic to Archaean component in some zircon grains and show that generation of the parent magmas involved a Neoproterozoic juvenile contribution and recycling of an older crustal component. These new data allow reinterpreting the geochemical and isotopic data of the granitoids, and revisiting the structural significance to the Igoudrane massif, which was assumed until now to be coeval with the major Pan-African event of the Central Anti-Atlas. They also bring significant constraints to discuss the context and age of deposition of the Saghro Group, which is still a matter of debate. All these data provide evidence of an emplacement of the Imiter granitoids in a subduction complex, which affected all of the Anti-Atlas chain during the Late Proterozoic time.

International audience; The palladium-mediated C–H radio-iodination of arenes using sodium iodide as the primary isotopic source is reported and performed without chemical know-how in 30 min and applied to the synthesis of complex radio-iodinated compounds of biological interest.

V. Ngako and E. Njonfang addressed in their comment an interesting and debated issue about the collision geodynamics of the Pan-African Central African Orogenic Belt (CAOB) in Cameroon. However, the reason for this comment is still not clear to us since it mainly deals with issues far away from the scope of our study, namely, the pre-collisional set up of the belt. The comment raises two main points – the reworking process during plate collision and the Pan-African strain pattern – not discussed in our paper for the simple reason that it was not our goal and because our data set does not even allow such discussion. Having said that, the comment gives us the opportunity to clarify our view on the nature of the Adamawa-Yade domain (Central Cameroon) and the early evolution of the CAOB. We will successively discuss two other points raised in the comment: (1) our Fig. 12 depicting a possible pre-collisional configuration at the northern and southern margin of the Congo craton in the Early Neoproterozoic, and (2) the nature and extent of the Adamawa-Yade domain.

The Marbat basement (Sultanate of Oman) belongs to the Neoproterozoic accretion domain of the Arabian-Nubian shield. We present new geochronological, petrological and geochemical data as an extension of our previous study (Denele et al., 2017) re-interpreting this basement as a metamorphic core complex (MCC). We showed that this MCC consists of a metamorphic unit (Juffa complex) separated by an extensional detachment from a plutonic unit (Sadh complex and Tonalite plutons). Geochemical data show that the Juffa metasediments correspond to volcanogenic graywackes, suggesting deposition in front of a juvenile magmatic arc. New in situ U-Pb zircon data show that the protolith of the Juffa paragneisses is Tonian in age (960-830 Ma). The Juffa complex recrystallized under amphibolite facies conditions (950 MPa, 630 degrees C) corresponding to thermal gradient of 17-18 degrees C/km, i.e. close to that observed in fore-arc environment subjected to tectonic underplating. It was then retrogressed (< 400 MPa, < 400 degrees C) during exhumation of the MCC. Phase assemblages of the Sadh complex and Tonalite plutons record magmatic temperatures estimated at 700-840 degrees C and 610-840 degrees C from hornblende and zircon-saturation thermometry, respectively; pressures are grossly estimated at ca. 250 MPa. These data and structural evidence led us to consider that the Sadh complex is a plutonic unit emplaced during exhumation of the MCC. Hence, we re-interpret the previously published zircon core U-Pb ages of the Banded gneisses (ca. 860-830 Ma) as inherited, and zircon rim ages (ca. 815 Ma) as the age of their intrusion. This suggests that the parent magma of all these granitoids could have interacted with volcanic material equivalent to the Juffa complex. Overall, the Marbat area developed during the Tonian and involved (i) deposition of volcanosediments (Juffa complex) in an island-arc environment (960-830 Ma); (ii) metamorphism under middle pressure conditions during tectonic underplating at ca. 820-815 Ma, followed by emplacement of plutonic rocks in the upper crust during initiation of the MCC at ca. 815-810 Ma; and (iii) late-tectonic intrusions associated with MCC amplification at ca. 800-790 Ma (Mahall intrusives and Tonalite plutons).

International audience

New field observations, ages and geochemical data are presented for the Adamawa-Yade domain, forming part of Central African Orogenic Belt in Cameroon. This belt delineates the northern margin of the Congo craton and is part of the Braziliano/Pan-African orogenic system, which was formed during amalgamation of the West Gondwana continent at the end of the Neoproterozoic. U–Pb dating indicates that the protoliths of some orthogneisses from the Adamawa-Yade domain were emplaced during three distinct periods. Tonalite-Trondhjemite-Granodiorite (TTG) suites in the Makenene area intruded at ca. 3.0–2.5 Ga, and were affected by partial melting at ca. 2.08–2.07 Ga, during the Eburnean orogeny, and by a magmatic event with a metamorphic overprint at 0.64–0.61 Ga, during the Pan-African orogeny. A dioritic orthogneiss from the Maham area, north of Makenene, was emplaced at 2.07 Ga and also reworked at 0.62–0.61 Ga. The youngest granitic orthogneisses, sampled in the vicinity of Bafia, Bep and Ngaa-Bape, yield intrusion ages of 0.64–0.63 Ga. Some of these Neoproterozoic plutonic rocks show shoshonitic affinity and reveal eNd (630 Ma) values ranging from −1.2 to −6.9 (1.7 > T DM > 1.1 Ga), and 87 Sr/ 86 Sr initial ratios of 0.706 and 0.704, providing evidence for crustal reworking during the Pan-African collision. The isotopic geochemical characteristics provide evidence that potassic magmas result from the interaction between the Archaean TTG continental crust and magmas derived from a mantle enriched in silica and incompatible elements during subduction underneath a continental margin. The Bafia group appears as a complex geological entity comprised of an Archaean/Palaeoproterozoic basement and its Neoproterozoic sedimentary cover, both deformed and recrystallized at ca. 0.61 Ga. The crustal evolution of the Adamawa-Yade domain is very similar to that inferred for the northern margin of the Congo craton (the Ntem complex and Nyong series). This and the sedimentary record suggest that the Adamawa-Yade domain represents an Archaean/Palaeoproterozoic microcontinent, which was detached from the northern margin of the Congo craton in the early Neoproterozoic, but became re-accreted together with the Mayo Kebbi (magmatic) arc during the Pan-African orogeny.

We investigate the development of a Neoproterozoic metamorphic core complex (MCC) in the Marbat area (southern Arabian Peninsula). The MCC is a gneiss dome emplaced in a releasing bend along a dextral strike-slip fault system. Dome emplacement-related extension was at a high angle to the long axis of the dome and 65 degrees from the strike-slip fault system. Shortening is recorded in the upper plate of the MCC in a direction normal to the extension direction. Extensional emplacement of the gneiss dome accommodated lower crust exhumation and contributed to the formation of a ductile strike-slip releasing bend from an initial fault step. The Marbat example allows defining transversal stretching-dominated strike-slip MCCs, which would represent the early development stages of longitudinal stretching-dominated strike-slip MCCs. Conversely, longitudinal stretching-dominated strike-slip MCCs produced at low finite extension would result from strike-slip-dominated transtension. This study bears important implications for lower crust exhumation under pulla-part basin systems in obliquely convergent or divergent settings.

The Tchollire massif, in central north Cameroon, consists of elongated granite plutons that crop out along the Pan-African Tchollire-Banyo shear zone (TBSZ), a potential suture zone within the Central Africa Orogenic Belt. New structural and geochronological data on these granites constrain the tectonic regime and timing of the TBSZ. The plutons consist of syntectonic granites and granodiorite containing dioritic mafic enclaves. They show an S2 sub-vertical foliation, that trends NE-SW to ENE-WSW. The related L2 lineation is subhorizontal to shallowly plunging to the SW or NE. Kinematic indicators such as asymmetric folds, sigmoidal-shape boudins, shear bands, imbricated feldspar phenocrysts along antithetic fractures point to a sinistral sense of shear. Microstructural analysis shows that structures are acquired from the submagmatic to the low temperature solid state suggesting progressive deformation of the magma during its emplacement, crystallization and cooling. U-Pb zircon dating on this massif yields emplacement ages of 719 ± 12 Ma for the biotite-amphibole granite and muscovite granite, 652.2 ± 5.4 Ma for the biotite-granite and 632 ± 13 Ma for the leucogranite. These geochronological data show in addition, Palaeoproterozoic inherited ages of 1631 ± 30 Ma on the leucogranites of this massif, and point to a Palaeoproterozoic contribution in their genesis. The range of ages (ca. 87 Ma) points to the timing of syntectonic emplacement of felsic magmas coeval with sinistral transpression along the TBSZ during the Pan-African orogeny. These results show that the TBSZ has recorded prolonged deformation associated with crustal magmatism between the Palaeoproterozoic Adamawa-Yade domain to the southeast and the Sinassi-Mayo Kebbi Neoproterozoic magmatic arc to the Northwest.

In this article, we discussed about the petrography and geochemistry of magmatic rocks of the Mbip massif located SW of Tchollire, in Central North Cameroon (Central African Fold Belt). Petrographic study shows that this massif is made of granodiorite, amphibole-biotite granite, and biotite granite which often contain enclave of mafic rocks (gabbro). Granodiorites and granites show porphyritic texture and consist dominantly of plagioclase and alkaline feldspar phenocrysts, quartz, biotite and often few amphibole. The gabbro enclaves are characterized by a granular porphyroid texture constituted of amphibole, plagioclase and olivine phenocrysts, all in a matrix of small crystals of plagioclase, olivine, amphibole, pyroxene and opaque minerals. All the analyzed rocks provide geochemical features of sublkaline serie and have nothing to do with the alkaline nature previously signaled in the former works. Granodiorites and granites are shoshonitic to calc-alkaline strongly potassic affinity consistent with emplacement in the continental collision setting. They present positive anomalies in Rb, Th, U; negative anomalies in Sr, P, Ti, Nb, Ta and some facies contain hydrated minerals such as amphibole. These characters are consistent with crustal and mantle contribution in their genesis. The mafic rocks (gabbro) have geochemical characteristics conferring a mantle origin, as confirmed by the high Mg# value (49.9). On the whole, the fractional crystallization of the magma formed by melting of crustal material and the magmatic mixing are the main petrogenetic process in the Mbip massif. Petrographic studies and geochemical data shows that the Mbip massif was emplaced in an active continental margin, into transitional regime from the end of maximum compression to the beginning of relaxation.

International audience; We reassess the geodynamic context close to the Congo craton during the pre-collisional period of the Pan-African orogeny from whole-rock major and trace element compositions and isotopic data obtained in the westward extension of the Yaounde series (Boumnyebel area, Cameroon). The series consists of metasediments (micaschists, minor calc-silicate rocks and marbles) and meta-igneous rocks (hornblende gneisses, amphibolites, metagabbros, pyroxenites and talcschists) recrystallized under high-pressure conditions.Chemically, the micaschists correspond to shales and greywackes similar to the Yaounde high-grade gneisses. 87Sr/86Sr initial ratios (0.7084–0.7134), moderately negative εNd(620 Ma) values (−5.75 to −7.81), Nd model ages (1.66 < TDM < 1.74 Ga) and radiometric ages point to the conclusion that the Yaounde basin was filled with siliciclastic sediments derived from both reworked older continental crust (Palaeoproterozoic to Archaean in age) and Neoproterozoic juvenile volcanogenic material. This occurred in the same time span (625–1100 Ma) as the deposition of the Lower Dja, Yokadouma, Nola and Mintom series (Tonian–Cryogenian). Dolomitic marble associated with mafic/ultramafic rocks and characterized by high Cr (854–1371 ppm) and Ni (517–875 ppm) contents, are considered to result from chemical precipitation in relation with submarine magmatic activity.Talcschists (orthopyroxenitic to harzburgitic in composition) show primitive-mantle-normalized multi-element patterns with significant negative Nb–Ta anomalies, and slopes similar to that of average metasomatically altered lithospheric mantle. These rocks could be mantle slices involved in the collision tectonics. Amphibolites show the compositions of island-arc basalts with systematic negative Nb–Ta anomalies, 87Sr/86Sr initial ratios mostly

International audience; The Tcholliré and Banyo high-pressure granulites occur mainly as highly strained small lenses, bands or elongated bodies interbedded with gneisses and migmatites in the Central African Fold Belt (CAFB) in north-central Cameroon. They were previously attributed to Palaeoproterozoic but are now shown to be Pan-African. These granulites are made up of two occurrences of metapelites with garnet-kyanite-sillimanite-cordierite-biotite-quartz-plagioclase and metabasites containing garnet-clinopyroxene-orthopyroxene-hornblende-quartz-plagioclase.Eight samples were analysed in detail by electron microprobe for mineral chemistry.Parageneses in both metapelites and metabasites highlight three main stages witnessed by prograde, peak and retrograde mineral assemblages. The prograde stage is preserved as well-defined inclusion trails of kyanite, biotite, plagioclase, quartz, and rutile within porphyroblasts of garnet in metapelites; or with more or less clinopyroxene, hornblende, plagioclase, quartz, ilmenite, rutile and apatite, within porphyroblasts of garnet in metabasites. The peak stage, displaying heterogranular granoblastic texture is characterised by porphyroblastic garnet-kyanite-K-feldspar-biotite in metapelites and garnet-clinopyroxene-plagioclase-quartz in metabasites. This was followed by decompression and cooling during the retrograde stage marked by aggregate of sillimanite prisms presumably after kyanite and cordierite corona around garnet in metapelites and by symplectites or vermicular structures of orthopyroxene-plagioclase and orthopyroxene corona around garnet in metabasites. Geothermobarometric study shows that granulite facies metapelites and metabasites from both Tcholliré and Banyo regions recrystallised under peak pressure-temperature conditions of 13–14 kbar and 800–900 °C. They experienced similar clockwise P-T path with nearly isothermal decompression.Our results provide evidence for a substantial crustal thickening during the Pan-African continent–continent collision but show that there is no significant isothermal decompression as commonly observed in recent collisional orogens. The reconstructed P-T paths are in some ways reminiscent of the ones reported in Precambrian “mixed-hot orogens”.

International audience; This paper discusses the exhumation history of Palaeoproterozoic high-grade units from the Lapland Granulite Belt (northern Finland) through a reappraisal of previous structural and metamorphic data and a new structural analysis. The Lapland Granulite Belt is located between two cratons (Inari Craton and South Lapland Craton). It is marked by a major thrusting event associated with the development of an inverse metamorphic gradient within the underlying Tanaelv and Karasjok Belts. The review of published metamorphic data combined with our new structural analysis suggests that the exhumation history of the Lapland Granulite Belt was accommodated by the development of coeval basal thrusting and early normal-sense shear-zones, and later by distributed erosion. We propose also that the early exhumation stages of the Lapland granulite unit were associated with heating of both the overlying Inari Craton and the underlying South Lapland Craton. The occurrence of coeval thrusts and normal-sense shear-zones combined with the important role of distributed erosion during the final exhumation stages suggest that this Palaeoproterozoic collisional belt may represent an intermediate stage between ultra-hot accretionary orogens involving weak lithospheres and modern orogens involving stiff lithospheres (mixed-hot orogen of Chardon et al., 2009). Our analysis emphasizes that the transition between ancient-type orogens and modern-type ones was gradual in space and time, being firstly dependent on the thermal and rheological state of the sub-continental lithospheric mantle of the lithospheres involved in compression.

This study deals with the origin of igneous layering in plutons, and, especially, the extent layering is related to mafic–silicic magma interactions. The Budduso pluton (Sardinia) shows three main scales of organization. (i) Large scale lithological variations correspond to three main magmatic units, with differentiation increasing from the Outer (hornblende-bearing biotite granodiorite/monzogranite) to the Middle (biotite monzogranite) and the Inner (leucomonzogranite) units. The striking homogeneity of 87 Sr/ 86 Sr initial ratios (0.7090 ± 4) and e Nd(t) values (− 5.6 ± 0.1) strongly suggests that magma isotopic equilibration was achieved prior to emplacement, whereas mixing/mingling structures observed within the pluton reflect second-stage processes involving broadly cogenetic components. (ii) Metre to decametre-scale igneous layering may be isomodal or modally-graded, locally with cross-layering. Biotite and plagioclase compositions are similar in both biotite-rich and quartzofeldspathic layers, as are the trace-element patterns which differ only by relative abundances. This precludes an origin by fractional crystallization. A penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation. (iii) Composite layering and schlieren are commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones or disrupted synplutonic dykes. In that case, there is a progressive shift in biotite X Fe values from the core of enclave (∼ 0.65) to the host monzogranite (∼ 0.72): schlieren in the monzogranite show biotite X Fe values similar to that of the host rock, whereas schlieren close to mafic enclaves show lower X Fe values (∼ 0.69) towards those of enclave rims. These features can be ascribed to three main processes: (i) assembly of differentiated (± mixed/mingled) magmatic pulses; (ii) local hydrodynamic sorting related to density currents in a mush, and segregation of residual melt; (iii) mechanical disruption and chemical hybridization of mafic magmas during ascent or within the pluton related to magma dynamics. None of these processes affect the whole pluton but they are limited to specific magmatic units. Therefore, pluton growth by incremental assembly of magma batches is not incompatible with magma chamber processes.

International audience; A new structural and kinematic study of the Hospitalet dome (Pyrenees) is presented. This dome corresponds to the eastern half of an EW-trending antiformal structure made of an orthogneissic core intruded by granitoids, partly covered by Upper Proterozoic to Lower Ordovician metapelites. Its Variscan evolution can be split into four stages: (i) development of a strong high temperature pervasive deformation associated with subhorizontal foliations and lineations, and with non-coaxial top-to-the-east kinematics; (ii) formation of a south-verging overturned megafold; (iii) emplacement of calc-alkaline granitoids; and (iv) formation of mylonitic bands on the southern border of the dome, with reverse dextral kinematics. The flat lying pervasive high-T deformation is interpreted as a large lateral flow developed in a dextral transpressive regime inducing an important uncoupling between the middle and upper crusts. The next stages happened in a progressive deformation in the same transpressive regime.

We discuss the significance of igneous layering with respect to pluton growth processes. The case study is the Tarcouate Laccolith (Morocco), whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves, contrasting with peripheral, non-layered biotite granodiorites with low amount of enclaves. Rhythmic layering, with modal grading, cross-stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves. Its steep dips ≥ 45° result from tilting that occurred above solidus conditions, as indicated by sub-vertical and synmagmatic granite, aplite and monzodiorite dykes cutting across the layering. The systematic association of igneous layering with mafic enclaves in calc-alkaline plutons suggests that layering originates from recurrent injection of mafic magma. Viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the Tarcouate Laccolith. Intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection, formation of mafic enclaves and development of igneous layering through protracted crystallization.

Mineral chemistry, major and trace elements and Sr-Nd isotopes are presented for basalts and trachybasalts from the Quaternary alkaline Tepi shield from southwest Ethiopia. The lavas are variably porphyritic with phenocrysts of olivine (Fo67-87), clinopyroxene (Wo45-47En38-40Fs13-16), plagioclase (An57-68) and Ti-magnetite set in a microcrystalline matrix. Although there are two high-MgO lavas (10.6-10.8 wt.% MgO), the majority of specimens are more evolved (MgO = 4.7-6.2 wt.%). The major element variations can be explained by olivine + clinopyroxene ± plagioclase fractionation, most likely consistent with low P fractionation. The geochemical variations observed in the Tepi lavas are interpreted in terms of variable open system fractional crystallization of a magma sourced from primitive mantle like source.

Structural, mineralogical and chemical studies show that the rocks from the Dabakala area, previously reported as gneisses and migmatites, are in fact syntectonic granitoid bodies. Three chemical associations are distinguished: (i) trondhjemitic (Dabakala tonalites and granodiorites), calc-alkaline (Finessigue granodiorites and undifferentiated biotite granodiorites and granites) and peraluminous (Sarala hololeucocratic granites and Kowara muscovite trondhjemites). Most granitoids display deformation patterns typical of an interference between pluton emplacement and transpressional tectonics induced by a NNW-SSE to NW-SE compression which led to three major NS sinistral shear zones (N’Zi, Katidougou, Ouango-Fitini). Geochronological data (U–Pb ID-TIMS and SIMS zircon ages) yielded 2312±17 Ma for the zircon cores from the Dabakala tonalite, 2154±1 Ma for the zircon rims of the same tonalite, 2162±32 Ma for Sarala, 2118±2 Ma for Kowara, and 2103±1 Ma for Finessigue. Sr–Nd isotopic data further indicate that all these rocks are isotopically primitive ( 0.7000 87 Sr / 86 Sr , +1.8 Nd (2.1 Ga ) +3.7 , 2039

The Ethiopian continental flood basalt (CFB) province (∼30 Ma, > 3 × 105 km3) was formed as the result of the impingement of the Afar mantle plume beneath the Ethiopian lithosphere. This province includes major sequences of rhyolitic ignimbrites generally found on top of the flood basalt sequence. Their volume is estimated to be at least 6 × 104km3, which represents 20% of that of the trap basalts. Their phenocryst assemblage (alkali feldspar, quartz, aegyrine-augite, ilmenite ± Ti-magnetite, richterite, and eckermanite) suggests temperatures in the range of 740 to 900°C. Four units were recognized in the field (Wegel Tena, Jima, Lima Limo, and Debre Birhan areas), each with its own geochemical specificity. Zr/Nb ratios remain constant between basalt and rhyolite in each area, and rhyolites associated with high-Ti or low-Ti basalts are, respectively, enriched or depleted in titanium. Their trace element and isotope (Sr, Nd, O) signatures (high 143Nd/144Nd and low 87Sr/86Sr ratios, compared to those of rhyolites from other CFB provinces) are clearly different from those of typical crustal melts and indicate that the Ethiopian rhyolites are among the most isotopically primitive rhyolites. Their major and trace element patterns suggest that they are likely to be derived from fractional crystallization of basaltic magmas similar in composition to the exposed flood basalts with only limited crustal contribution. Since Ethiopian high-Ti basalts have been shown to form from melting of a mantle plume, it is likely that Ethiopian ignimbrites, at least those that are Ti-rich, also incorporated material from the deep mantle. Rb-Sr isochrons on whole rocks and mineral separates (30.1 ± 0.4 Ma for Wegel Tena and 30.5 ± 0.4 Ma for Jima ignimbrites) show that most of the silicic volcanism occurred within 1.4 × 1015 mol) and Cl (6.4 × 1015 mol) into the atmosphere over a short time span, with the global cooling event at 30.3 Ma suggests that this volcanism might have accelerated the climate change that was already underway.

The Tarcouate pluton (Anti-Atlas, Morocco) is an inversely zoned laccolith emplaced 583 Ma ago into low-grade metasediments, with the following succession: leucocratic granites, biotite–granodiorites (±monzodiorites), hornblende–granodiorites (±monzodiorites) and monzodiorites syn-plutonic dykes. These rocks form two distinct, chemically coherent, units: (1) A main unit consists of layered (57

International audience; We describe a practical method of synthesis of fluorphlogopite single crystals suited to common laboratoryconditions. The l-atm batch melting technique was adapted using starting compositions having a slight excessof fluorine, added as K2SiF6. The oxide-fluoride mixture was melted above the liquidus temperature and thencooled at a rate of a few degrees per hour between 1400 and 13OO°C. Large (millimetre- to centimetre-size), clearand detachable single crystals were obtained by adding a quench of the charge during the cooling stage. XRD,TEM and electron microprobe analyses confirm that the micas produced are mostly monoclinic IM polytypeshaving chemical compositions very close to the end-member fluorphlogopite. Heating experiments confirm thatmelting of fluorphlogopite is congruent. From both heating experiments and thermal analysis, the melting temperatureof fluorphlogopite is located at values ⩾ 1390°C. Synthetic fluor-mica single crystals are of practical interestas analytical standards, and for several applications in experimental petrology.

Crystallization of magmatic liquids in plutonic environments is considered from an experimental point of view, through the study of Crystal Size Distribution (CSD), and from the petrological study of two layered intrusions: a mafic complex (Skaergaard, Greenland) and a granitic pluton (Dolbel, Niger). The evolution of plagioclase textures during controlled cooling of a basaltic liquid shows that the CSD cannot be simply used to reconstitute the thermal history. Textural and chemical studies of minerals from layered rocks (plagioclases of the Lower Zone of Skaergaard, amphibole and feldspars of the Dolbel pluton) show the importance of interaction between petrological and mechanical process. In the Skaergaard, convection, magmatic sedimentation and crystallization are inferred to be the dominant factors. In the Dolbel pluton, the successive stages of crystallization result from the interaction between fractional crystallization and deformation., La cristallisation des liquides magmatiques est abordée par l'étude expérimentale de la distribution des tailles de cristaux (CSD) et par l'étude pétrologique de deux exemples naturels lités: un complexe mafique (Skaergaard, Groenland) et un pluton granitique (Dolbel, Niger). L'évolution des textures du plagioclase lors du refroidissement contrôlé d'un liquide basaltique, montre que les CSD peuvent difficilement être employées pour reconstituer l'histoire thermique. Les études texturales et chimiques sur les minéraux de litages naturels (plagioclases de la Lower Zone du Skaergaard, amphibole et feldspaths du pluton de Dolbel) montrent l'importance de l'interaction entre processus pétrologiques et mécaniques dans la genèse des intrusions litées. Pour le Skaergaard, il y a interaction entre convection, sédimentation magmatique et cristallisation. Pour le pluton de Dolbel, les différentes étapes de cristallisation résultent de l'interaction entre cristallisation fractionnée et déformation.

This work consists of geochronological and petrological studies of the augen gneisses outcropping in Calabria (southern Italy). The aim was :1) to characterize the augen gneisses (field and petrographic study) and the magmatism of their protoliths (geochemistry); 2) to fixe the emplacement age of protoliths (U-Pb geochronology on zircon); 3) to obtain information about the source materials (Rb-Sr and Sm-Nd determinations). The overall data point to a similarity between the augen gneisses and the high-K calc-alkaline magmatic products of central Europe and northern-western Africa. The Neo-Proterozoic-Cambrian acidic magmatism in Calabria is related to syn and post-collisional phases of Pan-african orogeny. These results reinforce the idea that the Calabro-Peloritan terrane was a part of the Alboran microplate, localized at northern margin of Gondwana between Proterozoic and Cambrian ages (peri-Gondwana terranes)., L'objet de ce travail était l'étude pluridisciplinaire des gneiss oeillés de Calabre (Italie méridionale). Les objectifs étaient de : (i) caractériser les gneiss oeillés (terrain et pétrographie), (ii) définir les caractères du magmatisme de leurs protolites (géochimie), (iii) déterminer l'âge de mise en place des protolites (géochronologie U-Pb sur zircon) et (iv) obtenir des informations sur la source des gneiss (géochimie isotopique). De fortes analogies sont mises en évidence entre les protolites des gneiss oeillés et les produits calco-alcalins potassiques d'Europe centrale et d'Afrique nord-occidentale. Le magmatisme acide Néoprotérozoïque-Cambrien de la Calabre est rapporté aux phases syn- et post-collisionelles de l'orogenèse panafricaine. Ces résultats renforcent l'idée que le terrane Calabro Péloritain constituait une partie de la microplaque Alboran, terraine exotique qui appartenait à la bordure septentrionale du supercontinent Gondwana, à la limite Protérozoïque-Cambrien (peri-Gondwana terranes).

This multidisciplinary work has two major objectives: (i) understanding the structures and textures related to solidification of mafic-felsic magma interactions (mixing and mingling) and their implications ta mechanisms of magma emplacement and pluton construction and (ii) understanding the geodynamic and temporal relationships between two major structures of the Pan-African orogeny in Northeast Africa which met in Ethiopia : the ArabianNubian Shleld (ANS) and the Mozambique Belt (MB). based on a comparative study of Negash (ANS) and Konso plutons (MB). Malic-felsic interactions. Two major types of mafic-feisic magma interactions characterize the Negash pluton: (i)mingling and mixing at the lower mafic-felsic interfaces and (il) strongly mixed and mingled monzodiorites. Structural,mineralogical and chemical data suggest that the pluton was construcled by a successive assemblage of four differentiated magma batches (at intermediate chambers), which were forcefully injectedinto pre-existing foliatedcountry rocks and that the different types of hybridisation are not random but are related ta the dynamics and mechanismof pluton emplacement: (i) monzogranitic followed by granodioritic magmas; (ii) injection of a malt-richmonzodioritic/monzogabbroic tangue into the partially crystaliized felsic magmas resulting in inverted density gradient which in tum led to interactions at the lower interfaces; and (iii) simultaneous rising of granodioritic and monzodioriticmagmas along the same conduit resulting in the strongly hybridised magma which represents the last intrusion. The hybrid rocks are not results of simple binary mixing but involve atleast three end-members (monzoqabbres,monzodiorites and monzogranites/granodiorites). All these data suggest emplacement of differentiated, low viscosity magma batches and that the pluton was constructed by an assembly of successive melt-rich catches (dyking)ANS and MS. The ANS, which is composed of calc-alkaline and juvenile magmatic rocks without any significant pre-Pan-African continental crust, is essentially a zone of accretion. The MB, consisting of juvenile magmatic rocks gneissic-granulitic assemblages, is not only a zone of accretion but also a zone of recycling of older crustal material. Both terrains display similar succession of contemporaneous events and both are zones of accretion, but correspond to distinct geodynamic environments. The Negash and Konso plutons represent late stages of the geodynamic evolution of the Pan-African orogeny in Ethiopia, representing different stages of the Wilson cycle where the Negash pluton is related ta late-tectonic magmatism during the closing stages of arc-arc accretion in the ANS, while the emplacement of the Konso pluton marked a transition from a post-collisional ta anorogenic intra-plate magmatism in the MB. The ANS and the MB in Ethiopia cduld be considered as contemporaneous and representing the same Wilson cycle but they reilect distinct geodynamic contexts and different levels of erosion., Cette étude pluridisciplinaire a deux objectifs principaux: (i) la compréhension des structures et des textures liées aux mélanges magmatiques en relation avec les mécanismes de mise en place des magmas et la construction des plutons granitiques et (ii) la compréhension des relations entre deux domaines géodynamiques de l'orogenèse panafricaine de l'Afrique de NE qui se rejoignent en Ethiopie : le bouclier Arabo-Nubien (ANS) et la chaîne Mozambique (MB), sur une étude comparative de plutons de Negash (dans l'ANS) et de Konso (dans le MB). Mélanges magmatiques. Deux types d'interactions magmatiques acides-basiques caractérisent le pluton de Negash : (i) des mélanges et hybridations à l'interface acide-basique inférieure et (ii) des monzodiorites fortement mélangées et hybridées. Les données structurales, minéralogiques et chimiques suggèrent que le pluton est construit par l'assemblage successif de quatre pulses magmatiques différenciées dans des chambres magmatiques intermédiaires, qui ont été injectées dans un encaissant schistosé, et que les différents types de mélanges ne sont pas aléatoires mais sont liés à la dynamique de mise en place du pluton : (i) injection de magmas monzogranitiques puis granodioritiques ; (ii) injection d'une langue de monzodiorites/monzogabbros dans les faciès précédents créant une instabilité dynamique ; les mélanges à l'interface se sont produits en réponse à l'injection de ce magma basique dans le magma acide partiellement cristallisé ; et (iii) montée simultanée de magmas granodioritiques et monzodioritiques le long d'un même conduit conduisant à des roches fortement hybridées constituant la dernière venue magmatique. Les roches hybrides ne sont pas le résultat d'un mélange binaire simple mais impliquent au moins trois pôles magmatiques (monzogabbros, monzodiorites et monzogranites/granodiorite). Ces interactions magmatiques impliquent de magma de faible viscosité et suggèrent que le pluton s'est formé par agrégations de venues magmatiques riches en liquide. L'ANS et le MB. L'ANS, constitué de roches magmatiques calco-alcalines et juvéniles, sans aucune croûte continentale anté-panafricaine, est essentiellement une zone d'accrétion. Le MB, constitué de roches magmatiques juvéniles et des assemblages gneissiques-granulitiques, est non seulement une zone d'accrétion mais aussi une zone de recyclage de matériaux plus ancien. Les deux domaines montrent une succession des événements similaires de même âges mais représentent deux contextes géodynamiques distincts. Les plutons de Negash et de Konso sont des plutons tardifs dans l'évolution géodynamique du Panafricain, associés à des stades différents du cycle de Wilson, où le pluton de Negash représenterait un magmatisme tardi-tectonique en fin d'accrétion arc-arc dans l'ANS, alors que la mise en place du pluton de Konso marquerait la transition d'un magmatisme post-collision à un magmatisme d'intra-plaque dans le MB. L'ANS et le MB peuvent être considérés comme contemporains et représentent un même cycle de Wilson mais ils reflètent des contextes géodynamiques et des nivaux d'érosion distincts.

Non disponible / Not available, La Province Métallifère de Carajas, située au Sud-est du craton Amazonien, renferme une extensive séquence métavolcano-sédimentaire d'âge archéen (-2.76 Ga) recoupée par des granites fini-archéens (-2.57 Ga). Nous avons caractérisé pétrologiquement et structuralement le Complexe Granitique Estrela et son encaissant métavolcano-sédimentaire immédiat. La séquence métavolcano-sédimentaire est constituée essentiellement de métabasites auxquelles sont subordonnées des ultrabasites, formations ferrifères, quartzites, métapélites et roches calco-silicatées. Les métabasites présentent la signature chimique des tholéiites riches en fer. Cette association lithologique est comparable aux ceintures de roches vertes archéennes.L'évolution métamorphique de cette séquence comprend trois phases. La première phase (Mo) correspond à des transformations hydrothermales de faciès schiste-vert ou plus bas, sans destruction des textures magmatiques initiales. La phase Mt se traduit par des transformations minéralogiques de faciès schiste-vert et le développement d'une schistosité -EW localisée. La phase M2 est liée à l'auréole de contact du Complexe Granitique Estrela. Trois domaines de métamorphisme croissant ont été reconnus: auréole externe (450-550°C), auréole interne (550650°C) et zone d'enclaves (650-750°C). Les roches de l'auréole interne montrent une fabrique forte à l'opposé des enclaves présentant une texture granoblastique. L'ubiquité des veines àamphibole est attribuée à la phase M2. Différents critères indiquent que l'auréole de contact s'est formée sous des conditions de basse pression « 4.5 kbar) et de basse fugacité d'oxygène. Le Complexe Granitique Estrela a une forme grossièrement elliptique allongée selon la direction E-W. Cependant, les structures et la répartition spatiale des types pétrographiques montrent que le massif est constitué de plusieurs plutons. Les monzogranites sont prédominants (parmi lesquels plusieurs faciès ont été distingués en fonction des proportions de minéraux mafiques) sur des syénogranites, granodiorites et tonalites. Ces roches ont une signature subalcaline avec des rapports FeO*/MgO et Ga/Al et des teneurs en Zr, Ce, Nb, Y et terres rares (Eu excepté) élevés. Deux groupes contrastés sont identifiés: l'un métalumineux (roches riches en hornblende) et l'autre faiblement peralumineux (roches riches en biotite). Les caractéristiques chimiques sont celles des granites de type A post-archéens. Les conditions de mise en place sont estimées à: P?4.5 kbar, T= 750-850°C, basse fugacité d'oxygène (avec oxydation au cours de la consolidation). Deux surfaces principales ont été reconnues dans les plutons constitutifs du Complexe Granitique Estrela. Une première surface (S0), subhorizontale au centre et subverticale enpériphérie est marquée par un rubanement et une fabrique. Une seconde surface (S1) marquée par un rubanement et/ou une schistosité subverticaux reprend la surface initiale. S1 est associée à des plis dont les axes sont proches de EW (sauf dans la partie NE) mais dont le plongement est variable (horizontal à vertical). Des zones mylonitiques (S1m) se développent postérieurement. S0 est considérée comme liée au premiers stades de la mise en place des plutons, SIest interprétée comme résultant d'une interférence entre la mise en place et un contexte régional compressif NS, au moment de la consolidation et S1m correspond à la création de zones d'instabilité mécanique en fin de consolidation du massif. La présence plus à l'Ouest de granites semblables (Old Salobo) par leur âge (2.57 Ga), leur chimisme (granites de type A) et l'évolution métamorphique de leur encaissant (BP, HT), suggère que cet épisode magmatique n'est pas localisé mais qu'il a une extension régionale. Ceci semble d'autant plus réel que les régions de Carajas et de Rio Maria ont subi une reprise des systèmes isotopiques Rb-Sr et K-Ar à la même époque. Enfin, cette similitude pétrographique, chimique, géochronologique et métamorphique entre le domaine Estrela et le domaine Old Salobo permet de considérer que les différentes séquences volcano-sédimentaires (Salobo, Pojuca, Grao Para et Rio Novo) appartiennent à une seule et même unité.

Not available, La région de Marajoara, dans le sud-est du craton amazonien, au brésil, est formée par trois groupes de granitoïdes archéens (2.96 à 2.87 Ga): la tonalite Arco Verde (suite TTG), le granite Guaranta (monzogranite) et la granodiorite rio maria (granodiorite riche en mg). La pétrogenèse de la tonalité peut être expliquée par la fusion partielle de sources tholéiitiques à grenat suivie d'une cristallisation fractionnée. Les structures des granitoïdes ont été acquises au cours de leur refroidissement, dans un gradient de température décroissant et en réponse à un régime de contrainte régional coaxial. Les granitoïdes ont subi un raccourcissement horizontal important, qui a imprimé un fort aplatissement dans la tonalité Arco Verde et dans le granite Guaranta. Cependant, l'absence de structures tangentielles dans la région est remarquable. L’aplatissement n'est pas un épisode tardif dans l'histoire de la région de Marajoara, car la déformation n'affecte pas des roches déjà orthognéissifiées, mais des roches ignées au cours de leur refroidissement (à partir de l'état submagmatique)

Not available, Le dôme du Velay, occupant la partie orientale du Massif Central Français, est un dôme anatectique caractérisé par la succession de deux stades de fusion (M3 et Mv). Les relations entre déformation D3 et fusion M3 montrent que la fusion est précoce par rapport au développement des structures. La déformation engendre un ensemble de plis dissymétriques, à déversement général vers le nord. Les assemblages minéralogiques sont à biotite-sillimanite-quartz sans cordiérite, suggérant que la fusion n'a pas impliqué la biotite (T < 750°C, P > 5 kbar). Le collectage des mobilisats a été contrôlé par la tectonique et s'est produit à petite échelle sans transfert important de matière. Des plans à sillimanite fini-D3 se développent par lessivage acide en régime de déformation. Ils sont l'indice d'une chute de la température entre M3 et les événements ultérieurs, la partie supérieure de l'édifice anatectique repassant en conditions subsolidus. La phase Mv se caractérise par des assemblages cordiérite-orthose et grenat-orthose, correspondant à un accroissement sensible de la température (750 < T < 850°C, P = 4-5 kbar). Dans les migmatites, la cordiérite se développe de façon mimétique sur les mélanosomes M3. Elle atteint son développement maximal dans les granites vellaves (nodules, dendrites, cristaux isoles automorphes). La phase d'anatexie Mv reconnue comme la phase d'individualisation du dôme vellave, est régionalement considérée comme extensive (grandes failles de détachements fini-hercyniennes). Néanmoins, dans la bordure sud du dôme, les structures distensives syn-Mv restent d'importance limitée par rapport aux structures compressives méridiennes ubiquistes, interprétées comme le résultat d'un déversement du dôme du Velay vers le sud. Des cisaillements synmigmatitiques tardifs montrent un collectage, à petite échelle, de liquide anatectique à biotite. Ils sont liés à la retombée thermique du domaine vellave. Ceci suggère que les orthogneiss était encore partiellement fondus, mais avec une proportion de liquide faible, inferieure au seuil rhéologiquement critique. La baisse des températures entre M3 et Mv permet de dissocier les deux stades de migmatisation. La phase 3 marque la fin de l'épisode compressif lié à la mise en place des nappes et correspond au réchauffement d'une pile crustale épaissie. La phase Mv correspond à un autre régime de contraintes et à un autre régime thermique dont la dynamique est à rechercher dans l'effondrement gravitaire post-collision et dans une anomalie thermique liée à l'injection de magmas basiques mantelliques dont les vaugnerites seraient les témoins

Not available, Sur le versant alsacien des vosges septentrionales, les massifs devonodinantiens de schirmeck et de la bande médiane du champ de feu sont caractérisés par la présence de trois séries magmatiques différenciées par cristallisation fractionnée: la série de Schirmeck est une série tholéiitique continue, dans laquelle l'enrichissement en titane reste faible, analogue à celui des roches orogéniques. Une comparaison avec la série tholeiitique du rabodeau formée par les roches basiques a montré, d'une part que cette dernière est plus enrichie en terres rares légères que la série de Schirmeck, d'autre part les roches tholeiitiques acides du rabodeau pourraient dériver des termes basiques de Schirmeck. Dans la bande médiane du champ du feu, deux séries magmatiques ont été distinguées: la première présente des caractères des roches orogéniques calco-alcalines; la deuxième série présente des caractères comparables à ceux des séries shoshonitiques. Elle peut être témoin de l'épaississement de la croute continentale dans les Vosges du nord et pourrait représenter la dernière manifestation magmatique du remplacement progressif d'un magmatisme tholeiitique par un magmatisme calco-alcalin. Dans cette étude nous avons montré que le complexe magmatique des vosges du nord présente des caractères typiques des zones de convergence de plaques. Tout modèle géodynamique expliquant l'évolution de la chaine hercynienne en Europe doit tenir compte de ces caractères

Not available, Sur le versant alsacien des vosges septentrionales, les massifs devonodinantiens de schirmeck et de la bande médiane du champ de feu sont caractérisés par la présence de trois séries magmatiques différenciées par cristallisation fractionnée: la série de Schirmeck est une série tholéiitique continue, dans laquelle l'enrichissement en titane reste faible, analogue à celui des roches orogéniques. Une comparaison avec la série tholeiitique du rabodeau formée par les roches basiques a montré, d'une part que cette dernière est plus enrichie en terres rares légères que la série de Schirmeck, d'autre part les roches tholeiitiques acides du rabodeau pourraient dériver des termes basiques de Schirmeck. Dans la bande médiane du champ du feu, deux séries magmatiques ont été distinguées: la première présente des caractères des roches orogéniques calco-alcalines; la deuxième série présente des caractères comparables à ceux des séries shoshonitiques. Elle peut être témoin de l'épaississement de la croute continentale dans les Vosges du nord et pourrait représenter la dernière manifestation magmatique du remplacement progressif d'un magmatisme tholeiitique par un magmatisme calco-alcalin. Dans cette étude nous avons montré que le complexe magmatique des vosges du nord présente des caractères typiques des zones de convergence de plaques. Tout modèle géodynamique expliquant l'évolution de la chaine hercynienne en Europe doit tenir compte de ces caractères