BSGF - Earth Sciences Bulletin最新文献

{"title":"Geometry and tectonic history of the Northeastern Ce vennes Fault System (Southeast Basin, France): new insights from deep seismic reflection profiles","authors":"Camille Thomasset, J. Ritz, Sylvain Pouliquen, K. Manchuel, Romain Le-Roux-Mallouf","doi":"10.1051/bsgf/2024016","DOIUrl":"https://doi.org/10.1051/bsgf/2024016","url":null,"abstract":"Following the Mw4.9 Le Teil surface-rupturing earthquake that occurred on the Northeastern Cévennes Fault System (NCFS) in France on 11 November 2019, many studies have quantified the earthquake and associated surface deformation (slip distribution and kinematics) to analyze previous events, understand the local structures of the NCFS in 3D, and evaluate the rheology of sedimentary layers within the hypocenter area. However, the geometry of the NCFS at the scale of the Southeast French Basin is poorly constrained and it remains difficult to locate its trace beneath the Quaternary sediments of the Rhône river valley. To address this issue, Électricité de France (EDF) carried out a deep reflection seismic survey along the NCFS, which we interpreted using surface data, well data, and previous seismic data. The resulting 3D model allows us to reconstruct a polyphase geological history during the past 270 Ma, which we divide into three major tectonic phases. We show that all structures in the basin were initiated as normal faults during the Lias and the Early Cretaceous. These structures became more complex during the Late Cretaceous in a transfer fault regime before reactivation as normal faults during the Oligocene extension. The NCFS is directly related to the morphology and structures of the pre-Triassic basement top. We are also able to update knowledge on the geology of the Vivaro-Cévenol area and the structures that have affecting the Southeast Basin since the Mesozoic. In the context of the unprecedented Le Teil earthquake, our new structural model provides further impetus for continuing paleoseismological work that better constrains the seismic hazard in this region, which has been considered a moderately active seismic area until now.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"41 25","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141654872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reappraisal of the Messinian canyons morphology of the Rhône and Ardèche (Rhône valley): new insights from seismic profiles","authors":"D. do Couto, Edward Marc Cushing, L. Mocochain, J. Rubino, Florian Miquelis, Franck Hanot, B. Froment, Céline Gélis, Hubert Camus, Nanaba Bagayoko, Olivier Bellier","doi":"10.1051/bsgf/2024015","DOIUrl":"https://doi.org/10.1051/bsgf/2024015","url":null,"abstract":"12 available two-way time high-resolution seismic reflexion profiles located on the central part of the middle Rhône valley have been interpreted. In addition, one of the profiles was reprocessed to determine the P-wave velocities of the main geological units and to convert this line into a depth cross-section. On all these profiles, the Lower and Upper Cretaceous units are clearly identifiable, as is the Messinian Erosion Surface (MES) carved out during the Messinian Salinity Crisis (MSC) by the paleo Rhône and its tributaries, the Ardèche and Cèze paleo-canyons. The Plio-Quaternary fill of these paleo-canyons shows at least 4 main units showing an overall transgression. The combination of geological data from geological maps, geological field surveys and borehole data has made it possible to model the MES in 3D at the scale of the region, and in depth/altitude. This surface is compared to the velocity contrast surface that could be derived from the H/V method, highlighting some differences in interpretation between the two geophysical methods. From a geological point of view, the interpretation of the seismic lines led to propose a reconstruction of the stages in the sub-aquatic filling of the Messinian-Pliocene aggradation of the paleo-river. Several occurrences of Mass Transport Deposits (MTDs) were identified during the fall of the Mediterranean sea level as well as during the rise of sea level. From a geomorphological point of view, this study provides new information on the route and longitudinal profile of paleo-rivers and, in particular, it deepens the profile of the Paleo-Rhône at the latitude of the Tricastin region (up to 700m bsl) and significantly modifies the course of the Ardèche as proposed in previous studies. The Paleo-Ardèche river, known to develop a karstic system during the MSC, is connected to a deep canyon, most likely through a karstic pocket valley as suggested by the very steep longitudinal profile of the MES. Finally, from a structural point of view, interpretation of the seismic lines shows a broad ENE-trending anticlinal structure associated with a normal fault apparently not affecting the Mio-Pliocene fill. In the southern part of the area, near the Uchaux anticline, the imaged structures suggest the presence of a recent (syn to post-Pliocene) fold propagation fault. In addition to all the new information provided by this study on the geology, morphology and methods of excavation and filling of the Messinian paleocanyon, the proposal of a topographic model of the paleo-canyon is crucial for modelling seismic movement in the context of a basin with a complex geometry and, in particular, for the numerical assessment of site effects in a context of low seismicity.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"204 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141681309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dating the Late Miocene marine sediments around the Southern Middle Durance Valley (Provence, SE France): new evidences for a Tortonian age","authors":"Francois Demory, D. Delanghe, R. Braucher, P. Blard, Alexis Nutz, Gilles Conesa, Gaëlle Ségué, Fabrice Hollender, Cédric Duvail, Anna Fioravanti, L. Léanni, O. Bellier","doi":"10.1051/bsgf/2024014","DOIUrl":"https://doi.org/10.1051/bsgf/2024014","url":null,"abstract":"Based on burial dating by in situ produced cosmogenic nuclides (10Be, 26Al and 21Ne), and paleomagnetic analyses performed along the topmost 50 m of a 115 m long core retrieved from the Cadarache Area (Upper Provence, South East France), a Tortonian age was determined for the sedimentary succession exhibited in the core. In addition, thin sections, grain size analyses and quartz morphoscopy were used to characterize a shallow marine environment and to correlate the sediment core to the surrounding exposed sections. When comparing the studied sedimentary record to global sea level estimates, we establish that the Tortonian transgression was locally not synchronous with the global scale sea level high-stand, but happened more likely later, during a global regressive trend. The timing of the Tortonian flooding in Upper Provence was therefore most probably driven by regional tectonic forcings. \u0000Finally, the Tortonian shallow marine sediments are topped by lacustrine tight carbonates protecting the marine sediments from the following major erosional events resulting from the Messinian sea level drop and from interglacial-glacial fluctuations that both yielded to the present-day valley topography. \u0000","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"09 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141359192","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From ID-TIMS U-Pb dating of single monazite grain to APT-nanogeochronology: application to the UHT granulites of Andriamena (North-Central Madagascar)","authors":"M. Turuani, A. Seydoux‐Guillaume, A. Laurent, D. Fougerouse, Simon L. Harley, Steven M. Reddy, Philippe Goncalve, D. Saxey, Julie Michaud, J. Montel, Christian Nicollet, Jean-Louis Paquette","doi":"10.1051/bsgf/2024013","DOIUrl":"https://doi.org/10.1051/bsgf/2024013","url":null,"abstract":"Monazite and zircon grains from the ultra-high temperature (UHT) granulite of the Andriamena unit in the centre north of Madagascar, previously investigated using micro-drilled single grain isotopic dissolution geochronology and in-situ electron microprobe chemical dating by Paquette et al. (2004), are reinvestigated using high spatial resolution techniques: atom probe tomography (APT), transmission electron microscopy (TEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS). The dated grains are located in quartz, garnet belonging to the peak UHT metamorphic assemblage and in retrograde coronitic texture composed of biotite, cordierite and orthoamphibole. Monazite grains show complex discordant trends with several radiogenic Pb (Pb*) loss dispersions, that were previously interpreted as recording at least four geologic episodes occurring from the Archean (~2.7 Ga) to the Proterozoic-Cambrian (~0.5 Ga). Multiscale investigations with SIMS, TEM and APT have been carried out on monazite and LA-ICP-MS on zircon. Zircon grains hosted in garnet and those in quartz record concordant ages at 2758 ±28 Ma and 2609 ±51 Ma, respectively. Monazite grains show age dispersion and a Pb*-loss trend correlated with the grain petrographic position. Grains located in garnet and quartz present less Pb*-loss than those located in the coronitic texture. The discordia indicates a crystallisation age at 2555 ±71 Ma and monazite grains hosted in quartz and garnet record a disturbance event at 1053 ±246 Ma. TEM investigations show that monazite located in quartz and garnet contain numerous Pb-bearing nanophases compared to monazite located in coronitic texture. There is an inverse correlation between the number of Pb-bearing nanophases and the percentage of Pb*-loss in monazite grains. 232Th/208Pb ratio obtained with APT in monazite matrix (i.e. excluding Pb-bearing nanophases) located in quartz and garnet indicated a mean age of 1092 ±127 Ma. This date is interpreted as a hitherto undetected geochronological record in Andriamena unit.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"3 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141384937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE TECTONOSTRATIGRAPHIC LATITUDINAL RECORD OF THE EASTERN RED SEA MARGIN","authors":"Guillaume Baby, Antoine Delaunay, D. Aslanian, Abdulkader M. Afifi","doi":"10.1051/bsgf/2024009","DOIUrl":"https://doi.org/10.1051/bsgf/2024009","url":null,"abstract":"We characterize the eastern Red Sea necking domain through its north-south structural and stratigraphic record. Along-strike segmentation occurred during rifting (~28-14 Ma), with tilted blocks filled by siliciclastic sediments structuring the northern poor-magmatic segment (28°N-21.5°N), while siliciclastic/volcanoclastic sediments and volcanic flows interpreted as SDRs characterize the southern magmatic segment (21.5°N-13°N). Tectonic and magmatic activity stopped in this portion of the margin when a thick salt layer precipitated during the Middle Miocene (~14-13 Ma). The stratigraphy of the margin then became homogeneous between the two segments suggesting similar post-salt subsidence and common crustal characteristics throughout the Red Sea. This work provides new insights into understanding the Red Sea geology and, more broadly, on the tectonostratigraphic evolution of rifted margins in magma-poor and magma-rich settings.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"333 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140703655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revised _ Periglacial silicifications in the Paris Basin: compendium of observations, data, hypothesis and perspectives","authors":"M. Thiry, Anthony Mil","doi":"10.1051/bsgf/2024008","DOIUrl":"https://doi.org/10.1051/bsgf/2024008","url":null,"abstract":"In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly shown to occur only near outcrops in Plio-Pleistocene plateau landscapes and were related to groundwater flows. These arrangements, together with dating of encased calcites, led us to consider that silicification occurred during Plio-Pleistocene glacial stages. The precipitation of silica was most likely triggered by cooling of groundwaters as they approached cold zones in the regolith close to points of discharge. \u0000Here we describe the arrangement and morphologies of quartzites in Tertiary sand formations in the Paris Basin to demonstrate how cold climates could have influenced hydrologic regimes and promoted silicification. The coeval precipitation of calcite and silica in gypseous formations at the edges of plateaux-bordering valleys, along with the dissolution of gypsum, also points to interactions between silica-laden groundwater and carbonate host rocks during cold periods. In parallel, the distribution and micromorphology of silicifications in associated Tertiary limestone formations suggests that they formed during cold climates in the Quaternary. These are key pointers to the role of groundwater in regolith environments in controlling silicification processes. \u0000We also detail a link to palaeosurfaces of the distinctive meulières facies in the Paris Basin. Geotropic structures and micromorphological organisations are the basis of new ideas about their origin in a combination of vadose and phreatic environments and proximity to impervious cold horizons. The active zone in a permafrost landscape is a good hydrological example. \u0000In our view, all silicifications in Tertiary formations in the Paris Basin can be linked to the hydrology of Quaternary periglacial environments in a single model. This could apply more widely to similar silicifications elsewhere and be tested using new analytical techniques that date silicifications and unravel the isotopic relationships between silicification, groundwater composition and the prevailing climate. \u0000","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"12 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140352497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Salt Tectonics in the Provençal Basin, Western Mediterranean Sea","authors":"M. Bellucci, E. Leroux, D. Aslanian, M. Moulin, Romain Pellen, M. Rabineau","doi":"10.1051/bsgf/2024007","DOIUrl":"https://doi.org/10.1051/bsgf/2024007","url":null,"abstract":"The Messinian Salt Giant in the Provençal basin is an opportune area to study salt tectonics: salt deposition occurred throughout the basin well after basin opening, with a tectonic context stable since ~16 Ma, in a closed system. Also, the youth of salt tectonics has led to less mature structures and an evolutionary history that is easier to decipher than in older salt-bearing margins. We conducted an analysis of the chronology of salt deformation, from its deposition to the present-day, thanks to the basin-wide correlation of the Late Miocene and Pliocene-Pleistocene stratigraphic markers. The large seismic dataset provided detailed analysis of the causes and timing of salt deformation at a regional level. The salt tectonics started relatively early, during the Messinian Upper Unit (UU) deposition (phase 1) in the deepest part of the basin. From the Pliocene to the present-day, salt movement is divided into two more main phases (phases 2 and 3), the first of small intensity, occurred during the Pliocene and the second, more intense, during the Pleistocene. The geometric relationship between salt tectonics and crustal nature domains has revealed, whatever the timing deformation phases, a more rapid and intense salt deformation above the proto-oceanic crust domain than in the continental or transitional crust domain. This observation remains unexplained for the time being and could question the role of the influence of crustal nature and associated temperature on salt tectonics. \u0000 \u0000","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":" 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140218468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Pliocene Succession of Lyon Metropolis (SE France): an Overfill of a Messinian Incised-Valley","authors":"J. Suc","doi":"10.1051/bsgf/2024006","DOIUrl":"https://doi.org/10.1051/bsgf/2024006","url":null,"abstract":"The Pliocene ria, a narrow seaway running up the Rhône Valley, has been mapped for a while by field geologists. Only much later, after the DSDP Leg 13 in 1970, a consensus was reached that this unique geological feature of the Rhône Valley was created by the major Mediterranean sea-level drop associated with the Messinian Salinity Crisis, followed by a sudden sea-level rise caused by the breach of the Strait of Gibraltar and the invasion of the Mediterranean Basin by the Atlantic waters. At the regional level of the Lyon Metropolis in the upper Rhône Valley, main issues were however remaining about the course and depth of the Messinian valley, and about the valley fill, namely where and how do the Pliocene marine strata of the Rhône Valley pass to the continental deposits of the Bresse Basin to the north? These are key-questions in that the Plio-Pleistocene makes up a large fraction of a basement that holds up a large city, not free from potential geological hazards and subject to problems of groundwater management, high-cost tunneling projects, etc. Our work is based on a review of the historical researches - descriptions of the outcrops and fossil assemblages, followed by an unprecedented analysis and physical correlation of a thousand boreholes drilled over the last decades. Sections across the Messinian valley reveal a proper canyon morphology for the segments that cut the crystalline basement. The magnitude of the incision has been calculated as 335 m to a minimum, which yields a local erosion rate of about 2,400 m.Myr-1. Three major depositional systems are distinguished for the Pliocene - Lower Pleistocene succession. The valley that initially ran much farther north of Lyon was occupied in the Zanclean by a series of pounded lakes, dammed by transverse local alluvial fans, filled by minor Gilbert-type deltas, and repeatedly flooded by marine ingressions. The valley was then overfilled during the Piacenzian by a major transverse fluvial system that onlapped the valley wings. At the level of Lyon, the Alps-sourced, fluvial deposits were deflected to the north (Sables de Trévoux) and to the south (Alluvions jaunes inférieures et supérieures) as a dichotomy. The Pliocene was then capped by an Early Pleistocene, gravel-dominated alluvial fan (Alluvions jaunes sommitales) that spread out from the north-east to the south, and intersected the previous overfill due to the sudden shift to the north, i.e., South Jura, of the feeder stream. The depositional and current elevations of the marine-influenced episodes, i.e. marker bands that punctuate the regional Neogene succession, are used to bring out alternating uplift and subsidence phases we tentatively relate to the unload - reload of the Mediterranean Basin by the marine waters. Finally, we interpret the major shift in the depositional patterns of the Pliocene - Pleistocene transition in the Lyon area as reflecting a major change from an inactive thrust belt to vertical uplift in the Western Alps.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"5 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140439127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The continental depositional record of climate and tectonics around the Eocene-Oligocene transition in the Vistrenque Basin (Camargue, Southeast France)","authors":"N. Semmani, François Fournier, P. Léonide, J. Suc, S. Fauquette, M. Séranne, Lionel Marié, J. Borgomano","doi":"10.1051/bsgf/2024005","DOIUrl":"https://doi.org/10.1051/bsgf/2024005","url":null,"abstract":"Based on detailed sedimentological analyses of cores, interpretation of well logs and a set of geochemical measurements performed on lacustrine sediments, the palaeoenvironmental evolution and the sedimentary architecture of the Paleogene continental Vistrenque Basin (SE France) have been reconstructed. The analysis of sedimentary archives revealed three main stages of basin infill evolution: 1) a transgressive deep-lake basin (Priabonian-earliest Rupelian) whose sedimentation was dominated by terrigenous gravity-driven deposits during a period of high subsidence rate and fault activity and under a prevailing humid climate; 2) a forced-regressive, evaporative deep lake (early Rupelian) characterized by a drastic reduction in terrigenous supplies and deposition of evaporites in disconnected, compartmentalized sub-basins; 3) an overall long-term normal regressive stage (middle Rupelian to earliest Chattian) of lake infill characterized by an increase in terrigenous supplies and a vertical upward transition from deep-lake gravity-driven deposits to marginal lake and floodplain sedimentation. The onset of lake volume reduction and forced regression during the early Rupelian is recorded by 1) the reworking of marginal lake carbonates into the deep lake areas, 2) the deposition of organic-rich sediments (TOC>10%) coupled with sulphate-reduction processes in the deepest areas of the lake, 3) an important decrease in terrigenous supplies and 4) a long-term increase in δ18O of matrix-supported carbonates. This early Rupelian forced regression of the Vistrenque lacustrine system is interpreted to result from a terrestrial lowering in precipitation in response to global cooling during the Eocene-Oligocene Transition (EOT). The final infill of the Vistrenque lake system (late Rupelian-early Chattian) and the installation of a floodplain occurred in more humid conditions during a stage of decreased activity of the Nîmes Fault, prior to or during an early stage of the Liguro-Provençal rifting.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"13 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140439161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Short-lived active margin magmatism preceding Variscan collision in the Western French Massif Central","authors":"Julien Berger, Léa Beau-Hurdebourcq, Julien Serrano, Mathieu Benoit, Michel Grégoire, Anissa Benmammar, Stéphanie Duchene, O. Bruguier, J. Baele","doi":"10.1051/bsgf/2024003","DOIUrl":"https://doi.org/10.1051/bsgf/2024003","url":null,"abstract":"This paper presents and discusses new geochronological and petrological data on a suite of calc-alkaline plutons composed predominantly of diorites and tonalites from the West Massif Central. Their petrochemical fingerprints are compatible with partial melting of a hydrous mantle wedge followed by fractional crystallization of amphibole and plagioclase before final emplacement between 5 and 8 kbar within the continental upper plate of a subduction system. In situ U-Pb zircon dating on tonalites yields a fairly narrow age range of 362-356 Ma for igneous crystallization. These calc-alkaline plutons imply active margin magmatism near the Devonian-Carboniferous boundary and are contemporaneous with the back-arc magmatism and HP metamorphism as dated by recent studies. However, such isolated igneous bodies do not form a transcrustal magmatic arc but rather represent dispersed plutons emplaced within less than 20 Myr when all data from the Variscan belt of France are considered. In Limousin, they intrude migmatitic paragneisses and retrogressed eclogites from the Upper Gneiss Unit (UGU), suggesting that the high pressure rocks were already exhumed at 19-30 km depth before 362 Ma. Moreover, the diorites and tonalites are never found within units below the UGU. It therefore proves that these tectono-metamorphic units of the Western French Massif Central were piled up after 356 Ma. Altogether these results support the monocyclic model for Variscan geodynamics in the French Massif Central, with the transition between oceanic subduction and continental collision taking place between Upper Devonian and Lower Carboniferous.","PeriodicalId":202681,"journal":{"name":"BSGF - Earth Sciences Bulletin","volume":"16 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139775428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}