Le tournoi à la Renaissance : l'esthétique Française d'un jeu de guerre

Actes du colloque tenu au château de Bournazel le 24 septembre 2016. Textes réunis par Thierry Verdier.International audienc

Le tournoi à la Renaissance : l'esthétique Française d'un jeu de guerre

Actes du colloque tenu au château de Bournazel le 24 septembre 2016. Textes réunis par Thierry Verdier.International audienc

Tectónica de sobrecorrimiento y sus implicaciones estructurales en el área Pamplona-Labateca Cordillera Oriental de Colombia

Al oriente de la población de Pamplona (Norte de Santander, Colombia) y en dirección SSE-NNW se presenta un alineamiento con aproximadamente 20 Km de largo que corresponde al trazo superficial de la Falla de Labateca. Esta falla en su extremo sur presenta un ángulo mayor de 60° al W, sigue una dirección N-S y pone en contacto unidades sedimentarias del Paleozoico Superior con sedimentos del Terciario Inferior. Hacia el N el salto de la falla disminuye y su trazo está representado por ramificaciones verticales a subverticales con dirección SE-NW. 15 Km al NNW de la localidad de Labateca, una falla inversa de bajo ángulo (40°) con una orientación S-N a SW-NE (falla de sobrecorrimiento de Durán) es cortada por la Falla de Labateca. Al W del trazo de la Falla de Labateca y al S de la intersección de las dos fallas tenemos la Unidad Tectónica de Labateca (alóctono) y la región ubicada al W de la Falla de Durán y al E de la Falla de Labateca corresponde a la Unidad Tectónica de Chinácota (autóctono). Como resultado de la acción de esfuerzos de compresión orientados W-E, la unidad de Labateca se desplazó hacia el  E y sobremontó a la Unidad de Chinácota

Glacial-interglacial trench supply variation, spreading-ridge subduction, and feedback controls on the Andean margin development at the Chile triple junction area (45-48°S)

International audienceDuring the Chile triple junction (CTJ) cruise (March–April 1997), EM12 bathymetry and seismic reflection data were collected in the vicinity of the Chile triple junction (45‐480S), where an active spreading ridge is being subducted beneath the Andean continental margin. Results show a continental margin development shaped by tectonic processes spanning a spectrum from subduction‐erosion to subduction‐accretion. The Andean continental margin and the Chile trench exhibit a strong segmentation which reflects the slab segmentation and the Chile triple junction migration. Three segments were identified along the Andean continental margin: the presubduction, the synsubduction, and the postsubduction segments, from north to south. Both climate‐induced variations of the sediment supply to the trench and the tectonic reorganization at the Nazca‐Antarctica plate boundary involving postsubduction ridge jump are the two main factors that control the tectonic regime of this continental margin. Along the survey area we infer the succession of two different periods during the last glacial‐interglacial cycle: a glacial period with ice‐rafted detrital discharges restricted to the shoreline area and low river output and a warmer period during which the Andean ice cap retreat allowed the Andes to be drained off. During these warm periods, rapid increase in trench deposition caused the margin to switch from subductionerosion or nonaccretion to subduction‐accretion: (1) along the presubduction segment after the last deglaciation and (2) along the postsubduction segment after the interglacial episode at 130–117 ka. Conversely, a nonaccretion or subduction‐érosion mode characterized the presubduction and postsubduction segments during glacial maximums. The major effects of subduction of the buoyant Chile ridge include a shallow trench which diverts trench sediment supply and tectonic instabilities at the Nazca‐Antarctica plate boundary. We suggest that a postsubduction westward jump of the Chile ridge occurred during the past 780 kyr. It produced slab fragmentation and individualization of an ephemeral microplate north of the Taitao fracture zone: the Chonos microplate. In 780 kyr, two episodes of subduction‐accretion separated by an episode of subduction‐erosion occurred in relation with the Chonos microplate individualization and subduction. The current northward migration of the triple junction along the Chonos microplate‐South America plate boundary introduces a sharp change in the tectonic mode from subduction‐erosion to the north to subduction‐accretion to the south. The data collected along the Taitao ridge have revealed the complex three‐dimensional structure of an accretionary wedge which includes a midslope thrust sheet exhibiting the characteristics of an ophiolite: the Taitao Ridge ophiolite. No connection exists between the Taitao Ridge ophiolite and the Bahia Barrientos ophiolite cropping out onland in the Taitao peninsula

Formation à et par la recherche : Bilan des années 2017, 2018 et 2019

Rapport sous copyright IRSNCe document présente la politique de la Formation à et par la recherche mise en œuvre au sein de l’IRSN, ainsi qu’une analyse détaillée des thèses et post-doctorats menés sur la période 2017 – 2019. Les informations fournies concernent les sujets, les Ecoles doctorales, les universités, l’encadrement par les Habilités à diriger les recherches, les publications réalisées et le devenir professionnel de ces jeunes chercheurs. Des annexes clôturent le document

La Purísima volcanic field, Baja California Sur (Mexico): Miocene to Quaternary volcanism related to subduction and opening of an asthenospheric window

Geological mapping and geochemical analyses combined with 40K–40Ar ages for lavas from the Late Miocene to Quaternary La Purísima volcanic field (Baja California Sur) provide evidence for five volcanic events. These, in turn, may reflect plate interactions in the region. The oldest event (event 1), prior to 11 Ma, corresponds to the emission of normal to K-rich calc-alkaline lavas, exposed as large mesas in the eastern part of the studied area and as pyroclastic breccias and volcaniclastic sediments to the west. It is associated with the end of the Comondú arc activity resulting from subduction of the Farallon and Guadalupe plates. Between 10.6 and 8.8 Ma (event 2), magnesian andesites and tholeiites were emplaced. At 5.5 Ma (event 3) and 2.5 Ma (event 4) small volumes of magnesian andesites erupted in the central and southern parts of the volcanic field. Finally, between 1.2 Ma and Holocene (event 5), numerous basaltic and magnesian andesitic fissural and central emissions resulted in the formation of strombolian cones and associated lava flows, mainly distributed within a NNW–SSE trending graben located SE of the town of La Purísima. Magmatic events 2 to 5 occurred well after the supposed end of the subduction event. Their geochemical characteristics are still typical of subduction-modified sources and possibly indicate partial melting of hot slab and formation of an asthenospheric window due to a slab rupture event which followed ridge–trench collision, prior to the continental breakup of the Gulf of California extensional provinc

From science to safety: the long way to risk management assessment in nuclear industry

International audienceNon-nuclear countries started to express their interest in building electronuclear programs in the early 2000s, with the consequence of creating the “nuclear renaissance” concept. This resulted in rising the number of power reactors under construction up to 65 according to IAEA’s PRIS –Therefore, the development of high-level safety analysts is a burning issue, in particular for “newcomers” who have the wish to set up independent safety authorities and/or technical support organizations’ (TSO) for risk management assessment. Some of emerging nuclear countries have planned to reach this objective by fully integrating the development of research reactors into their strategy of human resources development. For instance, for Jordan, “the research and test reactor would serve as an integral part of the nuclear technology infrastructure. It will become the focal point for a Nuclear Science and Technology Center and play the primary role in educating and training the upcoming generations of nuclear engineers and scientists”. Thus this paper presents three aspects of this topic. First, it will enlighten the French TSO’s point of view (IRSN) regarding the strategy to be set up to turn a scientific engineer into a safety analyst. It will then introduce the role that can play the construction and the operation of a research reactor in this frame. As a conclusive topic, this paper approaches the role that a nuclear country’s’ TSO can play to sustain the development of “newcomers” safety analysis skills. These three aspects could benefit any country within the step 2 of the IAEA’s Milestone frameworkNuclear reactors involve numerous and highly technical sciences: they cover fields from fundamental neutronics to thermohydraulics, from fuel thermomechanics to radiological gas diffusion… These sciences are in complete interactions with each other and computational tools are often required to simulate their effects on a research reactor safety. As these topics have to be examined together, with interaction between each other and in relation to the specificities of the facility, it is crucial to get a keystone engineer to manage these specialized analyses. Consequently, safety assessment requires also specific skills that are not based only on these sciences and that are not initially held by a nuclear engineer. Thus the first objective program is to define the inherent human, professional, and technical characteristics required by a safety analyst. Formalizing a safety analyst profile imposes to identify a set of applicable knowledge, hard and soft skills requirements in these topics: Level of nuclear sciences background ; Risk assessment methodology (defence in depth, implementation of barriers, graded approach…), Human behaviour and capability to interact with operators, scientific experts, safety authority, Construction of comprehensive and justified surveys capabilities.Several routes can be explored to build a safety analyst from a nuclear engineer: Implementing nuclear safety into universities programs ; Theoretical training programs tutoring programs; such topics can be dealt with by dedicated instances such as ENSTTI and “Field-based” approaches emerging from case by case analysis,In this context, it is important to notice that research reactors require the same basic sciences and are not as complex as nuclear power plants. Hence holding a comprehensive set of knowledge allowing the global safety assessment of the reactor is more easily achievable by a safety analyst. Research reactors are the first object on which this set of knowledge will be applied. It would then be eventually extrapolated to any nuclear installation, and profitably nuclear power plants

From science to safety: the long way to risk management assessment in nuclear industry

International audienceNon-nuclear countries started to express their interest in building electronuclear programs in the early 2000s, with the consequence of creating the “nuclear renaissance” concept. This resulted in rising the number of power reactors under construction up to 65 according to IAEA’s PRIS –Therefore, the development of high-level safety analysts is a burning issue, in particular for “newcomers” who have the wish to set up independent safety authorities and/or technical support organizations’ (TSO) for risk management assessment. Some of emerging nuclear countries have planned to reach this objective by fully integrating the development of research reactors into their strategy of human resources development. For instance, for Jordan, “the research and test reactor would serve as an integral part of the nuclear technology infrastructure. It will become the focal point for a Nuclear Science and Technology Center and play the primary role in educating and training the upcoming generations of nuclear engineers and scientists”. Thus this paper presents three aspects of this topic. First, it will enlighten the French TSO’s point of view (IRSN) regarding the strategy to be set up to turn a scientific engineer into a safety analyst. It will then introduce the role that can play the construction and the operation of a research reactor in this frame. As a conclusive topic, this paper approaches the role that a nuclear country’s’ TSO can play to sustain the development of “newcomers” safety analysis skills. These three aspects could benefit any country within the step 2 of the IAEA’s Milestone frameworkNuclear reactors involve numerous and highly technical sciences: they cover fields from fundamental neutronics to thermohydraulics, from fuel thermomechanics to radiological gas diffusion… These sciences are in complete interactions with each other and computational tools are often required to simulate their effects on a research reactor safety. As these topics have to be examined together, with interaction between each other and in relation to the specificities of the facility, it is crucial to get a keystone engineer to manage these specialized analyses. Consequently, safety assessment requires also specific skills that are not based only on these sciences and that are not initially held by a nuclear engineer. Thus the first objective program is to define the inherent human, professional, and technical characteristics required by a safety analyst. Formalizing a safety analyst profile imposes to identify a set of applicable knowledge, hard and soft skills requirements in these topics: Level of nuclear sciences background ; Risk assessment methodology (defence in depth, implementation of barriers, graded approach…), Human behaviour and capability to interact with operators, scientific experts, safety authority, Construction of comprehensive and justified surveys capabilities.Several routes can be explored to build a safety analyst from a nuclear engineer: Implementing nuclear safety into universities programs ; Theoretical training programs tutoring programs; such topics can be dealt with by dedicated instances such as ENSTTI and “Field-based” approaches emerging from case by case analysis,In this context, it is important to notice that research reactors require the same basic sciences and are not as complex as nuclear power plants. Hence holding a comprehensive set of knowledge allowing the global safety assessment of the reactor is more easily achievable by a safety analyst. Research reactors are the first object on which this set of knowledge will be applied. It would then be eventually extrapolated to any nuclear installation, and profitably nuclear power plants

Slab-tearing following ridge-trench collision: Evidence from Miocene volcanism in Baja California, México

International audienceNeogene magmatic activity in Central Baja California underwent a major change at ca. 12.5 Ma, when the Pacific–Farallon active oceanic ridge collided with the trench east of Vizcaíno Peninsula. The calc-alkaline magmatism which built the Comondú volcanic arc vanished and was replaced by unusual volcanic associations, which were erupted within six Late Miocene to Quaternary volcanic fields (Jaraguay, San Borja, San Ignacio, Santa Rosalía, Santa Clara, La Purísima), delineating a 600 km array along the Baja California Peninsula. New fieldwork, K–Ar datings and geochemical analyses on Jaraguay and San Borja lavas, combined with previous data, allow us to show that these associations include: (1) adakites emplaced between 12.5 and 8.2 Ma in the Santa Clara, Santa Rosalía and Jaraguay volcanic fields; (2) niobium-enriched basalts (NEB) in Santa Clara and Santa Rosalía (11.2 to 7.4 Ma); (3) tholeiitic basalts and basaltic andesites (11.3 to 7.2 Ma) displaying a very weak subduction imprint in La Purísima and San Ignacio; (4) alkali trachybasalts in Mesas San Carlos and Santa Catarina, northwest of Jaraguay (9.3 to 7.5 Ma), and finally (5) basalts and associated magnesian basaltic andesites and andesites. Locally referred to as “bajaites”, the latter lavas display very specific geochemical characteristics, including very high Sr and Ba contents. They were emplaced in all the above-mentioned volcanic fields between 14.6 and 5.3 Ma. The origin of these Late Miocene volcanics has been considered linked either to the opening of an asthenospheric window through which they ascended (tholeiites and alkali trachybasalts), or to the melting of its edges due to thermal erosion (adakites) and the subsequent reaction between adakitic melts and the supraslab mantle (NEB and “bajaites”). However, the identification of the remnants of the Pacific–Farallon fossil ridge south of Vizcaíno Peninsula indicates that active ridge subduction was not responsible for the opening of the asthenospheric window. We propose that the emplacement of slab window-related volcanic rocks between 13 and 7 Ma from ca. 25°N to 30°N, was due to a process of slab-tearing, which started when the active ridge collided with the trench east of Vizcaíno Peninsula. The oldest part of the downgoing plate sunk into the mantle, leading to the opening of a tear-in-the-slab, which likely started from the southern limit of the already existing Southern Californi

Petrologic diversity of Plio-Quaternary post-subduction volcanism in northwestern Mexico: An example from Isla San Esteban, Gulf of California

National audienceDuring the Plio-Quaternary, numerous volcanic centres of contrasted compositions were emplaced in the Baja California Peninsula and adjacent Gulf of California. The 43 km2 Isla San Esteban (28o 42 N and 112o 34' W), located in the central part of the gulf near the Pliocene extinct spreading centre of Lower Tiburón basin, is mostly made of andesitic, dacitic and rhyolitic subaerial lava flows, domes, and pyroclastic deposits. A new geological sketch map of the island is presented, as well as new K-Ar ages ranging from 4.5 to 2.5 Ma. Isla San Esteban lavas belong to two nearly contemporaneous magmatic series emplaced within an extensional tectonic framework related to the continental breakoff followed by the progressive oceanization along the Gulf of California. The first one is medium-K calc-alkaline, and its magmas evolved from basaltic andesites to rhyolites by fractionation of plagioclase, pyroxenes, titanomagnetite and apatite. The second one includes genuine adakites, and dacites derived from them through separation of plagioclase plus amphibole. We propose that these adakites originated from the partial melting of oceanic crust slivers, incorporated to the subcontinental lithospheric mantle during the Late Miocene opening of a slab window followed by the detachment of the deep part of the Farallon slab. The high thermal flux linked to the opening of the Gulf would have triggered their melting, as well as that of the subduction-modified mantle, which represents the likely source of the associated calc-alkaline lavas