Pyroxene microstructure in the Northwest Africa 856 martian meteorite     

Hugues Leroux  Bertrand Devouard  Patrick Cordier  Franois Guyot 《Meteoritics & planetary science》2004,39(5):711-722

Abstract— Transmission electron microscopy was used to examine pyroxene microstructure in the Northwest Africa (NWA) 856 martian meteorite to construct its cooling and shock histories. All pyroxenes contain strained coherent pigeonite/augite exsolution lamellae on (001). The average width and periodicity of lamellae are 80 and 400 nm, respectively, indicating a cooling rate below 0.1 °C/hr for the parent rock. Pigeonite and augite are topotactic, with strained coherent interfaces parallel to (001). The closure temperature for Ca‐Fe, Mg interdiffusion, estimated from the composition at the augite pigeonite interface, is about 700 °C. Tweed texture in augite reveals that a spinodal decomposition occurred. Locally, tweed evolved toward secondary pigeonite exsolutions on (001). Due to the decreasing diffusion rate with decreasing temperature, “M‐shaped” concentration profiles developed in augite lamellae. Pigeonite contains antiphase boundaries resulting from the C2/c to P2₁/c space group transition that occurred during cooling. The reconstructive phase transition from P2₁/c clinopyroxene to orthopyroxene did not occur. The deformation (shock) history of the meteorites is revealed by the presence of dislocations and mechanical twins. Dislocations are found in glide configuration, with the [001](100) glide system preferentially activated. They exhibit strong interaction with the strained augite/pigeonite interfaces and did not propagate over large distances. Twins are found to be almost all parallel to (100) and show moderate interaction with the augite/pigeonite interfaces. These twins are responsible for the plastic deformation of the pyroxene grains. Comparison with microstructure of shocked clinopyroxene (experimentally or naturally shocked) suggests that NWA 856 pyroxenes are not strongly shocked.  相似文献   

A micro-investigation of unsaturated sand in mini-triaxial compression based on micro-CT image analysis     

Wang  Ji-Peng  Luan  Ji-Yuan  Gao  Xu-Guang  Liu  Tai-Heng  Andò  Edward  François  Bertrand 《Acta Geotechnica》2022,17(11):4799-4821

Acta Geotechnica - The mechanical behaviours of unsaturated soils are highly related to the water content and pore water and air distributions. Under the context of climate change, geo-disasters...  相似文献   

Chemical and isotopic investigations (δ<Superscript>18</Superscript>O, δ<Superscript>2</Superscript>H, <Superscript>3</Superscript>H, <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr) to define groundwater processes occurring in a deep-seated landslide in flysch     

M. Deiana  F. Cervi  M. Pennisi  M. Mussi  C. Bertrand  A. Tazioli  A. Corsini  F. Ronchetti 《Hydrogeology Journal》2018,26(8):2669-2691

Deep-seated landslides are complex systems. In many cases, multidisciplinary studies are necessary to unravel the key hydrological features that can influence their evolution in space and time. The deep-seated Berceto landslide, in the northern Apennines of Italy, has been investigated in order to define the origin and geochemical evolution of groundwater (GW), to identify the slope system hydrological boundary, and to highlight the GW flow paths, transit time and transfer modalities inside the landslide body. This research is based on a multidisciplinary approach that involves monitoring GW levels, obtaining analyses of water chemistry and stable and unstable isotopes (δ¹⁸O-δ²H, ³H, ⁸⁷Sr/⁸⁶Sr), performing soil leaching tests, geochemical modelling (PHREEQC), and principal component analysis (PCA). The results of δ¹⁸O-δ²H and ⁸⁷Sr/⁸⁶Sr analyses show that the source of GW recharge in the Berceto landslide is local rainwater, and external contributions from a local stream can be excluded. In the landslide body, two GW hydrotypes (Ca-HCO₃ and Na-HCO₃) are identified, and the results of PHREEQC and PCA confirm that the chemical features of the GW depend on water–rock interaction processes occurring inside the landslide. The ³H content suggests a recent origin for GW and appears to highlight mixing between shallow and deep GW aliquots. The ³H content and GW levels data confirm that shallow GW is mainly controlled by a mass transfer mechanism. The ³H analyses with GW levels also indicate that only deep GW is controlled by a pressure transfer mechanism, and this mechanism is likely the main influence on the landslide kinematics.  相似文献   

Neogene tectonostratigraphic history of the southern Neuquén basin (39°–40°30′S,Argentina): implications for foreland basin evolution          下载免费PDF全文

Damien Huyghe  Cédric Bonnel  Bertrand Nivière  Bertrand Fasentieux  Yves Hervouët 《Basin Research》2015,27(5):613-635

Although the Neuquén basin in Argentina forms a key transitional domain between the south‐central Andes and the Patagonian Andes, its Cenozoic history is poorly documented. We focus on the sedimentologic and tectonic evolution of the southern part of this basin, at 39–40°30′S, based on study of 14 sedimentary sections. We provide evidence that this basin underwent alternating erosion and deposition of reworked volcaniclastic material in continental and fluvial settings during the Neogene. In particular, basement uplift of the Sañico Massif, due to Late Miocene–Pliocene intensification of tectonic activity, led to sediment partitioning in the basin. During this interval, sedimentation was restricted to the internal domain and the Collon Cura basin evolved towards an endorheic intermontane basin. From stratigraphic interpretation, this basin remained isolated 7–11 Myr. Nevertheless, ephemeral gateways seem to have existed, because we observe a thin succession downstream of the Sañico Massif contemporaneous with the Collon Cura basin‐fill sequence. Comparisons of stratigraphic, paleoenvironmental and tectonic features of the southern Neuquén basin with other foreland basins of South America allow us to classify it as a broken foreland with the development of an intermontane basin from Late Miocene to Late Pliocene. This implies a thick‐skinned structural style for this basin, with reactivation of basement faults responsible for exhumation of the Sañico Massif. Comparison of several broken forelands of South America allows us to propose two categories of intermontane basins according to their structural setting: subsiding or uplifted basins, which has strong implications on their excavation histories.  相似文献   

Constitutive analysis of the mechanical anisotropy of Opalinus Clay   总被引：1，自引：0，他引：1  

Simon Salager  Bertrand François  Mathieu Nuth  Lyesse Laloui 《Acta Geotechnica》2013,8(2):137-154

This paper aims to analyse the anisotropic features of behaviour of Opalinus Clay using the theory of plastic multi-mechanisms. The results of triaxial tests conducted with different load levels and directions showed that the mechanical behaviour of this shale is cross-anisotropic. The stiffer samples are those in which the loading direction is parallel to the bedding plane. This indicates that the preconsolidation stress depends on the orientation of the load with respect to the fabric of Opalinus Clay. It is proposed to interpret the observed cross-anisotropy with an elastoplastic model based on four plastic strain mechanisms that may be successively mobilised depending on the loading direction. The predicted stress–strain responses vary according to the directions of the space as a result of the hardening process, depending on the number of plastic strain mechanisms that have been mobilised. The numerical predictions show overall good agreement with the experimental data in terms of deviatoric stress versus axial strain, demonstrating that multi-mechanism plasticity is a suitable constitutive tool for the interpretation of the mechanical anisotropy of this shale.  相似文献   

Co-seismic ruptures and deformations recorded by speleothems in the epicentral zone of the Basel earthquake     

Francis Lemeille  Marc Cushing  David Carbon  Bertrand Grellet  Thomas Bitterli  Christine Flehoc 《Geodinamica Acta》2013,26(3-4):179-191

Abstract

The study of growth anomalies of speleothems in a karstic environment can provide potential evidence or palaeoearthquakes. These data are used to study the recurrence times of major earthquakes in areas where evidence for historic seismicity is lacking. A study has been carried out in the epicentral area of the 1356 Basel earthquake (epicentral intensity = VII-VIII, macroseismic magnitude = 6.2). The Bättlerloch and Dieboldslöchli caves, situated in the area of greatest damage, show growth anomalies of speleothems possibly related to a seismic event (several breaks of speleothems an offsets of the axis of the regrowths). The first U/Th disequilibrum measurements by alpha spectrometry show recent ages (less than several tens of thousands of years and pro a y historic). ¹⁴C dating by AMS of carbonate laminations taken on both sides of the anomalies confirm the evidence of a seismic event around 1300 AD. More accurate datings by U/Th TIMS are carried out in order to compare the information provided by the two different dating methods. © Elsevier, Paris  相似文献   

On the Influence of a Simple Microphysics Parametrization on Radiation Fog Modelling: A Case Study During ParisFog     

Xiaojing Zhang  Luc Musson-Genon  Eric Dupont  Maya Milliez  Bertrand Carissimo 《Boundary-Layer Meteorology》2014,151(2):293-315

A detailed numerical simulation of a radiation fog event with a single column model is presented, which takes into account recent developments in microphysical parametrizations. One-dimensional simulations are performed using the computational fluid dynamics model Code_Saturne and the results are compared to a very detailed in situ dataset collected during the ParisFog campaign, which took place near Paris, France, during the winter 2006–2007. Special attention is given to the detailed and complete diurnal simulations and to the role of microphysics in the fog life cycle. The comparison between the simulated and the observed visibility, in the single-column model case study, shows that the evolution of radiation fog is correctly simulated. Sensitivity simulations show that fog development and dissipation are sensitive to the droplet-size distribution through sedimentation/deposition processes but the aerosol number concentration in the coarse mode has a low impact on the time of fog formation.  相似文献   

Review: From multi-scale conceptualization to a classification system for inland groundwater-dependent ecosystems   总被引：1，自引：0，他引：1  

Guillaume Bertrand  Nico Goldscheider  Jean-Michel Gobat  Daniel Hunkeler 《Hydrogeology Journal》2012,20(1):5-25

Aquifers provide water, nutrients and energy with various patterns for many aquatic and terrestrial ecosystems. Groundwater-dependent ecosystems (GDEs) are increasingly recognized for their ecological and socio-economic values. The current knowledge of the processes governing the ecohydrological functioning of inland GDEs is reviewed, in order to assess the key drivers constraining their viability. These processes occur both at the watershed and emergence scale. Recharge patterns, geomorphology, internal geometry and geochemistry of aquifers control water availability and nutritive status of groundwater. The interface structure between the groundwater system and the biocenoses may modify the groundwater features by physicochemical or biological processes, for which biocenoses need to adapt. Four major types of aquifer-GDE interface have been described: springs, surface waters, peatlands and terrestrial ecosystems. The ecological roles of groundwater are conditioned by morphological characteristics for spring GDEs, by the hyporheic zone structure for surface waters, by the organic soil structure and volume for peatland GDEs, and by water-table fluctuation and surface floods in terrestrial GDEs. Based on these considerations, an ecohydrological classification system for GDEs is proposed and applied to Central and Western-Central Europe, as a basis for modeling approaches for GDEs and as a tool for groundwater and landscape management.  相似文献   

Stages of evolution of a Toarcian compacted claystone around galleries excavated between 1 and 124 years ago by the study of noble gases dissolved in pore water at the Tournemire Underground Research Laboratory (France)     

Bernard Lavielle  Jean-Michel Matray  Bertrand Thomas  Alexandre Dauzères  Fethi Bensenouci  Eric Gilabert 《Applied Geochemistry》2012

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Micro-drilling ID-TIMS U-Pb dating of single monazites: A new method to unravel complex poly-metamorphic evolutions. Application to the UHT granulites of Andriamena (North-Central Madagascar).     

Jean-Louis?PaquetteEmail author  Philippe?Goncalves  Bertrand?Devouard  Christian?Nicollet 《Contributions to Mineralogy and Petrology》2004,147(1):110-122

In terranes subject to complex metamorphic evolution, zircon and monazite U-Pb system can record successive growth and/or resetting episodes. Conventional isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) dating of fractions or single grains from conventionally separated zircon and monazite populations may produce inaccurate ages. A new technique combining textural analysis and ID-TIMS dating on single monazite crystals is proposed. This method is applied directly on thin sections with three successive steps comprising (1) a characterisation of textural relationships using electron microprobe analyses and images, (2) extraction by micro-drilling of selected monazites and (3) U-Pb dating of each extracted grain by ID-TIMS. The potential for this in situ dating technique are tested on Ultra High Temperature (UHT) granulites from North-Central Madagascar. Four distinct events on a single thin section were distinguished. The UHT metamorphism was dated at 2.5 Ga, while two retrogression events were dated at 790 and 500 Ma. Finally, a single crystal shielded in quartz seems to preserve a pre-metamorphic age around 2.7 Ga.Editorial responsibility: J. Hoefs  相似文献