Direct dating of mid‐crustal shear zones with synkinematic allanite: new in situ U‐Th‐Pb geochronological approaches applied to the Mont Blanc massif     

Bénédicte Cenki‐Tok  James R. Darling  Yann Rolland  Bruno Dhuime  Craig D. Storey 《地学学报》2014,26(1):29-37

Dating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U‐Th‐Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA‐ICP‐MS U‐Th‐Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common‐Pb component. The use of measured Pb‐isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common‐Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean ²⁰⁸Pb/²³²Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite.  相似文献   

Impact of the LMDZ atmospheric grid configuration on the climate and sensitivity of the IPSL-CM5A coupled model   总被引：3，自引：3，他引：0  

Frédéric Hourdin  Marie-Alice Foujols  Francis Codron  Virginie Guemas  Jean-Louis Dufresne  Sandrine Bony  Sébastien Denvil  Lionel Guez  François Lott  Josefine Ghattas  Pascale Braconnot  Olivier Marti  Yann Meurdesoif  Laurent Bopp 《Climate Dynamics》2013,40(9-10):2167-2192

The IPSL-CM5A climate model was used to perform a large number of control, historical and climate change simulations in the frame of CMIP5. The refined horizontal and vertical grid of the atmospheric component, LMDZ, constitutes a major difference compared to the previous IPSL-CM4 version used for CMIP3. From imposed-SST (Sea Surface Temperature) and coupled numerical experiments, we systematically analyze the impact of the horizontal and vertical grid resolution on the simulated climate. The refinement of the horizontal grid results in a systematic reduction of major biases in the mean tropospheric structures and SST. The mid-latitude jets, located too close to the equator with the coarsest grids, move poleward. This robust feature, is accompanied by a drying at mid-latitudes and a reduction of cold biases in mid-latitudes relative to the equator. The model was also extended to the stratosphere by increasing the number of layers on the vertical from 19 to 39 (15 in the stratosphere) and adding relevant parameterizations. The 39-layer version captures the dominant modes of the stratospheric variability and exhibits stratospheric sudden warmings. Changing either the vertical or horizontal resolution modifies the global energy balance in imposed-SST simulations by typically several W/m² which translates in the coupled atmosphere-ocean simulations into a different global-mean SST. The sensitivity is of about 1.2 K per 1 W/m² when varying the horizontal grid. A re-tuning of model parameters was thus required to restore this energy balance in the imposed-SST simulations and reduce the biases in the simulated mean surface temperature and, to some extent, latitudinal SST variations in the coupled experiments for the modern climate. The tuning hardly compensates, however, for robust biases of the coupled model. Despite the wide range of grid configurations explored and their significant impact on the present-day climate, the climate sensitivity remains essentially unchanged.  相似文献   

Small melt inclusions can record bulk magma compositions: A planetary example from the Martian basalt (shergottite) Tissint          下载免费PDF全文

Yann Sonzogni  Allan Treiman 《Meteoritics & planetary science》2015,50(11):1880-1895

Melt inclusions in igneous minerals can provide constraints on magma compositions, especially for planetary samples where mass is severely limited. Small inclusions (<15 μm diameter) are more abundant than large ones, but have been used little from concern that they did not entrap average magma, but are rich in melt of a diffusional layer against the host mineral. We compared bulk compositions and calculated original compositions of small and large melt inclusions in the Martian basalt meteorite (shergottite) Tissint. Small and large melt inclusions are consistent with the same line of igneous differentiation, have the same abundance ratios for incompatible elements (P, Ti, Al, K, Na), and are consistent with derivation from the bulk composition of Tissint (inferred to represent its parent melt composition). For Tissint, then, small melt inclusions show no evidence of entrapping diffusional boundary layers, and appear to have entrapped bulk magma. Thus, its small inclusions can be as useful as larger ones; this may be so for other planetary samples, and thus provides an additional tool for investigating planetary magmas.  相似文献   

Influence of high-resolution wind forcing on hydrodynamic modeling of the Gulf of Lions   总被引：2，自引：2，他引：0  

Amandine Schaeffer  Pierre Garreau  Anne Molcard  Philippe Fraunié  Yann Seity 《Ocean Dynamics》2011,61(11):1823-1844

The impact of the choice of high-resolution atmospheric forcing on ocean summertime circulation in the Gulf of Lions (GoL; Mediterranean Sea) is evaluated using three different datasets: AROME (2.5 km, 1 h), ALADIN (9.5 km, 3 h), and MM5 (9 km, 3 h). A short-term ocean simulation covering a 3-month summer period was performed on a 400-m configuration of the GoL. The main regional features of both wind and oceanic dynamics were well-reproduced by all three atmospheric models. Yet, at smaller scales and for specific hydrodynamic processes, some differences became apparent. Inertial oscillations and mesoscale variability were accentuated when high-resolution forcing was used. Sensitivity tests suggest a predominant role for spatial rather than temporal resolution of wind. The determinant influence of wind stress curl was evidenced, both in the representation of a mesoscale eddy structure and in the generation of a specific upwelling cell in the north-western part of the gulf.  相似文献   

黄金岸线海滩能否抵挡极端事件的冲击     

Bruno Castelle  Yann Le Corre  刘锐 《海洋地质前沿》2008,24(9):21-24

砂质海滩是最变化莫测和脆弱的海岸带类型之一。众所周知，海滩在高能环境中会被侵蚀，但海滩上不同位置点对于极端事件的抵御能力则大不相同。而且，侵蚀速率通常受控于海滩状况、机械结构和前期补给。  相似文献   

Light-curve classification in massive variability surveys – II. Transients towards the Large Magellanic Cloud     

Vasily Belokurov  N. Wyn Evans  Yann Le Du 《Monthly notices of the Royal Astronomical Society》2004,352(1):233-242

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Investigating the pace of temperature change and its implications over the twenty-first century     

Yann Chavaillaz  Sylvie Joussaume  Amaury Dehecq  Pascale Braconnot  Robert Vautard 《Climatic change》2016,137(1-2):187-200

Most climatological studies characterize the future climate change as the evolution between a fixed current baseline and the future. However, as climate continues to change, ecosystems and societies will need to continuously adapt to a moving target. Here, we consider indicators of the pace of temperature change estimated from CMIP5 projections of an ensemble of climate models. We define the pace as a difference in relevant metrics between two successive 20-year periods, i.e. with a continually moving baseline. Under the strongest emission pathway (RCP8.5), the warming rate strongly increases, and peaks before 2080. All latitudes experience at least a doubling in the warming rate compared to the current period. Significant shifts in temperature distributions above twice the standard deviation between two successive 20-year periods expand from 9 % of continents on average currently to 41 % by 2060 onwards. In these regions, a warm year with a return period of about 50 years would become quite common 20 years later. The fraction of the world population exposed to such shifts will grow from 8 % to about 60 % on average, i.e. 6 billion people. Tropical areas are strongly affected, especially West Africa and South-East Asia. Low mitigation (RCP6.0) limits the warming rate to current values. Medium mitigation (RCP4.5) even reduces population exposure to significant shifts in temperature distributions to negligible values by the end of the century. Strong mitigation (RCP2.6) is the only option that generates a return to values similar to the historical period for all our indicators related to the pace of temperature change. This alternative way to analyze climate projections can yield new insights for the climate impacts and adaptation communities.  相似文献   

A pilot study of genetic differentiation between two phenotypes of a Mediterranean population of the bivalve Cerastoderma glaucum and genetic discrimination with other Cerastoderma glaucum and Cerastoderma edule populations outside the Mediterranean     

Rim Ladhar‐Chaabouni  Amel Hamza‐Chaffai  Yann Hardivillier  Benoît Chénais  Françoise Denis 《Marine Ecology》2010,31(2):355-363

The internal transcribed spacer 1 (ITS1) region of 29 individuals of Cerastoderma glaucum (from the Mediterranean Sea, the Atlantic and the North Sea) and 18 individuals of Cerastoderma edule (from the Atlantic and the North Sea) and the cytochrome c oxidase subunit I (COI) region of 43 individuals of C. glaucum (from the Mediterranean Sea, the Atlantic and the North Sea) and 9 individuals of C. edule (from the Atlantic and the North Sea) were PCR amplified and sequenced. The ITS1 sequences led us to describe 27 genetic haplotypes, while 21 genetic haplotypes were determined via the COI sequences. The ITS1 and the COI sequences revealed an important genetic variability within the Mediterranean population of C. glaucum, which contained two different phenotypes: orange foot and yellow foot. A genetic differentiation between the two phenotypes was revealed by the nucleotide diversity index (π) and is strengthened by the AMOVA analysis. This result leads us to suspect the presence of two different groups in the same population of C. glaucum. Nevertheless to be confirmed this hypothesis requires further studies using more locations and a larger number of sample sizes.  相似文献   

In situ and laboratory investigations of fluid flow through an argillaceous formation at different scales of space and time, Tournemire tunnel, southern France     

Jean-Yves Boisson  Lucien Bertrand  Jean-François Heitz  Yann Golvan 《Hydrogeology Journal》2001,9(1):108-123

In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron, France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10^–12 to 2×10^–11 m²/s) and hydraulic conductivities derived from different types of laboratory tests (10^–14 to 10^–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements) were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10^–13 to 10^–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling, based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture network do not permit reduction of uncertainties on these estimations at this stage. Electronic Publication  相似文献   

Experimental Melting of Carbonated Peridotite at 6-10 GPa   总被引：2，自引：0，他引：2  

Brey  Gerhard P.; Bulatov  Vadim K.; Girnis  Andrei V.; Lahaye  Yann 《Journal of Petrology》2008,49(4):797-821

Partial melting of magnesite-bearing peridotites was studiedat 6–10 GPa and 1300–1700°C. Experiments wereperformed in a multianvil apparatus using natural mineral mixesas starting material placed into olivine containers and sealedin Pt capsules. Partial melts originated within the peridotitelayer, migrated outside the olivine container and formed poolsof quenched melts along the wall of the Pt capsule. This allowedthe analysis of even small melt fractions. Iron loss was nota problem, because the platinum near the olivine container becamesaturated in Fe as a result of the reaction Fe₂SiO₄^Ol = Fe^Fe–Ptalloy + FeSiO₃^Opx + O₂. This reaction led to a gradual increasein oxygen fugacity within the capsules as expressed, for example,in high Fe³⁺ in garnet. Carbonatitic to kimberlite-like meltswere obtained that coexist with olivine + orthopyroxene + garnet± clinopyroxene ± magnesite depending on P–Tconditions. Kinetic experiments and a comparison of the chemistryof phases occasionally grown within the melt pools with thosein the residual peridotite allowed us to conclude that the meltshad approached equilibrium with peridotite. Melts in equilibriumwith a magnesite-bearing garnet lherzolite are rich in CaO (20–25wt %) at all pressures and show rather low MgO and SiO₂ contents(20 and 10 wt %, respectively). Melts in equilibrium with amagnesite-bearing garnet harzburgite are richer in SiO₂ andMgO. The contents of these oxides increase with temperature,whereas the CaO content becomes lower. Melts from magnesite-freeexperiments are richer in SiO₂, but remain silicocarbonatitic.Partitioning of trace elements between melt and garnet was studiedin several experiments at 6 and 10 GPa. The melts are very richin incompatible elements, including large ion lithophile elements(LILE), Nb, Ta and light rare earth elements. Relative to theresidual peridotite, the melts show no significant depletionin high field strength elements over LILE. We conclude fromthe major and trace element characteristics of our experimentalmelts that primitive kimberlites cannot be a direct productof single-stage melting of an asthenospheric mantle. They rathermust be derived from a previously depleted and re-enriched mantleperidotite. KEY WORDS: multianvil; carbonatite melt; peridotite; kimberlite; element partitioning  相似文献