Cumulating processes at the crust-mantle transition zone inferred from Permian mafic-ultramafic xenoliths (Puy Beaunit,France)     

Julien Berger  Olivier Féménias  Nicolas Coussaert  Jean-Claude C. Mercier  Daniel Demaiffe 《Contributions to Mineralogy and Petrology》2007,153(5):557-575

Ultramafic and mafic xenoliths of magmatic origin, sampled in the Beaunit vent (northern French Massif Central), derive from the Permian (257 Ma) Beaunit layered complex (BLC) that was emplaced at the crust-mantle transition zone (∼1 GPa). These plutonic xenoliths are linked to a single fractional crystallisation process in four steps: peridotitic cumulates; websteritic cumulates; Al-rich mafic cumulates (plagioclase, pyroxenes, garnet, amphibole and spinel) and finally low-Al mafic cumulates. This sequence of cumulates can be related to the compositional evolution of hydrous Mg basaltic magma that evolved to high-Al basalt and finally to andesitic basalt. Sr and Nd isotopic compositions confirm the co-genetic character of the various magmatic xenoliths and argue for an enriched upper mantle source comparable to present mantle wedges above subduction zones. LILE, LREE and Pb enrichment are a common feature of all xenoliths and argue for an enriched sub-alkaline transitional parental magma. The existence of a Permian magma chamber at 30 km depth suggests that the low-velocity zone observed locally beneath the Moho probably does not represent an anomalous mantle but rather a sequence of mafic/ultramafic cumulates with densities close to those of mantle rocks.  相似文献   

An experimental investigation of water level effects on the dynamic behaviour of a large arch dam     

Jean Proulx  Patrick Paultre  Julien Rheault  Yannick Robert 《地震工程与结构动力学》2001,30(8):1147-1166

The need for full‐scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam–reservoir–foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods. The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced‐vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one‐year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three‐dimensional finite element model for the dam–reservoir–foundation system is also presented. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Determination of Total Organic Carbon Content and δ¹³C in Carbonate-Rich Detrital Sediments     

Valier Galy  Julien Bouchez  Christian France-Lanord 《Geostandards and Geoanalytical Research》2007,31(3):199-207

The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (C_org) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble C_org respectively. In Himalayan and Amazon river sediments, the proportion of C_org solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the C_org content for the dissolved organic carbon content measured after decarbonation. Data presented here show that C_org dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment.  相似文献   

Mid-Holocene to present-day evolution of the Indian monsoon in transient global simulations     

Crétat  Julien  Braconnot  Pascale  Terray  Pascal  Marti  Olivier  Falasca  Fabrizio 《Climate Dynamics》2020,55(9-10):2761-2784

The low-frequency evolution of Indian rainfall mean-state and associated interannual-to-decadal variability is discussed for the last 6000 years from a multi-configuration ensemble of fully coupled global transient simulations. This period is marked by a shift of Indian Summer Monsoon Rainfall (ISMR) distribution towards drier conditions, including extremes, and a contraction of the rainy season. The drying is larger in simulations with higher horizontal resolution of the atmosphere and revised land surface hydrology. Vegetation–climate interactions and the way runoff is routed to ocean modulate the timing of the monsoon onset but have negligible effects on the evolution of seasonal rainfall amounts in our modeling framework in which carbon cycling is always active. This drying trend is accompanied by changes in ISMR interannual-to-decadal variability decreasing over north and south India but increasing over central India (20°–25° N). The ISMR interannual-to-decadal variability is decomposed into six physically consistent regimes using a clustering technique to further characterize its changes and associated teleconnections. From 6 to 3.8 kyr bp, the century-to-century modulations in the frequency of occurrence associated to the regimes are asynchronous between the simulations. Orbitally-driven trends can only be detected for two regimes over the whole 6–0 kyr bp period. These two regimes reflect increased influence of ENSO on both ISMR and Indian Ocean Dipole as the inter-hemispheric energy gradient weakens. Severe long-term droughts are also shown to be a combination of long-term drying and internally generated low-frequency modulations of the interannual-to-decadal variability.

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The M_L 5.3 Épagny (French Alps) earthquake of 1996 July 15: a long-awaited event on the Vuache Fault     

François Thouvenot  Julien Fréchet  Paul Tapponnier  Jean-Charles Thomas  Benoît Le Brun  Gilles Ménard  Robin Lacassin  Liliane Jenatton  Jean-Robert Grasso  Olivier Coutant  Anne Paul  & Denis Hatzfeld 《Geophysical Journal International》1998,135(3):876-892

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On the interactions between planetary geostrophy and mesoscale eddies     

Ian Grooms  Keith Julien  Baylor Fox-Kemper 《Dynamics of Atmospheres and Oceans》2011,51(3):109-136

Multiscale asymptotics are used to derive three systems of equations connecting the planetary geostrophic (PG) equations for gyre-scale flow to a quasigeostrophic (QG) equation set for mesoscale eddies. Pedlosky (1984), following similar analysis, found eddy buoyancy fluxes to have only a small effect on the large-scale flow; however, numerical simulations disagree. While the impact of eddies is relatively small in most regions, in keeping with Pedlosky’s result, eddies have a significant effect on the mean flow in the vicinity of strong, narrow currents.First, the multiple-scales analysis of Pedlosky is reviewed and amplified. Novel results of this analysis include new multiple-scales models connecting large-scale PG equations to sets of QG eddy equations. However, only introducing anisotropic scaling of the large-scale coordinates allows us to derive a model with strong two-way coupling between the QG eddies and the PG mean flow. This finding reconciles the analysis with simulations, viz. that strong two-way coupling is observed in the vicinity of anisotropic features of the mean flow like boundary currents and jets. The relevant coupling terms are shown to be eddy buoyancy fluxes. Using the Gent-McWilliams parameterization to approximate these fluxes allows solution of the PG equations with closed tracer fluxes in a closed domain, which is not possible without mesoscale eddy (or other small-scale) effects. The boundary layer width is comparable to an eddy mixing length when the typical eddy velocity is taken to be the long Rossby wave phase speed, which is the same result found by Fox-Kemper and Ferrari (2009) in a reduced gravity layer.  相似文献   

Merger histories in warm dark matter structure formation scenarios     

Alexander Knebe  Julien E. G. Devriendt  Asim Mahmood  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2002,329(4):813-828

Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs.  相似文献   

Reflection at large distance from the central engine in Seyferts     

Julien Malzac  Pierre-Olivier Petrucci 《Monthly notices of the Royal Astronomical Society》2002,336(4):1209-1216

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Laser Ablation (U-Th-Sm)/He Dating of Zircons: Analytical Age Bias and its Consequence for Studying Detrital Zircon Populations     

Julien Léger  Raphaël Pik  Bouchaïb Tibari  Sébastien Ternois  Mary Ford  Chantal Peiffert  Julien Mercadier 《Geostandards and Geoanalytical Research》2023,47(2):219-242

The in situ (U-Th-Sm)/He and U/Pb laser-ablation double-dating procedure is a valuable method that can provide a large dataset relatively efficiently in contrast with conventional bulk helium thermochronometry. In this study, we evaluate the potential age error associated with the double ablation procedure and report the in situ (U-Th-Sm)/He double-ablation dating of 249 zircons from the Fish Canyon Tuff locality. With LA-ICP-MS pseudo-depth profiling and 3D numerical modelling, we show that the concentric double-ablation procedure in minerals with U-Th-Sm zoning can generate a significant (U-Th-Sm)/He age error (positive or negative), resulting in over-scattering and/or an offset of the mean age. Pseudo-depth profiling is insufficient to predict the individual age error, partly because of the superimposed ablations. To evaluate the consequence of this inherent bias, we confront a synthetic age distribution to the error expected for U-Th-Sm zoned zircons analysed with double-ablation (U-Th-Sm)/He thermochronometry. As expected, a strong age bias causes the spreading of peak ages, downgrading the original signal. Yet, the throughput of the ablation-based method can allow intra- and inter-sample peak age identification and comparison, and the coupling of (U-Th-Sm)/He and U/Pb ages extends our ability to deconvolute a multimodal age spectrum.  相似文献   

Experimental petrology constraints on the recycling of mafic cumulate: a focus on Cr-spinel from the Rum Eastern Layered Intrusion,Scotland     

Julien?LeutholdEmail author  Jonathan?D.?Blundy  Richard?A.?Brooker 《Contributions to Mineralogy and Petrology》2015,169(2):12

The ¹⁷⁶Lu–¹⁷⁶Hf and ¹⁴⁷Sm–¹⁴³Nd decay systems are routinely used to determine garnet (Grt)–whole-rock (WR) ages; however, the ¹⁷⁶Lu–¹⁷⁶Hf age of garnet is typically older than the ¹⁴⁷Sm–¹⁴³Nd age determined from the same aliquots. Here we present experimental data for Lu³⁺ and Hf⁴⁺ diffusion in garnet as functions of temperature, pressure and oxygen fugacity and show that the diffusivity of Hf⁴⁺ in almandine/spessartine garnet is significantly slower than that of Lu³⁺. The diffusive closure temperature (T _C) of Hf⁴⁺ is significantly higher than that of Nd³⁺, and although this property is partly responsible for the observed ¹⁷⁶Lu–¹⁷⁶Hf and ¹⁴⁷Sm–¹⁴³Nd Grt–WR age discrepancies, the difference between the T _C-s of Lu³⁺ and Hf⁴⁺ could lead to apparent Grt–WR ¹⁷⁶Lu–¹⁷⁶Hf ages that are skewed from the age of Hf⁴⁺ closure in garnet. In addition, the slow diffusivity of Hf⁴⁺ indicates that the bulk of metamorphic garnets retain a substantial fraction of prograde radiogenic ¹⁷⁶Hf throughout peak metamorphic conditions, a phenomenon that further complicates the interpretation of ¹⁷⁶Lu–¹⁷⁶Hf garnet ages and invalidates the use of analytical T _C expressions. We argue that the diffusion of trivalent rare earth elements in garnet becomes much faster when their concentration level falls below a few hundred ppm, as in the experiments of Tirone et al. (Geochim Cosmochim Acta 69: 2385–2398, 2005), and further argue that this low-concentration mechanism is appropriate for modeling the susceptibility of ¹⁴⁷Sm–¹⁴³Nd garnet ages to diffusive resetting.  相似文献