Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna     

Caroline Marie Clémence Tramier  Pierre Genthon  Quentin Réginald Camille Paul Delvienne  Nicolas Luc Sauvan  Jean-Jérôme Olivier Cassan  Etienne Ebrard  Pascal Sébastien Dumas  Yann Queffélean 《水文研究》2021,35(3):e14071

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.  相似文献   

Lobes in deep-sea turbidite systems: State of the art   总被引：1，自引：0，他引：1  

T. Mulder  S. Etienne 《Sedimentary Geology》2010,229(3):75-80

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First-principles study of the structural and isotopic properties of Al- and OH-bearing hematite     

Marc Blanchard  Guillaume Morin  Michele Lazzeri  Etienne Balan 《Geochimica et cosmochimica acta》2010,74(14):3948-14056

A series of hematite structures containing various amounts of aluminum and hydroxyl groups was modeled using first-principles methods based on the density functional theory. Evolution of the lattice parameters was quantified as a function of Al and H concentrations. The a and c lattice parameters decrease with the aluminum content and increase with the water content. This allows explaining experimental data reported for synthetic hematites, in particular the observed deviation from the Vegard’s rule. Investigation of several hydroxyl configurations associated with cationic vacancies suggests that the speciation of water also significantly affects the hematite structure. The ⁵⁷Fe and ¹⁸O reduced partition functions (β-factor) were determined. Results show a linear dependence of the iron and oxygen β-factors on the aluminum content. An incorporation of 18 mole % Al₂O₃ in hematite would increase the iron β-factor of about 0.6‰ and the oxygen β-factor of about 5.5‰ at 0 °C. This effect is sufficiently large to be measurable and to affect the interpretation of natural isotopic compositions. On the other hand, the effect of water is found to be negligible for the hydroxyl configuration investigated.  相似文献   

Behavior of trace elements in relation to Lu–Hf and Sm–Nd geochronometers during metamorphic dehydration–hydration in the HP domain of Vårdalsneset, Western Gneiss Region, Norway     

Céline Martin  Stéphanie Duchêne  Béatrice Luais  Philippe Goncalves  Etienne Deloule  Céline Fournier 《Contributions to Mineralogy and Petrology》2010,159(4):437-458

The geochemical and isotopic characterization of an eclogite and the associated retrogressive amphibolite at Vårdalsneset, WGR, Norwegian Caledonide was undertaken to investigate the mobility of REE and Hf and the behavior of Lu–Hf and Sm–Nd geochronometers during metamorphic dehydration/rehydration. Eclogitic garnets display a distinct core–rim chemical zoning. Thermodynamic modeling indicates that both cores (13–22 kbar, 500–580°C) and rims (>16 kbar, 610–660°C) crystallized under eclogite-facies conditions. The core–rim zoning corresponds to the dehydration of the system. This petrographic disequilibrium is associated with Lu–Hf and Sm–Nd disequilibrium, which prevents dating of the eclogitic stages. At the rock scale, the incoming fluid responsible for eclogite–amphibolite retrogression brought in Sm and Nd, leached Lu, and had no influence on Hf. At the grain scale, mass balance shows that Sm and Nd were stored in clinozoisite since the first eclogitic stage, whereas Lu and Hf, which were more thoroughly redistributed among minerals during retrogression, enable the dating of the amphibolitic facies at 378 ± 17 Ma.  相似文献   

Phase equilibrium investigations of the Adirondack class basalts from the Gusev plains,Gusev crater,Mars     

Anna G. MONDERS  Etienne MDARD  Timothy L. GROVE 《Meteoritics & planetary science》2007,42(1):131-148

Abstract— Phase equilibrium experiments have been performed on a synthetic analog of the Gusev plains basalt composition from the Spirit landing site on Mars. Near‐liquidus phase relations were determined over the pressure range of 0.1 to 1.5 GPa and at temperatures from 1125 to 1390 °C in a piston cylinder apparatus and 1 atm gas mixing furnace. The composition is multiply saturated with olivine, orthopyroxene, and spinel near its liquidus at 1320 °C and 1.0 GPa, or 85 km depth on Mars, placing an upper limit constraint on the thickness of the Martian lithosphere at the time of eruption. Our experimental work suggests that the Gusev basalts are anhydrous batch melts of a primitive Martian mantle similar to the composition estimated by Dreibus and Wänke (1984). The temperature of multiple saturation indicates the persistence of high mantle potential temperatures on Mars, similar to those on the modern Earth, until at least the very latest Noachian (3.7 Ga). These high mantle temperatures would be responsible for persistent basaltic volcanism throughout the southern highlands during the first billion years of Mars's history. The source for Gusev basalts differs strongly from the source for shergottite meteorites, reinforcing the idea of the absence of global mantle convection and mixing on Mars. The existence of a relatively primitive mantle reservoir requires that at least part of the mantle underwent little modification during early planetary differentiation.  相似文献   

Analytical Developments in Secondary Ion Mass Spectrometry 2003     

Etienne Deloule  Michael Wiedenbeck 《Geostandards and Geoanalytical Research》2005,29(1):37-40

This annual review of secondary ion mass spectrometry (SIMS) highlights significant progress in the application of the technology for the following areas: U-Pb geochronology (notably in the fields of reference material zircons), sources of uncertainty during analysis and secondary ion yields. Major publications introduced a new zircon reference sample and dealt with an intercomparison study of a suite of established calibrators, some of which have been shown to have certain limitations. Another publication claimed that the principal uncertainty in U-Pb dating is related to variations in the Pb and U relative emission yields over a complete analytical session. 2003 saw the introduction of an automated particle identification procedure applied to the analysis of a chondritic meteorite, as well as new geometries of SIMS hardware (NanoSIMS) and techniques (time-of-flight SIMS). NanoSIMS allows a two to three order of magnitude reduction in sampling volume as a result of a reduced beam diameter, and time-of-flight SIMS allows the study of sample surfaces, and can provide data for elements concurrently.  相似文献   

Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition   总被引：2，自引：1，他引：2  

E. Deloule 《中国科学D辑(英文版)》2006,49(1):68-76

~~Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition@E. Deloule$CRPG-CNRS Nancy,54501,France1. Vavra, G, Gebauer. D., Schmid. R. et al., Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Tri-assic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study, Contrib. Mineral Petrol., 1996, 122:337-358 2. Vavra, G, Schmid, R., Gebauer, D., Internal morphology, ha…  相似文献   

The isotopic composition of zircon and garnet: A record of the metamorphic history of Naxos, Greece     

L. Martin  S. Duchêne  E. Deloule  O. Vanderhaeghe 《Lithos》2006,87(3-4):174-192

Growth of zircon with respect to that of garnet has been studied using a combination of petrography, U–Pb dating and oxygen isotope analysis. The aim is to document the mechanism and pressure–temperature conditions of zircon growth during metamorphism in order to better constrain the Tertiary metamorphic history of Naxos, Greece. Two metamorphisms are recognised: (1) an Eocene Franciscan metamorphism (M1) and (2) a widespread Miocene Barrovian metamorphism (M2) that increases from greenschist facies up to partial melting. An amphibolite sample contains zircon crystals characterised by a magmatic core and two metamorphic rims, denoted as A and B, dated at 200–270, 42–69, and 14–19 Ma, respectively. The first metamorphic rim A (δ¹⁸O = 7 ± 1‰) preserves the δ¹⁸O value of the magmatic core (6.2 ± 0.8‰), whereas rim B is characterised by higher δ¹⁸O values (7.8 ± 1.8‰). These observations indicate the formation of A rims by solid-state recrystallisation in a closed system with regard to oxygen and those of B in an open system. Compositional zoning in garnet is interpreted as the result of decompressional heating. Zircon B rims and garnet rims display similar δ¹⁸O values which indicates a contemporaneous growth of garnet and zircon rims during the Miocene Barrovian event (M2). Calcic gneiss and metapelite samples contain zircon crystals with single metamorphic overgrowths aged 41–57 Ma. δ¹⁸O values measured in zircon overgrowths (11.8 ± 1.4‰) from the calcic gneiss are similar to those measured in garnet rims (11.4 ± 1.1‰) from the same rock. This suggests that garnet rims and zircon overgrowths grew during the high pressure–low temperature event in equilibrium with prograde fluids. In the metapelite sample, δ¹⁸O values are similar in garnet cores (14.8 ± 0.2‰) and in zircon metamorphic overgrowths (14.2 ± 0.5‰). As zircon overgrowths have been dated at ca. 50 Ma by U–Pb, garnet cores and zircon overgrowths are interpreted to have grown during the high pressure event.

As demonstrated here for the island of Naxos, correlating the crystallisation of zircon with that of metamorphic index minerals such as garnet using stable isotope composition and U–Pb determination is a powerful tool for deciphering the mechanism of zircon growth and pin-pointing zircon crystallisation within the metamorphic history of a terrain. This approach is potentially hampered by an inability to verify the degree of textural equilibrium of zircon with other mineral phases, and the possible preservation (in metamorphic rims) of isotopic signatures from pre-existing zircon when they form by recrystallisation. Nevertheless, this study illustrates the application of this approach in providing key constraints on the timing and mechanism of growth of minerals important to understanding metamorphic petrogenesis.  相似文献   

Water penetration through fractured rocks: Test of a tridimensional percolation description     

Stephan Wilke  Etienne Guyon  Ghislain de Marsily 《Mathematical Geosciences》1985,17(1):17-27

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Development of a high resolution runoff routing model, calibration and application to assess runoff from the LMD GCM   总被引：3，自引：0，他引：3  

Agns Ducharne  Catherine Golaz  Etienne Leblois  Katia Laval  Jan Polcher  Emmanuel Ledoux  Ghislain de Marsily 《Journal of Hydrology》2003,280(1-4):207-228

Large-scale runoff routing models (RRMs) are important as a validation tool for GCMs, and to close the hydrological cycle in fully-coupled climate models. The model RiTHM was developed to simulate the discharge of large rivers from the total runoff simulated by the LMD GCM. It uses a 1024×800 grid, nested in the 64×50 grid of the LMD GCM. The runoff simulated in a GCM grid cell is uniformly distributed over the underlying cells, where a series of two reservoirs accounts for the delay related to infiltration through the unsaturated zone and aquifers. The resulting riverflow is routed assuming pure translation along the drainage network, extracted with a GIS from a 5 min DEM. The transfer time from a cell to the outlet depends on topography, and on a basin-wide parameter, the time of concentration. RiTHM was calibrated in 11 river basins, using a realistic runoff forcing (computed by the land surface model SECHIBA from reanalyzed meteorological forcing). This led to a very satisfactory reproduction of observed hydrographs. The main problems were related to hydraulic processes neglected in RiTHM (reservoirs, diversion of riverflow because of flooding or irrigation). These results helped to validate SECHIBA, except for its snow processes, shown to be too simple. With the same parameters, RiTHM was also forced with runoff from the LMD GCM. This induced an important degradation of the simulated hydrographs, regarding both volume and timing. It was largely explained by errors in precipitation, and more generally climate, in the GCM. The direct calibration of RiTHM under the GCM-runoff forcing markedly improved the timing of simulated discharge, which could be interesting for land–atmosphere–ocean coupling. This work demonstrated that the usefulness of RRMs for GCMs strongly depends on their adequate calibration.  相似文献