Tectonic evolution of the Dabieshan orogen: In the view from polyphase deformation of the Beihuaiyang metamorphic zone   总被引：1，自引：0，他引：1  

LIN Wei    Faure Michel  WANG Qingchen & Arnaud Nicolas . LTE  Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China  . Department of Earth  Planetary Sciences  Graduate School of Science  Nagoya University  Japan  . ISTO  UMR CNRS  Batiment Géosciences  Orléans Université d’Orléans  Orléans Cedex  France  . UMR "Magmas et Volcans"  Rue Kessler  Clermont-Ferrand  France 《中国科学D辑(英文版)》2005,48(7)

The Dabieshan and its geological counterpart in the Sulu area represent the eastern part of the Qinling-Dabie orogenic belt in Eastern China. This Orogen corresponds to the collision zone between the North and South China blocks (denoted as NCB and SCB, respectively) during the Early Mesozoic. Since the discovery of ultra-high-pressure (UHP) metamor- phism[1?3], research of the Dabieshan has made great progress from petrological work (e.g. Cong and Wang, 1999 and enclosed references)[…  相似文献   

The dissolution kinetics of a granite and its minerals—Implications for comparison between laboratory and field dissolution rates     

Jiwchar Ganor  Emmanuelle Roueff  Joel D. Blum 《Geochimica et cosmochimica acta》2005,69(3):607-621

The present study compares the dissolution rates of plagioclase, microcline and biotite/chlorite from a bulk granite to the dissolution rates of the same minerals in mineral-rich fractions that were separated from the granite sample. The dissolution rate of plagioclase is enhanced with time as a result of exposure of its surface sites due to the removal of an iron oxide coating. Removal of the iron coating was slower in the experiment with the bulk granite than in the mineral-rich fractions due to a higher Fe concentration from biotite dissolution. As a result, the increase in plagioclase dissolution rate was initially slower in the experiment with the bulk granite. The measured steady state dissolution rates of both plagioclase (6.2 ± 1.2 × 10⁻¹¹ mol g⁻¹ s⁻¹) and microcline (1.6 ± 0.3 × 10⁻¹¹ mol g⁻¹ s⁻¹) were the same in experiments conducted with the plagioclase-rich fraction, the alkali feldspar-rich fraction and the bulk granite.Based on the observed release rates of the major elements, we suggest that the biotite/chlorite-rich fraction dissolved non-congruently under near-equilibrium conditions. In contrast, the biotite and chlorite within the bulk granite sample dissolved congruently under far from equilibrium conditions. These differences result from variations in the degree of saturation of the solutions with respect to both the dissolving biotite/chlorite and to nontronite, which probably was precipitating during dissolution of the biotite and chlorite-rich fraction. Following drying of the bulk granite, the dissolution rate of biotite was significantly enhanced, whereas the dissolution rate of plagioclase decreased.The presence of coatings, wetting and drying cycles and near equilibrium conditions all significantly affect mineral dissolution rates in the field in comparison to the dissolution rate of fully wetted clean minerals under far from equilibrium laboratory conditions. To bridge the gap between the field and the laboratory mineral dissolution rates, these effects on dissolution rate should be further studied.  相似文献   

Redox potential measurements and Mössbauer spectrometry of Fe adsorbed onto Fe (oxyhydr)oxides     

Ewen Silvester  Laurent Charlet  Antoine Géhin  Emmanuelle Liger 《Geochimica et cosmochimica acta》2005,69(20):4801-4815

The redox properties of Fe^II adsorbed onto a series of Fe^III (oxyhydr)oxides (goethite, lepidocrocite, nano-sized ferric oxide hydrate (nano-FOH), and hydrous ferric oxide (HFO)) have been investigated by rest potential measurements at a platinum electrode, as a function of pH (−log₁₀[H⁺]) and surface coverage. Using the constant capacitance surface complexation model to describe Fe^II adsorption onto these substrates, theoretical values of the suspension redox potential (E_H) have been computed, under the assumption that Fe^II adsorption occurs at crystal growth sites of the substrate surface. Good agreement between calculated and experimental E_H values is observed for nano-FOH and HFO, however the redox potentials measured for lepidocrocite and goethite are significantly more oxidizing than predicted. Mössbauer spectroscopic analysis of ⁵⁷Fe^II adsorbed onto HFO and goethite shows that in both cases the adsorbed ⁵⁷Fe^II is incorporated into the crystal structure of the substrate, in broad agreement with the thermodynamic model, but is almost completely oxidized to ⁵⁷Fe^III. The mechanism by which the adsorbed ⁵⁷Fe^II is oxidized is not resolved in this work, but is thought to be due to electron transfer to the substrate, rather than a net oxidation of the suspension. The disagreement between experimental and calculated rest potential measurements in the goethite and lepidocrocite systems is thought to be due to the poor electrochemical equilibration of these suspensions with the platinum electrode, rather than a failure of the thermodynamic model. The model developed for the redox potential of adsorbed Fe^II allows direct assessment of the reactivity of this species towards oxidized pollutants.  相似文献   

Survival of eclogite xenolith in a Cretaceous granite intruding the Central Dabieshan migmatite gneiss dome (Eastern China) and its tectonic implications   总被引：3，自引：0，他引：3  

Wei Lin  Masaki Enami  Michel Faure  Urs Schärer  Nicolas Arnaud 《International Journal of Earth Sciences》2007,96(4):707-724

Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new ⁴⁰Ar/³⁹Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.  相似文献   

Distribution of silver in mussels and oysters along the French coasts: data from the national monitoring program     

Chiffoleau JF  Auger D  Roux N  Rozuel E  Santini A 《Marine pollution bulletin》2005,50(12):1719-1723

  相似文献   

Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation model   总被引：1，自引：1，他引：0  

Hans Renssen  Hugues Goosse  Thierry Fichefet  Victor Brovkin  Emmanuelle Driesschaert  Frank Wolk 《Climate Dynamics》2005,24(1):23-43

The response of the climate at high northern latitudes to slowly changing external forcings was studied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO₂ and CH₄ content were prescribed. The experiment reveals an early optimum (9–8 kyr BP) in most regions, followed by a 1–3°C decrease in mean annual temperatures, a reduction in summer precipitation and an expansion of sea-ice cover. These results are in general agreement with proxy data. Over the continents, the timing of the largest temperature response in summer coincides with the maximum insolation difference, while over the oceans, the maximum response is delayed by a few months due to the thermal inertia of the oceans, placing the strongest cooling in the winter half year. Sea ice is involved in two positive feedbacks (ice-albedo and sea-ice insulation) that lead regionally to an amplification of the thermal response in our model (7°C cooling in Canadian Arctic). In some areas, the tundra-taiga feedback results in intensified cooling during summer, most notably in northern North America. The simulated sea-ice expansion leads in the Nordic Seas to less deep convection and local weakening of the overturning circulation, producing a maximum winter temperature reduction of 7°C. The enhanced interaction between sea ice and deep convection is accompanied by increasing interannual variability, including two marked decadal-scale cooling events. Deep convection intensifies in the Labrador Sea, keeping the overall strength of the thermohaline circulation stable throughout the experiment.  相似文献   

Influence of rainfall spatial variability on flood prediction   总被引：9，自引：0，他引：9  

Patrick Arnaud  Christophe Bouvier  Leonardo Cisneros  Ramon Dominguez 《Journal of Hydrology》2002,260(1-4):216-230

This paper deals with the sensitivity of distributed hydrological models to different patterns that account for the spatial distribution of rainfall: spatially averaged rainfall or rainfall field. The rainfall data come from a dense network of recording rain gauges that cover approximately 2000 km² around Mexico City. The reference rain sample accounts for the 50 most significant events, whose mean duration is about 10 h and maximal point depth 170 mm. Three models were tested using different runoff production models: storm-runoff coefficient, complete or partial interception. These models were then applied to four fictitious homogeneous basins, whose sizes range from 20 to 1500 km². For each test, the sensitivity of the model is expressed as the relative differences between the empirical distribution of the peak flows (and runoff volumes), calculated according to the two patterns of rainfall input: uniform or non-uniform. Differences in flows range from 10 to 80%, depending on the type of runoff production model used, the size of the basin and the return period of the event. The differences are generally moderate for extreme events. In the local context, this means that uniform design rainfall combining point rainfall distribution and the probabilistic concept of the areal reduction factor could be sufficient to estimate major flood probability. Differences are more significant for more frequent events. This can generate problems in calibrating the hydrological model when spatial rainfall localization is not taken into account: a bias in the estimation of parameters makes their physical interpretation difficult and leads to overestimation of extreme flows.  相似文献   

UPb emplacement and 40Ar/39Ar cooling ages of the eastern Mont-Louis granite massif (Eastern Pyrenees,France)     

Olivier Maurel  Jean-Patrick Respaut  Patrick Monié  Nicolas Arnaud  Maurice Brunel 《Comptes Rendus Geoscience》2004,336(12):1091-1098

Zircon UPb dating by SIMS of the Mont-Louis granite yields an age of 305±5 Ma, intrepreted to reflect the igneous emplacement age of the massif. It is in agreement with the Hercynian syntectonic character of Pyrenees granite. ⁴⁰Ar/³⁹Ar on hornblende, biotite and K-feldspar permit, to estimate the massif cooling. A rapid temperature decrease (≈30 °C/Ma) is revealed from Westphalian to Late Stephanian, coeval with the emplacement of a laccolithe in the upper crust. Then, the cooling rate decreases to ≈1 °C/Ma. This would be consistent with a long time residence for the pluton from the Late Palaeozoic to the Early Cainozoic at 6–8 km depth. To cite this article: O. Maurel et al., C. R. Geoscience 336 (2004).  相似文献   

Impact of ocean optical properties on seasonal SST: results with a surface ocean model coupled to the LMD AGCM     

Emmanuelle Cohen-Solal  Hervé Le Treut 《Climate Dynamics》1996,12(6):417-433

As the accuracy of ocean models improves, determination of the solar irradiance within the ocean may become important to simulate precisely the seasonal evolution of the SST. As ocean optical properties are not well documented in space and time, we have undertaken a sensitivity study to measure the corresponding SST uncertainties at a global scale using a model coupling the LMD AGCM with an integral mixed layer model and a thermodynamic sea ice representation. The downwelling irradiance formulation is that of Paulson and Simpson which has been tuned for the five water types of the Jerlov classification. Two sensitivity, and academic, experiments corresponding to a uniformly clear ocean or turbid ocean are carried out. Turbid waters exhibit, in general, a stronger seasonal cycle of the SST of about 2°C. The sensitivity is far from uniform, with a maximum in the subtropics and the mid-latitudes of the summer hemisphere. It corresponds precisely to the area in which the observed optical properties present a large temporal variability which is therefore likely to have an action on the seasonal cycle of the ocean surface temperatures. We perform a decomposition of the model sensitivity in four terms, corresponding to the direct impact of the water type change, feedback due to the mixed layer change, feedback due to the surface solar irradiance change, and feedback due to the non solar heat fluxes change. The first two terms dominate the SST change. The direct effect tends to increase the warming of the mixed layer. In addition, the mixed layer depth diminishes because of a higher stabilizing effect of solar radiation on the TKE budget. This tends to increase further summer warming of the SST as well as their winter cooling.  相似文献   

Evidence for excess argon during high pressure metamorphism in the dora maira massif (Western Alps,Italy), using an ultra-violet laser ablation microprobe 40Ar-39Ar technique     

N. O. Arnaud  S. P. Kelley 《Contributions to Mineralogy and Petrology》1995,121(1):1-11

 Ultra-high pressure eclogite/amphibolite grade metamorphism of the Dora Maira Massif in the western Alps is a well established and intensively studied event. However, the age of peak metamorphism and early cooling remains controversial. The ⁴⁰Ar-³⁹Ar step-heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 Ma which have been interpreted as the time of early cooling after the high pressure event. Recent U/Pb and Sm/Nd results challenge this assertion, indicating a much younger age for the event, around 45 Ma, and hence a radically different timing for the tectonic evolution of the western Alps. In a new approach to the problem, samples from the undeformed Hercynian metagranite, Brossasco, were studied using an ultra-violet laser ablation microprobe technique for ⁴⁰Ar-³⁹Ar dating. The new technique allowed selective in situ analysis, at a spatial resolution of 50 μm, of quartz, phengite, biotite and K-feldspar. The results demonstrate the frequent occurrence of excess argon with high ⁴⁰Ar-³⁶Ar ratios (1000–10000) and a strong relationship between apparent ages and metamorphic textures. The highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases. The best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event, then mixed with an atmospheric component during rapid cooling and retrogression, producing a wide range of argon concentrations and ⁴⁰Ar/³⁶Ar ratios. Step-heating analysis of minerals with this mixture would produce linear arrays on a ³⁶Ar/⁴⁰Ar versus ³⁹Ar/⁴⁰Ar correlation diagram, leading to geologically meaningless plateau ages, older than the true closure age. In the present case, some ages in the range 60–110 Ma could be explained by the presence of excess argon incorporated around 40–50 Ma ago. Similar results found in other high pressure terrains in the Alps may reconcile the argon geochronometer with other systems such as Rb/Sr, U/Pb or Sm/Nd. This study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of ⁴⁰Ar/³⁹Ar ages in many high pressure terrains. Received: 6 January 1994/Accepted: 4 April 1995  相似文献