Earliest Eocene (53 Ma) convergence in the Southwest Pacific: evidence from pre‐obduction dikes in the ophiolite of New Caledonia     

Dominique Cluzel  Sebastien Meffre  Pierre Maurizot  Anthony J. Crawford 《地学学报》2006,18(6):395-402

Uncertainty about the timing and location of the initiation of convergence in the western and south‐western Pacific greatly hinders accurate plate tectonic reconstructions of subduction systems in that area. The chemistry and age of dikes intruding mantle peridotite in the ophiolite of New Caledonia infer that subduction‐related magmatism began before 53 Ma. These new results infer that obduction in the south‐west Pacific is unrelated to the reorientation of the Pacific plate motion that occurred c. 43 Ma and confirm new interpretations showing that changes in mantle flow, hotspot and plate motion may have occurred as soon as late Paleocene or early Eocene.  相似文献   

Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa     

Alfred Ngomanda  Dominique Jolly  Ilhem Bentaleb  Alex Chepstow-Lusty  M'voubou Makaya  Jean Maley  Michel Fontugne  Richard Oslisly  Nicaise Rabenkogo 《Quaternary Research》2007,67(3):411-425

Pollen and δ¹³C_TOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” ( 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ¹³C_TOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ¹³C_TOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available.  相似文献   

Morphological evolution of a well‐constrained,subaerial–subaqueous source to sink system: Wabush Lake          下载免费PDF全文

Dominique Turmel  Jacques Locat  Gary Parker 《Sedimentology》2015,62(6):1636-1664

Since 1964, the Iron Ore Company of Canada has deposited iron tailings resulting from mining operations into Wabush Lake, Western Labrador, Canada. This activity has resulted in a continuous hyperpycnal flow flowing over the lake floor. Bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental Iron Ore Company of Canada plans to maintain safe disposal strategies of tailings into the lake. Here, this dataset is used to study the evolution of different channels present in Wabush Lake and their link with knickpoints found at the head of most of these channels. The channels show notable evolution from one survey to the next. Some knickpoints and channels may be followed throughout more than one survey; the evolution of these knickpoints is the process responsible for the creation of erosional channels. The context in which they appear, as well as the evolution of some of the subaqueous channels is analysed. Cyclic steps and sediment waves are also found in the lake. These rhythmic bedforms, also created by the passage of turbidity currents, are analysed. Sediment waves found in Wabush Lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment.  相似文献   

Caractérisation de l'effluent de vidange d'un étang de pisciculture extensive     

Dominique Vallod  Benoit Sarrazin 《水文科学杂志》2013,58(3):394-402

Résumé Afin d'évaluer l'impact potentiel de la vidange, les flux de nutriments et de matières sont quantifiés lors du remplissage et de la vidange d'un étang construit en dérivation, à l'aval d'une chaîne d'étangs. La cinétique de vidange a été établie à l'aide d'un modèle numérique de terrain restituant la surface topographique de l'étang. Les matières en suspension et les principaux nutriments ont été régulièrement quantifiés. La qualité hydrobiologique du cours d'eau récepteur a été contrôlée pendant et après la vidange. L'étang a exporté 8.5 tonnes de matières en suspension et des quantités de nutriments relativement élevées. Nos résultats confirment l'existence de deux phases critiques, ne concernant cependant qu'un très faible volume d'effluent. Compte tenu des capacités élevées de sédimentation des matières en suspension, la courte durée d'exposition associée à un linéaire de fossés suffisant pourrait limiter l'impact de ces matières rejetées.

Citation Vallod, D. & Sarrazin, B. (2010) Caractérisation de l'effluent de vidange d'un étang de pisciculture extensive. Hydrol. Sci. J. 55(3), 394–402.  相似文献   

Methodology and Application of Hafnium Isotopes in Ilmenite and Rutile by MC‐ICP‐MS     

Caroline‐Emmanuelle Morisset  James S. Scoates  Dominique Weis  André Rahier 《Geostandards and Geoanalytical Research》2014,38(2):159-176

The high abundances of the high field‐strength elements in ilmenite and rutile make these minerals particularly suitable for hafnium isotopic investigations. We present a technique for separating Hf by ion exchange chemistry from high‐TiO₂ (> 40% m/m) minerals to achieve precise Hf isotopic composition analyses by MC (multiple collector)‐ICP‐MS. Following digestion and conversion to chlorides, the first elution column is used to separate iron and the rare earth elements, the second column is designed to separate most of the titanium from Hf, an evaporation step using HClO₄ is then performed to remove any trace of HF in preparation for the third column, which is needed to eliminate any remaining trace of titanium. The modified chemistry helped to improve the yields from < 10 to > 78% as well as the analytical precision of the processed samples (e.g., sample 2033‐A1, ¹⁷⁶Hf/¹⁷⁷Hf = 0.282251 ± 25 before vs. 0.282225 ± 6 after). The technique was tested on a case study in which the Hf isotopic ratios of ilmenite and rutile (analysed prior to the chemistry improvement) were determined and permitted to evaluate that the origin of rutile‐bearing ilmenite deposits is from the same or similar magma than their, respectively, associated Proterozoic anorthosite massifs (Saint‐Urbain and Lac Allard) of the Grenville Province in Québec, Canada.  相似文献   

Efficiency of policy instruments for CCS deployment     

Dominique Finon 《Climate Policy》2013,13(2):237-254

Policy instruments for carbon capture and storage (CCS) technology investment during the learning phase are analysed and compared. The focus is on specific barriers to investment in learning during early commercial deployment. Imperfections in the carbon price signal and market failures from barriers indicate a need for support during the learning investment phase and the initial roll out of CCS in electricity generation. Different ways for CCS technology to cross the so-called investment ‘death valley’ are analysed and compared: a command and control instrument (CCS mandate), investment support (grant, tax credit, loan guarantee, subsidy by trust fund) and production subsidies (guaranteed carbon price, feed-in price, etc.). Three criteria are used in this comparison: effectiveness, static efficiency and dynamic efficiency. Policy instruments need to be adapted to the technological and commercial maturity of the CCS system. Mandate policies require handling with much care, and subsidization mechanisms must be designed to be market-oriented.  相似文献   

Age, geology, geophysics, and geochemistry of Mahukona Volcano, Hawai`i     

Michael O. Garcia  Diane Hanano  Ashton Flinders  Dominique Weis  Garrett Ito  Mark D. Kurz 《Bulletin of Volcanology》2012,74(6):1445-1463

The size, shape, and magmatic history of the most recently discovered shield volcano in the Hawaiian Islands, Mahukona, have been controversial. Mahukona corresponds to what was thought to be a gap in the paired sequence (Loa and Kea trends) of younger Hawaiian volcanoes (<4?Ma). Here, we present the results of marine expeditions to Mahukona where new bathymetry, sidescan sonar, gravity data, and lava samples were collected to address these controversies. Modeling of bathymetric and gravity data indicate that Mahukona is one of the smallest Hawaiian volcanoes (～6,000?km³) and that its magmatic system was not focused in a long-lived central reservoir like most other Hawaiian volcanoes. This lack of a long-lived magmatic reservoir is reflected by the absence of a central residual gravity high and the random distribution of cones on Mahukona Volcano. Our reconstructed subsidence history for Mahukona suggests it grew to at least ～270?m below sea level but probably did not form an island. New ⁴⁰Ar–³⁹Ar plateau ages range from 350 to 654?ka providing temporal constraints for Mahukona’s post-shield and shield stages of volcanism, which ended prematurely. Mahukona post-shield lavas have high ³He/⁴He ratios (16–21?Ra), which have not been observed in post-shield lavas from other Hawaiian volcanoes. Lava compositions range widely at Mahukona, including Pb isotopic values that straddle the boundary between Kea and Loa sequences of volcanoes. The compositional diversity of Mahukona lavas may be related to its relatively small size (less extensive melting) and the absence of a central magma reservoir where magmas would have been homogenized.  相似文献   

A radiative transfer scheme for cosmological reionization based on a local Eddington tensor     

Dominique Aubert  Romain Teyssier 《Monthly notices of the Royal Astronomical Society》2008,387(1):295-307

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First-arrival traveltimes inversion based on a minimal number of parameters in shallow cross-well GPR tomography     

Madeleine Mangu  Herv Perroud  Dominique Rousset 《Journal of Applied Geophysics》2009,67(4):278-287

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Track of fluid paleocirculation in dolomite host rock at regional scale by the Anisotropy of Magnetic Susceptibility (AMS): An example from Aptian carbonates of La Florida,Northern Spain     

Mourad Essalhi  Stanislas Sizaret  Luc Barbanson  Yan Chen  Yannick Branquet  Dominique Panis  Pierre Camps  Pierre Rochette  Angels Canals 《Earth and Planetary Science Letters》2009,277(3-4):501-513

The present study aims to apply the AMS method (Anisotropy of Magnetic Susceptibility) at a regional scale to track the fluid circulation direction that has produced an iron metasomatism within pre-existing dolomite host rock. The Urgonian formations hosting the Zn–Pb mineralizations in La Florida (Cantabria, northern Spain) have been taken as target for this purpose. Sampling was carried out, in addition to ferroan dolomite host rock enclosing the Zn–Pb mineralizations, in dolomite host rock and limestone to make the comparison possible between magnetic signals from mineralized rocks, where fluid circulation occurred, and their surrounding formations. AMS study was coupled with petrofabric analysis carried out by texture goniometry, Scanning Electron Microscopy (SEM) observations and also Shape Preferred Orientation (SPO) statistics. SEM observations of ferroan dolomite host rock illustrate both bright and dark grey ribbons corresponding respectively to Fe enriched and pure dolomites. SPO statistics applied on four images from ferroan dolomite host rock give a well-defined orientation of ribbons related to the intermediate axis of magnetic susceptibility K₂. For AMS data, two magnetic fabrics are observed. The first one is observed in ferroan dolomite host rock and characterized by a prolate ellipsoid of magnetic susceptibility with a vertical magnetic lineation. The magnetic susceptibility carrier is Fe-rich dolomite. These features are probably acquired during metasomatic fluid circulations. In Fe-rich dolomite host rock, ?c? axes are vertical. As a rule, (0001) planes (i.e. planes perpendicular to ?c? axes) are isotropic with respect to crystallographic properties. So, the magnetic anisotropy measured in this plane should reflect crystallographic modification due to fluid circulation. This is confirmed by the texture observed using the SEM. Consequently, AMS results show a dominant NE–SW elongation interpreted as the global circulation direction and a NW–SE secondary elongation that we have considered as sinuosities of the fluid trajectory. The second type of magnetic fabric is essentially observed in the limestone and characterized by an oblate form of the ellipsoid of magnetic susceptibility, a horizontal magnetic foliation and mixed magnetic susceptibility carriers. It is interpreted as a sedimentary fabric.  相似文献