Global thermal and dynamical perturbations due to Cretaceous mantle avalanche     

Philippe Machetel 《Comptes Rendus Geoscience》2003,335(1):91-97

The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone.  相似文献   

Exhumation during crustal folding in the Namche-Barwa syntaxis   总被引：6，自引：0，他引：6  

Jean-Pierre Burg  Philippe Davy  Peter Nievergelt  Felix Oberli  Diane Seward  Zhizhong Diao  Martin Meier 《地学学报》1997,9(2):53-56

Geological observation in the eastern end of the Himalaya shows that the Asia/India Suture is folded. Metamorphic rocks derived from India occur structurally below the suture, in the core of a regional antiform. Isotopic and fission track dating establish cooling-exhumation of rocks from c.30 km depth within the last 4 Myr. We argue that exhumation is caused by ～ 10 mm yr^-1 erosion coeval with crustal scale folding.  相似文献   

Curvature analysis of triangulated surfaces in structural geology   总被引：6，自引：0，他引：6  

Philippe Samson  Jean-Laurent Mallet 《Mathematical Geology》1997,29(3):391-412

This paper addresses the problem of characterizing the shape of a geological surface on the basis of its principal curvatures. The surface is assumed to be modeled as a set of adjacent triangles defined by the location of their vertices and a method is proposed for estimating numerically the principal curvatures at the vertices of the triangles using a local C² interpolant. Also shown is how principal curvatures can be useful for studying the deformation of a geological surface (with application to 3D balanced unfolding), and analyzing the folding or faulting of the interface between two adjacent layers.  相似文献   

Greenhouse Gas Emissions from Hydroelectric Reservoirs in Tropical Regions   总被引：2，自引：1，他引：2  

Luiz Pinguelli Rosa  Marco Aurelio dos Santos  Bohdan Matvienko  Ednaldo Oliveira dos Santos  Elizabeth Sikar 《Climatic change》2004,66(1-2):9-21

This paper discusses emissions by power-dams in the tropics. Greenhouse gas emissions from tropical power-dams are produced underwater through biomass decomposition by bacteria. The gases produced in these dams are mainly nitrogen, carbon dioxide and methane. A methodology was established for measuring greenhouse gases emitted by various power-dams in Brazil. Experimental measurements of gas emissions by dams were made to determine accurately their emissions of methane (CH₄) and carbon dioxide (CO₂) gases through bubbles formed on the lake bottom by decomposing organic matter, as well as rising up the lake gradient by molecular diffusion.The main source of gas in power-dams reservoirs is the bacterial decomposition (aerobic and anaerobic) of autochthonous and allochthonous organic matter that basically produces CO₂ and CH₄. The types and modes of gas production and release in the tropics are reviewed.  相似文献   

Aerosol polarized phase function and single-scattering albedo retrieved from ground-based measurements     

Zhengqiang Li  Philippe Goloub  Claude Devaux  Xingfa Gu  Yanli Qiao  Fengsheng Zhao  Hongbin Chen 《Atmospheric Research》2004,71(4):233-241

Aerosol optical parameters, polarized phase function and single-scattering albdeo, have been retrieved from ground-based sun photometer measurements in Beijing 2003. The measured aerosol optical thickness varies from 0.12 to 0.77 with an average value of 0.39. The measured Ångström coefficient ranges from 0.75 to 1.47 with an average value of 1.21. The retrieved single-scattering albedo at 870 nm is within the 0.76–0.94 range and the average value is 0.85, suggests there are considerable aerosol absorptions in Beijing. The maximum value of retrieved polarized phase function at 870 nm ranges from 0.068 to 0.225 with an average value of 0.16, and it illustrates good correlations with the Ångström coefficient, i.e. the relative size of aerosol particles. Analyses of measurements and theoretical calculations show the polarized phase function is sensitive to aerosol size distribution and complex refractive index, especially the imaginary part of the refractive index which denotes aerosol light absorbing effects. These results suggest that the polarized phase function is an effective and unique aerosol optical parameter and is able to improve the retrieval of aerosol physical properties.  相似文献   

Dérive à la surface de l'océan sous l'effet des vagues     

Fabrice Ardhuin  François-Régis Martin-Lauzer  Bertrand Chapron  Philippe Craneguy  Fanny Girard-Ardhuin  Tanos Elfouhaily 《Comptes Rendus Geoscience》2004,336(12):1121-1130

We model the drift velocity near the ocean surface separating the motion induced by the local current, itself influenced by winds and waves, and the motion induced by the waves, which are generated by local and remote winds. Application to the drift of ‘tar balls’, following the sinking of the oil tanker Prestige-Nassau in November 2002, shows that waves contribute at least one third of the drift for pollutants floating 1 m below the surface, with a mean direction about 30° to the right of the wind-sea direction. Although not new, this result was previously obtained with specific models, whereas the formalism used here combines classical wave and circulation forecasting models. To cite this article: F. Ardhuin et al., C. R. Geoscience 336 (2004).  相似文献   

Corrigendum to “Deformation of polycrystalline iron up to 30 GPa and 1000 K” [Phys. Earth Planet Inter. 145 (2004) 239–251]     

Sbastien Merkel  Hans-Rudolf Wenk  Philippe Gillet  Ho-kwang Mao  Russell J. Hemley 《Physics of the Earth and Planetary Interiors》2005,150(4):351-352

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Modeling of in-situ crystallization processes in the Permian mafic layered intrusion of Mont Collon (Dent Blanche nappe, western Alps)     

Philippe Monjoie  Fran  ois Bussy  Henriette Lapierre  Hans-Rudolf Pfeifer 《Lithos》2005,83(3-4):317-346

The Mont Collon mafic complex is one of the best preserved examples of the Early Permian magmatism in the Central Alps, related to the intra-continental collapse of the Variscan belt. It mostly consists (> 95 vol.%) of ol + hy-normative plagioclase-wehrlites, olivine- and cpx-gabbros with cumulitic structures, crosscut by acid dikes. Pegmatitic gabbros, troctolites and anorthosites outcrop locally. A well-preserved cumulative sequence is exposed in the Dents de Bertol area (center of intrusion). P–T calculations indicate that this layered magma chamber emplaced at mid-crustal levels at about 0.5 GPa and 1100 °C. The Mont Collon cumulitic rocks record little magmatic differentiation, as illustrated by the restricted range of clinopyroxene mg-number (Mg#_cpx = 83–89). Whole-rock incompatible trace-element contents (e.g. Nb, Zr, Ba) vary largely and without correlation with major-element composition. These features are characteristic of an in-situ crystallization process with variable amounts of interstitial liquid L trapped between the cumulus mineral phases. LA-ICPMS measurements show that trace-element distribution in the latter is homogeneous, pointing to subsolidus re-equilibration between crystals and interstitial melts. A quantitative modeling based on Langmuir's in-situ crystallization equation successfully duplicated the REE concentrations in cumulitic minerals of all rock facies of the intrusion. The calculated amounts of interstitial liquid L vary between 0 and 35% for degrees of differentiation F of 0 to 20%, relative to the least evolved facies of the intrusion. L values are well correlated with the modal proportions of interstitial amphibole and whole-rock incompatible trace-element concentrations (e.g. Zr, Nb) of the tested samples. However, the in-situ crystallization model reaches its limitations with rock containing high modal content of REE-bearing minerals (i.e. zircon), such as pegmatitic gabbros. Dikes of anorthositic composition, locally crosscutting the layered lithologies, evidence that the Mont Collon rocks evolved in open system with mixing of intercumulus liquids of different origins and possibly contrasting compositions. The proposed model is not able to resolve these complex open systems, but migrating liquids could be partly responsible for the observed dispersion of points in some correlation diagrams. Absence of significant differentiation with recurrent lithologies in the cumulitic pile of Dents de Bertol points to an efficiently convective magma chamber, with possible periodic replenishment.  相似文献   

Sedimentary aspects and paleoenvironmental evolution of a rift basin: Salta Group (Cretaceous–Paleogene), northwestern Argentina     

Rosa A. Marquillas  Cecilia del Papa  Ignacio F. Sabino 《International Journal of Earth Sciences》2005,94(1):94-113

The rift history of the Salta basin is related to the evolution of the Central Andes and to the activity of the Pacific margin, owing to its geographic location. Sedimentation occurred from the Neocomian to the Paleogene, with deposits reaching up to 5,000 m in thickness. Paleoenvironmental analysis reveals an evolutionary history controlled by tectonic and climatic changes. Isolated grabens characterized the early synrift stage; differential subsidence provoked distinct environments in the southern and northern subbasins. In the southern subbasins, alluvial-fan, fluvial-fan and lacustrine deposits prevail, whilst in the northern subbasins eolian and fluvial environments dominate. During the Maastrichtian, two major factors controlled the basin fill: the decrease in tectonic subsidence and a relative sea-level rise as recorded in South America. An extensive and shallow Atlantic marine ingression installed a carbonate system coincident with mainly humid conditions until the Danian. Until the Middle Eocene, the fluvial and lacustrine environmental evolution of the sag basin was controlled especially by the alternation of temperate with dry and humid periods. Paleontological records reflect these climatic changes and show their relationship to the sedimentation regime.  相似文献   

Lateglacial palaeoenvironments and palaeoclimates from Conty and Houdancourt, northern France, reconstructed from Beetle remains     

Philippe Ponel  Russell Coope  Pierre Antoine  Nicole Limondin-Lozouet  Chantal Leroyer  Andr-Valentin Munaut  Jean-Franois Pastre  Frdric Guiter 《Quaternary Science Reviews》2005,24(23-24):2449-2465

Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley, both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology, geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it. Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe.  相似文献