Nd and Sr isotopic compositions of tektite material from Barbados and their relationship to North American tektites     

Henry H. Ngo  Gerald J. Wasserburg  Billy P. Glass 《Geochimica et cosmochimica acta》1985,49(6):1479-1485

Isotopic analyses of Nd and Sr on individual microtektites and a bulk microtektite sample from Barbados show them to have a very well defined isotopic composition. These data plot on an ε_Srε_Nd diagram precisely within the narrow field determined by North American tektites (ε_Sr ≈ 111; ε_Nd ≈ ?6.2). They yield an Nd model age of 0.6 AE. These results show that the microtektites from the Oceanic beds of late Eocene age are derived from the same target as the North American tektites and should be associated with the same event. Samples of the deep sea sediments in which the Barbados microtektites occur are found to have isotopic signatures which appear to reflect ambient sea water and detrital sediments. They cannot be the source of Sr or Nd in the tektites. Following the arguments of Shaw and Wasserburg (1982) we conclude that the target area which produced the North American tektite field was composed of sediments (Eocambrian or younger) derived from very late Precambrian crust. Glass beads from Lake Wanapitei Crater are isotopically different from all other tektites (ε_Sr ≈ 960; ε_Nd ≈ ?31.4) and cannot be related to the North American tektites.  相似文献   

An examination of the cataclastic fabrics and structures of parts of Nisutlin,Anvil and Simpson allochthons,central Yukon: test of the arc-continent collision model     

Philippe Erdmer 《Journal of Structural Geology》1985,7(1):57-72

Collision of an arc complex against the Yukon part of the North American craton during the Mesozoic resulted in northeastward transport of arc rocks onto the craton. The arc rocks comprise three distinguishable tectonostratigraphic assemblages called: Nisutlin Allochthon, quartz muscovite and chlorite schist derived from sedimentary and intermediate volcanic protoliths; Anvil Allochthon, amphibolite, gabbro, ultramafic rocks and sepentinite; and Simpson Allochthon, granitic and granodioritic rocks and schist derived from them. Deformation, recovery and recrystallization structures show that parts of the allochthons are blastomylonite, formed at temperatures of 350–700°C and at depths between 15 and 40 km. The stacking order of the allochthons is inconsistent and complex, and locally, the cataclastic rocks are overthrust by autochthonous strata. The allochthons are truncated by late steep faults that have mainly strike-slip displacement, and may be contemporaneous with Tintina Fault. The proposed tectonic history of the region is supported by detailed results of the study.  相似文献   

Modelling Spatial Variability Along Drainage Networks with Geostatistics   总被引：1，自引：0，他引：1  

Jean-Stéphane Bailly  Pascal Monestiez  Philippe Lagacherie 《Mathematical Geology》2006,38(5):515-539

Local characteristics of drainage networks such as cross-section geometry and hydraulic roughness coefficient, influence surface water transfers and must be taken into account when assessing the impact of human activities on hydrological risks. However, as these characteristics have not been available till now through remote sensing or hydrological modelling, the only available methods are interpolation or simulation based on scarce data. In this paper we propose a statistical model based on geostatistics that allows us to take account of both the spatial distribution and spatial uncertainties. To do this, we modify the geostatistical framework to suit directed tree supports corresponding to drainage network structures. The stationarity concept is specified assuming conditional independence between parts of the network; variogram fitting and modelling are then modified accordingly. A sequential multi Gaussian simulation procedure going upstream along the network is proposed. We illustrate this approach by studying the width of an 11-km long artificial drainage network in the south of France.  相似文献   

From granitoid to kyanite-bearing micaschist during fluid-assisted shearing (Ile d’Yeu, France)     

Caroline Sassier  Philippe Boulvais  Denis Gapais  Ramon Capdevila  Hervé Diot 《International Journal of Earth Sciences》2006,95(1):2-18

We describe amphibolite-facies shear zones affecting an orthogneiss from the Armorican Hercynian belt (Ile d’Yeu, western France). The deformation pattern is consistent with top-to-the-South thrusting followed by E–W extension, as documented elsewhere in the region. Shearing was accompanied by channelled fluid flow that transformed the orthogneiss into a peraluminous micaschist. Structural and mineralogical data indicate rather early strain localization. Then, temperature increase associated with crustal thickening favoured more distributed deformations marked by shear zone stretching and the development of a HT regional foliation. Chemical analyses made across five shear zones show mass transfers that mainly implied losses in Ca and Na, and gains in H₂O, Mg, and K. Most results indicate constant volume transformation, but some suggest records of either gains or losses of volume (between +20% and −30%). This might reflect variable records of fluid-rock interactions according to the timing of initiation and subsequent evolution of individual shear zones, early thrusting stages being marked by up-temperature flow, and late thrusting stages by down-temperature flow. δ¹⁸O analyses suggest that fluids experienced significant isotopic exchange with orthogneisses.  相似文献   

Potential Flank-Collapse of Soufrière Volcano, Guadeloupe, Lesser Antilles? Numerical Simulation and Hazards     

Anne Le Friant  Georges Boudon  Jean-Christophe Komorowski  Philippe Heinrich  Michel P. Semet 《Natural Hazards》2006,39(3):381-393

The past history of recurrent flank collapses of la Soufrière volcano of Guadeloupe, its structure, its well-developed hydrothermal system and the current activity constitute factors that could promote a future flank collapse, particularly in the case of a significant increase of activity, with or without shallow magmatic input. To address the hazards associated with such a collapse, we model the emplacement of the debris avalanche generated by a flank-collapse event in 1,250 BC (3,100 years B.P.). We use a finite-difference grain-flow model solving mass and momentum conservation equations that are depth-averaged over the slide thickness, and a Coulomb-type friction law with a variable basal (minimum) friction angle. Using the parameter values determined from this simulation, we then simulate the debris avalanche which could be generated by a potential collapse of the present lava dome. We then discuss the region which could be affected by such a future collapse, and additional associated hazards of concern.  相似文献   

Hierarchical aggregation in percolation model     

Ilya Zaliapin  Henry Wong  Andrei Gabrielov   《Tectonophysics》2006,413(1-2):93

There is a growing belief that the complex dynamics of seismicity can be better understood by studying the collective behavior of numerous lithosphere instability sources rather than focusing on the details of each of them. Classical site-percolation is a simple and tractable model which exhibits such important general features of complex systems as criticality and phase transitions of second kind. It also illustrates the mechanism of hierarchical aggregation, which is very important for explaining collective phenomena in material fracture and earthquake nucleation processes. We study the dynamics of a 2D site percolation model on a square lattice using the hierarchical approach introduced by Gabrielov et al., Phys. Rev. E., 5293–5300, 1999. The key elements of the approach are the tree representation of clusters and the Horton–Strahler scheme for cluster ranking. Accordingly, the evolution of percolation model is considered as a hierarchical inverse cascade of cluster aggregation. We analyzed the growth of the percolation cluster and established the time-dependent rank distribution of its subclusters, as well as corresponding laws for its mass, rank, and their relationship. We report several phenomena premonitory to the onset of percolation that complement the traditional power-law increase of the model's observables. In addition, we have shown that the Tokunaga side-branching constraint uniquely determines the mass–rank relationship for a general aggregation process (not necessarily originated from the percolation model). The results can be used for development and improvement of earthquake prediction techniques.  相似文献   

Rhizosphere: A new frontier for soil biogeochemistry   总被引：9，自引：0，他引：9  

Philippe Hinsinger  Claude Plassard  Benoît Jaillard 《Journal of Geochemical Exploration》2006,88(1-3):210

A range of key biological functions of plant roots such as uptake, respiration and exudation can considerably alter biogeochemical parameters of the soil in the vicinity of the roots, i.e., the rhizosphere: concentrations of nutrients, toxic elements (e.g., aluminium) and pollutants, concentrations of complexing or chelating compounds, pH and redox potential, partial pressures of gases such as O₂ and CO₂, etc. Such parameters can also be directly influenced by the activities of soil microorganisms that are known to be stimulated by root exudation in the rhizosphere. Changes of biogeochemical parameters of the soil solution occurring in the rhizosphere influence a whole range of reactions at the soil solid/soil solution interface. Higher plants thereby play a key role in (i) the weathering of soil minerals, (ii) soil formation processes (pedogenesis) and (iii) the biogeochemistry of elements that are either beneficial or toxic to themselves and other soil biota.  相似文献   

Making New Zealanders through commemoration: Assembling Anzac Day in Auckland, 1916–1939     

Matthew Henry 《New Zealand geographer》2006,62(1):3-12

Abstract:  Anzac Day in New Zealand has been traditionally framed within a nationalist discourse, in which the events of the day have provided the medium for the remembrance of a singular national event. Moving beyond this interpretative tradition the paper examines Anzac Day as a moment in the exercise of an ongoing governmental power concerned with issues of contemporary conduct. Focusing on interwar Auckland the paper traces the assemblage of time, space and rhetoric, which enabled the production of a commemorative, governmental landscape.  相似文献   

Geostatistical integration of near-surface geophysical data   总被引：1，自引：0，他引：1  

A. Vesnaver  R. Bridle  B. Henry  R. Ley  R. Rowe  A. Wyllie 《Geophysical Prospecting》2006,54(6):763-777

Accurate statics calculation and near‐surface related noise removal require a detailed knowledge of the near‐surface velocity field. Conventional seismic surveys currently are not designed to provide this information, and 3D high‐resolution reflection/refraction acquisition is not feasible for large survey areas. Satellite images and vibrator plate attributes are dense low‐cost data, which can be used in spatially extrapolating velocities from sparse uphole data by geostatistics. We tested this approach in two different areas of Saudi Arabia and found that the optimal recipe depends on the local geology.  相似文献   

Interaction of tectonics, eustasy, climate and carbonate production on the sedimentary evolution of an early/middle Jurassic extensional basin (Southern Provence Sub-basin, SE France)     

Philippe Léonide  Marc Floquet  Loïc Villier 《Basin Research》2007,19(1):125-152

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).  相似文献