Short‐term changes in the plan shape of a sandy beach in response to sheltering by a nearshore mud bank,Cayenne, French Guiana     

Edward J. Anthony  Antoine Gardel  Franck Dolique  Daniel Guiral 《地球表面变化过程与地形》2002,27(8):857-866

Montjoly is a headland‐bound embayed sandy beach in Cayenne, French Guiana, that shows long‐term plan shape equilibrium in spite of periodic changes in accretion and erosion that alternately affect either end of the beach. These changes are caused by mud banks that move alongshore from the Amazon. The mechanisms involved in changes in the plan shape of the beach in response to the passage of one of these mud banks were monitored between 1997 and 2000 from airborne video imagery and field work. The beach longshore drift to the northwest, driven by the incident easterly to northeasterly swell usually affecting this coast, became temporarily reversed as the mud bank, migrating from east to west, initially sheltered the southeastern end of the beach. The difference in exposure to waves engendered a negative wave height gradient alongshore towards the southeast, resulting in the setting up of a cell circulation and counter‐active longshore drift from the exposed northwestern sector to the southeast. Sand eroded from the exposed sector accumulated first in the southeastern, and then the central sectors of the beach. The effect of increasing beach sheltering by the mudbank moving west is highlighted on the videographs by an ‘arrested’ pattern of beach shoreline development. The videographs show hardly any changes in beach plan shape since January 1999, due to sheltering of the beach from wave attack by the mud bank. It is expected that the eroded sector will recover in the future as the mud bank passes, leading to re‐establishment of the northwesterly sand drift. This temporally phased bi‐directional drift within the confines of the bounding headlands results in a rare example of mud‐bank‐induced beach rotation, and probably explains the long‐term equilibrium plan shape of Montjoly beach. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The UV-Visible Absorption Cross-Sections and Atmospheric Photolysis Rate of HOI     

David M. Rowley  Juliane C. Mössinger  R. Anthony Cox  Roderic L. Jones 《Journal of Atmospheric Chemistry》1999,34(1):137-151

The UV-visible absorption cross-sections of HOI have been recorded over the wavelength range 278-494 nm and at 298 K following generation of HOI in the gas phase using laser flash photolysis. The gas phase reaction of OH with I₂ was used to produce HOI, and the absorption spectrum of HOI was calibrated relative to the consumption of I₂. The HOI spectrum recorded exhibits 2 broad absorption maxima of = 3.99 × 10^-19 cm² and = 2.85 × 10^-19 cm², centred at 338.4 nm and 404.8 nm respectively. The spectrum is adequately described by a parameterisation consisting of two semi-logarithmic Gaussian distribution functions. The HOI spectrum is more intense than that recorded in previous work of Jenkin, but is in good agreement with more recent work by Bauer et al. The parameterised HOI absorption spectrum recorded in this work was used in a radiative model to calculate the atmospheric photolysis rate (J-value) of HOI. These results indicate that, under most sunlit conditions, HOI has a lifetime with respect to solar photolysis of the order of minutes. Experiments attempting to generate HOI by the reaction of O atoms with C₂H₅I led to complex absorption spectra containing a negative contribution to the absorption from the photolytic removal of an unidentified species. In addition, evidence was found for adsorption and desorption of an iodine-containing species in the reaction vessel. This behaviour is rationalised in terms of the disproportionation of HOI to I₂O, and an uncalibrated spectrum tentatively attributed to I₂O has been recorded.  相似文献   

Strontium isotope geochemistry of megacrysts and host basalts from southeastern Australia     

John S Stuckless  Anthony J Irving 《Geochimica et cosmochimica acta》1976,40(2):209-213

Strontium isotopic data for megacrysts and lavas from six eruptive centers within the Newer Basalts province of southeastern Australia show that megacrysts of clinopyroxene are in isotopic equilibrium with associated basalts, but that megacrysts of kaersutite, ferrokaersutite, orthopyroxene and anorthoclase may exhibit slight disequilibrium with their host basalts. Furthermore, the anorthoclase megacrysts may be either more or less radiogenic than their hosts. The ⁸⁷Sr/⁸⁶Sr ratios for 14 basalts from throughout the province vary from 0.7035 to 0.7045 and it is proposed that anorthoclase, amphibole and orthopyroxene megacrysts which crystallized in isotopic equilibrium with one magma may have been caught up in a pulse of a later magma of a different isotopic composition. The variations in the ⁸⁷Sr/⁸⁶Sr ratios for the basalts are attributed to variations in the isotopic composition of their source regions. Such isotopic heterogeneity is supported by published data for ultramafic xenoliths which occur in the Newer Basalts lavas.  相似文献   

A preliminary review of the stratigraphic relationships and distribution of metamorphism in the northern part of the Natal-Namaquarides,South Africa     

Anthony C. Cain 《International Journal of Earth Sciences》1975,64(1):192-216

Highly deformed regionally metamorphosed rocks of the Natal-Namaqua belt north of Durban preserve the features of a major Precambrian geosynclinal sequence, with possible reactivated oceanic and continental floor material. The broad scale grouping of similar lithologies into mappable geologic units is possible. Formation status is assigned to certain units, classified in the Natal group. Variation of lithologic character of these rocks within the belt is correlated with facies of orogenic deposition. Three zones of regional progressive metamorphism are recognised, and the metamorphosed rocks of the belt can be divided into a high-pressure intermediate, intermediate-pressure and intermediate-low pressure facies series types corresponding to the upper-greenschist facies, low-amphibolite facies and middle-amphibolite facies respectively. These three metamorphic terrains display considerable differences in composition and structural style, and correspond to the major tectonic units of the belt. Evidence gained from a study of the distribution of regional metamorphism in the Natal-Namaquarides north of Durban, has reinforced the favourability of applying the theory of plate tectonics to the development of the orogen in an attempt to obtain a broader understanding of the geologic history of the belt. Furthermore, the complex suite of metamorphites and associated intrusive phases constituting the belt involves the deformation and metamorphism of lithological types similar to those described in orogenic belts in other parts of the world.  相似文献   

Secondary circulations near sand banks and in coastal embayments     

Anthony D. Heathershaw  Francis D. C. Hammond 《Ocean Dynamics》1980,33(4):135-151

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A numerical model for summer flows in Lake Michigan     

Mr. Anthony G. Kizlauskas U. S. E. P. A.  Dr. Philip L. Katz 《Meteorology and Atmospheric Physics》1974,23(2):181-197

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Towards integrated essential variables for sustainability     

Anthony Lehmann  Joan Masò  Stefano Nativi  Gregory Giuliani 《International Journal of Digital Earth》2020,13(2):158-165

ABSTRACT

Measuring the achievement of a sustainable development requires the integration of various data sets and disciplines describing bio-physical and socio-economic conditions. These data allow characterizing any location on Earth, assessing the status of the environment at various scales (e.g. national, regional, global), understanding interactions between different systems (e.g. atmosphere, hydrosphere, biosphere, geosphere), and modeling future changes. The Group on Earth Observations (GEO) was established in 2005 in response to the need for coordinated, comprehensive, and sustained observations related to the state of the Earth. GEO’s global engagement priorities include supporting the UN 2030 Agenda for Sustainable Development, the Paris Agreement on Climate, and the Sendai Framework for Disaster Risk Reduction. A proposition is made for generalizing and integrating the concept of EVs across the Societal Benefit Areas of GEO and across the border between Socio-Economic and Earth systems EVs. The contributions of the European Union projects ConnectinGEO and GEOEssential in the evaluation of existing EV classes are introduced. Finally, the main aim of the 10 papers of the special issue is shortly presented and mapped according to the proposed typology of SBA-related EV classes.  相似文献   

Volatile characteristics of peralkaline rhyolites from Kenya: an ion microprobe,infrared spectroscopic and hydrogen isotope study   总被引：1，自引：0，他引：1  

Martin C. Wilding  Ray Macdonald  J. Eric Davies  Anthony E. Fallick 《Contributions to Mineralogy and Petrology》1993,114(2):264-275

Peralkaline rhyolites of the Greater Olkaria Volcanic Complex, Kenya Rift Valley, were derived from separated, though closely related, magma chambers. Ion microprobe analyses of glass inclusions in quartz phenocrysts show pre-eruptive water contents of up to 3.4 wt% contrasting with previous estimates that the magmas were anhydrous. The values approach predicted solubility levels corresponding to water saturation at low crustal pressures (1 kbar). The glass matrices of the rhyolites have low water contents, ranging from 0.07 to 0.46 wt%, suggesting significant degassing during, or prior to, eruption. Infrared measurements of the matrix glasses show variation in the relative proportions of the two hydrous species dissolved in the glasses. The amount of molecular water, determined semi-quantitatively, apparently increases with increased fluorine content and peralkalinity. This suggests a competition between hydroxyl groups and fluoride ions for similar sites within the melt structure. The mechanism of degassing has been investigated using hydrogen isotopes. The range of D values in most rocks can be produced by varied degrees of open-system degassing of rhyolite melt initially in equilibrium with water of a fixed, or limited, D value. There is evidence to suggest that closed-system degassing may also have been a significant component in some rhyolites. The exact mechanisms of degassing remain uncertain. Particular problems include the relative contribution of open-and closed-system degassing during eruption and the initial vapour compositions and solubility relationships.  相似文献   

Petrology of the Chilliwack batholith,North Cascades,Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity   总被引：18，自引：1，他引：17  

Jeffrey H. Tepper  Bruce K. Nelson  George W. Bergantz  Anthony J. Irving 《Contributions to Mineralogy and Petrology》1993,113(3):333-351

Calc-alkaline granitoid rocks of the Oligocene-Pliocene Chilliwack batholith, North Cascades, range from quartz diorites to granites (57–78% SiO₂), and are coeval with small gabbroic stocks. Modeling of major element, trace element, and isotopic data for granitoid and mafic rocks suggests that: (1) the granitoids were derived from amphibolitic lower crust having REE (rare-earth-element) and Sr-Nd isotopic characteristics of the exposed gabbros; (2) lithologic diversity among the granitoids is primarily the result of variable water fugacity during melting. The main effect of f_{H 2 O} variation is to change the relative proportions of plagioclase and amphibole in the residuum. The REE data for intermediate granitoids (quartz diorite-granodiorite; Eu/Eu^*=0.84–0.50) are modeled by melting with f_{H 2 O}<1 kbar, leaving a plagioclase + pyroxene residuum. In contrast, data for leucocratic granitoids (leuco-granodiorites and granites; Eu/Eu^* =1.0–0.54) require residual amphibole in the source and are modeled by melting with f_{H 2 O}=2–3 kbar. Consistent with this model, isotopic data for the granitoids show no systematic variation with rock type (⁸⁷Sr/⁸⁶Sr_i =0.7033–0.7043; Nd(0)=+3.3 to +5.5) and overlap significantly with data for the gabbroic rocks (⁸⁷Sr/⁸⁶Sr_i =0.7034–0.7040; Nd(0)=+3.3 to +6.9). The f_{H 2 O} variations during melting may reflect additions of H₂O to the lower crust from crystallizing basaltic magmas having a range of H₂O contents; Chillwack gabbros document the existence of such basalts. One-dimensional conductive heat transfer calculations indicate that underplating of basaltic magmas can provide the heat required for large-scale melting of amphibolitic lower crust, provided that ambient wallrock temperatures exceed 800°C. Based on lithologic and geochemical similarities, this model may be applicable to other Cordilleran batholiths.  相似文献   

Ab initio valence force field calculations for quartz     

Paul F. McMillan  Anthony C. Hess 《Physics and Chemistry of Minerals》1990,17(2):97-107

We have derived valence force constants for the tetrahedral SiO₄ unit and the inter-tetrahedral SiOSi linkage from previous ab initio molecular orbital calculations on H₄SiO₄ and H₆Si₂O₇ using a split-valence polarized Gaussian basis set (6-31G^*), and used these to calculate the infrared and Raman active vibrational modes of α-quartz. The calculation gives frequencies approximately 15% greater than experiment, as expected from harmonic force constants obtained at this level of Hartree-Fock theory, but the calculation gives the correct distribution of modes within each frequency range. Calculated 28–30 Si and 16–18 O isotope shifts and pressure shifts to 6 GPa are also in reasonable agreement with experiment. We have also used our ab initio force field to calculate the vibrational spectrum for β-quartz. The results suggest either that inclusion of a torsional force constant is important for determining the stability of this high temperature polymorph, or that the β-quartz has a disordered structure with lower symmetry (P6₂) domains, as suggested by earlier diffraction studies.  相似文献