Ab initio elasticity of FeS2 pyrite from 0 to 135 GPa     

Y. Le Page  J. R. Rodgers 《Physics and Chemistry of Minerals》2005,32(8-9):564-567

Polynomial expressions for the elastic tensor coefficients, the bulk, the shear and Young’s moduli, the speed of sound for longitudinal and transverse waves, the equation of state and the x coordinate of the sulfur atom in pyrite are reported based on ab initio calculations in the range of 0–135 GPa. Comparison with published experimental data indicates good agreement for the equation of state and for values at 0 GPa as well as reasonable agreement for first derivatives. All modeling and interpretation was performed with Materials Toolkit v.2.0 and all ab initio computations with VASP.  相似文献   

Geometry and growth of an inner rift fault pattern: the Kino Sogo Fault Belt, Turkana Rift (North Kenya)   总被引：1，自引：0，他引：1  

William Vtel  Bernard Le Gall  John J. Walsh 《Journal of Structural Geology》2005,27(12):2204-2222

A quantitative analysis is presented of the scaling properties of faults within the exceptionally well-exposed Kino Sogo Fault Belt (KSFB) from the eastern part of the 200-km-wide Turkana rift, Northern Kenya. The KSFB comprises a series of horsts and grabens within an arcuate 40-km-wide zone that dissects Miocene–Pliocene lavas overlying an earlier asymmetric fault block. The fault belt is 150 km long and is bounded to the north and south by transverse (N50°E and N140°E) fault zones. An unusual feature of the fault system is that it accommodates very low strains (<1%) and since it is no older than 3 Ma, it could be characterised by extension rates and strain rates that are as low as 0.1 mm/yr and 10⁻¹⁶ s⁻¹, respectively. Despite its immaturity, the fault system comprises segmented fault arrays with lengths of up to 40 km, with individual fault segments ranging up to 9 km in length. Fault length distributions subscribe to a negative exponential scaling law, as opposed to the power law scaling typical of other fault systems. The relatively long faults and segments are, however, characterised by maximum throws of no more than 100 m, providing displacement/length ratios that are significantly below those of other fault systems. The under-displaced nature of the fault system is attributed to early stage rapid fault propagation possibly arising from reactivation of earlier underlying basement fabrics/faults or magmatic-related fractures. Combined with the structural control exercised by pre-existing transverse structures, the KSFB demonstrates the strong influence of older structures on rift fault system growth and the relatively rapid development of under-displaced fault geometries at low strains.  相似文献   

Hierarchical modelling of archaeomagnetic data and curve estimation by moving average technique     

Philippe Lanos  Maxime Le Goff  Mary Kovacheva  Elisabeth Schnepp 《Geophysical Journal International》2005,160(2):440-476

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Distortion of the geomagnetic field in volcanic terrains: an experimental study of the Mount Etna stratovolcano     

Jean-Claude Tanguy  Maxime Le Goff 《Physics of the Earth and Planetary Interiors》2004,141(1):59-70

The inclination (I), declination (D) and total intensity (F) of the geomagnetic field were measured on Mount Etna in 1989-1991 at a dozen sites previously sampled for archeomagnetic studies. The purpose of the work was to determine the variations of these parameters at 30 cm above ground level, and how the distortion from the main field can affect the archeomagnetic record of volcanic rocks. Ten measurements were usually performed at each site with a three-component flux-gate magnetometer, whose estimated precision is ±0.2° on direction and ±50 nT on intensity. This was considered sufficient on volcanic areas with highly magnetized rocks and where the geomagnetic gradient may be in excess of 1000 nT/m. Results averaged for each site generally show small variations in intensity (±3% of the total field) and direction (±1.5°). The averaged values of the 12 sites (I=52.6°, D=0.3°, F=44010 nT) are very close to those measured in sedimentary terrain away from the volcano (I=52.9°, D=0.35°, F=44110 nT), themselves consistent with the interpolated IGRF in eastern Sicily. The largest deviations of the geomagnetic direction have been observed on four sites, three of them located on the South flank between 1900 and 700 m elevation. It is suggested that these anomalies are mainly related to dyke swarms which are common within the South Rift Zone of Mount Etna. Our findings show that reliable archeomagnetic results can be obtained from volcanic rocks, provided that lavas of the same eruption are sampled on several sites distributed over the largest possible area.  相似文献   

Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii: Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars     

R.V. Morris  D.W. Ming  R.E. Arvidson  S.W. Squyres  J.E. Gruener  L. Le 《Earth and Planetary Science Letters》2005,240(1):168-178

Iron-rich spherules (> 90% Fe₂O₃ from electron microprobe analyses) ∼10-100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe / Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H₂O and/or OH^− 1. The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe₂O₃) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al³⁺ for Fe³⁺ substitution and structural H₂O and/or OH^− 1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.  相似文献   

Cratons and orogenic belts of the Brazilian Shield and their contained gold deposits   总被引：2，自引：0，他引：2  

Leó A. Hartmann  Inácio Delgado 《Mineralium Deposita》2001,36(3-4):207-217

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Brood patch temperature during provocation of common eiders in Ny-Ålesund, Svalbard     

Francois Criscuolo  Michel Gauthier-Clerc  Yvon Le  Maho Geir W. Gabrielsen 《Polar research》2001,20(1):115-118

In this short note we describe the behaviour and body changes of three incubating female common eiders ( Somateria mollissima ) during provocation made by humans approaching the nest. The study site was near the settlement of Ny-Ålesund, Svalbard. Temperture transmitters were implanted subcutaneously at the brood patch and data recorded using a VHF receiver. We found that the female experiment exhibited a passive defence response ("freezing"), accompanied by a significant drop in brood patch temperature (0.6 °C) during provocation; this temperature drop lasted for 5 minutes. These accord with other studies of the physiological changes which the passive defence response in birds and other animals.  相似文献   

Precession‐induced flows in liquid‐filled containers and in the Earth's core     

M. A. Pais  J. L. Le Mouël 《Geophysical Journal International》2001,144(3):539-554

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Climate, flora and fauna changes in the Sahara over the past 500 million years     

Henry N. Le Houérou 《Journal of Arid Environments》1997,37(4):619-647

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Productivity, management and development problems in the arid rangelands of the central Mendoza plains (Argentina)     

J.C Guevara  J.B Cavagnaro  O.R Estevez  H.N Le Houérou  C.R Stasi 《Journal of Arid Environments》1997,35(4):575-600

The central Mendoza plains (56,000 km²), located in the eastern foothills of the Andes, belong to the vast phytogeographic province of ‘Monte’ (c.500,000 km²) in Argentina. This area is a typical warm arid zone and vegetation is typically a shrubland. Perennial grasses are predominantly C₄species. Land-use is for livestock grazing; the average stocking rate is 28 ha per large stock unit (LSU), year-long. Ecological and range research have been actively pursued in the region by IADIZA over the past 25 years. Two experiment stations were established 25 and 10 years ago, respectively: The Ñacuñán Biosphere Reserve and the El Divisadero Cattle and Range Station. Primary production and its relationship to climatic and edaphic parameters were analysed and compared in the two stations. Rain-use efficiency (RUE, kg DM ha⁻¹year⁻¹mm⁻¹) and useful rains efficiency (URE, P −0·1 PETp) were similar in both cases (RUE = 1·7 and 2·0; URE = 3·0 and 2·9, respectively), when herbs are concerned. However, the variability of annual production was much higher on the silty soils of Ñacuñán than on the coarse sands of El Divisadero; PRVR (Production to Rain Variability Ratio) was 2·5 and 0·53, respectively. Utilization of such experimental figures allows for the prediction of primary production and carrying capacity for a given year, based on rainfall probabilities and, therefore, to determine stocking rates in a rational manner. Basing stocking rates on annual dependable rains (f 0·8) and on useful rains probability (P − 0·1 PETp) proved to be a sound and realistic assessment, validated by long-term experiments and experience. The results of the studies on brush control, cattle diet composition, animal productivity and feed value of forage species were analysed. Current and future research programmes in IADIZA for the Mendoza plains are mentioned. Although research on resource inventory and basic ecological processes in the Mendoza plains should carry on, the emphasis and therefore the resources should henceforth be devoted to the consequences of resource management alternatives on overall arid land productivity, i.e. research for development. A better integration of applied ecology for management and investigations on basic arid land ecological processes should appear in IADIZA programmes.  相似文献