Luna 20: mineralogy and petrology of fragments less than 125 μm size

Two milligrams of less than 125 μm size particles from the Luna 20 soil sample (22001,17) have been examined. The results of the mineral identification and analysis verify earlier assumptions that the nature of the lunar highlands is predominantly anorthositic in composition. The presence of highly magnesian clinopyroxene, orthopyroxene and olivine suggests crystallization of Highland rocks in an ultrabasic environment. No fragments were observed that could be unequivocally assigned to mare basalt types.     

Aluminous hematite: A mössbauer study

Aluminous hematites prepared in three different ways have been examined at 300K and 4.2K using the Mössbauer technique. The results indicate significant differences between the behaviour of aluminous hematites that have been subjected to high temperatures (>600° C) and those which have not. The magnitude of the room temperature quadrupole splitting of the former increases with aluminium content, approaching at ～16 mole percent substitution the value (?0.22 mm/s) exhibited by all of the low temperature specimens. This variation may be explained qualitatively in terms of a preferential c-axis contraction of the lattice upon incorporation of aluminium, which does not occur unless a c-axis defect structure is removed by subjection of the hematite to high temperatures. The solid solubility limits of high and low temperature hematites (～15 mol % and ≥19 mol % respectively) also differ, as do the room temperature decreases in hyperfine splitting (?0.82 kOe/mol % Al and ?0.86 kOe/mol % Al). At 4.2 K only low temperature hematite exhibits a decrease in hyperfine splitting with increasing Al content (?0.40 kOe/mol % Al). The absolute values of the recoil free fractions of hydrothermally prepared aluminous hematites have been determined at 4.2 K (0.70±0.02 — pure hematite, 0.82±0.02, 14±2 mol % Al substitution) and exhibit a similar increase with Al content to that previously observed for aluminous goethites. The room temperature recoil free fraction of pure hematite has been measured to be 0.64±0.02. The effects of particle size on both hyperfine splitting and recoil free fraction have been investigated.     

高应变率作用下岩石的微观损伤特征

摘要：为研究岩石在高应变率作用下的微观损伤特征,用三轴ＳＨＰＢ装置对混合花岗岩和磁铁矿矿石进行高速冲击,用光学显微镜和扫描电镜观察矿物颗粒的受损状态,得出岩石的微观损伤特征     

Studies of colloids and suspended particles,Cigar Lake uranium deposit,Saskatchewan, Canada

The Cigar Lake U deposit is located in northern Saskatchewan in the eastern part of the Athabasca Sandstone Basin, and consists of a high-grade ore body (up to 55% U) located at a depth of ∼430 m. As part of a study to evaluate the analog features of this deposit with respect to a disposal vault for waste nuclear fuel, colloids (1–450 nm) and suspended particles (450nm) in groundwater have been investigated to evaluate their effect on element transport through the U deposit. Tangential-flow ultrafiltration was used to concentrate particles from 501 groundwater samples in order to characterize the size distribution, concentration, composition and natural radionuclide content of particles in representative parts of the U deposit. Although Cigar Lake groundwaters contain particles in all sizes ranging from 10 nm to slightly larger than 20 μm, most samples contained a relatively high concentration of colloids in the 100–400 nm size range. Particle compositions are similar to the composition of minerals in the sandstones and ore body, suggesting that particles in groundwater are generated by the erosion of fracture-lining minerals. As a result, particle concentrations in groundwater are affected by the integrity of the host rock. In some piezometers the high initial concentrations of suspended particles, which may have been drilling artifacts, decreased during the collection of the first 350 1. Although colloid concentrations fluctuated during sampling, there are no indications that these concentrations will be permanently reduced by continued groundwater pumping. The observed colloid and suspended particle concentrations in the deep groundwaters are too low to have a significant impact on radionuclide migration, provided that radionuclide sorption is reversible. If radionuclides are irreversibly sorbed to particles they cannot sorb to the host rock and their migration can only be evaluated with an understanding of particle mobility. The data for dissolved and particulate U, Th and Ra were used to calculate field-derived distribution ratios (R_d) between particles and groundwater. The wide range of observed R_d values indicates that these radionuclides in particulate form are not in equilibrium with groundwater. U-series isotope data indicated that most of the U and Ra on particles was derived from groundwater. Some particles could have retained their U for as long as 8000 a. The U and Ra contents of particles in the ore and surrounding clay zones are significantly higher than in particles from sandstone, suggesting that the clay has been an effective barrier to particle migration.     

Petrographische und Kalium-Argon-Untersuchungen an basischen tertiären Vulkaniten zwischen Westerwald und Vogelsberg

Between the upper tertiary volcanic areas of Westerwald and Vogelsberg (central Western Germany) occur more than 40 isolated tertiary volcanic dikes, eroded necks, plugs and domes. Twelve of these volcanic rocks have been investigated petrographically and chemically and classified by means of their modal and chemical composition. Additional modal analyses have been performed on seven other volcanics. On seventeen volcanic occurences K-Ar-whole rock age determinations have been made. The K-Ar age determinations yield- with the exception of an olivine-nephelinite — values between 27 and 15 Ma. Regarding the known intervals of volcanic activities of the Westerwald- and Voge1sberg-areas, most of the examined volcanics can be related genetically with one of the adjacent volcanic areas. There seems to be no geographical overlapping of volcanics showing Westerwaldages and Vogelsberg-ages. A possible influence of excess-Ar-bearing phases (e. g. mantle xenoliths) and an Ar-loss of constituent matter of the groundmass have been estimated by additional age determinations of enriched samples. These influences — partially compensating each other — may shift the K-Ar whole rock age to a maximum of 5 % and thus do not exceed the dimension of the standard deviations. A distinct NNE-SSW-striking fault in the region between Marburg and Gießen is situated parallel with the eastern border of the “Rheinisches Schiefergebirge”. Volcanics showing Westerwald-age and Vogelsberg-age respectively reach this fault, but obviously do not overlap it. Relations between rock-type an rock age, as it has been observed for the volcanics of the northern Hessian Depression (Kreuzer et al. 1973;Wedepohl 1982) cannot be proved certainly. On the other hand, similar to the basaltic rocks of the northern Hessian Depression, the youngest volcanic product is an olivine-nephelinite (9 Ma).     

Electro-flotation of chalcopyrite fines

Electro-flotation tests were conducted on chalcopyrite particles with a modified Hallimond tube designed for electro-flotation, using platinum anode—copper cathode and graphite anode—copper cathode systems. Flotation tests were carried out for fines of chalcopyrite of size below 20 microns with potassium ethylxanthate as collector. Studies were done on flotation with hydrogen and oxygen separately with the usual variables. Dissolution of chalcopyrite at various current densities, with reagent at optimum conditions and without reagent was also studied. It is observed that electro-flotation particularly with oxygen, is effective in the flotation of fine particles of chalcopyrite.     

Assessment of heavy metals contamination and their potential toxicity in the surface sediments of Sfax Solar Saltern,Tunisia

Concentrations of six heavy metals such as Fe, Pb, Zn, Cu, Ni and Cd have been examined in 20 surface sediment samples from Sfax solar saltern in order to evaluate their contamination levels; such concentrations (expressed in mg/kg of dry weight) have shown that Fe varied from 8750 to 8889.1, Pb from 18.98 to 233.46, Zn from 39.92 to 574.89, Cu from 13 to 98, Ni from 17.47 to 160.92, and Cd from 4.86 to 37.42. Importantly, the highest metal concentrations—except for Fe—have been more significant in sites frequently exposed to the industrial plumes of the local pollutant sources on the one hand and in sites often overwhelmed by high tide marine’s water draining industrial waste from the port area on the other hand. Calculated enrichment factors have shown a spatial distribution in consistency with that related to concentrations. Complementary statistical approaches based on principal component analysis and hierarchical cluster analysis have proved that Fe is natural and other analyzed metals are anthropogenic. The geoaccumulation index has shown different contamination and toxicity levels, which have been confirmed by the study of mean-effect range medium-quotient, demonstrating a high probability of toxicity ranging from 49 to 76%, especially at sites with the highest metal concentrations. It has been suggested by the potential ecological risk index that the combined ecological risk of anthropogenic metal differ from one site to another, which highly significant in the case of Cd.     

Primordial refractory metal particles in the Allende meteorite

Refractory metal particles containing Os, Re, W, Mo, Ir, and Ru were observed in a Ca-Al-rich inclusion in the Allende meteorite. These particles are the closest to unaltered primordial metal condensates from a nebula yet reported, and appear to have been isolated from the nebula before the condensation of refractories was complete. Computer calculations of condensation indicate that the temperature of isolation appears to be close to the calculated temperature of first formation of oxides (~ 1620 K at 10^?4 atm) indicating that isolation may have been effected by coating of the particles by oxides.     

我国煤层气储层研究现状及发展趋势

通过对煤层气储层描述及储层评价，煤储层分布，预测及选区评价，煤储层研究方法及实验技术等方面的系统评述后认为，我国目前已基本掌握了煤储层地质特征研究和地质评价选区技术，煤层气储层工程技术和储层模拟软件系统，并在煤层气储层研究方面有所突破，但我国煤储层的构造复杂，煤层多强烈变形，煤层结构常呈碎粒状及糜棱状等，煤储层多为贫煤和无烟煤，呈“三低一高”（煤层压力较低，煤层渗透率低，在水压裂等强化措施下形成的常规破裂裂缝所占比较低；煤层普遍具有较高的吸附力）的物性特征，且变质程度偏高，高煤级煤（贫煤一无烟煤）占49％，独具“中国特色”，进而讨论了当前我国煤层气储层研究急待解决的8个方面的科技问题和难点，指出了在21世纪初中我国煤层气储层研究的7个发展趋势。     

Tectonics and petroleum potential of the East Arctic province

Tectonics and petroleum potential of the underexplored East Arctic area have been investigated as part of an IPY (International Polar Year) project. The present-day scenery of the area began forming with opening of the Amerasia Ocean (Canada and Podvodnikov—Makarov Basins) in the Late Jurassic—Early Cretaceous and with Cretaceous—Cenozoic rifting related to spreading in the Eurasia Basin. The opening of oceans produced pull-apart and rift basins along continental slopes and shelves of the present-day Arctic fringing seas, which lie on a basement consisting of fragments of the Hyperborean craton and Early Paleozoic to Middle Cretaceous orogens. By analogy with basins of the Arctic and Atlantic passive margins, the Cretaceous—Cenozoic shelf and continental slope basins may be expected to have high petroleum potential, with oil and gas accumulations in their sediments and basement.     

Geochemical investigations to explain iodine-overabundances in Antarctic meteorites

Iodine, bromine, and chlorine concentrations were determined in different Antarctic meteorite specimens (eucrites, high-iron and low-iron chondrites) with isotope dilution mass spectrometry. In all Antarctic meteorites I-overabundances have been analysed compared with the concentrations for non-Antarctic meteorites of the same class. Half of the Antarctic specimens show especially high concentrations of more than 1 μ/g. A similarly high enrichment effect in Antarctic meteorites was not found for Br and Cl, but smaller Cl excesses could be observed in some eucrites and high-iron chondrites.By analysing different types of Antarctic rocks, a significant decrease of the I concentration—but not of the Br and Cl concentration-was determined from the surfaces to the centers of the rocks. This shows that atmospheric I compounds interact with the surfaces of Antarctic rocks and, therefore, with those of Antarctic meteorites as well. Analyses of atmospheric halogens show that the gaseous compound CH₃I is probably responsible for the I-overabundance in Antarctic meteorites and rocks. Chloride and bromide are found in particles derived from sea-spray in Antarctic aerosols. Deposition of halogens in Antarctic snow near the coast shows I/Cl ratios 10–190 higher than the average value for seawater. The corresponding Br/Cl ratios are in the same range as seawater. On the basis of our results and of other reported data we construct a preliminary hypothesis for a geochemical I cycle in Antarctica, taking into consideration long-distance and short-distance transportation of different I compounds from the coast to inland Antarctica.     

Proof of formation of organic matter in upper Devonian carbonate and carbonate-siliceous sediments of the South-Tatar uplift in constant photic layer anoxia

Samples of carbonate and siliceous-carbonate deposits of Semiluk—Sargaev horizons of the N?NE slope of the South Tatar uplift, Volga-Ural petroliferous basin, have been studied. Specific feature of the source rocks—high concentration of compounds—anoxia testifiers in the photic layer has been identified. That is, organic matter has been deposited under the conditions of the constant presence of anoxia in the photic layer of the sedimentation basin at sufficiently high thickness of the water column contaminated with hydrogen sulfide. Since by the composition of saturated hydrocarbons the studied samples are typical for deposits of the Semiluk horizon of the central part of the Volga-Ural basin, we can assume a fairly wide prevalence of such conditions within the South-Tatar arch. Changes in the concentrations of the components—anoxia markers—show cyclical changes in output layer contaminated with hydrogen sulfide or its bioproduction within the studied time.     

Evolution of pore structure and hydraulic conductivity of randomly distributed soluble particle mixture

The plane strain behavior of particulate mixtures containing soluble particles was investigated by conducting both laboratory tests and numerical analysis. To perform the laboratory experiments, soluble mixtures were prepared using photoelastic disks and ice disks with diameters in the ratios (D_{ice disk}/D_{photoelastic disk}) of 0.5 and 0.7, and the evolution of the force chain and pore structure was monitored during the dissolution of the ice disks. Subsequently, numerical analysis was conducted by using the 2‐dimensional discrete element method for the soluble mixtures, and it was compared with the experimental results. Additionally, parametric studies were implemented by varying the particle size ratios between the soluble and non‐soluble particles and the volumetric fraction of the soluble particles. The results of the laboratory experiments and numerical analysis demonstrate that (1) after the dissolution of the soluble particles, the pore fabric of the specimens changed, resulting in a force chain changes, local void increases, and coordination number decreases; (2) the effects of soluble particles on the macro‐behaviors of the mixtures could be divided into 3 zones based on the particle size ratios between the soluble and non‐soluble particles and volumetric fraction of soluble particles. These zones were as follows: (Zone 1)—with a small total soluble volume, slight decrease in the in situ lateral pressure (K₀), and minor increase in the hydraulic conductivity (k); (Zone 2)—with a moderate soluble particle; the dissolution generated a honey‐comb particle structure; (Zone 3)—the total soluble volume was very large, and the high volumetric fraction of the dissolving particle collapsed the pore structure, decreasing in the in situ lateral pressure (K₀) but increasing the hydraulic conductivity (k). The horizontal stress returned to almost the original level, and the internal arching formation increased significantly with the hydraulic conductivity (k).     

Effects of internal pores on the mechanical properties of marine calcareous sand particles

Calcareous sand is a typical problematic marine sediment because of its angular and porous particles. The effects of internal pores on the mechanical properties of calcareous sand particles have rarely been investigated. In this paper, the apparent morphology and internal structure of calcareous sand particles are determined by scanning electron microscopy and computed tomography tests, finding that the superficial pores connect inside and outside of the particles, forming a well-developed network of cavities and an internal porosity of up to 40%. The effects of particle morphology and internal porosity on the mechanical responses of particle were investigated by conducting photo-related compression test and 3D numerical simulations. Two failure modes are observed for the porous calcareous sand, i.e., compressive failure indicates that the particle skeleton is continually compressed and fragmented into small detritus without obvious splitting, and tensile failure indicates that the particles are broken into several fragments when the axial force clearly peaks. Calcareous sand particles with a high internal porosity or with small and dense pores often exhibit compressive failure, and vice versa. The particle strength is considerably reduced by increasing the internal porosity, but affected by pore size in nonlinear correlation. The crushing stress–strain points can be well fitted by an exponential curve, which is supplied for discussion.

     

Petrology, Metamorphic Process and Genesis of The Dabie--Sulu Eclogite Belt, Eastern--Central China

The Qinling-Dabie-Sulu high-pressure and ultra-high pressure metamorphic belt wasformed by subduction and collision between the North China and Yangtze plates. The study ofthe eclogite belt is very important in understanding the evolution of the Qinling Dabie orogen. Inthe present paper the geology, petrology, minerology and chronology of the eclogites in the Dabieand Sulu areas are described. The principal conclusions of this work are as follows: (1) Based up-on the field occurrence and the P-T conditions of the eclogites, two types of eclogite can be dis-tinguished: Type 1—the low-temperature and high-pressure eclogite in the mid-late Proterozoicmetamorphic series, and Type 2—the ultra-high pressure eclogite in the late Archaean to earlyProterozoic metamorphic complex. In the Dabie area, the ultra-high-pressure eclogite,high-pressure eclogite and epidote-blueschist units are nearly parallel to each other and stretchintermittently from north to south. (2) The P-T conditions of the high-pressure eclogites and ul-tra-high pressure eclogites have been estimated. The former are formed at 450-550℃ and1.4-1.6 GPa; while the latter at 650-870℃ and >2.7-2.9 GPa in the Dabie area and at820-1000℃ and >2.8-3.1 GPa in the Sulu area. The metamorphic temperatures of the eclogitesincrease progressively from west to east. (3) The ultra-high pressure eclogites were subjected to 5stages of metamorphism: pre-eclogite epidote amphibolite facies, peak coesite eclogite facies,post-eclogite amphibolite facies, epidote-blueschist facies or epidote amphibolite facies andgreenschist facies. The general features of the PTt path of the ultra-high pressure eclogite are:clockwise pattern, progressive metamorphism being a process of slow increasing temperature andrapid increasing pressure, and the retrogressive section with nearly isothermal decompression atthe early stage, isobaric cooling at the middle stage and nearly isothermal decompression at thelate stage. (4) At least two stages of high-pressure metamorphism occurred in the orogenic belt:the high-pressure eclogite and ultra-high pressure eclogite were formed by the subduction of theoceanic crust northward beneath the North China plate or the Dabie block during theCaledonian; while the epidote-blueschist belt came into being by subdution and collision be-tween the two continental plates during the Indosinian. (5) Due to the continuous sequentialsubduction of the cold plate, the ultra high-presssure metamorphic rocks were uplifted to thecrust by the underplating processes. They can be preserved just because of the "frozen effect" re-sulting from the continuous subduction of the cold plate. (6) The carbonates, such as magnesite,breunnerite, aragonite and dolomite, and the H_2O-bearing minerals, such as phengite, epidoteand zoisite, were stable during the high-pressure and/or ultra-high pressure metamorphism.     

Effect of Aspect Ratio on the Monotonic Shear Behaviour: Micromechanical Interpretations

The effect of aspect ratio on the mechanical behaviour and micromechanics of two different assemblies during drained triaxial shearing are reported in this paper. Discrete element simulations are done on two different sets of assemblies—first assembly consists of particles with aspect ratio 1.0 and second assembly consists of particles with aspect ratio 1.5. A log normal distribution of particle size is adopted for both the samples. The constitutive behaviour of the assemblies and the evolution of the microstructure of the samples under shearing are closely examined and is related to the aspect ratio of the particles constituting the assembly. The spherical harmonic distributions of contact forces and contact normals along with 3-D histograms are plotted to give quantitative information of the variation of these parameters as the loading progresses. The results indicate that as the aspect ratio increases, there is an increase in the maximum deviatoric stress at the macroscopic level. At the microscopic level, the values of the anisotropic coefficients which are representative of the microparameters also show an increase in the magnitude for the assembly with higher aspect ratio particles.     

An experimental and theoretical study of the seepage migration of suspended particles with different sizes

This study experimentally investigates the effect of particle size, particle concentration and flow velocity on the migration of suspended particles of size 1.02–47 μm in porous media. The results show that at the same flow velocity, the peak values of the breakthrough curves decrease and corresponding pore volumes increase slightly with increasing particles size. The migration velocity of smaller suspended particles is even greater than water flow velocity, which is attributed to the size exclusion effect. With increase of the injected particle concentration, the deposition coefficients of small single particles increase at first and then tend to a steady state or even decrease slightly, explained by the maximum retention concentration. The dispersivity of small particles decreases with increasing velocity. However, at a high flow velocity, the hydrodynamic dispersivity becomes increasingly dominant with the increase of particle size. The deposition coefficients for large-sized particles are higher than those for small-sized particles, which is attributed to considerable mass removal due to straining. An analytical solution, considering the release effect of sorbed particles, is developed to account for the one-dimensional flow and dispersive effect using a source function method, and then three transport parameters—dispersivity, deposition coefficient and release coefficient—are fitted using the experimental results. Finally, suspended-particle migration is predicted by the proposed model for short-time constant-concentration injection and repeated three-pulse injection. Overall, particle size has a significant effect on the seepage migration parameters of suspended particles in porous media such as the particle velocity, dispersivity and deposition coefficient.     

Microclimatology and forest plague(Dendroctonus adjunctus) in Central Mexico

It has been observed in at least eight places in Central Mexico that hilly zones with certain orientation and slopes have a higher-than-normal incidence of plague. In this paper, the potential insolation and the total microclimatology of an infested and a healthy zone have been studied, with the purpose of determining the condition of natural climatic stress in the vegetation that makes it susceptible to the attack and proliferation of plagues. The infested slope (NE-NW), in contrast to the healthy slope (SE-SW), has greater annual variability in the potential reception of insolation, besides a minor energy availability disposition — on a daily basis — in quantity and in number of hours, by conduction from the ground, which produces more heterogeneity in the gradient of temperature at different depths in the ground; and the wind effect tends to be more frequent, intense and prolonged. The area studied is in the National Park “La Malinche” Tlaxcala in Central Mexico.     

Dynamic characteristics of multiscale longitudinal stress and particle rotation in ballast track under vertical cyclic loads

Loads transfer in ballast track through contacts among randomly distributed ballast particles and have strong heterogeneity. Since the size ratio between ballast track and ballast particles is generally small, using averaged stress to describe the internal mechanical state in ballast track faces practical difficulties. For example, particle movements and high local concentration stress tend to be ignored. The inter-particle contact stress is crucial to evaluate the particle behaviors, such as abrasion, movements, and furtherly the performance of ballast track. However, the contact stress on ballast particles is hard to predict or measure. We conduct a full size model test to investigate the dynamic characteristics of longitudinal stress on ballast particles as well as different lateral regions under vertical cyclic loads with various loading magnitudes and frequencies. An obvious seesaw effect of longitudinal contact stress is observed: the stresses at some contact areas have the same phase with applied cyclic load while at other contact areas have an opposite phase. The seesaw effect of contact stress is then used to evaluate the rotational movements of ballast particles. The variation of contact area and stress of the ballast particles with loading magnitudes demonstrates that the rigid contact assumption is appropriate when analyzing the contact behavior of ballast particles. The cumulative probability distribution of contact stress with stress level can be described by an inversely proportional function, based on which the maximum contact stress can be estimated according to the longitudinal average stress. Besides, the lateral dispersion angle of the vertical loads in the ballast track is about 35°, which is independent of the given loading magnitudes and frequencies.

     

Variations in the type and distribution of organic matter in some Carboniferous sediments from northern England

The organic content of a number of sediments from the Carboniferous of northern England have been examined as a function of their depositional environment. Extraction of the sediments yielded the soluble organic matter whilst microscopic examination of polished blocks of shales enabled the detection of particles of organic detritus. A relationship between the amount of extract and the quantity of terrestrial plant material in the sediments has been established. However, the yield of extract (mg/g org. C) is higher in the more marine environment than the nonmarine environment. The proportion of saturated hydrocarbons in the extract appears to be related to the amount of identifiable organic matter (coal macerals) in the sediment. The n-alkane distribution patterns have been compared with these obtained from coal macerals. The suggestion that the pristane to phytane ratios may reflect the source material of the organic matter has been examined.