含五次对称的准晶体的点群与单形

应该把有关准晶体的研究纳入晶体学领域,扩大晶体学的内容与涵义。作者把含有五次对称的准晶体的点群与单形作了推导,与经典结晶学相比,增加了14种新点群和24种新单形。此外,作者根据准晶态的构筑原理,又推导出4种准晶格。     

History of the stereographic projection and its early use in geology

The origin of the polar and equatorial stereographic projections can be traced back to Hipparchos (d. 125 bc). The equatorial projection became an essential tool in astronomy and from the 2nd to mid-17th Century it enabled the development of the astrolabe as a navigational tool and later became important in mapmaking. Examples of equatorial stereographic nets by the astronomer al-Zarqul (ad, 10701 and the cartographer Blaeu (1624) are illustrated. By the early 19th Century, mathematics was beginning to be applied outside the fields of astronomy, physics and mechanics. The stereographic net was first applied to mineralogy by Neumann (1823) and its use was subsequently popularized by Federov (1892), inventor of the universal microscope stage, and by the introduction of the Wulff net (1902). It also proved of considerable use in the correct interpretation by W.L. Bragg of Laue X-ray diffraction patterns of crystals which led to the development of X-ray crystallography. The Lambert (1772) equal-area projection, developed for cartographic use and subsequently termed the Schmidt net by Sander in 1925, was essential to the development of petrofabric analysis in the late 1920s. The transition to macroscopic structural analysis, which largely took place over the period 1930–55 is briefly touched upon.     

The use of inclined hemisphere projections for analyzing failure mechanisms in discontinuous rocks

This paper demonstrates the advantages of using inclined stereographic projections in kinematic analysis of rock blocks in discontinuous rock masses. Some examples of limiting cases are presented. The application of inclined projections is illustrated by its use in a mine slope in Brazil. It is clear from the discussion of these examples that inclined hemisphere projections provide better results than horizontal projections. It is also demonstrated that horizontal projections can lead to incorrect results in limiting cases.     

赤平投影的程序化方法与实现

对于存在构造面岩石边坡的稳定分析 ,赤平投影方法是一种行之有效的方法 ,但是赤平投影理论较为抽象 ,图解方法较为繁琐 ,手工绘制误差较大 ,因此编制了赤平投影程序 ,能够很方便、准确地进行边坡稳定性判断。     

Modified perspective cylindrical map projection

Some of the famous cylindrical projections are defined by a geometric process that is based on the perspective. This process can be imagined as a semitransparent sphere wrapped by a tube, secant, or tangent, with the same center; then all features of the sphere surface are projected onto the tube surface by light rays from a source in the equatorial plane. Just by changing the light source’s position and tube’s diameter, different maps can result. In every cylindrical perspective projections, distortions are functions of latitude only, thus, the value of distortion is fixed along a parallel (or a small circle). Therefore, distortion isograms are parallels (or small circles), symmetrical in relation of the equator. Consequently, it is suitable for territories having narrow band shape, extended by the equator (or an oblique equator). The proposed projection in this paper introduces another possible adjustment in cylindrical projections, in which axis of cylinder does not pass through the center of the sphere. This may satisfy case, where territories have a closed curve shape. By comparing the distribution of distortions in other famous perspective cylindrical projections (Lambert, stereographic, and central), with that in the proposed modified perspective cylindrical projection, it was found that distribution of area distortion in the proposed projection can be considered better than others. Therefore, in relation to area representation, the modified perspective cylindrical projection can be considered suitable for mapping regions, having shape close to an ellipse.     

Diamondiferous Archean rocks of the Olondo greenstone belt (western Aldan–Stanovoy shield)

Diamond from metaultramafic rocks of the Mesoarchean (2.96–3.0 Ga) Olondo greenstone belt, located in the western Aldan–Stanovoy shield, has been studied. Diamonds occur in lenses of olivine–serpentine–talc rocks within metaultramafic rocks of intrusive habit, whose composition corresponds to peridotite komatiites. All diamonds from the metaultramafic rocks are crystal fragments 0.3 to 0.5 mm in size. Morphological examination has revealed laminar octahedra, their transitional forms to dodecahedroids, crystals with polycentric faces, and spinel twins. The crystals vary in photoluminescence color: dark blue, green, yellow, red, or albescent. Characteristic absorption bands in crystals point to nitrogen impurities in the form of A and B1 defects and tabular B2 defects. The crystals studied belong to the IaA/B type, common among natural diamonds. The overall nitrogen content varies from < 100 to 3800 ppm. The relative content of nitrogen in B1 centers varies from 0 to 94%, pointing to long stay in the mantle. The carbon isotope ratio in the diamonds, ¹³C = ? 26‰, is indicative of involvement of subducted crust matter in diamond formation in the Archean.     

Hypogeal geological survey in the “Grotta del Re Tiberio” natural cave (Apennines, Italy): a valid tool for reconstructing the structural setting

As karst systems are natural windows to the underground, speleology, combined with geological surveys, can be useful tools for helping understand the geological evolution of karst areas. In order to enhance the reconstruction of the structural setting in a gypsum karst area (Vena del Gesso, Romagna Apennines), a detailed analysis has been carried out on hypogeal data. Structural features (faults, fractures, tectonic foliations, bedding) have been mapped in the ”Grotta del Re Tiberio” cave, in the nearby gypsum quarry tunnels and open pit benches. Five fracture systems and six fault systems have been identified. The fault systems have been further analyzed through stereographic projections and geometric-kinematic evaluations in order to reconstruct the relative chronology of these structures. This analysis led to the detection of two deformation phases. The results permitted linking of the hypogeal data with the surface data both at a local and regional scale. At the local scale, fracture data collected in the underground have been compared with previous authors’ surface data coming from the quarry area. The two data sets show a very good correspondence, as every underground fracture system matches with one of the surface fracture system. Moreover, in the cave, a larger number of fractures belonging to each system could be mapped. At the regional scale, the two deformation phases detected can be integrated in the structural setting of the study area, thereby enhancing the tectonic interpretation of the area (e.g., structures belonging to a new deformation phase, not reported before, have been identified underground). The structural detailed hypogeal survey has, thus, provided very useful data, both by integrating the existing information and revealing new data not detected at the surface. In particular, some small structures (e.g., displacement markers and short fractures) are better preserved in the hypogeal environment than on the surface where the outcropping gypsum is more exposed to dissolution and recrystallization. The hypogeal geological survey, therefore, can be considered a powerful tool for integrating the surface and log data in order to enhance the reconstruction of the deformational history and to get a three-dimensional model of the bedrock in karst areas.     

Stability analysis of invariant points using Euler spheres, with an application to FMAS granulites

Alternative assignment of invariant point stabilities in a possible P – T  phase diagram is given by a family of grids that derives from a form of the Euler equation. Invariant points are represented by great circles that divide the surface of a sphere (the Euler sphere) into polygonal regions that correspond to the number of potential solutions or grids in n -component systems with n +3 non-degenerate phases. A particular invariant point is stable in all grids on one side of the great circle and metastable on the other. The advantage of this representation is the ease and efficiency by which all grids consistent with experimental and theoretical constraints can be identified. The method is well suited for systems of n +3 phases in which the thermochemical data necessary for direct calculation of the phase diagram is either uncertain or non-existent for one or more of the phases. The mass balance equations among the n +3 phases of interest define the Euler sphere for any particular system. There is a unique Euler sphere for unary systems, and another for binary systems. Ternary and quaternary systems have four and 11 different types of Euler spheres, respectively. In the ternary case with six phases, the 16 non-degenerate chemographies belong to four groups that are associated with the four Euler spheres. An analysis of those groups shows a close relationship between the topologies of the chemographies and the topologies of the grids represented on the Euler sphere. Euler spheres for degenerate chemographies are characterized by a smaller number of spherical polygons. A useful application of the Euler sphere concept is the systematic derivation of possible FMAS petrogenetic grids from subsystem constraints. Assumption of just one stable invariant point in each of MAS and FAS systems is consistent with seven FMAS grids involving cordierite, garnet, hypersthene, quartz, sapphirine, sillimanite and spinel.     

某水电站引水洞进口侧山体边坡块体识别

某水电站进口侧山体边坡岩体为完整性较差的中--薄层状灰岩,岩体中主要发育3 条断层、1 组岩脉和4 组优势节理,严重影响了该山体边坡的稳定性。根据结构面分布,采取块体理论搜索边坡上的关键块体,通过赤平投影法找出边坡上所有的非空裂隙锥,将这些非空裂隙锥与临空面组合,从而获得所有可动块体; 利用矢量法计算不同运动形式下块体JP 编号、净滑力即可获得关键块体。结果表明: 该水电站引水洞进口侧山体边坡有4 块关键块体( JP 编号为00010111、00110111、10110111、 10111011) ,为该边坡稳定性的进一步研究提供了基础。     

Aspects of Proterozoic stromatolite biostratigraphy in Western Australia

Stromatolites are abundant at many horizons in the Proterozoic of Western Australia. Recent advances in knowledge of Proterozoic stratigraphy of the state have provided a more detailed framework for interpreting the stromatolite data than has been available previously. In the 1.7 Ga Earaheedy Group of the Nabberu Basin a characteristic stromatolite assemblage occurs, and within the basin a biostratigraphic succession can be recognized. The assemblage contains several new forms which belong to new groups. The need to erect new groups for these early Proterozoic stromatolites is in agreement with recent studies in Canada, northern Europe and South Africa, and suggests that the problem of ‘younger’ or late Proterozoic stromatolite groups in early Proterozoic rocks mentioned by previous workers is a result of a lack of rigour in defining taxa. Examination of type material is necessary to determine how closely the Earaheedy forms resemble those described from these other regions.In Western Australia some stromatolite forms have a restricted vertical range and similar taxa occur in beds of approximately the same age in widely-separated areas: e.g. Kimberley Group and Earaheedy Group; Scorpion Group and Limbunya, Birrindudu, McArthur, Mt. Rigg and Mt. Albert Groups and Bungle Bungle Dolomite; Tolmer and Bullita Groups; Moora and Bangemall Groups; Kai Ki Beds, Louisa Downs, Mount House and Albert Edward Groups.Stromatolite diversity shows a decline in the number of taxa at about 1.1. Ga in the Bangemall Group. More data are required to determine whether this decline is universal or specific to the Bangemall Group. This study indicates that a stromatolite biostratigraphy for Western Australia is feasible and is consistent with data from other parts of Australia. Thus emphasis on correlation should be placed on the stromatolite form rather than the group, and intercontinental correlations should be attempted only when local biostratigraphic schemes have been firmly established.     

Discontinuity controlled probabilistic slope failure risk maps of the Altindag (settlement) region in Turkey

The evaluation of potential rock slope problems using stereographic projection techniques known as kinematic analysis is one of the most important parts of a slope stability investigation to be carried out in jointed rock media. In conventional stereoprojection techniques for the assessment of possible rock slope failures, the peak orientations of joints together with the slope geometry and the friction angle of the weakness planes are used. Other possible joint orientations which may be encountered in the rock media are ignored, although they belong to the group of joint peak orientations. In this study, nearly vertical jointed andesites cropped out at the Altindag settlement region in Ankara were studied in order to evaluate the relevance of this ignored discontinuity orientation data on slope stability. As a result, probabilistic risk maps for planar, toppling and wedge failures were produced using the kinematic rules and digital elevation model of the study area. The comparison of the distribution of the actual failures in the area and the probabilistic risk maps prepared for the study area revealed that all of the identified failures are found to be located in the higher risk zones on the probabilistic risk maps.     

湘南多金属矿床方解石形态及表面微形貌的研究

对湘南多金属成矿区方解石的研究表明，产于钨矿床中的方解石以层状晶体发育为特征，晶体形态主要为｛０００１｝和｛０１２｝＋｛１０１０｝，晶体表面具有菱形生长阶梯；产于铅锌矿床中的方解石一般不出现层解石，晶体形态主要为｛２１３１｝，｛０１１２｝＋｛１０１０｝和｛０００１｝＋｛１０１０｝＋｛０１１２｝，晶体表面平行纹发育；远矿正常灰岩内方解石晶体形态主要为｛４０４１｝。     

Internal reduction of (Mg,Ni) O: Effect of a NiO-Concentration gradient

Single crystals of (Mg, Ni) O with a Ni-concentration gradient from the outer surface to the interior have been reduced so that metallic nickel particles precipitate in the wüstite matrix. The internal reduction morphology is very different from the one observed in reduced homogeneous (Mg, Ni) O single crystals: pores develop and the precipitates grow along preferential crystallographic directions. The addition of iron ions to the inhomogeneous mixed oxide crystals suppresses the porosity. The observations are described and discussed in terms of point defects and transport kinetics.     

The infrastructure and Origin of Upper Sinian Cherts on the Southeast Continental Margin of the Yangtze Platform

Through microscopic and SEM observations and X-ray diffraction and energy spectrum analyses, the oldest sponge spicules and radiolarians have been found in bedded cherts and it is proposed that microbial activity of algae and bacteria played an important role in silica precipitation. The microbial activity resulted in the formation of a series of single crystals and crystal aggregates with peculiar shapes. Biogenic single crystals usually occur in spherical, rod, platy, colloidal and granular forms. The most common aggregates are framboidal aggregates composed of dense spherical quartz crystals, which are considered to be of typical bacterial origin. Other aggregates, such as favositic, double-spherical, chain-spherica'l and coccoid ones, are considered to be probably the result of silicification of algal cells and mainly of primary sedimentary origin. This paper also discusses the ultrastructural features and diagnostic indications of jasper rocks formed in a submarine hydrothermal environment and cher     

The Ultrastructure and Origin of Upper Sinian Cherts on the Southeast Continental Margin of the Yangtze Platform1

Abstract Through microscopic and SEM observations and X-ray diffraction and energy spectrum analyses, the oldest sponge spicules and radiolarians have been found in bedded cherts and it is proposed that microbial activity of algae and bacteria played an important role in silica precipitation. The microbial activity resulted in the formation of a series of single crystals and crystal aggregates with peculiar shapes. Biogenic single crystals usually occur in spherical, rod, platy, colloidal and granular forms. The most common aggregates are framboidal aggregates composed of dense spherical quartz crystals, which are considered to be of typical bacterial origin. Other aggregates, such as favositic, double-spherical, chain -spherical and coccoid ones, are considered to be probably the result of silicification of algal cells and mainly of primary sedimentary origin. This paper also discusses the ultrastructural features and diagnostic indications of jasper rocks formed in a submarine hydrothermal environment and cherts formed by replacement and diagenetic recrystallisation.     

Adsorption mechanisms of the nonequilibrium incorporation of admixtures in a growing crystal

The nonequilibrium partition of components between a crystal and solution is mainly controlled by impurity adsorption on the surface of the growing crystal. The specificity of adsorption on the faces of various simple forms leads to the sectorial zoning of crystals. This effect was studied experimentally for several crystallizing systems with different impurities, including isomorphous, 2d-isomorphous, and nonisomorphous, readily adsorbed impurities. In all systems, the sectorial selectivity of impurity incorporation into host crystals has been detected with partition coefficients many times higher than in the case of equilibrium partition. Specific capture of impurities by certain faces is accompanied by inhibition of their growth and modification of habit. The decrease in nonequilibrium partition coefficients with degree of oversaturation provides entrapment of impurities in the growing crystals. Thereby, the adsorption mechanism works in much the same mode for impurities of quite different nature. The behavior of partition coefficient differs drastically from impurity capturing by diffusion mechanism.     

Geochemistry and petrography of gold-quartz-tourmaline veins of the Okote area, southern Ethiopia: implications for gold exploration

Summary Quartz-tourmaline vein-hosting rocks of the Okote area belong to the Neoproterozoic Adola Belt. Metasomatic auriferous quartz-tourmaline veins occur in ductile N–S trending, sinistral shear zones. These veins commonly contain quartz, carbonates, and tourmaline, with minor pyrite, and accessory chalcopyrite, pyrrhotite, and gold. Tourmaline forms isolated euhedral crystals in the fracture surfaces of quartz carbonate veins. Many of the tourmaline crystals are optically zoned with a bluish core and a bluish to brown rim. Electron microprobe analyses show that the tourmalines comprise an intermediate dravite-schorl solid solution with a mean FeO/(FeO + MgO) = 0.47. Abrupt transitions between the colour zones within single tourmaline crystals are accompanied by relative variations in the FeO/(FeO + MgO) ratios. The tourmaline separates indicate that the tourmalines contain highly variable average contents of trace elements. Chondrite-normalized rare earth element (REE) abundances of tourmaline separates from auriferous veins show LREE-enriched to LREE-depleted patterns with negative to positive Eu anomalies and a flat, near-chondritic HREE pattern. The auriferous quartz-tourmaline veins have LREE-enriched patterns without a Eu anomaly and a flat HREE pattern, but tourmaline-free gold-quartz veins have very low REE contents and LREE-depleted patterns also without Eu anomalies. The FeO/(FeO + MgO) ratios, major and trace element compositions, and the types of wall-rock alteration are used to suggest that the sources of boron are dominantly metamorphic (dehydration and devolatilization processes), but do not totally exclude the possibility of a magmatic source. The occurrences of high-grade gold associated with tourmaline make tourmaline a valuable prospecting guide for hydrothermal gold mineralization in the Adola Belt, southern Ethiopia. Received November 17, 1999; revised version accepted July 23, 2001     

Structural data extraction from stereographic or equal area projections using image processing

Structural orientation data from the field are commonly represented on stereographic or equal area projections, and the raw data are usually not accessible to other workers for integration into larger datasets or comparative study. We have developed a technique for retrieving raw planar structural data from the above projection types using image analysis techniques. The principle involves two steps: (i) conversion of the foliation pole plots in the image into Cartesian coordinates, and (ii) inversion of the data soobtained into a geographic reference frame. The process involves either scanning of the target projection, or cropping of the projection figure from a pdf file using image processing software, followed by tracing of the data points and generation of an image file that can be subsequently input into a MATLAB supported program, “StrucExtract”. The results from the program are displayed in the form of dips and dip directions. The program has been tested with synthetic and natural examples, and may be invaluable for retrieval of structural data from older structural literature.     

北京雁栖镇典型危岩基本特征及稳定性分析

本文以北京市怀柔区雁栖镇研究区崩塌体为研究对象,通过现场调查和岩块试验检测,查明了崩塌体的基本特征。采用赤平投影分析法,对崩塌危岩带整体稳定性进行定性分析;运用极限平衡法,针对不同工况条件,对单体危岩崩塌进行定量评价。在此基础上,提出了具有针对性的治理措施。研究结果表明:（1）研究区内崩塌隐患点所在斜坡危岩带基本处于不稳定状态;（2）单体危岩W1、W2、W3在自重+裂隙水压力（天然状态）工况条件下,稳定系数1.02～1.17,均处于欠稳定状态;在自重+裂隙水压力（暴雨期间）工况条件下,稳定系数0.82～0.98,均处于不稳定状态;在自重+裂隙水压力（天然状态）+地震力工况条件下,稳定系数0.72～0.83,均处于不稳定状态。（3）提出的以清理危岩为基础,“主动+被动防护网”的综合工程治理措施在北京地区是可行的。研究成果可以作为北京地区开展崩塌灾害工程治理的参考。