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1.
Partition of Fe2+ and Mg between coexisting (Mg, Fe)2SiO4 spinel and (Mg, Fe)SiO3 pyroxene was investigated at pressures 80 and 90 kbar and at temperatures 840 and 1050° C, using tetrahedral-anvil type of high pressure apparatus. Olivine-spinel solid solution equilibria in the system Mg2SiO4-Fe2SiO4 were discussed in the light of the partition reaction. Partition of Fe2+ and Mg in both olivine-spinel and pyroxene-spinel systems can not be regarded as that between ideal solid solutions. By applying the simple solution model for the partition of Fe2+ and Mg, sign of the heat of mixing was estimated to be positive for all olivine, spinel and pyroxene. Relative concentration of Fe2+ in spinel in the pyroxene-spinel system is likely to cause some change in the chemical composition of modified spinel () or spinel () in the transition zone of the mantle. A considerable change is also expected in the transition pressure of to ( + ) and ( + ) to .Presented at the symposium Recent Advances in the Studies of Rocks and Minerals at High Pressures and Temperatures held in Montreal, 1972. Jointly sponsored by the International Mineralogical Association and the Commission on Experimental Petrology. 相似文献
2.
The suggestion that Sudbury-type ores may be formed by the introduction of country rock sulfur into still hot intrusions (i.e., sulfurization) suffers from a reputed lack of field evidence. Permissive evidence for sulfurization includes the epigenetic nature of many Sudbury-type ores and that many Sudbury-type ores crystallized from sulfide melts. Visual evidence exists for sulfurization of a gabbro in Zambia. The lead isotopic composition of ore minerals at Sudbury implies that at least some of the metals were derived from the erruptive. Published sulfur isotopic data from several Sudbury-type ores differ from and do not exhibit a common pattern of isotopic enrichment with respect to sulfides within associated intrusions. Evidently the sulfur was derived from the country rocks. Sudbury-type ores exhibiting magmatic textures commonly occur within more siliceous dikes than the host intrusions. Inorganic reduction of sulfate occurs only above 600° C. Reduction of sulfate with resultant sulfurization of ferrous iron and traces of other metals originally present in the still hot parental intrusive rock would make the rock more siliceous. Above 1100° C the silicate-residue and newly formed sulfides would form immiscible magmas. Therefore, ore magmas within and near mafic intrusives can be epigenetic. The processes by which sulfur is introduced into intrusions are still speculative.
Zusammenfassung Für die Annahme, daß Erze vom Sudbury-Typus sich durch Zuführung von Nebengesteinsschwefel in noch heiße Intrusionen bilden können (sulfurization), fehlt es angeblich an Feldunterlagen. Folgende Tatsachen lassen sich mit einer Schwefelung (sulfurization) vereinigen: der epigenetische Charakter vieler Erze vom Sudbury-Typ; auch sind viele Erze von Sudbury-Typus aus sulfidischen Schmelzen kristallisiert. In einem Gabbro in Zambia ist der Beweis für Schwefelung (sulfurization) direkt sichtbar. Die Isotopen-Zusammensetzung von Blei in Erzmineralien in Sudbury zeigt, daß mindestens einige der Metalle aus dem Eruptivgestein stammen. Schwefelisotop-Daten, die für mehrere Lagerstätten von Sudbury-Typen veröffentlicht worden sind, haben hinsichtlich der Isotop-Anreicherung keine gemeinsamen Züge. Offensichtlich stammt der Schwefel aus dem Nebengestein. Erze vom Sudbury-Typ mit magmatischem Gefüge finden sich oft in Gängen, die saurer sind als das Wirtsgestein. Anorganische Reduktion von Sulfat findet nur oberhalb 600°C statt. Reduktion von Sulfat und die entstehende Schwefelung (sulfurization) von zweiwertigem Eisen und Spuren anderer Metalle, die ursprünglich in dem noch heiß eruptiven Gestein anwesend sind, machen das Gestein noch saurer. Oberhalb 1100°C würden der Silicat-Rest und die neugeformten Sulfide nicht mischbare Magmen bilden. Deshalb können sich sulfidische Schmelzen innerhalb und in der Nähe von Mafic-Intrusionen später gebildet haben. Die Prozesse, durch die Schwefel in Intrusionen eingeführt wird, sind noch unbekannt.相似文献
3.
The product covariance model, the product–sum covariance model, and the integrated product and integrated product–sum models have the advantage of being easily fitted by the use of marginal variograms. These models and the use of the marginals are described in a series of papers by De Iaco, Myers, and Posa. Such models allow not only estimating values at nondata locations but also prediction in future times, hence, they are useful for analyzing air pollution data, meteorological data, or ground water data. These three kinds of data are nearly always multivariate and because the processes determining the deposition or dynamics will affect all variates, a multivariate approach is desirable. It is shown that the use of marginal variograms for space–time modeling can be extended to the multivariate case and in particular to the use of the Linear Coregionalization Model (LCM) for cokriging in space–time. An application to an environmental data set is given. 相似文献
4.
Summary In saturated rocks and soils it is possible to define different coefficients of thermal expansion depending on the drainage conditions. This topic is first examined from the theoretical point of view with regard to an ideal isotropic thermo-elastic porous medium. Some special features of the behaviour of natural soils and rocks during thermal expansion tests are subsequently discussed. An experimental evaluation of some of these coefficients is presented in the second part of the paper. The material investigated is a pyroclastic rock, the so-called Neapolitan Yellow Tuff. Thermal expansion coefficient in drairend conditions has been evaluated, when this material is saturated with water. The e pressure increase induced by heating has been measured in undrained tes temperatures investigated range between room temperature up to 225°C.Different types of apparatus have been used and, when possible, a comparison between the results has been proposed. The results obtained in undrained thermal expansion tests are in agreement with theoretical predictions. This research is part of an on-going study of the complex phenomena known as Bradyseism, which is occurring in a volcanic area a few kilometers from Naples (Italy). Some considerations on this phenomenon are drawn in the last paragraph of the paper.List of Symbols
l
linear thermal expansion coefficient
-
s
volumetric thermal expansion coefficient of the solid phase
-
ss
volumetric drained thermal expansion coefficient of the solid skeleton
-
st
volumetric drained thermal expansion coefficient that takes into account variations of porosity induced by heating
-
t
volumetric drained thermal expansion coefficient of the whole system
-
u
volumetric undrained thermal expansion coefficient of the whole system
-
v
volumetric thermal expansion coefficient
-
w
volumetric thermal expansion coefficient of the water
-
l
*
volumetric thermal expansion coefficient of the distilled water
-
Biot's coefficient
-
d
dry specific gravity
-
s
specific gravity of the solid phase
-
r
'
uniaxial compressive strength
-
r
'
yield stress in isotropic compression
-
B
T
parameter relating undrained thermally generated pore pressure with temperature change
-
d
0
maximum uplift during Bradyseismic crises
-
d
f
residual uplift during Bradyseismic crises
-
K
s
compressibility modulus of the solid phase
-
K
ss
compressibility modulus of the solid skeleton
-
K
w
compressibility modulus of the water
-
n
porosity
-
T
temperature
-
T
0
initial temperature in thermal expansion, tests performed in thermal expansion cell
-
T
m
temperature at which the volume of waterV
Eexpelled from thermal expansion cell. is measured
-
V
volume of the solid skeleton
-
V
E
volume expelled from thermal expansion cell
-
V
0
volume of the expansion cell at temperatureT
0
-
V
s
volume of the solid phase 相似文献
5.
Frequent sampling during an annual cycle of dissolved(<0.45 m) and suspended (>0.45 m) elementshas been conducted in the Kafue River at Raglan'sFarm, upstream from the mining activities within theCopperbelt Province, Zambia. Additional sampling ofsediment and interstitial pore water was conductedduring low water discharge. The presence of carbonateswithin the drainage basin naturally gives rise to highelement concentrations in the dissolved phase(Ca = 626, Mg = 494, Na = 360 and K = 24 mmol l-1).During the rainy season the relative composition ofthe dissolved elements indicated a wash out ofaccumulated weathering products and mineralisedorganic material from the unsaturated zone of the soilprofile. High concentrations of dissolved Al, Fe andMn were measured during high water discharge. At lowwater discharge the sediment was a major source of Fe,Mn and associated Co and Cu to the water column.Enhanced concentrations of dissolved and suspended S,Co and Cu during the rainy season indicated thatatmospheric deposited particles from the mining areawere washed out into the river. Autochthonousformation of particles rich in Si indicated diatomproduction during low water discharge. 相似文献
6.
The issue of farmland retention or preservation must focus on both the farmland base and the economic viability of agriculture. Most jurisdictions in North America have tended to concentrate their concern on the land issue, often to the detriment of structural issues in agriculture and production. The following essay outlines the structural components of significance which must also be addressed if agricultural land retention policy is to be relevant in terms of enhancing and retaining a strong agricultural base. The components include: marketing —getting a price; reducing costs of agriculture; new farmer entry; the right to farm, and improving managerial capability of farmers. 相似文献
7.
Richards Paul 《GeoJournal》1995,35(2):197-203
Indigenous wetland management systems, rice cultivation, and technological change are described for two areas in Sierra Leone. Management involves knowledge-intensive versus capital-intensive manipulation of water and soil. Irrigation is as much brain work as it is ground work. Sensitive observation and use is made of variable soil conditions up and down slopes. A suite of numerous rice varieties and supplementary crops is maintained and used as appropriate under different physical conditions. The paper also explores the reasons why certain technological changes such as the introduction of tractors in one area in the 1950s and the introduction of a specific rice cultivar in another area by the author in 1983 succeeded (ie persist without outside encouragement), while other innovations have disappeared. Successful technologies were highly compatible with pre- existing patterns of thought, social relations, and ecological practices.The cases contradict the view that development must shape landscape with machines on a massive scale. If the electronic future really is all about lightness, modularity, and the kind of standardization that permits maximal flexibility in combination and communication, then the poor, forced to dodge and weave with great mental agility on their refractory wetlands, are in touch with the future. 相似文献
8.
The concept of space is one of the most fundamental of geographical concepts. There is no work in geography that does not certain it. Nevertheless, geography has not as yet formulated an explicit and unambiguous definition of geographical space. This fact has had negative consequences for geographical theory, methodology and application. In the effort of contributing to its elimination we will try to outline the basic connotations of the concept.The concept of geographical space is a relational one. It acquires meaning and sense only when related to other concepts. The concept of space may be conceived as a supplement to things, i.e. substantively conceived objects. Space conceived in this way is the synonym of emptiness. The concept of space may be also conceived in relation ti individual landscape elements as their environments. Space conceived in this way has the character of a field of force. And, finally, space may be conceived also with respect to the totality of landscape elements, i.e. the system expressed by the term synergic. It is only this third variant of space which should be understood as the geographical space in the full menaing of the term. It is only this conception of geographical space as the space filled with qualities in relations and proportions that is considered as one of the basic prerequisites for the formulation of the theory of geography as science capable of prediction and thus also of practical utilization. 相似文献
9.
This paper describes an alternative nondestructive technique for bulk density and water content determination in soils using dual-energy computerized tomography. A first generation tomographic system (STAC-1) was used in the analysis of the specimens. The system used 137Cs (662 keV), 192Ir (316 keV) and 241Am (60 keV) as radiation sources and a Sodium Iodine crystal (NaI(Tl)) with photomultiplier tube as the detector. The specimens of soil tested were from different regions, one from São Paulo, and the other from Rio de Janeiro. The bulk density and the water content were determined point by point, in a transverse section of the soil specimens, using a computational algorithm that generated images of bulk density and water content. By utilizing the average pixel values of linear attenuation coefficient in these images, for each specimen, a characteristic curve could be built for each soil. The linear attenuation coefficient values agreed with the expected data. The compaction curves presented good agreement between the tomographic technique and the standard geotechnical method. 相似文献
10.
Relation between dislocation density and subgrain size of naturally deformed olivine in peridotites 总被引：1，自引：0，他引：1
Mitsuhiro Toriumi 《Contributions to Mineralogy and Petrology》1979,68(2):181-186
The subgrain size and the dislocation density of subgrain interiors were measured by the oxidation-decoration method under the optical microscope on naturally deformed olivine from peridotite xenoliths and alpine-type peridotites. Relation of the subgrain size, d and the dislocation density, , within subgrains is represented by the equation, d=15/. Combining with relations of the differential stress and the dislocation density proposed by Kohlstedt and Goetze (1974), relation between the stress () and the subgrain size becomes d=45 Gb/, where G and b are the rigidity and the magnitude of the Burgers vector of olivine. This relation is in good agreement with those in a simple oxide (MgO), and alkali halides (NaCl, LiF) given by Hüther and Reppich (1973), Poirier (1972), and Streb and Reppich (1973), respectively. 相似文献
11.
Randall L. Gresens 《Contributions to Mineralogy and Petrology》1969,24(2):93-113
The petrogenesis of Franciscan-type blueschists is controversial or paradoxial in regard to the possible significance of the serpentinite-blueschist association, the isochemical vs. allochemical character of blueschist metamorphism, the significance of high pressure mineralogy, and the physical-geologic-tectonic conditions existing during metamorphism. A model for blueschist alteration during serpentinization is presented that departs from conventional treatments of metamorphism because the reaction path rather then the thermodynamically lowest energy state is considered to be a controlling factor.Alteration of ultramafic rocks to serpentinites requires oxidation of iron in the rock and selective withdrawal of water from saline pore fluids derived from surrounding eugeosynclinal rocks. Pore fluids become concentrated and chemically reducing in the vicinity of serpentinites.The activated pore fluids may react with surrounding rocks via reactions that include a reduction step. The pore fluids may also affect the reaction path through surface chemical effects existing between mineral surfaces and/or growth units and the reducing pore fluid. The degree of polarization of oxygen ions in the silicate structural types, a function of polymerization and aluminum substitution, may control the surface effects and result in the preferential growth of chain silicates, and, more generally, of silicates with low amounts of tetrahedral aluminum.The ratio Mg+2/H+ in the pore fluid can change during serpentinization depending on the extent to which magnesium is lost from the original mafic rock. This ratio may be an important control on the growth of jadeite vs. glaucophane in the presence of excess quartz.The reduction reactions and those involving conventional fluid-solid equilibria cause a change in pore fluid chemistry as the reaction proceeds. Such reactions may explain short-range metasomatic transitions observed in some blueschists. The kinetic controls involving surface chemical effects are catalytic and may explain isochemical phenomena.The ultimate drive for the process is the large negative free energy change of serpentinization that results when ultramafic rocks are emplaced in eugeosynclinal rocks with which they are not in equilibrium. Removal of this overwhelming disequilibrium may induce secondary disequilibrium and activation of pore fluids, producing Franciscan-type blueschists. 相似文献
12.
The Araripe Plateau in northeastern Brazil has an area of about 8,000 km2, confined by 39°05E and 40°55E, and 7°10S and 7°50S. Due to high permeability of soils, a surface drainage system is practically inexistent. Water is stored in excavations with clayey soil, the barreiros. Monthly samples were taken for 18O measurements, from September 1999 to August 2000, from four barreiros, three dug wells and five drilled wells. Results show that (1) groundwaters in the eastern part of the plateau are derived from present-day rainfall (18O–3.2), whereas groundwaters in the western portion are isotopically different (18O–5.0); (2) barreiros are strongly marked seasonally by elevated 18O during the dry period due to elevated evaporation; (3) a dug well at a distance of 30 m from a barreiro exhibits 18O similar to that of the reservoir, indicating a strong interaction between groundwater and surface water; and (4) a tubular well of 242-m depth, located in a fault, exhibits strong seasonal changes in 18O and electrical conductivity, revealing downward leakage between aquifers. 相似文献
13.
Summary The paper describes the application of a recently developed joint element to the analysis of a jointed rock foundation of an arch dam. The most relevant joint system and the concrete-rock interfaces were simulated by means of joint elements. Parameters for the constitutive behaviour of the joints were derived from large scale in situ shear tests. The analysis showed the suitability of the jointed model to predict not only stresses and deformations but also the shape of the failure surface al ultimate conditions. This allows an easy determination of conventional safety factors. A parallel no tension analysis incorporating a cohesion threshold was also carried out. The comparison of both approaches indicates that the no tension hypothesis is a crude approximation of the rock response to dam loads and may lead to unsafe estimates of stability and stress conditions.The analysis performed also showed the relevance of initial stress conditions inside the rock mass in controlling the overall foundation response. 相似文献
14.
A numerical investigation to determine the existence or otherwise of congruence between laboratory-based and field-based models for predicting hydraulic conductivity of compacted clay liners has been conducted. The comparisons here are based on values of the reliability index estimated with the use of the two models for cases when hydraulic conductivity is assumed to be normally and lognormally distributed. The laboratory reduced Proctor and modified Proctor compactive efforts were assumed to correspond to the lowest and highest compactor weights (165kN and 338kN for sheepsfoot rollers only from literature) respectively. The standard Proctor compactive effort was assumed to correspond to the mean compactor weight of 261.4kN. Reliability estimates from the laboratory-based model were consistently higher than the corresponding values from the field-based model for each of the variables common to the two models. As laboratory samples usually involve small samples which are often unrepresentative of field situations, it is considered that reliability levels estimated with the use of the field-based model provide more realistic assessment of compacted lateritic soils as hydraulic barriers. Compactor weight of 300kN and above may be needed for effective compaction of lateritic soil liners. Reliability-based designs of lateritic soil liners should incorporate appropriate probability distribution types for variables in the field-based model. 相似文献
15.
Hydrological tracing practice on underground contaminations 总被引：1，自引：0，他引：1
W. A. Käss 《Environmental Geology》1994,23(1):23-29
The hydrological tracing technique is an important tool for the risk assessment of problem sites, the so-called Altlasten (old underground contaminations). The penetration of leachate through the unsaturated zone, the transport velocity, the migration pathways, as well as the dispersion in the aquifer can be determined by tracing experiments. A wide range of tracers offer sufficient possibilities to get the necessary hydrogeologic parameters for any kind of Altlasten. This is shown by some examples.An English version of Hydrologische Markierungstechnik bei der Altlastensanierung in: Die Geowissenschaften, Weinheim 10(2): 199–205 相似文献
16.
The axial base and skin capacities of piles bored in cohesion less soils are often estimated using empirical, semi-empirical and theoretical methods. The aim of this paper is to assess the applicability and evaluate the accuracy of different predictions methods available in the literature, via comparison with data from 43 field pile load tests conducted on shafts drilled in the region of the United Arab Emirates. Janbu's theoretical method (1989) with the parameter (=75°) and Vesics theoretical method (1975) yielded accurate predictions for the base resistances. Burlands approach (1973) overpredicts the skin capacities with an average predicted-to-estimated ratio (q
p
/q
e) of three times greater than the unity while using values of the coefficient of earth pressure (k=05k
o
) and the angle of soil-pile friction (=23). 相似文献
17.
Ross Large 《International Journal of Earth Sciences》1990,79(2):265-278
Four major high grade polymetallic massive sulphide deposits (Rosebery, Hercules, Que River and Hellyer) occur within the Cambrian Mount Read Volcanic arc in western Tasmania. The Central Volcanic Complex which is host to the ores is a high-K calc-alkaline andesite-dacite-rhyolite suite which has erupted through thick continental crust along an ancient continental margin. The presence of longitudinal faults which control both the locations of mineralization and younger grabben fill volcanic sequences indicate late stage rifting during the development of the arc.The youngest and least deformed deposits at Hellyer and Que River contain primary textural features within the sulphide mound such as colloform pyrite and chalcopyrite diseased and zoned sphalerits. Isoclinal folding of the Que River ores has caused partial sulphide recrystallization and a cleavage induced lamination which is easily confused with the primary sulphide lamination. The older Rosebery deposit has a sheet like form and a poorly developed alteration pipe. The massive sulphide sheet has been strongly deformed by folding and thrusting leading to a series of imbricate ore lenses. All primary sulphide textures at Rosebery have been destroyed by the later deformation and annealing events.The classic metal zonation within these deposits of Fe->Cu->Pb-Zn->Ag-Au->Ba enables a reconstruction of the original form of the sulphide mounds and the location of primary hydrothermal seafloor outlets. The mean gold grade of the polymetallic massive sulphides varies from 2–4 ppm with the best grades concentrated toward the stratigraphic hanging wall of the deposits associated with either the high grade zinc zone or the barite zone. Mt. Lyell, which is a large copper stock-work orebody in the southern part of the volcanic arc, shows a distinctly different association of gold with copper in the deepest part of the stock-work system. This bipartite association of Au-Zn in the hanging wall (e. g. Hellyer, Que River and Rosebery Zn-Ba zone) and Au-Cu in the footwall (e. g. Mt. Lyell and Rosebery Cu zone) has been observed in other seafloor massive sulphide ores world wide, and is considered to relate directly to the gold transporting mechanism.The footwall gold-copper association is the result of deposition of gold from the high temperature soluble gold-chloride complex due to decreasing temperature and increasing pH as the fluids move up towards the seafloor. On the other hand, concentration of gold in the upper lead-zinc-barium rich parts of massive sulphide lenses at Hellyer, Que River and Rosebery results from remobilization and transport of gold as the bisulphide complex, as the hydrothermal fluids move up through the previously deposited sulphide mound or blanket and out onto the seafloor continually mixing with sea water and becoming more oxidized. Gold is ultimately concentrated at the upper-most surface of the massive sulphide lens due to the continuation of this zone refining process throughout the evolution of the orebody.
Zusammenfassung In dem kambrischen Vulkanbogen des Mount Read, Westtasmanien, gibt es vier hochwertige polymetallische, massive Sulfidlagerstätten: Rosebery, Hercules, Que River und Hellyer. Alle Lagerstätten liegen innerhalb des zentralen Vulkanit-komplexes, eines K-reichen, kalk-alkalischen Andesit-Dacit-Rhyolithes, der entlang eines alten Kontinentalrandes durch eine mächtige kontinentale Kruste eruptierte. Späte Riftphasen während der Bildung des Vulkanbogens werden durch längsgerichtete Störungen, die sowohl Ausfällungsorte als auch jüngere Grabenfüllungen steuern, angedeutet.Hellyer und Que River, die jüngsten und am schwächsten deformierten Vorkommen, enthalten innerhalb der Sulfide primäre texturelle Merkmale, wie kolloidalen Pyrit und Kupferkies, sowie zonierten Sphalerit. Isoklinale Faltung der Que River Lagerstätten verursachte eine teilweise Rekristallisation der Sulfide und eine schieferungsbedingte Lamination, die schwer von der primären Sulfidlamination zu unterscheiden ist. Die ältere Rosebery Lagerstätte hat eine plattenartige Form und einen schwach entwickelten Schlot. Die massive Sulfidplatte wurde durch Faltung und Überschiebung intensiv deformiert, so daß es zu einer dachziegelartigen Lagerung des Lagerstättenkörpers kam. Sämtliche primären Strukturen wurden so durch die spätere Deformation zerstört.Die klassische Zonierung der Metalle innerhalb der Lagerstätte, nämlich Fe->Cu->Pb-Zn>Ag-Au->Ba ermöglicht die Rekonstruktion der ursprünglichen Form und Lage der Sulfide am primären Ausfällungsort. Der durchschnittliche Goldgehalt der Sulfide liegt zwischen 2 und 4 ppm, mit Maxima innerhalb des Hangenden von hochwertigen Zinkoder Baritvorkommen.Mt. Lyell, eine große Kupferlagerstätte im Süden des Vulkanbogens, zeigt eine unterschiedliche Kupfer-Gold-Vergesellschaftung im tiefsten Teil der Lagerstätte. Dieses zweigeteilte Vorkommen, einmal von Gold und Zink in oberen Bereichen (z. B. Hellyer, Que River und der Rosebery Zn-Ba-Zone) und zum anderen von Gold und Kupfer in tieferen Stockwerken (z. B. Mt. Lyell und die Rosebery Cu-Zone) wurde weltweit bei mehreren Sulfidlagerstätten beobachtet. Dieses Phänomen wird direkt auf die Art des Transportme-chanismusses des Goldes zurückgeführt. Die Gold-Kupfervorkommen im tieferen Stockwerk resultieren aus einer Fällung von Hochtemperatur-Gold-Chlorid-Komplexen durch Abkühlung und steigenden pH-Wert während des Aufstiegs der Lösungen. Die Anreicherung von Gold in den höher gelegenen Blei-Zink-Barium-reichen Teilen bei Hellyer, Que River und Rosebery resultiert aus einer Remobilisation und einem Transport von Gold als Bisulfid-komplex, als Folge des Aufstiegs hydrothermaler Lösungen durch ältere Sulfide. Dabei werden die Lösungen auf dem Weg zum Ozeanboden kontinuierlich mit Meerwasser vermischt und bekommen einen mehr oxidierenden Charakter.Die Goldanreicherung direkt an der Oberfläche des massiven Sulfidkörpers ist die direkte Folge dieses fortlaufenden Prozesses während der Entwicklung der Lagerstätte.
Résumé Dans l'arc volcanique combrien du Mont Read (Tasmanie occidentale), existent quatre dépôts de sulfures polymétalliques massifs à haute teneur: Rosebery, Hercules, Que River et Hellyer. Tous ces dépôts sont contenus dans le Complexe Volcanique Central, lequel consiste en une série andésitodacito-rhyolitique calco-alcaline riche en K, qui a fait éruption à travers une croûte continentale épaisse, le long d'une ancienne marge continentale. La présence de failles longitudinales, qui déterminent à la fois l'emplacement des minerais et l'existence de séries volcaniques jeunes de comblement de graben, témoigne de processus de rifting tardifs au cours de l'histoire de l'arc.Les dépôts de Hellyer et de Que River, qui sont les plus jeunes et les moins déformés, présentent dans les sulfures des structures primaires telles que: pyrite et chalcopyrite colloformes et blende zonaire. Le minerai de Que River a subi un plissement isoclinal, responsable d'une recristallisation partielle des sulfures et d'une foliation de schistosité, difficile à distinguer de la lamination originelle des sulfures. Le dépôt de Rosebery, plus ancien, présente la forme d'un feuillet avec une cheminée d'altération peu développée. Ce feuillet de sulfure massif a été fortement déformé par le plissement et par des failles de chevauchement qui ont engendré une série de lentilles de minerai imbriquées. Ces déformations ont provoqué la destruction de toutes les structures primaires des sulfures à Rosebery.La distribution zonée classique des métaux dans ces dépôts (FeCaPbZnAgAuBa) permet de reconstituer la forme originelle des ames de sulfures et de localiser les points d'émissions primaires sur le fond marin. La teneur moyenne en or dans les sulfures massifs polymétalliques varie de 2 à 4 ppm, les teneurs les plus élevées se concentrant vers le toit stratigraphique des sédiments associés, dans les zones à zinc ou à barite. Le Mont Lyell, formé d'un grand gisement de cuivre dans la partie sud de l'arc volcanique, présente une situation nettement différente: l'or y est associé au cuivre dans la partie inférieure du gisement. Une telle dualité d'association Au-Zn au toit (p.ex. Hollyer, Que River et Zone à Zn-Ba de Rosebery) et Au-Cu au mur (p.ex. Mt Lyell et zone à Cu de Rosebery) a été observée dans des amas de sulfures massifs en d'autres endroits du monde et est considérée comme résultant directement du mécanisme de transport de l'or.L'association Au-Cu au mur résulte du dépôt de l'or à partir de complexes solubles de chlorure d'or de haute température, dépôt provoqué par la baisse de température et l'augmentation du ph lorsque les fluides montent vers le fond marin. D'autre part, la concentration de l'or dans les parties supérieures à Pb-Zn-Ba des gisements de Hellyer, Que River et Rosebery résulte d'une remobilisation de l'or sous forme de complexes bisulfurés, lorsque les fluides hydrothermaux montent à travers les sulfures déjà déposés et arrivent sur le fond marin où ils s'oxydent et se mèlent continuellement à l'eau de mer. L'or est finalement concentré à la surface supérieure des lentilles de sulfure massif, grâce à la poursuite de ce processus au cours de l'évolution du gisement.
Mount Read, , 4 , : Rosebery, Hercules, Que River Hellyer. , - -- , . , , , . Hellyer Que River, , , .: . Que River , . Rosebery . , . . , F- > - > Pb- > Zn- > Ag> . 2 4 m, . Mt. Lyell , . : (.: Zn-Ba Hellyer, Que River Rosebery) (.: Mr. Lyell Rosebery). . pH . , , , , . . .相似文献
18.
Prof. Dr. M. Raith Dr. P. Raase Dr. D. Ackermand Dr. R. K. Lal 《International Journal of Earth Sciences》1982,71(1):280-290
The Archaean craton of southern India is characterized by a highly complicated and not yet fully understood geological history comprizing several cycles of sedimentation and volcanism, deformation and metamorphism in the span between about 3400 and 2500 m. y. The large scale regional variation in metamorphic grade observed today is essentially related to a metamorphic event at about 2600 m. y. ago which affected an older migmatite, gneiss-greenstone terrain (2900–3400 m. y.).The southern area is characterized by granulite facies (700–750° C/8–10 kb). An extensive charnockite-khondalite belt has been generated by atectonic transformation of the migmatite-gneiss terrain through the influx of a CO2-rich fluid. Towards the north of the terrain the metamorphic grade decreases to amphibolite facies (600° C/6–8 kb) and to greenschist facies (400° C) which is restricted to the Dharwar greenstone belts. Metamorphism related to younger shear zones in the southern part of the craton led to retrogression of the charnockite-khondalite series under conditions of amphibolite to greenschist facies.The P-T conditions of metamorphism have been evaluated applying mineral stability data and methods of geothermometry and geobarometry in an area between Shimoga-Chitradurga (North) and Coimbatore-Karur (South).
The present study is part of a joint project of Benaras Hindu University at Varanasi and University of Kiel. Financial Support by the Deustche Forschungsgemeinschaft is gratefully acknowledged.
We especially thank M. N. Viswanatha, Geological Survey of India, for his cooperation during the field work. 相似文献
Zusammenfassung Der archaische Kraton Südindiens ist durch eine komplexe, noch nicht vollständig aufgeklärte geologische Entwicklungsgeschichte gekennzeichnet. Sie umfaßt mehrere Zyklen von Sedimentation und Vulkanismus, Deformation und Metamorphose in der Zeitspanne von etwa 3400 bis 2500 Ma. Die großregionale metamorphe Zonierung wird im wesentlichen als das Ergebnis eines Metamorphose-Ereignisses vor ca. 2600 Ma angesehen, das den gesamten archaischen Komplex aus granitoiden Gneisen, Migmatiten und Greenstone-Serien erfaßte.Das südliche Gebiet ist durch Bedingungen der Granulitfazies (700–750° C/8–10 kb) charakterisiert. Hier entstand eine ausgedehnte Charnockit-Khondalit-Zone durch post-tektonische Umwandlung der Migmatit-Gneisserien infolge Zufuhr einer CO2-reichen fluiden Phase. Nach Norden zu nimmt der Metamorphosegrad bis zur niedrigtemperierten Amphibolitfazies (600° C/6–8 kb) und in den Dharwar-Greenstone Belts sogar bis zur Grünschieferfazies (400° C) ab.Eine jüngere Metamorphose von Amphibolit-bis Grünschieferfazies ist auf proterozoische Scherzonen beschränkt. Im südlichen Gebiet führte sie zu einer örtlich unterschiedlich intensiven retrograden Überprägung der Charnockit-Khondalit-Serie.Die P-, T-Bedingungen der Regionalmetamorphose wurden anhand von Mineralstabilitätsdaten und mit Methoden der Geothermometrie und Geobarometrie für das Gebiet zwischen Shimoga-Chitradurga (Norden) und Coimbatore-Karur (Süden) abgeleitet.
Résumé Le craton archéen de l'Inde méridionale est caractérisé par une évolution géologique complexe et mal connue. Elle comprend plusieurs cycles de sédimentation et de volcanisme, de déformation et métamorphisme d'une durée d'environ 3400 jusqu'à 2500 Ma.La variation du degré de métamorphisme observée aujourd'hui est considérée comme le résultat d'un épisode de métamorphisme datant d'environ 2600 Ma, qui a affecté l'ensemble du domaine archéen composé de granitoïdes et de ceintures de roches vertes.La région méridionale de craton est caractérisée par le faciès granulite (700–750 °C/ 8–10 kb). Une zone étendue de charnockites et khondalites est le produit d'une transformation postdéformative résultant de l'apport d'une phase fluide riche en CO2. Vers le nord le degré de métamorphisme décroit jusqu'au faciès amphibolites (600 °C/6–8 kb) et même jusqu'au faciès schistes verts (400 °C) dans les ceintures dharwariennes de roches vertes.Un épisode tardif de métamorphisme de faciès amphibolites et schistes verts est limité aux zones à décollement intense d'âge protérozoïque. Dans la région méridionale il s'est produit un rétromorphisme des roches granulitiques dans la zone des charnockites et khondalites.Les conditions de pression et température ont été déduites de l'application de données sur la stabilité des minéraux et de méthodes de géothermométrie et de géobarométrie pour la région entre Shimoga-Chitradurga (nord) et Coimbatore-Karur (sud).
, . , , 3400 2500 . , , 2600 , , , . (700–750 °, 8–10 ). / - , 2. (600 °, 6–8 ) Dharwar (400 °). . / , . , Shimoga-Chitradurga () Coimbatore-Karur ().
The present study is part of a joint project of Benaras Hindu University at Varanasi and University of Kiel. Financial Support by the Deustche Forschungsgemeinschaft is gratefully acknowledged.
We especially thank M. N. Viswanatha, Geological Survey of India, for his cooperation during the field work. 相似文献
19.
Dr. Pavel Röhlich 《International Journal of Earth Sciences》1978,67(2):401-412
The northern Cyrenaic headland situated north of 32 degrees latitude between Benghází and Tubruq was subject of a geological mapping. This paper draws attention to the results of this geological survey concerning Upper Cretaceous and Tertiary facies development, paleogeography, tectonic and geomorphologic evolution.The essential part of the investigated area corresponds to Jabal al Akhdar (Green Mountains), a gently uparched plateau built of Upper Cretaceous and Tertiary sediments (mostly limestones, subordinate dolomites and marls). These sediments were deposited at the southern margin of the Tethys sea and were moderately folded, mainly during the intra-Senonian (pre-Campanian) and early Ypresian intervals.From Middle Eocene till Middle Miocene, the area was subject to a slight warping followed by oscillating transgressions of a shallow sea.The youngest tectonic movements resulted in a gentle doming of the area associated with downfaulting of certain zones. Some prominent faults revealed rejuvenated activity, partly with movement inversion. Deep faulting probably controlled the paleogeographic and tectonic development of certain zones.The present gross geomorphology of Jabal al Akhdar roughly corresponds to its final uparching dated after the Middle Miocene. Topographic evolution of the northern slope of the mountains has been importantly influenced by marine erosion. Two broad littoral terraces bordered by cliffs were formed successively.
Zusammenfassung Die nördliche Cyrenaica nördlich des 32. Breitengrades, zwischen Benghazi und Tobruk, wurde geologisch kartiert. Ergebnisse dieser Aufnahmen sind unten wiedergegeben und umfassen die fazielle Entwicklung der Oberkreide und des Tertiär sowie die paläogeographische, tektonische und geomorphologische Entwicklung.Der wesentliche Teil des untersuchten Gebietes liegt im Djebel el Akhdar. Er repräsentiert ein herausgehobenes Plateau, das sich aus Oberkreide und Tertiärsedimenten (meistens Kalke, untergeordnet Dolomite und Mergel) zusammensetzt. Diese Sedimente wurden am Südrand der Tethys abgelagert und sind vorwiegend während des Senon (Prä-Campan) und frühen Ypresien schwach verfaltet worden.Vom mittleren Eozän bis ins mittlere Miozän wurde das Gebiet teilweise gehoben und von oszillierenden Transgressionen einer Flachsee erfaßt.Die jüngsten tektonischen Bewegungen führten zu einer domartigen Aufwölbung und zu Bruchtektonik entlang bestimmter Zonen. Dabei wurden markante Störungen mehrfach regeneriert, wobei auch inverse Bewegungen nachgewiesen werden konnten. Tiefgreifende Lineamente kontrollierten wahrscheinlich die paläogeographische Situation wie auch die tektonische Entwicklung entlang bestimmter Zonen.Die augenblickliche geomorphologische Ausgestaltung des Djebel el Akhdar korrespondiert mit der zuletzt stattgefundenen Aufwölbung nach dem mittleren Miozän. Die topographische Entwicklung seines nördlichen Randes ist weitgehend beeinflußt durch marine Erosionen. Zwei breite Küstenterrassen — durch Steilküsten begrenzt — haben sich dabei sukzessive herausgebildet.
Résumé La Cyrénaique septentrionale au Nord du 32ème parallèle, entre Benghazi et Tobrouk, a été l'objet d'un lever géologique. Les résultats donnés ici concernent le développement des facies au Crétacé supérieur et au Tertiaire, ainsi que l'évolution paléogéographique, tectonique et géomorphologique.La plus grande partie du territoire se trouve dans le Djebel el Akhdar, plateau soulevé composé de sédiments du Crétacé supérieur et du Tertiaire (la plupart des calcaires, plus rarement des dolomites et des marnes). Ces sédiments se sont déposés dans la bordure meridionale de la Téthys et furent faiblement plissés principalement au cours du Sénonien (Précampanien) et au début de l'Yprésien.De l'Eocène moyen au Miocène moyen, cette région fut en partie soulevée et soumise à des transgressions oscillatives de mer peu profonde.Les mouvements tectoniques les plus récents ont eu pour conséquence un faible bombement de la région accompagné d'affaissements de certaines zones le long de failles. Certaines failles importantes ont rejoué plusieurs fois, partiellement avec inversion de mouvement. Des failles profondes ont influencé l'évolution paléogéographique et tectonique de certaines zones.La géomorphologie générale actuelle du Djebel el Akhdar correspond grosso-modo a son bombement final d'après le Miocène moyen. L'évolution topographique du versant septentrional de la chaîne a été influencée d'une façon importante par des érosions marines. Il s'est formé successivement deux terraces littorales bordées de falaises.
32° . , . Djebel el Akhdar. , — ; . . . . , , , . . , . , .相似文献
20.
The Palaeozoic rocks of the Veleta nappe (Nevado-Filábride complex, Betic Cordilleras, Southern Spain) consist of graphite-mica schists with oxychlorite — chloritoid — albite — garnet porphyroblasts. Crystal chemistry of the minerals, their phase relations and microfabrics are consistent with a normal prograde metamorphic evolution and a slight retrograde overprint. The basis of the overlying Mulhacén nappe consists also of Palaeozoic graphite-mica schists, but with clear signs of polymetamorphic development. An early low-pressure metamorphism with andalusite and chloritoid is overprinted by high-pressure metamorphism with kyanite and Mg-rich chloritoid. This later development is of Alpine age, which is demonstrated by the metamorphic conditions of Permo-Triassic rocks in the upper part of the Mulhacén nappe, included formation of eclogites, followed by an amphibolite facies overprint. The metamorphism of the Veleta nappe is regarded as pre-Alpine: a possible Alpine overprint did not cause an increase in temperatures. No inverse metamorphic gradient exists between Veleta and Mulhacén nappes, because of the different ages of metamorphism.
Zusammenfassung Die paläozoischen Gesteinsserien der Veletadecke im Nevado-Filábride Komplex (Betische Kordillere, Südspanien) bestehen aus Graphitglimmerschiefern mit Oxichlorit — Chloritoid — Albit — Granat — Porphyroblasten. Die Kristallchemie der Minerale, ihre Phasenbeziehungen und Mikrogefüge sind konsistent mit einer normalen prograden Metamorphoseentwicklung und leichter retrograder Überprägung. Die Basis der darüberliegenden Mulhacendecke besteht ebenfalls aus paläozoischen Graphitglimmerschiefern, die jedoch deutliche Anzeichen für polymetamorphe Entwicklung zeigen: Eine frühe Niedrigdruckmetamorphose mit Andalusit und Chloritoid wird überprägt von einer Hochdruckmetamorphose mit Disthen und Mg-reichem Chloritoid. Diese spätere Entwicklung ist, wie die Metamorphosebedingungen der im Hangenden folgenden permotriadischen Gesteine der Mulhacendecke zeigen, frühalpin und schließt Eklogitbildung mit ein, gefolgt von einer amphibolitfaziellen Überprägung. Die Metamorphose der Veletadecke wird als präalpine Metamorphose angesehen: Eine mögliche alpine Überprägung hat keinen Temperaturanstieg verursacht. Zwischen Mulhacendecke und Veletadecke besteht kein inverser Metamorphosegradient, sondern ein Sprung in den Metamorphosealtern.
Résumén El Paleozoico del Manto del Veleta (complejo Nevado-Filábride, Cordilleras Béticas, suroeste de España) está formado por micasquistos grafitosos con porfiroblastos de oxicloritas — chloritoide — albita — granate. La cristalquímica de los minerales, sus relaciones de fase y microfábrica son coherentes con una evolución metamórfica progresiva normal y con un ligero retrometamorfismo. La base del suprayacente Manto del Mulhacén está también formado por micasquistos grafitosos paleozoicos, pero muestran signos evidentes de un desarrollo polimetamórfico. El metamorfismo más antiguo tiene unas caracteristicas de baja presión con la formación de andalucita y cloritoide. Estas rocas sufren los efectos de un nuevo proceso metamorfico de edad alpina, lo que puede ser demostrado por comparación con las rocas Permo-Triásicas de la parte superior del Manto del Mulhacén, en las cuales las eclogitas formadas en la primera fase son afectadas por otra en la facies de las anfibolitas. El metamorfismo del Manto del Veleta puede ser probablemente considerado como pre-Alpino: si está afectado por el metamorfismo alpino, éste no ha causado un incremento de temperatura. No existe, por tanto, inversión del gradiente metamórfico entre los Mantos del Veleta y del Mulhacén puesto que la edad del metamorfismo en ambos es diferente.
-/ , / . . , , , . , . Mulhacen - , : , , , . , - Mulhacen, , . , - : . , Mulhacen Veleta ; .相似文献