共查询到20条相似文献，搜索用时 75 毫秒
1.
Read (1934b) described the mineralogy and regional setting of spectacularly zoned ultrabasic bodies occurring in Unst, Shetland. Chemical and phase compositional data are presented here for a selection of samples taken from each of the several monomineralic zones.The phase sequence and elemental distribution are discussed in some detail since both are complicated. It is shown that virtually all distributional features may be explained on the basis of a diffusion model: transport most probably having occurred via aqueous solutions in pore space.The present configurations represent frozen reaction intermediates. Controls upon the nature and extent of reaction are analysed. Certain features may be explained on the basis of local equilibrium thermodynamics. These arguments, however, are inadequate. Fairly simple kinetic considerations lead to a much more satisfactory analysis.Some of the problems associated with concepts of element mobility are discussed briefly. 相似文献
2.
An objective replacement method for censored geochemical data 总被引：1，自引：0，他引：1
Geochemical data are commonly censored, that is, concentrations for some samples are reported as less than or greater than some value. Censored data hampers statistical analysis because certain computational techniques used in statistical analysis require a complete set of uncensored data. We show that the simple substitution method for creating an uncensored dataset, e.g., replacement by3/4 times the detection limit, has serious flaws, and we present an objective method to determine the replacement value. Our basic premise is that the replacement value should equal the mean of the actual values represented by the qualified data. We adapt the maximum likelihood approach (Cohen, 1961) to estimate this mean. This method reproduces the mean and skewness as well or better than a simple substitution method using3/4 of the lower detection limit or3/4 of the upper detection limit. For a small proportion of less than substitutions, a simple-substitution replacement factor of 0.55 is preferable to3/4; for a small proportion of greater than substitutions, a simple-substitution replacement factor of 1.7 is preferable to4/3, provided the resulting replacement value does not exceed 100%. For more than 10% replacement, a mean empirical factor may be used. However, empirically determined simple-substitution replacement factors usually vary among different data sets and are less reliable with more replacements. Therefore, a maximum likelihood method is superior in general. Theoretical and empirical analyses show that true replacement factors for less thans decrease in magnitude with more replacements and larger standard deviation; those for greater thans increase in magnitude with more replacements and larger standard deviation. In contrast to any simple substitution method, the maximum likelihood method reproduces these variations. Using the maximum likelihood method for replacing less thans in our sample data set, correlation coefficients were reasonably accurately estimated in 90% of the cases for as much as 40% replacement and in 60% of the cases for 80% replacement. These results suggest that censored data can be utilized more than is commonly realized. 相似文献
3.
Richard M. Forester 《Mathematical Geology》1977,9(6):619-633
A new method of measuring the relative abundance of microorganisms by using a set of interrelated coefficients, termed abundance coefficients or AC, is proposed. These coefficients provide a means of recording abundance for geometric density categories, and each density measurement represents an approximation of the Poisson parametert. The AC is the natural logarithm of a characteristic value, which is a particular number for each geometric density category. The characteristic values are based upon a probabilistic error statement derived from the Poisson formula, and they present evidence for separation of the geometric category boundaries bye = 2.71828. The proposed AC provide a means for recording species abundance in a manner suitable for arithmetic manipulation, for population structure studies, and for the determination of practical limits for defining the presence or absence of a species. Further, these coefficients provide for both intrasample and intersample abundance comparisons. 相似文献
4.
P. Weichhart Dr. 《GeoJournal》1979,3(6):523-531
The term environment has been used in various and inconsistent ways by scientists from many disciplines and can frequently be regarded as an empty formula. The author argues that this term has an ascertained meaning only within the concept of ecology. Therefore, any attempt to use the relative term environment in an absolute way and apart from this context must necessarily lead to its hypostatization, giving it the character of an entity of its own. The different aspects of the ecology concept — here called dimensions — should rather be defined according to the specific approaches of particular empirical studies. The paper briefly discusses the meaning of those dimensions which are interrelated and form a multidimensional space. Depending on the position of a particular approach within this multidimensional concept, a specific, ontologically neutral definition of environment may be developed, whose meaning (in accordance with the scale of reflections) can now be specified.This text is the enlarged and altered version of a lecture given on 1979-08-27 at the Third Vienna International Meeting on Human Ecology (Vienna, 1979-08-27–1979-08-31). 相似文献
5.
W. Manshard Prof. Dr. 《GeoJournal》1990,20(2):151-156
After an outline of some developments leading to the present wave of globality, the two new programmes: IGBP (International Geosphere-Programme) and HDGC (Human Dimension of Global Change-Programme) are briefly introduced.The significance of both approaches to geographical science is commented upon, Special reference is made to the important concept of sustainable development.Paper presented to the IGU-Commission: History of Geographical Thought, Hamburg, August 1990. 相似文献
6.
Cecilie Bjørlykke 《GeoJournal》1996,39(2):221-227
This paper analyses the meeting between the international petroleum industry and two local communities. The building of an oil terminal in a local community is both a major event, and a generator of processes on the local level. Three different angles is used to enlighten these processes; categorised as as place, people and mind. The place analysis consentrates on the effects on population and workforce development, the people analysis look at the institutional and planning processes, and the mind analysis the effects on the feeling of local identification. The paper demonstrates that local factors are of crucial importance even for the international petroleum industry. 相似文献
7.
The Kolan geothermal field is located 24 km northwest of the Karakoçan area of Elaz city in southeastern Turkey. The Keban crystallized limestone of Permo-Carboniferous age is the oldest unit in the area. This unit is overlain by the middle-upper Eocene Krkgeçit formation consisting of conglomerate, sandstone, limestone and marl alternations. The youngest unit in the area is the Upper Miocene-Lower Pliocene Karabakr formation consisting of basalt, andesite and tuffs. Thermal Springs in the Kolan field issue along two major fault zones. The temperature of the hot springs is between 38°C and 45°C. Thermal waters in the area are heated by the geothermal gradient. The waters are classified as hot or very hot and as brackish waters. On the basis of International Association of Hydrogeologists Classification (IAH), waters are grouped as Ca–Na-HCO3–CO2-bearing thermal and mineral waters. Chemical analyses indicate a chemical composition of Ca>(Na+K)>Mg - HCO3>SO4>Cl. Saturation calculations reveal that the waters are oversaturated with respect to calcite, dolomite and aragonite while undersaturated with respect to gypsum, anhydrite and halite minerals. On the basis of 18O, 2H and 3H isotope data, Kolan waters are of meteoric origin, recharged from high elevations and then circulated deeply. 相似文献
8.
Summary Anhydrous partial melting experiments on four peridotite compositions have been conducted at 10 kbar providing a relatively internally consistent set of data on the character of primary melts expected from the oceanic upper mantle in the mid-ocean ridge setting. The four peridotite compositions are: MORB pyrolite (considered to be suitable for the production of primitive (Mg#0.68) MORB glasses at 10 kbar), Hawaiian pyrolite (representative of enriched upper mantle), Tinaquillo lherzolite (representative of more depleted upper mantle), and the spinel lherzolite KLB-1 which is a suitable composition for the production of primitive MORB glasses. The equilibrium liquids were determined by sandwich experiments. The primitive MORB glass DSDP 3-18-7-1 was used in experiments using MORB pyrolite and KLB-1, while a calculated 10 kbar liquid composition fromJaques andGreen (1980) was used in experiments with Hawaiian pyrolite and Tinaquillo lherzolite. The results of the experiments are used to test a 10 kbar melt model for the generation of primitive MORB glasses, which are parental magmas to typical MORB compositions. The melt compositions from the four peridotites studied are significantly different from primitive MORB glasses in major element chemistry and plot away from the field of primitive MORB glasses in the CIPW molecular normative Basalt tetrahedron. The results indicate that primitive MORB glasses are derivative compositions lying on olivine fractionation lines from picritic parents, which themselves are primary magmas at pressures greater than 10 kbar. The results of this study are integrated with previous 10 kbar experimental studies.
With 10 Figures 相似文献
Wasserfreie partielle aufschmelzung von MORB pyrolit und andere peridotit-zusammensetzungen bei 10 kbar: bedeutung für die entstehung primitiver MORB gläser
Zusammenfassung Vier Peridotit-Zusammensetzungen wurden bei 10 kbar unter wasserfreien Bedingungen partiell aufgeschmolzen, und die Ergebnisse mit möglichen primitiven Schmelzen Mittel-Ozeanischer Rücken verglichen.Die folgenden perioditischen Zusammensetzungen wurden untersucht: MORB pyrolite [mögliche Ausgangszusammensetzung für primitive (Mg# > 0.68) MORB-Glaszusammensetzungen bei 10 kbar], Hawaiian pyrolite (representativ für angereicherten Oberen Mantel); Tinaquillo lherzolite (representativ für verarmten' Oberen Mantel) und spinel lherzolite, KLB-1 (im Gleichgewicht mit primitiver MORB-Glaszusammensetzung). Die Schmelzen im Gleichgewicht mit diesen Ausgangszusammensetzungen wurden mittels Sandwich-Experimenten ermittelt.Die primitive MORB-Glaszusammensetzung DSDP 3-18-7-1 wurde mit MORB pyrolite und KLB-1 equilibriert, während eine Modell-Zusammensetzung vonJaques and Green (1980) in Verbindung mit Hawaiian pyrolite und Tinaquillo lherzolite vermischt wurde. Die Resultate der Experimente werden mit einem 10 kbar Aufschmelzungsmodell zur Entstehung primitiver MORB-Gläser verglichen. Die Schmelzen im Gleichgewicht mit den vier Peridotit-Ausgangszusammensetzungen unterscheiden sich wesentlich von primitiven MORB-Gläsern, sowohl hinsichtlich ihrer Hauptelemente als auch ihrer Plot-Parameter im Basalttetraeder. Primitive MORB-Glaszusammensetzungen stellen keine primären Schmelzen dar, sondern sind durch Olivinfraktionierung von primitiven Magmen abzuleiten. Die Resultate dieser Untersuchungen werden mit früheren 10 kbar Experimenten verglichen.
With 10 Figures 相似文献
9.
I. Gams 《Environmental Geology》1993,21(3):110-114
The limestone region northeast of Trieste Bay is named kras in Slovenian, karst in German, and carso in Italian, from a pre-Indo-European word karra meaning stony. The natural vegetation was deciduous forest. Clearance and burning to create pasture for sheep began in the first millenium BC and resulted in considerable losses of soil into underground karstic channels. By the Middle Ages, the region was known as a rocky, treeless land; the first legislation to conserve or re-establish forests was passed but it did not succeed. In the 19th century the regional name came to be adopted as the generic name for all dissolutional landscapes and hydrogeological systems, whether natural or modified. During this period a change from sheep rearing to dairying with cattle, plus new legislation and experimental plantings with black pine (Pinus nigra), began the restoration of the forests in the Karst itself. Since 1945 their extent has more than doubled again, partly as consequences of rural depopulation and the banning of goats; approximately 50 percent of the region is now covered by woodlands. Soil erosion is much reduced, but evapotranspiration losses have probably increased. It is hypothesized that there will be effects of restoration upon such karstic parameters as the discharge of springs or rates of travertine deposition in the caves. 相似文献
10.
Dr. E. Piso 《Mineralogy and Petrology》1970,14(2):103-139
Zusammenfassung Die Basalte des Pauliberges und von Stoob-Oberpullendorf im nördlichen Burgenland sind dem Finalvulkanismus der alpinen Orogenese zuzuordnen. Es handelt sich hierbei um Alkaliolivinbasalte.Die Basalte des Pauliberges sind an einer NW—SE verlaufenden Spalte aufgedrungen und lagern dem Kristallin direkt auf, die von Stoob-Oberpullendorf liegen auf Sanden und Tegeln und werden zum Unterschied von den Pauliberger Basalten wieder mit tertiären und quartären Sedimenten bedeckt. Den Pauliberger Basalten wird ein dazisch-levantines Alter zugeschrieben, die Stoob-Oberpullendorfer Basalte dürften schon etwas früher an der Grenze Sarmat-Pannon entstanden sein.Innerhalb der Basalte des Pauliberges sind vier verschiedene Basalttypen festzustellen: ein dunkler und heller Alkaliolivinbasalt, ein Sonnenbrenner und ein doleritischer Trachybasalt, die drei aufeinanderfolgenden Eruptionsphasen, ausgehend vom dunklen Alkaliolivinbasalt über hellen Alkaliolivinbasalt und Sonnenbrenner zum doleritischen Trachybasalt, zuzuschreiben sind. Die Entstehung dieser einzelnen Basalttypen, die in einer Differentiationsreihe vom Alkaliolivinbasalt über Trachybasalt zum Trachyt hin liegen, kann durch fraktionierte Kristallisationsdifferentiation erklärt werden.Der doleritische Trachybasalt als letztes Eruptionsprodukt ist in bereits abgekühlte Basaltmassen eingedrungen und hat die Oberfläche nicht mehr ganz erreicht, wobei er hypabyssisch erstarrt ist. Der Sonnenbrenner weist einen beträchtlichen Gehalt an Analzim, der primär aus der Restschmelze gebildet wurde, auf; der fleckenhaften Verteilung dieses Minerals hat dieses Gestein seine Sonnenbrennerstruktur zu verdanken.An den Basalten von Stoob-Oberpullendorf sind keine Differentiationserscheinungen festzustellen gewesen, wenn auch übereinanderlagernde Basaltdecken auf mehrere Eruptionen hinweisen.
Mit 10 Abbildungen 相似文献
Composition and genesis of the basalts from the Pauliberg and from Stoob-Oberpullendorf (Burgenland, Austria)
Summary The basalts comprising the Pauliberg and from the Stoob-Oberpullendorf region in nothern Burgenland are a part of the final vulcanic activity of the Alpine orogenesis. They consist chiefly of alkaline olivine basalts.The Pauliberg basalts were extruded along a fracture trending NW—SE and overlie the cristalline basement while those from Stoob-Oberpullendorf flowed onto sands and green marls and were, in contrast to the Pauliberg basalts, subsequently covered with Tertiary and Quartary sediments. The Pauliberg basalts are Dazic-Levantinic in age whereas those of Stoob-Oberpullendorf were probably extruded somewhat earlier: possibly near the Pannon boundary.The Pauliberg basalts are divided into four different types: dark alkaline olivine basalt, light alkaline olivine basalt, bunch light basalt, and doleritic trachybasalt. These four types crystallized in three successive erruptive phases. In the first phase the dark alkaline olivine basalt was extruded. The light alkaline olivine basalt comprises the second phase along with the bunch light basalt. During the third phase the doleritic trachybasalt crystallized. The origin of these individual flows, whose compositions lie along the differentiation line from alkaline olivine basalt through trachybasalt to trachyte, can best be explained by differentiation through fractional crystallization. The last phase, the doleritic trachybasalt, intruded the earlier cooled basaltic rocks, and is only found as hypabyssal bodies. The bunch light basalt contains considerable analcime, formed primarily from the residual melt, and gives rise to the bunch light structure due to the spotty distribution of the analcime.Features of differentiation are not found in the Stoob-Oberpullendorf basalts, although superposed basalt flows indicate several periods of eruption.
Mit 10 Abbildungen 相似文献
11.
Dr. Wolfram Keidel 《Contributions to Mineralogy and Petrology》1965,11(5):487-506
Zusammenfassung Durch Ausmessung der Chondrenquerschnitte an Anschliffen van sechs Chondriten und Messungen an isolierten Chondren von Borkut ergab sich:Die Häufigkeitsverteilung der Chondren ist symmetrisch, das Maximum liegt bei einem Durchmesser von 0,6–0,8 mm. Chondren Bind Rotationsellipsoide oder allgemeine Ellipsoids und zum geringen Teil Kugeln (etwa 12%). Kleinere Chondren sind kugelähnlicher als große. Die ellipsoidischen Chondren zeigen bei Borkut and Bluff sine deutliche Einregelung.Der Chondrit Borkut besteht aus Bronzit, Olivin, Nickeleisen, Troilit, Chromic und Glas mit Feldspatmikrolithen. Er enthält Pyroxen-, PyroxenOlivin-und Olivinchondren. Des Orthopyroxen ist ein Bronzit mit 24,5 Mol.-% FeSiO3, der Olivin enthält 31 Mol.-% Fe2S04.Das spezifische Gewicht ist 3,609 g/cm3, das Porenvolumen beträgt 19,06%.Der Gesamtmeteorit und die Chondren wurden getrennt chemisch analysiert. Nach Chernismus und Mineralbestand gehört Borkut dem L-Typ der Chondrite an.Die Pyroxenchondren von l3orkut bestehen aus Lamellensystemen nach (100) oder (101) and einem Feldspatglas mit Mikrolithen. Sie haben sich ebenso wie gemischte and Olivinchondren als Tröpfchen aus einer Schmelze gebildet, die schnell abgekühlt wurden. Die verschiedenen Chondrentypen können dadurch entstehen, daß ein Magma mit bereits ausgeschiedenen Olivinkristallen zu kleinen Tröpfchen zerrissen wurde, wobei Tröpfchen mit Olivinkristallen (gemischte Chondren) und solche ohne Olivin (Pyroxenchondren) entstanden.
Measurements of cross-sections of chondrules in. sections of 6 chondrites and measurements of isolated chondrules from Borkut yielded te following results:The grain size distribution of chondrules is symmetrical, its maximum being at a diameter of 0.6 to 0.8 mm. Chondrules are rotation ellipsoids or ordinary ellipsoids, a minor part are spherules (some 12%). Smaller chondrules form more perfect spherules than bigger ones. Elliptical chondrules in Borkut and Bluff show an evident orientation.The chondrite Borkut consists of bronzite, olivine, nickeliron, troilite, chromite, and glass with microlithic felspar. It contains pyroxene chondrules, pyroxene olivine chondrules, and olivine chondrules. The orthopyroxene is a bronzite containing 24.5 mol.-% FeSiO3, the olivine contains 31 mol.-% Fe2SiO4,Its specific gravity is 3.609 g/cm3, its porosity amounts to .19.06%.The whole meteorite and the chondrules had been chemically analyzed separately. According to its chemical composition and mineral content, Borkut has to be classified under type L of chondrites. The pyroxene chondrules of Borkut consist of systems of lamellae parallel (100) or (101) and of felspar glass with microlithic crystals. They, as well as mixed chondrules and olivine chondrules, originated from a melt as droplets, which cooled down rapidly. The different types of chondrules may originate, when magma containing already crystallized olivine is disrupted to droplets; the result is then either droplets containing olivine crystals (mixed chondrules) or droplets without olivine (pyroxene chondrules).相似文献
12.
Barbara J. Cummings 《GeoJournal》1995,35(2):151-160
This paper analyzes the history and consequences of two large scale hydroelectric projects in Amazonian Brazil. The argument makes three points. First, environmental impacts of such projects are inseparable from issues of human rights, regional economic development, and social justice. The implication of this view is that another development, something quite different from the industrial ideal of modernization, is necessary in Amazonia and elsewere.Second, analytical fragmentation of problems into specialist concerns with such topics as ecology (often only meaning wildlife), environment (often concerned only with soil erosion and regional climate), and human rights (sometimes only focusing on the rights of indigenous people, not small farmer migrants tempted to settle in such areas) is mirrored by a fragmented, and therefore weak, resistance to hydroelectric development. The paper traces the early signs of a more unified resistance movement capable of overcoming these special interests and fragmentation.Third, the paper provides data on an economic monstrosity. The Balbina dam was begun in 1981, had cost $ 700 million by 1988, will not be viable withoutanother $ 700 million of design correction, andeven then will not provide enough electricity for Manaus city: this is a monument to an apparent inability to learn from history.Funding provided by the Luce Program in Food, Resources, and International Policy of Hampshire College; The Peggy Howard Fund; Public Service/Social Change Program of Hampshire College; The Explorer's Club; Patrick T. Knight. Special Thanks to Dorothy and Egydio Schwade, Paulinho Paiakan Kaiapo. In Memory of Chico Mendes. 相似文献
13.
New Sm–Nd isotopic data for eight samples of basalt and komatiite from the Tjakastad Subgroup (lower Onverwacht Group) of the Barberton Greenstone Belt (BGB) of the Kaapvaal craton in southern Africa are reported. They give new constraints on the interpretation of Sm–Nd ages for the Subgroup and highlight the petrogenesis of Tjakastad volcanics. Although Sm–Nd isotopic data earlier reported for volcanic rocks from the Tjakastad Subgroup yielded an isochron age of 3526±48 Ma, the new results give a much younger isochron date of 3269±84 Ma. The 3526±48 Ma isochron age has been obtained in combining samples ranging in composition from felsic volcanics to ultrabasic komatiites and is thus considered suspect with regard to the pre-requisite of geochronology that all the studied rocks must have had identical initial isotopic compositions. The new isochron date of 3269±84 Ma has been obtained in combining samples solely of basic/ultrabasic composition. It might thus represent a more correct age for the eruption of the Tjakastad Subgroup volcanism. In fact, owing to the potential problem of source heterogeneity and also in the light of geochronological and geochemical arguments we show that this date also has little chance to have any strict chronological meaning. Most likely, the Tjakastad volcanics were formed 3450 Ma ago. Also most likely, their source rocks were isotopically heterogeneous and the 3530 Ma and 3270 Ma linear arrays are not true but apparent isochrons. Based on the calculated Nd (3450) values and other geochemical arguments, we show that three possible sources might have been involved: depleted mantle, primitive mantle and older continental crust. 相似文献
14.
Poul E. Holm 《Contributions to Mineralogy and Petrology》1982,79(3):308-310
Continental tholeiites cannot be identified using the Ti-Y-Zr diagram. Two-hundred and thirteen analyses from 16 localities representing 7 continental tholeiitic provinces all plot outside the within-plate basalt field of this diagram.Analyses representing about 50% of the population plot in the ocean-floor basalt field, the rest plots in the calc-alkali basalt field. Therefore problems might arise when attempts are made to classify ancient tectonomagmatic environments using the Ti-Y-Zr diagram. 相似文献
15.
Glenn B. Stracher 《Mathematical Geology》1995,27(4):499-511
Coal seams and culm banks associated with mine fires in the anthracite region of eastern Pennsylvania have been burning for decades. Many of the fires may have ignited by spontaneous combustion or by the burning of trash. Minerals associated with the combustion of anthracite form by the condensation of gas exhaled through surficial gas vents or anthracite smokers. A Pressure-Temperature (P-T) stability diagram is constructed for the condensation of orthorhombic sulfur from anthracite gas using Thermodynamic Loop Analysis (TL analysis). This method of analyzing chemical systems incorporates Kirchhoff's Law into a four step procedure structured around a closed thermodynamic cycle or thermodynamic loop. The four steps, referred to us The Four S S of Thermodynamic Loop Analysis, include: (1) Set Up—graphical characterization of the problem. (2) Sum—the application of thermodynamic principles. (3) Substitute—the use of materials data available from the literature, and (4) Solve—computation of one or more variables. The example presented demonstrates that thermodynamic loops can incorporate any number of polymorphic phase transformations. In addition, thermodynamic loop analysis is applicable to any geologic process involving the condensation of minerals from a gas. The stability diagram derived by TL analysis may have applicability in monitoring the release of sulfur gas into the atmosphere. 相似文献
16.
Dr. A. Rice 《Mineralogy and Petrology》1995,54(1-2):137-147
Summary Fine-scale igneous layering consisting of alternating bands of chromitite and plagioclase often occurs in the Bushveld Complex where it is commonly known as stringers. The origin of these features has been unclear but they do have both quantitative and qualitative characteristics of a type of microsegregation (compositional nonhomogeneity) known as solute banding which frequently occurs in solidifying industrial melts. The cause of solute banding is due to temperature fluctuations arising from unsteady convection in the melt which generates cotectic shifting at the solidification front, leading to alternating deposition of one phase, then another.
With 3 Figures 相似文献
Zusammenfassung Feiner magmatischer Lagenbau, der aus alternierenden Lagen von Chromitit und Plagioklas besteht, ist häufig im Bushveld zu beobachten und wird weithin als Stringers bezeichnet. Die Entstehung dieser Erscheinung war bisher nicht geklärt, aber sie zeigt sowohl quantitative wie qualitative Aspekte einer Art von Mikrosegregation (Inhomogenität der Zusammensetzung), die als Solute Banding bekannt ist und häufig in erstarrenden industriellen Schmelzen zu beobachten ist. Der Grund für Solute Banding liegt in Temperaturschwankungen, die auf ungleichmäßige Konvektion in der Schmelze zurückgeht. Letztere führt zu Verschiebung der kotektischen Positionen an der Verfestigungsfront, die schliesslich in alternierender Ablagerung der beiden Phasen resultiert.
With 3 Figures 相似文献
17.
Evaluation of biotite-garnet geothermometers: application to the English River subprovince,Ontario 总被引：1，自引：0，他引：1
In recent years, there have been numerous calibrations of the biotite-garnet Fe-Mg exchange geothermometer. The Eastern Lac Seul region of the English River subprovince, Ontario, provides an excellent field area in which to compare these calibrations.Trend surface analysis using the temperatures obtained from garnet cores and matrix biotites-showed almost identical trends in the eastern Lac Seul region regardless of the calibration used. The absolute temperatures and the precision of each calibration do, however, show large variation. Geothermometers based solely on lnKD were found to give more precise results than the calibrations that attempt to incorporate non-Fe-Mg components. The Perchuk and Lavrent'eva (1983) thermometer yields the most precise and accurate results. If a sufficient number of samples are collected over a region, it can be used to estimate metamorphic temperature trends to ±30° C. Metamorphism and migmatization of the English River subprovince occurred during the Kenoran orogeny, 2.68 b.y. ago. Our results show that a thermal anticline has been preserved, with temperatures of 600° C at the north and south contacts with Uchi and Wabigoon Greenstone belts, increasing to 725 °C at the center of the subprovince. A garnet-cordierite in isograd occurs at 650° C and an orthopyroxene in isogradat 700° C. 相似文献
18.
R. M. Spang 《Rock Mechanics and Rock Engineering》1976,8(3):185-198
ZusammenfassungMöglichkeiten und Grenzen des Base Friction Konzepts Der vorliegende Beitrag befaßt sich mit einer von Goodman eingeführten neuen Technologie für zweidimensionale Modellversuche in der Felsmechanik. Bei diesen Modellen sollen die im Prototyp durch die Gravitation erzeugten Körperkräfte durch Reibungskräfte simuliert werden, die dieselbe Richtung wie die Erdbeschleunigung besitzen müssen und die entstehen, wenn das zweidimensionale Modell in einer horizontalen Ebene aufgebaut und zwischen dem Modell und der horizontalen Basis eine entsprechende Relativbewegung erzwungen wird.Nach einem kurzen Überblick über die einschlägige Literatur wird anhand eines Stabilitätsdiagramms für einen Einzelkörper an der Schiefen Ebene untersucht, ob die im geklüfteten Fels auftretenden Bruchmechanismen Gleiten, Kippen und Kippen bei gleichzeitigem Gleiten im Base Friction Modell exakt modellierbar sind.Aus dieser Untersuchung ergibt sich, daß in den Bereichen Kippen und Gleiten bezüglich der Kinetik mit Schwerkraftmodellen übereinstimmende Ergebnisse zu erzielen sind. Im Bereich Kippen bei gleichzeitigem Gleiten treten dagegen wesentliche Abweichungen auf, weil die Simulation der Schwerkraft durch Reibungskräfte nicht vollständig gelingt. Fälle, bei denen Aussagen über Geschwindigkeits-und Beschleunigungsverhältnisse im Prototyp gemacht werden sollen, können aus demselben Grund mit einem Base Friction Modell nicht untersucht werden.Nach einer ausführlichen Kritik wird dann der Schluß gezogen, daß das Base Friction Modell zwar als Entwurfshilfsmittel ungeeignet ist, daß es aber als Methode für die Grundlagenforschung in der Felsmechanik mit Aussicht auf Erfolg eingesetzt werden kann.
Mit 9 Abbildungen 相似文献
SummaryPossibilities and Limitations of the Base Friction Model The paper deals with a new technology for two-dimensional model tests in rock mechanics introduced by Goodman. In this model gravity is simulated by base friction forces. Their direction is to be that of gravity. The two-dimensional model is placed on a horizontal base. A movement of this base relative to the model produce frictional forces which model gravity.First a single model element placed on an inclined plane is analysed resulting in a stability diagram. The purpose of the subsequent analysis is to assess whether the mechanisms of failure being investigated, i. e. sliding, toppling, and toppling combined with sliding, are adequately reproduced by the base friction model.The specific mechanisms toppling and sliding produce kineticly valid results. Considerable errors are to be expected for toppling combined with sliding, because of the specific base friction feature. Mechanisms including velocity and acceleration cannot be modeled by base friction.Finally the limitations of the base friction model as a design tool and instrument for rock mechanics research are discussed.
RésuméPossibilités et limites du base friction model Le présent article traite d'une nouvelle technologie des essais à deux dimensions, introduite par Goodman, sur la mécanique des roches. Par cette technologie les forces en prototype, produites par la gravitation, doivent être remplacées par des forces de frottement. Leur direction doit être la même que celle de la gravitation. Le modèle à deux dimensions est posé sur un plan horizontal. Le mouvement relatif du modèle contre la base horizontale produit des forces de frottement, qui modèlent la gravitation.A l'aide d'un diagramme de stabilité pour un élément isolé sur un plan incliné, on fait des analyses pour savoir si les états de mouvement aparaissant à la rupture de la roche, c'est-à-dire le fait de glisser, basculer, et basculer en même temps que glisser, peuvent être modelés exactement avec le base friction model.Les mécanismes glisser et basculer produisent des résultats qui sont cinétiquement réels. Des fautes remarquables doivent être attendues pour le fait de basculer en même temps que glisser à cause de la mécanique spécifique du modèle. A modeler des vitesses et des accélérations le modèle n'est pas propre.En conclusion on expose une critique détaillée pour savoir jusqu'à quel point cette méthode peut servir comme moyen de dimensionnement dans la pratique et comme instrument pour la recherche en mécanique des roches.
Mit 9 Abbildungen 相似文献
19.
Prof. Dr. Hans Ramberg 《International Journal of Earth Sciences》1962,51(2):405-439
The contact strain which develops in a host rock during compression-folding of a more competent layer is treated mathematically and demonstrated by tests on composite models of rubber sheets and blocks with different rigidities.The contact strain is found to be negligible outside a zone about one initial wavelength wide on either side of the folded sheet. This theoretical conclusion based upon the contact deformation resulting from the initial small-amplitude buckles is also, according to the experimental tests, valid for rather strong buckling.Second-order folding of a thin competent layer laying within the contact zone of a thicker buckled competent layer is demonstrated by experimental tests.Considerations of the stresses connected with the contact strain and the stress distribution in the buckling competent layer itself give a simple expression for the initial stable wavelength which develops in response to compression parallel to the layering.The strain distribution in folded multilayers consisting of a set of thin competent sheets evenly spaced in an uniform less competent body is considered theoretically.In such multilayers the stable initial wavelength as developed during compression will, according to the theory, increase somewhat with decreasing spacing between the competent layers if all other conditions are equal. If the spacing is close enough (the limit depends upon the relative mechanical properties of the two substances) the multilayer will buckle as an unit in the sense that one half-wave covers the whole length of the body. This agrees with compression tests on multilayered rubber blocks.In the last two sections of the paper a theory of viscous buckling of thick layers is developed both for the case of a single layer enclosed in a large uniform body and for the case of a multilayer of alternating competent and incompetent layers. In this theory shear parallel to layering plays an important part. For a single embedded layer the thick-layer model gives a little smaller wavelength/thickness ratio than the simple but less realistic thin-layer model. For multilayers strain parallel to layering becomes very significant, particularly when the spacing between the competent layers is small, and the thick-layer model differs considerably from the simpler thin-layer model.A theory of buckling of a multilayer withn alternating competent-incompetent layers sandwiched between two very thick uniform bodies is also developed. 相似文献
20.
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