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1.
Moderate to strong biaxiality (2V = 10 °–45 °) in experimentally deformed calcite (in single crystals and in marble) is attributed to overlap between one or two thin {01¯12} twin lamellae and the enclosing host. A perfectly centered conoscopic figure (section normal to [0001]) is perceptibly asymmetric about the trace of the optic axial plane. This asymmetry is pronouned in thick sections (> 0.04 mm) and completely distrupts the biaxial configuration of the figure if the overlapping lamella exceeds about 0.0025 mm in thickness. In sections somewhat oblique to [0001] and cut at 20 ° or less to the plane of twinning the conoscopic figure may appear to be perfectly biaxial-expecially in thin sections ( 0.02 mm) enclosing thin ( 0.001 mm) but still visible twins.Similar values of 2V recorded for natural calcite likewise are attributed to twinning on a visible scale.  相似文献   

2.
The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, 18O values of normal metapelites decrease from 14–16 to as low as 9.0, while 18O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (18O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO2 mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in 18O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x109 moles/m2 (105 m3/m2). If fluid flow occurred over 105–106 years, estimated intrinsic permeabilities are 10-20 to 10-16m2. Variations in 18O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO2 values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both 18O and XCO2 values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes  相似文献   

3.
Five specimens deformed at differential stresses between 220 and 980 bar were selected for a transmission electron microscopy study from the suite of Yule Marble specimens of Heard and Raleigh (1972). The electron micrographs show twinning, curved free dislocations, sessile dislocation loops, and small angle boundaries. Both free dislocations and dislocation boundaries contain dislocation reactions which most likely involve the Burgers vectors 1/61¯102 and 1/121¯210 reacting to form 1/1210¯14. The dislocation densities of specimens deformed at the higher stresses were greater than the starting density and fit the relation . However, the dislocation densities of specimens deformed at the lower stresses decreased only partially with respect to the starting density during the deformation experiments and thus are larger than predicted by this relation.  相似文献   

4.
Pyroxenes of pigeonitic and augitic bulk compositions in H3–4 chondritic meteorites commonly exhibit sigmoidal precipitates, rather than the elsewhere common lamellar associations. Most often, submicrometric sigmoids with calcic clinopyroxene composition occur within clinoenstatite; more rarely, clinoenstatite sigmoids occur within calcic clinopyroxene. The sigmoids appear as 001 terminated lamellae, with terminations rotated in opposite directions towards the 100 orientation. Pre-exsolution pigeonite and augite formed at temperatures higher than 980 °C, whereas sigmoidal exsolution occurred between 990 and 830 °C. Local anomalous lattice parameters determined by electron diffraction suggest that lattice parameters are most strained where the exsolution texture is most poorly defined. Shear strain occurs during exsolution due to mismatching lattice parameters and variable angles. In response to shear stress, the lamellae relax and assume sigmoidal strained morphologies. Sigmoidal exsolution is strongly controlled by (100) orthoenstatite stacking faults that possibly trigger exsolution.  相似文献   

5.
Diffusion rates of18O tracer in quartz ( c, 1 Kb H2O) and Amelia albite ( 001, 2 Kb H2O) have been measured, using Secondary Ion Mass Spectrometry (SIMS). A new technique involving hydrothermal deposition of labelled materials has removed the possibility of pressure solution-reprecipitation processes adversely affecting the experiments. Reported diffusion constants are:-quartz ( c), ,Q=98±7 KJ mol–1 (600–825° C, 1 Kb); Amelia albite ( 001), ,Q=85±7 KJ mol–1, (400–600° C, 2 Kb). Measured quartz18O diffusivities decrease discontinuously at the- transition, reflecting strong structural influences. The reported albite data agree with previously recorded studies, but-quartz data indicate significantly lower activation energies. Possible causes of this discrepancy, and some geological consequences, are noted.  相似文献   

6.
The Muratdagi region is rich in antimony deposits having the following common characteristics: post Miocene age, location on the down-thrown blocks next to normal faults, in the vicinity of active or fossil thermal springs, and in contact with carbonate rocks. The isotopic composition of — 7. SMOW of the mineralizing fluid calculated from the measured ° 18O of quartz and the fluid inclusion microthermometry, is indicative of meteoric water origin. The ° 13C of the inclusion CO2 of — 19.1 to — 25.4 PDB is indicative of interaction with organic material-graphite. The ° 34S of stibnite — 3.6 to — 0.7 is, in view of the mineral assemblage, indicative of magmatic origin of the sulphur. A tightly confined set of structural, lithological, hydrological and geochemical features define a sequence of geochemical processes; formation of acid and reducing fluid, leaching and transport of antimony complexes and precipitation of stibnite within defined lithological units. The set of processes seems to have taken place within a space of 5000 m lateral and 1000 m vertical extension.  相似文献   

7.
Summary On Diego de Almagro Island in Chilean Patagonia (51°30S), a convergent strike slip zone, the Seno Arcabuz shear zone, separates the Diego de Almagro Metamorphic Complex from very low grade metagreywackes in the east, which were intruded by Jurassic granitoids. The Diego de Almagro Metamorphic Complex is composed of a metapsammopelitic sequence containing blueschist intercalations in the west and (garnet) amphibolite lenses in the east. Peak metamorphic conditions (stage I) at 9.5–13.5kbar, 380–450°C in the blueschist and at 11.2–13.2, 460–565°C in the amphibolite indicate subduction and accretion at different positions within the deepest part of the accretionary wedge. A K–Ar age of 117±28Ma of amphibole approximately dates the peak of metamorphism in the amphibolite. The early retrograde stage of metamorphism occurred under static conditions and resulted in localized equilibration (stage II) at 6.3–9.6kbar, 320–385°C in the blueschist and 6.1–8.4kbar, 310–504°C in the amphibolite. Both P-T paths converge within a midcrustal level.In contrast, an orthogneiss of trondhjemitic composition occurring within the Seno Arcabuz shear zone is associated with a garnet mica-schist containing a high temperature/intermediate pressure assemblage formed at 4.9–6.5kbar, 580–690°C. A muscovite K–Ar age of 122.2±4.6Ma dates cooling after this event which is related to a concomitant magmatic arc. These rocks were overprinted by a mylonitic deformation, which is caused by convergent strike slip shearing and ends during formation of a retrograde phengite-chlorite-stilpnomelane assemblage at a minimum pressure of approximately 5.7kbar (at 300°C).Zircon fission track ages from rocks of the Seno Arcabuz shear zone are 64.9±2.7 and 64.9±2.7Ma; they record the end of shearing in the Seno Arcabuz shear zone that juxtaposed all rocks in the middle crust. Zircon fission track ages ranging from 78 to 105Ma in the South Patagonian batholith to the east indicate earlier cooling through 280°C. The rocks of the Diego de Almagro Metamorphic Complex were initially slowly exhumed and resided at a midcrustal level before being emplaced via shearing in the Seno Arcabuz shear zone. Apatite fission track ages (54±8Ma) from the Seno Arcabuz shear zone show that exhumation and cooling rates increased after this event. The incorporation of continental crust within the subduction system was a late process, which modified the Cretaceous accretionary wedge, resulting in considerable shortening of the convergent margin.  相似文献   

8.
New sulphur and sulphate-oxygen isotope measurements for the main discordant and stratiform lead-zinc-barite orebodies at Silvermines Co. Tipperary, allow reappraisal of previously offered differing interpretations (Graham, 1970; Greig et al., 1971) of the bearing of sulphur isotopes on the genesis of this important Irish deposit. The following aspects of the data are confirmed: barite 34 S-values range from 17–21, similar to lower Carboniferous seawater sulphate: stratiform sulphide lens pyrites have 34 S-values ranging from –13 to –36; vein sulphide 34 S-values range from –8 to 4; sulphide 34 S-values increase upwards and outwards respectively in the related discordant and stratiform G orebodies; galena-sphalerite isotope palaeotemperatures are not too consistent, ranging from 40 to 430°C (using the calibration of Czamanske and Rye (1974). New facts are as follows: barite 18O-values range from –13 to –17, stratiform barites ranging from 13 to 14.5; sulphides separated from a single stratiform ore lens hand specimen usually have 34 Ssl > 34 Sga > 34 Spy; the outward decrease in 34 S-values in the stratiform G orebody is confined to the first few hundred feet only; pyrite 34 S-values progressively increase downwards through one stratiform sulphide orebody; yet variations of 13 occur within a single colloform pyrite structure from another stratiform orebody. It is concluded that there were at least two sources of sulphur, seawater sulphate and deep-seated sulphur. The former was the dominant source of all sulphate and, via biogenic reduction, of the sulphur in the bulk of the stratiform sulphide. The latter was the source of the sulphur in the vein sulphides. There was minimal isotopic interaction between the cool seawater sulphate and the warm unwelling ore fluid sulphur species, even though the latter precipitated under near isotopic equilibrium conditions when the temperature dropped and/or the pH and Eh increased. The lack of isotopic equilibrium between pyrite and ore sulphides in the stratiform ore lenses may result from the latter having precipitated slightly later than the former because of solubility relationships. Overall the present isotopic evidence supports considerable geological evidence favoring a syngenetic origin for the stratiform Silvermines orebodies.  相似文献   

9.
DC and AC electrical conductivities were measured on samples of two different crystals of the mineral aegirine (NaFeSi2O6) parallel () and perpendicular () to the [001] direction of the clinopyroxene structure between 200 and 600 K. Impedance spectroscopy was applied (20 Hz–1 MHz) and the bulk DC conductivity DC was determined by extrapolating AC data to zero frequency. In both directions, the log DC – 1/T curves bend slightly. In the high- and low-temperature limits, differential activation energies were derived for measurements [001] of EA 0.45 and 0.35 eV, respectively, and the numbers [001] are very similar. The value of DC [001] with DC(300 K) 2.0 × 10–6 –1cm–1 is by a factor of 2–10 above that measured [001], depending on temperature, which means anisotropic charge transport. Below 350 K, the AC conductivity () (/2=frequency) is enhanced relative to DC for both directions with an increasing difference for rising frequencies on lowering the temperature. An approximate power law for () is noted at higher frequencies and low temperatures with () s, which is frequently observed on amorphous and disordered semiconductors. Scaling of () data is possible with reference to DC, which results in a quasi-universal curve for different temperatures. An attempt was made to discuss DC and AC results in the light of theoretical models of hopping charge transport and of a possible Fe2+ Fe3+ electron hopping mechanism. The thermopower (Seebeck effect) in the temperature range 360 K < T <770 K is negative in both directions. There is a linear – 1/T relationship above 400 K with activation energy E 0.030 eV [001] and 0.070 eV [001]. 57Fe Mössbauer spectroscopy was applied to detect Fe2+ in addition to the dominating concentration of Fe3+.  相似文献   

10.
Zusammenfassung Eine geochemische Beprobung des triadischen Nebengesteines der kalkalpinen Blei-Zinklagerstätten ließ Zinkspurenhöfe von mehreren Metern Ausdehnung um die Erzkörper erkennen. Dies führte in der Grube zur Auffindung von Erz. Die regionale Aufnahme im Gelände zeigte die Bindung des Metallgehaltes an Verwerfungen.
The triassic wallrocks of the Pb-Zn-deposits in the Kalkalpen are showing halos of zinc around the deposits. The halos have an extension of several meters and could be used for finding new ore bodies in the Mine of Bleiberg. A geochemical field survey proved the connection of the anomalies with certain faults.
Résumé Les roches triasiques encaissant les gisements de plomb et zinc dans les Kalkalpen sont caractérisées par des auréoles de zinc, de quelques mètres d'épaisseur. Cela a conduit à la découverte du minerai dans les mines de Bleiberg. Le prélèvement géochimique sur le terrain a démontré la relation des anomalies avec certaines failles.
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11.
Morphological and geological investigations along the Western Rift in the Lake Mobutu area (formerly Lake Albert), Uganda, East Africa are reviewed.Morphotectonic analyses reveal a complex interplay between rift faulting, erosion processes and sedimentation; an inversion of laterite surfaces in zones of subsidence and sedimentation is suggested. At least three phases of rift faulting can be recorded. The initiation of rift faulting is regarded as younger than the upper latente surface but pre lower Miocene.
Zusammenfassung Morphologische und geologische Untersuchungen am westlichen Zweig des ostafrikanischen Grabens im Bereich des Mobutu-Sees (früher Albert-See) in Uganda werden zusammen mit den Ergebnissen der bisherigen Arbeiten in einer Gesamtschau dargestellt.Morphotektonische Analysen ergeben ein kompliziertes Wechselspiel zwischen Grabentektonik, Erosions- und Sedimentationsprozessen, Eine Inversion der latente surfaces im Absenkungs- und Sedimentationsbereich wird angenommen.Wenigstens drei Bewegungsphasen an der Grabenrandverwerfung sind zu erfassen. Das Einsetzen der aktiven Grabentektonik beginnt nach Bildung des upper latente surface und vor der Ablagerung unter-miozäner Sedimente.
Résumé Des recherches géologiques et morphologiques du rift occidental dans la région du lac Mobutu (préalablement de lac Albert) en Ouganda, coordonnées avec les résultats d'études antérieures, sont offertes en vue d'ensemble.Les analyses morpho-tectoniques font ressortir des relations complexes entre la tectonique du fossé, l'érosion et la sédimentation. La possibilité d'une « inversion » des horizons latéritiques dans la région de subsidence et sédimentation s'annonce.Au moins trois phases de mouvement ont été ofservées le long de la faille qui délimite le fossé. L'activité tectonique du fossé commence après la formation de la «surface latéritique supérieure » et avant la sédimentation des couches du Miocène Inférieur.
- — — . - . « » «laterite surfaces» . - . «upper laterite surface» - .
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12.
A method to demonstrate the simultaneous development of different minerals is discussed. Minerals are contemporaneous when they have formed before and after a point in time. Points in time are supplied by phases of deformation. The relations between deformation and crystallization can be deduced from the internal and external structures of porphyroblasts and matrix.This method is applied to unravel the metamorphic history of the Bosost area. Four metamorphic zones succeed one another: the biotite-zone, stauroliteandalusite-cordierite-zone, andalusite-cordierite-zone and cordierite-sillimanitezone. This zonal distribution represents a progressive metamorphic series and each higher metamorphic zone has passed through one or more lower metamorphic zones. Even within one zone a further subdivision of the crystallization history can be made.The described mineral associations are the result of low pressure metamorphism. They can be assigned to a low pressure faciesgroup of the amphibolite facies. The geothermal gradient during metamorphism was approximately 15° C pro 100 meter.
Zusammenfassung Eine Methode, um das gleichzeitige Wachstum verschiedener Minerale zu zeigen, wird hier näher erklärt. Minerale sind gleichzeitig, wenn sie vor und nach einem Zeitpunkt gebildet worden sind. Zeitpunkte werden durch Deformationsphasen geliefert. Die Verhältnisse zwischen Deformation und Kristallisation kann man aus dem Intern- und Externgefüge ablesen.Diese Methode wird angewandt, um die metamorphe Geschichte vomBosost-Gebiet zu entziffern. Vier metamorphe Zonen folgen aufeinander: Biotit-Zone, Staurolith-Andalusit-Cordierit-Zone, Andalusit-Cordierit-Zone und Cordierit-Sillimanit-Zone. Diese Zoneneinteilung stellt eine progressiv metamorphe Reihenfolge dar, wobei jede höher metamorphe Zone durch die weniger metamorphen Zonen gewandert ist. Auch innerhalb einer Zone kann noch eine weitere Unterteilung nach der Kristallisationsfolge gemacht werden.Die beschriebenen Mineralassoziationen sind unter niedrigen hydrostatischen Druckverhältnissen entstanden. Sie werden in der Amphibolit-Fazies, und zwar in einer niedrigen Druck-Faziesgruppe untergebracht. Der geothermale Gradient ist ungefähr 15° C pro 100 Meter gewesen.
Résumé Une méthode pour démontrer la croissance simultanée de minéraux différents est discutée. Des minéraux sont contemporains quand ils sont formés avant et après un certain instant qui peut être déterminé par des phases de déformation. Les relations entre déformation et crystallisation peuvent être déterminées à l'aide des structures internes et externes des porphyroblastes et de la matrice.Cette méthode est appliqué afin de déchiffrer l'histoire métamorphique de la région de Bosost, où quatre zones métamorphiques se suivent dans le temps: zone à biotite, zone à staurotide, andalousite et cordierite, zone à andalousite et cordierite et zone à cordierite et sillimanite. Cette classification en zones représente une série à métamorphisme progressif et chaque zone plus métamorphique a passé par une ou plusieurs zones moins métamorphiques. Même dans certains zones métamorphiques une subdivision plus détaillée est possible.Les associations de minéraux décrites sont formées sous des conditions de basse pression. Elles peuvent être placées dans un groupe de facies à basse pression du facies amphibolite. Le gradient géothermique pendant le métamorphisme était environ 15° C par 100 mètres.
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13.
An analytical approach to the analysis of zoning profiles in minerals is presented that simultaneously accounts for all of the possible continuous reactions that may be operative in a given assemblage. The method involves deriving a system of simultaneous linear differential equations consisting of a Gibbs-Duhem equation for each phase, a set of linearly independent stoichiometric relations among the chemical potentials of phase components in the assemblage, and a set of equations describing the total differential of the slope of the tangent plane to the Gibbs free energy surface of solid solution phases. The variables are the differentials of T, P, chemical potentials of all phase components, and independent compositional terms of solid solution phases. The required input data are entropies, volumes, the compositions of coexisting phases at a reference P and T, and an expression for the curvature of the Gibbs functions for solid solution phases. Results derived are slopes of isopleths (dP/dT, dX/dT or dX/dP) which can be used to contour P-T diagrams with mineral composition.To interpret mineral zoning, T and P can be expressed as functions of n independent composition parameters, where n is the variance of the mineral assemblage. The total differentials of P and T are differential equations that can be solved by finite difference techniques using the derivatives obtained from the analytical formulation of phase equilibria.Results calculated from Zone I and Zone IV garnets of Tracy et al. (1976) indicate that Zone I garnets grew while T increased (T+72° C) and P decreased sharply (P–3 kb). Zone IV garnets zoned in response to decreasing T (T–17° C) and P (P–1 kb). A P-T path calculated for a zoned garnet from the Greinerschiefer series, western Tauern Window, Austria, also indicates growth during decompression (–3kb) and heating (T+15° C). A P-T path calculated for the Wissahickon schist (Crawford and Mark 1982) indicates growth during cooling and compression (T–25 C, P+2.2 kb). The calculated P-T paths differ according to structural environment and can be used to relate mineral growth to tectonic processes.  相似文献   

14.
A field of volcanic rocks in Kenya includes numerous effusions of fragmental character and sodic alkaline composition — phonolites and trachytes. They show similarities to, and differences from, rhyolite / dacite suites referred to variously as ignimbrites, ash flows, welded tuffs and tuffolavas elsewhere. They are transitional into normal, well-crystallised lavas and cannot reasonably be explained by invoking eitherMarshall's classic ignimbrite hypothesis or its later modification, the ash flow hypothesis ofRoss andSmith. These are considered to be froth flows or foam lavas.The primary process leading to heterogeneity is believed to have been one of very irregular volatiles segregation, due to the stirring effect of flow through conduits and over the surface. A varied range of fragmental, banded, eutaxitic and autobrecciated lava types has stemmed from effects of such segregation, and all these types of structure may be seen within indivual flows, termed structurally composite lava flows.
Zusammenfassung Natronreiche Effusiva — wie Phonolite und Trachyte — finden sich in Kenya in zahlreichen kleinen Vorkommen. Die Vulkanite zeigen trotz kennzeichnender Unterschiede gewisse Ähnlichkeiten mit einer Dazit-Rhyolith-Serie, die Strukturen aufweist, die man verschieden als ignimbritisch bezeichnet, oder als Aschestrom, Schmelztuffe und Tufflaven beschreiben kann. Die Vulkanite zeigen einen Übergang in wohl auskristallisierte Laven und können nicht mit derMarshallschen Ignimbrit-Hypothese erklärt werden; ebensowenig befriedigt die Hypothese vonRoss &Smith als Aschen-Glutfluß. Sie sollen hier als Schaum-Laven betrachtet werden.Der primäre Prozeß, der zur heterogenen Ausbildung dieser Laven führt, beruht auf einer ungleichmäßigen Entgasung, die sowohl im Schlot als auch an der Oberfläche stattfindet. Die dabei entstehenden Strukturen — wie Brekziierung, Bänderung und Schmelzstrukturen — können alle innerhalb eines Lavastromes beobachtet werden und sollen hier unter dem Begriff structurally composite lava flows zusammengefaßt werden.
Résumé Une association des coulées de lave renferment des fragments est décrit ici. Les rochers sont semblable aux des rochers rhyolite/dacite qu'on les appelle ignimbrite, ash-flow, welded-tuff ou tuffolava. Ils sont transitionnel aux des laves d'une espèce normal et beaucoup crystallins; ainsi, une explication comme cette deMarshall (hypothèse ignimbrite) ou cette plus tard avancé parRoss etSmith (hypothèse ash-flow) est incroyable. L'auteur dit que les laves fragmentales de Kenya sont froth-flows — des laves écumeux.Le processus primaire qui faisait cette hétérogénéité fût le ségrégation des volatils par l'effet d'agitant la coulée en passant le conduit et en effusion a plein air. Une série des laves, fragmentales, rayées, eutaxitiques, et autobrecciées fut nées de cette ségregation, et toutes ces espèces se trouvent dedans cóulees individuelles, qu'on appelle de structure composite.
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15.
Denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass. Recent empirical results from a wide range of sources are presented on the rates of these processes. Denudation alone can cause non-tectonic (isostatic) surface uplift of the right magnitude predicted by theory. A case is made, following Ahnert, for a single linear relationship (although with much scatter) between denudation rate and mean drainage basin relief for large basins. Some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation. Application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one-dimensionality and neglect of suspended and washload contributions. Basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland, but problems arise in the apportionment of the various hinterland fluxes that occur in »real-world« three dimensional basins. Sediment yields in smaller half-graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields. Examples are given from extensional basins in the Western USA and Greece. The »length« of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed (through the fractal form of Hack's Law) and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands.
Zusammenfassung Denudation und vertikale Krustenbewegungen sind verbunden durch das isostatische Gesetz über den Erhalt der lithosphärischen Masse. Neuerliche empirische Ergebnisse aus einem weiten Quellenbereich werden im Verhältnis zu diesen Prozessen präsentiert. Denudation allein, kann nicht tektonisch bedingte (isostatische) Oberflächenhebungen hervorrufen, die in der richtigen Größenordnung liegen, wie sie auch theoretisch ermittelt wurden. Es wird in Anlehnung an Ahnert ein Fall geschaffen, in der eine einfach lineare Beziehung (obgleich mit vielen Streuungen) zwischen der Denudationsrate und dem durchschnittlichen Abflußbeckenrelief für große Becken vorliegt. Einige neue Ermittlungen der Denudationszeitkonstanten wurden vernachlässigt, um tektonische und isostatische Begriffe einzufügen, welche sich der Verringerung des Reliefs durch Denudation widersetzen. Die Anwendung des Verbreitungstransportmodells zum Bestimmen der Sedimentationsrate sind streng begrenzt durch die ihm innewohnende Eindimensionalität, und der Vernachlässigung der Schwebe- und Schwämmfrachtbeteiligung. Bekkenfüllungssequenzen können benutzt werden um vergangene Sedimenttransferkoeffizienten aus dem Hinterland festzulegen; aber es treten auch Probleme bei der Verteilung der verschiedenen Hinterlandeinträge auf, die bei einem realen dreidimensionalen Becken vorhanden sind. Sedimenteinträge in kleineren Halbgräben und Growth-fold Becken müssen die Größe des Abflußbeckens widerspiegeln, sowie die komplexen lokalen Steuerungen auf die Sedimenteinträge. Beispiele von Dehnungsbecken aus dem Westen der USA und Griechenlands werden angesprochen. Die Länge des tektonischen Reliefs in verkippten Blöcken und Growth-Folds wird die Fläche des entwickelten Abflußbeckens kontrollieren (durch die fraktale Form des Gesetzes von Hack), und daher die Ablagerungsmenge von Sedimentbecken in der Nähe von tektonischen Hochlagen.
Résumé L'érosion et les mouvements crustaux verticaux sont liés par l'équation isostatique de conservation de la masse lithosphérique. Des résultats empiriques récents provenant d'un large éventail de sources sont présentés en relation avec ces processus. L'érosion seule peut être la cause d'une montée non tectonique (isostatique) dont l'ampleur est prévue exactement par la théorie. Un cas est présenté, d'après Ahnert, qui montre, pour de grands bassins, une relation linéaire simple (mais avec une forte dispersion des points) entre le taux de dénudation et le relief moyen de l'aire de drainage. Certaines déterminations récentes des constantes de temps de dénudation ont omis de tenir compte des termes tectonique et isostatique qui s'opposent à la destruction du relief par érosion. L'utilisation de modèles de transport diffus en vue de déterminer le taux d'accumulation des sédiments est sévèrement limitée par le caractère unidimensionnel de tels modèles et par le fait qu'il ne tiennent pas compte de la fraction en suspension. Les séquences de comblement d'un bassin sédimentaire peuvent être utilisées pour déterminer les anciens cfficients de transfert à partir de l'hinterland; mais des difficultés surgissent à propos de la répartition des différents flux en provenance de l'hinterland dans le cas réel d'un bassin à 3 dimensions. Les apports sédimentaires dans les bassins de demi-graben et de »growth-fold« doivent traduire la grandeur des aires de drainage et les facteurs locaux complexes qui régissent ces apports. Des exemples sont présentés, relatifs à des bassins d'extension de l'ouest des USA et de Grèce. La »longueur« des reliefs tectoniques en relation avec les blocs basculés et les »growth-folds« déterminent, par la forme fractale de la loi de Hack, la surface des aires de drainage ainsi engendrées et, en conséquence, l'importance des dépôts dans les bassins sédimentaires voisins des reliefs tectoniques.
. , . () , . , ( ) . , , , . , . , , ; , . « » (GrowthFolds) . . — « » Hack'a , , .
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16.
Axial-symmetric and real triaxial deformation tests on Solnhofen limestones were made in the range of 20 to 650° C. Stress, strain and time observations as functions of temperature and the ratios of the external stresses are plotted as stress-strain and strain-time curves. Mechanical twinning on e (01¯12) and syntectonic recrystallization (at temperatures above 500° C) is assumed to be the dominant flow mechanism. On samples of high permanent strain the textural changes and development of preferred orientations were investigated by means of the X-ray diffractometer. In all tests the symmetry of the polefigures is exactly identical with the symmetry of the external stress-field.In tests with 1>2=3 the poles of the planes investigated (10¯11; 10¯12; 11¯20) occupy girdles about the unique principle compressive axis. When all principle stresses are different (1>2>3) the poles of the planes investigated tend to maxima (in the case of plane strain) ore to girdle-occupations about the principle axis of maximum extension. The deduced c-diagrams show a fairly similar tendency of the spacial orientations.The pole figures (as well as the calculated orientation of the c-axis) must be explained by the superposition of reflected intensities on planes in twinned and untwinned grains. In every diagram partial occupations—possibly representing the orientations of twinned grains-are in fairly good agreement with the orientation predicted by the theory of Brace-MacDonald for the stable orientation of anisotropic minerals in a non-hydrostatic stress-field.

Herrn Prof. Dr. F. Karl danke ich sehr herzlich für zahlreiche Diskussionen sowie für die kritische Durchsicht des Manuskripts. Mein Dank gilt auch der Deutschen Forschungsgemeinschaft, welche die Untersuchung durch eine Sachbeihilfe unterstützte.  相似文献   

17.
The Grythytte field sequence forms a NNW belt of acid-basic metavolcanic and metasedimentary rocks. The geology shows characteristics of a dynamic process of trough-forming and infilling which to a large extent post-dates the Hjulsjö volcanoplutonic complex situated to the east. In the latter complex acid metapyroclastics strike around a centre of granite and granophyre, which cut and are cut by basic sills and dykes. Field and petrochemical evidence points to a distinct bimodal magmatism that ist manifested during one short phase of a rifting period.
Zusammenfassung Die Grythytte Schichtenfolge bildet einen NNW verlaufenden Gürtel aus sauren und basischen Metavulkaniten und Metasedimenten. Die geologischen Befunde weisen auf einen dynamischen Entstehungsprozeß von Grabenbildung und Füllung hin. Im weiter östlich gelegenen vulkanisch-plutonischen Hjulsjö-Komplex streichen älteren metamorphen pyroklastischen Gesteine rund ein Granit-Granophyr Zentrum. Dieser Komplex durchschneidet und wird durchschnitten von basischen Sills und Gängen. Feldgeologische und geochemische Untersuchungen weisen deutlich auf einen bimodalen Magmatismus hin, der während einer kurzen Phase der Grabenbildung stattfand.
Résumé La séquence de Grythytte forme une ceinture de roches métavolcaniques et métasédimentaires de direction NNO. La géologie fait apparaître les caractéristiques d'un processus dynamique de formation de fosse et de remplissage, qui s'est produit, pour la plus grande partie, après la formation du complexe volcano-plutonique de Hjulsjö situé à l'Est. Dans ce dernier complexe des produits pyroclastiques acides sont disposés autour d'un centre granitoïde et granophyrique, qui à son tour recoupe et est recoupé par des sills et des dykes basiques. Les observations de terrain et les faits pétrochimiques indiquent un procèssus magmatique distinctement bimodal qui s'est manifesté pendant une phase courte dans une période de «rifting».
Grythytte , NNW . . Hjulsj -- . . , , .
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18.
Résumè Le batholite de San Ramon est constitue par un granite à gros grains ou porphyroïde, à biotite et parfois hornblende, de teinte rouge à grise. Il s'étend sur 90 km du Nord au Sud à la bordure est de la Cordillère Orientale du Pérou Central. Il recoupe des terrains carbonifères et on le retrouve en galets dans des conglomérats rouges sous-jacents aux calcaires triasico-liasiques. Son âge est précisé par une isochrone Rb/Sr en roches totales qui le fixe à 238±10 MA. Il s'agit donc d'un granite d'âge permien supérieur à trias inférieur en partie contemporain du volcanisme rhyolitique à andésitique qui accompagne le dépôt des molasses rouges Mitu post-léonardiennes et pré-ladiniennes. Avec d'autre granitoïdes tardi-hercyniens de la Cordillère Orientale, il témoigne de l'importance insuffisamment reconnue jusqu'alors du plutonisme associé à ce volcanisme »permo-triasique«.
The batholith of San Ramon is made of a coarse-grained to porphyritic granite that bears biotite and also hornblende at some places. It extends over 90 km from north to south along the eastern boundary of the Eastern Cordillera of Central Peru. It intrudes Carboniferous and Lower Permian strata and is included as cobbles into the red conglomerates that underlie Triassic to Liassic carbonates. A Rb/Sr whole-rock isochron gives a Late Permian to Early Triassic age of 238±10 m. y. Thus the San Ramon granite appears to be in part coeval with the andesite to rhyolitic volcanism associated to the red Mitu molasses, that as a whole were deposited after the Late Leonardian and before the Lower Ladinian. Some other radiometric ages from the Eastern Cordillera granitoïds stress the extension of this Late Variscan plutonism.
Zusammenfassung Der Batholit von San Ramon besteht aus einem grobkörnigen bis porphyrartigen Granit mit Biotiten und bisweilen Hornblenden von rötlicher bis grauer Farbe. Er erstreckt sich über 90 km in N—S-Richtung längs dem Ostrand der östlichen Cordillere von Zentralperu. Er durchschneidet Karbon- und Permablagerungen und findet sich in Gerollen des triadisch-liassische Kalke unterlagernden Konglomerats. Aus der Rb/Sr-Gesamtisochrone ergibt sich ein Alter von 238±10 M. J. Es handelt sich also um einen Granit aus dem Grenzbereich Perm—Trias, der zum Teil gleichaltrig mit dem rhyolitischen bis andesitischen Vulkanismus ist, der die Ablagerung der postleonardischen und praeladinischen roten Molasse Mitubegleitet. Im Verein mit anderen spätvariszischen Granitoïden weist er auf die bisher ungenügend erkannte Bedeutung des diesen permo-triadischen Vulkanismus begleitenden Plutonismus hin.
Resumen El batolito de San Ramón esta localizado a lo largo del limite este de la Cordillera Oriental en el Perú Central. Esta compuesto por un granito de grano grueso que puede tambien ser porfiroide, contiene biotita y tambien hornablenda y su color varia de rojo a gris. Dicho granito intruye terrenos carboniferos y eo-pérmicos y se le encuentra formando parte de los cantos en los conglomerados rojos infrayacentes a la serie carbonatada triásico-liásica. Una isocrona Rb/Sr en rocas totales le da una edad de 238±10 m. y. es decir del Permico terminal o de la base del Triásico. Por lo tanto, el granito de San Ramón es contemporáneo con parte del volcanismo riolitico a andesítico asociado a la sedimentacion de las molasas rojas del grupo Mitu, la cual ocure entre el Leonardiano superior y el Ladiniano inferior. Junto con otros granitoïdes de la Cordillera oriental, el batolito de San Ramón demuestra la importancia del plutonismo asociado a este volcanismo »permo-triásico«.
- , , . 90 - . , , . — Rb/Sr — 238± 10 , .. - . .. , - - «». , , , - .
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19.
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   

20.
Recently published accounts of the chronology of various Plinian explosive eruptions, notably that of Askja, Iceland, in 1875, have stressed the role of basic magma injected into the lower parts of stagnant semi-crystalline magma reservoirs as triggers for the violent surface activity and caldera formation. The evidence for mixing of acid and intermediate magmas at two stages during the emplacement of the Eocene granite sequence of the Western Redhills, Skye, Scotland, is interpreted in a similar manner. Within the British Tertiary Igneous Province as a whole, there is evidence for repeated refusion and partial hybridisation during the evolution and upward penetration of the acid magmas to the crustal levels where they now form plutons. The repetitive operation of such processes may explain why geochemical studies of these granites, seeking to discover their origins in terms of simple one-stage processes (such as partial fusion of sialic crust or fractional crystallisation of basic magma), give conflicting results.
Zusammenfassung Einige explosive plinische Eruptionen (z. B. Askja, Island. 1875) sind in neuerer Literatur beschrieben worden. Explosive Tätigkeit an der Erdoberfläche sowie die Entstehung einer Caldera sind als eine Folge der Injizierung basischer Magmen in die unteren Teile von semi-schmelzflüssigen Magmakammern anzusehen. Die Eocänen Granite von Western Redhills, Skye, Schottland, weisen auf eine zweimalige Mischung von sauren und intermediären Magmen während der Intrusion hin. In der gesamten britischen Magmenprovinz des Tertiärs gibt es Nachweis für mehrmalige Wiederaufschmelzung und Teilhybridisierung während des Aufstiegs von saurem Magma zum Niveau der heutigen Plutone. Geochemische Studien an solchen Graniten, die zunächst eine einfacherere Entstehungsweise vermuten lassen (z. B. Partialschmelzen von der sialischen Erdkruste oder fraktionierte Kristallisation), führen oft zu widersprechenden Ergebnissen. Eine Erklärung dafür liegt mit der wahrscheinlich mehrmals wiederholten Magmenhybridiesierung.
Résumé Des comptes-rendus récemment publiés concernant la chronologie de différentes éruptions explosives de type plinien, notamment celle d'Askja, Islande, en 1875, ont souligné le rôle du magma basique qui injecté dans les parties inférieures de réservoirs où stagne du magma semi-cristallin, serait la cause d'une violente activité en surface et de la formation de calderas. On interprête de semblable manière la mélange de magmas acide et intermédiaire en deux stades pendant la mise en place de la série granitiques éocène des Redhills occidentales, Skye, Ecosse. Dans la Province ignée tertiäre de Grande Bretagne, vue dans son ensemble, il y a des preuves d'une refusion répétée et d'une hybridisation partielle durant l'évolution et la pénétration vers le haut des magmas acides vers les niveaux crustaux où ils forment maintenant des plutons. L'opération répétée de tels processus peut expliquer pourquoi des études géochimiques de ces granités cherchant à découvrir leur origine en termes de processus simples à un stade (tels que fusion partielle d'une croûte sialique ou par cristallisation fractionnée d'un magma basique) conduisent à des résultats contradictoires.
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