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1.
Zusammenfassung Die geophysikalischen Untersuchungen am Störkörper von Bramsche, ca. 20 km N Osnabrück, deuten auf einen basischen Intrusivkörper in ca. 5 km Tiefe. Hohe Inkohlungsgrade in karbonischen bis kretazischen Sedimenten lassen eine starke Wärmequelle mit einem bis zu den Karbonhorsten südlich und westlich Osnabrück reichenden Kontakthof vermuten, mit einem Maximum der Inkohlung im Gebiet der geophysikalischen Anomalie.Während sich an den Karbonhorsten um Osnabrück sulfidisch-barytische Erze kretazischen Alters finden, fehlen jegliche Vererzungsspuren im Zentrum der Anomalie. Hier könnten lediglich Pyrophyllit und Quarzitisierungen im Malm des Gehns und das Vorkommen von Gümbelit im Piesberg-Karbon auf Auswirkungen der Intrusion hinweisen. Ausbildung (Faseraggregate der Phyllosilikate) und geologisches Auftreten (keine laterale Verteilung) sprechen aber für eine im weitesten Sinne lateral-sekretionäre Entstehung.Experimente vonNoll (1936) undAlthaus (1966) ergaben eine Bildungstemperatur für Pyrophyllit von ca. 390° C. Es finden sich jedoch keine pegmatitisch-pneumatolytischen oder katahydrothermalen Mobilisate in diesem Gebiet. Somit sollte die Bildungstemperatur für den Pyrophyllit niedriger gewesen sein. Selbst wenn die Bildungstemperatur bekannt wäre, wäre es schwierig, den hydrothermal gebildeten Pyrophyllit als geologisches Thermometer zu benutzen.- Geothermische Überlegungen zur Kalkulation der Intrusionstemperatur lassen sich hier somit nur noch mit Hilfe des Inkohlungsgrades vornehmen.
Geophysical researches at the Bramsche anomaly, about 20 km north of Osnabrück in NW-Germany indicate a basic intrusive body at the depth of about 5 km. A big source of heat with a contact zone reaching to the Carboniferous horsts south and west of Osnabrück is supposed by the increase of coalification in Carboniferous up to Cretaceous sediments, which has the highest degrees of coalification in the region of the geophysical anomaly.While there are sulfide deposits with barytic gangue of Cretaceous age at the Carboniferous horsts near Osnabrück, there are no ore-traces in the centre of the anomaly. Only the occurence of pyrophyllite and quartzites in the Malm of the Gehn-hills and the occurrence of gümbelite (Mg-hydromuscovite) in the Carboniferous sediments of Piesberg-horst may indicate the influence of the intrusion. - But habit (fibre-aggregates of the phyllosilicates) and geologic occurence (no lateral distribution) of these mineralisations suggest a formation by lateral secretion in a broader meaning of the term.Experiments byNoll (1936) andAlthaus (1966) proved a temperature of about 390° C for the formation of pyrophyllite. But there are no pegmatitic-pneumatolytic or kata-hydrothermal mobilisations in this district. Therefore it is assumed that the temperature of the formation may be lower under other conditions. Even if the temperature of this formation were known, it would be difficult to use pyrophyllite — formed under hydrothermal conditions — as a geologic thermometer. - Geothermal conclusions to calculate the temperature of the intrusion are only possible by using the decrease of volatile matter of the coals.
Résumé Les recherches géophysicales du corps failleux de Bramsche, à environ 20 km au nord d'Osnabrück font penser à un corps intrusit basique à 5 km sous la surface. De grands degrés d'houillification en des sédiments carbonifères et crétacés révèlent une forte source de chaleur avec une auréole de contact s'étendant jusqu'aux horsts carbonifères au sud et à l'ouest d'Osnabrück, avec un maximum d'houillification dans la région de l'anomalie géophysicale.Bien qu'on trouve des airains crétacés sulfurés avec barytine, aucune trace de minéralisation n'est visible au centre de l'anomalie. Ce n'est que la pyrophyllite et les quartzites dans le Malm du Gehn et l'existence de gümbelite (Mghydro-muscovite) dans le Piesberg-Karbon qui peuvent indiquer des effets d'intrusion. La structure et l'existence géologique font plutôt penser à une genèse latéralement sécrétionaire. Des conclusions géothermiques pour calculer la température d'intrusion ne sont à entreprendre qu'à l'aide du degré d'houillification.
(Bramsche) 20 (Osnabrück), , 5 . , - , * — . (Osnabrück) , . () (Gehn) - (Piesberg) . . , , . ()

Meinem verehrten Lehrer, Herrn Prof. Dr. H.Harder danke ich für die Anregung zu dieser Arbeit im Rahmen einer regionalen lagerstättenkundlichen Dissertation. Für weitere Hinweise und Diskussionen bin ich Herrn Prof. Dr. B.Brockamp verpflichtet.  相似文献   

2.
Zusammenfassung Kurze Übersicht über paläogeographische, paläotektonische und paläoklimatologische Probleme der Trias, unter Ausklammerung des Germanischen Beckens; allgemeiner Rahmen zu den Referaten der Trias-Tagung 1982 in Würzburg.
Short review of paleogeographic, paleotectonic and paleoclimatological problems of the Triassic system, outside of the Germanic Basin. General framework to the papers presented at the 1982 symposium on the Triassic.
Résumé Brève vue d'ensemble des problèmes paléogéographiques, paléotectoniques et paléoclimatiques du Trias, en dehors du bassin germanique. Cadre général des communications présentées lors du symposium sur le Trias de 1982.
, , .
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3.
It is valuable in earthquake prediction to determine the occurrence probability of major earthquakes by making use of data obtained from precursory phenomena up to the time of the evaluation. In this study, the time evolution of the state determined by earthquakes and precursory phenomena was modelled using Markov chains. Various probabilities suitable for earthquake prediction were derived from the transition probability of the Markov chain with a chosen length of memory time. As an example, earthquake sequence records for northern China, which covered a period of about two thousand years, were examined and the results were also obtained from modern scientific observations of the radon anomaly which covered a period of about 10 years.Assuming moderate-sized earthquakes of two magnitude ranges 4 3/4 M 5 3/4, 6 M 6 3/4 as precursors to large earthquakes of a magnitude range, 7 M 8 1/2, transition probabilities were calculated for a time interval from 2 to 40 yr. The results showed that the precursory time of moderate-sized earthquakes is mainly distributed in a time span of around several years and that the earthquake occurrence probability is considerably large when the precursory earthquakes occur successively. Furthermore, it was shown that a larger moderate-sized earthquake (4 3/4 M 5 3/4) is a more effective precursor than an entire moderate-sized earthquake (4 3/4 M 6 3/4).Second, a multiple precursor case was tried by means of simulation based on the radon anomaly data obtained during a limited observation period. Simultaneous occurrence of two precursors makes the earthquake occurrence probability increase by 1.5–2.0 for a reasonable choice of a mean recurrence interval of the radon anomaly compared with the case where only a moderate-sized earthquake was treated as the precursor. However, the probability is much the same if the average recurrence interval of the radon anomaly is the same through time, including the preparatory period before the earthquake.  相似文献   

4.
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   

5.
Comparison between two types of multifractal modeling   总被引：1，自引：0，他引：1  
The interrelationships between two previously developed multifractal models are discussed. These are the Evertsz-Mandelbrot model developed on the basis of the multifractal spectrum f(), and the Schertzer-Lovejoy model based on the codimension function C() where and represent Hölder exponent and field order, respectively. It is shown how these two models are interrelated: they are identical for values of within the range D–(0)D–min. where D is the Euclidean dimension. For D–maxD–(0), however, f() remains a continuous function of whereas C() assumes constant value. In this respect, the fractal spectrum f() can provide more information about the multifractal measure than the codimension function C(). The properties of the two models are illustrated by application to the binomial multiplicative cascade model.  相似文献   

6.
Synthesis experiments in the system MgAl2O4–MgFe2O4 [MgAl2–xFexO4 (0 x 2)] were carried out using a PbF2 flux. The crystalline products synthesized in the compositional range of 0.6 <x 1.2 consisted of two spinel phases, whereas those synthesized in the compositional ranges of 0.0 x 0.6 and 1.2 < x 2.0 crystallized as single spinel phases. Structure refinements of the spinel single crystals, which grew in the ranges of 0.0 x 0.6 and 1.2 < x 2.0, show that the degree of randomness of cation distribution between A and B sites increases as x approaches the two-phase region. This means that the degree of the size mismatch among Mg2+, Fe3+ and Al3+occupying each equivalent mixing site increases as x approaches the two-phase region. Consequently, if the coexistence of two spinels observed in the intermediate compositions reveals the existence of a miscibility gap at low temperatures, this increase in the degree of the size mismatch among the three cations is suggested as a factor of energetic destabilization to form the miscibility gap.  相似文献   

7.
34 igneous clasts of predominantly rhyolitic composition of the Parishholm- and Hareshaw-Conglomerate (Silurian, Hagshaw Hills inlier, Midland Valley, Scotland) have been analysed for major and trace element contents. The geochemical composition of the clasts indicates different source areas. Firstly, some clasts are derived from rhyolites of a within-plate setting (peralkaline rhyolites of oceanic islands or continental rifts) and secondly, other clasts are derived from calc-alkaline to high-K rhyolites. Such rhyolites erupt mainly above convergent plate boundaries, but occur also in continental areas of crustal extension. Both conglomerates were shed from the direction of the Southern Uplands into the Midland Valley. Since no calc-alkaline rhyolites are known in the Southern Uplands, a volcanic terrane should have been situated during the Silurian in the area where the Southern Uplands lie now. The geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts. Therefore several models are discussed.
Zusammenfassung 34 Gerölle magmatischer Gesteine vorwiegend rhyolithischer Zusammensetzung aus dem Parishholm- und dem Hareshaw-Konglomerat (Silur, Hagshaw Hills inlier, Midland Valley, Schottland) wurden auf Haupt- und Spurenelementgehalte hin analysiert. Die geochemische Zusammensetzung der Gerölle deutet auf verschiedene Liefergebiete hin. Es handelt sich einmal um Gerölle von Rhyolithen aus einem Intraplatten-Gebiet (Peralkali-Rhyolithe ozeanischer Inseln oder kontinentaler Gräben) und zum zweiten um Gerölle von kalkalkalischen und kaliumreichen Rhyolithen. Solche Rhyolithe werden vorzugsweise über konvergierenden Plattengrenzen gefördert, sie treten aber auch in kontinentalen Dehnungsgebieten auf. Beide Konglomerate wurden aus der Richtung der Southern Uplands in das Midland Valley geschüttet. Da kalkalkalische Rhyolithe in den Southern Uplands unbekannt sind, dürfte im Silur ein vulkanisches Terraine in dem Gebiet, in welchem sich die Southern Uplands heute befinden, gelegen haben. Der geotektonische Charakter dieses vulkanischen Terraines lä\t sich mit Hilfe der Spurenelement-Daten der Gerölle nicht eindeutig festlegen. Es werden deshalb mehrere Modelle diskutiert.
Résumé Les auteurs ont analysé les éléments majeurs et en traces de 34 galets de roches magmatiques, en majorité rhyolitiques, prélevés dans les conglomérats de Parishholm et de Hareshaw (Silurien, Hagshaw Hills inlier, Midland Valley, Ecosse). Leur composition géochimique indique différentes provenances. D'une part, il s'agit de galets rhyolitiques d'une région intra-plaque (rhyolites peralcalines d'Îles océaniques ou de fossés continentaux), d'autre part, il s'agit de galets de rhyolites calco-alcalines et de rhyolites riches en potassium. Des rhyolites de ce type sont émises d'ordinaire au-dessus de sutures de plaques convergentes, mais elles se rencontrent aussi dans des régions continentales en extension. Les deux conglomérats proviennent du Sud, de la région des Southern Uplands. Comme des rhyolites calco-alcalines sont inconnues dans les Southern Uplands, on est amené à supposer l'existence, au Silurien, d'une accrétion («terrane») de nature volcanique dans la région occupée aujourd'hui par les Southern Uplands. Les teneurs des éléments en trace ne permettent pas de déterminer sans équivoque le caractère géotectonique de cette accrétion volcanique. Dans ces conditions, plusieurs modèles sont discutés.
34 Parishholm Hareshaw, , Hagshaw Hills inlier, Midland Valley, /, . . . , Intraplatten-Gebiet / , / - . . . , . . - , , , . . .
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8.
In hypersthene bearing hornblende metadiorites near Milford Sound garnet replaces hornblende in 5 cm wide subplanar zones, patterned almost certainly on joints. The alteration has been accompanied by a change in bulk rock composition (increase of Al, decrease of Na) and the occurrence constitutes good evidence for external chemical control of the overprinting of hornblende granulites with garnet.  相似文献   

9.
The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H+ – FeOH –AuCl 4 - – Cl-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 pH 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were log 1,1,0,0(int) s = 7.10 ± 0.06 andlog -1,1,0,0(int) s = - 7.80 ±0.06. The density of proton active surface sites was 2.85nm-2 and the specific capacitance 2.5 C V-1 m-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 pH 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: FeOHAuCl3(log 0,1,1,-1 s = 1.45 ± 0.03),FeOHAuCl2OH (log -1,1,1,-2 s = -3.89 ± 0.02), FeOHAu(OH)3 (log -3,1,1,-4 s = -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(FeO)2Au(OH)H2O. However, based onstructural arguments this complex was rejected.  相似文献   

10.
Summary The Dumont Sill is an Archaean komatiitic intrusion, whichDuke (1986) subdivided into a mafic (MZ) and ultramafic zone (UMZ). The UMZ comprises an upper (UPZ) and a lower peridotite subzone (LPZ) consisting of olivine + chromite cumulates and a dunite subzone (DZ) between them, consisting of olivine ± sulfide cumulates.Three sulfide-rich layers in the DZ are delineated by anomalously high Ni, Cu, S and Se concentrations (Ni 0.95 wt %, Cu 0.07 wt.%, S 1.0 wt.%, Se 2.7 ppm). They also contain elevated contents of noble metals (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb). Unmineralized samples contain 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir, and 1–6 ppb Os.Samples belonging to the LPZ and UPZ and lying above and beneath the mineralized horizons have rather high Ir contents, generally between 2.9 to 4.4 ppb. In contrast, Ir contents of sulfide-free samples from the DZ and UPZ which lie immediately above the mineralized zones have significantly lower Ir concentrations, ranging from 0.1 to 1.5 ppb. This zone of Ir depletion coincides with a zone of Ni-depleted olivine and sulfide which crystallized just above sulfide-rich horizons in the DZ (Duke, 1986). It is suggested that Ir and Ni depletion in cumulates which lie between or above sulfide-rich zones are due to the lower Ir and Ni contents in olivine which crystallized from a silicate magma from which a sulfide liquid had already been segregated. Alternatively, if metal alloys control the distribution of Ir and Os in the DZ, the Ir depletion in the cumulates above the ore' horizons implies that crystallization of the metal phase ceased. This would be the case if, due to the segregation of sulfides, the Ir concentration in the silicate liquid falls below the solubility limit of the metal phase.The sulfide mineralization probably formed by fractional segregation of a sulfide/ oxide liquid, as the PGE concentrations in the sulfide liquid and PGE/Se, or PGE/S ratios tend to decrease from the bottom to the top in the mineralized zones.Duke (1986) proposed that sulfide saturation was caused by mixing of primitive komatiite magma with fractionated interstitial liquid, which was squeezed out of the cumulate pile. Sulfide segregation at the floor of the magma chamber is likely to have been a very localized event implying low R-factors. The small PGE-enrichment in the sulfide horizons of the Dumont Sill and the narrow zones of Ir-depletion just above the sulfide zones are consistent with the proposed process.
Die Verteilung von Platingruppen-Elementen im Dumont Sill, Quebec und ihre Bedeutung für die Bildung von Ni-Sulfid MIneralisationen
Zusammenfassung Der Dumont Sill ist eine komatiitische Intrusion, die von Duke (1986) in eine mafische (MZ) und eine ultramafische (UMZ) Zone untergliedert wurde. Die UMZ setzt sich aus einer oberen (UPZ) und einer unteren (LPZ) peridotitischen Subzone, die aus Olivinund Chromft-Kumulaten besteht, und einer dunitischen Subzone (DZ), zwischen diese beiden eingeschaltet, zusammen. Letztere besteht aus Olivin- und Sulfid-Kumulaten.Drei sulfidreiche Lagen innerhalb der DZ sind durch anomal hohe Gehalte an Ni, Cu, S und Se (Ni 0.95 Gew. %, Cu 0.07 Gew. %, S 1.0 Gew. %, Se 2.7 ppm) charakterisiert. Erhöhte Gehalte an Edelmetallen (Au 31.5 ppb, Pd 210 ppb, Pt 180 ppb, Ir 8.4 ppb, Os 6 ppb) sind ebenfalls an diese Lagen gebunden. Unvererzte Proben enthalten < 3–8 ppb Pd, 1–20 ppb Pt, 0.2–3.6 ppb Au, 0.5–6 ppb Ir und 1–6 ppb Os.Proben aus der LPZ und UPZ und solche aus dem Hangenden und Liegenden der Mineralisationshorizonte zeigen relativ hohe Ir-Gehalte; im allgemeinen zwischen 2.9 und 4.4 ppb. Im Gegensatz dazu sind die Ir-Gehalte sulfidfreier Proben unmittelbar über vererzten Lagen deutlich erniedrigt; sie variieren zwischen 0.1–1.5 ppb. Diese an Ir verarmte Zone entspricht einer Zone nickelarmer Olivine und Sulfide, die unmittelbar oberhalb der sulfidreichen Horizonte in der DZ kristallisierten (Duke, 1986). Es wird vermutet, daß die Ir- und Ni-Abreicherung in den Kumulaten, die oberhalb und zwischen den sulfid-reichen Zonen liegen, mit den niedrigeren Ir- und Ni-Gehalten der Olivinen zusammenhängt. Die Olivine kristallisierten aus einem Silikatmagma, von dem sich bereits eine Sulfidschmelze abgeschieden hatte.Soferne metallische Verbindungen die Ir- und Os-Verteilung in der DZ kontrollieren, würde die Ir-Abreicherung in den Kumulaten oberhalb des Erzhorizontes auf ein Ende der Kristallisation einer metallischen Phase hinweisen. Dieser Fall könnte eintreten, sobald durch die Ausscheidung von Sulfiden, die Ir-Konzentration in der silikatischen Schmelze unter die Löslichkeitsgrenze der Metallphase fällt.Die Sulfidvererzung bildete sich wahrscheinlich infolge von fraktionierter kristallisation einer Sulfid/Oxidschmelze, da die PGE Konzentrationen der Sulfidschmelze, und das PGE/S Verhältnis vom Liegenden zum Hangenden hin in den mineralisierten Horizonten abnehmen. Duke (1986) schlug ein Modell vor, in dem die Sulfid-Sättigung der silikatischen Schmelze durch eine Vermischung eines komatiitischen Magmas mit einer fraktionierten, interstitialen, aus den Kumulaten ausgequetschten Schmelze erklärt wird. Die Sulfidausfällung an der Basis der Magmenkammer scheint ein lokal recht begrenztes Phänomen gewesen zu sein, die niedrige R-Faktoren bedingt. Die geringfügige PGE-Anreicherung in den Sulfidlagen des Dumont Sills und die schmale Zone der Ir-Abreicherung unmittelbar oberhalb dieser sulfidischen Zone stehen mit diesen vorgeschlagenen Prozessen im Einklang.

With 6 Figures  相似文献   

11.
The rocks of the Maru and Anka regions of northwestern Nigeria comprise a polycyclic, migmatite-gneiss, basement sequence with an infolded cover of low grade metasediments. Both basement and cover are intruded by a suite of syn-tectonic to latetectonic granites and granodiorites.Evidence from contrasting lithologies and geochronological data suggest that at least three depositional cycles may be represented in the Anka and Maru Belts of low-grade metasediments. An attempt is made to correlate these three cycles with the Kibaran (c. 1100 m. y.) and Pan-African (c. 550 m. y.) events.Structural similarities between the two belts are explained by continued reactivation of Kibaran basement structures during Pan-African times.Calc-alkaline volcanics of late Pan-African age are restricted to the Anka Belt. Recent work shows that volcanism in the Anka Belt is not all of late-orogenic type: a volcano-sedimentary pile, containing possible crystal tuff units, being intruded by acid-intermediate dykes and sills, and deformed during the Pan-African event. Syenitic plutonism restricted to the Maru Belt is shown to be post-tectonic.The recognition of a significant Kibaran event in the basement of northwestern Nigeria is in accord with workers who record a similar event in other parts of the Nigerian basement and in the Precambrian basements of Mali and the Ahaggar.
Zusammenfassung Die Gesteine der Maru- und Anka-Region im nordwestlichen Nigeria umfassen eine Grundgebirgsserie mit Migmatit-Gneisen, in die eine schwach metamorphe Metasedimentserie eingefaltet ist. Beide Serien werden von synbis spättektonischen Graniten und Granodioriten durchdrungen.Aus der abweichenden Lithologie und den Altersdatierungen folgt, da mindestens 3 sedimentäre Zyklen in den Metasedimenten von Anka und Maru vorliegen. Es wird versucht, diese 3 Zyklen mit der Kibaran (ca. 1100 m. y.) und der Pan African Orogenese (ca. 550 m. y.) zu korrelieren.Strukturelle Ähnlichkeiten zwischen den beiden Regionen erklären sich aus einer Reaktivierung des Kibaran-Grundgebirges während der Pan-African-Orogenese.Kalkalkali-Vulkanite von Pan-African-Alter sind auf die Anka-Region beschränkt. Der Vulkanismus der Anka-Region ist nicht nur von einer spätorogenen Phase geprägt, es liegen vielmehr vulkano-sedimentäre Serien vor, die von sauren bis intermediären Gängen durchdrungen werden, die wiederum von der Pan-African Orogenese erfaßt werden. Ein syemitischer Plutonismus ist auf die Maru-Region beschränkt und dort als posttektonisch anzusehen.Das Auftreten einer Kibaran-Orogenese im Grundgebirge von NW-Nigeria steht im Einklang mit Beobachtungen aus anderen Teilen Nigerias, Malis und Ahaggars.
Résumé Les roches des régions de Maru et d'Anka du nord-ouest de la Nigérie comprennent une série de socle polycyclique avec gneiss migmatitiques, au sein de laquelle une couverture de métasédiments faiblement métamorphiques est impliquée par plissement. Socle et couverture sont recoupés par une série d'intrusions granitiques et granodioritiques, snytectoniques á tardi-tectoniques.Le contraste des lithologies et les données géochronologiques permettent de penser qu'au moins 3 périodes de dépôt pourraient être représentées parmi les métasédiments peu métamorphiques de la région de Maru et d'Anka. Un essai est tenté de corréler ces 3 cycles avec de Kibarien (c. 1100 M.) et le Panafricain (c. 550 M.).On peut expliquer les ressemblances structurales entre les deux zones par une réactivation des structures du socle kibarien pendant l'époque panafricaine.Les volcanites cale-alcalines du Panafricain tardif se limitent à la zone d'Anka. Les travaux récents montrent que le volcanisme de la zone d'Anka n'est pas du tout d'un type orogénique tardif; il s'agit d'en ensemble volcano-sédimentaire pouvant renfermer des tuffs cristalins, récoupé par des filons et des sills acides à intermédiaires, et déformé au cours du Panafricain. Le plutonisme syénitique confiné à la zone de Maru apparaît comme post-tectonique.L'enregistrement d'un évènement kibarien dans le socle du nord-ouest de la Nigérie est en accord avec les résultats des recherches mentionnant un évènement semblable dans d'autres parties du socle nigérien et dans les socles précambriens du Mali et d'Ahaggar.
- - . , - - . . — 1100 — — 550 . - .- - . , - : - , , - . - . - , .
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12.
The marble band of supposedly Raialo (Precambrian) age around Rajnagar in the Udaipur district of Rajasthan represents a large isoclinal fold with the two limbs coalesced and with the terminations marking the sharp hinges. The arcuate map pattern is due to coaxial refolding of the axial surface of the isoclinal fold, on which open, NNE-trending upright folds have been overprinted. The isoclinal folds of small scale are reclined or inclined in style and plunge gently westward where not involved in the upright folding. The axes of the isoclinal folds have been scattered by superposed folding, so that some of the isoclinal folds now plunge even to the south. The plunge of the upright folds is gentler and steeper in the limb zones of reclined and inclined isoclinal folds respectively. Subvertical upright folds occur only in the hinges of the westerly trending reclined folds. Interference patterns of dome-and-basin type and mirror-image type have formed in zones where both hinges and limbs of the early folds have been affected by upright folding. The structure of the marble band, the stratigraphic relations that the marble bears with the supposedly older Aravalli mica schists and migmatites of the Banded Gneissic Complex engulfing it, and the stratigraphic findings in adjacent terrains indicate that the Banded Gneissic Complex represents migmatized portions of the metasediments of the Aravalli and the Raialo groups, and is not the basement rock in central Rajasthan. Evidence for granitic rocks of at least two generations in the Early Precambrians of central Rajasthan is adduced.
Zusammenfassung Das Marmorband von vermutlichem Raialo-Alter (Präkambrium) in der Gegend um Rajnagar, Udaipur-Distrikt, Rajasthan, bildet eine große isoklinale Falte, deren beide Flanken sich zu einem scharfen Scharnier vereinigten. Das bogenförmige Muster auf der Karte entstand durch koaxiale Wiederfaltung der Axialfläche der isoklinalen Falte; auf dieser sind offene NNE-streichende senkrechte Falten überlagert. Die kleineren isoklinalen Falten liegen oder sind geneigt und tauchen flach nach W, soweit sie nicht in die senkrechte Faltung eingeschlossen sind. Die Achsen der isoklinalen Falten sind gestört durch überlagerte Faltung, so daß einige der isoklinalen Falten jetzt sogar nach Süden eintauchen. Das Eintauchen der senkrechten Falten ist flach an den Flanken der liegenden Falten und steil an den Flanken der geneigten Falten. Senkrecht abtauchende Falten treten nur in den Scharnieren der nach Westen streichenden, liegenden Falten auf. Überlagerungsmuster vom Dom-und-Becken-Typ und Spiegelbild-Typ bildeten sich in Zonen, wo die Scharniere und die Flanken der früheren Falten durch senkrechte Faltung beeinflußt worden sind. Die Struktur des Marmorbandes wie auch die stratigraphischen Wechselbeziehungen zwischen dem Marmor und dem vermutlich älteren Aravalli-Glimmerschiefer sowie den Migmatiten des gebänderten Gneiskomplexes weisen zusammen mit stratigraphischen Funden aus angrenzenden Gebieten darauf hin, daß die Gneise die migmatisierten Teile der Metasedimente der Aravalli- und der Raialogruppe darstellen und daß sie nicht das älteste Grundgebirge (Basement) von Zentral-Rajasthan sind. Hinweise für das Auftreten von Granitgesteinen von mindestens zwei Generationen des Frühpräkambriums von Zentral-Rajasthan werden angeführt.
Résumé La couche de marbre du précambrien présumé de la région de Rajnagar, district d'Udaipur, Rajasthan, forme un grand pli isoclinal dont les deux flancs fusionnent en une charnière aiguë. Le dessin en arc de la carte résulte d'un replissement coaxial de la surface axiale du pli isoclinal. Là, se superposent des plis ouverts, perpendiculaires, de direction NNE. Les plus petits plis isoclinaux sont couchés ou sont inclinés en nappes plongeantes vers l'Ouest jusqu'à ce que le pli vertical les englobe.Les axes des plis isoclinaux sont interrompus par un second plissement plus récent de sorte que quelques uns d'entre eux plongent. même aujourd'hui, vers le sud.L'inclinaison des plis verticaux est douce du côté des plis couchés et à pic du côté des plis inclinés. Des plis verticaux plongeants ne se présentent que dans les charnières des plis couchés et dirigés vers l'Ouest. La superposition des dessins de dôme et bassin-type avec le reflet-type se produisit dans les zônes où les charnières et les flancs des plis primitifs subirent l'influence des plis verticaux.La structure de la couche de marbre, les rapports des variations stratigraphiques entre le marbre et le mica-schiste, présumé plus âgé d'Aravalli, ainsi que le matériel métatectique du complexe rubané de gneiss indiquent en accord avec les fossiles de régions limitrophes, que les gneiss représentent les parties migmatisées des métasédiments des groupes Aravalli et Raialo et qu'ils ne forment pas le plus ancien socle du Rajasthan Central.
, , Raialo ( ) Rajnagar, Udaipur, Rajasthan, , . , , NNE. , , , . ; . , . . , , . , Aravalli, , , blli Raialo; Rajasthan. , - , Kajasthan'e.
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13.
The rocks of the Nasafjäll Window comprise Proterozoic granitoids with a metasedimentary cover of Late Precambrian to Ordovician age, the Mierkenis Group. The metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part. The metamorphic maximum is syn- to post-kinematic in relation to the formation of the thrust-related pervasive foliation. This suggests a rapid basement heating in response to the Late Silurian to Early Devonian nappe emplacement. The Caledonian metamorphism terminated in Middle Devonian times and the retrograde phase was characterized by decompression. This implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the Nasafjäll Window.
Zusammenfassung Die Gesteine im Nasafjällfenster in den nördlichen Skandinavischen Kaledoniden bestehen aus proterozoischen Granitoiden mit einer spätpräkambrischen bis ordovicischen Decke, der Mierkenis Gruppe. Im Fenster erhöht sich der Metamorphosengrad von der Grünschieferfazies im Osten zur Amphibolitfazies im Westen. Bezüglich der penetrativen Verschieferung, die während der Überschiebungen entstanden ist, ist das metamorphe Maximum synbis post-kinematisch. Zur Erklärung dieser Beobachtungen ist vorgeschlagen, daß zur Folge der spätsilurischen bis frühdevonischen Überschiebungen sich die Temperatur des Grundgebirges schnell erhöhte. Die kaledonische metamorphe Phase war von Druckentlastung geprägt. Diese Interpretationen schlagen auch vor, daß die späteren Stadien der Überschiebungen nicht mit einer Zunahme der Mächtigkeit von der Überschiebungsdecke verbunden waren.
Résumé Les roches de la fenêtre de Nasafjäll (Calédonides scandinaves) comprennent des granitoïdes protérozoïques et une couverture métasédimentaire d'âge précambrien supérieur à ordovicien. Ces métasédiments font partie du groupe Mierkenis. Le degré métamorphique varie du faciès des schistes verts dans l'est de la fenêtre au faciès des amphibolites dans l'ouest. Le métamorphisme maximal est syn- à post-cinématique; il est lié à la genèse de la schistosité pénétrative, en relation avec le charriage. Cette observation suggère un échauffement rapide du socle consécutif à la mise en place de la nappe au Silurien supérieur et au Dévonien inférieur. Le métamorphisme calédonien a pris fin au Dévonien moyen et sa phase rétrograde a été caractérisée par une baisse de la pression. En conséquence, la dernière phase du charriage n'a pas été associée à une augmentation de l'épaisseur de la nappe sur les roches de la fenêtre de Nasafjäll.
Nasfjäll — Mierkenis. . , , . , . . , .
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14.
A suite of vanadian magnesiochromites from the Sludyanka metamorphic complex (South Lake Baikal, Russia) were investigated by means of X-ray single-crystal structural refinements and microprobe analyses. Various morphological types of Cr–V-bearing Mg spinels are located in calc–silicate metamorphic rocks, in an assemblage that also contains other Cr–V minerals such as escolaite–karelianite, uvarovite–goldmanite, Cr–V-bearing clinopyroxene, tourmaline, amphibole, mica, etc. Along the suite there is widespread V–Cr substitution (0.14 V3+ 0.95 afu, 1.02 Cr3+ 1.80 afu), and minor, variable Al contents. The Mg content of slightly lesser than 1 afu, is almost constant. Cell parameters and octahedral bond distances increase with V3+. Unexpectedly, the Mg–O tetrahedral bond distance also increases slowly with V3+. This weak dragging effect contributes towards maintaining distortion of the oxygen array with respect to the ideal CCP, thus providing a shielding effect, which reduces V3+–V3+ repulsion. This leads to the energetic stabilization of the structure, in spite of the increase of bond strain with increasing V3+ contents.  相似文献   

15.
The concept of self-organizedcriticality evolved from studies of three simplecellular-automata models: the sand-pile, slider-block,and forest-fire models. In each case, there is asteady input and the loss is associated with afractal (power-law) distribution of avalanches. Each of the three models can be associated with animportant natural hazard: the sand-pile model withlandslides, the slider-block model with earthquakes,and the forest-fire model with forest fires. We showthat each of the three natural hazards havefrequency-size statistics that are well approximatedby power-law distributions. The model behaviorsuggests that the recurrence interval for a severeevent can be estimated by extrapolating the observedfrequency-size distribution of small and mediumevents. For example, the recurrence interval for amagnitude seven earthquake can be obtained directlyfrom the observed frequency of occurrence of magnitudefour earthquakes. This concept leads to thedefinition of a seismic intensity factor. Both globaland regional maps of this seismic intensity factor aregiven. In addition, the behavior of the modelssuggests that the risk of occurrence of large eventscan be substantially reduced if small events areencouraged. For example, if small forest fires areallowed to burn, the risk of a large forest fire issubstantially reduced.  相似文献   

16.
Zusammenfassung Durch Kartierung in der südlichen Serra do Espinhaço in Minas Gerais, Brasilien, konnten laterale Fazies-Übergänge zwischen mio -und eugeosynklinalen Metasedimenten der proterozoischen Minas-Serie bestätigt werden. Der Übergangsbereich ist durch±mächtige Itabirite sowie einen ausgeprägten Magmatismus gekennzeichnet. Die Metamagmatite bilden mit sauren bis ultrabasischen Gesteinen eine ±vollständige alpinotype Assoziation desinitialen Magmatismus. Fazieswechsel und Magmatismus weisen die Ablagerungen der Minas-Serie als Bildungen einer Orthogeosynklinale aus.
Geological fieldwork in the southern part of the Serra do Espinhaço, Minas Gerais, Brazil confirmed lateral facies transitions between mio- and eugeosynclinal metasediments of the Proterozoic Minas Series.The miogeosyncline is formed by thick quartzites, phyllites, and diamond bearing conglomerates. This sequence reaches a total thickness of 5000 m or more. The eugeosyncline consists of gneisses which probably originate from graywackes and similar sediments. The transition of facies is well shown by a stratigraphic unit which can be followed for approx. 100 km along strike. This unit, located in the east of the mapped area, is formed by quartzites, phyllites, and diamond bearing conglomerates in its northern part, whereas to the south it gradually changes to predominantly phyllites and ferruginous quartzites with intraformational beds of itabirites (iron formation). Even in the southernmost part, some conglomerates are still intercalated within the itabirites.The transition zone is characterized in addition by metamorphosed igneous rocks, which range chemically from acid to ultramafic. There are four types: rhyolitic metavolcanites, hematite phyllites, green schists, and ultramafic rocks. The latter are often altered to talc-carbonate rocks (soapstone), due to CO2-metasomatism. The occurrence of this nearly complete magmatic sequence at an early geosynclinal stage within the Minas Series of Eastern Brazil is pointed out for the first time. The close association of the magmatic belt and the itabirites suggests a genetic relation between the volcanic activity and the sedimentation of the iron formation.Both, transition of facies and magmatism, indicate a typical orthogeosynclinal evolution for the Minas Series.
Resumo Um levantamento geológico na Serra do Espinhaço meridional, Minas Gerais, Brasil, confirma a transição lateral das facies entre os metasedimentos mio- e eugeossinclinais da Série Minas.O miogeossinclinal é formado por uma seqüência de quartzitos espêssos, filitos e conglomerados diamantíferos com uma espessura total de 5.000 m ou mais. O eugeossinclinal constitue-se de gnaisses, provàvelmente provenientes de grauvacas e sedimentos similares. Uma unidade estratigráfica, que pode ser acompanhada por aprox. 100 km, mostra nitidamente a transição das fácies. Essa unidade, situada na parte oriental da área em aprêço, é composta de quartzitos, filitos e conglomerados diamantíferos no norte, enquanto que no sul gradualmente começam a predominar os filitos e quartzitos ferruginosos com itabiritos intraformacionais. Mesmo na parte mais meridional os itabiritos ainda têm algumas intercalações de conglomerados.A zona de transição também é caracterizada por metamagmatitos, que variam químicamente de rochas ácidas a ultrabásicas. Existem quatro tipos: efusivas acidas de composiçao riolítica, filitos hematíticos, xistos verdes e rochas ultrabásicas. Estas últimas transformam-se várias vezes em esteatitos (pedra sabão), devido a um metasomatismo de CO2. A ocorrência dessa seqüência magmática quase completa, num estágio eugeossinclinal primário dentro da Série Minas, é ressaltada pela primeira vez. A associação estreita da faixa magmática com os itabiritos indica uma relação genética entre a atividade vulcânica e a sedimentaçâo dos itabiritos.Ambos, transição das fácies e magmatismo, mostram a existência de um ortogeossinclinal típico durante a formação da Série Minas.
Serra do Espinhaco Minas Cerais, , , , Minas. , . , , , . , Minas .
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17.
Compositional Data Analysis of Some Alkaline Glasses   总被引：1，自引：0，他引：1  
The approach to the analysis of compositional data involving log-ratio transformation of the data has not been generally adopted by researchers wishing to analyse such data. In the context of exploratory methods of multivariate analysis, such as principal components analysis, where the hope is to identify (cluster) structure in the data, this may be because traditional methods can produce more interpretable results than the log-ratio approach. After illustrating this with an example, circumstances under which the log-ratio approach performs poorly when traditional approaches work well are identified. Log-ratio analysis can be dominated by variables having low absolute presence and high relative variation that do not contribute to, and can obscure, structure in the data. Traditional methods can detect certain kinds of structure in the data that correspond to structure on a ratio scale, after a suitable redefinition of the composition. Since traditional methods often detect such structure more directly than log-ratio analysis it can be concluded that claims that the traditional analysis is inappropriate or meaningless are exaggerated. This conclusion is based on empirical experience rather than theoretical concerns. The arguments are illustrated using compositional data for alkaline glasses, but have more general application.  相似文献   

18.
Hydrolysis constants of dimethyltin(IV) cation, in different salt solutions (CaCl2: 0.15 I 0.90; MgCl2: 0.30 I 0.60; NaCl-–NaClO4, NaCl-–NaNO3 mixtures: I = 3; NaCl-–Na2SO4 mixtures: I = 1 mol dm-3) were determined by potentiometric ([H+]-glass electrode) measurements. These data, together with previous data (De Stefano et al., 1996b) were interpreted in terms of DHT (Debye–Hückel type) and Pitzer equations. The mixed electrolyte solution results also allowed us to obtain and parameters for the Pitzer equation. Calorimetric measurements were made at different ionic strengths in order to find the temperature dependence of hydrolysis constants and of the relative interaction parameters. The body of results allows us to determine the speciation of natural waters in a wide range of ionic strengths and temperatures.  相似文献   

19.
Repeat times of strong intermediate depth (60 km h 180 km) earthquakes have been determined by the use of instrumental and historical data for six seismogenic sources in the Benioff zone of the southern Aegean area. For four of these sources, at least two interevent times (three mainshocks) are available for each source. By using the repeat times for these four sources, the following relation has been determined: logT t = 0.20M min + 0.19M p +a, whereT t is the repeat time (in years),M min the surface wave magnitude of the smallest earthquake considered,M p the magnitude of the preceding mainshock and a parameter which varies from source to source. A multilinear correlation coefficient equal to 0.91 was determined for this relation, which indicates that the time predictable model holds to a satisfactory degree for the strong mainshocks of intermediate focal depth in the southern Aegean.By assuming that the ratioT/T t, whereT is the observed andT t the calculated repeat time, follows a lognormal distribution, the conditional probabilities for the occurrence of strong (M s 6.5) and very strong (M s 7.5) earthquakes during the period 1991–2001 in these four seismogenic sources have been calculated. These probabilities are very high (P > 0.9) for the strong and high (P > 0.5) for the very strong intermediate depth earthquakes which occur in the three sources of the shallower (h < 100 km) part of the Benioff zone where coupling occurs between the front parts of the Mediterranean lithosphere (downgoing) and the Aegean lithosphere.  相似文献   

20.
An understanding of the irregular coordination polyhedra exhibited by the M2 cations in clinopyroxenes is of prime importance in connection with the behaviour of solid solutions and polymorphism in pyroxenes.As shown by unfolding the silica chains in pigeonite, cations with octahedral stereochemistry like Mg++and Fe++ cause kinking of the silica chains, whereas larger cations like Ca++and Na+have an opposite namely straightening effect. This is a probable factor causing immiscibility in the Mg++-Ca++ solid solutions in pyroxenes. In pyroxene structures with kinked silica chains the arrangement of oxygen atoms approaches close packing; consequently different stacking sequences will be energetically possible leading to polymorphism in pyroxenes.When Pauling's electrostatic valence rule is applied to clinopyroxenes, the charge balance will be exceedingly improved if effective coordination number of M2 cation is assigned and if the distortions of M 2 coordination polyhedron is considered.  相似文献   

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