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1.
Evolution of Shear-Zone Structure in Undrained Ring-Shear Tests   总被引：4，自引：4，他引：0  
Undrained monotonic torque-controlled tests were conducted on fine-grained silica sand to study the shear-deformation process in granular materials by using a ring-shear apparatus. Shear-zone structures at various stages in the undrained shear tests were observed during a series of tests in which the experiments were terminated at different shear displacement. For undisturbed samples, the shear zone was only developed during the post-failure stage and its thickness increased with progressed shearing. First the shear surfaces had undulating and asymmetric structures; later they gradually became smooth and parallel to the shearing direction. During this process, pore water pressure was generated, and the effective friction angle decreased correspondingly. Generally, the shear zone could be divided into three parts: the compacted core, the adjacent zone above the core, and the adjacent zone below the core. Grain-size analysis on the sample from the shear zone revealed that grain crushing occurred during each stage and the extent of grain crushing differed for different shear stages. An interesting phenomenon occurred during the steady-state deformation where the coarse and fine particles within the shear zone segregated during motions and a parallel orientation structure developed. These results are helpful for understanding the mechanism of progressive failure in granular material as well as the rapid landslide with long runout study.  相似文献   

2.
An experimental investigation of olivine morphology   总被引：1，自引：0，他引：1  
Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines hopper olivines branching olivines randomly oriented chain olivines parallel-growth chain olivines chain+lattice olivines plate or feather olivines, with increase in cooling rate and with increase in degree of supercooling. This sequence involves changes from complete to progressively less complete crystals and from equant habit to elongate bladed habit (c>ab) to tabular habit (ac b). The sequence is not affected by the phase relations of the melt. The larger the olivine content of a melt the slower the cooling rate at which a particular olivine shape grows, whereas the lower the melt viscosity, the greater the cooling rate. Irrespective of the melt composition, comparable crystal shapes grow at the same degrees of supercooling. By comparison of the shapes of olivine crystals in experiments with those in rocks of similar composition, it is possible to deduce the cooling rate through the olivine crystallization interval and the approximate degree of supercooling at which the olivine crystals nucleated and grew in the rocks. The various shapes of skeletal olivines in many picrites, olivine-rich basalts and the Archaean spinifex rocks are not due to rapid cooling, but to rapid olivine growth caused by the high normative olivine content of the magma.  相似文献   

3.
The Proterozoic basement of the Province of Zambezia (Mozambique) is located near the southern end of the so called Mozambique Belt. Rb-Sr data derived from the analyses of 66 whole rocks and a few mineral samples bear witness of a magmatic and metamorphic episode referable to the Kibaran (ca. 1000 Ma) and helped to model the late-Proterozoic evolution as follows. At 1100–1050 Ma a pre-orogenic, calc-alkaline magmatism was responsible for the emplacement of now deformed granite and granodiorite. This phase was accompanied by rhyolitic volcanism. A subsequent peak of deformation and metamorphism occurred at 1000-950 Ma and was associated with a second generation of substantially post-tectonic granites. A thermal event resulting in the emplacement of a final generation of granites and pegmatites can be dated to around 500-450 Ma.The metamorphic basement has not preserved its protolith age, probably as a result of extensive isotopic homogeneization of Sr in Kibaran times. Its maximum time of differentiation from the mantle should be around 1600 Ma.The very low values of initial Sr isotopic ratios suggest the absence of Archean crustal precursors and support the rather young, yet pre-Pan-African evolution of the southernmost Mozambique Belt.
Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in der Nähe des südlichen Endes des sogenannten Mozambique Belt. Rb/Sr Daten aus 66 Ganzgesteins- und einigen Mineralanalysen zeugen von einer magmatischen und metamorphen Episode die sich dem Kibaran (ca. 1000 Ma) zuordnen läßt, und wie sich im folgenden zeigt, hilfreich bei der Modellisierung der spätproterozoischen Entwicklung ist. Um 1100 bis 1050 Ma erfolgte ein präorogener kalkalkalischer Magmatismus, bestehend aus Graniten und Granodioriten, die heute deformiert vorliegen. Diese Phase wurde von rhyolithischem Vulkanismus begleitet. Von 1000 bis 950 Ma folgte der Höhepunkt der Deformation und Metamorphose, begleitet von einer bedeutenden 2. Generation posttektonischer Granite. Bedingt durch ein weiteres thermales Ereignis intrudierte die letzte Granit- und Pegmatitgeneration vor 500 bis 450 Ma.Im metamorphen Grundgebirge ist das Eduktalter vermutlich aufgrund der starken isotopischen Homogenisierung von Sr während der Kibara-Zeit nicht erhalten. Seine maximale Differentiationszeit vom Mantel muß vor 1600 Ma gewesen sein.Die sehr niedrigen Gehalte der initialen Sr-Isotopenverhältnisse lassen die Abwesenheit von archaischen Krustenvorläufern vermuten, und unterstützen die sehr junge, bis jetzt Prä-Pan-Afrikanische Entwicklung des südlichsten Mozambique Belts.
Résumé Le socle protérozoïque de la province du Zambèze, au Mozambique, se trouve à proximité de l'extrémité sud du «Mozambique Belt». Des mesures Rb/Sr effectuées sur 66 roches totales et sur quelques minéraux témoignent d'un épisode magmatique et métamorphique attribuable au Kibarien (environ 1.000 Ma), ce qui permet de se représenter comme suit l'histoire de cette région au Protérozoïque supérieur. Il y a 1.100 à 1.050 Ma, la région a connu une phase de magmatisme calco-alcalin qui s'est traduite par la mise en place de granites et granodiorites, aujord'hui déformés. Cette phase s'est accompagnée d'un volcanisme rhyolitique. Elle a été suivie, entre 1.000 et 950 Ma, d'une activité tectono-métamorphique majeure, à laquelle est associée une deuxième et importante génération de granites, post-tectoniques. Ultérieurement, la région a connu encore un épisode thermique, daté à 500-450 Ma, responsable de la mise en place d'une dernière génération de granite et de pegmatite.Le socle métamorphique n'a pas gardé de témoins de l'âge de son protolithe, en raison probablement de la forte homogénisation isotopique du Sr à l'époque kibarienne. Lâge maximal de sa différenciation à partir du manteau doit se situer autour de 1.600 Ma.La valeur très basse des rapports isotopiques initiaux du Sr suggère l'absence de précurseurs crustaux archéens et incite à admettre une évolution relativement jeune — bien que pré-panafricaine — du «Mozambique Belt» méridional.
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4.
Generalized development of calc-silicate bands in several alpujarride units of the central and western segments of the Betic Zone, is interpreted as the result of metamorphic differentiation from original calcium-rich sedimentary beds in the sequence. Presence of Scapolite suggests that this phenomenon may have been made possible by the catalizing action of high anion concentrations in the pore fluid medium during metamorphism, probably caused by the existence of evaporic material in the original sediments. This hypothesis, which is further supported by anomalous high Ca, Na and K contents of the enclosing metapelites, leads to the correlation of the present calc-silicate bearing metamorphic formations with well-known permo-werfenian evaporitic series in other units of the Betic Zone. The use of this new criterion of stratigraphic correlation would indicate that highly metamorphosed permo-triassic sequences have often been misidentified as more ancient formations, thus causing an underestimation of the importance of alpine HT-LP metamorphism in the alpujarride tectonic domain.
Zusammenfassung Das häufige Auftreten von Kalksilikatbändern (manchmal mit Skapolith) in einigen alpujarriden Einheiten, besonders im zentralen und westlichen Abschnitt der betischen Kordillere, wird erklärt als Ergebnis einer metamorphen Differentiation von ursprünglich Ca-reichen Schichten. Die Anwesenheit von Skapolith legt eine hohe Anionenkonzentration der intergranularen fluiden Phasen während der Metamorphose nahe, bedingt durch evaporitisches Material der ursprünglichen Sedimente. Diese Hypothese, zusätzlich gestützt durch den extrem hohen Gehalt der umgebenden Pelite an löslichen Kathionen (Ca, Na, K), erlaubt die Korrelation der Kalksilikatbänder-haltigen Formationen mit aus anderen betischen Einheiten bekannten evaporitischen Serien des Permowerfenïan. Auf die stratigraphische Korrelation angewendet, legt dies nahe, daß öfters hochmetamorphe, permotriadische Serien fälschlicherweise als älter betrachtet wurden, was zu einer Unterschätzung der alpinen Metamorphose (Niederdruck-Hochtemperatur) im alpujarridem Bereich führte.
Resumen El desarrollo bastante generalizado de bandas de silicatos calcicos, entre los cuales se encuentra a veces una escapolita, en varias unidades alpujárrides de los segmentos central y occidental de la Zona Bética, es interpretado como el resultado de un proceso de diferenciación metamórfica a partir de lechos sedimentarios originalmente ricos en calcio. La presencia de escapolita sugiere que este hecho ha sido probablemente posible gracias a la existencia de una alta concentración de aniones en el fluido metamórfico intergranular, condicionada por la existencia de material evaporitico en los sedimentos originales. Esta última hipótesis que es ulteriormente apoyada por un contenido anómalamente alto de cationes solubles (Ca, Na, K) en las metapelitas encajantes, permite correlacionar las formaciones que contienen los lechos de silicatos calcicos con conocidas series evaporiticas de edad permowerfenense en otras unidades de la Zona Bética. La aplicación de este nuevo criterio de correlación estratigráfica sugiere que series permotriásicas altamente metamorfizadas han sido a menudo erróneamente interpretadas como más antiguas, hecho que ha conllevado a una substimación de la importancia del metamorfismo (BP-AT) alpino en el dominio tectónico alpujárride.
Résumé Le developpement très fréquent de roches litées à silicates calciques dans quelques unités alpujarrides des regions centrale et occidentale de la Zone Bétique, est interpreté comme la conséquence d'un processus de différenciation métamorphique à partir de lits riches en calcium dans les sequences sédimentaires originelles. La présence de scapolite suggére que ce phénomène a été rendu possible par l'intervention d'un cataliseur naturel, tel que des hautes concentrations en anions dans le milieu fluide intergranulaire pendant le métamorphisme, occasionées probablement par l'existence de materiel évaporitique dans les sédiments originels.Cette hypothese, qui se trouve additionellement supportée par des teneurs élevées en cations solubles des métapelites encaissantes, permet d'assimiler les formations qui contiennent les lits à silicates calciques avec des séries évaporitiques permowerféniennes, bien connues dans d'autres unités des zones internes des Cordilléres Bétiques. L'application de ce nouveau critère de corrélation stratigraphique indiquerait que des séquences permotriasiques fortement affectées par le métamorphisme ont été souvent à tort interprétées comme plus anciennes, amenant ainsi a une sous-estimation de l'importance du métamorphisme alpin (BP-HT) dans le domaine tectonique alpujarride.
- — — , , , , . , . , : , Na, , , - Permowerfenian, . , - , — — .
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5.
Zusammenfassung Das Symvolon-Gebirge bei Kavala in Griechisch-Mazedonien wird von einem blastomylonitisch verformten Granitmassiv aufgebaut mit einheitlicher passiver Gefügeregelung. Es sind zwei altersverschiedene Biotite enthalten, nur die primären Biotite zeigen pleochroitische Höfe um Zirkon, die jüngeren, bei der Verformung umkristallisierten Biotite dagegen nicht. Dies spricht für eine bedeutende Differenz zwischen Erstarrung und Deformation. Eine noch jüngere Beanspruchung führt zur Entstehung von Myloniten in Grünschieferfazies. Hervorgehoben wird das Vorkommen junger metasomatischer Aplite, die den gefalteten Bau diskordant durchsetzen.
The Symvolon-Mts. near Kavala (Greece) consist of a granite-complex with blastomylonite-deformation and a uniform, secondary fabric. The rock contains two biotites of different ages of whom only the older type displays pleochroitic halos around Zircons. This might indicate that, the time interval between solidification and, the deformation might have been considerable. A still more recent deformation produced mylonites in a Greenschist Facies. Late metasomatic Aplites cut the whole complex obliquely.
Résumé La chaîne du Symvolon près de Kavala dans la Macédoine grecque est constituée par un massif granitique déformé par voie blasto-mylonitique, avec une régulation structurale passive uniforme. Il contient 2 biotites d'âge différent; seules les biotites primaires montrent des auréoles pléochroïques autor du zircon, à l'inverse des biotites plus jeunes qui ont cristallisé au cours de la déformation. Ceci plaide en faveur d'une notable différence entre consolidation et déformation. Une nouvelle déformation engendre des mylonites à faciès de schistes verts. On souligne l'intervention d4aplites métasomatiques plus jeunes qui recoupent la structure plissée de façon discordante.
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6.
Six sedimentary formations, and two separate members recently were described byJansa, et al. (1979) from the western North Atlantic Ocean basin. We have investigated the mineralogical composition of these lithostratigraphic units by qualitative X-ray diffraction analyses of about five hundred samples from DSDP Sites 105, 106, 386, 387, and 391. The sedimentary section studied, from bottom to top, consists of: argillaceous limestones (Cat Gap Formation); limestones (Blake-Bahama Formation); claystones and shales (Hatteras Formation); zeolitic claystones (Plantagenet Formation); nannofossil marls (Crescent Peaks Member); siliceous oozes, clays, and cherts (Bermuda Rise Formation), and hemipelagic muds (Blake Ridge Formation) that locally contain redeposited shallow-water carbonates (Great Abaco Member). The section ranges in age from Oxfordian at the base to Quaternary at the sea-floor.Most of the formations and members described byJansa, et al. (1979) have a characteristic mineralogical composition. Thus it is possible to recognize boundaries between formations and members by changes in mineral components, although these changes range from sharp to transitional. Within the same formation local differences in mineral spectra between sites can be explained by changing distance from terrigenous sources, lateral changes in surface paleoproductivity, and varying diagenetic conditions.
Zusammenfassung Sechs sedimentäre Formations und zwei dazugehörige Members wurden vor kurzem durchJansa, et al. (1979) aus dem Ozeanboden des westlichen Nordatlantik beschrieben. Wir haben die Mineralzusammensetzung dieser lithostratigraphischen Einheiten anhand von etwa 500 qualitativen röntgenographischen Analysen untersucht; die Proben dazu entstammen den DSDP-Bohrungen 105, 106, 386, 387 und 391. Vom Liegenden zum Hangenden lassen sich folgende Einheiten unterscheiden: Tonige Kalksteine (Cat Gap Formation); Kalksteine (Blake-Bahama Formation); Tonsteine und shales (Hatteras Formation); Zeolithische Tonsteine (Plantagenet Formation); Nannofossil-Mergel (Crescent Peaks Member); Kieselige Schlamme, Tone und Hornsteine (Bermuda Rise Formation) und Hemipelagische Schlamme (Blake Ridge Formation), die lokal umgelagerte Flachwasser-Karbonate (Great Abaco Member) enthalten. Das Gesamtprofil reicht altersmäßig von Oxfordium an der Basis bis zum Quartär.Die meisten der vonJansa, et al. (1979) beschriebenen Formations und Members haben eine charakteristische Mineralzusammensetzung; es ist daher möglich, Grenzen sowohl zwischen Formations als auch zwischen Formations und Members anhand ihrer Mineralkomponenten zu erkennen; der entsprechende Wechsel kann scharf sein oder fließende Übergänge aufweisen. Lokale Unterschiede in den Mineralspektren einer Formation zwischen einzelnen Bohrpunkten lassen sich auf wechselnde Entfernungen vom Liefergebiet bzw. unterschiedliche Liefergebiete selbst, auf laterale Wechsel in der oberflächennahen Paläo-Produktivität und/oder auf unterschiedliche diagenetische Bedingungen zurückführen.
Résumé Six »formations« sédimentaires ainsi que deux »members« séparés ont été ré cemment décrits parJansa, et al. (1979) dans la partie nordouest du bassin de l'océan Atlantique. Nous avons étudié, d'un point de vue qualitatif, la composition minéralogique de ces unités lithostratigraphiques à partir de l'analyse diffractométrique d'environ 500 échantillons provenant des sites DSDP 105, 106, 386, 387 et 391. Les sections sédimentaires examinées comprennent de bas en haut: Des calcaires argileux (Cat Gap Formation); des calcaires (Blake-Bahama Formation); des argilites et des argiles schisteuses (Hatteras Formation); des argilites zéolitiques (Plantagenet Formation); de la marne aux nannofossiles (Crescent Peaks Member); des boues silicieuses, des argiles et du silex (Bermuda Rise Formation), ainsi que des boues hémipélagiques (Blake Ridge Formation) qui contiennent par endroits des carbonates resédimentaires provenant d'un milieu peu profond (Great Abaco Member). Leur âge s'échelonne de l'Oxfordien à la base jusqu'au Quaternaire au fond océanique.La plupart des »formations« et des »members« décrits parJansa, et al. (1979) ont une composition minéralogique caractéristique. Il est donc possible de reconnaître les limites entre des »formations« et des »members« à partir des changements de la composition minéralogique, bien que ces changements varient du net au transitoire. Dans une même formation on peut expliquer les différences locales des spectres minéraux entre les sites, par la variation de distance des sources terrigènes, des changements latéraux de la paléoproductivité de surface et des conditions diagénétiques variables.
Jansa . (1979) 6 2 . 500 . 105, 106, 386, 387, 391. : — Cat Gap —, — Blake-Bahama —, — Hatteras'a —, — Plantagenet —, - — Crescent Peaks —, , — Bermuda Rise — — Blake Ridge —, — Great Abaco. . Jansa ; , , , . , ., , / .
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7.
A discussion is made on the general significance of an Early Miocene (22–23 Ma, K/Ar dating) basaltic dike swarm that outcrops within large areas of the central and western Betic Zone of the Betic Cordilleras (Southern Spain). This dike swarm is thought to represent the remains of one of the earliest magmatic episodes within the the Neogene volcanic province that is associated with the late orogenic evolution of the Alboran region, and undoubtedly offers the best preserved igneous material related to this early stage that is known at present. The dike rocks (hypabyssal equivalents of andesitic basalts and basaltic andésites) have both major and trace-element abundance patterns that are akin to those of arc-tholeiitic suites. The field relationships and areal distribution of the dike swarm suggest, on the other hand, that a major E-W-trending rifting belt could have been developing within the Alboran Block in oligo-miocene times, previous to its collision with adjacent continental borderlands in the Early-Middle Miocene.Because of their magmatic character and wide distribution, it is proposed that these dike rocks may be regarded as an indication of the existence of roughly contemporaneous (Oligo-Miocene) Benioff-Wadati zone activity under the Alboran Area, which also points towards the previous existence of subductable lithosphere in its surroundings. The main dilatational vector during dike emplacement was already normal to the present E-W stretching of the Alboran Basin proper, which also adds to the possibility that the latter had already started to individualize tectonically in Oligo-Miocene times, and that some of its present crustal features, especially a prominent E-W-trending pattern of magnetic anomalies, had been generated in relation with the dike event. Continued postcollisional Middle Miocene to Pliocene calc-alkaline to ultrapotassic volcanism in the same area could hence have resulted from decompression partial melting of an already contaminated, and still thermally anomalous, mantle wedge, connected with the occurrence of traverse strike-slip and extensional deep faulting within a crustal segment that stretches from southeastern Spain to Morocco.
Zusammenfassung Über die generelle Bedeutung einer Vielzahl von Gängen (22–23 Ma, K/Ar-Datierung) wird diskutiert, die in einem weiten Gebiet der Betischen Zone aufgeschlossen sind. Diese Vielzahl von Gängen repräsentiert wahrscheinlich eine der ersten magmatischen Episoden innerhalb der vulkanischen neogenen Provinz, welche mit der späten tektonischen Entwicklung der Region des Alboranischen Meeres verbunden ist. Diese Gänge bieten in jedem Fall das besterhaltene magmatische Material, verglichen mit denen, die man bis jetzt kennt. Die Gesteine, die diese Gänge bilden (hypoabyssiche Aequivalente andesitischer Basalte und basaltischer Andesite), besitzen ebenso Hauptelemente wie auch Spurenelemente, die den Tholeiit-Serien der Inselbögen ähnlich sind. Ihre Flächenverteilung und Feldbeziehungen geben auch an, daß ein ausgedehnter Gürtel in der Zone von Alboran in oligo-miozänen Zeiten in Entwicklung war, bevor sich der Zusammenstoß des sogenannten Alboranblocks mit der naheliegenden Kontinentalzone im unteren-mittleren Miozän produzierte.Diese Gesteine geben das gleichzeitige Vorhandensein einer Benioff-Wadati-Zone aktiv unter der Region von Alboran an, sowohl auf Grund ihres magmatischen Aussehens wie auch auf Grund ihrer weiten Flächenverteilung, und deshalb zeigen sie auch die vorige Existenz subduktionsfähiger Lithosphäre in ihrer Nähe. Der Hauptdilatationsvektor war schon während der Intrusion der Gänge normal zur jetzigen Elongation des Alboran-Beckens gerichtet, was auch vermuten läßt, daß jenes Becken schon während des Oligozäns oder des unteren Miozäns begonnen hatte, sich tektonisch zu individualisieren. In diesem Fall könnte die durch die Gänge repräsentierte vulkanische Episode einige der Charakteristika der dem Becken unterliegenden Kruste erklären und speziell das Vorhandensein eines wichtigen Netzes von magnetischen Anomalien, das Ost-West verläuft. Die spätere Entwicklung des Vulkanismus in dieser Provinz konnte sich aus der Partialschmelzung einer vorher kontaminierten und sogar thermisch anomalen Zone des Mantels ergeben haben, verbunden mit dem Wirken von Verwerfungen und zerrenden Brüchen in einem lithosphärischen Gürtel, der sich vom Südosten der Iberischen Halbinsel bis Marokko ausbreitet.
Resumen Se hace una discusión sobre la significación general de un enjambre de diques (22–23 M.a., datación K/Ar) que aflora en una amplia extensión de la Zona Bética (Cordilleras Béticas, España Meridional). Este enjambre de diques représenta probablemente uno de los primeras episodios magmáticos dentro de la provincia volcánica neógena asociada a la evolución orogénica tardia de la región del Mar de Alborán, y ofrece en todo caso el material igneo mejor preservado en relación con este estadio de los conocidos hasta el presente. Las rocas que constituyen los diques (equivalentes hipoabisales de basaltos andesiticos y andesitas basálticas) poseen caracteres geoquímicos tanto de elementos mayores como de trazas que son afines a los de las series toleáticas de arcos insulares. Su distribución areal y relaciones de campo indican, por otra parte, que una banda dilatacional podría haberse estado desarrollando en el área de Alborán en tiempos oligo-miocenos, con anterioridad a la colisión del Bloque de Alborán con las áreas continentales adyacentes en el Mioceno Inferior-Medio.A causa tanto de su afinidad magmática como de su amplia distribución areal, estas rocas vienen a indicar la existencia, contemporánea, de una zona de Benioff-Wadati activa bajo la región de Alborán y, por ende, la presencia previa de litosfera subducible en sus inmediaciones. El principal vector dilatacional durante la intrusión de los diques era ya normal a la actual elongación de la cuenca de Alborán, lo cual también sugiere la posibilidad de que aquella hubiese comenzado a individualizarse tectónicamente durante el Oligoceno ó Mioceno Inferior. En tal caso el episodio volcico representado por los diques podría explicar algunas de las características de la corteza subyacente a esta cuenca, y en especial la existencia de una prominente red de anomalias magnéticas de dirección E-W, paralela a la red de dikes. El desarrollo posterior del volcanismo en esta provincia podria haber resultado de la fusión partial de una zona del manto previamente contaminada, y aún térmicamente anómala, en conexión con la actuación de desgarres y fracturación distensiva en una banda litosférica que se extiende desde el sureste de la peninsula ibérica hasta Marruecos.
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8.
In the sedimentary sequence of the Lower Himalayas monotonous geosynclinal deposits are overlain by various shallow-water deposits and a carbonate rock complex at the top. The age of this nonfossiliferous sequence is discussed. Transgressive Jurassic-Tertiary beds are evidence for a minimum thrust distance of 90 km of the Chail Nappes. The facies distribution points to the importance of an axis parallel to the Himalayan strike direction since Lower Paleozoic at least. The metamorphism of the overthrust units is described and the relation to the evolution of the orogen is discussed. An outline of the structure is given. The type of deformation and other features characteristic of the different tectonic units, as well as the relationship to the geology of the whole Himalayas are discussed. It is emphasized that structural development during the Himalayan orogenesis was largely determined by the earlier paleogeographic history. The picture of the structural development in successive stages is given.
Zusammenfassung In der Sedimentfolge des Niederen Himalaya folgen über einförmigen Geosynklinalsedimenten wechselhafte Scichtwassersedimente mit einem abschließenden Karbonatgesteinskomplex. Das Alter dieser fossilleeren Schichtfolge ist noch nicht endgültig gesichert und wird diskutiert. Darüber liegen transgressiv Jura-Tertiär, deren Vorkommen bis 90 km unter die überschobenen Einheiten nach N reichen. Aus der Faziesanordnung ergibt sich eine Anlage der Himalaya-streichrichtung schon mindestens seit dem Altpaläozoikum. Die Metamorphose der überschobenen Decken wird beschrieben und die Möglichkeiten des Zusammenhanges mit der Orogenentwicklung diskutiert. Es werden die Grundzüge des tektonischen Baues, der charakteristische tektonische Stil der einzelnen Einheiten und deren Beziehungen zur Geologie des gesamten Himalayas beschrieben. Die Entwicklung während der Himalayaorogenese ist stark von der paläogeographischen Ausgangssituation bestimmt. Ein Bild der tektonischen Entwicklung in aufeinanderfolgenden Stadien wird gegeben.
Résumé Dans la séquence sédimentaire du Bas Himalaya les sédiments géosynclinaux monotones sont couverts par des dépôts variables de faciès peu profond qui se terminent avec un ensemble de roches carbonatées. L'âge de cette séquence de couches non fossilifères n'est pas encore fixé et sera discuté. Audessus se trouvent des couches transgressives du Jurassique au Tertiaire qui s'étendent vers le N jusqu'à 90 km au-dessous des nappes chevauchantes. La position des faciès montre que la direction axiale du Himalaya existe au moins depuis le Paléozoique inférieur. Le metamorphisme des nappes charriées est décrit et les possibilités d'une connection avec l'évolution orogénique sont discutées. Les principaux traits de la structure et le style téctonique caractéristique des différentes unités ainsi que leur position dans l'ensemble géologique du Himalaya sont décrits. L'orogénèse du Himalaya est déterminée notamment par la situation paléogéographique. Enfin les différentes phases de l'évolution tectonique sont décrites.
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9.
Gediz Graben is an important area for geothermal activity in Turkey. Menderes Massif rocks consisting of gneisses, schists, marbles and granodiorite, comprise the aquifers of the geothermal systems. Neogene terrestrial sediments made up mainly of sandy and clayey conglomerates cap the systems. Gediz Graben geothermal areas are physically divided into seven main groups: Turgutlu-Urganl, Sart-Çamur, Caferbeyli, Üfürük, Kurunlu, Kavakldere-Sazdere and Alaehir geothermal areas. The third highest aquifer in Turkey temperature (182 °C) after Kzldere (242 °C) and Germencik (232 °C) was discovered in the Kavakldere-Sazdere area. The thermomineral waters of the Gediz Graben geothermal areas have outlet temperatures of 25–95 °C and an electrical conductivity of 874–6020 S/cm. Mineralization is mostly dominated by Na+ (188–2027 ppm) and HCO3– (544–2950 ppm). Kavakldere-Sazdere area shows the highest boron content among the entire geothermal aquifers of Turkey. Major geochemical processes for thermomineral waters are carbonate and silicate dissolution and mixing.  相似文献   

10.
Shear zones in granular material   总被引：2，自引：0，他引：2  
Summary Shear Zones in Granular Materials. An Experimental Study of Their Structure and Mechanical GenesisA special ring-shear apparatus was designed to study in granular materials under continued shearing the development of shear zones and the accompanying changes in texture and stress state.Various series of experiments were run with densely packed, cohesionless materials in both dry and fluid-saturated states. For comparison, in a few tests also moderately cohesive materials were used. Materials and vertical load were chosen to either allow or suppress shear dilatancy, the latter case being characterised by severe grain crushing (cataclasis) in the shear zone proper. While growth and texture of dilating and non-dilating shear zones differ quite systematically, the build-up of stresses is quite similar in both cases, in particular with respect to the peak in shear stress.In many experiments stress measurements were carried out inside the granular pack, mainly by inserting small photoelastic cylinders, to establish the orientation of the maximum compressive stress in the vicinity of the shear band. The results leave little doubt that the shear bands produced between rigid platens are bounded by planes of maximum shear stress rather than by Coulomb-type slip planes. Inside a shear band, however, Coulomb slips are operative in deforming the softened shear zone material. This may be concluded from the regularly observed sets of oblique minor slips (Riedels) and discrete gliding planes.
Zusammenfassung Scherzonen in körnigen Stoffen. Eine experimentelle Studie ihrer Strukturen und mechanischen EntstehungEin Ringschergerät wurde eigens entwickelt, um bei hinreichend langem Schervorgang die Entwicklung von Scherzonen in körnigem Material sowie die zugehörigen Struktur- und Spannungsänderungen studieren zu können.Verschiedene Versuchsreihen wurden mit dicht gepackten, nicht-kohäsiven Stoffen durchgeführt, sowohl in trockenem Zustand als auch gesättigt mit Flüssigkeit. Zum Vergleich wurde in einigen Versuchen auch mäßig verfestigtes, körniges Material verwendet. Geeignete Wahl von Material und vertikaler Belastung erlaubte es, Scherdilatanz zuzulassen oder zu unterdrücken; im letzteren Falle mit starker Kornzertrümmerung innerhalb der eigentlichen Scherzone (Bruchfließen). Während sich dilatierende und nicht dilatierende Scherzonen hinsichtlich Wachstum und Struktur systematisch unterschieden, war der Spannungsaufbau in beiden Fällen ähnlich. Dies gilt im besonderen für die Schubspannungsspitze (peak stress).In vielen Experimenten wurden Spannungsmessungen innerhalb der Körnerpackung ausgeführt, und zwar hauptsächlich mittels eingelegter photoelastischer Zylinderchen, um die Richtung der größten Druckspannung in Nähe der Scherzone zu ermitteln. Die Ergebnisse lassen wenig Zweifel, daß die zwischen starren Platten erzeugten Scherbänder von Ebenen größter Schubspannung begrenzt sind und nicht von Coulombschen Gleitebenen. Im Inneren der Scherbänder sind allerdings Coulombsche Gleitflächen an der Verformung des entfesteten Materials maßgeblich beteiligt, wie die regelmäßig wahrgenommenen, gestaffelten Sekundärgleitflächen (Riedel-Gleitflächen) und Gleitebenen zeigen.
Résumé Zones de cisaillement en milieu granulaire. Etude expérimentale de leur structure et du mécanisme de genèseOn a conçu un dispositif annulaire spécial pour étudier le développement des zones de cisaillement en milieu granulaire, sous l'effet d'un effort de cisaillement continu ainsi que des modifications qui en résultent aussi bien dans la texture du milieu étudié que dans l'état de contrainte.Plusieurs séries d'expériences ont été effectuées sur un matériau fortement comprimé et denué de cohésion, tour à tour sec ou saturé de fluide. Dans un but de comparaison, on a aussi utilisé dans quelques cas, un matériau légèrement consolidé. Matériau et charge verticale furent choisis en sorte que l'effet de dilatation dû au cisaillement existe ou non: en l'absence de dilatation on a un important broyage des grains (cataclase) au sein de la zone de cisaillement. Alors que le développement et la texture des zones de cisaillement en dilatation ou sans dilatation présentent des différences systématiques, le développement des contraintes est très semblable dans les deux cas, en particulier en ce qui concerne la résistance au pic.Dans de nombreuses expériences, des mesures de contraintes furent faites à l'intérieur du milieu granulaire, par insertion de cylindres photoélastiques afin d'établir l'orientation de l'effort principal de compression, au voisinage de la zone de cisaillement. Les résultats laissent peu de doute sur le fait que la bande de cisaillement, entre les plaques rigides du dispositif est limitée par des plans de contrainte de cisaillement maximum et non par des plans de glissement du type des plans de Coulomb. Cependant, à l'intérieur d'une bande de cisaillement, des plans de glissement du type de Coulomb contribuent essentiellement à la deformation du matériau affaibli de la bande. On est amené à cette conclusion par l'observation systématique de familles de glissements obliques secondaires (Riedels) et de plans de glissements individualisés parallèles au cisaillement principal.

With 33 Figures  相似文献   

11.
The shear strength of rock joints in theory and practice   总被引：62，自引：10，他引：62  
SummaryThe Shear Strength of Rock Joints in Theory and Practice The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficientJRC, the joint wall compressive strengthJCS, and the residual friction angle r . All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 100 joint samples have demonstrated that r can be estimated to within ± 1° for any one of the eight rock types investigated. The mean value of the peak shear strength angle (arctan/ n ) for the same 100 joints was estimated to within 1/2°. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle (arctan/ n ) at which sliding occurs provides an estimate of the joint roughness coefficientJRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that bothJRC andJCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests.With 20 Figures  相似文献   

12.
The coastline of Southeast Britain is formed in sedimentary rocks of Jurassic, Cretaceous and Tertiary age, the majority of these deposits containing thick strata of mudrocks, which have very low angles of dip. Where these strata are appropriately exposed, particularly at the foot of a coastal slope, they give rise to landslides where all or part of the sliding surface follows a single bed of mudrock. Where the dip of the bedding is steep, such landslides are referred to as dip-slope failures. However, landslides where the basal sliding surface is controlled by the location and orientation of a single argillaceous bed in the sequence are better termed bedding-controlled landslides. In addition, where coastal slopes contain several layers of mudrocks, geometrically similar landslides may occur with perched slide surfaces breaking out at a higher level within the slopes. Landslides with strong bedding-controlled basal shear surfaces are the predominant form of instability along the southeast coastline of Britain. Many of the individual landslide cases used in this paper have been studied separately over many years. The general similarity of the different records is discussed, drawing important inferences on a number of aspects of these landslides with a variety of basal sliding surface geometries.  相似文献   

13.
Local modification of rock chemistry by deformation   总被引：1，自引：0，他引：1  
Metabasalts subjected to progressive deformation in large-scale shear zones at Yellowknife display corresponding changes in major element abundances. Deformation, under conditions of greenschist facies metamorphism, has involved grain size reduction from 1200 m to <20 m, depletion of SiO2 (5%) and Na2O, together with hydration, and a decrease in specific gravity from 2.97 to 2.80. Chemical redistribution by deformation has been accomplished through a decrease in grain diameter of quartz and albite by intercrystalline diffusive mass transport (pressure solution), with concomitant transfer of material into extension veins. The degree of chemical modification is related to the finite strain. Deformation has involved a redistribution of 7.1015g of SiO2 over a volume of about 50km3.The microstructure of an adamellite deformed in a shear zone at higher temperature, under conditions of amphibolite facies metamorphism is indicative of dominant dislocation creep. A low degree of tectonic grain refinement is present. Constant values of major element abundances and specific gravity determined across the shear zone at increasing states of strain imply isochemical and isovolumetric deformation. These results are taken to support the precept that crustal deformation is characterised by a low temperature deformation regime dominated by pressure solution, with local changes of rock chemistry and volume; and a high temperature regime in which strain is accommodated principally by dislocation creep, an isochemical and isovolumetric deformation mechanism.  相似文献   

14.
Optically visible Albite glide twins in a peristerite (An9Or1.6), identified from their tapering shape and relationship to grain boundaries, were studied by transmission electron microscopy. Near the tips in sections a, the microstructure consists of small (400 nm long) lensshaped Albite twins centred exclusively on the oligoclase lamellae. The lenses extend partly outwards into the two adjacent low albite lamellae and induce strong inhomogeneous strain. Where the lenses are closer together, they form, depending on the sense of shear, nearly linear left or right-stepping en échelon arrays, with overlap of the strain fields. Slightly farther in from the tip, the twin domains coalesce to form continuous pinch-and-swell lamellae, being always thicker in the oligoclase. Because of Si,Al order, only elastic glide pseudotwins are possible in low albite. In oligoclase glide pseudotwins may be mechanically stable (metastable relative to Si,Al order) and may deviate only slightly from true twins. Pseudotwins develop first in the oligoclase, propagate dynamically by jumping across the intervening albite lamellae, extend lengthways and thicken sideways and finally coalesce. They are stabilized by diffusion-controlled inversion of Si,Al order giving rise to true twins described in a companion paper.C.R.P.G. contribution 799  相似文献   

15.
A combined field, stable isotope, and whole-rock chemical study was made on late Cretaceous to Tertiary metasomatic shear zones cutting Hercynian gneisses in the Aston Massif, Pyrenees, France. Mylonitisation occurred during the early stages of Alpine compression under retrograde conditions at 400–450°C and about 10 km depth. Whole-rock 18O values of (+11 to +12 in the gneisses) was lowered to +5 to +9 in the shear zones, with the quartz-muscovite 18O/16O fractionations of about 2 to 4 essentially unchanged. These 18O/16O systematics, together with D muscovite=-40 to-50 indicate that large volumes of formation waters or D-rich meteoric waters passed through the shear zones during deformation. The same fluids also redistributed major elements, as shown by the correlation of 18O shift with muscovitisation and albitisation reactions in granitic wall rocks. However, even though 18O was universally lowered within the shear zones, the 18O/16O ratios were not homogenised, nor do they correlate in detail with the presence or absence of muscovitisation, suggesting that fluid flow was probably fracture-controlled and episodic. Field mapping shows that, along the length of a particular shear zone, muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss. Thus, muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re-equilibration of acidic, chloride-rich, aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss. Extremely high material-balance fluid-rock ratios (103) are required to explain the extent of muscovitisation along this shear zone, implying integrated fluid mass fluxes of about 108 kg/m2; this is probably close to the maximum value for other shear zones in the network. Similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites, showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux. For reasonable pressure gradients and time scales of fluid movement, effective permeabilities of 10-15 to 10-17 m2 are required. Such values can be accounted for by short-lived, widely-spaced cracks produced during seismic activity. A model is presented in which formation waters were seismically pumped down an underlying, shallow, southward-dipping decollement and then upward through the steeply-dipping shear zone network.Contribution No 4711: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA  相似文献   

16.
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   

17.
Disasters of geological nature, caused by the 1920 Haiyuan earthquake (Ms = 8.5), were studied in hilly loess areas. Dynamic characteristics of loess landslides of seismic origin and an approach for predicting landslide in loess are presented. Subsidence of seismic origin in loess is described.This study Geological Disasters during 1920 Haiyuan Earthquake was first published in Performance of Ground and Soil Structures during Earthquakes, Thirteenth International Conference on Soil Mechanics and Foundation Engineering, New Delhi 1994, published by The Japanese Society of Soil Mechanics and Foundation Engineering who generously have permitted reprinting inGeoJournal on May 25, 1995, which is gratefully acknowledged.  相似文献   

18.
Zusammenfassung Die Schichten der Kreuznacher Gruppe im Nordosten des Saar-Nahe-Gebietes kann man in 3 Faziesgebiete aufteilen, und zwar 1. in die Kreuznacher-, 2. die Niersteiner- und 3. in die Rötelschiefer-Fazies. Ihre Sedimente zeigen Merkmale einer Ablagerung unter semiariden Bedingungen, die sich ebenfalls in einer Zunahme ihres Dolomit- wie Borgehaltes zum Hangenden widerspiegeln. Dies trifft besonders auf die Rötelschieferfazies zu, wo in der Zone stärksten Anstiegs dieser Komponenten auch eine Anreicherung der wichtigsten Spurenelemente vorhanden ist. Diese Kennzeichen einschließlich der Tatsache, daß in der nahegelegenen Bohrung Wolfskehlen 4 (Rheintalgraben) mariner Zechstein nachgewiesen werden konnte, sprechen für eine Einstufung der Schichten der Kreuznacher Gruppe in den Zechstein.
The Sediments of the Kreuznacher Gruppe in the northeastern part of the Saar-Nahe-region can be divided in the following facies: 1. The facies of Kreuznach, 2. the facies of Nierstein and 3. the facies of the Rötelschiefer. They all show features of sediments deposited under partly arid conditions, which are also demonstrated in an increase of dolomite- and boron-content of the younger sediments. This trend is quite clear in the facies of the Rötelschiefer, where in the zone of maximal increase in these components an enrichment of the most important trace elements can be observed as well. These characteristics and the fact, that in the cores of the nearby bore Wolfskehlen 4 (Upper Rhinegraben) Zechstein in a marine facies was found, admit the conclusion, that the sediments of the Kreuznacher Gruppe belong to the Zechstein, too.
Résumé Les couches du Kreuznacher Gruppe dans la partie Nord-Est du bassin de la Sarre/Nahe peut-on subdiviser de la manière suivante: 1. La facies de Kreuznach, 2. la facies de Nierstein et S. la facies des Rötelschiefer. Toutes les trois facies indiquent des documents d'une climat semiaride, lequel se montre aussi en forme d'une augmentation de bore et de dolomie vers la partie supérieure des couches. C'est particulièrement réalisé dans la facies des Rötelschiefer, où on trouve dans la zone d'une montée maximale de bore et de dolomie aussi un enrichissement des oligoéléments les plus importants. Ces indices et le fait, qu'on a constaté du Zechstein marin tout près dans les carottes d'un sondage (Wolfskehlen 4) au graben du Rhin, permettent de conclure, que les couches du Kreuznacher Gruppe appartiennent au Zechstein.
Saar-Nahe' : ) , ) , ) . .
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19.
In the last few years, an increasing number of practical studies using so-called kriging estimation procedures have been published. Various terms, such as universal kriging, lognormal kriging, ordinary kriging, etc., are used to define different estimation procedures, leaving a certain confusion about what kriging really is. The object of this paper is to show what is the common backbone of all these estimation procedures, thus justifying the common name of kriging procedures. The word kriging (in French krigeage) is a concise and convenient term to designate the classical procedure of selecting, within agiven class of possible estimators, the estimator with a minimum estimation variance (i.e., the estimator which leads to a minimum variance of the resulting estimation error). This estimation variance can be seen as a squared distance between the unknown value and its estimator; the process of minimization of this distance can then be seen as the projection of the unknown value onto the space within which the search for an estimator is carried out.  相似文献   

20.
The island of Kod Ali is a small diatreme cone lying close to the Ethiopian coast at latitude 13° 57 N, longitude 41° 49 E. This volcanic structure, produced by geologically Recent volcanic activity, consists, almost entirely, of pyroclastic debris. Evidence of a liquid phase is confined to the thin veneers of markedly alkalic olivine basalt which coat many of the abundant gabbroic, pyroxenitic and lherzolitic fragments found on the island. As silicic inclusions are completely absent and as the alkalic liquid phase and the tholeiitic inclusions are seemingly genetically unrelated, it is proposed that the latter might have been derived from a tholeiitic plutonic layered sequence that underlies the tholeiitic basalts of an oceanic Red Sea floor.  相似文献   

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