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1.
Summary The provenance of the Mid-Devonian clastic sediments in the Teplá-Barrandian Unit (TBU) of the Bohemian Massif was investigated by laser ablation ICP-MS U–Pb zircon dating, bulk sediment geochemistry and mineralogical study of the heavy mineral fraction. In contrast to the island arc provenance of the TBU Neoproterozoic sediments, the Early Palaeozoic sediments contain significant amounts of differentiated crustal material. The detrital zircon populations in the Barrandian Mid-Devonian siltstones and sandstones show ages ranging from Archaean (3.0Ga) to Early Palaeozoic (0.39Ga). Major age maxima are at 2.6Ga, 2.0–2.25Ga, 0.62 and 0.51Ga. The youngest identified zircons so far correspond to Lower and Mid-Devonian ages. The extensive mechanical abrasion of zircons having Archaean (3.0, 2.8 and 2.6Ga) to Paleoproterozoic ages (2.25–2.0Ga) suggest their provenance from recycled old sedimentary sequences. The relatively large number of zircons with ages between 2.0 and 3.0Ga may indicate the presence of relicts of the Archaean/Paleoproterozoic crust in the source areas of the studied Mid-Devonian sediments. The absence of detrital zircon ages between 0.9 and 1.2Ga and the presence of zircon ages of 2.0–2.25 and 0.5–0.8Ga correspond to the zircon age pattern from the Gondwana-related North African, rather than Gondwana-related South American and Baltic terranes. The material was entering the basin predominantly from the west and consisted primarily of detrital material of Cambrian granitoids and recycled material of Neoproterozoic meta-sedimentary sequences.  相似文献   

2.
Archean basement gneisses and supracrustal rocks, together with Neoproterozoic (Sinian) metasedimentary rocks (the Penglai Group) occur in the Jiaobei Terrane at the southeastern margin of the North China Craton. SHRIMP U–Pb zircon dating of an Archean TTG gneiss gave an age of 2541 ± 5 Ma, whereas metasedimentary rocks from the Neoproterozoic Penglai Group yielded a range in zircon ages from 2.9 to 1.8 Ga. The zircons can be broadly divided into three age populations, at: 2.0–1.8 Ga, 2.45–2.1 Ga and >2.5 Ga. Detrital zircon grains with ages >2.6 Ga are few in number and there are none with ages <1.8 Ga. These results indicate that most of the detrital material comes from a Paleoproterozoic source, most likely from the Jianshan and Fenzishan groups, with some material coming from Archean gneisses in the Jiaobei Terrane. An age of 1866 ± 4 Ma for amphibolite-facies hornblende–plagioclase gneiss, forming part of a supracrustal sequence within the Archean TTG gneiss, indicates Late Paleoproterozoic metamorphism. Both the Archean gneiss complex and Penglai metasedimentary rocks resemble previously described components of the Jiao-Liao-Ji orogenic belt and suggest that the Jiaobei Terrane has a North China Craton affinity; they also suggest that the time of collision along the Jiao-Liao-Ji Belt was at 1865 Ma.  相似文献   

3.
The relation of volcanism to tectonics in the Central American region has been established by a review of the literature as well as by field and photogeological work of the authors. The association of a deep trench off the Pacific coast, a parallel seismic belt, and a similarly oriented chain of volcanic vents farther inland, has been recognized by numerous earlier workers. These features form a tectonic unit, and are here termed the Pacific marginal zone.Seismic foci on the northeastern edge of the southern part of the Middle American Trench define a fault zone which dips under the continent and suggests movement of the oceanic plate underneath the Central American continent.An impressive chain of volcanic cones and associated shallow seismic foci is aligned along a prominent graben, best developed in Nicaragua where it is known as the Nicaraguan Depression. This feature probably originated in late Tertiary time. The southeastern end of the graben terminates at the northern ranges of the Talamanca Cordillera in Costa Rica. At the Gulf of Fonseca the trend of the graben changes from NW to E-W; the graben continues as the Central Depression of El Salvador at a higher elevation. Only the fault of the seaward border of the graben is defined in Guatemala, where it is represented by a NW trending volcanic chain.In Nicaragua and El Salvador the oldest cones are situated on the north-eastern boundary fault zone of the graben. These include remnants of the largest volcanic structures of the region. All the active volcanoes are on the southwestern boundary fault belt. Cross fracturing of this fault system controlled later northerly trending cone alignments, often with the youngest cones on the south end.The main graben and associated faults are considered results of tensional stresses on the crest of geanticlinal arching on the landward side of the Middle American Trench. This arching is believed to be due to regional compression originated by the movement of the oceanic plate against the mainland.In northwestern Central America the youngest stresses produced N-S normal faults that are marked by well-defined scarps. These stresses may be the result of right-lateral motion along the underthrust fault zone. The complex Comayagua graben north of the Gulf of Fonseca, the Ipala graben and associated faults in southeastern Guatemala, and the Guatemala City graben are all north-south features illustrating the extent and youth of this structural trend.The distribution of volcanic vents along the Nicaraguan Depression and the N-S trends underscores the close tectonic control of volcanism.
Zusammenfassung Der Zusammenhang zwischen Tektonik und Vulkanismus im mittelamerikanischen Raum wird aufgezeigt aufgrund einer Literaturdurchsicht und feldgeologischer Arbeiten der Verfasser. Die Beziehungen zwischen einem Tiefseegraben vor der pazifischen Küste, einem dem Festland parallelen seismischen Gürtel und einer ebenso orientierten Vulkankette weiter im Inland sind von früheren Bearbeitern bereits erkannt worden. Diese drei Einheiten werden hier zusammengefaßt und als pazifische Randzone bezeichnet.Erdbebenherde am Nordostrand des mittelamerikanischen Tiefseegrabens weisen auf eine Störungszone hin, die unter den Kontinent einfällt. Der Bewegungssinn spricht für ein Abtauchen der ozeanischen Platte unter das mittelamerikanische Festland.Eine eindrucksvolle Vulkankette und die mit ihr verbundenen Erdbebenherde sind längs eines bedeutenden Grabens aufgereiht, der in Nicaragua am deutlichsten ausgebildet ist und dort Nicaragua-Senke genannt wird. Diese tektonische Einheit entstand wahrscheinlich im Jung-Tertiär. Der Graben beginnt im Südosten an den nördlichen Ausläufern der Talamanca-Kordillere in Costa Rica.In Nicaragua verläuft er NW. Am Golf von Fonseca schwenkt er in eine E-W-Richtung und setzt sich in El Salvador in einem höheren Niveau als Zentral-Depression fort. In Guatemala ist nur der Südrand des Grabens erkennbar. Er ist gekennzeichnet durch eine in NW-Richtung aufgereihte Vulkankette. In Nicaragua und El Salvador liegen die ältesten Vulkane auf dem nordöstlichen Grenzbruch des Grabens. Zu dieser Gruppe zählen die größten Rumpfvulkane. Die meisten Kegel und alle tätigen Vulkane liegen hingegen auf dem südwestlichen Grenzbruchstreifen. Auf Querbrüchen haben sich jüngere, nördlich ausgerichtete Kegelreihen gebildet. Die jüngsten Kegel liegen meistens am südlichen Ende der Querbrüche.Es wird angenommen, daß der Hauptgraben und seine Störungen im Scheitel einer zum mittelamerikanischen Tiefseegraben parallel verlaufenden Aufwölbung entstanden sind. Die Aufwölbung kann auf Kompression der ozeanischen Platte gegen das Festland zurückgeführt werden.Im nordwestlichen Zentralamerika bewirkten jüngere Beanspruchungen die Bildung von N-S-Brüchen, die heute morphologisch als Steilkanten hervortreten. Diese Beanspruchungen können durch rechtslaterale Bewegungen entlang der pazifischen Störungszone ausgelöst worden sein. Beispiele dieser N-S-Struktur sind: Die Comayagua-Grabenzone, nördlich des Golfs von Fonseca, der Ipala-Graben und sein Störungssystem in Südost-Guatemala und der Guatemala-Stadt-Graben. Diese N-S-Störungen kennzeichnen das Ausmaß und das geringe Alter der Grabenbildung.Die Anordnung der Vulkane entlang der Nicaragua-Senke und der N-S-Brüche stellen die engen Beziehungen zwischen Tektonik und Vulkanismus in der pazifischen Randzone Mittelamerikas heraus.
Resumen Mediante información tomada de la literatura, trabajos de campo e interpretation fotogeológica, se establece la relación entre el volcanismo y la tectónica en la región de América Central. Se usa la denominación de zona marginal del Pacífico para identificar, como una unidad, la asociación ya reconocida por otros autores de la profunda Fosa Mesoamericana frente a la costa del Pacífico de America Central y las franjas paralelas de actividad sísmica y de cadenas volcánicas.Los focos sísmicos en el borde nororiental de la Fosa Mesoamericana definen una gran zona de afallamiento inclinada hacia el continente, cuyos movimientos indican que un bloque de la corteza oceánica se sumerge bajo la porción continental de America Central.Una imponente serie de conos volcánicos, asociada a focos sísmicos poco profundos, está situada a lo largo de un gran graben conocido como Depresión de Nicaragua, por ser en ese país donde aparece más claramente definido. Este graben, que posiblemente se originó durante el Terciario tardío, termina en su extremo suroriental contra las estribaciones de la parte norte de la Cordillera de Talamanca, en Costa Rica. En Nicaragua el graben está orientado hacia el NW hasta el Golfo de Fonseca donde toma un rumbo E-W a través de El Salvador, donde se encuentra a mayor elevación. En Guatemala se conoce únicamente una línea de fallas, la más próxima al mar, definida por una cadena de volcanes que tiene nuevamente dirección NW.En Nicaragua y El Salvador los conos volcánicos más antiguos están situados a lo largo de las fallas que limitan al graben en su lado nororiental. Allí se encuentran las ruinas de los edificos volcánicos más grandes de la región. La mayoría de los conos que incluye todos los actualmente activos, se localizan a lo largo de las fallas del borde suroccidental del graben. Fracturas transversales controlan la localization de varios grupos de conos alineados de N-S. Los volcanes más jóvenes se encuentran frecuentemente en el extremo sur.Se postula que el graben principal y otras fallas del mismo sistema han sido formados como resultado de esfuerzos de tensión, en la cresta de un geanticlinal que resultó del arqueamiento del lado terrestre de la zona marginal del Pacífico. Dicho arqueamiento se cree que resulta de la compresión regional debida al movimiento del bloque oceánico contra el continente.En la parte noroccidental de América Central los esfuerzos más recientes produjeron fallas orientadas N-S, fácilmente identificables por sus bien marcadas escarpas. Estos esfuerzos pueden haber resultado del desplazamiento dextromóvil a lo largo de las zonas de afallamiento paralelas a la Fosa Mesoamericana.El complejo graben de Comayagua, al norte del Golfo de Fonseca, y los graben de Ipala y de la Ciudad de Guatemala, orientados también de norte a sur, ilustran la extension y la joven edad de las fracturas.La distribución de los focos volcánicos a lo largo de la Depresión de Nicaragua y de las fracturas N-S muestran de manera evidente, la estrecha relación que existe entre la tectónica y la localización del volcanismo en la zona marginal del Pacifico de America Central.
, - . - , . . , , . , , - . - Talamanca Kordillere -. - - . Fanseca . . , , . - . . . , . . - N-S , . . : Comayagua, Fanseca, Ipala - . - . , .
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4.
Résumé Partant de la grandiose conception d'Edouard Suess, la géologie de la Méditerranée a été divisée en quatre étages méditerranéens.Si le premier représente le début de la création d'une mer transgressive, le deuxième représente l'extension maximum de cette mer au delà de la chaîne alpine, puis il est suivi par une regression très générale. Au quatrième méditerranéen ou Pliocène, la mer pénètre dans toutes les vallées, dépressions du continent, réalisant la forme actuelle de cette mer où, depuis le Plaisancien se déposent les mêmes « argiles bleues » extraordinairement uniformes. Ces dépôts sont toujours très épais.Les unités morphologiques de la Méditerranée actuelle sont à peu près les mêmes que celles que les océanographes des Etats-Unis ont reconnu dans l'Atlantique: plaine littorale, plateau continental, pente continentale, plaine abyssale. Les sea-mounts ont même été reconnus en Tyrrhénienne et en Méditerranée Orientale. Les modifications du fond de la mer sont presque toujours dues au jeu des failles, soit d'effondrement comme en Tyrrhénienne, soit au contraire, de surrection, qui amènent à émerger d'anciens fonds de la mer.Les modifications corrélatives du fond de la mer, par abaissement et surtout par disjonction de la surface des continents, ont comme conséquences une regression depuis le Crétacé, entrecoupée de transgressions accompagnées d'épanchements de nature basaltique sur le fond de la mer. Ces mouvements se font de part et d'autre du pied de la Pente continentale qui est presque linéaire.A mon sens, les transformations de la Méditerranée se sont faites beaucoup plus autour des failles que par des plissements.
Since the grand conception ofEdouard Suess, the geology of the Mediterranean has been divided into four Mediterranean stages.If the first stage represents the beginning of the creation of a transgressive sea, the second represents the maximum extension of this sea beyond the Alpine range, and is then followed by a general regression. At the fourth stage, Mediterranean or Pliocene, the sea imades all valleys, depressions of the adjoining continent, realizing the present form of this sea, where, since the Plaisancian, the same blue clays form thick deposits of extraordinarily uniform character.The morphologic units of the present Mediterranean are about the same as the cones that have been found in the Atlantic by the oceanographers of the United States: coastal plain, continental shelf, continental slope, abyssal plain. Even sea-mounts have been found in the Tyrrhenean sea and in the Eastern Mediterranean. The modifications of the bottom of the sea are mostly due to tectonics, either by lowering as in the Tyrrhenean sea, or, by rising, causing emergences.The correlative modifications of the sea-bottom, by subsidence and mostly by disjunction of the surface of the continents consequently display a regression since Cretaceous times, intersected by transgressions accompanied by submarin extrusions of a basaltic nature. Such movements occur at the foot of the (almost linear) continental slope.In my opinion, the transformations of the Mediterranean have occurred much more by faulting than by folding.
Zusammenfassung Nach der grandiosen Konzeption von E.Suess ist die Geologie des Mittelmeeres in vier mediterrane Phasen gegliedert worden.Die erste Phase stellt den Beginn eines transgressiven Meeres dar, die zweite bezeichnet die maximale Ausdehnung dieses Meeres jenseits der Alpen, darauf folgt eine allgemeine Regression. Während der vierten Phase, dem Pliozän, dringt das Meer in alle Täler und Depressionen des Kontinents ein, wobei die heutige Form des Mittelmeeres entsteht, und mit dem Plaisancien kommt es zur Ablagerung der blauen Tone, die außerordentlich einheitlich und stets sehr mächtig sind. Die morphologischen Einheiten des heutigen Mittelmeeres sind etwa dieselben, wie sie die Ozeanographen der USA im Atlantik vorgefunden haben: Litoralebene, Kontinentalplateau, Kontinentalabhang, Tiefsee-Ebene. Die Seeberge (sea-mounts) wurden wiedererkannt im Tyrrhenischen Meer und im östlichen Mittelmeer. Die Veränderungen des Meeresgrundes sind fast immer auf die Wirkung von Verwerfungen zurückzuführen, wobei Senkung, wie im Tyrrhenischen Meer, stattfand oder aber Hebung zur Emersion des alten Meeresbodens führte. Die wechselseitigen Veränderungen des Meeresbodens durch Senkung und besonders durch Trennung der Kontinentoberflächen haben seit der Kreide eine Regression zur Folge, die von Transgressionen mit Basaltergüssen auf dem Meeresboden unterbrochen wurde. Diese Bewegungen fanden auf beiden Seiten am Fuße des Kontinentalabhanges statt, der fast linear ist.Nach meiner Meinung wurden die Umwandlungen des Mittelmeeres mehr durch Verwerfungen als durch Faltungen hervorgerufen.
, . , . .
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5.
This paper presents the case histories of two catastrophic landslips in hard rock terrains with varied climatic and geological environments. The first slip is associated with a power project in very close proximity (200 m) of the Porthimund Dam (11°22N, 76°3430E), in a charnockitic terrain in the Nilgiri hills (Tamil Nadu), and the second is associated with a railroad structure (19°525N, 78°1720E), in Adilabad district (Andhra Pradesh), in a basaltic terrain.The landslip in the charnockites is attributable to: (1) a high degree of saprolitization in the charnockites, with maximum intensity in the crest portion; (2) the coincidence of a major joint pattern in a NE-SW direction, with the strike of the foliation; and (3) the poor-to-fair physical rock quality in the crest and scarp portions.The slips in the basaltic terrain are due to: (1) the partially altered, highly jointed nature of the regional trap rocks with boulder sizes varying from 20 cm to 250 cm in diameter and the debris accumulating in a precarious condition on the northeast side of the rail track, with unfavorable alignment direction; and (2) the instability created in the weak rock mass by the vibrational forces of heavily loaded running trains.The weathered state of the rock masses in both the cases, showing good agreement with their physical state, accounts for the landslips. The remedial measures suggested are also discussed.  相似文献   

6.
Wang Wenying 《GeoJournal》1988,17(4):513-516
The SW-mountain region of Xizang in this paper is taken to extend between 27° 10 – 30° 10N / 84° 50–91° 30 E, that is the vast area stretching from the Himalayas to the South Range of Xizang. The author has been in the area many times over 20 years surveying and conducting scientific investigations. In 1984 the author took part in the Sino-German Joint Expedition for further survey and the interpretation of aerial photographs and satellite images of the same area. The paper presents the data collected during this period.  相似文献   

7.
Formation constants for silver thiolates were obtained by titration of the ligand in a constant temperature, ionic strength and pH medium and measuring the potential change at a Ag2S electrode. A non-linear equation was derived from which the first and second silver formation constants, 1 and 2, and the sulfide group acid dissociation constant, Ka, were determined. An overall estimate of the uncertainty in the derived parameters was obtained using a Monte Carlo approach. The procedure was compared to a previous work on AgHS°. Log 1, log 2 and - log Ka results were obtained for cysteine (11.9 ± 0.5, 15.2 ± 0.4, 7.8 ± 0.1), glutathione (12.3 ± 0.3, 14.3 ± 0.8, 8.8 ± 0.3) and 3-mercaptopropanoic acid (12.0± 0.4, 14.0 ± 0.4, 10.5 ± 0.3) at 20 °C and 0.01 m ionic strength.  相似文献   

8.
The ca. 2.7–2.5 Ga Slave Province is a granitegreenstone terrane comprising deformed sedimentary and subordinate volcanic belts extensively intruded by granitoid rocks. The Nd isotopic data are reported for 58 samples of supracrustal and granitoid rocks exposed along a 400 km, east-west, transect at 65°N across the structural grain of the province. Initial Nd values reveal distinctly different crustal sources in the eastern compared to the western parts of the province, as expected from tectonic assembly of the province through accretion of juvenile crust to older continental crust. Supracrustal sequences (ca. 2.71–2.65 Ga) from the central and eastern parts of the province have positive Nd(1) values (+0.3 to +3.6), consistent with juvenile sources and formation remote from significantly older crust. Syn to late-deformation (ca. 2.63–2.60 Ga), mantle-derived diorites and related tonalites (type I) from the central and eastern parts of the province have similar initial Nd values (-0.1 to +2.7). In contrast, samples from the westernmost plutons, which intrude exposed pre-3.1 Ga crust, have much lower Nd(1) values (-1.0 to4.6) suggesting contamination of these magmas by older crust. The Nd(1) values of post-deformation granites (s.s.) (type II) also vary systematically across the province: values for granites west of longitude 110°30W range from-0.2 to -5.3; those to the east range from +0.6 to +3.7. These data suggest mixed crustal sources dominated by Mid to Early Archean material ( Nd-2.6 to- 17 at 2.6 Ga) for the western granitoid rocks and juvenile sources for the eastern granites. The Nd isotopic data are consistent with the geology of the province in that exposures of Mid to Early Archean crustal rocks, predating the principal 2.7–2.5 Ga orogenic event are restricted to the western part of the province. The asymmetric pattern defined by the Nd isotopic data indicates the presence of distinct crustal rocks beneath the Slave Province. Similar isotopic variations observed across Phanerozoic collisional orogens have been interpreted to reflect tectonic assembly of crust by accretion of juvenile crustal terranes to an older continental margin. This process may also have been an important mechanism in the cratonization of the Slave Province.  相似文献   

9.
《International Geology Review》2012,54(16):2057-2079
ABSTRACT

In southern Egypt, Neoproterozoic granitoids intrude the crust from Libya in the west to the Nile River in the east. Best exposed at Gebel Uweinat, Gebel Kamil, Bir Safsaf, Gebel El Asr and Gebel Umm Shaghir, these rocks represent the transition between the rejuvenated Archean to Paleoproterozoic crust of the east Saharan craton and the juvenile Neoproterozoic crust of the Arabian–Nubian Shield to the east. We present U-Pb zircon geochronology and whole rock geochemistry from 16 Neoproterozoic (c. 628–580 Ma) granitoids across southern Egypt which document the synchronous production of diverse compositions indicative of an intraplate or intracontinental tectonic setting. Our data better constrain the age relationships, petrogenesis, and Pan-African crustal growth associated with the amalgamation of Gondwana and contribute to understanding the crust-modifying processes that led to the development of the Saharan metacraton in the Ediacaran.  相似文献   

10.
Initial Nd isotopic ratios are reported for 23 samples representing magmatic crustal components in the Svecokarelian terrain of South Finland. U-Pb zircon ages are determined for all geologic units, involving 21 separate upper concordia intercept ages based on more than 100 UP-b analyses. The ages range for all the rocks from 1.90 Ga for primitve plutonic rocks to 1.79 Ga for post-tectonic intrusions. The well-known gabbro-diorite-tonalite-trondhjemite association of the Kalanti district appears to consist of components with different ages: trondhjemites are probably 1.90 Ga or older, diorites/tonalites belong to the main Svecokarelian plutonic eposide at 1.89-1.87 Ga, and at least some gabbro has a post-tectonic age of 1.80 Ga. Nd (T) values range between +2 to +3 for meta-andesites, large gabbros and primitive granitoids to –0.5 for more evolved granitoids. A magma source with Nd of at least +2 to +3 was available during 1.90 to 1.87 Ga, but evolved granitoids have Nd close to zero. The preferred interpretation is that depleted mantle with Nd=+4 to +5 was present beneath the Svecokarelian crust forming during 1.9-1.8 Ga, and that all rocks have been affected more or less by addition of an Archean crustal component with Nd=–9 to –13. The primitive rocks with Nd=+2 to + 3 were only slightly affected, while granitoids with Nd close to zero include a 10% Archean component. The widespread nature of the Archean addition and the distance of up to 500 km to actual exposed Archean crust make it most realistic that the Archean component was added to the form of sediments delivered by subducting Proterozoic ocean crust. The plutonic rocks of the Finnish Svecokarelian crust in areas away from Archean cratons consist of 90% newly mantle-derived material.  相似文献   

11.
Measurements of the directions of remanent magnetization of samples from sixty nine sites in the volcanic igneous rocks of Lower Silesia are reported. The activity spanned the time from Oligocene to Pliocene or Pleistocene, the magnetic data suggest the possible equivalence of the onset of vulcanity in Poland and East Germany. The stratigraphic control is too poor to permit the distinction of a sequence of magnetic zones.
Zusammenfassung An Proben aus vulkanischen Eruptivgesteinen von 69 Lokalitäten in Niederschlesien nahmen die Autoren Messungen der Richtungen remanenter Magnetisierung vor. Die Vulkantätigkeit umfaßte die Zeit vom Oligozän bis Pliozän oder Pleistozän. Die magnetischen Daten lassen vermuten, daß der Vulkanismus in Polen und Ostdeutschland gleichzeitig einsetzte. Die Stratigraphie ist noch zu wenig bekannt, um eine Folge magnetischer Zonen aufzustellen.
Résumé Les mesures de l'aimantation rémanente sur les échantillons prélevés de 69 sites dans les roches volcanique de Basse Silésie ont été faites. L'activité volcanique a duré de l'Oligocène jusqu'au Pliocène ou même Pleistocène; les résultats magnétiques indiquent qu'il est possible que le commencement du volcanisme en Pologne et Allemagne de l'est date de la même époque. La stratigraphie est mal connue et il n'est pas encore possible d'établir une série de zones magnétiques.
. . , . .

Contribution no. 45, Geology Department, Case Western Reserve University, Cleveland, Ohio 44106.  相似文献   

12.
Zusammenfassung Die untersuchten Gesteine wurden im Altproterozoikum als Schelfsedimente vorwiegend in Flachwasserfazies abgelagert. In ihrer Verbreitung sind Unterschiede zwischen Bildungen turbulenter Bereiche (Sande, Konglomerate und vereinzelte Breccien) und Stillwasserbildungen (Hämatitquarzit, Itabirit und Phyllit) festzustellen. Im Übergangsbereich beider Faziesbereiche kam es zu Verzahnungen von klastischen mit chemischen Sedimenten. Die chemisch gefällten Bändererze sind in zwei Typen zu trennen, zum einen in klastisch beeinflußte aus Bereichen unruhiger Sedimentationsbedingungen, zum anderen in klastisch nicht beeinflußte aus ruhigen Bereichen. Klastische Beeinflussung und intraformationale Aufarbeitung der BIF fand während allen Stadien der Verfestigung statt. Intraformationale Aufarbeitungsprodukte der Bändererze treten gemeinsam mit Konglomeraten großer Gerölldurchmesser entlang einer Nord-Süd streichenden Zone auf, wo sie sich lateral mit ungestörten chemischen Eisenerzen verzahnen. Konglomerate und BIF wurden zeitgleich sedimentiert. Charakteristisch für diese Zone sind außerdem synsedimentär aufgedrungene Vulkanite, deren Vorkommen einen Bereich tektonischer Unruhe nachzeichnet.
The investigated rocks were deposited as shelf-sediments during the lower Proterozoic, predominantly in a shallow marine environment. It can be distinguished between sediments formed under turbulent conditions (sands, conglomerates and occasional breccias) and sediments of undisturbed environments (hematite-quartzite, itabirite and phyllite). In the transition of both facies-zones detritic and chemical sediments are interfingering. The chemically precipitated banded iron ores can be separated into two types — clastically influenced BIF formed in areas of agitated sedimentary conditions, and BIF with no clastic admixtures formed in quiet regions. Banded iron ores were clastically influenced and intraformationally reworked during all states of lithification. Products of intraformationally reworked BIF appear together with conglomerates of large diameters along a north-south-striking zone where they interfinger laterally with undisturbed chemically precipitated iron ores. Conglomerates and BIF were deposited here at the same time. Significant for this zone are also synsedimentary volcanites accentuating the presence of a tectonically active zone.
Resumo Os metasedimentos aqui analisados foram predominantemente depositados em ambientes plataformais do Proterozoico inferior. Na sua distribuição constata-sc depósitos de águas calmas (hematita-quartzitos, itabiritos e filitos) e turbulentas) areias, conglomerados e esporadicamente brechas). Na zona de transição entre as duas facies sedimentares ocorreu interdigatação de sedimentos clásticos e químicos. Os minérios bandeados de ferro (BIF), quimicamente precipitados, podem ser classificados em dois grupos: o primeiro com interferência clástica, típico de ambientes agitados de sedimentação; o segundo sem componentes clásticos e característico de ambientes calmas. Interferência clástica como retrabalhamento intraformational ocorreu durante todos os estágios de processo sedimentar e de consolidação de BIF. Produtos do retrabalhamento intraformacional dos minérios bandeados ocorrem simultaneamente com conglomerados (seixos de diámetros grandes) ao longo de uma faixa Norte-Sul e interdigitados lateralmente com sedimentos químicos não perturbados. Conglomerados e BIF foram sedimentados concomitantemente. Característico para esta faixa são vulcanitos de extrusão sinsedimentar cuja presença tipifica um ambiente de instabilidade tectônica.
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13.
Zusammenfassung Im östlichen Rheinischen Schiefergebirge konnten innerhalb der im Allgemeinen gering permeablen paläozoischen Festgesteinskomplexe Bereiche guter Wasserwegsamkeit festgestellt werden. Sie sind vornehmlich an Nord-Süd oder Ost-West gerichtete Zonen junger (tertiärer) Tektonik gebunden und vorwiegend feldgeologisch nicht kartierbar. Mit Hilfe der Satellitenbildauswertung lassen sich diese Bereiche gut erfassen, da sie als Lineare abgebildet werden.Die Erfassung und Abgrenzung der Zonen junger Tektonik stellt eine wichtige Grundlage zur Sicherung der Trinkwasserversorgung für Gemeinden im Rheinischen Schiefergebirge dar. Sie ist außerdem ein Hilfsmittel zur Beurteilung von Fragen des Grundwasserschutzes.An Hand eines LANDSAT-1 Bildes wurde eine Linearkarte angefertigt, die mit einem umfangreichen Abflußmeßprogramm verglichen wurde. Dabei ergab sich, daß die von Linearen durchzogenen Teilgebiete normalerweise überdurchschnittliche Abflußspenden haben. Auch die in diesen Bereichen gelegenen Tiefbrunnen weisen überdurchschnittliche Förderraten auf.Über die jungen tektonischen Schwächezonen besteht eine gute Verbindung zwischen Oberflächen- und Grundwasser. Daraus resultiert die Gefahr einer möglichen Grundwasserkontamination durch verunreinigtes Oberflächenwasser. Dies bezieht sich besonders auf in Linearbereichen liegende Mülldeponien. So konnte zum Beispiel eine Verunreinigung von oberflächennahem Grundwasser durch die Schlammdeponie Hirzenhain nachgewiesen werden.Die Linearkarte stellt eine Basis für vorbeugende Maßnahmen des Trinkwasserschutzes dar, da mit ihrer Hilfe eine Ausweisung bzw. Neuabgrenzung von Trinkwasserschutzgebieten möglich ist, wie am Beispiel der Tiefbrunnen von Biedenkopf ausgeführt wird.
Linear zones of good permeability were recognized within the paleozoic strata of the Rheinisches Schiefergebirge, where the permeability of these intensively folded strata normally is low. These zones are related to young tectonic events of Tertiary. They follow North-Southern or East-Western directions and they can generally not be detected by methods of field-geology. The zones were mapped by interpretation of satellite-images where they show up as linear structural elements.The method can be used to back groundwater research and to prevent groundwater contamination. A LANDSAT-1 image was used for the structural interpretation. The resulting map was compared to a program of run-off measurements. Run-off rates above the average were proved at areas effected by linear elements. Also the production-rates of waterwells in these areas was proved to be above the average.Good communication between surface-water and ground-water has been recognized. This includes the possibility of groundwater pollution for example of refuse-deposits. Contamination of this kind has been found at several localities.
Résumé Dans le Rheinische Schiefergebirge oriental, on a pu déterminer au sein du complexe paléozoïque, en général peu perméable, des domaines à bonne perméabilité due à l'existence de joints et de fissures.Ces domaines sont avant tout liés à des zones à tectonique récente (tertiaire), de direction Nord-Sud ou Est-Ouest, pratiquement impossibles à cartographier pour la plupart d'entre elles. L'interprétation des photos prises par satellite permet de les bien définir car ils apparaissent sous forme de lignes. La considération et la délimitation des zones à tectonique récente constitue une base importante pour assurer l'alimentation en eau potable des communes dans le Massif schisteux rhénan, et, en outre, un moyen de porter un jugement sur les questions concernant la protection des nappes souterraines. Une carte de ces lignes a été établie à partir d'un photo de LANDSAT-1; elle fut ensuite comparée à un vaste programme de mesures de l'écoulement. Cette étude montra que les régions traversées par de telles lignes ont normalement des débits au-dessus de la moyenne. Il en est de même en ce qui concerne les puits creusés dans ces domaines.Dans les zones à tectonique récente faible, il existe une bonne liaison entre les eaux de surface et les nappes souterraines, d'où le danger de contamination possible de ces mêmes nappes par les eaux de surface polluées. Cela concerne particuli-rement les dépôts d'immondices; a titre d'exemple, il a été possible de prouver la pollution des nappes souterraines à partir de la surface à la suite du dépôt de boues à Hirzenhain.La carte des lignes représente une bonne base pour décider des mesures de protection des eaux potables, puisqu'il est possible, grâce à elle, de faire une nouvelle délimitation des domaines de protection des eaux potables, comme par exemple, au puits de Biedenkopf.
, , , . , N—S, E—W. , .. . . . LANDSAT-1 , , . , . . .
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14.
The study area is in the southeastern part of the city of Elaz between 38°17–38°43 latitudes and 38°36–39°07 longitudes. Formations of Paleozoic, Mesozoic and Cenozoic age comprise confined and unconfined aquifers. Unconfined aquifers are represented by Na-Cl and Na-HCO3 type waters while confined aquifers are characterized by Ca-HCO3, Mg-HCO3 and Na-HCO3 type waters. Due to sodium pollution, as a result of irrigation from waters of Hazar lake in the plain, as well as intense use of artificial fertilizer and improper storage of animal fertilizers, NH4-N, NO3-N and total PO4-P pollution are detected in waters of the unconfined aquifer. Organic material contents in waters of well nos. S27, S29 and S32 completed in the unconfined aquifer are above 3.5 mg/l of Turkish Standard Institute (TSE), (266) standard. In confined aquifers, total PO4-P pollution in four wells and NH4-N pollution in three wells were observed to be above the TSE (266) standard.  相似文献   

15.
The Delakhari sill (maximum thickness cf. 200 m) is the most extensive Deccan Trap instrusion which occurs in central India, between longitutdes 78°3835 to 78°2240 and latitudes 22°26 and 22°2230. Based on petrographic examination, the sill is divided, from bottom to top, into (1) the Lower Chilled Zone (LCZ), up to 8 m thick, marked by abundant interstitial glass and an overall fine grain size, (2) the Olivine-Rich Zone (ORZ), 27 m thick, enriched in olivine (relative to the other zones in the sill), (3) the Central Zone (CZ), 70 m thick, marked by depletion in olivine and overall coarse grain size, (4) the Upper Zone (UZ), 55 m thick, marked by the presence of two chemically and morphologically distinct olivine types and abundant interstitial granophyre, and (5) the Upper Chilled Zone (UCZ), 10–25m thick, marked by abundant interstitial glass.Compositions of the pyroxenes and olivines show an overall increase in Fe/Mg with crystallization, but extensive interzonal and intrazonal variations and overlaps exist. Olivine ranges from Fa24 (ORZ) to Fa95 (UZ). In the UZ and inner UCZ, an equant (Fa44–50, called type-A olivine) and interstitial skeletal olivine (Fa70–95, called type-B olivine) occur together. Compositions of the Ca-rich and Ca-poor pyroxenes fall in the range Wo38En34Fs28 to Wo33En8Fs59 and Wo14En41Fs45 to Wo16En19Fs65, respectively. Overall, the two pyroxene trends converge with Fe-enrichment except for one anomalous sample from the UZ which contains a Ca-rich (Wo34En8Fs58) and a Ca-poor (Wo10En18Fs72) pyroxene well within the Forbidden Zone of Smith (1972).Compositions of coexisting oxide minerals indicate that the sill crystallized at oxygen fugacities from 10–10 atm (ORZ) to 10–13 (UZ). The magma prior to intrusion appears to have been derived from a more primitive melt from which a considerable amount of olivine and plagioclase have fractionated out. A model of open, interrupted fractional crystallization in the sill is proposed to explain the compositional variations exhibited by the major mineral phases.A previous study (Crookshank 1936) concluded that the sill is actually a multiple intrusion and has given rise to the lowermost (flow I) and the topmost (flow III) lava flows in the neighboring area around Tamia (78°4015, 22°2035). The olivines of flows I and III have compositions Fo87 and Fo88 respectively, and are much more Mg-rich than the maximum Mg-rich olivine (Fo76) of the Delakhari sill, refuting the possibility of the sill being the feeder of the lava flows I and III.Geosciences Department, University of Texas at Dallas Contribution No. 338  相似文献   

16.
Initial Nd isotope ratios are determined for components of 1.9-1.7 Ga age continental crust in the Ketilidian terrain of South Greenland. The Ketilidian has well-documented ages of migmatization/metamorphism (1.80 Ga) and post-tectonic granitoid intrusion (1.76-1.74 Ga) from U-Pb zircon studies. The Nd results show that: (1) metatholeiites with chondritic 147Sm/144Nd have Nd=+4 to +5 at 1.8 Ga; (2) migmatites, paragneisses and an early granitoid have Nd close to zero; (3) post-tectonic norites have Nd +1.5, while spatially associated more-abundant granitoids have Nd=0 to +1. The metatholeiites show that a normal depleted mantle (Nd=+4 to +5) was present beneath this 1.9-1.7 Ga orogenic zone, as is the case in such environments today. However, metatholeiites are an insignificant part of the Ketilidian crust, and the bulk initial ratio of the whole terrain lies close to Nd=0. Rather than invoking depleted and undepleted mantle sources whose products did not mix, we infer the Nd=0 value to be caused by mixing of a component derived from depleted mantle (Nd=+ 4 to +5) with Archean crustal material (Nd=-9 to -13). As there are no proven relics of Archean crust beyond the border zone of the Ketilidian, and the Nd= 0 value appears to be a wellhomogenized feature, we propose that the Archean material was added in the form of sediments transported to the orogenic zone on oceanic crust. The Archean component comprised between 5 and 17% of the Ketilidian, and the most reasonable estimate is 10%. Thus this 1.9-1.7 Ga terrain consisted of 90% new mantle-derived crust.  相似文献   

17.
Résumé Les chaînes subalpines des Alpes françaises offrent un bon exemple de plis de couverture décollés au niveau du Keuper à évaporites. Leur partie méridionale, au S du Vercors et au N et NE des Chaînes Provençales, montre en outre l'entrecroisement de deux systèmes plissés presque orthogonaux: un système E-W, dit pyrénéoprovençal, dont la genèse s'étale du Crétacé supérieur à l'Eocène moyen, et un système N-S à NW-SE, dit alpin, qui date de l'Oligocène et du Néogène. Il y a donc eu deux étapes majeures de plissements qui se sont succédées dans le temps; mais on doit se demander si chacune de ces étapes était faite d'une succession de phases tectoniques courtes séparées par des intervalles relativement plus longs de calme tectonique, ou bien si elles correspondent à de longues périodes de déformations continues; ces deux postulats paraissent ici également vraisemblables. La première période, celle des plis pyrénéens, semble avoir fait naître des plis droits assez simples, parfois de style éjectif, dont les anticlinaux ont souvent, dès l'Eocène, été érodés jusqu'au Jurassique supérieur. A l'Oligocène et au Miocène, des plis N-S à NW-SE sont nés, dans les domaines qui n'étaient pas déjà plissés, tandis que les plis E-W déjà existants ont été accentués et rompus, dégénérant parfois en chevauchements caractérisés par des troncatures des flancs inverses des plis. A l'échelle des Alpes Occidentales comme à celle des Chaînes Subalpines Méridionales et des « arcs » élémentaires qui les composent, les structures plissées disposées en arc ne sont pas simples, mais sont l'aboutissement d'une évolution tectonique longue et complexe.
The Subalpine Chains of the French Western Alps give a good example of cover folds, which are detached along evaporite-bearing upper-Triassic beds. Their southern half shows also the intersection of two successive folded systems: E-W pyrenean folds (upper Cretaceous-middle Eocene), followed by N-S to NW-SE alpine folds (Oligocene—Miocene). It is therefore possible to distinguish two successive stages of tectonic deformation, but the problem remains to decide whether these stages can be divided into a certain number of short tectonic phases, or are long and continuous periods of tectonic deformation. It is shown that these two answers to the problem are two postulates, which seem to be equally probable. The first pyrenean stage of deformation gave rise to relatively simple folds, often of the ejective style type. The second, alpine, stage, occurred after and during subaerial erosion. In the areas where earlier E-W folds did not occur, new alpine N-S to NW-SE folds rose, whereas in the areas where earlier E-W folds were present, refolding of these folds only occurred, often accompanied by breaks, i. e. wrench faults and overthrusts, the latter often showing subhorizontal truncation of nearly vertical beds. In the same manner as for the entire Western Alps arc, the fold arcs in the southern subalpine chains are not simple virgations, but the result of a long and complex tectonic evolution.
Zusammenfassung Die subalpinen Ketten der französischen Westalpen sind ein gutes Beispiel von abgescherten Falten einer sedimentären Serie. Ihr südlicher Teil zeigt die Kreuzung von zwei Faltensystemen: Pyrenäische E-W-Falten (Obere Kreide -Mittleres Eozän) und alpine N-S-oder NW-SE-Falten (Oligozän-Miozän). Es bleibt das Problem, ob diese zwei Faltungsperioden in verschiedene tektonische Phasen gegliedert werden müssen oder nicht. Beide Hypothesen scheinen gleich wahrscheinlich zu sein. Während der ersten pyrenäischen Faltungsperiode entstehen nur einfache ejektive Falten. Die zweite, alpine Periode verlief während und nach kontinentaler Erosion; die ersten E-W-Falten wurden überkippt und zerbrachen, so daß Überschiebungen entstanden. Für die Westalpen sowie für die einzelnen Ketten der subalpinen Ketten sind Faltenbögen nicht einfache Virgationen, sondern verwickelte Strukturen, deren Geschichte lang und verschieden war.
. : E-W ( — ) N-S, NW-SE ( — ). , - , . . , , , , . E-W , . , , , , .
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18.
Mean and turbulent velocity measurements of supersonic mixing layers   总被引：1，自引：0，他引：1  
The behavior of supersonic mixing layers under three conditions has been examined by schlieren photography and laser Doppler velocimetry. In the schlieren photographs, some largescale, repetitive patterns were observed within the mixing layer; however, these structures do not appear to dominate the mixing layer character under the present flow conditions. It was found that higher levels of secondary freestream turbulence did not increase the peak turbulence intensity observed within the mixing layer, but slightly increased the growth rate. Higher levels of freestream turbulence also reduced the axial distance required for development of the mean velocity. At higher convective Mach numbers, the mixing layer growth rate was found to be smaller than that of an incompressible mixing layer at the same velocity and freestream density ratio. The increase in convective Mach number also caused a decrease in the turbulence intensity ( u /U).List of Symbols a speed of sound - b total mixing layer thickness betweenU 1 – 0.1U andU 2 + 0.1U - f normalized third moment ofu-velocity,f u 3/(U)3 - g normalized triple product ofu 2 v,g u 2 v/(U)3 - h normalized triple product ofu v 2, h uv' 2/(U)3 - l u axial distance for similarity in the mean velocity - l u axial distance for similarity in the turbulence intensity - M Mach number - M c convective Mach number (for 1=2),M c (U 1–U 2)/(a 1+a 2) - P static pressure - r freestream velocity ratio,rU 2/U 1 - Re unit Reynolds number,Re U/ - s freestream density ratio,s 2/ 1 - T t total temperature - u instantaneous streamwise velocity - u deviation ofu-velocity,u u–U - U local mean streamwise velocity - U 1 primary freestream velocity - U 2 secondary freestream velocity - U average of freestream velocities, ¯U (U 1 +U 2)/2 - U freestream velocity difference,U U 1 –U 2 - v instantaneous transverse velocity - v deviation ofv-velocity,v v – V - V local mean transverse velocity - x streamwise coordinate - y transverse coordinate - y 0 transverse location of the mixing layer centerline - ensemble average - ratio of specific heats - boundary layer thickness (y-location at 99.5% of free-stream velocity) - similarity coordinate, (y –y 0)/b - compressible boundary layer momentum thickness - viscosity - density - standard deviation - dimensionless velocity, (U –U 2)/U - 1 primary stream - 2 secondary stream A version of this paper was presented at the 11th Symposium on Turbulence, October 17–19, 1988, University of Missouri-Rolla  相似文献   

19.
Zusammenfassung Wasserfreies Eisen(III)sulfat, Fe2(SO4)3, existiert in zwei Modifikationen. Nach Einkristallaufnahmen kristallisiert die eine wahrscheinlich in Raumgruppe (arh=8,791±0,004 Å, =55°52±2; Z=2), die andere in Raumgruppe C 2h 5 –P21/n (a=8,296±0,002 Å, b=8,515±0,002 Å, c=11,60±0,002 Å, =90°30; Z=4). Von Cr2(SO4)3 und Ga2(SO4)3 konnten für die rhomboedrischen Modifikationen, die isotyp zu jener von Fe2(SO4)3 sind, aus Pulveraufnahmen die Gitterkonstanten bestimmt werden.
Summary Anhydrous iron(III)sulfate exists in two modifications. From single-crystal work, one of the modifications crystallizes probably in space group (arh=8.791±0.004 Å, =55°52±2; Z=2), whereas the other in space group C 2h 5 –P21/n (a=8.296±0.002 Å, b=8.515±0.002 Å, c=11.60±0,002 Å, =90°30; Z=4). The lattice constants of the rhombohedral modifications of Cr2(SO4)3 and Ga2(SO4)3, which are isomorphous with rhombohedral Fe2(SO4)3, have been determined from powder photographs.

Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.  相似文献   

20.
The axial base and skin capacities of piles bored in cohesion less soils are often estimated using empirical, semi-empirical and theoretical methods. The aim of this paper is to assess the applicability and evaluate the accuracy of different predictions methods available in the literature, via comparison with data from 43 field pile load tests conducted on shafts drilled in the region of the United Arab Emirates. Janbu's theoretical method (1989) with the parameter (=75°) and Vesics theoretical method (1975) yielded accurate predictions for the base resistances. Burlands approach (1973) overpredicts the skin capacities with an average predicted-to-estimated ratio (q p /q e) of three times greater than the unity while using values of the coefficient of earth pressure (k=05k o ) and the angle of soil-pile friction (=23).  相似文献   

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