Sedimentary provenance of Mid-Devonian clastic sediments in the Teplá-Barrandian Unit (Bohemian Massif): U–Pb and Pb–Pb geochronology of detrital zircons by laser ablation ICP-MS

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.     

SHRIMP U–Pb zircon dating of the Neoproterozoic Penglai Group and Archean gneisses from the Jiaobei Terrane, North China, and their tectonic implications

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.     

Tectonics and volcanism along the Pacific Marginal Zone of Central America

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.

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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.

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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.

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Catastrophic landslip activity in two hard rock terrains of peninsular India

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.     

Neodymium isotopic evidence for the tectonic assembly of Late Archean crust in the Slave Province,northwest Canada

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.     

From the Libyan border to the Nile – Neoproterozoic magmatism and basement evolution of southern Egypt

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.     

Palaeomagnetic investigations of the tertiary and quaternary igneous rocks: V. The basic tertiary basalts of Lower Silesia,Poland

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.

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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.

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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.

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

Origin of continental crust of 1.9-1.7 Ga age: Nd isotopes and U-Pb zircon ages in the Svecokarelian terrain of South Finland

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.     

Faziesverzahnung von diamantführenden Konglomeraten und Bändererzen (BIF) in der südlichen Serra do Espinhaço (Minas Gerais,Brasilien)

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.

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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.

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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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Morphologie de la Méditerranée Occidentale

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.

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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.

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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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Variations of existing glaciers in the Southwestern mountain region of Xizang (Tibet)

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.     

Origin of continental crust of 1.9-1.7 Ga age defined by Nd isotopes in the Ketilidian terrain of South Greenland

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.     

Rythme et Modalités des Plissements Superposés dans les Chaînes Subalpines Méridionales des Alpes Occidentales Françaises

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.

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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.

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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.

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. : E-W ( — ) N-S, NW-SE ( — ). , - , . . , , , , . E-W , . , , , , .

     

Mineralogical variations in the Delakhari sill,Deccan trap intrusion,central India

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 (Fa_44–50, called type-A olivine) and interstitial skeletal olivine (Fa_70–95, 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     

Potentiometric Determination of Silver Thiolate Formation Constants Using a Ag2S Electrode

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.     

Röntgenuntersuchung der wasserfreien Sulfate der dreiwertigen Metalle Eisen,Chrom und Gallium

Zusammenfassung Wasserfreies Eisen(III)sulfat, Fe₂(SO₄)₃, existiert in zwei Modifikationen. Nach Einkristallaufnahmen kristallisiert die eine wahrscheinlich in Raumgruppe (a_rh=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.

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Summary Anhydrous iron(III)sulfate exists in two modifications. From single-crystal work, one of the modifications crystallizes probably in space group (a_rh=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.

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.     

The pyroxmangite-rhodonite transformation for the MnSiO3 composition

The polymorphic transformation between synthetic pyroxmangite and rhodonite of MnSiO₃ composition has been reversibly bracketed in the presence of water at 3 kbar (between 425 ° and 450 ° C), 6 kbar (between 475 ° and 525 ° C), 20 kbar (between 500 ° and 900 ° C), 25 kbar (between 800 ° and 900 ° C) and 30 kbar (between 900 ° and 1,000 ° C), using standard cold-seal pressure vessels and piston cylinder apparatus. Oxygen fugacities buffered by the bomb walls and piston-cylinder cell assemblies sufficed to keep manganese in the divalent state. Pyroxmangite of MnSiO₃ composition is shown to be the high-pressure, low-temperature polymorph with respect to rhodonite of the same composition. It is a stable phase at atmospheric pressure below 350–405 ° C.X-ray data for synthetic pyroxmangite are presented. The unit-cell parameters (a₀=6.717(2) Å, b₀=7.603(1)Å, c₀=17.448(5) Å, =113 °50(1), = 82 °21(2), =94 °43(1); space group P-1) give a unit-cell volume (807.5(0.3) ų) which, in accordance with other recent least squares lattice refinements of hydrothermally synthesized material, is slightly smaller than that obtained by single-crystal work on anhydrously synthesized material.Application of the present results to natural rocks is severely restricted due to the great variety and extent of cationic substitutions observed in natural pyroxenoids. The univariant polymorphic transformation determined for the MnSiO₃ composition is thus replaced in natural systems by a divariant field in which pyroxmangite and rhodonite of differing composition will stably coexist.     

Comparison between measured and predicted values of axial end bearing and skin capacity of piles bored in cohesionless soils in the Arabian Gulf Region

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).     

Isotopic composition of oxygen and hydrogen in mud-volcanic waters from Taman (Russia) and Kakhetia (Eastern Georgia)

The ¹⁸O and D values in mud-volcanic waters of the Taman Peninsula and Kakhetia vary from +0.7 to +10.0 and from –37 to –13 , respectively. These values increase as the Greater Caucasus is approached. The increase in 18O and D also positively correlates with fluid generation temperatures based on hydrochemical geothermometers. This is accompanied by changes in the chemical composition of waters, in which contents of alkali metals, HCO^– ₃ ion, and boron increase, while the content of halogen ions (Cl, Br, J) decreases. Changes in the isotopic composition of water are also accompanied by the increase of ¹³ in methane and decrease of ¹¹ B in clays. Analysis of formal models of the evolution of isotopic composition of mud-volcanic waters showed that mud volcanoes are recharged by freshened water from the Maikop paleobasin with an inferred isotopic composition of D –40 and ¹⁸ O –6. Based on this assumption, the ¹⁸O and D values observed in mud-volcanic waters can be explained not only by processes of distillation and condensation in a closed system, but also by combined processes of isotopic reequilibration in the water-illite-methane system.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 143–158.Original Russian Text Copyright © 2005 by Lavrushin, Dubinina, Avdeenko.     

Age of granitic activity associated with copper–molybdenum mineralization at Malanjkhand, Central India

The Malanjkhand copper–molybdenum deposit in the Bhandara Craton, Central India, is hosted by a granite complex which consists of regionally dominant grey granitoid and pink granitoid confined to the mineralized zone. New SHRIMP RG data on zircons from both granite types are inferred to have crystallized during the same magmatic pulse at ca 2.48 Ga. The discrepancy between zircon age and earlier obtained Rb–Sr whole-rock age is attributed to modification of the Rb–Sr system by hydrothermal overprint. Similarity in petrographic features and chemical affinity in combination with identical age strongly indicate that the pink granite is the hydrothermally altered variety (microclinization and silicification) of the grey granite. The spatially associated, main Cu–Mo mineralization event at Malankhand appears to be broadly contemporaneous with and genetically related to the emplacement of the host granitoids at about 2.48 Ga.