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1.
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   

2.
We report the result of H2O-undersaturated melting experiments on charges consisting of a layer of powdered sillimanite-bearing metapelite (HQ36) and a layer of powdered tonalitic gneiss (AGC150). Experiments were conducted at 10 kbar at 900°, 925° and 950°C. When run alone, the pelite yielded 40 vol% strongly peraluminous granitic melt at 900°C while the tonalite produced only 5 vol% weakly peraluminous granitic melt. At 950°C, the pelite and the tonalite yielded 50 vol% and 7 vol% granitic melt, respectively. When run side by side, the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone. In the pelite, the melt abundance increased by 25 vol%. When run alone, biotite dehydration-melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt. When run side by side only garnet was produced in addition to granitic melt. Experiments of relatively short duration, however, also contained Al-rich orthopyroxene. We suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of Al2O3 in the melt, which lowers the temperature of the biotite dehydration-melting reaction. In the pelite, the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite-layer to the pelite-layer. This has the effect of changing the bulk composition of this layer in the direction of minimum-temperature granitic liquids. Our results show that rocks which are poor melt-producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase(s) and facilitate dehydration-melting. Because of this effect, the continental crust may have an even greater potential for granitoid melt production than previously thought. Our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks, which will be reflected in their isotopic and geochemical compositions.  相似文献   

3.
The carbon isotopic fractionation between CO2 vapour and sodamelilite (NaCaAlSi2O7) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag2C2O4 was the source of CO2 and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined by stepped heating and the 13C of coexisting vapour was determined directly by capsule piercing. CO2 solubility in SM displays a complex behavior with temperature. At pressures up to 10 kbars CO2 dissolves in SM to form carbonate ion complexes and the solubility data suggest slight negative temperature dependence. Above 20 kbars CO2 reacts with SM to form immiscible Na-rich silicate and Ca-rich carbonate melts and CO2 solubility in Na-enriched silicate melt rises with increasing temperature above the liquidus. Measured values for carbon isotopic fractionation between CO2 vapour and carbonate ions dissoived in sodamelilite melt at 1200°–1400° C and 5–30 kbars average 2.4±0.2, favouring13C enrichment in CO2 vapour. The results are maxima and are independent of pressure and temperature. Similar values of 2 are obtained for the carbon isotopic fractionation between CO2 vapour and carbonate melts at 1300°–1400° C and 20–30 kbars.  相似文献   

4.
Thermal treatments of anorthite carried out at up to 1,547° C show that the unit cell parameter changes as a function of the treatment temperature. The best fit curve found by non-linear least squares analysis is: =91.419-(0.327·10-6)T 2+(0.199·10-12)T 4-(0.391·10)T 6. The results obtained support significant Al,Si disorder (Al0.10, where Al=t 1(0)-1/3 [t 1(m)+t 2(0)+t 2(m)], Ribbe 1975), in anorthite equilibrated near the melting point and confirm a high temperature series differentiated from the low temperature series for calcic plagioclases in the An85–An100 range also. In the plot vs. An-content the high and low temperature curves intersect at An85 composition and progressively diverge in the An85–An100 range. The trends of the high and low temperature curves in this range are interpretable on the basis of the degree of Al, Si order in the average structures of calcic plagioclases.  相似文献   

5.
Temperatures of the formation of mud-volcanic waters are determined based on concentrations of some temperature-dependent components (Na–Li, Mg–Li). Estimates obtained for the Taman and Kakhetia regions are similar and range from 45 to 170°, which correspond to depths of 1–4.5 km. The calculated temperatures correlate with the chemical (Li, Rb, Cs, Sr, Ba, B, I, and HCO3) composition of water and 13 (2) and 13 (CH4) values in spontaneous gases. The isotope values indicate that mechanisms of the formation of 13-rich gases, i.e., gases with high 13 values (up to +16.0 in 2 and –23.4 in CH4) in mud-volcanic systems of Taman and Kakhetia are governed by fluid-generation temperatures rather than the supply of abyssal gases. The 11 value was determined for the first time in mud-volcanic products of the Caucasus region. This value ranges from +22.5 to +39.4 in the volcanic water of Georgia, from –1.2 to +7.4 in the clayey pulp of Georgia, and from –7.6 to +13.2 in the clayey pulp of Taman. It is shown that the 11 value in clay correlates with the fluid-generation temperature and 11 correlates with 13 in carbon-bearing gases. These correlations probably testify to the formation of different phases of mud-volcanic emanations in a single geochemical system and suggest the crucial role of temperature in the development of isotope-geochemical features.  相似文献   

6.
In this paper, we present boron isotope analyses of variably degassed rhyolitic glasses from Long Valley, California. The following results indicate that pre-eruptive boron isotopic signatures were preserved in degassed glasses: (1) averaged secondary ionization mass spectrometry (SIMS) measurements of H2O-rich (~3 wt%) melt inclusions from late erupted Bishop Tuff pumice are indistinguishable from positive thermal ionization mass spectrometry (PTIMS) analysis of vesiculated groundmass glass (11B=+5.0±0.9 and +5.4±5, respectively); (2) SIMS spot-analyses on H2O-poor obsidian (~0.15 wt% H2O) from younger Glass Mountain Dome YA (average 11B=+5.2±1.0) overlap with compositionally similar late Bishop Tuff melt inclusions; and (3) four variably degassed obsidian samples from the 0.6 ka Mono Craters (H2O between 0.74 and 0.10 wt%) are homogeneous with regard to boron (average 11B=+3.2±0.8, MSWD=0.4). Insignificant variations in 11B between early and late Bishop Tuff melt inclusion glasses agree with published experimental data that predict minor 11B depletion in hydrous melts undergoing gas-saturated fractional crystallization. Melt inclusions from two crystal-rich post-caldera lavas (Deer Mountain and South Deadman Dome) are comparatively boron-rich (max. 90 ppm B) and have lower 11B values (average 11B=+2.2±0.8 and –0.4±1.0 ) that are in strong contrast to the boron isotopic composition of post-caldera crystal-poor rhyolites (27 ppm B; 11B=+5.7±0.8). These variations in 11B are too large to be caused by pre-eruptive degassing. Instead, we favor assimilation of 11B depleted low-temperature hydrothermally altered intrusive rocks subsequent to fresh rhyolite recharge.Editorial responsibility: J. HoefsAn erratum to this article can be found at  相似文献   

7.
Zusammenfassung Die einzelnen tektonischen Einheiten des Iran werden in ihrer faziellen und strukturellen Entwicklungsgeschichte dargestellt. Fazies und Paläogeographie sprechen dafür, daß vom Infrakambrium bis in die Trias der gesamte Raum zwischen dem Persischen Golf und dem Elburs-Gebirge eine einheitliche Entwicklung genommen hat. Eine zusammenhängende Plattformsedimentation in Schelffazies kennzeichnet dieses Gebiet während des gesamten Zeitraums. Es ist ein Teil Gondwanas. Paläomagnetische Befunde stützen diese Aussage. Ozeanische Kruste und damit Hinweise auf die Tethys als eine strukturelle Einheit fehlen während dieser Zeit in diesem Gebiet. Lediglich als Faunenprovinz in Flachmeerfazies ist sie wirksam. Das offene Meer lag vom Infrakambrium bis zur oberen Trias im Norden. In der Trias tritt mit einer Heraushebung, die mit tiefgreifender Lateritisierung verbunden ist, und einer anschließenden Transgression ein grundlegender Wechsel des geodynamischen Regimes ein. Von jetzt an erfolgen die Ingressionen in den Iran von Süden. Eine engräumige fazielle Differenzierung setzt ein. Kontinental beeinflußte Sedimente im Jura zeigen, daß im Iran ein Hochgebiet entstanden ist. Gleichzeitig tretenwahrscheinlich in Anlehnung an langlebige Geosuturen — Ophiolith-Radiolarit-Zonen auf, die als das Ergebnis intrakratonischer Zerbrechung gedeutet werden. Die Ingressionen gehen wahrscheinlich von Tiefseerinnen aus, in denen auch die Ophiolithe konzentriert sind. Der Aufstieg des ophiolithischen Materials an die Oberfläche erfolgte entlang von Linien, an denen sich flach geneigte Unterschiebungen von Kruste unter Kruste ereigneten. Dabei kam es zu erheblichen Krustenverkürzungen. Möglicherweise fällt der Umbruch des tektonischen Regimes in der Obertrias mit der Plattenkollision Arabia-Iran/ Eurasia zusammen. Die Grenze zwischen Arabia-Iran und Eurasia liegt aber nicht im Gebiet des Persischen Golfes und der Zagros-Ketten, sondern muß nördlich des Elburs-Gebirges gesucht werden.
The individual tectonic units of Iran are represented with respect to the history of the development of their facies and structure. Facies and paleogeography indicate that the entire area between the Persian Gulf and the Elburz Mountains had a uniform development until the Triassic. During the whole period a coherent platform sedimentation remained characteristic of this area, which is part of Gondwana. Paleomagnetic data support this statement. Oceanic crust and thus any indications of the Tethys as a structural unit are absent in this area for that period of time. Its existence is only demonstrated in faunal provinces in shallow-marine facies. From the Infra-Cambrian to the Late Triassic the northern part of the area was open sea. During the Triassic, uplifting processes combined with deep lateritization and subsequent transgression initiated a basic change in the geodynamic regime. From this time on the ingressions into Iran proceeded from the south. At this time differentiation of facies began within small areas. Continental influences in the Jurassic sediments show that an elevated area was formed in Iran. At the same time ophiolite-radiolarite zones occurred, probably along long-lived geosutures. These zones are interpreted to be the result of processes breaking up the craton. Probably, the ingressions started from deep-sea furrows where ophiolite concentrations are found. The ascension of the ophiolitic material to the surface occurred along lines where gently dipping subduction of crust under crust took place. During this process it came to considerable crustal shortening. It is possible that the change in the tectonic regime during the Late Triassic coincided with the collision of the Arabia-Iran and Eurasia plates. The boundary between the Arabia-Iran and Eurasia plates is, however, not to be found in the area of the Persian Gulf and the Zagros mountain ranges, but is assumed to be north of the Elburz Mountains.
Résumé Chacune des unités tectoniques de l'Iran font l'objet d'un exposé concernant leur développement du point de vue de leur facies et de leur structure. Le facies et la paléogéographie indiquent que, de l'Infracambrien au Trias, tout le territoire compris entre le Golf persique et la chaîne de l'Elbours a eu un développement unitaire. Une sedimentation de plateforme cohérente, à facies de shell, caractérise cette région pendant toute cette période. C'est une partie du Gondwana. Des données paléomagnétiques appuient cette affirmation. Toute croûte océanique et, de ce fait toute indice d'une Téthys en temps qu'unité structurale, sont absent dans cette région à ce moment. Une mer ouverte s'y étend au nord de l'Infracambrien jusqu'au Trias supérieur. Au Trias, un soulèvement, auquel est liée une forte latéritisation, et la trangression qui lui est liée, entraînent un changement radical du régime géodynamique. A partir de ce moment, des ingressions se produisent en Iran à partir du sud introduisant des différences de facies. Des sédiments montrant une influence continentale montrent qu'au Jurassique un fort soulèvement s'est produit en Iran. En même temps, vraisemblablement suivant une géosuture depuis longtemps active, apparurent des zones ophiolothiques à radiolarites, qui indiquent une rupture intracratonique. Les ingressions émanent vraisemblablement d'un sillon océanique profond dans lequel sont également concentrées les ophiolithes. La montée du matériau ophiolithique à la surface s'en suivit le long de lignes suivant lesquelles se sont produits dessous-charriages intracrustaux, d'où sont résultés de notables racourcissements de la crôute. Il est possible que cette rupture du régime tectonique coïncide, au Trias supérieur, avec la collision des plaques de l'Arabie Iran et de l'Ewrasie. La limite entre l'Arabie-Iran et l'Eurasie ne se trouve donc pas dans la région du Golfe persique et des chaînes du Zagros, mais doit être recherchée au nord de la Chaîne de l'Elbours.
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8.
Iron- and vanadium-bearing kyanites have been synthesized at 900 and 1100° C/20 kb in a piston-cylinder apparatus using Mn2O3/Mn3O4- and MnO/Mn-mixtures, respectively, as oxygen buffers. Solid solubility on the pseudobinary section Al2SiO5-Fe2SiO5(-V2SiO5) of the system Al2O3-Fe2O3(V2O3)-SiO2 extends up to 6.5 mole% (14mole %) of the theoretical end member FeSiO5(V2SiO5) at 900°C/20 kb. For bulk compositions with higher Fe2SiO5 (V2SiO5) contents the corundum type phases M2O3(M = Fe3+, V3+) are found to coexist with the Fe3+(V3+)-saturated kyanite solid solution plus quartz. The extent of solid solubility on the join Al2SiO5-Fe2SiO5 at 1 100°C was not found to be significantly higher than at 900° C. Microprobe analyses of iron bearing kyanites gave no significant indication of ternary solid solubility in these mixed crystals. Lattice constants a 0, b 0, c 0, and V0 of the kyanite solid solutions increase with increasing Fe2SiO5- and V2SiO5-contents proportionally to the ionic radii of Fe3+ and V3+, respectively, the triclinic angles ,, remain constant. Iron kyanites are light yellowish-green, vanadium kyanites are light green. Iron kyanites, (Al1.87 Fe 0.13 3+ )SiO5, were obtained as crystals up to 700 m in length.  相似文献   

9.
Zusammenfassung Glendonite sind Pseudomorphosen von überwiegend Calcit (in mehreren Generationen) nach Thenardit (Na2SO4). Die meistens sternförmigen Kristallaggregate von Walnuß- bis Faustgröße bildeten sich im unterkühlten Meereswasser (cold salinity currents) in oder auf der oberen Lage des Meeresbodens. Sie sind an marine Tonsteine gebunden und kommen in ihrem Verbreitungsgebiet in großer Zahl vor. Rezente Glendonite treten nur im Arktischen Ozean und seinen Nebenmeeren (Weißes Meer) auf. Fossile gibt es in Perm und Kreide Australiens (permisches Vereisungsgebiet) und in den jeweils hohen Breiten der Nordhalbkugel im Domerium, mittleren Jura, Valangin, Ober-Apt/Unter-Alb, Oligozän/Miozän und Pleistozän/Holozän. Für diese Zeiten ist eine erhebliche Abkühlung zu postulieren.Beim Vergleich mit den entsprechenden Schichtenfolgen Mitteleuropas fällt auf, daß in den Zeiten der Glendonit-Vorkommen der arktischen Gebiete im borealen Europa dunkle Tonsteine abgelagert wurden. In Zeiten starker Kalksedimentation (Ober-Oxford, Kimmeridge, Ober-Kreide) und arider oder subtropischer Klimate in Mitteleuropa (Tithon: Münder Mergel-Fazies und Berrias: Wealden-Fazies) fehlen Glendonite auch im hohen Norden.Alle diese Befunde verweisen auf ausgeprägte, langfristige Klimaschwankungen vom Lias ab. Zur Zeit der kälteren Phasen müssen in den hohen Breiten mit den heutigen Verhältnissen vergleichbare polare Klimate geherrscht haben.
Glendonites are pseudomorphs of mainly calcite (in several generations) after Thenardit (Na2SO4). The crystal aggregates are preponderantly star shaped and range in size between walnut and fist dimensions. They were formed by cold salinity currents in the uppermost layer of the ocean floor. They are restricted to marine shales and mudstones and occur in great quantities in their area of distribution. Recent glendonites are known only from the Arctic Ocean and adjacent seas (e. g. the White Sea). Fossil glendonites occur in the Permian and Cretaceous of Australia (Permian area of glaciation) and in high latitudes of the Northern hemisphere in the Domerian, middle Jurassic, Valanginian, late Aptian — early Albian, Oligocene — Miocene, and Pleistocene — Holocene. For these periods a considerable cooling has to be postulated.If the sediments of these periods are compared with the corresponding ones of central Europe it is obvious that in those periods during which glendonites were formed in high latitudes dark shales were deposited in the boreal part of Europe. In periods of high lime accumulation (Upper Oxfordian, Kimmeridgian, Upper Cretaceous) and arid or subtropical climates in central Europe (e. g. the Münder Mergel facies of the Tithonian and the Purbeck and Wealden facies of the Berriasian) glendonites are absent from the high latitudes.All these observations point to intensive and long term variations of climate from the early Jurassic on. During the cold phases, comparable polar climates must have predominated in the high latitudes as exist today.
Résumé Les glendonites sont des pseudomorphoses, principalement de calcite (en plusieurs générations), de thénardite (Na2SO4). Les agrégats, le plus souvent de forme radiée, de la taille d'une noix à celle du poing, se sont formés dans de l'eau marine surrefroidie (»courants de salinité froide«) dans la couches supérieure des fonds marins ou à sa surface. Ils sont liés à des argiles marines et se présentent en grande quantité dans leur aire d'extension. Les glendonites récentes se rencontrent seulement dans l'Océan arctique et dans les mers annexes (Mer blanche). Elles existent à l'état fossile dans le Permien et le Crétacique de l'Australie (région de la glaciation permienne) et dans les hautes latitudes de l'époque de l'hémisphère nord dans le Domérien, le Jurassique moyen, le Valanginien, l'Aptien supérieur/inférieur, l'Oligocène/Miocène, et le Pleistocène/Holocène. Pour ces périodes il y a lieu de postuler un net refroidissement.Par comparaison avec les séries correspondantes de l'Europe centrale, il apparaît que des argiles foncées ont été déposées, lors des occurrences de Glendonites des régions arctique, dans l'Europe boréale. Lors de sédimentations calcaires intenses (Oxfordien supérieur, Kimméridgien, Crétacique supérieur) et dans les climats arides ou subtropicaux dans l'Europe centrale (Tithonique: facies marneux de Münder, et Berriasien: facies wealdien) les glendonites sont absentes également dans les hautes latitudes septentrionales.Toutes ces occurrences indiquent des modifications climatiques bien marquées, de longue durée à partir du Lias. Au moment des phases plus froides, il a dû régner dans les hautes latitudes un climat polaire comparable à celui de nos jours.
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10.
Impure limestones with interstratified metachert layers were contact metamorphosed and metasomatized by the Bufa del Diente alkali syenite. Massive marbles exhibit mineralogical and stable isotope evidence for limited fluid infiltration, confined to a 17 m wide zone at the contact. Influx of magmatic brines along most metacherts produced up to 4 cm thick wollastonite rims, according to calcite (Cc)+quartz (Qz)= wollastonite (Wo)+CO2, and were observed at distances of up to 400 m from the contact. The produced CO2 exsolved as an immiscible low density CO2-rich fluid. Chert protolith isotope compositions were 18O (Qz)=27–30%. and 18O (Cc)=24–27%.. Many wollastonites in infiltrated metacherts have low 18O ranging from 11–17 and confirm that decarbonation occurred in presence of a magmatic-signatured fluid. Large gradients in 18O (Wo) across the rims may reach 6 The 18O of remaining quartz is often lowered to 15–20 whereas caleites largely retained their original compositions. The isotopic reversals of up to 10 between quartz and calcite along with reaction textures demonstrate non-equilibrium between infiltrating fluid in the aquifer and the assemblage calcite+quartz+wollastonite. This is compatible with the assumption of a down-temperature flow of magmatic fluids that occurred exclusively in the remaining quarzite layer. The 13C (Cc) and 18O (Cc) of marble calcites measured perpendicular to two metachert bands reveal significant isotopic alterations along distances of 4.5 cm and 7.5 cm from the wollastonite-marble boundary only into the hanging wall marble, suggesting an advection process caused by a fluid phase which movel upwards. Covariation trends of 13C (Cc) and 18O (Cc) across the alteration front indicate that this fluid was CO2-rich. Mass balance calculations show that all CO2-rich fluid produced by the decarbonation reaction was lost into overlying marble. The metachert aquifers did not leak with respect to water-rich fluids.  相似文献   

11.
Three small intrusions in Ketilidian gneisses near Julianehaab comprise sheets and veins of olivine-magnetite-grunerite or magnetite-amphibole rocks partly surrounded by garnetiferous hornblende-biotite granitoid rock. The latter skin locally widens out into diffuse bodies of fayalite-orthopyroxene-quartz syenite or monzonite and biotite granite, which show layering similar to that resulting from gravity settling of crystals. Near the intrusions the country rocks lose their foliation and have been partially melted. Intrusion probably occurred at the close of regional metamorphism 1,750–1,780 m.y. ago, just prior to emplacement of the rapakivi granite suite of South Greenland. The mafic minerals of the intrusions are markedly enriched in iron and, in the case of olivine, orthopyroxene, grunerite and garnet, in manganese as well: olivine Fa90Te5Fo5; orthopyroxene (inverted pigeonite) Ca2Fe77Mn6Mg15; calciferous amphiboles are typically hastingsitic; biotites generally have Fe/Fe+Mg ratios of 0.8; garnets are almandine-grossularite-spessartine mixtures; essentially pure magnetite is the dominant oxide mineral and ilmenite is only moderately manganiferous. Crystallization of the mafic rocks appears to have followed the trend of the quartz-fayalite-magnetite buffer curve from perhaps 800°C to <550°C at pressures, calculated from thermodynamic considerations, of 4 to 5 kb. However, the presence of Mn makes estimates of pressure and temperature uncertain. Comparison with other late- to post-orogenic intrusions—the South Greenland and Finnish rapakivi granite suites, the Labrador adamellite complex and the Pikes Peak batholith of Colorado—reveals both similarities and differences, particularly with respect to mineral parageneses, depth of emplacement and manganese enrichment.  相似文献   

12.
Zusammenfassung Der Gebirgszug Raura im zentralen Peru (ungefähr 10° 25 südl. Breite und 76° 45 westl. Länge) ist ein wichtiger Gletscherkernpunkt an der Kontinentalwasserscheide. An seiner NO-Seite, wo der Marañon bzw. Amazonas entspringt, lassen sich im Gebiet von Lauricocha eine Reihe alter Gletschervorstöße nachweisen, die der letzten pleistozänen Vereisung der Anden zugeordnet werden (A.Cardich, 1958, 1963, 1964). Eine Radiokohlenstoffdatierung an eingelagertem organischen Material bestätigt das angenommene Alter und legt gleichzeitig ein Interstadial fest (Interstadial Aguamiro, 12 500 Jahre B.P.). Die Gletschervorstöße vor diesem Zeitpunkt waren bedeutender, sowohl in ihrer Ausdehnung und der Eismächtigkeit (bis 300 m) als auch in ihrer Dauer. Die späteren Vorstöße waren kleinräumiger und kurzlebiger, wie aus dem geringeren Volumen der glazialen Ablagerungen hervorgeht. Ein Vergleich mit anderen untersuchten Gebieten unterstützt bei Berücksichtigung der14C-Datierung größtenteils die früher aufgestellte Systematik.
The mountain chain Raura in the central region of Peru (about 10° 25 southern latitude and 76° 45 western longitude) is an important center of glaciers at the continental drainage divide. At its NE-side, from where the river Marañon and Amazonas, respectively, originates, in the region of Lauricocha it is possible to identify a series of old advances of glaciers, which are attributed to the last great glaciation of the Pleistocene (A.Cardich, 1958, 1963, 1964). Radiocarbon dating of deposited organic material confirms the assumed age and defines simultaneously an Interstade (Interstade Aguamiro, 12,500 B.P.). The glacial advance prior to this date were more important, not only in their extension and in the thickness of ice (up to 300 m) but also in their duration. The later advances were less extensive and of shorter duration, as may be concluded from the smaller volume of the glacial deposits. A comparison with other regions studied confirms mostly the earlier given classification with regard to the14C-dating.
Resumen En la región central del Perú, la Cordillera Raura (alrededor de 10° 25 de latitud sur y 76° 45 de longitud) es un centro de origen de rios y un núcleo de glaciación importantes. En la vertiente que corresponde a las nacientes del río Marañón o Amazonas se encuentra Lauricocha, una zona donde se hallan una serie de rasgos y depósitos originados por antiguos avances del glaciar procedente de Raura. Estas huellas glaciares fueron señaladas por nosotros como correspondientes a la última glaciación del Pleistoceno de los Andes y que luego de otras observaciones y estudios nombramos como Glaciación Lauricocha (A.Cardich, 1958, 1963, 1964). Esta edad estimada se confirma con el fechado por radiocarbono que presentamos en este trabajo y ademas fija un interstadial (interstadial Aguamiro) que tiene la caracteristica de determinar dos momentos diferentes en el proceso de esta Glaciación: los avances del hielo anteriores a esa fecha fueron de mayor importancia tanto por la mayor extensión como por un mayor espesor de los glaciares que habrían alcanzado alrededor de los 300 m, como por la mayor duración de estos estadios. Los avances glaciarios posteriores a la aludida fecha radiocarbónica alcanzaron extensiones algo menores y ante todo han sido de corta duración como se advierte por el mucho menor volumen de los depósitos de origen glaciar. Haciendo un ordenamiento de otros acontecimientos a partir del fechado radiocarbónico y mediante correlaciones con otras zonas estudiadas se confirma en gran parte las sistematizaciones adelantadas anteriormente.
Résumé La chaîne de montagnes Raura située au centre du Pérou (environ 10° 25 de latitude sud et 76° 45 longitude ouest) est un important centre de glaciers à la ligne de partage des eaux continentales. Du coté Nord-Est, là où le Maranon ou l'Amazonas a sa source, on peut prouver dans la région de Lauricocha, l'existence de vieilles avancées de glaciers, que l'ou peut attribuer à la dernière glaciation pléistocène des Andes (A.Cardich, 1958, 1963, 1964). La méthode radiocarbone14C appliqué à des matières organiques enclavées, confirme l'âge supposé et définit en même temps un Interstadial (Interstadial Aguamiro). Les avancées des glaciers avant cette époque étaient plus importantes, aussi bien par leur extension que par leur épaisseur (jusqu'à 300 m) et leur durée. Les avancées glaciaires ultérieures furent moins étendues et de plus courte durée, comme le montre le volume moindre des dépôts glaciaires. La comparaison avec d'autres régions déjà étudiées, corrobore, par la méthode14C, en grande partie la systematique établie antérieurement.
, ( 10°25 . 76°45 . ), . - , , , . (A. CARDICH, 1958, 1963, 1964). 14 . (Interastadlei Aguamiro, 12 500 ). , (300 ), . - , , , , , . 14 .
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13.
The Iforas (60 000 km2) falls within the Pan-African mobile belt bordering the West-African craton in north-eastern Mali Republic. It is characterized by major N-S shear belts parallel to the edge of the craton which delimit longitudinal blocks some of which have undergone considerable horizontal displacements. The central core of the Iforas which consists largely of reactivated pre-Pan-African basement injected by Pan-African syn- and post-tectonic intermediate and acid plutonic rocks, has behaved as a relatively rigid blocks during the Pan-African dividing the orogenic belt into a western Iforas and an eastern Iforas.Western Iforas displays W to E zonation: an ophiolitic suture (Timetrine); trench volcano-sedimentary deposits cut by gabbros diorites and acid granitoids (Tilemsi); and a late orogenic composite »coastal range batholith intruding the pre-Pan-African basement of Central Iforas and its overlying volcano-sedimentary deposits which here display a littoral facies and a tillite.Central Iforas consists of two major units: a polycyclic pre-Pan-African basement metamorphosed under high amphibolite facies conditions of presumed Eburnean age and the Iforas granulite block bound to the W, N and E by shear zones.Eastern Iforas was totally separated during metamorphism and deformation from the Iforas granulite block. From West to East, three lithological assemblages have been recognised separed by shear belts: a Quartzite Group, a Gneissic Group and a Pelitic Group the latter representing the southern prolongation of the central Hoggar Pharusian province.Shear zones are an essential feature of Pan-African tectonism East of the West-African craton. The superimposed stress fields have been recognised producing: early N20° trending sinistral shear zones, a north-south dextral shear zone (Andjour-Tamaradant shear zone) and late conjugating sinistral NNW and dextral ENE wrench faults.Late Pan-African events reflect the uplift and unroofing of the Pan-African composite batholith, the intrusion of circular granite plutons often located close to shear zones and alternating episodes of distension and compression.Lastly the simple model proposed for the closing stages of the Pan-African in the Iforas is that of an active continental plate margin separated from the West African craton by an oceanic domain. Subsequent continental collision to the South with a promotory of the West African craton led to the formation of the Dahomeyan thrust front and modified the stress field. Closure of the oceanic domain of western Iforas is thought to have taken place by continued eastward subduction of the oceanic plate and sinistral movement along an inferred north westerly trending transform fault coinciding with the future Cretaceous Gao trough and an alignement of strong positive gravity anomalies. It was accompanied by the northerly migration of central and western Iforas along the conjugating dextral N-S Andjour-Tamaradant shear zone. Further shortening led to folding of the arcuate Timetrine-Ydouban-Gourma fold belt overlying the deformed margin of the West African craton.
Zusammenfassung Das Iforas-Gebiet (60 000 km2) gehört zur pan-afrikanischen Bewegungszone, die in Mali an das westafrikanische Kraton grenzt. Diese Zone wird von N-S Scherbewegungen parallel zum Kraton durchzogen, wobei größere horizontale Versetzungsbeträge langgestreckte Blöcke herausgetrennt haben. Der zentrale Teil von Iforas besteht im wesentlichen aus reaktiviertem prae-panafrikanischem Basement, das in pan-afrikanischer Zeit von syn- und posttektonischen, intermediären und sauren Plutoniten intrudiert wurde. Dieses Gebiet wirkt als relativ starrer Block, der während der pan-afrikanischen Orogenese den Orogengürtel in einen westlichen und einen östlichen Ast teilt. Das westliche Iforas-Gebiet zeigt eine E-W Zonierung: eine Ophiolith-Sutur, einen vulkano-sedimentären Gürtel und einen Rand-Batholithen.Zentral-Iforas wird aus zwei Einheiten aufgebaut: ein mehrfach metamorphisiertes Basement und einen Granitblock.In den überregionalen Scherzonen lassen sich drei Stress-Felder erkennen: eine ältere 20° streichende sinistrale Scherzone, eine N-S dextrale Scherzone und jüngere NNW und dextrale ENE Bruchzonen.Spät-pan-afrikanische Ereignisse sind durch Heraushebung und Abtrag, Granitintrusionen und wechselnden Dehnungs- und Kompressionsbewegungen gekennzeichnet.
Résumé L'Adrar des Iforas (60 000 km2) fait partie de la zone mobile pan-africaine en marge du craton ouest-africain au Nord-Est de la République du Mali. La région est caractérisée par d'importants accidents mylonitiques parallèles à la bordure du craton qui délimitent des compartiments longitudinaux dont certains ont subi des déplacements horizontaux considérables. La zone dorsale des Iforas qui consiste essentiellement en un socle pré-pan-africain réactivé et injecté au Pan-Africain par des roches plutoniques intermédiaires et acides, syn- et post-tectoniques, s'est comportée en compartiments relativement rigides au cours du Pan-Africain, divisant la chaîne en un rameau occidental et un rameau oriental.Le rameau occidental présente une zonation d'Ouest en Est: une suture ophiolitique (Timetrine); des dépôts volcano-sédimentaires de fosse recoupés par des gabbros et des diorites; et un vaste batholite composite tardi-orogénique qui recoupe le socle pré-pan-africain de la zone dorsale des Iforas et sa couverture de dépôts volcanosédimentaires ici à faciès littoral.La zone dorsale des Iforas comprend deux unités majeures: un socle prépan-africain polycyclique métamorphisé dans le faciès amphibolite, d'âge éburnéen présumé et le môle granulitique des Iforas, délimité à l'W, au N et à l'E par des accidents mylonitiques.Le rameau oriental était séparé du môle granulitique des Iforas lors du métamorphisme et de la déformation. D'W en E, on trouve trois unités séparées par des zones mylonitiques: un Groupe de Quartzites, un Groupe de Gneiss et un Groupe de Pélites. Ce dernier représente le prolongement vers le Sud de la province pharusienne du centre Hoggar.Les grands accidents de cisaillement sont un fait marquant du tectonisme pan-africain à l'Est du craton ouest-africain. Trois champs de contraintes superposées ont produit des accidents précoces sénestres de direction N20, un accident N-S dextre (Andjour-Tamaradant), et des failles cisaillantes tardives conjuguées d'orientation NNW sénestres et ENE dextres.Les événements pan-africains tardifs sont marqués par la surrection et l'érosion des batholites pan-africains, la mise en place de plutons granitiques souvent à proximité des grands accidents et par des alternances de distensions et de compressions.Enfin un modèle simple est proposé pour les stades ultimes du Pan-Africain dans l'Adrar des Iforas: une marge continentale active séparée du craton ouest-africain par un domaine océanique; suite à une collision au Sud avec un promontoire du craton ouestafricain qui aurait produit le front de chevauchement dahomeyen et modifié le champ de contraintes, la fermeture du domaine océanique de l'Ouest Iforas se serait produite par subduction à l'E de la plaque océanique et une translation sénestre le long d'une faille transformante orientée NW et coincidant avec le fossé crétacé de Gao et un alignement d'anomalies gravimétriques positives. Elle aurait été accompagnée par le déplacement vers le N de l'Iforas occidental et central le long de l'accident cisaillant dextre d'Andjour-Tamaradant. Cette fermeture aurait provoqué les plissements de la chaîne du Timetrine-Ydouban-Gourma qui repose sur la bordure déformée du craton ouestafricain.
(60000 2) - , . , , . , , -- , - . , - . - : , - . : . : , 20° ; , , -- -- . - , , .
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14.
Summary ¶This study experimentally investigated the transformation kinetics of synthetic polycrystalline aragonite to calcite at four temperature/pressure conditions (330°C/200MPa, 380°C/325MPa, 430°C/580MPa, and 480°C/875MPa), close to the calcite-aragonite equilibrium phase boundary. The extents of transformation measured as a function of time in a synthetic system, using in-situ annealed, high purity samples, are consistent with the kinetic model for grain-boundary nucleation and interface-controlled growth. The growth rates are slightly lower than those previously determined for a natural polycrystalline sample at 330 and 380°C. The activation energy (158kJ/mol) for calcite growth from synthetic samples is lower than that (247kJ/mol) from natural samples, but is close to the previously reported value (163kJ/mol) from a single crystal aragonite. The extrapolation of our experimental data to natural conditions reveals unusually fast transformation rates, in contrast to those of natural samples. The presence of deformational strain, fractures, defects or impurities in natural samples, and other factors may account for the discrepancy. This study suggests that the retrograde metamorphism of aragonite to calcite may proceed in a wide range of rates also depending on other geological factors than temperature and pressure.Received July 15, 2002; revised version accepted May 15, 2003  相似文献   

15.
Provisional activity-composition relations have been developed for spinels in the system FeO-MgO-Fe2O3-Al2O3-Cr2O3-TiO2. These relations are based on a Temkin type model for the configurational entropy combined with a third-degree Taylor's series expansion to describe the excess Gibbs energy of mixing that is the result of describing spinels in terms of a set of fictive ordered and inverse spinel components. The coefficients of this expansion have been identified as (1) reciprocal Mg-Fe exchange terms, (2) binary asymmetric Margules parameters, and (3) Margules and Bragg-Williams type terms which make explicit provision for mixing of Fe and Mg on two sites in ulvospinel. Provisional values have been assigned to these terms for the temperature range 900–1,250°C based on inferred and experimentally determined spinel miscibility gaps, Fe-Mg olivine-spinel exchange data reported in the literature, and 40 experimental determinations of Fe-Mg partitioning between olivines and spinels in basanitic to uganditic silicate liquids between 1,092 and 1,300°C ( QFM).  相似文献   

16.
This study deals with the oxygen isotope composition of hematite-rich ore bodies in the Iron Quadrangle, Brazil. The area studied can be divided into two different regions: a western (W) zone of greenschist facies assemblages and an eastern (E) zone of amphibolite facies with transitions into granulite facies assemblages.The 18O values of 136 quartz-iron oxide pairs have been determined and temperatures of formation have been calculated. The 18O values of quartz vary between +6 and 20 except one value near +23, whereas the iron oxides fall between –4 and +10, with nearly 80% of the iron oxide values between –0.5 and 4.0. The regional distribution of the 18O values is as follows: in the W-region 85% of the quartz are >12, whereas in the E-region only 46% fall in this range, In contrast to quartz the iron oxides do not show any regional differences.The variation of oxygen isotope fractionations between quartz and iron oxides is obviously related to the complex deformation history of the iron ores. Samples with a primary schistosity (S1) only represent peak metamorphic conditions. In the E-region the (S1) high temperatures >700° C seem to correspond to orogenic events in the Archaen basement 2,700 m.y. ago. In the W-region S1-temperatures between 460° and 560° C seem to represent peak metamorphic conditions of the Proterozoic Minas metamorphism 2,000 m.y. ago. Iron ores which have been overprinted by later deformation events are selectively reset to lower isotopic temperatures. The more closely spaced the schistosity planes the larger the extent of a temperature lowering.The genetic processes associated with these hematite-rich ore bodies appear to be sedimentary-metamorphic rather than metasomatic processes. Furthermore, there is no evidence for secondary leaching by weathering solutions.  相似文献   

17.
Zusammenfassung Das Cu kommt in häufigen Eruptivgesteinen nicht wie das Pb und Zn großenteils im Gitter der mineralischen Hauptbestandteile, sondern als Kupferkies vor (Proportionalität zwischen Cu- und S-Werten). Basaltische Gesteine haben wesentlich höhere Kupfergehalte (Mittel: 88 ppm = g/t Cu) als granitische (Mittel: 8 ppm Cu). Das Verhalten des Cu bei der Verwitterung und hydrothermalen Gesteinszersetzung und die Begrenzung des Transports in Gewässern (durch Löslichkeit der Karbonate, Hydroxyde, Sulfide und Adsorption an Tonminerale) wird diskutiert. Kalke enthalten im Mittel 15 ppm Cu, bitumenarme Tone landnaher Ablagerungen: 55 ppm Cu. Über diese Werte hinaus können organogene Rückstände, Sulfidfällung, Kalkauflösung und sehr langsame Sedimentbildung im küstenfernen Tiefseebereich (Pazifiktone 400 ppm Cu) zu Kupferanreicherungen führen.Die abnormen Kupfergehalte in bestimmten Ablagerungsgebieten des Kupferschiefers können nicht aus normalem Meeroder Flußwasser durch Sulfidfällung oder die oben genannten Prozesse erklärt werden. Die Aufarbeitung von Rotliegend-Sedimenten gilt als möglicher Lieferant.
In abundant igneous rocks copper does not mainly occur like lead and zinc in the lattice of the mineral constituents but as chalcopyrite (proportionality between Cu- and S-values). The basaltic rocks have substantial higher copper contents (average: 88 ppm Cu) than the granitic rocks (average: 8 ppm Cu). The behavior of Cu during weathering and hydrothermal alteration and the limitation of transport in waters (as a function of the solubility of carbonates, hydroxides, sulfides and the adsorption on clay minerals) is discussed. Calcareous rocks contain in average 15 ppm Cu, clays and shales from nearshore environments low in carbonaceous matter: 55 ppm Cu. Enrichment of copper exceeding these averages may be due to organic residues, environments of sulfide precipitation or limestone dissolution or very slow sediment accumulation in pelagic areas (Pacific clays: 400 ppm Cu).The abnormal high copper contents in special areas of the Kupferschiefer cannot be derived from normal sea- or riverwater by sulfide precipitation or the above mentioned processes. The reworking of Lower Permian sediments represents a possible source.
Résumé Le cuivre, dans les roches éruptives, ne se présente pas comme le plomb et le zinc en majeure partie dans le réseau des principaux minéraux, mais comme chalcopyrite (proportionnalité entre les pourcentages de cuivre et de soufre). Les roches basaltiques ont une teneur en cuivre considérablement plus élevée (moyenne: 88 ppm = g/t Cu) que les roches granitiques (8 ppm Cu). Le comportement du cuivre au cours de l'altération atmosphérique et lors de la décomposition des roches par voie hydrothermale et la limitation du transport par les eaux (grâce à la solubilité des carbonates, des hydroxydes, des sulfides et à l'adsorption des minéraux argileux) sont discutées. Les calcaires contiennent en moyenne 15 ppm Cu, les argiles pauvres en bitume de dépôts proches du rivage 55 ppm Cu. Des résidus organogènes, des dépôts de sulfures, la dissolution du calcaire et la formation très lente de sédiments dans des zones de mer abyssale éloignées des côtes (argiles du Pacifique: 100 ppm Cu) peuvent conduire à des enrichissements de la teneur en cuivre au-dessus de ces valeurs. Les teneurs en cuivre s'écartant de la normale dans certaines zones de dépôts de schistes cuivreux ne peuvent pas s'expliquer par le dépôt de sulfures provoqué par l'eau de la mer ou des fleuves ou par les processus ci-dessus mentionnés. Le remaniement de sédiments du rotliegend est considéré comme l'agent possible de ces apports.
, , . . . — , ( , ). (. . 88 = g/t u) (8 ), (15 u) (55 u). , . , . , .
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18.
Zusammenfassung Es wurden Albite mit verschiedenen Strukturzuständen hydrothermal bei 340–700°C und 1000 bar synthetisiert; die Versuchsdauer betrug bis zu 8 1/2 Monaten. Von einem synthetischen Tiefalbit und neun Albiten mit teilgeordneten Strukturzuständen wurden die Gitterkonstanten aus Röntgenpulverdaten verfeinert. Die b-c- und *—*-Beziehungen dieser Albite und deren K-Austauschprodukte werden dargestellt. Gläser der Zusammensetzung NaAlSi3O8 mit Gehalten von 0,1 0,2, 0,4 Mol% Fe, 1,0 und 2,0 Gew.% Na2Si2O5 wurden zur Kristallisation gebracht, um katalytische Einflüsse auf die Al/Si-Ordnungsgeschwindigkeit zu bestimmen. Eine beträchtlich erhöhte Al/Si-Ordnung wurde nur bei Zugabe von 2 Gew.% Na2Si2O5 erhalten.Die hydrothermale Temperung von intermediären synthetischen Albiten bei 700°C bewirkte eine Verbreiterung der Linienabstände, also eine Änderung in Richtung zum Hochalbit. Bei 650°C und allen tieferen Temperaturen wurde jedoch nach genügend langer Temperdauer stets eine Änderung in Richtung zum Tiefalbit festgestellt auch an Albiten mit bereits weitgehend geordneter Al/Si-Verteilung. Hieraus wird geschlossen, daß der Stabilitätsbereich von strukturell geordnetem Tiefalbit bis etwa 680°C reicht und intermediäre Albite unterhalb dieser Temperatur nur metastabil auftreten. Die Kinetik der Umwandlung von Hochalbit in Tiefalbit und umgekehrt wird diskutiert. Eine Klarstellung der Definitionen von Albit-Modifikationen wird auf Grund der Experimente vorgenommen. Die oberhalb 680°C stabilen Na-Feldspäte mit -Werten größer als ca. 1,70° sollten Hochalbite genannt werden, nur aibite mit =2,00—2,03° können als Analbite bezeichnet werden, da diese bei hohen Temperaturen monoklin sind (Monalbite). Der Ausdruck intermediärer Albit sollte auf metastabile Phasen zwischen Hochalbit und dem strukturell geordneten Tiefalbit beschränkt bleiben.Das Vorkommen intermediärer Albite in der Natur und ihre Bedeutung insbesondere für die Genese von Spiliten werden abschließend diskutiert.
On the synthesis and stability of albite polymorphs
Summary New results of the hydrothermal synthesis of albite at 340–700°C and 1 kb water pressure are presented. The cell constants of one synthetic low albite and of 9 intermediate to high albites were refined from X-ray powder diffraction data. The b-c and *—*-Beziehungen relations for these albites and their K-exchanged structural equivalents are shown. NaAlSi3O8-glasses containing 0.1, 0.2, 0.4 mol% Fe, 1.0, and 2.0 wt.% Na2Si2O5 have been crystallized hydrothermally to evaluate catalytic effects on the Al/Si ordering. A considerable increase of the ordering rate was attained only by the addition of 2 wt.% Na2Si2O5.Hydrothermal treatment at 700°C causes an increase of the Al/Si disorder in synthetic intermediate albites, whereas at 650°C and lower temperatures a change always towards low albite was observed, even for albites with a predominantly ordered Al/Si distribution. It is concluded that low albite is the stable form of NaAlSi3O8 up to about 680°C. In this light the nomenclature of the albite polymorphs is reviewed. Na-feldspar with values of higher than ca. 1.70° which is stable at temperatures higher than 680°C should be called high albite, except Na-feldspar with =2,00—2,03° which should be called analbite because it changes to monalbite on heating. The term intermediate albite should be confined to metastable forms between high albite and ordered low albite.The occurrence of intermediate albite in natural rocks and its significance especially with regard to the spilite problem is discussed.

Mit 3 Abbildungen  相似文献   

19.
Zusammenfassung Es wird über gravimetrische Messungen berichtet, die im Gebiet der Felbertauern ober- und untertägig (Straßentunnel der Felbertauern AG und Pipelinestollen der Transalpinen Ölleitung TAL) durchgeführt wurden.Die Ergebnisse der Feldmessungen sind in Profilen der Bouguer-, Regional- und Restanomalien dargestellt.An diesen Restanomalien wird zusätzlich eine Korrektur zur Berücksichtigung der Oberflächengeologie angebracht.Die Ergebnisse der ober- und untertägigen Messungen werden miteinander kombiniert und mit den Ergebnissen von Berechnungen digital simulierter Modelle verglichen.Hiermit läßt sich ein Bild vom geologischen Aufbau des Meßgebietes entwerfen, das gravimetrisch konsistent ist.
Underground and surface gravity measurements have been carried out in the area of the Felbertauern. The results of the measurements are presented as profiles of Bouguer and Regional and Residual anomalies.An additional correction is made to take into account the surface geology.The results of the underground and surface measurements are combined and compared with the calculations by digital simulated models.From this it is possible to construct a gravimetric consistent figure of the geological structure.
Résumé Rapport concernant des mesures gravimétriques effectuées dans la région du Felbertauern en surface et au fond (Tunnel routier de la «Felbertauern AG» et galerie pour le pipe-line de l'oléoduc transalpin — TAL —).Les résultats des mesures sont représentés en profile des anomalies de Bouguer, des anomalies régionales et des anomalies résiduelles.En outre, on corrige ces anomalise résiduelles tenant compte de la géologie de surface.On combine les résultats des mesures effectuées en surface et au fond les uns avec les autres et on les compare aux résultats de calculs de modèles simulés à l'ordinateur.Ainsi, on peut concevoir un plan de la structure géologique de la région étudiée.
, : Felbertauern AG, Pipelinestollen der Transalpinen Oelleitung TAL. : Bouguer'a, . . . , .
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20.
Zusammenfassung Viele Kennzeichen der metamorphen Gesteine des venezolanischen Küstengebirges weisen auf starke differentielle Bewegungen mit Faltung und Überschiebung hin. Deformationskristalloblastese, z. T. mit metasomatischem Ersatz, spielt eine große Rolle. Stark verbreitet finden sich Albitgneise. Durchströmung mit natronhaltigen Lösungen kommt in stark durchbewegten Zonen gefalteter Gebiete vielfach vor.
In the Venezuelan Coastal Ranges many phenomena indicate strong differential orogenetic movement with folds and overthrusts Syncinematic recrystallization and metasomatic replacement, seem to be of much importance. Albitic gneiss is widespread; liquids, rich in sodium have often migrated through strongly disturbed zones of folded regions.
Résumé Les roches métamorphiques de la chaîne côtière de Venezuela ont des caractéristiques indiquant d'intenses mouvements différentiels avec plissements et chevauchements. La réeristallisation syncinématique associée à une métasomatose souvent sodique joue un rôle important. Les gneiss albitiques sont très répandus. Des solutions riches en soude ont fréquemment circulé dans les zones fortement déformées des régions plissées.
, , . .

Herrn Prof. Dr. Dr. h. c.Erich Bederke zum 70. Geburtstag gewidmet.  相似文献   

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