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1.
Satellite free air gravity anomalies over the Indian ocean region 79°E–86°E, 2°S–8°S were obtained from the website http://topex.ucsd.edu and a contour map was compiled. Five profiles of the anomaly have been interpreted in terms of two-dimensional structures in the ocean. Thickness of sediments lying on the oceanic crust determined from the interpretation of gravity profiles were used to compile an isopach map of the region 79°E–86°E, 2°S–8°S. This map in combination with one of the isopach maps compiled by previous workers, provides information regarding the thickness of sediments up to 6° S. According to this map sediment thickness varies from ～600 m over the middle part of the region to ～800 m further south, indicating that thinning of sediments in the middle part of the region is only localized. Information provided by this gravity study may be useful in planning detailed seismological studies to delimit the outer edge of the continental margin of Sri Lanka, defined according to the United Nations Convention of the Law of the Sea (UNCLOS).  相似文献   

2.
Oxygen isotopic exchange between quartz and water, using a novel technique in which both 18O/16O and 17O/16O fractionations were measured, yielded an equilibrium fractionation Δ18 = 9.0 at 250°C and 15 kbar. The reaction proceeds predominantly by solution of fine grains and growth of larger grains. Exchange by solid-state diffusion is immeasurably slow at this temperature. Under the same experimental conditions, cristobalite behaves quite differently, becoming transformed to sub-micron quartz crystals in a few minutes. The phase transformation is accompanied by a kinetic isotope effect yielding quartz in isotopic disequilibrium with water. It is possible that such disequilibrium products are also formed in other experiments involving phase transitions or mineral syntheses.  相似文献   

3.
Based on materials obtained in Cruises 33 and 34 of the R/V Professor Logachev, the paper addresses formation conditions, morphology, structures, mineral composition of the present-day oceanic sulfide ores, and their relationships with the host (biogenic carbonate) bottom sediments in the 19°–20° N MAR (Zenith-Victoria and Petersburg hydrothermal fields) region. The grain size distribution, mineral composition of the carbonate (background) and ore-hosting sediments, as well as physicochemical parameters of their interstitial waters, are examined. The results suggest a significant role of hydrothermal-metasomatic processes in the formation of ores and ore-bearing sediments. A model is proposed for the formation of sulfide mineralization in oceanic sediments at the geochemical barrier in the zone of their interaction with the acid hydrothermal (diffuse-type) ore-bearing solutions delivered from rocks of the ocean floor.  相似文献   

4.
Three major diastrophic cycles, defined by their structural style and their spatial distribution are recognized in the Andean Basement of this region. The oldest structures are related to the Panamerican Orogeny (500 to 700 m. a.) which produced in the Central Craton multiply deformed complexes of schists, gneisses and granites, that are covered discordantly by unmetamorphosed Cambrian and Ordovician beds. West of the Central Craton Ordovician sedimentary beds are folded with a simple structural style and intruded by granites. Both the sedimentry beds and the granites are covered discordantly by undeformed Devonian sequences. The folding of the Ordovician is attributed to the ocloyic phase of the Caledonian movements. West of the ocloyic belt is another foldbelt consisting of strongly folded Devonian beds attributed to the chanic phase (hercynian). The chanic belt is intruded by carboniferous and permian granites and covered discordantly by Carboniferous and Permian sequences.The features observed in the eastern slope of the Andes suggest that the Paleozoic foldbelts are intracratonic. Whether there are accreted terrains in the Pacific Coastal Cordillera is matter of controversy.
Zusammenfassung Im Andenbasement dieser Region lassen sich drei diastrophische Hauptzyklen, die durch ihren strukturellen Baustil und ihre geographische Verbreitung definiert sind, unterscheiden. Die ältesten Strukturen sind verknüpft mit den Bewegungen der Panamerikanischen Orogenese (500–700 m. a.), welche im Zentralkraton einen polydeformierten Komplex von Schiefern, Gneissen und Graniten erzeugte. Diesem lagern diskordant kambrische und ordovizische Sequenzen ohne Metamorphose und präandiner Deformation auf. Nach Westen zu gibt es einen Gürtel stark deformierter ordovizischer Sedimente, die einen einfacheren Baustil als das präkambrische Basement aufweisen, und diskordant von undeformierten devonischen Abfolgen bedeckt sind. Die Faltung des Ordoviziums wird der Ocloyischen Phase der Kaledonischen Bewegung zugerechnet.Weiter westwärts tritt ein jüngerer Faltengürtel aus devonischen Sedimenten auf, die während der Chanischen Phase der Herzynischen Bewegung intensiv deformiert wurden, und von karbonischen und permischen Sequenzen diskordant überlagert sind.Der Ocloyische Gürtel ist von postordovizischen Graniten die von devonischen Schichten überlagert sind, und der Chanische Gürtel von karbonischen und permischen Graniten intrudiert. Im präkambrischen Basement des Zentralkratons treten einerseits präkambrische Granite auf, denen diskordant kambrische Schichten auflagern. Andererseits findet man Granite mit paläozoischen Isotopenaltern, letztere aber in Gebieten, wo wegen des Fehlens von Deckschichten eine stratigraphische Kontrolle unmöglich ist.Die gemachten Beobachtungen scheinen darauf hinzudeuten, daß die paläozoischen Faltengürtel intrakratonisch sind. Ob es allochtone »terrains« in der pazifischen Küstenkordillere gibt, ist Gegenstand der Kontroverse.
Resumen En el basamento de los Andes de esta región se distinguen tres ciclos diastróficos mayores definidos por sus estilos estructurales y su distributión espacial. Las estructuras mas antiguas responden a movimientos que culminaron con la Orogénesis Panamericana (500–700 m. a.) que produjo en el Cratógeno Central un complejo de esquistos, gneises y granitos polideformados, al que se le superponen discordantemente secuencias cámbricas y ordovicicas sin metamorfismo ni déformatión preandina. Hacia el oeste hay un cinturón de sedimentos ordovícicos intensamente deformados con un estilo de plegamiento mas simple que el del basamento precámbrico y cubierto discordantemente por secuencias marinas devónicas sin deformatión. Los movimientos responsables de este plegamiento se atribuyen a la fase oclóyica de los movimientos caledónicos. Más hacia el oeste se manifiesta una franja de deformatión mas jóven atribuída a la Fase chánica de los movimientos hercínicos, en ella se encuentran sedimentitas devónicas intensamente plegadas cubiertas discordantemente por secuencias carbónicas y pérmicas.El cinturón oclóyico esta acompanãdo por granitos postordovícicos cubiertos por Devónico. Asimismo, el cinturón chánico (hercínico) esta intruido por granitos probablemente carbónicos. Con respecta a los granitos intruidos en el zócalo antiguo, hay algunos indudablemente precámbricos por estar cubiertos discordantemente por secuencias cámbricas sin metamorfismo, además hay granitos de edad dudosa que han dado valores isotópicos paleozoicos pero en lugares donde el control estratigráfico no es posible por ausencia de la cobertura paleozoica. De acuerdo a los hechos observados en la ladera oriental de los Andes surge la idea de que los cinturones de plegamiento paleozoicos son intracratónicos, aun es materia de controversia si en la Cordillera de la Costa junto al Pacifico hay terrenos alóctonos acrecionados.
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5.
The results of 0.97, 2.3, 3.9, 7.7, 11.1, and 21.7 GHz observations of a complete sample of radio sources obtained on the RATAN-600 radio telescope are presented. The sample is comprised of sources from the 4.85-GHz MGB survey, and contains all sources at declinations 10°–12°30′ (J2000) with Galactic latitudes |b|>15° and flux densities S4.85>200 mJy. Optical identifications have been obtained for about 86% of the radio sources with flat spectra and 59% of those with steep spectra. The spectra of the flat-spectrum sources have been decomposed into extended and compact components.  相似文献   

6.
The continental shelf and slope of southern Central Chile have been subject to a number of international as well as Chilean research campaigns over the last 30 years. This work summarizes the geologic setting of the southern Central Chilean Continental shelf (33°S–43°S) using recently published geophysical, seismological, sedimentological and bio-geochemical data. Additionally, unpublished data such as reflection seismic profiles, swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated. The outcome is an overview of the current knowledge about the geology of the southern Central Chilean shelf and upper slope. We observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope, due to local redistribution of fluvial input, mainly governed by bottom currents and submarine canyons and highly productive upwelling zones. Shelf basins show highly variable thickness of Oligocene-Quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land. Seismic velocity studies indicate that a paleo-accretionary complex that is sandwiched between the present, relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern Central Chile.  相似文献   

7.
The paper reports the results of ten-year centimeter-wavelength observations with the RATAN-600 radio telescope of a complete sample of 83 flat-spectrum sources from the GB6 catalog of the MGB Survey, with S 4.85 > 200 mJy at declinations 10°?C12°30??. Starting in 2000, the observations were conducted simultaneously at six frequencies in the range 0.97?C21.7 GHz. Seventy-six sources (including 54 quasars) have been identified with optical objects, which have redshifts in the range z = 0.331?C3.601. Analysis of light curves and spectra at different activity phases has shown that, in most cases, the dynamics of the development of flares is consistent with a model in which the variability results from the evolution of a shock in a radio jet. A relationship between the time scales for the rise and fall of the flares has been found. There is no redshift dependence of the true linear dimensions of the radiating regions and the variability indices obtained over ten years. These facts can be interpreted as an absence of cosmological evolution of quasars at least up to z ?? 3.  相似文献   

8.
Data presented in the paper suggest significant differences between the thermodynamic conditions under which magmatic complexes were formed in MAR at 29°–34° N and 12°–18° N. The melts occurring at 29°–34° N were derived by the melting of a mantle source with a homogeneous distribution of volatile components and arrived at the surface without significant fractionation, likely, due to their rapid ascent. The MAR segments between 12° and 18° N combine contrasting geodynamic environments of magmatism, which predetermined the development of a large plume region with the widespread mixing of the melting products of geochemically distinct mantle sources. At the same time, this region is characterized by conditions favorable for the origin of localized zones of anomalous plume magmatism. These sporadic magmatic sources were spatially restricted to MAR fragments with the Hess crust, whose compositional and mechanical properties were, perhaps, favorable for the focusing and localization of plume magmatism. The plume source between 12° and 18°N beneath MAR may be geochemically heterogeneous.  相似文献   

9.
The Pampas plain (30°–41°S) has historically been considered as a sector that evolved independently from the adjacent Andean ranges. Nevertheless, the study of the Pampas showed that it is reasonable to expect an important influence from the Andes into the extraandean area. The Pampas plain can be divided into two sectors: the northern portion, adjacent to the Pampean Ranges, has been studied by Davila (2005, 2007, 2010). The southern sector (34°–41°S) is the objective of the present work. The study of this area allowed to characterize two separate foreland basins: the Southern Pampa basin and the Northern Patagonian basin. The infill is composed of Late Miocene and Pliocene units, interpreted as distal synorogenic sequences associated with the late Cenozoic Andean uplift at this latitudinal range. These foreland basins have been defined based on facies changes, distinct depositional styles, along with the analysis of sedimentary and isopach maps. The basins geometries are proposed following De Celles and Gilles (1996) taking into account the infill geometry, distribution and grain size. In both cases, these depocenters are located remarkably far away from the Andean tectonics loads. Therefore they cannot be explained with short-wave subsidence patterns. Elastic models explain the tectonic subsidence in the proximal depocenters but fail to replicate the complete distal basins. These characteristics show that dynamic subsidence is controlling the subsidence in the Southern Pampas and Northern Patagonian basins.  相似文献   

10.
The main aim of the paper is to describe mesosphere and lower thermosphere (MLT) wind field observed between June 2000 and May 2002 by medium frequency (MF) radars at two locations near the equatorial region and at tropical latitude. We have presented and compared observations of mean horizontal winds in the mesosphere and lower thermosphere (MLT) region over Kolhapur (16.8°N, 74.2°E) and Tirunelveli (8.7°N, 77.8°E). Our analysis reveals annual oscillation in the zonal wind and semi-annual oscillation in the meridional wind over Kolhapur. On the other hand, results over Tirunelveli reveal semi-annual oscillation (SAO) in the zonal wind and annual oscillation in the meridional wind. Also we have observed enhanced magnitude of wind speed in spring equinox period of 2002 exhibiting the signatures of the quasi-biennial oscillation (QBO) over Tirunelveli.  相似文献   

11.
《Geochimica et cosmochimica acta》1999,63(19-20):3247-3259
The rate of Si release from dissolving bytownite feldspar in abiotic batch reactors increased as temperatures increased from 5° to 35°C. Metabolically inert subsurface bacteria (bacteria in solution with no organic substrate) had no apparent effect on dissolution rates over this temperature range. When glucose was added to the microbial cultures, the bacteria responded by producing gluconic acid, which catalyzed the dissolution reaction by both proton- and ligand-promoted mechanisms. The metabolic production, excretion, and consumption of gluconic acid in the course of glucose oxidation, and therefore, the degree of microbial enhancement of mineral dissolution, depend on temperature. There was little accumulation of gluconic acid and therefore, no significant enhancement of mineral dissolution rates at 35°C compared to the abiotic controls. At 20°C, gluconate accumulated in the experimental solutions only at the beginning of the experiment and led to a twofold increase in dissolved Si release compared to the controls, primarily by the ligand-promoted dissolution mechanism. There was significant accumulation of gluconic acid in the 5°C experiment, which is reflected in a significant reduction in pH, leading to 20-fold increase in Si release, primarily attributable to the proton-promoted dissolution mechanism. These results indicate that bacteria and microbial metabolism can affect mineral dissolution rates in organic-rich, nutrient-poor environments; the impact of microbial metabolism on aluminum silicate dissolution rates may be greater at lower rather than at higher temperatures due to the metabolic accumulation of dissolution-enhancing protons and ligands in solution.  相似文献   

12.
At the southern part of the East Pacific Rise (EPR), between 6°S and 30°S a survey on volcanic and hydrothermal activity was performed and samples were obtained by means of TV-controlled grab.This paper deals with altered and mineralized basalt sampled between 7°S and 23°S from five sites in a hydrothermal field.These basalts of tholeitic composition are vitreous to holocrystaline. They have suffered pervasive alteration during which rock-forming minerals (pyroxene, plagioclase) have been replaced by kaolinite, chlorite and smectite. As a consequence, strong depletion of Ca, Cr, Ni, Mg, Sr and Al took place, accompanied by an enrichment of Fe, Cu, Co, Mo, Zn, and Pb. The ore mineral assemblage is rather uniform and consists of pyrite, marcasite, wurtzite, sphalerite, chalcopyrite, covellite and goethite.The igneous and hydrothermal activities can be subdivided into different stages: lithification, high-temperature alteration (<400 C), medium to low temperature alteration and two substages of ore formation (250°C – 150°C and <150°C, respectively).This active present-day ore deposition is interpreted in terms of a peripheral zone of a volcanic-hosted ore mineralisation. It may be compared with fossil ophiolite-hosted massive sulfides that formed throughout the Alpine (e.g. Arabia, Cyprus) as well as Caledonian orogeny (e.g. Scandinavia).
Zusammenfassung Im Südteil des East Pacific Rise (EPR) zwischen 6°S und 30°S wurde eine Übersichtsbeprobung in einem Gebiet starker vulkanischer und hydrothermaler Aktivität durchgeführt. Diese Studie befaßt sich mit alterierten und mineralisierten Basalten die in einem Hyrothermalfeld, an 5 Positionen zwischen 7°S und 23°S genommen wurden. Die tholeiitischen Basalte sind z.T. hyalin. z.T. holokristallin strukturiert. Im Verlauf der sehr starken Alteration wurden die Minerale Pyroxen und Plagioklas in Kaolinit, Chlorit und Smektit ungewandelt. Dieser Verdrängungsprozeß wurde von einer starken Abreicherung an Ca, Cr, Ni, Mg, Sr, Al und einer Anreicherung an Fe, Cu, Co, Mo, Zn und Pb begleitet. Die Vererzung zeigt eine einfache Mineralvergesellschaftung mit Pyrit, Markasit, Wurtzit, Sphalerit, Chalkopyrit, Covellin und Geothit.Die magmatische und hydrothermale Aktivität läßt sich in verschiedene Stadien untergliedern: Basaltentstehung, Hochtemperturalteration (< 400°), Mittelbis Tieftemperaturalteration und Vererzung mit 2 Substadien (250°C–150°C, < 150°C).Diese rezenten Vererzungen lassen sich interpretieren als die Randzone einer vulkanitgebundenen Erzmineralisation. Sie läßt sich mit fossilen Vertretern ophiolit-gebundener massiver Sulfiderze, wie sie im Verlauf den alpidischen (z.B. Arab.-Halbinsel, Zypern) und kaledonischen Orogenese (z.B. Norwegen) entstanden sind, vergleichen.
Résumé Une étude des activités volcanique et hydrothermale a été effectuée dans la partie sud de l'East Pacific Rise, entre 6° et 30° de latitude sud. Des échantillons y ont été prélevés au moyen d'un engin dirigé par TV.La présente note se rapporte aux basaltes altérés et minéralisés récoltés en cinq points d'un champ hydrothermal, entre 7°S et 23°S.Ces basaltes, de composition tholéiitique sont tantôt vitreux, tantôt holocristallins. Ils ont été le siège d'une forte altération hydrothermale au cours de laquelle les minéraux de la roche (pyroxène, plagioclase) ont été remplacés par de la kaolinite, de la chlorite et de la smectite. Il en est résulté un appauvrissement marqué en Ca, Cr, Ni, Mg, Sr et Al, accompagné d'un enrichissement en Fe, Cu, Co, Mo, Zn et Pb. La minéralisation présente une association simple à pyrite, marcassite, wurtzite, sphalérite, covelline et goethite.On peut distinguer plusieurs stades d'activité magmatique et hydrothermale: formation du basalte, altération de haute température (<400°C), altération de moyenne à basse température avec deux stades de minéralisation (250-150°C; <150°C). Ces dépôts de la nature actuelle peuvent s'interpréter comme la zone périphérique d'une aire de minéralisation volcanogène. On peut les comparer à des gisements fossiles de sulfures massifs liés à des ophiolites, comme il s'en est formé au cours des orogenèses alpine (p. ex.: péninsule arabique, Chypre) et calédonienne (p. ex.: Norvège).
»East Pacific Rise (EPR)« 6° 30° . , 7° 23° . , . , , . , Cr, Ni, Mg, Sr, Al Fe, u, , Mo, Zn Pb. , , , , , . : , ( 400°), (250°–150°, <150°) . , , . , , (.: , ) (.: ).
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13.
Doklady Earth Sciences -  相似文献   

14.
Based on studies conducted on the 33rd cruise of the R/V Professor Logachev in 2010, a new type of sulfide mineralization of the mid-oceanic ridges has been established. It was formed in the present-day organic sediments due to diffuse penetration of hydrothermal fluids that emanated along the fractures in basalts on the slopes of the Mid-Atlantic Ridge.  相似文献   

15.
Summary Deformation experiments have been performed in a triaxial compression cell at a temperature of 300°C and confining pressures up to 65 MPa using samples of homogeneous, fresh two-mica-granite (RM) and monzogranite (CM). The cylindrical specimens (d=70 mm, h=140 mm, V=540 cm3) were tested undrained under dry (105°C), as received, and water saturated conditions at deformation rates between and . The mechanical behaviour of the two types of coarse-grained, crystalloblastic granites is critically influenced by mineralogical composition, porosity, and the amount of intergranular water present in the samples. The failure stress of the CM granite is at about 65% of that of the RM granite; in both rocks strength decreases with increasing porosity and water content.The presence of interstitial water causes a failure mode of non-localized, homogeneously distributed microcracking in the central parts of the samples, whereas, in runs with dry granites, strain localization along a single shear fracture was observed. When aqueous fluids are present, the macroscopic style of deformation of granites appears to be ductile even at lowP andT conditions. Strength and angle of internal friction are reduced to very low values. The style of deformation, as well as the reduction of strength of the water-saturated rock samples, is due to mechanical and chemical effects of intergranular water at elevated temperatures.The maximum differential stresses measured for these coarse-grained granites are much lower than the strength commonly reported for other granites, e. g. Westerly and Charcoal granites. Our data suggest that the strength of the granitic crust under differential stress is lower than currently deduced from laboratory experiments.  相似文献   

16.
The intramontane Lauca Basin at the western margin of the northern Chilean Altiplano lies to the west of and is topographically isolated from the well-known Plio-Pleistocene lake system of fluvio-lacustrine origin that covers the Bolivian Altiplano from Lake Titicaca to the north for more than 800 km to the Salar de Uyuni in the south. The Lauca Basin is filled by a sequence of some 120 m of mainly upper Miocene to Pliocene elastic and volcaniclastic sediments of lacustrine and alluvial origin. Volcanic rocks, partly pyroelastic, provide useful marker horizons. In the first period (6–4 Ma) of its evolution, the Lago Lauca was a shallow ephemeral lake. Evaporites indicate temporarily closed conditions. After 4 Ma the lake changed to a perennial water body surrounded by alluvial plains. In the late Pleistocene and Holocene (2-0 Ma) there was only marginal deposition of alluvial and glacial sediments. The basin formed as a half-graben or by pull-apart between 10 and 15 Ma (tectonic displacement of the basal ignimbrite sequence during the Quechua Phase) and 6.2 Ma (maximum K/Ar ages of biotites of tuff horizons in the deepest part of the basin). Apart from this early basin formation, there has been surprisingly little displacement during the past 6 Ma close to the Western Cordillera of the Altiplano. Also, climate indicators (pollen, evaporites, sedimentary facies) suggest that an arid climate has existed for the past 6 Ma on the Altiplano. Together, these pieces of evidence indicate the absence of large scale block-faulting, tilt and major uplift during the past 5–6 Ma in this area.  相似文献   

17.
Zabuye Salt Lake in Tibet, China is a carbonate-type salt lake, which has some unique characteristics that make it different from other types of salt lakes. The lake is at the latter period in its evolution and contains liquid and solid resources. Its brine is rich in Li, B, K and other useful minor elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15°C and 25°C. The crystallization sequence of the primary salts from the brine at 25°C is halite (NaCl) → aphthitalite (3K2SO4·Na2SO4) → zabuyelite (Li2CO3)→ trona (Na2CO3·NaHCO3·2H2O) → thermonatrite (Na2CO3·H2O) → sylvite (KCl), while the sequence is halite (NaCl) → sylvite (KCl) → trona (Na2CO3·NaHCO3·2H2O) → zabuyelite (Li2CO3) → thermonatrite (Na2CO3·H2O) → aphthitalite (3K2SO4·Na2SO4) at 15°C. They are in accordance with the metastable phase diagram of the Na+, K+-Cl?, CO32?, SO42?-H2O quinary system at 25°C, except for Na2CO3·7H2O which is replaced by trona and thermonatrite. In the 25°C experiment, zabuyelite (Li2CO3) was precipitated in the early stage because Li2CO3 is supersaturated in the brine at 25°C, in contrast with that at 15°C, it precipitated in the later stage. Potash was precipitated in the middle and late stages in both experiments, while boron was concentrated in the early and middle stages and precipitated in the late stage.  相似文献   

18.
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19.
Astronomy Reports - A search for pulse signals was carried out in a new sky area included in the monitoring program for the search for pulsars and transients. Processing of several months data...  相似文献   

20.
Marine Quaternary trench and slope sediments were sampled along the margin of the Southern Andes, Chile between 36° and 40°S. Major and trace element contents indicate only minor influence of weathering and transport fractionation. The whole rock composition of the sediments is similar to the average rock of the Cretaceous to Holocene magmatic arc of this section of the southern volcanic zone. Sr, Nd, and Pb isotope composition of the sediments also resembles closely the average composition of the magmatic arc. The contribution of compositionally distinct Palaeozoic crust, which makes up most of the volume of the forearc, is ~0–20% crustal Sr, Nd, and Pb according to the isotope record of the trench and slope sediments. Input of sediments from the continent into the subduction system was dominated by detritus from the magmatic arc at least for the last 20 My on the basis of the Oligocene to Holocene exhumation history of the margin.  相似文献   

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