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1.
Data from the revised Geneva-Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative metallicity gradient in the thin disk, are responsible for the observed negative correlation between the metallicities and angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do not depend on either age or metallicity. The velocity components of the Sun relative to the Local Standard of Rest derived using data for stars born at the solar Galactocentric distance are (U ⊙, V ⊙, W ⊙) LSR = (5.1 ± 0.4, 7.9 ± 0.5, 7.7 ± 0.2) km/s. The two coordinates of the apex of the solar motion remain equal to 〈l ⊙〉 = 70° ± 7° and 〈b ⊙〉 = 41° ± 2°, within the errors. The indices for the power-law age dependences of them ajor, middle, and minor semi-axes become 0.26±0.04, 0.32±0.03, and 0.07±0.03, respectively. As a result, with age, the velocity ellipsoid for thin-disk stars born at the solar Galactocentric distance increases only in the plane of the disk, remaining virtually constant in the perpendicular direction. Its shape remains far from equilibrium, and the direction of the major axis does not change with age: the ellipsoid vertex deviation remains constant and equal to zero within the errors (〈L〉 = 0.7° ± 0.6°, 〈B〉 = 1.9° ± 1.1°). Such a small increase in the velocity dispersion perpendicular to the Galactic plane with age can probably be explained by “heating” of the stellar system purely by spiral density waves, without a contribution from giant molecular clouds.  相似文献   

2.
The possibility to use some widely known standard discrimination diagrams such as the K2O/Na2O-SiO2/Al2O3, SiO2-K2O/Na2O, (Fe2O3* + MgO)-TiO2, F1-F2, Th-La-Sc, Sc-Th-Zr/10, and Sc/Cr-La/Y for deciphering the paleogeodynamic settings of sedimentary sequences is considered with reference to the Lower and Middle Riphean (Mesoproterozoic) deposits of the Uchur-Maya region (Far East) and the Bashkir meganticlinorium (South Urals). It was shown that only some of them can be used with a certain degree of confidence for reconstructing the settings of the platform sedimentary sequences made up of both sandstones and fine-grained terrigenous rocks.  相似文献   

3.
A metabasalt dredged at a junction of the median valley with the Atlantis fracture zone (30°01/tN, 42°04/tW) in the Mid-Atlantic Ridge shows complete recrystallization under a metasomatic condition, though the original igneous texture of a coarse-grained basalt is still recognizable. There is strong circumstantial evidence suggesting that this rock is not an ice-rafted erratic, but an authentic Mid-Atlantic Ridge rock. The 40Ar-39Ar age of this sample is 169 m.y. (Jurassic) which should represent the time of recrystallization. The initial value (87Sr/86Sr)O is 0.720, far above the values previously observed in oceanfloor basalts, including both tholeiitic and alkalic rocks (0.701–0.704). Sr with such a high isotopic ratio is considered to have been introduced by metasomatism during metamorphism by a solution coming from a continental mass or masses which were then located very close to the Mid-Atlantic Ridge. The 40Ar−39Ar age of sample AM50 may approximate the time of the commencement of the opening of the Atlantic. All these data support the possible existence of ancient rock masses in the Mid-Atlantic Ridge, as was formerly claimed by Bonatti, Melson and others.  相似文献   

4.
Based on the hypothesis that shearing stresses and normal tensile stresses both play a decisive role in fracturing and brittle failure of rock material, a novel strength criterion was developed in one of the earlier works of the author. In the criterion, a certain parameter ν′ occurs which depends on the structure of the material. Originally, the parameter was treated as a constant, which resulted in a linear form of the strength function F σ 1 = f(σ 3), where σ 3 = σ 2. Although the linear strength criterion is sometimes found to be applicable to various particular rock materials, it is not, in general, of a universal character. Analysis of the triaxial test results for 75 different sandstones revealed that parameter ν′ usually increases in an exponential or linear manner as confining pressure increases, and only in isolated cases does it seem to be independent of the confining pressure. For these three types of function ν′ = f(p) appropriate strength criteria F σ 1 = f(σ 3) are given in the present paper. These criteria were used to fit all of the collected empirical data sets. In general, a very good fit to the data was obtained.  相似文献   

5.
In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning.  相似文献   

6.
Here, we present new measurements of 32S, 33S, 34S, and 36S in sedimentary sulfides and couple these measurements with modeling treatments to study the sulfur cycle of a late Paleoproterozoic marine basin. We target the transition in ocean chemistry from the deposition of Paleoproterozoic iron formations (Gunflint Formation, Biwabik Formation, Trommald Formation, and Mahnomen iron formations) to the inferred sulfidic ocean conditions recorded by overlying shale (Rove Formation). The data suggest that certain features of the global sulfur cycle, such as a control by sulfate reducing prokaryotes, and low (mM) concentrations of oceanic sulfate, were maintained across this transition. This suggests that the transition was associated with changes in the structure of the basin-scale sulfur cycle during deposition of these sediments. Sulfide data from the iron formations are interpreted to reflect sedimentary sulfides formed from microbial reduction of pore-water sulfate that was supplied through steady-state exchange with an overlying oceanic sulfate reservoir. The sulfide data for the euxinic Rove Formation shales reflect the operation of a sulfur cycle that included the loss of sulfide by a Rayleigh-like process. We suggest that the prevalence of large and variable heavy isotope enrichments observed in Rove Formation sulfide minerals reflect a sustained and significant net loss of sulfide from the euxinic water column, either as a result of a shallow chemocline and degassing to the atmosphere or as a result of a water column pyrite sink. The inclusion of 36S measurements (in addition to 32S, 33S, and 34S) illustrates the mass-dependent character of these sedimentary environments, ruling out contributions from the weathering of Archean sulfides and pointing to at least modest levels of sustained atmospheric oxygen (>10−5 present atmospheric levels of O2).  相似文献   

7.
Summary The author proves that theDirac-Gilbert equation serving as a basis for the expansion theory has the consequence that the Earth's mantle must be, excepting the uppermost 200 kilometres, similar in constitution to a magma of intermediary composition rich in volatiles. A basic or ultrabasic composition characterizes exclusively the volatile-poor shells situated immediately beneath the acidic crust.Density does not increase monotonously with depth: on the contrary, after a local maximum between 50 and 100 kilometres, it has a slight local minimum. Consequently, theGutenberg-channel is due to changes in material composition rather than to thermal effects. The hydrosphere and most of the atmosphere must have come to exist simultaneously with the crust, in the first phases of the Earth's life. The evolution of the surface of the Moon is in a close parallelism with the evolution of the Earth's mantle.
Zusammenfassung Verfasser weist nach, daß dieDirac-Gilbertsche Gleichung, die die physikalische Grundlage der Erdexpansionstheorie bildet, betreffs der stofflichen Zusammensetzung des Erdmantels die Folge hat, daß diese, von der obersten etwa 200 km mächtigen Schicht abgesehen, einem intermediären Magma von hohem Leichtflüchtigengehalt nahestehen muß. Durch eine basische oder ultrabasische Zusammensetzung werden lediglich die an Leichtflüchtigen armen Schalen unmittelbar unter der sauren Kruste gekennzeichnet.Die Dichte nimmt mit der Tiefe nicht monoton zu, sondern besitzt zwischen 50 und 100 km Tiefe ein lokales Maximum, wonach sie ein schwaches lokales Minimum aufweist. DerGutenbergsche Kanal wird folglich nicht durch thermische Effekte, sondern durch Unterschiede der stofflichen Zusammensetzung bedingt. Die Hydrosphäre und der größte Teil der Atmosphäre muß zugleich mit der Kruste in den ersten Phasen der Erdentwicklung entstanden sein. Die Entwicklung der Mondoberfläche weist eine enge Parallelität mit der Entwicklung des Erdmantels auf.
  相似文献   

8.
SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard deviation s B of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields; i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23 and 24. Annual variations of s B were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance from the equator to the disk center and the increase of s B with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s B estimates.  相似文献   

9.
Currently, the species list of the macroalgae (excluding Charales) inhabiting the southern seas of Russia includes 388 species, specifically, 362 species in the Black Sea, 46 species in the Sea of Azov, and 70 species in the Caspian Sea. The species list has been increased by approximately 30% (96 species, most of them are registered in the Black Sea), compared to the data obtained 30 years ago. The green and red macroalgae of warm-water Mediterranean and tropical origin (Ceramium, Polysiphonia, Laurencia, Ulva, and Chaetomorpha) and brown algae (Sargassum and Cytoseira) were the key invaders. Nowadays the maximal species diversity is found on the Crimean coast and the Turkish coast of the Black Sea; and the species list of the Turkish coast differs significantly from all the other studied sites of the Black Sea. The number of the algae of the warm-water complex increased the most in 1990s–2000s in the Black Sea; species of boreal-tropical and subtropical origin dominate. However, such a tendency was not observed in the Sea of Azov and in the Caspian Sea, but expansion of the habitats of the brackish green algae has been registered.  相似文献   

10.
The paper investigates the question of whether or not determinations of the distance between the Sun and the Galactic center R 0 are affected by the so-called “bandwagon effect”, leading to selection effects in published data that tend to be close to expected values, as was suggested by some authors. It is difficult to estimate numerically a systematic uncertainty in R 0 due to the bandwagon effect; however, it is highly probable that, even if widely accepted values differ appreciably from the true value, the published results should eventually approach the true value despite the bandwagon effect. This should be manifest as a trend in the published R 0 data: if this trend is statistically significant, the presence of the bandwagon effect can be suspected in the data. Fifty two determinations of R 0 published over the last 20 years were analyzed. These data reveal no statistically significant trend, suggesting they are unlikely to involve any systematic uncertainty due to the bandwagon effect. At the same time, the published data show a gradual and statistically significant decrease in the uncertainties in the R 0 determinations with time.  相似文献   

11.
The first biozone (Anabarites trisulcatus Assemblage Zone) in the Siberian hypostratotype of the Vendian (northwestern slope of the Olenek Uplift) is represented by the Turkut Formation of the Khorbusuonka Group and most of the Syhargalakh Formation of the Kessyusa Group. The lower part of the Kessyusa Group in some of the sections includes stratiform breccia coeval with the middle part of the Syhargalakh Formation. The breccia is shown to be the alteration product of tuff breccia, which is widely distributed in the region and occurs as diatremes. A U-Pb zircon date of 543.9 ± 0.24 Ma for tuff breccia provides the best constraint on the age of the boundary between the Anabarites trisulcatus and Purella antiqua Assemblage Zones. The first appearance of small skeletal fossils Cambrotubulus decurvatus (which define the base of the Anabarites trisulcatus Assemblage Zone) is 1.4 m above the lower boundary of the Turkut Formation. Ichnofabric in the underlying Khatyspyt Formation is globally distributed in the strata 553-551 million years old, always predating the first appearance of small skeletal fossils of the Anabarites trisulcatus Assemblage Zone. The base of the Anabarites trisulcatus Assemblage Zone is therefore younger than 553-551 Ma, whereas the duration of the assemblage zone does not exceed six million years.  相似文献   

12.
Analysis of all available geological, geophysical, and field data on some gas condensate fields discovered within the Khapchagai megaswell (Vilyui syneclise of the Siberian Platform) as early as the 1960s shows the presence of oil rims in Lower Triassic (horizon T1-III in the Srednevilyuiskoe and Tolonskoe gas condensate fields and horizon T1-Kh in the Mastakhskoe gas condensate field) and Lower Jurassic (horizons J1-I and J1-II in the Mastakhskoe gas condensate field) deposits. The C3 oil reserves in these rims are estimated at several tens of millions of tons of oil. The results are indicative of the oil potential of the Lower Mesozoic deposits not only of the Vilyui syneclise but also of the Lena–Vilyui petroliferous province as a whole, which was always characterized as a gas-bearing province in summary reports.  相似文献   

13.
The Austroalpine basement to the south of the Tauern Window once was part of the northern margin of Gondwana. It includes the “Altkristallin” and the phyllitic Thurntaler Complex. In the Altkristallin (AMU, MPU), suites of arc-related metamafic sequences occur together with calc-alkaline metagranite. SHRIMP U–Pb dating of zircon from calc-alkaline metagranite associated with an eclogitic amphibolite give an age of 470 ± 3 Ma interpreted as the age of protolith emplacement. In the Thurntaler Complex, metaporphyroids occur together with tholeiitic as well as alkaline within-plate basalt-type metabasite. The metaryholites of this association give a crystallization SHRIMP age of 477 ± 4 Ma, which suggests contemporaneity of arc-related and extensional settings in the Austroalpine basement units. The age data demonstrate widespread magmatic activity associated with the Early-Ordovician amalgamation at the end of the 550–470 Ma subduction–accretion–collision cycle. The Pb–Pb and U–Pb systematics of step-wise leached staurolite and kyanite from the peak-metamorphic assemblage of the Altkristallin indicate that (1) step-wise leaching of staurolite and kyanite yields the age of inclusions rather than the host; (2) zircon inclusions in staurolite suggest an Ordovician or older age for the precursor of the staurolite-schists; (3) the weighted average of the 206Pb/238U data of the various leaching steps yields a Variscan age for the inclusions (ilmenite, biotite, and andesine). Since these inclusions are part of the metamorphic mineral assemblage, this age provides a minimum estimate for staurolite growth, i.e., metamorphism. Thus, the Pb–Pb and U–Pb systematics of staurolite provide evidence for a Variscan metamorphism of the Austroalpine basement, e.g., MPU, AMU and Thurntaler Complex, to the south of the Tauern Window.  相似文献   

14.
The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of B z together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of B z . Time intervals, in which negative values of the B z component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability.  相似文献   

15.
Data on the global magnetic field (GMF) of the Sun as a star for 1968–1999 are used to determine the correlation of the GMF with the radial component of the interplanetary magnetic field (IMF) |B r|; all data were averaged over a half year. The time variations in the GMF |H| are better correlated with variations in |B r|; than the results of extrapolating the field from the “source surface” to the Earth’s orbit in a potential model based on magnetic synoptic maps of the photosphere. Possible origins for the higher correlation between the GMF and IMF are discussed. For both the GMF and IMF, the source surface actually corresponds to the quiet photosphere—i.e., background fields and coronal holes—rather than to a spherical surface artificially placed ≈2.5 R ⊙ from the center of the Sun, as assumed in potential models (R ⊙ is the solar radius). The mean effective strength of the photospheric field is about 1.9 G. There is a nearly linear dependence between |H| and |B r|. The strong correlation between variations in |H| and |B r| casts doubt on the validity of correcting solar magnetic fields using the so-called “saturation” factor δ?1 (for magnetograph measurements in the λ 525.0 nm FeI line).  相似文献   

16.
基于2009年5月至2011年10月科其喀尔冰川的花杆观测资料,对其消融区的表面运动特征进行分析. 结果表明：冰川消融区的年水平运动速度最大值为86.69 m·a-1,年垂直运动速度最大值为15.34 m·a-1,均出现在冰川海拔4 000~4 200 m的消融区上部;在靠近冰川末端的冰舌下部,受冰量补给减弱、厚层表碛覆盖等影响,冰川运动缓慢,年水平运动速度小于5 m·a-1,而垂直运动速度值小于2 m·a-1. 大多数横剖面的水平运动速度具有从中部向边缘逐渐减小的特征,而有的剖面却出现局部速度增大的区域. 整体而言,冰川水平及垂直运动速度随海拔降低而减小,符合冰川运动的一般规律,但主要受地形作用的影响,垂直运动速度随海拔的变化会出现波动. 消融期月水平运动速度与同期气温和降水的变化具有一定的相关性,可能反映出气候快速变化对冰川运动的影响.  相似文献   

17.
A charophyte flora from the Upper Berriasian is described from the Lakota (Black Hills, South Dakota) and Cedar Mountain formations (San Rafael Swell, Utah) of the Western Interior Basin, United States of America. Whereas the latter is dominated by monotonous assemblages of the clavatoracean Nodosoclavator bradleyi (Harris, 1939), found in temporary lakes within palustrine facies, the flora of the Lakota Formation consists of more varied assemblages of the clavatoraceans N. bradleyi (Harris, 1939), Clavator grovesii grovesii Harris 1939, C. bilateralis Peck 1957 and early characeans (Mesochara sp. or Tolypella sp.). This flora was found in deposits related to permanent lakes in fluvial floodplains, i.e. lacustrine marls and limestones that do not show any evidence of subaerial exposure. To date, little is known about C. bilateralis, we provide a new definition on the basis of its particular structure, which shows lateral bract-cell units with a pinnate arrangement. This species appears to be endemic to North America and stratigraphically limited to the earliest Cretaceous. C. grovesii grovesii is part of a long-lasting charophyte lineage, which until now was considered to have originated in the Central Tethyan Archipelago (Europe) during the Early Berriasian, about 145 Ma, and limited to Eurasia until most of the Early Cretaceous. The new data presented here suggest that during the Berriasian this species was very broadly distributed, comprising North America, Europe and China.  相似文献   

18.
The area of the West Siberian platform is about 3.3 million km2, the average thickness of the Mesozoic—Cenozoic platform mantle of sediments is 3 km, and the volume of sedimentary infilling is 10 million km3. The formation of the platform took place during a major tectonic cycle which in turn is divided into tectonic-sedimentary cycles as follows: Triassic, early-Middle Jurassic, late Jurassic, Neocomian, Aptian—Cenomanian, Turonian—Maastrichtian, Paleocene—early Oligocene and Middle Oligocene—Middle Pliocene. During the Triassic period in the arctic part of the platform large depressions were formed and continued to subside to the end of the Cretaceous. During early—Middle Jurassic part of the Triassic postorogenic shield began to subside. The late Jurassic epoch is characterized by maximum transgression and low rate of uncompensated subsidence of the basin floor. In Neocomian and Aptian—Cenomanian time, differential subsidence is sharply intensified, its rate increasing from south to north in the direction of Triassic downwarp. Turonian—Maastrichtian time is distinguished by wide transgression and reduction of subsidence rate. In Paleocene—early Oligocene the extent of the sea decreased and took the form of a submeridional gulf, the axial line of which approached the Urals. In the middle of the Oligocene epoch the sea became freshened and divided into separate basins. Eastern and northern parts of the platform were subsequently involved in the uplift. In the Neogene the region of subsidence took the form of a sublatitudinal depression extending along the southern mountain-folded margin of the platform.  相似文献   

19.
Fluxes of Sr into the headwaters of the Ganges   总被引：1，自引：0，他引：1  
Himalayan weathering is recognized as an important agent in modifying sea water chemistry, but there are significant uncertainties in our understanding of Himalayan riverine fluxes. This paper examines causes of the variability, including that of the seasons, by analysis of downstream variations in Sr, 87Sr, and major ions in the mainstream, in relation to the composition of tributary streams from subcatchments with differing geologic substrates.Water samples were collected over four periods spanning the premonsoon, monsoon, and postmonsoon seasons. Uncertainties in the relative fluxes have been estimated, using Monte Carlo techniques, from the short-term variability of mainstream chemistry and the scatter of tributary compositions. The results show marked seasonal variations in the relative inputs related to high monsoon rainfall in the High and Lesser Himalaya, contrasting with the major contribution from glacial melt waters from the Tibetan Sedimentary Series (TSS) at times of low rainfall. Much of the spread in previously published estimates of the sources of Sr in Himalayan rivers may result from these seasonal variations in Sr fluxes.The annual fluxes of Sr into the headwaters of the Ganges are derived from the three main tectonic units in the proportions 35 ± 1% from the TSS, 27 ± 3% from the High Himalayan Crystalline Series (HHCS), and 38 ± 8% from the Lesser Himalaya. The particularly elevated 87Sr/86Sr ratios characteristic of the HHCS and the Lesser Himalaya enhance their influence on seawater Sr-isotope composition. The TSS contributes 13 ± 1%, the HHCS 30 ± 3%, and the Lesser Himalaya 57 ± 11% of the 87Sr flux in excess of the seawater 87Sr/86Sr ratio of 0.709.  相似文献   

20.
Wager's more general assumptions about the relations betweenthe layered series of Skaergaard and its parent magma form thebasis for a simple procedure by which, from the compositionof the proposed initial magma and the compositions and amountsof the exposed zones, the amount and composition of the hiddenzone and the compositions of liquids remaining after the consolidationof each zone are readily computed. Application of the procedure to the Skaergaard data—moreproperly, to the relevant summary statistics presented by Wager(1960) and by Wager & Brown (1968)—suggests that currentlyaccepted graphical solutions materially overestimate the extentof end-stage alkali enrichment and may materially understatethe magnitude of the hidden zone; the data are quite as compatiblewith numerical solutions yielding a considerably larger hiddenzone and virtually no perceptible end-stage alkali enrichment.Differences between numerical and graphical solutions seem tobe generated primarily by the zone weights used in the latter.  相似文献   

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