Photometric Survey of Galactic Open Clusters     

M.G. Lee  H.B. Ann  M.Y. Chun  S. L. Kim  Y. B. Jeon  B. G. Park  I. S. Yuk  H.Sung 《天文研究与技术》1999,(Z1)

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Inhomogeneous distribution of REE in scheelite and dynamics of Archaean hydrothermal systems (Mt. Charlotte and Drysdale gold deposits, Western Australia)   总被引：5，自引：0，他引：5  

Joël Brugger  Yann Lahaye  Sylvie Costa  David Lambert  Roger Bateman 《Contributions to Mineralogy and Petrology》2000,139(3):251-264

Scheelite is a widespread accessory mineral in hydrothermal gold deposits, and its rare earth element (REE) patterns and Nd and Sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity. Micro-analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the REE in single scheelite grains from the Mt. Charlotte and Drysdale Archaean gold deposits in Western Australia. Two end-member REE patterns are distinguished: type I is middle REE (MREE)-enriched, with no or minor positive Eu-anomaly, whereas type II is flat or MREE-depleted with a strong positive Eu-anomaly. The chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type I and type II patterns, with zone widths varying from below 1 to 200 μm. Intra-sectorial growth discontinuities, syn-crystallisation brittle deformation, and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions. The co-existence of MREE-enriched and MREE-depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions MREE relative to light and heavy REE. Scheelite itself has such characteristics, as does fluorapatite, which is locally abundant and has REE contents similar to that of scheelite. In this context, the systematic increase of the Eu-anomaly between type I and type II patterns is produced by the difference between the partition coefficients of Eu²⁺ and Eu³⁺, and not by fluid mixing or redox reactions. Consequently, the high positive Eu-anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid, but may reflect processes occurring during ore deposition. This case study demonstrates that in hydrothermal systems characterised by low REE concentrations in the fluid, and by the precipitation of a REE-rich mineral which strongly fractionates the REE, the REE patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system. Received: 1 November 1999 / Accepted: 4 February 2000  相似文献   

A Review on the Macromolecular Compositions of Phytoplankton and the Implications for Aquatic Biogeochemistry     

Bhavya  P. S.  Kim  Bo Kyung  Jo  Naeun  Kim  Kwanwoo  Kang  Jae Joong  Lee  Jae Hyung  Lee  Dabin  Lee  Jang Han  Joo  HuiTae  Ahn  So Hyun  Kim  Yewon  Min  Jun-Oh  Kang  Min Gu  Yun  Mi Sun  Kang  Chang Keun  Lee  Sang Heon 《Ocean Science Journal》2019,54(1):1-14

Ocean Science Journal - Biochemical composition of phytoplankton is a key indicator of the physiological and nutritional status of phytoplankton. A balanced biochemical pattern represents a healthy...  相似文献   

Detailed Study of Three Contiguous Segments of the Mid-Atlantic Ridge,South of the Azores (37° N to 38°30′ N), Using Acoustic Imaging Coupled with Submersible Observations     

Ondréas  Hélène  Fouquet  Yves  Voisset  Michel  Radford-Knoery  Joël 《Marine Geophysical Researches》1997,19(3):231-255

Using a new tool of seafloor characterisation (sonar images from FARA-SIGMA cruise; Needham et al., 1992), coupled with submersible observations (DIVA1 cruise) we compare, at different scales of observation, three contiguous segments of the Mid-Atlantic Ridge, South of the Azores Triple Junction, between 37° N and 38°30 N.The two northernmost segments (38°20 N and Menez-Gwen) show unusual morphological features for the MAR; the rift valley is absent and the present-day magmatism is focused on shallow axial volcanoes. On the third segment (Lucky Strike), the morphology is the one usually found on the MAR. On the Menez-Gwen and 38°20 N segments, volcanic constructional activity can obliterate, during periods of high magmatic supply, the morphology inherited from tectonic activity. The dive results constrain the recent evolution of each segment and show that a temporal variability in volcanic dynamics exists. On the three segments, outcrops of eruptive lavas alternate with large areas of explosive volcanic ejecta. This cycle in volcanic activity is influenced by changes in water depth, both spatially (i.e. between segments) and temporally (i.e. for the same segment through time).Each segment has known a specific history in its accretionary processes with a succession of tectonic and volcanic predominance and changes in its volcanic phases between volcanic ejecta and effusive dynamics.The hydrothermal activity is focused at the central part of each segment and is controlled by the presence of fresh lava and major tectonic features.  相似文献   

Resources,pollution and research in a South African economic zone     

Ann Darracott 《Marine Policy》1977,1(3):239-254

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Lunar mare domes: Classification and modes of origin     

James W. Head  Ann Gifford 《Earth, Moon, and Planets》1980,22(2):235-258

A classification of over 200 lunar mare domes shows that they have two major modes of occurrence: (1) low, flat, generally circular structures with convex shapes, slopes less than about 5°, and displaying summit craters, and (2) irregular structures often adjacent to highland regions and rarely containing summit craters. On the basis of morphologic and morphometric similarities, the first mode of occurrence appears to be analogous to small terrestrial shield volcanoes, and to represent primary volcanic constructs, while the second class of domes appears to result from secondary volcanic effects (flooding of highland material to produce kipukas and draping of lavas to produce irregular dome-like topography).Domes comparable to small shield volcanoes generally range from 3–17 km in diameter and up to several hundred meters in height and occur predominantly in groupings in the lunar equatorial region in northeast Tranquillitatis (Cauchy area), between Kepler and Copernicus (Hortensius area), and in the Marius Hills. In the Marius Hills, domes generally lack summit craters and have a rough surface texture formed in part by superposed cones and steep-sided flows. Elsewhere, domes representing volcanic sources are smooth-surfaced and usually contain a summit crater. These features are similar in general morphology to small terrestrial lava shields. They are generally intermediate in volume, slope, and height between small shields of terrestrial basaltic plains (such as the Snake River Plains) and larger Icelandic shields. Summit craters on lunar domes are considerably larger than craters on terrestrial shields of comparable diameters, apparently due to a combination of factors, including vent enlargement during extrusion, possibly higher lunar extrusion rates, different amounts of collapse, and impact erosion.Most vent-related domes appear to be associated with, and are thus approximately the same age as, surrounding lava plains, although relationships in specific areas have not yet been established. On the basis of age ranges of mare deposits established by Apollo samples, mare vent-related domes formed over an approximately one billion year period starting about 3.7 b.y. ago. Extrusion rates were apparently relatively low compared to the very high values characteristic of flows associated with major lunar sinuous rilles and terrestrial flood basalts, but may have been relatively high compared to similar terrestrial shields. Large shield volcanoes equivalent to the terrestrial Hawaiian-type or to the martian edifices such as Olympus Mons, do not occur on the Moon. Lack of these features may be due to the low viscosities and high effusion rates typical of many lunar eruptions and the lack of continuous eruptions from single sources.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献   

Comparative study of Langmuir probe characteristics in different ionospheric conditions     

Joëlle Margot-Chaker  A.G. McNamara 《Planetary and Space Science》1984,32(11):1427-1437

This paper examines the role played by the high energy tail of the electron distribution function on Langmuir probe characteristics. A model is developed to derive the mean energy and the density of the hyperthermal electrons from probe characteristics for two ionospheric rocket flights involving different plasma conditions. The hyperthermal electrons are shown to influence the electron temperature measurement even if they constitute only a small fraction of the total electron concentration. The influence of the geomagnetic field, the collisions and the velocity of the vehicle on the probe data are also examined.  相似文献   

An example of cluster analysis applied to a large geologic data set: Aerial radiometric data from Copper Mountain, Wyoming   总被引：1，自引：0，他引：1  

Fredric L. Pirkle  Jo Ann Howell  George W. Wecksung  Benjamin S. Duran  Newton K. Stablein 《Mathematical Geology》1984,16(5):479-498

One objective of the aerial radiometric surveys flown as part of the U.S. Department of Energy's National Uranium Resource Evaluation (NURE) program was to ascertain the spatial distribution of near-surface radioelement abundances on a regional scale. Some method for identifying groups of observations with similar -ray spectral signatures and radioelement concentration values was therefore required. It is shown in this paper that cluster analysis can identify such groups with or without a priori knowledge of the geology of an area. An approach that combines principal components analysis with convergentk-means cluster analysis is used to classify 6991 observations (each observation comprising three radiometric variables) from the Precambrian rocks of the Copper Mountain, Wyoming area. This method is compared with a convergentk-means analysis that utilizes available geologic knowledge. Both methods identify four clusters. Three of the clusters represent background values for the Precambrian rocks of the area, and the fourth represents outliers (anomalously high²¹⁴Bi). A segmentation of the data corresponding to geologic reality as interpreted by other methods has been achieved by perceptive quantitative analysis of aerial radiometric data. The techniques employed are composites of classical clustering methods designed to handle the special problems presented by large data sets.  相似文献   

Systematique U-Pb et Evolution du Gisement d'Uranium de Lodève (France)     

Joël R. Lancelot  Bruno de Saint André  Henri de la Boisse 《Mineralium Deposita》1984,19(1):44-53

Résumé Considérée comme syngénétique ou diagénétique précoce, la minéralisation uranifère de la couche 0 de l'Autunien du bassin de Lodève a été étudiée par la méthode U-Pb sur roches totales. Les données U-Pb démontrent l'existence de perte en radon, principalement dans la chaine de désintégration de ²³⁸U, et l'intérêt de l'utilisation du couple ²⁰⁷Pb-²³⁵U pour la détermination des âges de cristallisation des concentrations uranifères. Pour la couche 0, deux phases de remobilisation de l'uranium et du plomb ont pu être déterminées respectivement à 173±6 Ma et 108±5 Ma. La plus ancienne de ces deux phases est la plus marquée dans les échantillons étudiés, dont les systèmes U-Pb ne montrent pas la mémoire d'une concentration uranifère permienne. La première mobilisation de l'uranium et du plomb s'est faite lors d'une phase de distension à 160–170 Ma, affectant la croûte continentale du Sud du Massif Central. Cette phase a provoqué la circulation de fluides minéralisés et est marquée par une recristallisation des illites des pélites permiennes entre 100 et 200 °C (du fait de l'élévation du gradient géothermique) et par la mise en place d'un volcanisme d'origine mantellique daté à 155±6 Ma. La composition isotopique en plomb d'une galène de l'Autunien du Lodévois, est analogue à celles des feldspaths des granitoïdes du Massif Central français et à celles des galènes des minéralisations stratiformes de Pb-Zn des Causses, ce qui fournit un argument pour faire dériver au moins une partie des métaux en traces dans les pélites autuniennes de l'altération de la croûte continentale hercynienne environnante.

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In the Lodeve basin, the uraniferous mineralization associated with the autunian pelitic layer 0 is usually considered as syngenetic or early diagenetic. U-Pb isotopic data performed on U bearing whole rocks demonstrate occurrence of radon losses, mainly in the ²³⁸U decay series; the ²⁰⁷Pb-²³⁵U geochronometer is particularly suitable to date U-Pb systems disturbed by such radon losses. For the autunian layer 0, two U-Pb mobilization phases have been respectively recognized at 173±6 Ma and 108±5 Ma. The oldest phase is the most clearly expressed in the studied samples, no memory of a permian age could be recognized in the U-Pb systems. The first U-Pb mobilization occurred 170 Ma ago, during a distension phase of the continental crust. This phase induced circulations of mineralized fluids, illite recristallization in the permian pelites at temperatures ranging from 100 to 200 °C and emplacement of a mantellic volcanism recently dated at 155±6 Ma. A galena from the Autunian of the Lodeve basin, the feldspars of the surrounding variscan granitoïds and galenas of mesozoïc stratiform deposits in the Causses, present similar Pb isotopic composition, which is in agreement with the hypothesis that some metals of the autunian pelites originated in the surrounding weathered variscan continental crust.

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Wind profiles at the Boulder Tower     

Ann Korrell  H. A. Panosky  R. J. Rossi 《Boundary-Layer Meteorology》1982,22(3):295-312

Analysis of wind profiles at the Boulder Tower (BAO) leads to these conclusions:

1. The variation of roughness with wind direction found earlier is confirmed. Roughness lengths measured on the tower are larger than those measured close to the surface.
2. The profiles and measurements of Reynolds stress are consistent with a von-Karman constant of 0.35.
3. The form φ_m=(1?15z/L)^-1/3 fits best in the range -0.6 < z/L < 0. In the range 0 < z/L < 0.5, θ _m ～ 1 + 4.7z/L provides a good fit to the observations. For z/L < 0.1, φ _m also depends on h, the thickness of the PBL. For z/L < -0.6, Φ _m approaches the constant 0.5, in contrast to all previous suggestions. For larger stabilities, the upper level is usually not in the surface layer, and wind ratios become independent of z/L.
4. With snow cover, the effective roughness diminishes to about 1 cm, even for directions for which the roughness length without snow is large.
5. Estimation of winds at 100 or 150 m from information near the surface is best for similarity theory provided that the ratio of height to Monin-Obukhov L is less than 0.1. For larger z/L, simple power laws seem more appropriate.

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