U–Pb SHRIMP monazite ages of the giant Morro Velho and Cuiabá gold deposits, Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Minas Gerais, Brazil     

L.M. Lobato  J.O.S. Santos  N.J. McNaughton  I.R. Fletcher  C.M. Noce 《Ore Geology Reviews》2007,32(3-4):674

U–Pb SHRIMP results of 2672 ± 14 Ma obtained on hydrothermal monazite crystals, from ore samples of the giant Morro Velho and Cuiabá Archean orogenic deposits, represent the first reliable and precise age of gold mineralization associated with the Rio das Velhas greenstone belt evolution, in the Quadrilátero Ferrífero, Brazil. In the basal Nova Lima Group, of the Rio das Velhas greenstone belt, felsic volcanic and volcaniclastic rocks have been dated between 2792 ± 11 and 2751 ± 9 Ma, coeval with the intrusion of syn-tectonic tonalite and granodiorite plutons, and also with the metamorphic overprint of older tonalite–trondhjemite–granodiorite crust. Since cratonization and stable-shelf sedimentation followed intrusion of Neoarchean granites at 2612 + 3/− 2 Ma, it is clear that like other granite–greenstone terranes in the world, gold mineralization is constrained to the latest stages of greenstone evolution.  相似文献   

Water resources issues in South America     

J. A. A. Jones  O. E. Scarpati 《GeoJournal》2007,70(4):227-231

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On the quantitative evaluation of metamorphic fluid composition: Verification of the results of physicochemical simulations for water-mineral-rock reactions     

V. O. Khudolozhkin 《Russian Journal of Pacific Geology》2007,1(3):290-301

This paper reports the results of a comparison of the qualitative physicochemical simulations (by the Winsel program complex) of the composition of the reacting fluid with experimental data on the water-electrolyte (NaCl, HCl, NaOH, and KOH)-mineral (quartz, corundum, microcline, and plagioclase) system and the water-electrolyte-rock (granite and pelite) system at 400–800°C and 1–10 kbar. Constraints are proposed for the temperature, pressure, and the composition of the electrolyte at which the simulation results are consistent with the experimental data.  相似文献   

First Th-U-Pb single zircon dating of metasomatites from the Belomorian mobile belt     

N. S. Serebryakov  B. Yu. Astaf’ev  O. A. Voinova  S. L. Presnyakov 《Doklady Earth Sciences》2007,413(2):388-392

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Nonlinear dynamics of slope flows: Simple models and exact solutions     

O. V. Rudenko  A. L. Sobisevich  L. E. Sobisevich 《Doklady Earth Sciences》2007,416(1):1109-1113

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Analysis of currents near the Sakhalin southeastern coast from instrumental measurements     

G. V. Shevchenko  O. V. Kusailo 《Russian Meteorology and Hydrology》2007,32(10):658-667

Field experimental materials on the sea current measurements, carried out by the Sakhalin Research Institute for Fishery and Oceanography in September–December 2004 near the Sakhalin southeastern coast, are analyzed. The experiment included the installation of two coastal and one more remote autonomous buoy stations. The tidal flows in this region, unlike those on the northeastern shelf of the island, are relatively small and do not play a significant role in the dynamics of the coastal zone. The character of currents at coastal stations is determined primarily by their response to the wind effect. In particular, significant water temperature falls of 6–8°C, observed from 2–3 days to a week, are indicative of coastal upwelling induced by the wind. During the passage of a deep cyclone that caused a storm wave 1 m high, the flow velocity at coastal stations increased up to 1.5 knots. At a more remote station, in the region of Cape Svobodnyi, the flow character was determined by the East Sakhalin Current, whose autumn intensification was observed in the second ten-day period of October. It manifested itself in a sharp intensification of the flow, directed southward and southeastward throughout the entire water column, which practically was not pronounced at the coastal stations.  相似文献   

Impact of different convective cloud schemes on the simulation of the tropical seasonal cycle in a coupled ocean–atmosphere model     

P. Braconnot  F. Hourdin  S. Bony  J. L. Dufresne  J. Y. Grandpeix  O. Marti 《Climate Dynamics》2007,29(5):501-520

The simulation of the mean seasonal cycle of sea surface temperature (SST) remains a challenge for coupled ocean–atmosphere general circulation models (OAGCMs). Here we investigate how the numerical representation of clouds and convection affects the simulation of the seasonal variations of tropical SST. For this purpose, we compare simulations performed with two versions of the same OAGCM differing only by their convection and cloud schemes. Most of the atmospheric temperature and precipitation differences between the two simulations reflect differences found in atmosphere-alone simulations. They affect the ocean interior down to 1,000 m. Substantial differences are found between the two coupled simulations in the seasonal march of the Intertropical Convergence Zone in the eastern part of the Pacific and Atlantic basins, where the equatorial upwelling develops. The results confirm that the distribution of atmospheric convection between ocean and land during the American and African boreal summer monsoons plays a key role in maintaining a cross equatorial flow and a strong windstress along the equator, and thereby the equatorial upwelling. Feedbacks between convection, large-scale circulation, SST and clouds are highlighted from the differences between the two simulations. In one case, these feedbacks maintain the ITCZ in a quite realistic position, whereas in the other case the ITCZ is located too far south close to the equator.  相似文献   

Surface energy balance measurements at a tropical site in West Africa during the transition from dry to wet season   总被引：1，自引：0，他引：1  

M. Mauder  O. O. Jegede  E. C. Okogbue  F. Wimmer  T. Foken 《Theoretical and Applied Climatology》2007,89(3-4):171-183

Summary In one of the first micrometeorological experiments at a tropical site in West Africa, direct measurements of all surface energy balance components were carried out. The experiment NIMEX-1 in Ile-Ife, Nigeria (7°33′ N, 4°33′ E), was conducted from February 19, 2004 to March 9, 2004, during the transition from the dry to the wet season. Three typical weather situations could be observed: firstly, monsoonal winds from the southwest blew over desiccated soils. Almost 100% of the available energy at the surface was transformed into sensible heat flux. Secondly, after several thundershowers, monsoonal winds swept over soils of increased water content, which led to a partitioning of the available energy corresponding to Bowen ratios between 0.3 and 0.5. Thirdly, harmattan winds advected dry dusty air from northern directions, which reduced the incoming shortwave radiation. Again, Bowen ratios range from 0.3 to 0.5 during daytime, whereas latent heat fluxes are still high during the night due to the advection of very dry air. No systematic non-closure of the surface energy balance could be found for the NIMEX-1 dataset. Unlike other experiments in Europe, most of the ogives for the sensible and latent heat flux were found to be convergent during NIMEX-1 in Ile-Ife. This can be attributed to the homogeneity of the surrounding bush, which lacks the defined borders found in agriculturally cultivated landscapes.  相似文献   

Analysis of changes in air temperature in Russia and empirical forecast for the first quarter of the 21st century     

O. A. Anisimov  V. A. Lobanov  S. A. Reneva 《Russian Meteorology and Hydrology》2007,32(10):620-626

Changes in air temperature in administrative districts of the Russian Federation are studied. The in-regional homogeneity of modern climate changes is estimated based on several criteria for the first half of the 20th century and for the next period. The relation between regional changes in mean annual and seasonal temperatures and global air temperature is considered, and an empirical forecast for one or two decades is suggested to be made on its basis. Empirical regional forecasts of a rate of changes in mean annual air temperature are compared with the calculation results from five general circulation models.  相似文献   

Modern climate-related changes in heat supply,moistening, and productivity of the agrosphere in Russia     

O. D. Sirotenko  G. V. Gruza  E. Ya. Rankova  E. V. Abashina  V. N. Pavlova 《Russian Meteorology and Hydrology》2007,32(8):538-546

Climate changes observed in recent decades are analyzed, and the respective climate-related tendencies of changes in heat supply, moistening, and productivity of the agrosphere that determine the natural resourse of potential Russia are determined. The grain crop yield trends are used additionally as climate change indicators. It is shown that climate changes observed in the last 30 years promote the increase in potential agriculture productivity in most of the Russian Federation, where not less than 85% of agricultural products are produced. At the same time, the increase in climate aridity is observed in several regions of Siberia and Chernozem Center, which results in a reduced productivity of agriculture.  相似文献