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排序方式: 共有64条查询结果,搜索用时 15 毫秒
31.
Zorano Srgio de Souza Jean-Marc Montel Simone Maria Lima Costa Gioia Maria Helena Bezerra Maia de Hollanda Marcos Antonio Leite do Nascimento Emanuel Ferraz Jardim de S Venerando Eustquio Amaro Mrcio Martins Pimentel Jean-Marc Lardeaux Michelle Veschambre 《Gondwana Research》2006,9(4):441-455
The easternmost domain of the Borborema Province, northeastern Brazil, presents widespread, extensional-related high-temperature metamorphism during the Brasiliano (=Pan-African) orogeny. This event reached the upper amphibolite to granulite facies and provoked generalized migmatization of Proterozoic metapelitic rocks of the Seridó Group and tonalitic to granodioritic orthogneisses of the Archean to Paleoproterozoic basement. We report new geochronological data based on electron microprobe dating of monazite from metapelitic migmatite and leuconorite within the high-T shear zones that make up the eastern continuation of the huge E–W Patos shear belt. These data were also constrained by using the Sm–Nd isotopic systematic on garnet from a syntectonic alkaline granite and two garnet-bearing leucosomes. The results suggest an age of about 578 to 574 Ma for the peak of the widespread high-T metamorphism. This event is best recorded by Sm–Nd garnet-whole rock ages. The U–Th–Pb isotopes on monazite of the metapelitic migmatite show a younger thermal event at 553 ± 10 Ma. When compared to the Sm–Nd garnet-whole rock ages, the U–Th–Pb electron probe monazite ages seem to record an event of slightly lower temperatures after the peak of the high-T metamorphism. This may reflect the difference in the isotopic behavior of the geochronological methods employed. Otherwise, the U–Th–Pb ages on monazites could indicate an event not yet very well defined. In anyway, this paper reveals the partial or even complete re-opening and resetting of the U–Th–Pb isotopic system produced by the action of low-T Ca-rich fluid. 相似文献
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Pelotas Basin has the largest gas hydrate occurrence of the Brazilian coast. The reserves are estimated in 780 trillion cubic feet, covering an area of 45,000 km2. In this work we apply spectral decomposition technique in order to better understand a gas hydrate deep water system, performing a continuous time–frequency analysis of seismic trace, where frequency spectrum is the output for each time sample of the seismic trace. This allows a continuous analysis on the effects of the geologic structures and lithology over frequency content of the seismic wave. Spectral anomalies found were interpreted as variations of hydrates concentration inside the Gas Hydrate Stability Zone (GHSZ), as well free gas accumulations beneath and Below the GHSZ and gas chimneys. We concluded that this technique has a good potential to assist seismic study of structures associated with gas hydrates accumulations. 相似文献
34.
Dissipative heating and hurricane intensity 总被引:3,自引:0,他引:3
Summary Dissipative heating has not been accounted for in either numerical simulations of hurricanes or in theories for the maximum intensity of hurricanes. We argue that the bulk of dissipative heating occurs in the atmospheric boundary layer near the radius of maximum winds and, using both theory and numerical simulation, show that dissipative heating increases maximum wind speeds in tropical cyclones by about 20%.With 4 Figures 相似文献
35.
Charles I. Scaife Nitin K. Singh Ryan E. Emanuel Chelcy Ford Miniat Lawrence E. Band 《水文研究》2020,34(13):2949-2964
Linking quickflow response to subsurface state can improve our understanding of runoff processes that drive emergent catchment behaviour. We investigated the formation of non-linear quickflows in three forested headwater catchments and also explored unsaturated and saturated storage dynamics, and likely runoff generation mechanisms that contributed to threshold formation. Our analyses focused on two reference watersheds at the Coweeta Hydrologic Laboratory (CHL) in western North Carolina, USA, and one reference watershed at the Susquehanna Shale Hills Critical Zone Observatory (SHW) in Central Pennsylvania, USA, with available hourly soil moisture, groundwater, streamflow, and precipitation time series over several years. Our study objectives were to characterise (a) non-linear runoff response as a function of storm characteristics and antecedent conditions, (b) the critical levels of shallow unsaturated and saturated storage that lead to hourly flow response, and (c) runoff mechanisms contributing to rapidly increasing quickflow using measurements of soil moisture and groundwater. We found that maximum hourly rainfall did not significantly contribute to quickflow production in our sites, in contrast to prior studies, due to highly conductive forest soils. Soil moisture and groundwater dynamics measured in hydrologically representative areas of the hillslope showed that variable subsurface states could contribute to non-linear runoff behaviour. Quickflow generation in watersheds at CHL were dominated by both saturated and unsaturated pathways, but the relative contributions of each pathway varied between catchments. In contrast, quickflow was almost entirely related to groundwater fluctuations at SHW. We showed that co-located measurements of soil moisture and groundwater supplement threshold analyses providing stronger prediction and understanding of quickflow generation and indicate dominant runoff processes. 相似文献
36.
Twin Tsunamis Triggered by the 12 January 2010 Haiti Earthquake 总被引:2,自引:0,他引:2
Hermann M. Fritz Jean Vilmond Hillaire Emanuel Molière Yong Wei Fahad Mohammed 《Pure and Applied Geophysics》2013,170(9-10):1463-1474
On 12 January 2010, a magnitude M w 7.0 earthquake occurred 25 km west–southwest of Haiti’s capital Port-au-Prince causing an estimated 316,000 fatalities, thereby exceeding any previous loss of life from a similar size earthquake. In addition, tsunami waves triggered by the earthquake caused at least three fatalities at Petit Paradis due to a complete lack of tsunami awareness. The International Tsunami Survey Team (ITST) was deployed within weeks of the event and covered the greater Bay of Port-au-Prince and more than 100 km of Hispaniola’s southern coastline. The collected survey data include more than 21 tsunami heights along with observations of coastal land level change. Maximum tsunami heights of 3 m have been measured for two independently triggered tsunamis. 相似文献
37.
Samuel Beskow Luis Carlos Timm Vitor Emanuel Quevedo Tavares Tamara Leitzke Caldeira Leandro Sanzi Aquino 《水文科学杂志》2013,58(14):2567-2578
ABSTRACTThe objective of this study was to evaluate, based on a data-scarce basin in southern Brazil, the potential of the Lavras Simulation of Hydrology (LASH) model for estimating daily streamflows, annual streamflow indicators and the flow–duration curve. It was also used to simulate the different runoff components and their consistency with the basin physiographical characteristics. The statistical measures indicated that LASH can be considered suitable according to widely used classifications and when compared with other studies involving hydrological models. LASH also showed satisfactory results for annual indicators, especially for maximum and average annual streamflows, as well as for the flow–duration curve. It was found that the model was consistent with the basin characteristics when simulating runoff components. The results obtained in this study allowed us to conclude that the LASH model has the potential to aid practitioners in water resources management of basins with scarce data and similar soil and land-use conditions.
Editor A. Castellarin; Associate editor Y. Gyasi-Agyei 相似文献
38.
Maria Helena Bezerra Maia de Hollanda Mrcio Martins Pimentel Emanuel Ferraz Jardim de S 《Journal of South American Earth Sciences》2003,15(8):885-900
Late Neoproterozoic (ca. 580 Ma), high-K, mafic-intermediate rocks represent voluminous bimodal magmatism in the Borborema Province, northeast Brazil. These rocks show the following chemical signatures that reflect derivation from a subduction-modified lithospheric mantle source: (1) enrichment in large ion lithophile elements (Rb, Ba, K, Th) and light rare-earth elements (REE) (La/YbCN=11–70), (2) pronounced negative Nb anomalies, and (3) radiogenic Sr (0.71202–0.7059) and unradiogenic Nd (Nd from −9.3–−20.1) isotopic compositions. TDM model ages suggest that modification of the lithospheric mantle source (metasomatised garnet lherzolite) may have occurred in the Paleoproterozoic during the Transamazonian/Eburnean tectonics that affected the region. Interaction with asthenospheric fluids is believed to have partially melted this enriched source in the Neoproterozoic, probably as a result of asthenosphere-derived fluid percolation in the Brasiliano/Pan-African shear zones that controlled the emplacement of these mafic-intermediate magmas. The involvement of this asthenospheric component is supported by the nonradiogenic Pb isotopic ratios (206Pb/204Pb=16–17.3, 207Pb/204Pb=15.1–15.6, 208Pb/204Pb=36–37.5), which contrast with the enriched Sr and Nd compositions and thereby suggest the decoupling of Rb–Sr, Sm–Nd, and U–Pb systems at the time of intrusion of the mafic-intermediate magmas in the crust. 相似文献
39.
40.
The paper presents the results of an experimental study on the effects of the initial water content and dry density on the
soil–water retention curve and the shrinkage behavior of a compacted Lias-clay. The initial conditions after compaction (initial
water content and initial dry density) have been chosen on the basis of three Proctor tests of different compaction efforts.
According to the eight chosen initial conditions clay samples have been compacted statically. The relation between total suction
and water content was determined for the drying path starting from the initial conditions without previous saturation of the
specimens. A chilled-mirror dew-point hygrometer was used for the suction measurements. For the investigation of the shrinkage
behavior cylindrical specimens were dried to desired water contents step-by-step without previous saturation. The volume of
the specimens was measured by means of a caliper. Based on the test results the influence of different initial conditions
on the soil suction and the shrinkage behavior is analyzed. The soil–water retention curves obtained in terms of the gravimetric
water content are independent of the initial dry density. At water contents above approximately 11–12.5% a strong influence
of the compaction water content is observed. At smaller water contents, the soil–water retention curve is independent of the
compaction water content. The results of the shrinkage tests show that the influence of the compaction dry density on the
shrinkage behavior is negligible. Similar to the drying behavior of saturated samples a primary and a residual drying process
could be distinguished. The primary drying process is strongly influenced by the initial water content. In contrast, the rate
of the volume change of the residual drying process is unaffected by the initial water content. 相似文献