A dynamical solution of the triple asteroid system (45) Eugenia     

F. Marchis  V. Lainey  P. Descamps  J. Berthier  M. Van Dam  I. de Pater  B. Macomber  M. Baek  D. Le Mignant  H.B. Hammel  M. Showalter  F. Vachier 《Icarus》2010,210(2):635-643

We present the first dynamical solution of the triple asteroid system (45) Eugenia and its two moons Petit–Prince (diameter ∼ 7 km) and S/2004 (45) 1 (diameter ∼ 5 km). The two moons orbit at 1165 and 610 km from the primary, describing an almost-circular orbit (e ∼ 6 × 10⁻³ and e ∼ 7 × 10⁻² respectively). The system is quite different from the other known triple systems in the main belt since the inclinations of the moon orbits are sizeable (9° and 18° with respect to the equator of the primary respectively). No resonances, neither secular nor due to Lidov–Kozai mechanism, were detected in our dynamical solution, suggesting that these inclinations are not due to excitation modes between the primary and the moons. A 10-year evolution study shows that the orbits are slightly affected by perturbations from the Sun, and to a lesser extent by mutual interactions between the moons. The estimated J₂ of the primary is three times lower than the theoretical one, calculated assuming the shape of the primary and an homogeneous interior, possibly suggesting the importance of other gravitational harmonics.  相似文献   

Seismic anisotropy surrounding South China Sea and its geodynamic implications   总被引：1，自引：0，他引：1  

Mei Xue  Khanh Phon Le  Ting Yang 《Marine Geophysical Researches》2013,34(3-4):407-429

Several mechanisms have been proposed for the opening of the South China Sea. Here, we use SKS splitting analysis to investigate the mantle flow surrounding the South China Sea. We use a total of 23 seismic stations and 87 events. We applied spectral analysis and cluster analysis to find a stable splitting solution for each event. The main conclusions are: (1) In northern Vietnam, the NW–SE fast direction is parallel to the absolute plate motion as well as GPS observations with splitting times larger than 1 s, indicating a coupled lithosphere and mantle. In contrast, in southern Vietnam, the NE–SW fast direction suggests that the lithosphere and asthenosphere are decoupled. (2) The fast directions beneath the South China Block and central Taiwan are NE–SW and NS respectively, both parallel to surface deformations with splitting times greater than 1 s, indicating that mantle flow and surface deformation are related. (3) The observed NW–SE fast directions beneath Hainan Island reflect the India–Eurasia collision, and show no signatures of an upwelling mantle plume directly underneath Hainan Island. This implies that Hainan Island is tectonically closely related to the Red River Fault, not the South China Block. (4) In Borneo, the observed NE-SW direction is parallel to the Palawan Trench, consistent with flow associated with the inactive proto-South China Sea subduction system. The SKS splitting observations surrounding South China Sea cannot be explained by a single geologic process, with either the collision-driven extrusion model or the slab pull model fitting the data presented here.  相似文献   

The complete mitochondrial genome of the grey bamboo shark (Chiloscyllium griseum) (Orectolobiformes: Hemiscylliidae): genomic characterization and phylogenetic application     

CHEN Xiao  AI Weiming  YE Le  WANG Xuehui  LIN Chongwen  YANG Shengyun 《海洋学报(英文版)》2013,32(4):59-65

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Formation mechanism of large pockmarks in the subaqueous Yellow River Delta     

Zhuangcai Tian  Luzheng Qiao  Le Yu  Guohui Xu  Tao Liu 《Marine Georesources & Geotechnology》2013,31(6):651-659

Abstract

We have identified large pockmarks in an area of approximately 0.3?km² in the subaqueous Yellow River Delta in the Chengdao Sea. Gas eruption channels not been identified in the sediment layers in this area, and the formation mechanism of these large pockmarks remains unknown. To study the formation mechanism of these large pockmarks, we constructed a layered silty sediment model composed of appropriate geological materials. Then, we calculated the stress, displacement, and excess pore pressure in the layered silty sediment from the surface to a depth of 10?m using the Biot theory. A comparative analysis of the calculated results and the data measured in the field was then performed. Based on these results, we established a new formation mechanism for the large pockmarks. With the occurrence of storm waves, two extreme areas of displacement and excess pore pressure appeared in the layered silty sediment. These extreme values increased quickly in the seabed during the continuous action of storm waves. When the excess pore pressure surpassed the effective stress, the top silty layer instantly liquefied and then reconsolidated. Then, when the pore pressure of the interface position exceeded the effective stress produced by the overlying sediment, the sediments experienced “sand boil” damage. With the repeated action of strong waves, the boundary of the pockmark continued to expand, forming a large and stable pockmark. This work is of great value for further understanding and mitigating marine geologic hazards, such as coastal erosion, silt deposition, and unstable sediment, in the subaqueous Yellow River Delta.  相似文献   

SVM多窗口纹理土地利用信息提取技术   总被引：2，自引：0，他引：2  

张伐伐  李卫忠  卢柳叶  张青峰  康乐 《遥感学报》2012,16(1):67-78

针对单一窗口纹理分类时地物破碎,分类精度不高等问题,提出了一种基于支持向量机多窗口纹理的遥感图像分类方法。该方法在对SPOT5遥感影像进行纹理特征提取的基础上,构建了结合多窗口纹理的SVM模型。以陕西省佛坪县长角坝乡为试验区,利用此模型对该区域的土地利用类型进行分类研究,并将分类结果与单一窗口纹理SVM分类和单元数据(光谱)SVM分类结果进行了比较分析。结果表明:多窗口纹理参与的土地利用分类总精度达到85.33%,比单一窗口纹理分类提高了13.11%,而与单元数据SVM分类相比提高了近24.10%,取得了较好的分类效果,有效地解决了单一窗口纹理分类时地物破碎、分类精度不高等问题。  相似文献   

基于“嫦娥一号”干涉成像光谱数据的月表虹湾地区FeO及TiO_2含量评估     

郑小坡  刘福江  章颖  朱蒙  乔乐 《测绘通报》2012,(7):10-13

基于"嫦娥一号"干涉成像光谱数据对月表虹湾地区元素分布进行分析。首先对该数据进行辐射畸变校正、反射率反演和几何校正等预处理;然后基于Apollo月球样品含量的实验室实测数据,建立一套基于"嫦娥一号"干涉成像光谱数据的FeO及TiO2含量反演模型;最后计算获取月表虹湾地区FeO及TiO2含量的分布图,并针对分布结果对虹湾地区的成因提出假设。  相似文献   

Comparison of statistical algorithms for detecting homogeneous river reaches along a longitudinal continuum   总被引：1，自引：0，他引：1  

Thierry Leviandier  A. AlberF. Le Ber  H. Piégay 《Geomorphology》2012,138(1):130-144

Seven methods designed to delineate homogeneous river segments, belonging to four families, namely — tests of homogeneity, contrast enhancing, spatially constrained classification, and hidden Markov models — are compared, firstly on their principles, then on a case study, and on theoretical templates. These templates contain patterns found in the case study but not considered in the standard assumptions of statistical methods, such as gradients and curvilinear structures. The influence of data resolution, noise and weak satisfaction of the assumptions underlying the methods is investigated. The control of the number of reaches obtained in order to achieve meaningful comparisons is discussed. No method is found that outperforms all the others on all trials. However, the methods with sequential algorithms (keeping at order n + 1 all breakpoints found at order n) fail more often than those running complete optimisation at any order. The Hubert-Kehagias method and Hidden Markov Models are the most successful at identifying subpatterns encapsulated within the templates. Ergodic Hidden Markov Models are, moreover, liable to exhibit transition areas.  相似文献   

Quantification and causes of the terrigeneous sediment budget at the scale of a continental margin: a new method applied to the Namibia–South Africa margin     

F. Guillocheau  D. Rouby  C. Robin  C. Helm  C. Le Carlier de Veslud  J. Braun 《Basin Research》2012,24(1):3-30

The terrigeneous sediment budget of passive margin basins records variations in continental relief triggered by either deformation or climate. Consequently, it becomes a major challenge to determine sediment accumulation histories in a large number of basins found in various geodynamic contexts. In this study, we developed a GIS‐based method to determine the sediment budget at the scale of a whole basin (from the upstream continental onlap to the most distal deepest marine deposits) and the associated uncertainties. The volume of sediments preserved in the basin for each time interval was estimated by interpolation between cross‐sections and then corrected from in situ production and porosity to obtain terrigeneous solid volumes. This approach was validated by applying it to Namibia–South African passive margin basins for which independent data are available. We determined by a statistical approach the variances associated with each parameter of the method: the geometrical extrapolation of the section (8–43%), the uncertainties on seismic velocities for the depth conversion (2–10%), on the absolute ages of stratigraphic horizons (0.2–12%), on the carbonate content (0.2–46%) and on remaining porosities estimation (3–5%). Our estimates of the accumulated volumes were validated by comparison with previous estimates at a lower temporal resolution in the same area. We discussed variations in accumulation rates observed in terms of relief variations triggered by climate and/or deformation. The high accumulation rates determined for the Lower Cretaceous, progressively decreasing to a minimum in the Mid‐Cretaceous, are consistent with the progressive relaxation of a rift‐related relief. The following increase to an Upper Cretaceous maximum is consistent with a major relief reorganization driven either by an uplift and/or a change to more humid climate conditions. The lower accumulation rate in the Cenozoic suggests a relief reorganization of lesser amplitude over that period.  相似文献   

New experimental determination of Li and B partition coefficients during upper mantle partial melting   总被引：1，自引：1，他引：0  

Luisa Ottolini  Didier Laporte  Nicola Raffone  Jean-Luc Devidal  Brieuc Le Fèvre 《Contributions to Mineralogy and Petrology》2009,157(3):313-325

Despite the growing interest for Li and B as geochemical tracers, especially for material transfer from subducting slabs to overlying peridotites, little is known about the behaviour of these two elements during partial melting of mantle sources. In particular, mineral/melt partition coefficients for B and to a lesser extent Li are still a matter of debate. In this work, we re-equilibrated a synthetic basalt doped with ~10 ppm B and ~6 ppm Li with an olivine powder from a spinel lherzolite xenolith at 1 GPa–1,330°C, and we analyzed Li and B in the run products by secondary ion mass spectrometry (SIMS). In our experiment, B behaved as a highly incompatible element with mineral/melt partition coefficients of the order of 10⁻² (D ^ol/melt = 0.008 (0.004–0.013); D ^opx/melt = 0.024 (0.015–0.033); D ^cpx/melt = 0.041 (0.021–0.061)), and Li as a moderately incompatible element (D ^ol/melt = 0.427 (0.418–0.436); D ^opx/melt = 0.211 (0.167–0.256); D ^cpx/melt = 0.246 (0.229–0.264)). Our partition coefficients for Li are in good agreement with previous determinations. In the case of B, our partition coefficients are equal within error to those reported by Brenan et al. (1998) for all the mineral phases analyzed, but are lower than other coefficients from literature for some of the phases (up to 5 times for cpx). Our measurements complement the data set of Ds for modelling partial melting of the upper mantle and basalt generation, and confirm that, in this context, B is more incompatible than previously anticipated.  相似文献   

Comparative behavior of Sr, Nd and Hf isotopic systems during fluid-related deformation at middle crust levels     

Béatrice Luais  Christian Le Carlier de Veslud  Yves Géraud 《Geochimica et cosmochimica acta》2009,73(10):2961-2977

We have carried out a comparative Rb-Sr, Sm-Nd and Lu-Hf isotopic study of a progressively deformed hercynian leucogranite from the French Massif Central, belonging to the La Marche ductile shear zone, in order to investigate the respective perturbation of these geochronometers with fluid induced deformation. The one-meter wide outcrop presents a strongly deformed and mylonitized zone at the center, and an asymmetric deformation pattern with a higher deformation gradient on the northern side of the zone. Ten samples have been carefully collected every 10 cm North and South away from the strongest deformed mylonitic zone. They have been analyzed for a complete major, trace element data set, oxygen isotopes, Rb-Sr, Sm-Nd and Lu-Hf isotopic systematics.We show that most of major and trace elements except SiO₂, alkaline elements (K₂O, Rb), and some metal transition elements (Cu), are progressively depleted with increasing deformation. This depletion includes REE + Y, but also HFS elements (Ti, Hf, Zr, Nb) which are commonly considered as immobile elements during upper level processes. Variations in elemental ratios with deformation, e.g. decrease in LREE/MREE- HREE, Nd/Hf, Th/Sr, increase in Rb/Sr, U/Th and constant Sr/Nd, lead to propose the following order of element mobility: U ? Th > Sr = Nd ? Hf + HREE. We conclude in agreement with previous tectonic and metallogenic studies that trace element patterns across the shear zone result from circulation of oxidizing F-rich hydrothermal fluids associated with deformation. A temperature of the fluid of 470-480 °C can be deduced from the δ¹⁸O equilibrium between quartz-muscovite pairs.Elemental fractionation induces perturbation of the Rb-Sr geochronometer. The well-defined ⁸⁷Rb/⁸⁶Sr-⁸⁷Sr/⁸⁶Sr correlation gives an apparent age of 294 ± 19 Ma, slightly younger than the 323 ± 4 Ma age of leucogranites in this area. This apparent age is interpreted as dating event of intense deformation and fluid circulation associated with mass transfer, and exhumation of the ductile crust shortly after the leucogranite emplacement. Sm-Nd and Lu-Hf isochron-type diagrams do not define any correlation, because of the low fractionated Sm/Nd and Lu/Hf ratios. Isotopic data demonstrate that only the Lu-Hf geochronometer system is not affected by fluid circulation and gives reliable T_DM age (1.29 ± 0.03 Ga) and ε_Hf signatures. By contrast, the Sm-Nd geochronometer system gives erroneous old T_DM ages of 2.84-4 Ga. There is no positive ε_Nd-ε_Hf correlation, because of decreasing ε_Nd values with deformation at constant ε_Hf values. However, ε_Nd-ε_Hf values remain in the broad ε_Nd-ε_Hf terrestrial array, which strongly indicates that fluid-induced fractionation can contribute to the width of the terrestrial array. The strong ε_Hf negative values of the leucogranite are similar to metasedimentary granulitic xenoliths from the French Massif Central and confirm the generation of the leucogranite by several episodes of reworking of the lower crust.  相似文献