Steady-state drift-dominated modulation models for galactic cosmic rays     

R. A. Burger  M. Hattingh 《Astrophysics and Space Science》1995,230(1-2):375-382

A number of steady-state drift-dominated modulation models has been developed by the Potchefstroom modulation group. In this review a selection of these models is discussed and briefly compared. A short overview of the relevant drift theory incorporated into the models is also given.  相似文献   

Tin mineralization in the Dajing tin–polymetallic deposit, Inner Mongolia, China     

Y.W. Wang  J.B. Wang  L.J. Wang  Y.Z. Chen 《Journal of Asian Earth Sciences》2006,28(4-6):320-331

Dajing is a large-scale tin–polymetallic deposit that hosts the largest tin mine in North China. It is a hydrothermal vein-type deposit containing Sn, Cu, Pb, Zn, Ag, and minor components Co and In. The deposit consists of more than 690 veins hosted within Upper Permian sedimentary rocks.Three mineralization stages and six ore types are recognized with cassiterite constituting the dominant tin mineral. The SnO₂ content of cassiterite increases in the sequence of mineralization stages shear-deformation→cassiterite–quartz→cassiterite–sulfide (or chalcopyrite–pyrite) stage, while the content of FeO, TiO₂, Nb₂O₅, Ta₂O₅, and In₂O₅ tends to decrease with increases in NiO and Ga₂O₅. It is considered that the negative correlation between SnO₂ and FeO, Nb₂O₅, Ta₂O₅, and In₂O₅ results from elemental substitutions. The early stage cassiterite is much richer in Ta and the later stage cassiterite is much poorer in Ti and Fe than is usual in hydrothermal vein type tin deposits. This is interpreted to indicate that the component of early stage cassiterite reflects a granitic magma source while the composition of later stage cassiterite has a more obvious strata source. The compositional variation of cassiterite corresponds to decreasing crystallization temperatures within each stage and between sequential stages with time. The characteristics of REE in cassiterite from two stages are in accord with that of subvolcanic rocks and the Linxi formation. It suggests that tin transported during the cassiterite–quartz stage may have originated from subvolcanic dikes (e.g., dacite porphyry), while in the cassiterite–sulfide stage, tin may have been derived from wallrock (e.g. siltstone) of the Upper Permian-age Linxi Formation.  相似文献   

油气和含油气包裹体及其在油气地质地球化学研究中的意义   总被引：36，自引：3，他引：36  

潘长春  周中毅 《沉积学报》1996,14(4):15-23

本文在综合前人研究的基础上，结合笔者的工作经验，提出了一个实用的油气和含油气包裹体分类方案，详细论述了各类油气和含油气包裹体的相态、组成和均一温度特征。在同一油气藏，均一温度越高，油相包裹体中的气态烃和挥发份的含量也越高。依据油相包裹体的均一温度的变化及其与同生水溶液包裹体的均一温度的关系可以研究油气藏在充填过程中油气组成，特别是气态烃和挥发份含量的演变。进而可以研究油气藏的油源--生油岩的类型和热演化程度。本文评述了依据油相包裹体和同生水溶液包裹体ＰＶＴ相图推断其捕获温度和压力范围的有效性和局限性。最后讨论了各类油气和含油气包裹体的成因机制及其在油气地质和地球化学研究中的意义。  相似文献   

中国南方晚二叠世乐平煤的成因及成煤物质     

陈能贵 《海相油气地质》1996,1(2):29-33,T001

乐平煤是分布于苏浙皖赣地区龙潭组中的特有煤种(俗称树皮煤),也是一种具良好生烃潜力的烃源岩。乐平煤中,壳质组和可溶有机质含量高,母质类型为高等植物和低等生物双重来源,元素组成具富氢、低氧、高含硫的特征,应属海相成因的泥炭坪沉积。成煤物质主要来源于真蕨、种子蕨和科达类等植物的树皮体。树皮体又可分为茎皮体和根皮体两种亚组分。依据煤的显微组分组成和树皮体富集程度的不同,乐平煤可分为原地型、过渡型和微异地型三种成因类型。乐平煤的研究对整个南方二叠纪煤成烃资源的评价具重要的地质意义。  相似文献   

The bimodal composition of carbonatites: Reality or misconception?     

J. Gittins  R.E. Harmer  D.S. Barker   《Lithos》2005,85(1-4):129-139

The concept of compositional bimodality in carbonatites has become widely accepted and has been used to impose restrictions on the composition of carbonatite magmas. We agree that mineralogical bimodality exists in carbonatites (most are either calcitic or dolomitic/ankeritic), but we argue that there is no compositional bimodality. The idea of bimodality is based on the interpretation of a variety of element distribution diagrams which were compiled only from chemical analyses in which SiO₂ is < 10 wt.%. All others were rejected. Even with such a restricted data set the case for compositional bimodality is extremely weak, but the inclusion of analyses with higher SiO₂ content destroys it completely. Yet these more siliceous compositions must be included, for many carbonatites contain substantial amounts of Fe–Mg silicates which are an essential part of the magmatic mineralogy of the rocks. They account for much of the Mg in carbonatites that are otherwise calcitic. Many such carbonatites contain well in excess of 10 wt.% SiO₂. Supporters of the bimodality concept argue that liquids having compositions between calcite and dolomite can precipitate neither calcite nor dolomite because the minimum on the solid solution loops in the system calcite–dolomite permits only a carbonate of intermediate composition. Therefore, it is argued, liquids of such intermediate composition cannot be parental to calcitic and dolomitic carbonatites; their parent magmas must be calcitic and dolomitic. This deduction is incorrect. It is well established that dolomitic liquids have calcite as the liquidus phase over substantial temperature intervals, and that this is followed by dolomite precipitation. Mixed calcite–dolomite carbonatites are explicable in this way. Therefore, dolomitic liquids can be parental to calcitic carbonatites. However, dolomitic carbonatites cannot crystallize from a calcitic liquid. We suggest that intermediate composition carbonatite magmas are probably common. Bimodality in carbonatites is solely mineralogical, not compositional.  相似文献   

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation          下载免费PDF全文

Tim J Dempster  Julie La Piazza  Andrew G Taylor  Nicolas Beaudoin  Peter Chung 《Journal of Metamorphic Geology》2017,35(9):1111-1130

Metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase. Relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low‐temperature amphibolite facies metamorphic reactions. Garnet is widely assumed to be a reactant in staurolite‐isograd reactions, and the evidence for this has been assessed in the Late Proterozoic Dalradian pelitic schists of the Scottish Highlands. The 3D imaging of garnet porphyroblasts in staurolite‐bearing schists reveals a good crystal shape and little evidence of marginal dissolution; however, there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction. Staurolite forms directly adjacent to the garnet, and its nucleation is strongly associated with deformation of the muscovite‐rich fabrics around the porphyroblasts. “Cloudy” fluid inclusion‐rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet. Such cloudy garnet typically has a Mg‐rich, Mn‐poor composition and is interpreted to have formed during a coupled dissolution–reprecipitation process, triggered by a local influx of fluid. All garnet in the muscovite‐bearing schists present in this area is potentially reactive, irrespective of the garnet composition, but very few of the schists contain staurolite. The staurolite‐producing reaction appears to be substantially overstepped during the relatively high‐pressure Barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions. Fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history. The remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning. Such zoning in metamorphic garnet created during coupled dissolution–reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re‐equilibration. Fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists. In addition, the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history. However, the partial re‐equilibration of the porphyroblasts during coupled dissolution–reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions.  相似文献   

A Parametric Approach for Dealing with Compositional Rounded Zeros   总被引：2，自引：0，他引：2  

Javier Palarea-Albaladejo  Josep A. Martín-Fernández  Juan Gómez-García 《Mathematical Geology》2007,39(7):625-645

In this work, a parametric approach for replacing data below the detection limit, also known as rounded zeros, in compositional data sets is proposed. Compositional rounded zeros correspond to small proportions of some whole that cannot be reliably detected by the analytical instruments under given operating conditions. This kind of zeros appear frequently in the data collection process in geosciences. They must be treated in an adequate way before some multivariate analysis can be applied. Our procedure results from a modification of the Expectation-Maximization (EM) algorithm and is based on the additive log-ratio transformation. Its coherence with the nature of compositional data and with basic operations in the simplex sample space is checked. Using real data sets, we find that this approach improves other parametric and non-parametric techniques for compositional rounded zeros.  相似文献   

强震成组活动与潮汐力调制触发   总被引：14，自引：4，他引：14  

张国民  李丽  黎凯武  马宏生 《中国地震》2001,17(2):110-120

本文应用构造场体成组震模型的研究结果，探讨了中国大陆Ms≥7．0地震的成组活动的引潮力的调制触发关系。研究表明：我国陆区7级以上强震明显受潮汐力的调制触发，且主要表现为对活跃期内（即成组发生的）7级强震的调制触发。平静期内的7级以上地震基本不受潮汐力触发，而活跃期内82．4％的7级强震发生在受潮汐力触发的月相期，比本底概率高出36．4％。因此，潮汐力的调制触发对于强震活跃期的判断和活跃期内强震的临震（时间）预测有实际意义。文章还分析了潮汐力触发与强震活动的区域动力学环境之间的关系，并用构造场体成组孕震模型讨论了潮汐力对强震活动触发作用的力学机制。  相似文献   

Group Strong Earthquakes and Triggering by Tidal Stress   总被引：4，自引：1，他引：4  

Zhang Guomin  Li Li  Li Kaiwu  Ma Hongsheng 《中国地震研究》2001,15(4):354-364

The results obtained using the group model of earthquakes generated in tectonic blocks are fur ther used in this paper to analyze the relationship between the Ms ≥ 7.0 events in Chinese ma inland and the modulation and triggering from the earth tides. The research shows that the Ms 7.0 events in Chinese mainland have been significantly triggered by the tidal stress, especially within the active period with group strong earthquakes. In the quiescence period of strong earthquakes, no Ms7.0 events were triggered, while within the active period, over 82.4% of strong earthquakes took place within a special moon phase, which is 36.4 % higher than the average. Therefore, the modulation and triggering of tidal stress can be used to distinguish the active periods and to forecast the time of the strong earthquakes within the active period. The relationship between the tidal triggering and the tectonic dynamic condition is investigated and the mechanism of the modulation is simulated with the group model of earthquakes generated in tectonic blocks.  相似文献   

分块DPCM与5/3整数小波变换结合的天文图像无损压缩     

朱贵富  邓辉  王锋  季凯帆 《天文研究与技术》2011,8(1)

针对海量的天文图像数据与有限的存储空间和带宽资源之间矛盾日益突出这一问题,提出一种无损压缩方法,首先将超大天文图像分块,再使用差分脉冲编码调制和5/3整数小波变换,最后使用霍夫曼算法编码。对该方法的原理和具体实现做了详细的分析与介绍,通过实验验证该方法比天文中常用的tar、PKZip、WinZip、WinRar软件在压缩比上分别提高了30%、29%、26%、2%,压缩速度远大于WinZip和WinRar;且该算法实现简单,适合硬件实现和利于并行处理。  相似文献