中国南方离子吸附型稀土矿床成矿类型及其母岩控矿因素探讨

传统认为中国南方的离子吸附型稀土矿床可划分为以“足洞式”为代表的重稀土型和以“河岭式”(或“花山式”)为代表的轻稀土型两种矿化类型。然而，近年来发现的许多矿床(如清溪、寨背和馒头山等)的赋矿风化壳中出现了轻稀土矿与重稀土矿并存现象，表现出特殊的“上轻下重”双层矿体结构。这指示了除重稀土型和轻稀土型之外，还存在着轻重稀土共生型的过渡类型。本研究通过对三种不同成矿类型的若干典型矿床系统对比，指出成矿类型的多样性与母岩性质密切相关，尤其是母岩的稀土元素地球化学和稀土载体矿物属性是制约成矿类型变化的关键因素。统计数据表明，从重稀土型→轻重稀土共生型→轻稀土型，成矿母岩的全岩稀土总量变化不大(ΣREY: 200×10-6~450×10-6→200×10-6~500×10-6→200×10-6~800×10-6)，但轻重稀土配分值出现较显著的区间性差异(ΣLREE/ΣHREY: 02~1→1~5→2~10)。与之同时，母岩中能为离子相稀土提供物源且具有重稀土配分属性的稀土副矿物类型和数量明显减少，这与全岩稀土元素地球化学特征中重稀土分量占比的降低趋势也互相匹配。该结果指示，以往认为重稀土配分母岩形成重稀土矿床、轻稀土配分母岩形成轻稀土矿床的传统观点需要外延，即一部分具有低度轻稀土配分属性(1＜ΣLREE/ΣHREY＜5)且含有丰富易风化稀土副矿物的母岩还可能形成轻重稀土共生型矿床，该认识可为今后离子吸附型稀土矿床勘查工作提供新的找矿依据。     

Channel overflows of the Pōhue Bay flow,Mauna Loa,Hawai'i: examples of the contrast between surface and interior lava

A number of overflows from a large lava channel and tube system on the southwest rift zone of Mauna Loa were studied. Initial overflows were very low viscosity gas-rich phoehoe evidenced by flow-unit aspect ratios and vesicle sizes and contents. Calculated volumetric flow-rates in the channel range between 80 and 890 m³/s, and those of the overflows between 35 and 110 m³/s. After traveling tens to hundreds of meters the tops of these sheet-like overflows were disrupted into a surface composed of clinker and phoehoe fragments. After these 'a' overflows came to rest, lava from the interiors was able to break out on to the surface as phoehoe. The surface structure of a lava flow records the interaction between the differential shear rate (usually correlated with the volumetric flow-rate) and viscosity-induced resistance to flow. However, the interior of a flow, being better insulated, may react differently or record a later set of emplacement conditions. Clefts of toothpaste lava occurring within fields of clinker on proximal-type 'a' flows also record different shear rates during different times of flow emplacement. The interplay between viscosity and shear rate determines the final morphological lava type, and although no specific portion of lava ever makes a transition from 'a' back to phoehoe, parts of a flow can appear to do so.     

Diagenesis of vascular plant organic matter components during burial in lake sediments

Diagenetic changes are difficult to distinguish from variations in sources of organic matter to sediments. Organic geochemical comparisons of samples of wood, bark, and needles from a white spruce (Picea glauca) living today and one buried for 10,000 years in lake sediments have been used to identify the effects of diagenesis on vascular plant matter. Important biogeochemical changes are evident in the aged spruce components, even though the cellular structures of the samples are well preserved. Concentrations of total fatty acids dramatically diminish; unsaturated and shorter chainlength components are preferentially lost from the molecular distributions. Concentrations of total alcohols are similar in the modern and 10,000-year-old wood and bark but markedly lowered in the aged needles. Hydrocarbon concentrations and distributions show little diagenetic change in the 10,000-year-old plant materials. Cellulose components in the wood decrease relative to lignin components, although both types of materials remain in high concentration in comparison to other organic components. Aromatization of abietic acid proceeds more rapidly in buried spruce wood than in bark; retene is the dominant polyaromatic hydrocarbon in the aged wood. In contrast to the variety of changes evident in molecular compositions, neither ¹³C values nor C/N ratios differ significantly in the bulk organic matter of modern and aged spruce components.     

Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex,Czech Republic: Implications for Variscan orogenesis

The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated _Nd values and initial ⁸⁷Sr/⁸⁶Sr ratios. Five of the eight eclogite samples have high _Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower _Nd values (+ 5.4 to –0.8) and widely variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7096). Such low _Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.     

Comparison between a radiative wind model for be stars and high angular resolution data from the GI2T interferometer

I present theoretical line profiles and intensity maps from an axi-symmetric radiative wind model from a rapidly rotating Be star. The introduction of a viscosity parameter in the latitude-dependent hydrodynamic code enables us to consider the effects of the viscous force in the azimuthal component of momentum equations (Araújo et al. 1994). Both velocity field and density law derived from the hydrodynamic equations have been used for solving the statistical equilibrium equations. By adopting the Sobolev approximation, we could easily obtain a good estimate of both electronic density and hydrogen level populations throughout the envelope. The numerical calculation was performed for parameters characterisic of the Be star Cassiopeiae.     

Using numerical modelling to evaluate tsunami hazard near the Kuril Island

A sequence of computer experiments is used to study questions concerning the tsunami problem as a quantitative estimate of tsunami danger, detailed geographical tsunami classification, determination of the parameters of critical tsunami waves, and the conditions of their development. We call a wave critical, if its impact on the coast is most hazardous.Using the Middle Kuril Island as an example, we present the results of a computer experiment which includes determining the wavefields on the shelf and estimating the effects connected with the deep-water Bussol and Diana Straits.Numerical simulation of tsunami waves of different sources permits the assessment of the extent of tsunami danger in different areas of the coastal zone of Simushir Island, depending on the location of the focus zone and their geometry.The major singularities of the wavefield arise in the zones of the deep-water straits. The distribution of the amplification factors is determined by both the global parameters of the wavefields and the local properties of individual harbours. The results obtained for a particular harbour in the northern part of Simushir Island, formed the basis for the quantitative estimate of tsunami danger for this area.     

西安南郊丰水年秋季土壤水分研究

 通过对西安南郊丰水年秋季土壤含水量的测定，研究了地下0~6 m之间土壤含水量的变化与土壤干层的恢复问题。研究结果表明，丰水年西安南郊人工林下2~3 m的土壤含水量在20％左右，远远高于正常年份的土壤含水量，而且大于表层和深层的土壤含水量。分析得出，土壤干层发育较弱的地区在降水丰富的年份可以得到一定程度的恢复；西安地区基本适合进行人工造林；通过人工措施，增强降水入渗和土壤含水量，对树木成活和长期的生长应当具有明显的作用。     

梁子湖水体P的季节变化与沉积物P释放初步研究

采用分级测定的方法对梁子湖沉积物中无机磷酸盐进行了分析,测定了梁子湖水体P的季节变化,并以室内模拟的方法研究梁子湖沉积物在pH值和温度控制下P的释放特征。研究表明,梁子湖水体P的含量呈明显的季节变化,冬季高,夏季低。沉积物无机磷(P i)中以钙磷(Ca—P)为主(55%~61%),铁磷(Fe—P)次之(28%~33%),铝磷(A l—P)最少(3%~5%)。在梁子湖的入水口和出水口,由于沉积环境影响到P的形态,P的释放明显较湖心高。在试验初期,由于扰动的影响,使得P的释放在第1天比第2天和第3天高,其后P的释放量则迅速增加。温度对P释放影响明显,其具体表现为,30℃时P释放达到峰值的时间比4℃时提前4 d,而且前者峰值比后者高出9倍。pH值对沉积物P释放同样有明显的影响,与正常状态下的湖水条件(pH值为8.5)相比,偏酸(pH值为5.5)和偏碱(pH值为11.5)条件下,P的释放量增加。     

论(N-ζ)公式的内涵及推求N的精度

介绍了大地水准面(N)与似大地水准面(ξ)之差公式的推导方法，揭示了其物理内涵，论述了其在精化大地水准面中的重要作用。当似大地水准面精度达到cm级时，大地水准面也将达到同样的精度。     

水环境容量的影响因素及分析研究

本文采用流量级频率分析和统计分析方法,对黄河下游流量及泥沙含量对水环境容量的影响进行了研究分析.分析结果:河流在平滩流量时不仅输沙能力最大[8],而且输运污染物能力也最大,黄河下游水环境容量萎缩是平滩流量降低的必然结果.