海湾水环境影响的约瑟夫-新德那模式预测

对应用约瑟夫-新德那模式进行海湾水环境影响预测中存在的问题作了初步分析,海域水流、混合深度值的选取及特殊污染物的存在等是影响预测结果准确性的主要因素。潮流憩流状态时,污染物的迁移扩散主要取决于污染物的混合速度,污染物基本上以近似于半圆形呈π弧度的角度向水体混合扩散,预测结果与污染物实际迁移扩散状况大致吻合;潮流非憩流或大部分时间为非憩流状态时,海域水流对污染物的迁移扩散影响较大,混合角度与海流流速成反比,污染物向水体扩散的实际混合角度要小于π弧度,预测的结果与污染物实际迁移扩散状况存在较大差距。海域水流对污染物迁移距离产生很大影响,水流愈大,污染物迁移的距离就愈远。混合深度的取值也直接关系到预测结果的准确性,若按可能受影响范围海域的平均水深值作为混合深度取值,其预测结果要比水深取2m时的预测结果更接近真实状况。对已达标排放的废水进行影响预测时,结果与实际情况接近,而对高浓度石油类的废水含量的影响预测却与实际情况差异极大。     

Plume-Lithosphere Interaction and the Origin of Continental Rift-related Alkaline Volcanism--the Chyulu Hills Volcanic Province, Southern Kenya

Geochemical data are presented for primitive alkaline lavasfrom the Chyulu Hills Volcanic Province of southern Kenya, situatedsome 100 km east of the Kenya Rift Valley. In addition to theirprimitive compositions, a striking and ubiquitous feature isa strong but variable depletion in K relative to other highlyincompatible elements when normalized to primitive mantle values.Semi-quantitative models are developed that best explain thepetrogenesis of these lavas in terms of partial melting of asource that contained residual amphibole (but not phlogopite).The presence of amphibole implies a source in the subcontinentallithosphere rather than the asthenosphere. It is suggested thatthe amphibole is of metasomatic origin and was precipitatedin the lithospheric mantle by infiltrating fluids and/or meltsderived from rising mantle plume material. A raised geothermas a consequence of the continued ascent of the plume materialled to dehydration melting of the metasomatized mantle and generationof the Chyulu Hills lavas. It is proposed that the Chyulu HillsVolcanic Province represents an analogue for the earliest stagesof continental rift initiation, during which interaction betweena plume and initially refractory lithosphere may lead to thegeneration of lithospheric melts. KEY WORDS: rift-related alkaline volcanism; residual amphibole; subcontinental lithosphere     

New seismic stratigraphy and Late Tertiary history of the North Tanganyika Basin, East African Rift system, deduced from multichannel and high-resolution reflection seismic data and piston core evidence

Abstract We present here the initial results of a high-resolution (sparker) reflection seismic survey in Northern Lake Tanganyika, East African Rift system. We have combined these results with data from earlier multichannel reflection seismic and 5-kHz echosounding surveys. The combination of the three complementary seismic investigation methods has allowed us to propose a new scenario for the late Aliocene to Recent sedimentary evolution of the North Tanganyika Basin. Seismic sequences and regional tectonic information permit us to deduce the palaeotopography at the end of each stratigraphic sequence. The basin history comprises six phases interpreted to be responses to variations in regional tectonism and/or climate. Using the reflection seismic-radiocarbon method (RSRM), the minimum ages for the start of each phase (above each sequence boundary) are estimated to be: ?7.4 Ma, ? 1.1 Ma, ?393–363 ka, ?295–262 ka, ? 193–169 ka, ?40–35 ka. Corresponding lowstand lake elevations below present lake level for the last five phases are estimated to have been: ?650–700 m, ?350 m, ?350 m, ?250 m and ? 160 m, respectively. The latest phase from ?40–35 ka until the present can be subdivided into three subphases separated by two lowstand periods, dated at ?23 ka and ? 18 ka. From the late Miocene until the mid Pleistocene, large-scale patterns of sedimentation within the basin were primarily controlled by tectonism. In contrast, from the mid Pleistocene to the present, sedimentation in Lake Tanganyika seems to have responded dramatically to climatic changes as suggested by repeated patterns of lake level fluctuations. During this period, the basin infill history is characterized by the recurrent association of three types of deposits: ‘basin fill’ accumulations; lens-shaped ‘deep lacustrine fans’; and ‘sheet drape’ deposits. The successive low-lake-level fluctuations decreased in intensity with time as a consequence of rapid sedimentary filling under conditions of declining tectonic subsidence. The climate signal has thus been more pronounced in recent sedimentary phases as tectonic effects have waned.     

Dosage par Spectrométrie de Fluorescence X Du Nickel, du Zinc, du Rubidium, du Strontium, Du Zirconium Et du Niobium dans Trente Standards Geochimiques

Les roahes carbonatées et siliaatées appar-tiement à un domaine de compositions dans lequel la mesure d'un fond libre d'interférence ou d'une rate diffusée du tube peut permettre à la fois de aorriger les effets de pures absorptions et d'étalonner les fonds sous les raies analytiques. Cette propriété est illustrée sur I'exemple du dosage de 6 éléments en traces dans 30 standards géoahimiques.
La méthode proposée permet d'obtenir dans un domaine de concentration de 1 à 2000 ppm des ré-sultats dont la qualité est à rapprocher de la trés grarde rapidité de rmise en oeuvre.     

Garnet Lherzolites from the Kaapvaal Craton (South Africa): Trace Element Evidence for a Metasomatic History

Kimberlites from the Kaapvaal craton have sampled numerous mantlegarnet lherzolites in addition to garnet harzburgites. Traceelement characteristics of constituent clinopyroxenes allowtwo groups of garnet lherzolites to be distinguished. Traceelement compositions of all clinopyroxenes are characterizedby enrichment in light rare earth elements (LREE) and largeion lithophile elements and by a relative depletion in Ti, Nb,Ta, and to a lesser extent Zr and Hf. However, the LREE enrichmentand the depletion in Nb and Zr (Hf) are less in the Type 1 clinopyroxenesthan in the Type 2 clinopyroxenes. Our study suggests that thetwo melts responsible for the metasomatic imprints observedin the two garnet lherzolite groups are highly alkaline maficsilicate melts. Type 1 clinopyroxenes that have trace elementsimilarities to those of PIC (Phlogopite–Ilmenite–Clinopyroxene)rocks appear to have crystallized from, or been completely equilibratedwith, the same melt related to Group I kimberlite magma. TheType 2 clinopyroxenes have trace element similarities to thoseof MARID (Mica– Amphibole–Rutile–Ilmenite–Diopside)rocks and are therefore probably linked to melt related to GroupII kimberlite magma. KEY WORDS: garnet lherzolites; Kaapvaal craton; mantle xenoliths; mantle metasomatism; trace elements     

基于Web服务的分布式WebGIS设计与应用

分布式W ebGIS是目前GIS领域研究的重点,对于实现空间信息共享和GIS互操作具有重要的意义。传统上,用于构建分布式W ebGIS的分布式对象技术主要有对象管理集团(OMG)的COBRA、微软的COM/DCOM和Sun的J2EE/EJB。然而,由于这些分布式对象技术往往要求服务使用者和提供者之间必须进行紧密耦合,因此无法适应基于Internet计算要求的松散性。鉴于以上不足,这里提出了一种基于W eb服务构建分布式W ebGIS的新方法,并设计出了基于W eb服务的分布式W ebGIS系统结构框架。论文结合应用研究项目,示例了基于.NET平台实现分布式W ebGIS应用系统的过程。实践证明,基于W eb服务建立的分布式W ebGIS系统具有稳定性、可扩展性和部署灵活等优点。     

Upper Mantle Amphiboles and Micas and TiO2, K2O, and P2O5 Abundances and 100 Mg/(Mg+Fe2+ Ratios of Common Basalts and Andesites: Implications for Modal Mantle Metasomatism and Undepleted Mantle Compositions

Modal mantle metasomatism, involving the re-enrichment of depletedmantle by the introduction or production of new hydrous phases,apatite and other minerals, has been proposed as a criticalprecursor to alkaline volcanism. The merits of the modal metasomatismmodel are evaluated by examining whole-rock 100 Mg/(Mg+Fe²⁺)ratios and the abundances of TiO₂, K₂O and P₂O₅ in mafic volcanicsspanning the mafic alkaline-subalkaline compositional spectrum.Upper mantle amphiboles and micas are also discussed becausethey would be major donors of Ti, Fe, and K to melts duringanatexis of either modally metasomatized depleted mantle orundepleted mantle. Compared with tholeiitic and calc-alkaline basalts and andesites,basanites and alkali basalts and alkali andesites are neitherdistinctive nor unique by virtue of persistant or well-definedhigher abundances of TiO₂, K₂O, and P₂O₅ or lower 100 Mg/(Mg+Fe₂₊)ratios, features which might reflect precursor modal metasomatismof the alkaline sources. Some basanites and alkali basalts dohave higher abundances of TiO₂, K₂O, and P₂O₅ than some tholeiitesbut these abundances may be the result of lower degrees of meltingof similar undepleted mantle sources for both magma types. The most widespread mantle phases of inferred metasomatic originare interstitial amphiboles and micas in Group I spinel peridotitexenoliths. These have high 100 Mg/(Mg+Fe) ratios ({small tilde}90) and high Cr₂O₃ and low TiO₂ abundances, and the K₂O/Na₂Oratios of the amphiboles (chromian pargasites) are low, generallyless than 0?3. Interstitial amphiboles and micas developed asa result of near-isochemical hydration reactions which largelyinvolved Cr-spinel and Cr-diopside. Their formation was probablyinduced in many instances by fluids derived from crystallizingmafic magmas. Metasomatized Group I xenoliths with interstitialhydrous phases remain depleted in TiO₂, K₂O, and P₂O₅, and theyretain the high 100 Mg/(Mg+Fe) ratios characterizing depletedGroup I xenoliths. Together with the low K₂O/Na₂O ratios, thesefeatures preclude such peridotites as suitable sources of mostalkaline (and subalkaline) volcanics. It is suggested that modalmetasomatism plays an insignificant role in the genesis of mostmantle-derived mafic volcanics. Compared with the interstitial phases, kaersutitic amphibolesand titaniferous micas from vein, Group II inclusion and megacrystupper mantle parageneses have lower 100 Mg/(Mg+Fe) ratios andCr₂O₃ contents, and much higher TiO₂ abundances. K₂O/Na₂O ratiosof the Ti-amphiboles are also much more wide-ranging (0?3 togreater than 1?0). These Fe, Ti-rich amphiboles and micas areneither widespread nor pervasive phases in metasomatized mantle.They are directly related to alkaline magmatism in the uppermantle where they may be associated with incompatible elementenrichment of peridotite wallrocks in the immediate vicinityof frozen conduits of alkaline mafic magmas. The varying K₂O/Na₂O ratios of mafic volcanics (MORB constitutea major exception) indicate that the principal K-bearing phasesin undepleted mantle are kaersutitic amphibole and titaniferousmica, in varying proportions. The former is probably the majorsource of Ti and K for low K/Na volcanics (K₂O/Na₂O < 0?5)and also many medium K/Na types (0?5 < K₂O/Na₂O < 1?0),whereas mica is more likely to be the major K-bearing phasein the source regions of high K/Na extrusives (K₂O/Na₂ >1?0). Experimental data indicate that kaersutitic amphibole,mica and apatite probably coexist in undepleted spinel- andgarnet lherzolites at pressures up to 25 kb, with mica persistingto pressures as high as 50 kb. It is proposed that undepleted asthenospheric mantle is heterogeneouswith respect to its amphibole, mica, and apatite contents (andhence TiO₂, K₂O, and P₂O₅ abundances and K₂O/Na₂O ratios), andalso with respect to 100 Mg/(Mg+Fe²⁺ ) ratios which may be significantlyless than the ratios generally assigned to undepleted mantle,namely 88–90.     

Geochemistry, Mineralogy and Magmatic Evolution of the Basaltic and Trachytic Lavas from Gough Island, South Atlantic

The Gough Island lavas range from picrite basalt through tosodalite-bearing aegirine-augite trachyte. The basaltic lavasare predominantly nepheline normative alkali basalts, althougha group of hypersthene normative tholeiitic basalts does occur.The oldest lavas on the island, represented by the Lower Basaltseries, are approximately 1?0 m.y. old and the youngest arethe Upper Basalts with an age of {small tilde} 0?13 m.y. Relatively coherent variations are described by the basalticand trachytic lavas with respect to both bulk rock major andtrace element geochemistry and mineral chemistry, and quantitativepetrogenetic modelling suggests that most of the variation canbe attributed to crystal fractionation/accumulation processesacting on a number of geochemically distinct parental magmas.The Upper Basalts and Lower Basalts have (within the limitsof sampling) a relatively restricted composition compared tothe Middle Basalt series lavas, with the latter ranging frompicrite basalt through to trachyandesite. The picrite basaltsand coarsely pyroxene-olivine phyric basalts represent partialcumulates with varying proportions (up to 40 wt. per cent) ofaccumulated olivine and clinopyroxene. In contrast, the moderatelyphyric and aphyric/finely porphyritic lavas represent the productsof crystal fractionation with the most evolved lavas havingexperienced at least 40 per cent fractional crystallizationof clinopyroxene, olivine, plagioclase and minor Fe-Ti oxidesand apatite. The detailed abundance variations in these lavasindicate that a number of parental magma compositions have fractionatedto produce the overall variations in basalt geochemistry, andsome of the magmas have interacted through mixing processes. The trachytic lavas show a large range in trace element abundance,but have only a limited major element variation. Most of thisvariation can be attributed to extensive (up to 70 per cent)fractional crystallization of predominantly alkali feldsparwith minor clinopyroxene, olivine, biotite, titano-magnetiteand apatite. A number of genetically distinct trachytes canbe recognized which are probably not related to each other byany simple fractional crystallization process. The compositionof the least evolved trachytes can be adequately accounted forby relatively extensive (up to 60 per cent) fractionation ofthe more evolved Middle Basalt series lavas. The trace element and isotopic characteristics of primitiveGough Island basalts support the concept that the source region(s)giving rise to these lavas is extremely enriched in highly incompatibleelements relative to primordial or ‘undepleted’mantle of bulk earth composition. It is unlikely that the lavashave sampled undepleted mantle as might be suggested by thesimilarity of the Sr and Nd isotopic ratios to ‘bulk earth’values. Rather, a model is favoured whereby the lavas are derivedfrom previously enriched sub-oceanic mantle which was subsequentlyinvaded and further enriched, at some time prior to partialmelting, by melts or fluids highly enriched in incompatibleelements. The enrichment could have occurred as veining by smalldegree partial melts or by infiltration of metasomatic fluids.     

VLF GROUND SURVEYS,A POWERFUL TOOL FOR THE STUDY OF SHALLOW TWO-DIMENSIONAL STRUCTURES*

The suitability of VLF ground surveys in the investigation of shallow two-dimensional structures is analyzed. For such structures the polar formalism is derived, necessary in practice since the transmitters are generally not in the structural strike or profile. A simple vertical dike is considered to demonstrate the striking anisotropy which can be expected over such a structure, in particular the high apparent resistivity along the direction of a well-conducting dike and the low resistivity across it. The theory is then confronted with the practical example of an asymmetrical vertical dike resulting from a strike-slip fault. Modelling of the survey results is very successful and yields good confirmation of the polar behaviour. VLF ground surveys thus provide a quick and powerful tool for the study of geological accidents within about 100 m of the surface.