中国北方沙漠化的若干问题

随着经济、社会的发展,沙漠化问题对自然环境和社会发展的影响愈来愈深刻,已得到国际社会的普遍重视,作为沙漠化问题极其严重的国家,我国在对沙漠化的认识及治理上,经过多年工作取得了一些成就.本文根据已有的经验和研究成果,就中国北方沙漠化的成因、发展过程、灾害评价及防治机理等方面做一简单探讨,以便为今后更好地开展沙漠化研究工作起一定的参考作用.     

西辽河平原环境地质问题与可持续发展

西辽河平原的环境地质问题主要表现为土地沙漠化、土壤盐渍化、区域地下水位下降及地下水污染等.从可持续发展的角度,提出了环境地质问题的整治需科学合理地对沙漠化土地进行治理;加强盐渍土地的开发利用;合理利用地下水资源及切断污染源.     

陕北榆林地区沙漠化土地类型及时空变化分析

根据1987年和1999年两个时相TM遥感影像解译成果，运用地理信息系统空间分析方法及数理统计方法，分析了陕北榆林地区1987-1999年间土地沙漠化程度和土地沙漠化时空分布变化特征。并有所好转，这主要得益于当地政府对土地沙漠化的积极治理和有效政策，生态环境脆弱，气候干燥，多风是本区土地沙漠化的主要自然驱动因素，不合理的人类活动则是沙漠化的诱因，人为的积极治理措施可以有效控制沙漠化的进程。     

神北矿区煤炭开发对土地沙漠化的影响评价

以神北矿区为例,以遥感解译和野外调查为手段,选用煤矿开采初期(1987年)、中期(1992年)及近期(1999年)三期卫星遥感图像,分析了研究区内土地沙漠化三期分布特征及变化趋势,对比了煤炭开采区与煤炭未采区土地沙漠化变化趋势的不同,探讨了矿区内沙漠化面积年自然增长率以及煤炭开采对沙漠化影响程度,认为煤炭开发初期环境破坏加剧,造成土地沙化面积增加,矿井正常生产时期,由于环境治理力度加大,土地沙漠化趋势出现逆转,为矿区土地沙漠化恢复治理提供了依据.     

石油天然气开发对鄂尔多斯盆地水土流失的影响与对策

水土流失与土地沙漠化是当今危及全球人类生存最严重的环境与社会问题.鄂尔多斯盆地是我国七大水土流失区,四大沙尘源区之一[1]是北方沙暴和黄河粗沙的来源地.同时,又是我国新兴能源化工基地,战略资源重要接替区.就石油天然气勘探开发造成水土流失问题,提出防治治理与对策.     

基于RS和GIS的沙漠-黄土过渡带土地沙漠化分布与变化研究--以陕北榆林地区为例

选择毛乌素沙漠和黄土高原过渡带——陕北榆林地区作为研究区域,在地理信息系统支持下,对两个不同时期的遥感影像进行了解译,总结了该区10余年来沙漠化土地景观特征,分析了土地沙漠化空间格局的动态变化规律。结果表明,研究区内沙漠化土地形势仍十分严峻,沙漠化土地面积占土地总面积的67．7％,其空间分布具有明显的不平衡性,表现为西北部和中部区域沙漠化程度较为严重,土地沙漠化空间分布的不平衡性与该区自然因素和土地利用方式的空间差异有关。经过几十年的积极治理与改造,该区土地沙漠化过程逐渐趋于稳定。通过探讨土地沙漠化的成因,认为自然环境与人类行为的相互作用及在时间尺度上的矛盾造成了该区持续的土地沙漠化过程。     

毛乌素沙地东南部边缘不同成因类型土地沙漠化的特征

以毛乌素沙地南部边缘沙漠黄土地带的土地沙漠化为例,将研究区的土地沙漠化分为沙地内部就地起沙型沙漠化、河流谷地就地起沙型沙漠化、风化残积就地起沙型沙漠化和风沙侵入型沙漠化4种类型.深入分析了不同成因类型的沙漠化土地的粒度特征及其所代表的地质意义.同时,以遥感解译和野外路线地质调查为手段,分析了不同类型土地沙漠化的区域分布.最后,探讨了不同地质成因类型土地沙漠化划分的理论意义、环境地质学意义和对土地沙漠化防治的重要意义,提出了不同类型土地沙漠化防治的对策和建议.     

浑善达克沙地近30年来土地沙漠化研究进展与问题

浑善达克沙地地处环境脆弱的东亚夏季风北缘,沙漠化进程备受关注。综述了关于浑善达克沙地近30年来沙漠化的研究进展,并从沙漠化过程、成因和发展趋势等方面讨论了研究中存在的问题。认为沙漠化过程研究难以深入,主要原因是在沙漠化速度和程度方面存在分歧,对沙漠化概念理解、研究材料及评价指标选择上存在差异。浑善达克沙地沙漠化是自然和人为因素共同作用的结果,沙漠化过程研究结果的分歧导致了成因的多解性,其中自然和人为因素的耦合与反馈过程、生态系统阈值、极端事件的影响是成因分析中需要解决的问题。全球变暖将导致浑善达克沙地沙漠化在21世纪进一步发展。     

《西藏综合自然与沙漠化地图集》评介

正在"世界防治荒漠化和干旱日"即将到来的时候,由杨萍、李森、魏兴琥、董玉祥等同志编制的《西藏西藏综合自然与沙漠化地图集》已经由科学出版社正式出版发行,应作者邀请,向广大读者推荐这本图集。《西藏西藏综合自然与沙漠化地图集》生动直观,深入浅出,不同层次的读者可以各取所需,各有所获。一般读者可从中获得有关西藏土地沙漠化的知识;专业人员可从中看出土地沙漠化研究与防治的脉络与轨迹;政府部门可以从中了解西藏土地沙漠化的现状、成因和防治优化模式,以利于制定治理和开发利用的决策依据。     

民勤盆地水资源开发引起的环境地质问题及改善措施

民勤盆地位于石羊河下游,目前民勤绿洲沙漠化过程加快,部分群众背井离乡,沦为"生态难民","罗布泊"现象已经局部显现。本文从民勤盆地水资源开发利用现状出发,分析存在问题,提出治理措施。     

Gallium and germanium in the metal and silicates of L- and LL-chondrites

Concentrations of Ga and Ge in the metal of 31 L-, 8 LL- and 2 H-chondrites, and in the silicates of 12 L- and LL-chondrites have been determined by spectrophotometric methods. The ranges of Ga contents in the metal of L- and LL-chondrites are 1.1–36.9 ppm and 1.0–34.1 ppm, respectively. The Ge content in the metal is positively correlated with Ga and ranges from 89.1–160 ppm, and 126–308 ppm for L- and LL-chondrites, respectively. The Ga content in the silicates of L-chondrites varies from 4.0 to 8.9 ppm.The Ga and Ge contents in the metal are clearly lower in unequilibrated than in equilibrated L- and LL-group chondrites. Unequilibrated (type 3 and 4) and equilibrated (type 5 and 6) chondrites are well separated in the plots of Ga vs Ge in the metal and the L- and LL-groups are also well resolved. The Ga and Ge in the metal are well correlated with petrologic grade. This suggests that Ga and Ge variations in the metal are related to thermal metamorphism. There is evidence of an enrichment of Ga in the metal due to shock-reheating.     

红藻石和蓝藻石概念及分类归属的综述和修订

在分析和总结前人对红藻石和蓝藻石研究成果基础上,结合岩石薄片显微镜下观察实例,发现在以往碳酸盐岩颗粒分类中没有红藻石和蓝藻石的合适位置。鉴于红藻石重要的成因意义和造礁作用,有必要明确红藻石的概念和归属。珊瑚藻本身极易钙化,经生物矿化作用最终保存下来的珊瑚藻屑一直放在生物碎屑中,而红藻石是由非固着的珊瑚藻构成的钙质独立结核,因此也可以被划分到生物碎屑中。蓝藻石作为蓝细菌钙化作用的产物,同时鉴于蓝藻石的广泛存在,把钙化蓝细菌形成的核形石命名为蓝藻石,这一重要概念从提出到现在一直被使用。然而蓝绿藻概念已变更为蓝细菌,蓝藻石的形成与藻类无关,显然将其称作蓝菌石更加确切。因此,应将红藻石和蓝藻石分别归为生物碎屑和核形石当中,并用新的术语蓝菌石替代蓝藻石。其意义在于使红藻石和蓝藻石的概念及归属更为规范,并为碳酸盐岩颗粒的深入研究提供有益线索。     

矿物——成矿与找矿

单颗粒矿物微量元素激光原位定量分析测试数据的大量积累和研究,使矿物成为矿床地球化学研究和矿床勘查的重要示踪剂。本文重点选择磁铁矿、磷灰石、石榴子石、榍石、锆石、绿泥石和绿帘石等的原位分析研究所获得的认识,介绍单颗粒矿物成分组合及变化在矿床类型划分、成矿年龄测定、氧逸度、成矿过程与物质来源、找矿与勘探等方面的应用。不同矿床类型中普遍存在的矿物,如磁铁矿、磷灰石等的微量元素含量及组合差异,提供了矿床类型识别的标志。单颗粒矿物,特别是矿石矿物和密切共生矿物如锡石、铌钽铁矿、赤铁矿、石榴子石、方解石等的原位定年,使成矿年龄的直接准确测定成为现实。矿物中变价元素,如Fe、V、Mn、Ce、Eu含量和/或比值的变化,指示了成矿过程氧逸度及其变化特点。从矿物核部向震荡环带与边部的微量元素含量或同位素组成的变化,示踪了成矿过程中流体来源或性质的变化。斑岩和矽卡岩矿床中与成矿作用关系密切的蚀变矿物,如绿泥石、绿帘石的形成温度、特征微量元素比值,如Ti/Sr、Ti/Co、V/Ni、Mg/Sr等,与距矿床中心距离呈线性函数关系,可定量预测距矿床中心的距离,使以绿泥石、绿帘石为代表的找矿指示矿物研究迅速发展。     

Prograde destruction and formation of monazite and allanite during contact and regional metamorphism of pelites: petrology and geochronology

The conditions at which monazite and allanite were produced and destroyed during prograde metamorphism of pelitic rocks were determined in a Buchan and a Barrovian regional terrain and in a contact aureole, all from northern New England, USA. Pelites from the chlorite zone of each area contain monazite that has an inclusion-free core surrounded by a highly irregular, inclusion-rich rim. Textures and ²⁰⁸Pb/²³²Th dates of these monazites in the Buchan terrain, obtained by ion microprobe, suggest that they are composite grains with detrital cores and very low-grade metamorphic overgrowths. At exactly the biotite isograd in the regional terrains, composite monazite disappears from most rocks and is replaced by euhedral metamorphic allanite. At precisely the andalusite or kyanite isograd in all three areas, allanite, in turn, disappears from most rocks and is replaced by subhedral, chemically unzoned monazite neoblasts. Allanite failed to develop at the biotite isograd in pelites with lower than normal Ca and/or Al contents, and composite monazite survived at higher grades in these rocks with modified texture, chemical composition, and Th-Pb age. Pelites with elevated Ca and/or Al contents retained allanite in the andalusite or kyanite zone. The best estimate of the time of peak metamorphism at the andalusite or kyanite isograd is the mean Th-Pb age of metamorphic monazite neoblasts that have not been affected by retrograde metamorphism: 364.3Dž.5 Ma in the Buchan terrain, 352.9NJ.9 Ma in the Barrovian terrain, and 403.4LJ.9 Ma in the contact aureole. Some metamorphic monazites from the Buchan terrain have ages partially to completely reset during an episode of retrograde metamorphism at 343.1Nj.1 Ma. Interpretation of Th-Pb ages of individual composite monazite grains is complicated by the occurrence of subgrain domains of detrital material intergrown with domains of material formed or recrystallized during prograde and retrograde metamorphism.     

卡林型-类卡林型金矿床勘查与研究回顾及展望

20世纪60年代美国西部发现超大型卡林金矿及1000余千米的成矿带,引起世界各国重视,70年代卡林金矿找矿理论传入中国,经历了找矿实践和初步研究的认识时期,中国陕西与贵州同时发现卡林型金矿线索;80年代中后期中国找矿有重大突破,勘查确定了包含40多例大、中型卡林型-类卡林型金矿床,分布于环扬子地台的“西北金三角”和“西南金三角”,典型矿床研究取得较大进展;90年代找矿勘探又上一新台阶,除继续发现一批矿床外,成功勘查出数例特大型该类矿床,对矿床成因、成矿机理、矿床类型与成矿动力学进行综合性研究;跨入新世纪仍有金矿床的不断发现,显示出中国西北、西南地区寻找卡林型-类卡林型金矿床的巨大潜力和良好前景。     

Partition of magnesium and iron between Olivine and spinel,and between pyroxene and spinel

Partition of Fe²⁺ and Mg between coexisting (Mg, Fe)₂SiO₄ spinel and (Mg, Fe)SiO₃ pyroxene was investigated at pressures 80 and 90 kbar and at temperatures 840 and 1050° C, using tetrahedral-anvil type of high pressure apparatus. Olivine-spinel solid solution equilibria in the system Mg₂SiO₄-Fe₂SiO₄ were discussed in the light of the partition reaction. Partition of Fe²⁺ and Mg in both olivine-spinel and pyroxene-spinel systems can not be regarded as that between ideal solid solutions. By applying the simple solution model for the partition of Fe²⁺ and Mg, sign of the heat of mixing was estimated to be positive for all olivine, spinel and pyroxene. Relative concentration of Fe²⁺ in spinel in the pyroxene-spinel system is likely to cause some change in the chemical composition of modified spinel () or spinel () in the transition zone of the mantle. A considerable change is also expected in the transition pressure of to ( + ) and ( + ) to .Presented at the symposium Recent Advances in the Studies of Rocks and Minerals at High Pressures and Temperatures held in Montreal, 1972. Jointly sponsored by the International Mineralogical Association and the Commission on Experimental Petrology.     

Cumulate and Cumulative Granites and Associated Rocks

Abstract. Processes that move crystals relative to melt, that is crystal fractionation, are of major importance in producing variations that are observed within cogenetic suites of granites. In low‐temperature granite suites, crystal fractionation initially involves the progressive separation of crystals residual from partial melting from that partial melt. Once separation of those crystals, or restite, has been completed, further fractionation may occur through the separation of crystals that had precipitated from the melt, the process known as fractional crystallization. High‐temperature granite magmas are largely or completely molten and elements such as Ca, Mg and Fe, and their associated minor elements, are in that case dissolved in the melt. Such magmas, particularly those that are more potassic and hence contain a higher fraction of low temperature melt, may evolve compositionally through fractional crystallization. Cumulate rocks result, comprising a framework of cumulus minerals with interstitial melt. In this process some of the melt is also displaced to form more felsic rocks. Such cumulate rocks may have distinctive chemical compositions, but that is often not the case. Distinctive features include SiC>2 contents near or below 50 % in rocks that are transitional in the field to more felsic granites, very high Cr and Ni, very low K, P, Ba, Rb and Zr, and anomalous abundances of the anorthite components Ca and Al. These rocks may also have positive Eu anomalies. Cumulate rocks do not necessarily have distinctive textures, at least as such features are understood at this time. Fractional crystallization can also involve the movement of precipitated crystals relative to melt. We refer to rocks as cumulative when formed from the fractions in which the abundance of crystals has increased. The production of cumulative granites typically occurs at more felsic melt compositions than is the case for cumulate granites, and this process may have its greatest significance in the fractional crystallization of the felsic haplogranites. Relative to felsic granites of broadly similar compositions lying on a liquid line of descent, cumulative granites contain more Ca, reflecting the addition from elsewhere of plagioclase crystals with solidus compositions. The abundances of Sr and Ba may be high to very high, and sometimes there are positive Eu anomalies. Cumulative I‐type granites may have low abundances of Y and the heavy REE, while the S‐type granites can be very distinctive with anomalously high abundances of Th and the heavy REE resulting from the concentrating of monazite. Generally, but not always, those who propose fractional crystallization as a mechanism for producing compositional variation within a suite of granites do not state whether the rocks in that particular case are thought to lie on a liquid line of descent or are cumulates/cumulative, although it is generally presumed that they were melts. Our experiences in eastern Australia have shown that the mechanism of fractional crystallization was quantitatively not as important during granite evolution as many workers would expect. However, there are some excellent examples of that process, most notably the Boggy Plain Supersuite. Overall in eastern Australia, varying degrees of separation of restite is a much more common mode of crystal fractionation, and that may also be seen to be the case for some other granite provinces if they are examined with that possibility in mind.     

毫米波测云雷达的特点及其研究现状与展望

云在大气的能量分配、辐射传输,尤其是水循环系统中有不可忽视的作用。云探测对云物理、人工影响天气、气候变化和航空航天等领域有重要意义,是大气科学研究的热点之一。尽管目前已经发展了很多种遥感设备对云进行观测(如激光雷达、卫星、云幂仪等),但这些设备无法得到高时空分辨率的云水平和垂直结构,而毫米波雷达是云三维精细结构探测的重要工具。由于毫米波雷达具有更接近小粒子尺度的短波长,因此更适合用来探测弱云,同时毫米波雷达也存在衰减严重的缺点。介绍了毫米波雷达的特点以及其探测小粒子的优势;对比分析了其与新一代多普勒天气雷达、晴空风廓线雷达的差异,得出：毫米波雷达具有高时空分辨率,能够更精确地反映云的垂直和水平结构,比普通天气雷达更适合监测云的变化。概括了国内外毫米波测云雷达的发展现状以及在云物理研究方面的情况,并展望了国内毫米波雷达未来研究的方向。     

Etch and intracutaneous landforms and their implications

Many landforms, major and minor, and including plains of various types, inselbergs, boulders, flared slopes, Rillen and rock basins, are initiated beneath the land surface, at the weathering front. They have evolved in various lithological settings. Most are formed by differential moisture attack, either controlled, or strongly influenced, by bedrock structure. Such forms of subsurface derivation may be differentiated into etch or subcutaneous features that were initiated at the base of the regolith, and intracutaneous forms that had their origin within the weathering zone. Although the agent or agents responsible for eroding the regolith and exposing the bedrock forms have varied in space and time, the similarity of etch and intracutaneous forms is such that their basic morphology persists regardless of the climatic regime in which they now occur. As the regolith is widely developed on the land surface, the forms initiated beneath and within it cannot be taken as climatic indicators. Indeed, like structural forms, these convergent forms represent a varied but significant azonal element in the physiographic landscape.     

煤及其燃烧产物飞灰和底灰中稀土元素地球化学特征及集散规律

采用ICP—MS法测试了褐煤、肥煤和无烟煤以及在不同燃烧条件下获取的飞灰、底灰等29个样品的稀土元素含量;分析了稀土元素地球化学特征。结果表明,不同煤种的稀土元素含量不同,相同煤种在不同燃烧条件下获取的飞灰、底灰中的稀土元素含量也不同;褐煤、肥煤、无烟煤及其燃煤产物飞灰、底灰的稀土元素分布模式呈左高右低的宽缓的“V”型曲线;Eu存在明显负异常。研究了燃煤过程中稀土元素的分布及集散规律,稀土元素在飞灰、底灰中的含量比原煤有明显提高,其增加幅度为几倍至20多倍不等,表明煤炭燃烧后稀土元素在飞灰、底灰中进一步聚集;飞灰和底灰中稀土元素含量、飞灰和底灰对煤的稀土元素含量比和富集因子以及飞灰对底灰的稀土元素含量比和富集因子等,不仅与原煤中稀土元素有直接关系,而且还受锅炉燃烧方式、燃烧温度(炉温)等人为因素的影响。