海南石碌铁矿床构造变形特征及其与铁多金属成矿富集的关系

海南石碌铁矿曾被誉为“亚洲最大的富铁矿”,其形成、定位与褶皱变形及伴随的剪切、塑性流动等构造密切相关。石碌矿区构造变形大致分为早期(D1)复式向斜的形成时期、晚期(D2)褶皱叠加和剪切变形时期。后者又进一步分为韧-脆性变形(D2a),脆-韧性变形、层间滑脱断层形成(D2b)和脆性变形、矿体破坏(D2c)3个阶段。石碌铁矿床受NW—SE向复式向斜及其与NE—NNE向褶皱叠加所形成的横跨或斜跨褶皱的严格控制;褶皱过程所伴随的剪切变形和高温塑性流动是富铁矿形成的重要机制。复式向斜轴部,尤其是2期向斜褶皱轴的叠加部位往往可发现厚大的富铁矿体。     

川西坳陷南部须家河组—蓬莱镇组短期基准面旋回层序分析

本文运用短期基准面旋回界面的识别标志,将川西坳陷南部须家河组—蓬莱镇组短期基准面旋回层序划分为向上“变深”非对称型(A型)和向上变深复变浅的对称型(C型)两种基本结构类型;再根据可容纳空间大小和上下两个半旋回的厚度,进一步划分为5个亚类型:低可容纳空间向上“变深”非对称型(A₁型),高可容纳空间向上“变深”非对称型(A₂型),以上升半旋回为主的不完全对称型(C₁型),近完全—完全对称型(C₂型),以下降半旋回为主的不完全对称型(C₃型)。     

藏北羌塘南部地区基性岩墙与玄武岩的岩浆同源性

青藏高原羌塘南部地区沿龙木错－双湖缝合带南侧成群分布着近东西向的基性岩墙,形成时代为晚石炭世—早二叠世,其围岩是以晚石炭世—早二叠世裂谷型沉积为主并夹有基性火山岩的浅变质岩系。基性火山岩夹层的数量和厚度有由北向南由多变少的趋势。基性岩墙的岩石类型主要为辉绿岩,火山岩以玄武岩为主,玄武安山岩次之。基性岩墙与基性火山岩在空间上密切共生,形成于大致相同的地质时期内。二者均经历了低绿片岩相变质作用,且化学成分相近,稀土元素、微量元素组成均与板内玄武岩具有相似的特点。初步判定羌塘南部地区基性岩墙群与基性火山岩来自同一岩浆源,为晚石炭世—早二叠世冈瓦纳大陆北缘裂解的产物。     

藏南特提斯喜马拉雅带中段二叠纪-白垩纪的火山活动(Ⅰ):分布特点及其意义

在野外实地考察和追索的基础上,详细厘定了特提斯喜马拉雅带中段晚古生代以来火山岩的分布特点和迁移规律。结果表明,在特提斯喜马拉雅带中段晚古生代以来的地层系统中,从二叠纪→三叠纪→侏罗纪→白垩纪,共有11个层位含规模不等的火山岩,它们以透镜体、薄夹层或以块状玄武岩、玄武质安山岩等形式产出于不同地层系统中;从二叠纪→早中三叠世→晚三叠世→侏罗纪和白垩纪,具有由西向东、从南→北→南→北的迁移规律。这些火山活动的发现和厘定,对填补特提斯喜马拉雅带火山岩研究的空白,了解陆下岩石圈地幔和软流圈地幔之间的相互作用和新特提斯洋盆的形成演化都具有一定的指示意义。     

鄂尔多斯盆地南部环形区成因与秦祁海槽间构造关系

近年来,鄂尔多斯盆地南部环形影像特征逐渐引起人们的关注。这个独立于鄂尔多斯盆地的环形整体特殊形状的成因各有说法。在野外地质考察的基础上,通过分析对比和探究各种相关资料,发现：鄂尔多斯盆地南部环形区和秦祁海槽在各大构造运动中都有密切联系,二者处于同一应力场;鄂尔多斯盆地南部环形区的主要成因为其与秦祁海槽等周围块体之间的相互作用,包括挤压、碰撞、旋转和磨蚀;鄂尔多斯盆地南部环形区受到古生代到新生代多次构造运动的影响,其中燕山运动和喜马拉雅运动对其抬升及形状的形成起主要作用。     

南黄海中部沉积物微量元素的环境记录研究

通过对南黄海中部E2站位沉积柱样部分微量元素的特征研究,讨论了近200a来与南黄海中部沉积物相关的主要环境气候演变.铅和金、铂族元素显示人类现代工农业活动对环境的影响在南黄海中部沉积物有明显记录;过渡金属元素和不活泼元素的记录显示小冰期(泛指1550～1850年)的结束,气温的升高对南黄海中部沉积区的氧化-还原条件和黄河流域的风化程度产生了影响;黄河的改道对南黄海中部沉积物陆源碎屑的输入产生影响.     

CRETACEOUS AND TERTIARY BOUNDARY IN THE TINGRI REGION OF SOUTHERN TIBET

CRETACEOUS AND TERTIARY BOUNDARY IN THE TINGRI REGION OF SOUTHERN TIBETtheNNSFProject(49872 0 0 3)andtheNationalProject (G19980 40 80 0 )ofChina     

P–T conditions for the Arendal granulites, southern Norway: implications for the roles of P, T and CO2 in deep crustal LILE-depletion

Abstract The orthopyroxene-clinopyroxene, garnet-orthopyroxene and garnet-clinopyroxene geothermometers, and the garnet-orthopyroxene-plagioclase, garnet-clinopyroxene-plagioclase and anorthite-ferrosilite-grossular-almandine-quartz geobarometers are applied to metabasites and the garnetplagioclase-sillimanite-quartz geobarometer is applied to a metapelite from the Proterozoic Arendal granulite terrain, Bamble sector, Norway. P–T conditions of metamorphism were 7.3 ± 0.5 kbar and 800 ± 60°C.
This terrain shows a regional gradation from the amphibolite facies, into normal LILE content granulite facies rocks and finally strongly LILE deficient granulite facies gneisses. Neither P nor T vary significantly across the entire transition zone. The change in 'grade'parallels the increasing dominance of CO₂ over H₂O in the fluid phase.
LILE-depletion is not a pre-condition of granulite facies metamorphism: granulites may have either 'depleted'or 'normal'chemistries. The results presented herein show that LILE-deficiency in granulite facies orthogneisses is not necessarily related to variations in either P or T . The important mechanisms in the Arendal terrain were (a) direct synmetamorphic crystallization from magma, with primary LILE-poor mineralogies imposed by the prevailing fluid regime, and (b) metamorphic depletion, involving scavenging of LILEs during flushing by mantle-derived CO₂-rich fluids. The latter process is constrained by U–Pb and Rb–Sr isotopic work to have occurred no later than 50 Ma after intrusion of the acid-intermediate gneisses, and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin.     

Geographical Information Systems and Geostatistics for Modelling Radioactively Contaminated Land Areas

The Chernobyl plume contaminated vast lands of Europe with radiocaesium (¹37Cs) in 1986 because of the deposition of radionuclides on the ground by wet and dry deposition processes. Nevertheless, in a nuclear emergency, contamination data may be very sparse and there is need to make rapid and scientifically supported decisions. Here we analyze the rainfall field, an important precursor of the wet deposition, during the passage of the plume. Thus, estimating rainfall spatial variability can help to identify possible contaminated areas and associated risks when rainfall exceeded a given threshold. In this paper, we show that the conditional probabilities of exceeding threshold rainfall values could be spatially assessed using the mutual benefits of linking geostatistical and geographical information system (GIS) to quantify the evaluation of the risk involved in decision making. In particular, the non-parametric geostatistic technique, termed Indicator Kriging (IK), enables one to efficiently estimate the probability that the true value exceeds the threshold values by means of the indicator coding transform. Afterward, GIS has been used to find the areas probably affected by wash-out (probability >0.5 that rainfall is above a certain threshold). The experimental study has been focused on a test site in Beneventan agroecosystem (Southern Italy) to model the spatial uncertainty over a continuous area from sparse rainfall data. This enabled to generate probability maps delineating area potentially affected by to contamination to be monitored after wet deposition of Chernobyl releases.     

The magnetic properties of Quaternary and Tertiary sediments in the southern North Sea

Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex.