相山铀矿田地下水污染可能性的研究     

刘福林  乔万忠 《铀矿地质》1997,13(3):183-188,192

在相山铀矿床田东部地区，采用同位素技术和放射性水化学技术，对铀矿床地下水放射性污染问题从理论实践两方面方面进行研究，获得了当地雨水线的线性回归方程和在铀矿床的勘探开采过程中不会造成明显的地下水放射性污染的结论  相似文献   

构造层次与大陆壳动力学机制转变关系   总被引：6，自引：1，他引：6  

孙忠实  冯亚民 《吉林地质》1997,16(4):15-21

针对构造层次研究现状和存在的问题，把大陆壳划分为深部，中部，浅部和浅－表部四个构造层次。依据各自所处特定的构造位置、组成构造岩类型、形成的制约因素和地质时代等方面的区别，各构造层次分别是壳－幔间滑动，大陆张裂、隆－滑构造和变质核杂岩构造等多种大陆壳动力学机制转变过程中的产物。构造层次与大陆壳动力学机制转变关系的确定，更有利于古老板构造连续性、整体性的研究以及多期、多层次、多旋回大陆地壳演化模式的建  相似文献   

西昆仑山南侧甜水海湖岩芯铁变化的环境记录   总被引：11，自引：0，他引：11  

余素华  李世杰 《地球化学》1997,26(6):88-98

阐述了青藏高原西昆仑山南侧甜水海湖岩芯沉积物中氧化铁的丰度、频率分布和富集系数的变化规律。其丰度值范围FeO0．39％-3.95％，平均值为1．25％；Fe2O30．44％－8．09％，平均值为2．60％；Fe2O3／FeO0．21－3．60，平均比值1．12。说明该彻岩芯沉积物中铁平均丰度值较低，但其变化幅度较宽且清楚，在一定程度上反映了古气候环境具有较大幅度的波动。变异系数值表明，该湖岩芯沉积物中FeO的离散程度较Fe2O3大。大约距今23万年来氧化铁的沉积地球化学特征可划分出7个环境演化阶段，并基本上可与深海氧同位索阶段对比。揭示了甜水海湖演化与青藏高原强烈隆升引起的气候环境改变的密切关系。在距今23一15万年，沉积以河流相或冲积、洪积相为主，沉积环境以氧化环境为主导，气候以温干型波动；在距今15－7．4万年，沉积以湖相为主，沉积环境以还原环境为主导，气候以温湿型为主；在距今74万年以来，湖盆沉积环境多样化，沉积物以湖相和近源冲积、洪积相交替出现。气候出现冷湿、冷干、温湿和温干多种波动模式。这些资料分析初步认为甜水海古湖大约形成于距今15万年，即青藏高原第三成湖期，这也与青藏高原在距今15万年左右的再次构造隆升有关。  相似文献   

东川铜矿床同位素地球化学研究:I.地层年代与铅同位素化探应用   总被引：7，自引：0，他引：7  

常向阳  朱炳泉  孙大中  邱华宁  邹日 《地球化学》1997,(2)

采用Ｐｂ－Ｐｂ等时线法测定了昆阳群中亚群落雪组白云岩、黑山组碳质板岩和上亚群大营盘组碳质板岩样品，获得了（１７１６±５６）Ｍａ、（１６０７±１２８）Ｍａ和（１２５８±７０）Ｍａ的年龄，确定了昆阳群中亚群时代约为１６００—１８００Ｍａ，属晚古元古代，上亚群大营盘组约为１２００—１３００Ｍａ，属中元古代。还应用铅同位素化探技术系统研究了汤丹铜矿１号硐中段西１４穿脉岩石－矿石的铅同位素组成，结果表明铅同位素Ｖ１值与铜含量呈反相关系。这是运用系统剖面方法开展铅同位素化探的首次尝试。  相似文献   

华北克拉通-扬子克拉通与秦岭造山带古地幔组成及状态的对比   总被引：4，自引：1，他引：4  

路凤香  郑建平  王方正  孙平  刘永顺  赵磊 《地球科学》1997,6(3)

经研究，华北克拉通古地幔以含石榴石的二辉橄榄岩、方辉橄榄岩及纯橄榄岩为主．地幔交代作用强烈，岩石富集不相容元素，明显高于南非及西澳克拉通者．扬子克拉通古地幔主元素亏损程度差，交代作用较弱，岩石为石榴石／尖晶石二辉橄榄岩．秦岭造山带壳、幔交界带的岩石类型复杂，包括蛇纹石化尖晶石二辉橄榄岩（蛇纹岩）、石榴石辉石岩、榴闪岩、变辉长岩及变玄武岩等．蛇纹岩遭受强的塑性流变，剪切变形结构发育．与克拉通相比，地幔交代作用很弱．３个地幔域的古地温状态有差异，秦岭造山带最高，扬子克拉通居中，华北克拉通最低．上述结果表明，两克拉通的古地幔特征相差显著，暗示经历了不同的演化过程．交代作用可能发生在１７００Ｍａ以前和１１００～５００Ｍａ，后者强于前者．造山带地幔的剪切变形明显强于克拉通地幔  相似文献   

毛洋头铀（银,钼）矿床同位素地球化学研究   总被引：1，自引：0，他引：1  

陈迪云  章邦桐 《地球化学》1997,26(3):28-36

毛洋头铀矿床的（Ｈ、Ｏ）同位素特征表明：早期矿化热液主要为岩浆水，而晚期矿化热液则主要为大气降水。铅同位素组成反映该矿床中铅为不同来源的混合铅。Ｃ、Ｓ同位素组成变化范围小，且与火成岩的Ｃ、Ｓ同位素组成相当，说明矿床中的碳和硫主要淋取于火成围岩或源于地壳深部。  相似文献   

Attenuation differences in layer 2A in intermediate- and slow-spreading oceanic crust     

D. Goldberg  Y.F. Sun 《Earth and Planetary Science Letters》1997,150(3-4):221-231

In situ seismic attenuationQ⁻¹logs are derived from borehole velocity profiles and reveal sharp boundaries between morphologies of the extrusive volcanic layers in intermediate- and slow-spreading oceanic crust.Q⁻¹logs are calculated from the scattering attenuation associated with vertical velocity heterogeneity in Ocean Drilling Program Holes 504B and 896A and in Hole 395A, located in 5.9–7.3 Ma crust on the Pacific and Atlantic plates, respectively. Our results strongly tie crustal properties to seismic measurables and observed geological structures: we find that the scattering attenuation can be used to identify the extrusive volcanic sequence because it is closely related to changes in the degree of vertical heterogeneity. We interpret a distinct decrease in the Q⁻¹log at the transition below the extrusive volcanic layer to correspond with the seismic layer 2A/2B boundary. The boundary is located at 465 m depth below the sea floor in both Hole 395A and 504B, although this is likely to be a coincidence of the sediment thickness at these sites. Layer 2A is estimated to be approximately 150 m thick in Hole 504B and > 300 m thick in Hole 395A. Cyclic sequences of high-porosity pillows and low-porosity massive units in the uppermost 100 m of volcanics in Hole 395A result in large velocity heterogeneities which cause > 5 times more attenuation in this layer than in Hole 504B. In Hole 896A, by contrast, fewer pillows, more massive flows, and a greater volume of carbonate veins decrease the velocity heterogeneity and attenuation significantly over only 1 km distance from Hole 504B. We conclude that the attenuation in the extrusive volcanics of the ocean crust is largely controlled by variation in local heterogeneity and morphology as well as by subsequent hydrothermal alteration. The observed differences inQ⁻¹profiles and layer 2A thickness at these sites may be attributed to variations in the volume and duration of volcanic activity at mid-ocean spreading centers for these Pacific and Atlantic ridge segments.  相似文献   

Geochronology, geochemistry and tectonic implications of Xiongshan diabasic dike swarm, northern Fujian     

Shengli Ren  Jiliang Li  Xinhua Zhou  Min Sun 《中国科学D辑(英文版)》1997,40(4):411-417

Sm/Nd isotopic age determination showed that Xiongshan dike swarm was at 585.7 Ma ± 30 Ma. The trace element geochemistry and Sr/Nd/Pb isotope gemhemistry studies indicate that the dike swarm was products of back-arc basin spreading ridge and the magma originated from the depleted mantle region which was metasomatized by LILE-rich liquids/melts derived from subduction slab. Project supported by the National Natural Science Foundation of China.  相似文献   

Barotropic local instability and severe storm process     

Dasheng Yang  Lan Sun 《中国科学D辑(英文版)》1997,40(3):259-268

By means of barotropic model, the characteristic and initial value problems are investigated to reveal the local two-dimensional barotropic instability of the nonuniform current to the dynamic mechanism of the formation of the Yangtze-Huaihe River severe storm in July 1991. Analytical theory and numerical experiment show that (i) the unstable developing modes are chiefly the two periods of about 44 d and 10 d, which are fundamentally consistent with that of the precipitation change of the Yangtze-Huaihe River. (ii) The growth rate of the local perturbation is dominated by the meridional wave numbern = 1–5 and zonal wave numberk = 1–12, i.e. the severe storm over the Yangtze-Huaihe River results from the interaction of the systems at different latitudes and waves of different scales, (iii) The perturbation over the Yangtze-Huaihe River possesses the property of local intensification, which slowly migrates westward over the lower and middle reaches of the Yangtze-Huaihe River. (iv) The growth rate of the instability, especially the propagation velocity of the perturbation, is sensitive to the external parameters ū and α. Project supported by the National Natural Science Foundation of China.  相似文献   

Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau   总被引：5，自引：0，他引：5  

Donghuai Sun  Dongsheng Liu  Mingyang Chen  Zhisheng An  Shaw John 《中国科学D辑(英文版)》1997,40(4):337-343

Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau, solar radiation, global ice volume, etc. Project supported by the National Natural Science Foundation of China and the Foundation of Xi’an Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences.  相似文献