Analysis of Karst Tufa from Guangxi, China

The paper presents an analysis of characteristic karst tufa from Guangxi, China, which has not been studied before. A comparison with tufa from Dinaric Karst of Croatia is discussed in view of the C-type climate. The major mineral is calcite. Minor minerals are quartz and dolomite, depending on location. The content of calcium carbonate varies from 65% to 92%, and that of magnesium carbonate from 0.03% to 1.77%. Among other elements, the most abundant are Fe, from 0.02% to 1.50%, and Ti, from 0.15% to 0.27%. Many other trace elements (V, Cr, Mn, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Hg and Pb) are also present. Specific activity of radionuclides 40K, 232Th, 137Cs, 226Ra and 238U varies from sample to sample. Concentration of U in tufa is close to that reported for sedimentary carbonate. Low concentration of 137Cs indicates that this part of the world was not exposed to nuclear explosions. The concentration of 226Ra is the highest in Mashan County. The ratio 238U/226Ra (0.21-0.71) in tufa from Mashan Co     

Late Caledonian Ductile Thrusting Deformation in the Central East Kunlun Belt, Qinghai, China and Its Significance: Evidence from Geochronology

A high-angle ductile thrusting deformation with top-to-the-north movement penetratively developed in the Proterozoic-Early Paleozoic metamorphic rocks along the Central East Kunlun belt. The deformed rocks suffered epidote-amphibolite facies metamorphism. On the basis of our previous study, we present more data in this paper to further support that the ducdle thrust deformation occurred in the later Caledonian and more detailed information about the deformation. A zircon U-Pb concordant age of 446±2.2 Ma of a deformed granodiorite in the ductile thrust zone was obtained and can be interpreted as the lower limit of the deformation. A syntectonically crystallized and also strongly deformed hornblende Ar/ Ar dating gives an Ar/Ar plateau age of 426.5±3.8 Ma, which represents the deformation age. A strongly orientated muscovite gives an Ar/Ar plateau age of 408±1.6Ma, representing the cooling age after the peak temperature, constraining the upper limit of the ductile thrust deformation. This ductile thru     

An X-Ray Diffraction Study of an Inclusion in Diamond from the Luobusha Chromite Deposit in Tibet, China

Diamond was found in podiform chromitites of ophiolite and harzburgite from Luobusha, Tibet. There are silicate inclusions in some diamond grains from this area. In the present work, the CCD (charge coupled detector) technology of X-ray powder diffraction was applied to the study of the inclusion in diamond from the ophiolite of Tibet. Diffraction patterns are obtained even though the inclusion is only 20 μm in crystal size. The results show that the inclusion in diamond consists of talc and clinochrysotile. Therefore, it is clear that the diamond from the ophiolite of Luobusha, Tibet, is natural diamond rather than a synthetic one.     

SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane: Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton

The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane const     

An Experimental Calibration on the Sphalerite-Galena Sulfur Isotope Geothermometer

A new experimental calibration was undertaken in this study to get a more reliable sphalerite-galena sulfur isotope geothermometer. The experimental conditions selected in study were very similar to those of natural hydrothermal solution. The high-precision SF6 method was used in sulfur isotope analyses. The obtained calibration curve for sulfur isotope fractionation between sphalerite and galena can be expressed with the equation 10001nαSp-Gn= 0.74×106T-2+0.08.     

Cascaded Evolution of Mantle Plumes and Metallogenesis of Core- and Mantle-derived Elements

Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement.     

贵州峨眉山玄武岩喷发期的岩相古地理研究

贵州峨眉山玄武岩喷发，从动态的角度可以分为茅口期晚期和龙潭期（吴家坪期），龙潭期又可分为三个喷发旋回，对应于四个不同的岩相古地理环境，体现了东吴运动在造成贵州地区地壳抬升、下沉和接受最大海侵之后，又上升、拉张、沉陷带发生地裂（又称峨眉地裂）以及地幔物质喷溢等地质活动，具间歇性和多旋回性的特点。本文从研究海陆变迁入手，揭示峨眉山玄武岩喷发与沉积作用的内在联系，进而探讨其与金、锑等矿产的成因联系，提出该期各相区与成矿区的形成模式。通过对贵州峨眉山玄武岩不同喷发期岩相古地理的研究可以看到，茅口期晚期和龙潭期早期海域的沉积韵律和相带展布格局与玄武岩喷发的间歇性和多旋回性特征完全一致。玄武岩的喷发为成矿提供了物质基础，玄武岩喷发的间歇期又为沉积矿产的富集提供机遇。这种岩浆期后气液以富硅和二氧化碳为特征的玄武岩，本身富含铁、锰、铜、铅、锌、锑、砷、汞、金、银、氟、磷以及一些稀散和放射性元素等成矿组分。在喷发过程中，气液成分有一定变化，各阶段和离岩浆的远近距离不同以及喷发性质和环境差异，形成了火山气液矿床、火山沉积矿床和沉积矿床的不同成矿带。     

滨里海盆地的岩相古地理特征及其演化

滨里海盆地内充填了巨厚的古生代、中生代和新生代沉积物。在剖面上可分为三套地层组合，即盐下层系、含盐层系和盐上层系。盐下层系为下古生界-下二叠统，包括巨厚的碎屑岩和碳酸盐岩沉积，在泥盆纪-早二叠世，滨里海盆地周缘广大地区普遍发育碳酸盐岩，在许多古隆起上还发育生物礁体，说明这一时期盆地的滨、浅海地带具有浅、清、暖的沉积环境，盆外陆源碎屑供应较少。含盐层系为下二叠统上部孔谷阶。早二叠世中-后期由于持续构造抬升，盆地气候变得干旱，海水变浅，潮上带蒸发环境发育，以致这一时期广泛发育盐类沉积，形成含盐层系，主要由盐岩和硬石膏层构成，并形成许多大小不等的盐丘构造。盐上层系为上二叠统-第四系。晚二叠世-三叠纪盆地又经历了一次大的海侵，为浅海陆棚环境，局部为海陆过渡三角洲相。侏罗纪-白垩纪在总的浅海陆棚环境下，盆地不同地区也形成了湖泊和瀉湖环境。晚二叠世以后形成的盐上层系沉积，主要为碎屑岩，在局部地区有碳酸盐岩。     

发展中的中国煤田地质学

中国的煤和煤田地质特征具有鲜明的地域特色和独特的地质问题。煤炭是中国主要的一次能源。本文概要评述了近年来我国煤田地质学科的显著进展，认为未来的发展将取决于，引入新理论、新方法和广泛应用高新技术，强化与其他一些地学分支的交叉和渗透，今后将更突出研究煤的地球化学、支撑洁净煤技术和煤基材料利用技术的地质基础、煤层气，和高产、高效、安全开采煤炭生产的地质保障体系。     

鞍山市西郊区水位预测

根据鞍山市西郊区水文地质条件，建立了双层渗流二维平面系统的数学模型：应用Galerkin有限元法求解模型，从模型的计算结果可见该区观测点水位绝对误差较小，达到了规范要求的计算精度，同时，在此区内有一个大漏斗，在东南的铁西一带也有一个小漏斗。由于铁西一带是主要开采水源区，开采水量较大，所以漏斗逐渐向外扩大且水位有明显下降的趋势。这一变化规律与实际水位一致，说明计算水位基本上反映了实际水位空间变化的规律。因此根据模拟参数利用此模型对该地区进行了水位预测，共预测了四年的水位状况，并依据水位的预测结果对该区的水资源开发利用提出了合理建议。