安徽铜陵新桥铜-硫-铁-金矿床中石英闪长岩和辉绿岩锆石SHRIMP年代学及其意义   总被引：48，自引：3，他引：48       下载免费PDF全文

王彦斌刘敦一  蒙义峰曾普胜杨竹森  田世洪 《中国地质》2004,31(2):169-173

对安徽铜陵新桥铜-硫-铁-金矿床区内的石英闪长岩和辉绿岩中的锆石分别进行了SHRIMP精确定年研究,石英闪长岩中锆石206Pb/238U年龄为(140.4±2.2)Ma,辉绿岩中锆石的年龄较复杂,其中发现了元古代锆石颗粒,其锆石207Pb/206Pb年龄为(2261±14)Ma,(1612±8)Ma,(919±12)Ma,(831±17)Ma。另外还有一组早古生代年龄的锆石,锆石206Pb/238U年龄为(443±13)Ma。以上这些新资料说明该区可能存在元古代基底的信息,且燕山期岩浆活动对本区成矿具有重要意义。  相似文献   

A Corrected and Generalized Successive Random Additions Algorithm for Simulating Fractional Levy Motions     

Hui-Hai Liu  Gudmundur S. Bodvarsson  Silong Lu  Fred J. Molz 《Mathematical Geology》2004,36(3):361-378

Simulation of subsurface heterogeneity is important for modeling subsurface flow and transport processes. Previous studies have indicated that subsurface property variations can often be characterized by fractional Brownian motion (fBm) or (truncated) fractional Levy motion (fLm). Because Levy-stable distributions have many novel and often unfamiliar properties, studies on generating fLm distributions are rare in the literature. In this study, we generalize a relatively simple and computationally efficient successive random additions (SRA) algorithm, originally developed for generating Gaussian fractals, to simulate fLm distributions. We also propose an additional important step in response to continued observations that the traditional SRA algorithm often generates fractal distributions having poor scaling and correlation properties. Finally, the generalized and modified SRA algorithm is validated through numerical tests.  相似文献   

Kinetic-simulating experiment combined with GC-IRMS analysis: application to identification and assessment of coal-derived methane from Zhongba Gas Field (Sichuan Basin, China)   总被引：2，自引：0，他引：2  

Yongqiang Xiong  Ansong Geng  Jingzhong Liu 《Chemical Geology》2004,213(4):325-338

The main purpose of this study is to model the δ¹³C values of methane derived from coal by combining kinetic-simulating experiment with the gas chromatography-isotope ratio mass spectrum (GC-IRMS) analysis. The stable carbon isotopic variation of methane in pyrolysates with heating temperature indicates that the assumptions for both a constant kinetic isotope effect (α) and a uniform initial isotopic composition (δ¹³C_o) are impractical for explaining the carbon isotopic fractionation during coalification. For purposes of simplification, two approaches are used in this paper to deal with the heterogeneity of terrestrial organic matter. One is that, assuming a uniform initial isotopic composition (i.e., δ¹³C_{i, o}=δ¹³C_o) for all methane-generating precursors in coal, the isotopic variation of methane is fitted by adjusting ΔE_{a, i} (E_{a¹³C, i}−E_{a¹²C, i}) for each hypothetical reaction. The other is that, assuming a constant kinetic isotope effect during the whole gas formation, that is all ΔE_{a, i} values are identical, the modeling of methane isotopic composition is achieved by changing the ¹³CH₄ generation potential of each reaction (f_{i, ¹³C}), namely, by adjusting the initial δ¹³C value (δ¹³C_{i, o}) for each methane-generating precursor. Results of the kinetic calculation shows that the two simulating methods can yield a similar result at a geological heating rate of 2 °C/My, which further demonstrates that those natural gases with methane δ¹³C value being approximately −36‰ are possibly sourced from the upper Triassic coal measure strata in the Northwestern Sichuan Basin.  相似文献   

Estimating coefficients of volume compressibility from compression of strata and piezometric changes in a multiaquifer system in west Taiwan     

Chih-Hsi Liu  Yii-Wen Pan  Wei-Cha Hung 《Engineering Geology》2004,75(1):33-47

This paper estimates the coefficients of volume compressibility from variation in compressible layer thickness and changes in piezometric heads by using detail ground surface surveys and a multilayer monitoring well at a selected site (Shigang) within the Choshui River alluvial fan in west Taiwan. The paper integrates various types of in situ monitoring tools, including leveling surveys, continuous global position system (GPS) stations, multilevel layer compression and groundwater pressure head-monitoring wells, to investigate the situation and progress of the subsidence problem in the region. The results from the cross-analyses of the measured data show that surface settlement caused by the compression of strata is between the depths of 60 and 210 m where the clayey stratum within 120-180 m was most pronounced and contributes up to 53% of the total compression. The results indicate that the clayey stratum is under normal consolidation. The results also reflect the fact that 20% of settlement contribution comes from the sandy stratum within 90-120 m; the elasto-plastic behavior of this sandy stratum is clear. The coefficients of volume compressibility of the clayey and sandy stratum analysed from the stratum's compression records; they were 6.38×10⁻⁸ and 5.71×10⁻⁹ m²/N, respectively. Ultimately, this parameter estimation would permit to control and predict land subsidence based on change in pressure head which are related to groundwater extraction.  相似文献   

On the long-term seismic hazard analysis in the Zhangjiakou–Penglai seismotectonic zone, China     

Zhengxiang Fu  Jie Liu  Guiping Liu 《Tectonophysics》2004,390(1-4):75-83

The Zhangjiakou–Penglai seismotectonic zone (ZPSZ) lies in the northern part of North China and extends along the Zhangjiakou–Beijing–Tianjin–Bohai Bay–Penglai–Yellow Sea. It is about 900 km long and some 250 km wide in a northwest direction. The great Sanhe-Pinggu (M_S=8.0) earthquake occurred on September 1679 and the Tangshan (M_S=7.8) earthquake on July 1976 caused serious economic and life losses. According to some differences in crust structure and regional tectonic stress field, the ZPSZ is divided into western and eastern segment by the 117°E line for study on long-term seismic hazard analysis. An analysis of Gutenberg–Richter's empirical relation of earthquake-frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a Poisson process, and these calculations indicate that the earthquake occurrence probability of M_S=6.0–6.9 is 0.77–0.83 in the eastern segment and the earthquake occurrence probability of M_S=7.0–7.9 is 0.78–0.80 in the western segment of the ZPSZ during a period from 2005 to 2015.  相似文献   

Quasi-simultaneous VLBI and RATAN-600 observations of active galactic nuclei     

A. B. Pushkarev  Yu. Yu. Kovalev  I. E. Molotov  M. B. Nechaeva  Yu. N. Gorshenkov  G. Tuccari  C. Stanghellini  X. Hong  J. Quick  S. Dougherty  X. Liu 《Astronomy Reports》2004,48(11):900-908

VLBI observations of several quasars and BL Lacertae objects were carried out at 1.66 GHz in November–December 1999 using six antennas (Medvezh'i Ozera, Svetloe, Pushchino, Noto, HartRAO, and Shanghai). Maps of six sources (0420+022, 0420-014, 1308+326, 1345+125, 1803+784, and DA 193) obtained with milliarcsecond resolution are presented and discussed, together with their broad-band (1–22 GHz) spectra obtained on the RATAN-600 radio telescope at epochs close to those of the VLBI observations. Comparison of the VLBI maps with maps of these sources obtained on standard VLBI networks and with the RATAN-600 quasisimultaneous total-flux measurements indicates the reliability of the results obtained on this Low Frequency VLBI Network and the good efficiency of this network.  相似文献   

Soil moisture potential and water content in the unsaturated zone within the arid Ejina Oasis in Northwest China   总被引：2，自引：0，他引：2  

X. Zhou  L. Wan  B. Fang  W. B. Cao  S. J. Wu  F. S. Hu  W. D. Feng 《Environmental Geology》2004,46(6-7):831-839

Three soil profiles were selected in the Ejina Oasis, northwest China, to determine water content profiles and evolution of soil moisture potentials in the unsaturated zone within the arid area. The total soil moisture potentials have been monitored for about 3 months in 2001 at different depths in the soil profiles. The occurrence and movement of water in the unsaturated zone was analyzed using the zero flux plane (ZFP) method. It is shown that convergent ZFPs and divergent ZFPs may occur at depths between 0.5 and 3.0 m, and that the depth of the ZFPs was controlled by the root zone of plants growing on the land surface. Profiles of the total soil moisture potentials were observed to be coincident with those of the water contents at the three experimental sites. The total soil moisture potential showed a slight increasing trend and the ZFPs tend to vanish from summer to winter as the water extraction by roots decreased. Evapotranspiration through vegetation has an important bearing on the water content and the total potential in the unsaturated zone.  相似文献   

Improving Sequential Simulation with a Structured Path Guided by Information Content   总被引：1，自引：0，他引：1  

Yuhong Liu  Andre Journel 《Mathematical Geology》2004,36(8):945-964

Multiple-point simulation is a newly developed geostatistical method that aims at combining the strengths of two mainstream geostatistical methods: object-based and pixel-based methods. It maintains the flexibility of pixel-based algorithms in data conditioning, while enhancing its capability of reproducing realistic geological shapes, which is traditionally reserved to object-based algorithms. However, the current snesim program for multiple-point simulation has difficulty in reproducing large-scale structures, which have a significant impact on the flow response. To address this problem, we propose to simulate along a structured path based on an information content measure. This structured path accounts for not only the information from the data, but also some prior structural information provided by geological knowledge. Various case studies show a better reproduction of large-scale structures. This concept of simulating along a structured path guided by information content can be applied to any sequential simulation algorithms, including traditional variogram-based two-point geostatistical algorithms.  相似文献   

Transformation of garnet epidote amphibolite to eclogite, western Dabie Mountains, China   总被引：8，自引：0，他引：8  

J. Liu  K. Ye 《Journal of Metamorphic Geology》2004,22(5):383-394

Omphacite and garnet coronas around amphibole occur in amphibolites in the Hong'an area, western Dabie Mountains, China. These amphibolites consist of an epidote–amphibolite facies assemblage of amphibole, garnet, albite, clinozoisite, paragonite, ilmenite and quartz, which is incompletely overprinted by an eclogite facies assemblage of garnet, omphacite and rutile. Coronas around amphibole can be divided into three types: an omphacite corona; a garnet–omphacite–rutile corona; and, a garnet–omphacite corona with less rutile. Chemographic analysis for local reaction domains in combination with petrographical observations show that reactions Amp + Ab + Pg = Omp +Czo + Qtz + H₂O, and Amp + Ab = Omp ± Czo + Qtz + H₂O may lead to the development of omphacite coronas. The garnet–omphacite–rutile corona was formed from the reaction Amp + Ab + Czo + Ilm ± Qtz = Omp + Grt + Rt + H₂O. In garnet–omphacite coronas, the garnet corona grew during an early stage of epidote amphibolite facies metamorphism, whereas omphacite probably formed by the reactions forming the omphacite corona during the eclogite facies stage. It is estimated that these reactions occurred at 0.8–1.4 GPa and 480–610 °C using the garnet–clinopyroxene thermometer and omphacite barometer in the presence of albite.  相似文献   

Accurate U-Pb Age and Trace Element Determinations of Zircon by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry   总被引：190，自引：0，他引：190  

Honglin Yuan  Shan Gao  Xiaoming Liu  Huiming Li  Detlef Günther  Fuyuan Wu 《Geostandards and Geoanalytical Research》2004,28(3):353-370

Various zircons of Proterozoic to Oligocene ages (1060-31 Ma) were analysed by laser ablation-inductively coupled plasma-mass spectrometry. Calibration was performed using Harvard reference zircon 91500 or Australian National University reference zircon TEMORA 1 as external calibrant. The results agree with those obtained by SIMS within 2s error. Twenty-four trace and rare earth elements (P, Ti, Cr, Y, Nb, fourteen REE, Hf, Ta, Pb, Th and U) were analysed on four fragments of zircon 91500. NIST SRM 610 was used as the reference material and ²⁹Si was used as internal calibrant. Based on determinations of four fragments, this zircon shows significant intra-and inter-fragment variations in the range from 10% to 85% on a scale of 120 μm, with the variation of REE concentrations up to 38.7%, although the chondrite-normalised REE distributions are very similar. In contrast, the determined age values for zircon 91500 agree with TIMS data and are homogeneous within 8.7 Ma (2 s ). A two-stage ablation strategy was developed for optimising U-Pb age determinations with satisfactory trace element and REE results. The first cycle of ablation was used to collect data for age determination only, which was followed by continuous ablation on the same spot to determine REE and trace element concentrations. Based on this procedure, it was possible to measure zircon ages as low as 30.37 0.39 Ma (MSWD = 1.4; 2 s ). Other examples for older zircons are also given.  相似文献