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Electron microscopy study of the sakhaite from endogenous borate deposit in Hunan, china

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Science china earth sciences 2004年第3期47卷 232-238页

作者： LIU Xiangwen1,2, YANG Guangming2, ZOU Huamin3. QU Jing1 & ZHAO Wenxia4 1. Graduate School, china university of Geosciences,{3.074, china 2. Test Center, china university of Geosciences,{3.074, china 3. Physics and Technology College, wuhan university,{3.072, china 4. Test Center, Zhongshan university, Guangzhou 510275, china china Univ Geosci Grad Sch Wuhan 430074 Peoples R China china Univ Geosci Test Ctr Wuhan 430074 Peoples R China wuhan Univ Phys & Technol Coll Wuhan 430072 Peoples R China Zhongshan Univ Test Ctr Guangzhou 510275 Peoples R China

Sakhaite specimens from an endogenous borate deposit in Hunan Province, china have been studied in detail by means of transmission electron microscopy (TEM). The selected area electron diffraction (SAED) patterns obtained with different crystal zone axes show that the crystal system is cubic, with a = 1.463.nm. The convergent beam electron diffraction (CBED) patterns indicate that the point group and space group of sakhaite is m3. and Fd3., respec-tively. The space group of synthetic sakhaite determined by Chichagov (1974) is F413.. The possible reasons why the space groups of the natural and the synthetic sakhaites are different are discussed.

关键词： sakhaite, space group, convergent beam electron diffraction (CBED).

Simulation studies of high-latitude magnetospheric boundary dynamics

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Science china(Technological sciences) 2004年第4期47卷 421-435页

作者： PU Zuyin1, SHI Quanqi1,3. XIAO Chijie1, FU Suiyan1, ZHANG Hui1,2, ZONG Qiugang2 & LIU Zhenxing3.1. School of earth and Space sciences, Peking university, Beijing 100871, {3. 2. Center for Space Physics, Boston university, 725 Commonwealth Avenue, Boston, MA 02215, USA 3. Center for Space Science and Application Research, Chinese Academy of sciences, Beijing 100080, {3. 1. School of earth and Space sciences Peking University 100871 Beijing China 2. Center for Space Science and Application Research Chinese Academy of Sciences 100080 Beijing China 3. Center for Space Physics Boston University 725 Commonwealth Avenue 02215 Boston MA USA

Magnetic reconnection at the high-latitude magnetopause is studied using 2.5-dimensional Hall-MHD simulation. Concentric flow vortices and magnetic islands appear when both Hall effect and sheared flow are considered. Plasma mixing across the magnetopause occurs in the presence of the flow vortices. Reconnected structure generated in the vicinity of the subsolar point changes its geometry with increasing flow shear while moving to high latitudes. In the presence of flow shear, with the Hall-MHD reconnection a higher reconnection rate than with the traditional MHD is obtained. The out-of-plane components of flow and magnetic field produced by the Hall current are redistributed under the action of the flow shear, which makes the plasma transport across the boundaries more complicated. The simulation results provide some help in understanding the dynamic processes at the high latitude magnetopause.

关键词： magnetopause, entry layer, magnetic reconnection, vortex reconnection, Hall effect, flow shear.

Triassic Sequence Stratigraphy and Sea-Level Changes in Qomolongma Area, Southern Tibet, china: From Epicontinental Sea to Rift Basin

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Journal of earth Science 2000年第3期19卷 47-57页

作者： Shi Xiaoying faculty of earth sciences and Land Resources, {3. university of Geosciences, Beijing 100083. {3.

The Triassic in the Qomolongma area, southern Tibet, was deposited under an extensional tectonic setting from the Pangea supercontinent to continental rifting. From the Induan to Rhaetian, 12 depositional sequences (3.d order) have been recognized, which can be grouped into 5 sequence sets and in turn make up a well defined mesosequence (2nd order). Among the recognized marine transgressions, those at 250 Ma, 23. Ma, 23. Ma and 223.Ma respectively are particularly of significance and can be correlated widely across continents. The study shows that in Triassic the Qomolongma area experienced a sedimentary evolution from epicontinental sea to rift basin with the turning point at ca 228 Ma. During the early and middle epochs, the area was under epeiric sea, with carbonate ramp to mixed shoal environments predominant. In the late Carnian, the strong extension initiated listric faulting, thus resulting in rapid basement subsidence and the onset of a rift basin. From the late Norian to Rhaetian, it manifested as a rapid basin filling process in the area. Coupled with long term sea level fall, the excessive terrigenous influx led to the shift of environment from deep water prodelta to shore and finally to fluvial plain.

关键词： Triassic sequence stratigraphy sea level change cycles basin evolution southern Tibet.

Characteristics of vertical ozone distribution in the lower troposphere in the Yangtze River Delta at Lin'an in the spring of 2001

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Science china earth sciences 2005年第9期48卷 1519-1528页

作者： ZHENG Xiangdong1, CHAN Chuenyu2, CUI Hong2, QIN Yu3. CHAN Loyan2, ZHENG Yongguang3.& LEE Yusiang2 1. Chinese Academy of Meteorological sciences, Beijing 100081, china 2. Department of Civil and Structural Engineering, Hong Kong Polytechnic university, Hung Hom, Hong Kong, china 3. Department of Atmospheric sciences, Peking university, Beijing 100871, china 1. Chinese Academy of Meteorological sciences 100081 Beijing China 2. Department of Civil and Structural Engineering Hong Kong Polytechnic University Hung Hom Hong Kong China 3. Department of Atmospheric sciences Peking University 100871 Beijing China

We analyzed vertical distributions of ozone (O3. in the lower troposphere (< 5 km above ground) at Lin’an (119.75°E, 3..3.°N), Zhejiang Province using electrochemical concen- tration cell (ECC) ozonesonde data obta... 详细信息

We analyzed vertical distributions of ozone (O3. in the lower troposphere (3..3.°N), Zhejiang Province using electrochemical concen- tration cell (ECC) ozonesonde data obtained from February 21 to April 13. 2001. The results showed that the vertical O3.distributions are controlled by metrological conditions and the char- acteristics of O3.profiles are related to those of wet bulb potential temperature and wind field. O3.below 2 km showed that the strongest variability and enhanced O3.mixing ratios were associated with easterly winds that blow pollutants from the upwind source region of the Yangtze River Delta (YRD) region. Vertical O3.profiles below 5 km can be grouped into 5 categories: (1) peak mixing ratio type, (2) well-mixed type, (3. layered-structure type, (4) episodic pollution type and (5) alti- tudinal increasing type. Vertical distributions of O3.affected by regional transport of polluted air masses were investigated. Transport of polluted air from high latitudes of northern china, ac- companying subsiding motion of air and stagnant atmospheric conditions are important factors that lead to high mixing ratios of O3.at Lin’an. The stagnant atmospheric conditions associated with a continental high pressure system and pollution plume transported from the YRD and cen- tral-eastern china also lead to regional accumulation of O3.and high O3.mixing ratio at Lin’an. Long-range transport of O3.and pollutants from the Pearl River Delta in South china and in-situ O3.formation also resulted in elevated O3.mixing ratios at around 1 km altitudes and layered O3.distribution in the lower troposphere.

关键词： vertical ozone distribution, lower troposphere, Yangtze River Delta, Lin'an.

Relationships between bacterial-algal proliferating and mass extinction in the Late Devonian Frasnian-Famennian transition:Enlightening from carbon isotopes and molecular fossils

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Science china earth sciences 2005年第10期48卷 1656-1665页

作者： GONG Yiming1,2, XU Ran1, TANG Zhongdao1, SI Yuanlan3.& LI Baohua4 1. faculty of earth Science and State Key Laboratory of Geological Processes and Mineral Resources, china {3. of Geosciences, wuhan 4.0074, china 2. Institute of Resources & Environments, Henan Polytechnic {3., Jiaozuo 454.03. china 3. Department of Computer Science, South-Central {3. for Nationalities, wuhan 4.0074, china 4. Laboratory of Marine Geology, Tongji {3., Shanghai 200092, china faculty of earth Science and State Key Laboratory of Geological Processes and Mineral Resources china {3. of Geosciences wuhan china Institute of Resources & Environments Henan Polytechnic university Jiaozuo china Department of Computer Science South-Central university for Nationalities wuhan china Laboratory of Marine Geology Tongji university Shanghai china

Studies show positive shifts of inorganic and organic carbon isotope values (δ 13.carb and δ 13.kerogen) from +0.43.(‰ V-PDB) to +3.54 (‰ V-PDB) and from ?29.3. (‰ V-PDB) to ?24.14 (‰ V-PDB), respectively, B* (Ba* = Ba/ (Al2O3.X 15%)) values from 0.015 to 0.144, TOC values from 0.02% to 0.21%, V/Cr values from 0.3.to 2.0, Sr/Ba values from 3.20 to 49.50 in the Late Devonian Frasnian Upper rhenana zone to the top linguiformis zone of the Yangdi sec-tion deposited in carbonate slope facies of Guilin, Guangxi, South china, which indicates that biomass, productivity, organic carbon burial and salinity increase and that oxygenation near the boundary between sediments and waters decreases from the Late Devonian Frasnian Upper rhenana zone to the top linguiformis zone. Abundance of molecular fossils increases and normal alkanes, isoprenoid hydrocarbon, terpanes and steranes are dominated from the Late Devonian Frasnian to the bottom of Famennian, which shows that the predecessors of molecular fossils of the Frasnian-Famennian (F-F) transition are dominated by marine phytoplankton, zooplankton and benthic bacteria with no photosynthesis. Therefore, it is considered that the F-F transitional mass extinction with a multistage, selection and global synchronizing was caused by bacte-rial-algal proliferating, continuing deterioration of the shallow marine ecoenvironment of the mid-dle-lower latitudes. A simple cause and effect chain can be expressed as: appearance of seed plants and multi-storied forests → enhanced chemical and biochemical weathering and pe-dogenesis → wide development of soils → increasing riverine nutrient fluxes in epicontinental sea → from superoligotrophic to eutrophic in epicontinental sea → proliferating of marine phyto-plankton and zooplankton → frequent red tide and anoxia → mass extinction of shallow marine organisms in the middle-lower latitudes. It is worth notice that the factor drawdown of atmos-pheric Pco2, climatic cooling and sea level falling c

关键词： mass extinction, bacteria-algae, carbon isotopes, molecular fossils, biodiversity, Late Devonian, Guangxi, South china.

Geochemical constraints from hydrothermal fluid inclusions of altered deformation zone type Au(Ag)deposits in Yunkai area, South china

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Chinese Science Bulletin 1999年第S2期44卷 230-232页

作者： WANG Zuwei~1, ZHANG Haihua~2, YAO Dongliang~2 and ZHOU Yongzhang~3.1. Department of Geography, Tianjin Normal university, Tianjin 3.0071, china 2. Guangzhou Institute of Geochemistry, Chinese Academy of sciences, Guangzhou 510640, china 3. Department of earth sciences, Zhongshan university, Guangzhou 510275, china eeszhou@*** Department of Geography Tianjin Normal University Tianjin 300071 China Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou 510640 China Department of earth sciences Zhongshan University Guangzhou 510275 China

THE altered deformation zone type Au (Ag) deposits share an important part from the precious metallicore deposits in the Yunkai area, South china. Their formation is a history of poly-stage evolution. Pre- liminary source strata, Calidoniam metamorphism, Indosinian-Yanshanian ductile shear deformation andassociated hydrotheraml alteration all play certain roles in the history. This note discusses the geochemical conditional of the hydrothermal fluids during mineralization. Two representative ore deposits, the Pangxidong Ag(Au) deposit and Hetai Au deposits are selectedfor this study. They are hosted in altered ductile shear zones. Wall-rock hydrothermal alteration is bothspatially and temporally associated with the development of the ductile shear system. Silicification occurred throughout the whole alteration process. There are three groups of quartz: thepredeformational quartz, the early stage hydrothermal quartz, and the late stage hydrothermal quartz asso-

关键词： precious metallic deposit fluid inclusions mineralizing fluid South china.

New Findings in High-Pressure and Ultrahigh-Pressure Metamorphic Belt of Tongbaishan-Dabieshan Regions, Central china

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Journal of earth Science 2000年第3期19卷 34-39页

作者： You Zhendong Zhong Zengqiu Suo Shutian Zhang Zeming Wei Bize faculty of earth sciences, {3. university of Geosciences, wuhan 4.0074, {3.

The Tongbai Dabieshan high pressure (HP) and ultrahigh pressure (UHP) belt is sandwiched between the Yangtze and the Sinokorean cratons. It connects the Qinling orogenic belt in the west and links toward the east to the Sulu ultrahigh pressure (UHP) belt. At present there is a consensus that the UHP metamorphic rocks are the products of the oblique collision between the Yangtze and Sinokorean cratons during the Triassic. However, there is still a lot of controversies about the formation and exhumation of the HP and UHP metamorphic belts. The present research work on the composition and the structural geometry and kinetics of the HP and UHP metamorphic belt has shown the following new results: (1) The overall structural geometry pattern of Dabieshan is similar to the metamorphic core complex developed in the western North America; (2) The discoveries of HP and UHP metamorphic rocks in the north of Dabieshan indicate that the significance of Shuihou Wuhe fault should be re evaluated; (3. A series of micro structural evidence, including the newly found retrograde granulite facies assemblages in the garnet pyroxenites, substantiate the extensional processes following the collision event; (4) The discovery of partial melting phenomena in the UHP metamorphic belts illuminates the relationship between the HP and UHP metamorphic rocks and their associated granite gneiss. All of these new findings will greatly improve our understanding of the formation and exhumation of the high pressure and ultrahigh pressure metamorphic belts.

关键词： metamorphic core complex garnet pyroxenite retrogressive microstructure flecky gneiss partial melting.

Characteristics of Coal Accumulation of Transform-Extensional Basins in Linear Fracture Zones: A Case Study of the Meihekou Basin

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Acta Geologica Sinica(English Edition) 1999年第1期73卷 104-110页

作者： ZHUANG Xinguo Institute of Sedimentary Basin, faculty of earth Resources china {3. of Geosciences, wuhan, Hubei 4.0074 china Univ Geosci Fac Earth Resources Inst Sedimentary Basin Wuhan 430074 Hubei Peoples R China

This paper discusses the characteristics of coal accumulation of transfor-extensional basins in linear fracture zones on the basis of an analysis of tectonic evolution and sequence stratigraphy in the Meihekou basin. Coal accumulation of the basin occurred mainly in the accelerated rifting period of the transtentional regime and in the late period of tectonic transformation of the transpressional regime. In the former period, swamps developed in shallow lakes. The thickness of coal seams was controlled by the activity of fault block. Thick coal was formed in a downfaulted trough. In the latter period, swamps developed in a braided fan delta plain. The coal seams are thin and have poor lateral continuity. The thickness of coal seams was controlled by the migration of water channels in the braided plain.

关键词： coal accumulation sequence stratigraphy tectonic evolution Meihekou basin

Weathered Mantle Hosted Gold Deposit atShewushan, Hubei, Central china

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Journal of china university of Geosciences 2001年第1期12卷 60-67页

作者： Hong Hanlie Wang Qinyan The Center for Material Research and Testing, wuhan university of Technology, wuhan 4.0070 Bian Qiujuan {3. of earth sciences, china university of Geosciences, wuhan 4.0074 The Center for Material Research and Testing Wuhan University of Technology faculty of earth sciences China University of Geosciences

A supergene gold deposit is located at Shewushan, south Hubei, Central china. The Au mass fraction of the supergene deposits ranges from 1.0.10-6 to 19.5 10-6, with an average of about 2.2 10-6. Primary gold mineralization is closely associated with the well developed faults and fractures mainly on the crest of the reverse anticline with gold mass fraction exceeding1.0 X 10-6(average 0.6 X 10-6 ), the gold occurs as small Ag-bearing particles in association with illite and kaolinite, and partly incorporated within the lattice of pyrite. Fluid inclusion studies on the gold mineralization yield trapping temperatures and pressures from 110 to 290 and 4.0 105 to 4.0 105 pa, respectively. The salinities of mineralization fluids range from 2. 6 % to 8. 4 % w(NaCl, equivalent). Calculated (18O) values and measured (D) data of the hypogene fluids indicate a meteoric origin. These fluids underwent extreme 18 O enrichment by reacting with country carbonate rock. Supergene gold minerali- zation is confined largely to the lower portion at the weathered mantle; the gold occurs as small native gold particles accompanied by clay minerals, kaolinite and illite and Mn and Fe oxides. Geochemical investigation shows that Au, together with As and Sb, decreases progressively from the top of ore body to some 2 kilometers away and define a lateral dispersion halo. It is proposed that the gold is mobilized by surficial leaching and concentrated at the lower portion of the weathering profile, and thio-sulfate may play an active role in gold dissolution and re-precipitation.

关键词： gold deposit weathering inclusion temperature stable isotopes Shewushan.