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Numerical simulations of the bi-level and branched structure of intracloud lightning flashes

science china {2. sciences 2006年第6期49卷 661-672页

作者： TAN Yongbo1, TAO Shanchang1, ZHU Baoyou1, MA Ming2.& LU Weitao2.1. School of earth and space {2., University of science and technology of china, hefei 2.002., china 2. Chinese Academy of Meteorological {2., Beijing 100081, china 1. School of earth and space {2. University of Science and Technology of China Hefei 230026 China 2. Chinese Academy of Meteorological sciences Beijing 100081 China

Intracloud (IC) lightning flashes have been simulated in fine resolution (12.5 m) by using a bidirectional stochastic lightning parameterization scheme within 2.dimensional domain. The simu-lated results show that the IC flashes have a bilevel channel structure and the altitudes of the hori-zontal channels are at the same heights of potential wells, which are supported by the previous VHF source observations and balloon soundings of electric field profile in the thundercloud. Further con-clusions are: (1) After an IC flash is initiated near the boundary between positve and nagetive charge zone, the negative (or positive) leader tends to propagate into the positive (or negative) charge zone. Both types of positive and negative IC flashes have been reproduced and their polarity depends on the up and down disposition of the positive and negative charge regions. (2. The extension range of leaders is correlative with the cloud charge distribution. The leader is possible to extend through the inverted charge region all over where it is extending, but keeps away from the isolated charge area of the same polarity. (3) The channel structures also depend on the electric potential distributions in the thundercloud. Before propagating into the central area of potential wells, the leader tends to extend along the direction with the maximum of potential gradient. Once extending away from the center of potential wells, the leader tends to extend along the direction with the slowest potential change. (4) The IC flash channels have the fractal feature with fractal dimension 1.45 before leaders pass through the central area of charge regions. The exponent decreases rapidly once leaders extend into the low-density charge regions. (5) The induced charges of opposite polarity are deposited in the leader channels within preexisting positive and negative charge regions during IC flash discharges. This causes a new and complicated charge distribution in the thundercloud, and the potential

关键词： IC, lightning parameterization, branched bilevel structure, fractal feature, propagation tendency.

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SHRIMP dating of the Bangong Lake SSZ-type ophiolite: Constraints on the closure time of ocean in the Bangong Lake-Nujiang River,northwestern Tibet

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Chinese science Bulletin 2007年第7期52卷 936-941页

作者： SHI RenDeng1,2.1 School of earth and space {2., University of science and technology of china, hefei 2.002., china 2.Institute of Geology, Chinese Academy of Geological {2., Beijing 100037, china (email: shird@***) School of earth and space {2. University of Science and Technology ofChina Hefei 230026 China

The Bangong Lake ophiolite is located in the westernmost part of the Bangong Lake-Nujiang River suture zone. It is a tectonic mélange consisting of numerous individual blocks of peridotite, pillowed and massive lavas and mafic dykes with SSZ-type ophiolitic geochemical affinity formed at the end of a Wilson circle. The SHRIMP U-Pb ages of the co-magmatic zircon domains from one gabbroic dyke (Sample 01Y-155) range from 162.5±8.6 Ma to 177.1±1.4 Ma with an average of 167.0±1.4 Ma (n = 12. MSWD = 1.2., suggesting that the subduction of the Bangong Lake Neo-Tethyan Ocean started before the Middle Jurassic. It is inferred that the tectonic transform from spreading to subduction of the Neo-Tethyan Ocean began before the Middle Jurassic in the Bangong Lake area.

关键词：西藏班公湖怒江缝合带古海洋闭合时期 SSZ型蛇绿岩 SHRIMP 测年

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Genesis of excess argon in phengite and significance of ^(40)Ar-^(39)Ar age spectra for omphacite:A case study on UHP eclogite of South Dabie Terrain,china

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Chinese science Bulletin 2000年第15期45卷 1345-1351页

作者： WANG Songshan, GE Ningjie, SANG Haiqing & QIU Ji1. Institute of Geology and Geophysics, Chinese Academy of sciences, Beijing 10002., china 2. {2. of earth and space science, University of science and technology of china, hefei 2.002., china Correspondence should be addressed to Wang Songshan Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China department of earth and {2. science University of Science and Technology of China Hefei China

The Ar-Ar dating of phengite and omphacite in ultrahigh-pressure (UHP) eclogite of Bixiling and Hengchong in the South Dabie Terrain shows that the content range of excess argon is as high as (0.4-1.3)×10 8 mol· g 1. The genesis of the excess argon is discussed. The Ar-Ar age spectra of omphacite could not support the opinion that the UHP metamorphism occurred in Caledon epoch and pre-Caledon epoch.

关键词： South Dabie Terrain ultrahigh-pressure metamorphics phengite omphacite excess argon.

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Electron surfing acceleration in a current sheet of flares

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science china(Physics,Mechanics & Astronomy) 2009年第11期52卷 1810-1812页

作者： WANG DeYu1 & LU QuanMing2.1 Purple Mountain Observatory, Nanjing 2.0008, china 2.School of earth and {2. sciences, University of science and technology of china, hefei 2.002., china Purple Mountain Observatory Nanjing 210008 China School of earth and space {2. University of Science and Technology of China Hefei 230026 China

A model of electron acceleration in a current sheet of flares is studied by the analytical approximation solution and the test particle simulation. The electron can be trapped in a potential of propagating electrostatic wave. The trapped electron moving with the phase velocity v p of wave may be effectively accelerated by ev p/c × B z force along the outflow direction in the current sheet, if a criterion condition K > 0 for electron surfing acceleration is satisfied. The electron will be accelerated continuously until the electron de-trap from the wave potential at the turning point S.

关键词： electron acceleration electrostatic wave current sheet

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Application of rock creep experiment in calculating the viscoelastic parameters of earth medium

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science china {2. sciences 2006年第5期49卷 492-498页

作者： SHI Xingjue1, WEN Dan1, BAO Xueyang1, LI Chengbo1 & HUANG Yun2.1. School of earth and space {2., University of science and technology of china, hefei 2.002., china 2. Seismological Bureau of Jiangsu Province, Nanjing 2.0014, china 1. School of earth and space {2. University of Science and Technology of China Hefei 230026 China 2. Seismological Bureau of Jiangsu Province Nanjing 210014 China

Based on the rock creep experiment, the data of aftershock sequence and post-earth- quake deformation are used to estimate the viscosity of crust medium near earthquake focus. Firstly 9 samples that belong to 3 kinds of rock are conducted in creep experiment under constant pressure to obtain the creep curves directly. Inversion results show that the standard linear model is the best one to present the earth medium. It exhibits obvious elasticity within a short time, while it exhibits obvious rheology within a long time. The relationship between element module μ 2.and the whole module μ of standard linear model or the module of real earth medium is calculated and analyzed. On the basis of μ 2.= 2. μ, the sequence of aftershock of Gonghe earthquake in Qinghai Province is analyzed and the relationship between accumulated released strain and the time is obtained, which, combined with the creep experiment results, is used to estimate the viscosity of crustal medium in this area. The measured vertical deformation after the same earthquake also is combined with the creep experiment results, then it is used to calculate the relaxation time and viscosity through three different methods respectively, i.e. inversion of Kelvin model, difference method of deformation and viscoelastic dislo- cation theory. The viscosity of crustal medium in 32.km depth of earthquake focus of Gonghe area deduced from the different data and methods is about 1019 Pa·s, which is the same as the research results by other authors at home and abroad.

关键词： creep experiment, aftershock sequence, post-earthquake deformation, crustal viscosity.

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Magnetic Energy of Force-Free Fields with Detached Field Lines

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Chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 555-562页

作者： Guo-Qiang Li and You-Qiu HuSchool of earth and space {2., University of science and technology of china, hefei 2.002. School of earth and space {2. University of Science and Technology of China Hefei 230026

Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma β (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.

关键词： Sun: magnetic fields - Sun: coronal mass ejections (CMEs) -methods: numerical

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Source time-function as discriminant using empirical Green's function

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science china {2. sciences 2005年第12期48卷 2118-2122页

作者： HE Yongfeng1,2.& CHEN Xiaofei1 1. department of Geophysics, School of earth & {2. sciences, Peking University, Beijing 100871, china 2. North-West Institute of Nuclear technology, Xi’an 71002., china 1. department of Geophysics School of Earth & Space Sciences Peking University 100871 Beijing China 2. North-West Institute of Nuclear technology 710024 Xi’an China

The source mechanism of underground nuclear explosions is remarkably different from that of earthquakes in both spatial radiation pattern and source time-function (STF). Small underground nuclear explosions can be used as empirical Green’s functions (EGF) to isolate the source-time spectrum of a large suspected earthquake occurred in a Nuclear Test Site (target area) by the spectral division method. As this study shows, with high-quality data, the quotient spectrum can be transformed to the time domain, yielding the apparent far-field source-time function of the large suspected event. The relative source time-function (RSTF) of a nuclear ex-plosion is usually a simple pulse with a duration of about 1 s., while an earthquake’s is more complicated with a series of pulses and a longer duration. The RSTF can be used as a nice dis-criminant to distinguish the nature earthquakes from underground nuclear explosions in target areas.

关键词： target-area, empirical Green's function, RSTF.

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Re-Os(ICP-MS)dating of the massive sulfide ores from the Jinchuan Ni-Cu-PGE deposit

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science china {2. sciences 2005年第10期48卷 1672-1677页

作者： YANG Gang1,2. DU Andao1, LU Jiren3, QU Wenjun1 & CHEN Jiangfeng2.1. National Research Center of Geoanalysis, Beijing 100037, china 2. Laboratory for earth Material Cycling, School of earth and space sciences, University of science and technology of china, hefei 2.002., china 3. Institute of Mineral Resource, Chinese Academy of Geological sciences, Beijing 100037, china National Research Center of Geoanalysis Beijing china Laboratory for earth Material Cycling School of Earth and Space Sciences University of Science and Technology of China Hefei China Institute of Mineral Resource Chinese Academy of Geological sciences Beijing china

Massive sulfide ore from the Jinchuan Ni-Cu-PGE deposit was dated by Re-Os technique using Carius Tube digestion, Os distillation, Re extraction by acetone and ICP-MS measurement. An isochron giving an age of 833 ± 35 Ma, initial 187Os/188Os ratio of 0.2.9 ± 0.018 (MSWD = 1.7) and γOs = 130 ± 15 is obtained. The Re-Os age obtained agrees, within analytical uncertainties, with previous SHRIMP zircon U-Pb age of 82. ± 8 Ma (n=5, MSWD = 4.3). The result suggests that the deposit was formed at Neoproterozoic and that the formation of the Jinchuan Ni-Cu-PGE sulfide deposit may be closely related to the plume activity, which were attributed to the breakup of the Rodinia supercontinent. The high γOs of the massive ores sug-gests that crustal material was involved in the formation of the Jinchuan deposit, however, the quantity of the added crustal material is less than 10%.

关键词： Jinchuan Ni-Cu-PGE deposit, Re-Os dating, ICP-MS.

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Multi-isotopic system geochronology of low temperature eclogite from Huangzhen,Southern Dabie Terrain

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science china {2. sciences 2004年第10期47卷 931-942页

作者： CHEN Daogong1, E. Deloule2. CHENG Hao1, XIA Qunke1 & WU Yuanbao1 1. School of earth and space {2., University of science and technology of china, hefei 2.002., china 2. CRPG-CNRS Nancy, 54501, France 1. School of earth and space {2. University of Science and Technology of China 230026 Hefei China 2. CRPG-CNRS 54501 Nancy France

Zircon U-Pb thermal ionization mass-spectrometer (TIMS) and secondary ion mass-spectrometer (SIMS) dating, mica and amphibole 40Ar-39Ar dating and mineral Sm-Nd isotopic compositions of Huangzhen low temperature eclogite and country granitic gneiss are carried out. The zircon U-Pb weighted average SIMS age is (2.1.6?9.7) Ma for one eclogite. The mica 40Ar-39Ar isochron age is (2.2.6?2.1) Ma and the lowest plateau age is (2.1.7?2.4) Ma from same sample. U-Pb TIMS concordant ages from other eclogite zircons are from (2.1.3?1.4) Ma to (2.2.5?2.3) Ma. U-Pb SIMS low intercept age from country granitic gneiss is (2.1?35) Ma. The retrograde amphibole 40Ar-39Ar isochron age is (2.5.9?1.0) Ma. Except for mica, which may contain excess 40Ar, all the ages represent peak and retrograde metamorphism of low temperature eclogites. It is indicated that the Huangzhen low temperature eclogites differ from Xiongdian low temperature eclogites of north of the Northern Dabie Terrain in metamorphic ages. Huangzhen low temperature eclogites share one coherent HP-UHP terrain with high temperature eclogites from Southern Dabie Terrain and they may have differences in subduction depth and cooling rates during exhumation.

关键词： low temperature eclogite, multi-isotopic dating, HP-UHP metamorphism, Dabieshan.

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Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone,northeastern china

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science china {2. sciences 2005年第4期48卷 467-476页

作者： CHEN Jiangfeng1, YU Gang1, XUE Chunji2. QIAN Hui1, HE Jianfeng1, XING Zhi1 & ZHANG Xun1 1. School of earth and space {2., University of science and technology of china, hefei 2.002., china 2. department of Geology, Chang’an University, Xi’an 710054, china 1. School of earth and space {2. University of Science and Technology of China 230026 Hefei China 2. department of Geology Chang’an University 710054 Xi’an China

Pb isotopic analyses were reported for sulfide and hydrothermal carbonate minerals and marble of the Xiquegou lead-zinc, the Zhenzigou zinc-lead and the Gaojiapuzi silver deposits from the Qingchengzi ore field and the Beiwagou zinc-lead deposit in the west, Proterozoic Liaodong rift zone. Pb isotopic ratios of the marble from the Qingchengzi ore field range from 18.2. to 30.63 for 2.6 Pb/2.4Pb, 15.59 to 17.05 for2.7Pb/2.4Pb and 37.43 to 38.63 for 2.8Pb/2.4Pb. The marble gives a Pb-Pb isochron age of 182.±92.Ma, which is interpreted as the age of the metamorphism of the marble. Ore Pb, including Pb of sulfide and hydrothermal car- bonate minerals, from the Qingchengzi ore field shows limited variation with 2.6 Pb/2.4Pb=17.66- 17.96, 2.7 Pb/2.4Pb=15.60-15.74 and 2.8Pb/2.4Pb=37.94-38.60. In contrast, ore Pb from the Beiwagou deposit gives different Pb isotopic ratios with 2.6Pb/2.4Pb=15.68-15.81, 2.7 Pb/2.4Pb= 15.34-15.45 and 2.8Pb/2.4Pb=35.30-35.68. Pb of all deposits from the Liaodong rift zone is derived from the upper crust. Ore Pb of the Qingchengzi deposits is derived from a young upper crust. The model Th/U ratios of 4.40 to 4.74 for ore Pb are significantly different from that of 1.7 to 4.4 given by the marble of the Qingchengzi ore field, suggesting that marble is not the source of the ore Pb. Ore Pb of the Beiwagou deposit is extracted from its source and the deposit is formed at the Paleoproterozoic era. Different Pb isotopic ratios of the Qingchengzi ore field and the Beiwagou deposit are due to different ages of the deposits and suggest that the two types of deposits are derived from different sources and are possibly formed by different ore-forming processes.

关键词： Pb isotopes, source(s) of the ore-forming materials, origin of ore deposits, Liaodong rift zone.

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