Table of Content

20 September 1997, Volume 3 Issue 3

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Article

THEORETICAL STUDY OF OXYGEN ISOTOPE FRACTIONATION IN CARBONATE MINERALS

Zheng Yong-fei, Zhou Gen-tao, Gong Bin

1997, 3(3):  241-255. 

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The increment method is adapted to systematically evaluate oxygen isotope fractionations in carbonate minerals and the following sequence of 18O-enrichment is obtained: siderite>ankerite>magnesite> dolomite>calcite>aragonite>strontianite>cerussite≥witherlte．The internally consistent fractionation factors for the systems quartz carbonate and carbonate-water are acquired for a temperature range of 0 to 1200℃．There is good agreement between the present calculations and known experimental and/or empirical data．Therefore, this theoretical calibrations involving the carbonate minerals are applicable not only to determination of the formation temperature of mineral assemblages but also to tracing their formation mechanisms． The present calculations suggest that dolomite should behave isotopically like calcite, and the cauilibrium fractionation between dolomite and calcite is 0.56‰ at 25℃．Aragonite is predicted to be significantly depleted in 18O relative to calcite; equilibrium fractionation between calcite and aragonite is 4.47％ at 25℃．It is possible that polymorphic transition from aragonite to calcite could proceed through an essentially intact oxygen structure without isotopic resetting．In other words, the polymorphic transition involves only the breaking and rebinding of bonds between cation and carbonate complex rather than bonds between C and O inside the carbonate complex．It is hypothesized that the temperature dependence of oxygen isotope partitioning in aragonite could be conveyed to calcite in nature and in laboratory experiments．However, it remains to be tested whether oxygen isotope inheritance in calcite formation by the polymorphic transition is of critical importance in attempts to resolve dilemma involving fractionations in aragonite-calcite-dolomitewater systems.

STUDY ON THE MODE OF GOLD IN ARSENOPYRITE FROM HUANGJINDONG GOLD DEPOSIT，HUNAN, BY USING ELECTRON PROBE MICROANALYSIS

Zhang Wen-lan1, Hu Wen-xuan2,Hu Shou-x2i, Zhou Shun-zh2, Chen Gang2

1997, 3(3):  256-262. 

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The paper studies the mode of gold in arsenopyrite (Asp) of Huangjindong gold deposit, Hunan Province. The special X-ray scanning is applied to approach the existing state of invisible gold in Asp, and analysis condition is investigated. Back scatter electron image is firstly used to determine whether grain-gold occurs, then, using LIF crystal for measurement of AuL=88.76 Lal peak. The selected Au-bearing Asp (without visible gold) is continuously analyzed by means of special X-ray at increasing magnification(×300、× 1000、×5000、×30000、×200000). It is found that gold element always evenly distributes in Asp. The result suggests that gold exists as lattice-Au mode in arsenopyrite.

STUDY 0N C0MP0NENT VARIATION OF MYL0NITIZATION OF DUCTILE SHEAR Z0NES IN THE MEDIAN-DEEP LEVELS FROM THE S0UTHERN PART OF TANCHENG-LUJIANG FAULT BELT

Yang Xiao-yong, Liu De-liang, Wang Kui-ren

1997, 3(3):  263-271. 

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The paper focuses on the systematic study of two typical ductile shear zones in median- deep levels from the southern part of Tancheng-Lujiang fault belt. The influence and restrain on the chemical component migration and activation in the rocks by ductile deformation have been revealed. On the basis of simulant calculation of the migration of active component in the rocks, the authors have established the chemical reaction equations of different metamorphic rock pairs，The paper also discusses the important role played by fluids in the mylonitization.

GENETIC MECHANISM AND TECTONIC SETTING OF PROTEROZOIC MAFIC DYKE SWARM: ITS IMPLICATION FOR PALEOPLATE RECONSTRUCTION

Li Jiang-hai, He Wen-yuan, Qian Xiang-lin

1997, 3(3):  272-281. 

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Preterozoic mafic dyke swarms occur in nearly every Archean continental craton, and recorded significant geological events of continental evolution．It is generally recognized that the generation and emplacement time of dyke swarm is relatively short, while its genetic mechanism is complex. At different conditions, dyke swarms have different propagation mechanism. Commonly, each dyke fracture initially fills vertically, then propagates laterally and not always intrudes perpendicularly to the lowest normal stress axis. Dykes Can intrude in different crustal levels, but distinct with each other. Although there are different magma sources, the major source: of dyke swarm is continental asthenosphere or lithospheric mantle. The evidence of crystallization differentiation or crustal contamination is tardy documented. Dykes’ bulk geochemical feature is enriched and shows some small changes which could be used to detect the evolution of mantle process. Because extension can occur in different tectonic settings, where dykes actually generated still needs careful study. The plate tectonics had been operating at least from Neoarchean to Paleoproterozoic, and in the Proterozoic, the earth lithosphere was characterized by assembly and breakup of continental cratonic blocks. The occurrence of mafic dyke swarms marked the initial breakup of the supercontinents. A wide range of Preterozoic mafic dyke swarm, occurred in North China Craton, which will provide important constraints on reconstructing North China Craton and its position in the Mid-Proterozoic supercontinent.

KINEMATIC STUDY OF THE NORTHERN MARGINAL FAULT Z0NE OF WUYISHAN, S0UTH CHINA

Shu liang-shu1, Lu Hua-fu1, Charvet J2, Fauve M2

1997, 3(3):  282-292. 

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Wuyishan is an important tectonic domain which connects the late Proterozoic Jiangnan belt to the north with the Mesozoic-Cenozoic southeastern China Coastal zone to the south. Its northern boundary is the Dongxiang-Jiangshan-Shaoxing fault zone with 20- 50km wide, more than 800 km long along a NEE-NE direction. The ductile shear rocks and pre-Cambrian schist, gneiss, orthogneiss and migmatite occur in this zone, accompanied with serpentinized mafic-ultra- mafic blocks around 900 Ma. The kinematic analysis of the fault zone and neighbouring area to the south reveals polyphase tectonic deformation as follows: 1. The 1ate Proterozoic collision between Jiangnan arc and Southeastern China Precambrian metamorphic terrane took place during the interval of 800-9O0 Ma, accompanied with the formation of the Chencai-Longyou tectonic melange zone and a regional metamorphism of greenschist to amphibolite facies, strong folding with an axial plane dipping to southeast, and ductile deformation with a southeastward sense of shear. 2. The early Paleozoic thrusting deformation resulted in a progressive metamorphism and my1onitization. The biotite flakes of micasehist were replaced by hairy sillimanite; the mylonitic foliation and stretching lineation developed well and crosscut previous schistosities and fold. This thrusting made the metamorphic rocks refolded. An analysis of the non-coaxal ductile deformational indicators shows a sense of shear from north to south. Its geodynamic mechanism is likely related to the early Paleozoic amalgamation and accretion of the southeastern Fujian terrane along the Zhenghe-Dapu zone in the southern margin of Wuyishan toward the northwestern Fujian volcanic arc that developed on the Southeastern China metamorphic basement. The Sm- Nd isochron age of 399±8 Ma on gabbro and the 40Ar/39Ar age of 421±8 Ma on biotite grains of mylonitized micaschist recorded this geological-thermal event. This event also affected the southern margin of the Jiulingshan of the Jiangnan belt to the northwest. 3. The Indosinian sinistral brittle shear deformation occurred in a high tectonic leve1. This is an intracontinental deformation resulted from 1ate Triassic collision between Yangzi and North China plates. The sinistral brittle strike-slip deformation caused 1ate Paleozoic and the older rocks fractured and sheared displacement along NEE-NE direction; the Dongxing-Jiangshan-Shaoxing fault zone was finally placed.

DISCUSSION ON THE SEALING PROPERTY OF DEEPLY BURIED FAULTS

Wang Zhi-xin, Xin Quan-lin

1997, 3(3):  293-300. 

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Sealing ability of faults is the key which controls the migration and accumulation of oil and gas along fault. In this paper, the authors reviewed and analyzed the fundamental ideas, in the prevailing evaluation of fault sealing property, and some new thinking about this work was made on the basis of the theory of effective stress. (1) The mechanical properties of a fault plane depends on the magnitude and direction of normal and shear stresses on that plane; compressive normal stress suggests that the fault plane is sealed: the nature of normal stress depends on the effective ground stress，which is otherwise closely related with formation pore pressure. (2)The prevailing evaluation of fault sealing property which completely neglected the influences of formation fluid pressure is not perfect; the fault sealing property has been changing for all the history in an instant, repeatful and eventful way. (3)Under deep burial, nearly all faults are generally sealed in relatively peaceful tectonic background. (4)In nature, there are at least two mechanisms which have repeatedly resulted in the natural fracturing of confined aquifers by high pressure: the first is “high pressure fracturing triggered by earthquakes”, i.e. the instant changes of geostress field during earthquakes can result in entremely high formation pressure which will further result in the opening of formerly sealed faults and subtle fractures; the other mechanism is “high pressure chain fracturing due to upward intrusion of deeply seated fluids.”

RAPID INVERSION METHOD IN THE INTERPRETATION OF IP SOUNDING CURVES

Ruan Bai-yao

1997, 3(3):  301-307. 

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Based on the published paper of present author(Ruan ＆ Xu, 1996)and Siegel’S model of polarizability, this paper first derives a direct inversion method for interpretation of IP sounding curves. Then according to the works of Zohdy(1989) and Oldenburg(1991), a contrast iterated inversion method in the interpretation of IP sounding cur was presented to improve the inversion precision. The interpretation for the given IP sounding data shows that these methods are excellent.

EXPLOITATION MODEL OF THE HAMAR GEOTHERMAL FIELD, NORTHERN ICELAND

Li Cheng1, Tulinius H2, Arason P2

1997, 3(3):  308-313. 

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The Hamar geothermal field is one of many low-temperature geothermal fields in Northern Iceland. Since 1966 eleven wells have been drilled in the field. The purpose of modelling the behaviour of geothermal field under a variety of exploitation schemes is to obtain knowledge of the physical processes needed for further exploitation, control and management. On the basic data of observed water level, the physical behaviour of the Hamar geothermal field was simulated using a Lumped parameter mode1. Water level changes with varions production rates for the next 20 years are given. Conservative predicitous are obtained using dosed models, and optimistic from open models.

METHOD RESEARCH OF APPLYING FROM INFORMATION GE0LOGICAL MAP TO SPATIAL THINKING AND DIGITAL THINKING

LI Xin-zhong1, Zhao Peng-da2, Xu Zhen-bang1, Zen Fan-gang1

1997, 3(3):  314-323. 

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This paper discusses how to use analysis method of graphs and images as well as, idea of expert system to make geological map information quantitative, and how to apply linear or nonlinear model to indicate spatial relation and digital character of the information, so that geologist may quantitatively analyze geological map information. As exemplified by resources prediction of gold and polymetals in Mian-Lue-Nin region, Shanxi province in China, it illustrates how to apply geological map information for carrying out spatial thinking and digital thinking, and realizing rapid appraisal of regional resources quantity. At last the paper gives distribution map of resources potential that region.

APPLICATION OF ARTIFICIAL NEURAL NETWORK TO MACROSTRUCTURE INTERPRETATION OF COAL BEDS

Cui Ruo-fei, Wang Lei

1997, 3(3):  324-327. 

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Macrostructural change in coal beds is a common geological phenomenon in many coal fields of China, which greatly affects production and is an urgent structural problem in mines. Macrostructure of coal beds, including branching, mergence and disappearance, can be interpreted using artificial neural network, and exact geological data can hence be provided for mining and lunnelling in mines.

ARITHMETIC METHOD IN POLAR STEREOGRAPHIC PROJECTION

Qian Hui, Dong Huo-geng, Chen Chu-ming

1997, 3(3):  328-337. 

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According to basic principles of polar stereographic projection, a formula calculation method is introduced in this paper by using spatial analytical geometry knowledge. It can take the place of hand-operation and get more accurate results. For instance, it can draw projection curve on computer screen while its equation had been referred from its attitude; it can get the attitude of the co-plane between two lines or the intersect line of two planes; it can calculate the interangle and the bisectrix of two lines or two planes; it can perform the transition between apparent dip and true dip or between dip and pitch; it can model the rotation of a line or plane around 8n axis, so the original attitude of a joint can be recovered. The last part of the paper is about the computer algorithm of joint intensity statistics and the iso-intensity diagramming. This method directly shows the relationship between structural factors so that it can be used for computer Aided Instruction(CAI). It also makes satisfactory application in practice because its accuracy reaches 0.0l℃.

C0MPUTER ASSISTED INSTRUCTION C0URSEWARE F0R STRUCTURAL GE0L0GY: SGCAI

Shen Xiao-hua, Zeng Hua-sheng, Zou Le-jun, Yang Shu-feng

1997, 3(3):  338-341. 

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It is essential to develop quality geological CAI application software for teaching purpose. Here we present a course ware of Computer Aid Instruction for Structural Geology (SGCAI), which includes a large capacity of database, cartons and multimedia technique. The SGCAI can be used in theory geological courses. It constructs a properly module structure with a friendly interface and hence is easy to operate. The SGCAI is of full functions, in which teaching management and data processing functions are quite new and practical in operation. With the (environment of) SGCAI, students can fully take their initiative. The SGCAI is a new tool to improve teaching quality and train composite geological personnel for the 21st century.

PONDERING OVER SOME PROBLEMS IN THE STUDY OF CONTINENTAL GEOLOGY

Chen Guo-neng

1997, 3(3):  342-347. 

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Plate Tectonics has expounded the material cycle of oceanic crust, and Geosyncline Theory has done that of earth’s surface. Thus a model about the material evolution in continental interior is the necessity for establishing systematic theory of continental geology, and the key to the model is to clarify the genesis of granite which constitutes an important part of the continental crust. The traditional magmatic intrusion hypothesis is not able to hold various data concerning granite. It is a thinking fallacy for the research of granite genesis to use the method of “taking the present as the key to the past” in status of geothermal field.

KEY T0PICS 0N PHYSICS AND EVOLUTION OF THE EARTH’S INTERIOR: 1.EARTH STRUCTURE AND PHYSICAL PROPERTIES

Cheng Sheng-zao

1997, 3(3):  348-360. 

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Some important methods and main results from studies of physics and evolution of the Earth’s interior were reviewed in this paper, with an emphasis on the areas such as geophysical equations of state, seismic tomography, integrated inversions, high-temperature an d high-pressure experiments, and their comparative studies. The most updated findings have demonstrated that the Earth’s interior is heterogeneous and anisotropic, even though the homogeneous, isotropic, and symmetric spherical model nowadays can be still taken as a reference mode1. The lateral heterogeneity is mainly found in the upper mantle, while the lower mantle and the outer core of liquid state seem to be relatively homogeneous. The core-mantle boundary(CMB)transition zone (D″). however, is most likely a heterogeneous chemical boundary layer embedded in a thermal boundary layer, with a temperature drop of several hundred degrees, where its topographic undulation and lateral heterogeneity will affect the spherical symmetry of the Earth mode1. Results from 3-D seismic tomography reflect, in practice, the relationship between velocity and temperature anomalies, whereas the temperature variations further lea to on anomalous change in density, and hence, the parameter density is one of essential cont factors in mantle convection modeling.