Geological Journal of China Universities

A Review of the Mylonite

SUN Yan1, ZHU Wen－bin1, GUO Ji-chun1, LIU De-liang2, KAZUO Kosaka3

2001, 7(4): 369-378.

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Mylonite bears rich information of geological processes and is of great importance not only in the theoretic study but also in the geological practice. In this paper, the authors will review the progresses of mylonite petrology in the past two decades based on studies of micro-ultramicroscopic structure, solid state rheology, mineralization of dynamic metamorphism, modeling experiment of rock formation, tectono-gecchemistry, orogenic kinematics and isotopic chronology. Some new results of mylonite study, are discussed, which include discovery of mylonite in the shallow level, experiment of rock formation for the artificial mylonite and new data of chronological dating, etc., We also suggest that microscopic research of mylonite could be further extended into the new fields in studies of crust-mantle theology, tectono-chronology and the comparative geology of orogenetic belts. Fina1ly, it should be shown that some concerning laws of the physics (such as the Helmholty law) will be cited for the mylonite research in the microscopic scale, thus the dislocation forming rule and the mechanism of rock rheology could be completely interpreted. Moreover some results and models (example S-C foliation type) are also applied on a delineation deformation research, in particular, the discovery of the mylonite in the shallow level has helped to bring new discussion of the seismic rupturing genesis. The various rich informations in mylonites will be explored out through the parameters determinated by the rock mechanics, tectono-physics, geochemistry and rheology, further the new coupling mechanism of the geological action could he revealed in more detail.

Progress in the Research of Cobalt-Rich Crusts

WU Guang-hai1;2, ZHOU Huai-yang2;3, YANG Shu-feng1, CHEN Han-lin1

2001, 7(4): 379-389.

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Cobalt-rich crust is one of the most potentially valuable mineral resources. This article introduces the details in progress of the Co-rich crust research achieved in recent years. From the viewpoint of resources, the exploration region of Co-rich crust is enlarged significantly in recent years. Meanwhile, the Co-rich crust embedded below the sediments on seamounts is also found. Based on the geological and tectonic setting’s research, the genesis of Co-rich crust is interpreted to be related with the action of intense intraplate mantle plume. The thickness of the Co-rich crusts is also related with the types of basement rocks and with the weathering degree of the basement rocks. Due to the progress of modern analysis techniques, the research on the Co-rich crusts structures, mineral compositions and geochemistry has been deepened gradually. Especially on account of the microcosmic observation and test techniques and some new chronological methods, the research on resolution sections of the Co-rich crust has made great progress. Based on this, Co-rich crusts with lower growth rate and during the stage with no or few sediments are used to study the paleooceanographical features and the global changes Ten million years’scale changes of oceanic environment and the history of deposit gap can be reflected by studying the Co-rich crusts, which is impossible for the pelagic sediments．In the aspect of material source for the Co-rich crusts, the importance of the endogeneic materials from volcanoes, hydrothermal fluids, and low temperature water-basalt interactions etc, is gradually recognized. It is found that microbes play an important role in the formation of Co-rich crusts. Finally, the directions of future development in this aspect are forecasted in this paper.

Recent Advances in Research on Lithium Isotopes and Its Geological Applications

ZHAO Kui-Dong, JIANG Shao-Yong

2001, 7(4): 390-398.

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Lithium has two stable isotopes(6Li and 7Li)with nature abundance of 7.52% and 92.48%, respectively. Due to the large mass difference between the two lithium isotopes and low Li contents in geological samples, Li isotope measurements have met large difficulty in the past several decades. High precision Li isotope analytical methods are only developed recently, and three major methods are currently used: (1)TIMS method with analytical precision of

New Materials of Fusulinacean from Xinjiang and Their Significance in Structural Geology

YANG Xiang-ning, JIA Dong, LU Hua-fu

2001, 7(4): 399-407.

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Some new materials of the Early Permian fusulinacean from Keping and Wushi of Xinjiang are described, which provided further information for the analysis of fusulinacean biostratigraphy and paleobiogeograhy of the Permian. The study shows that the fusulinacean fauna of the Early Permian in Tarim basin is very similar to that of the same age in the southwestern China, particularly in sharing sortie endemic species of Robustoschwagerina, which the past have only been found in Guizhou, Guangxi and Yunnan province. The similarity of fusulinacean faunas indicates that the Tarim plate and southwestern China plate probably were at the similar latitudes in the Early Permian and close to each other geographically. However, this conclusion from the fusulinacean study is inconsistent with the paleomagnetic data, which suggested a N 30.6°for Trim plate and a S 7.0°for the upper Yangtze River plate in the Early Permian. Based on recent studies on the movement of micro-plates and the direct1cm of plaeocirculation of Tethys during the Carbon-Permian, the authors made a preliminary discussion on the possible mechanism that may cause the similarity of fusulinacean faunas between the two apart plates. It is suggested that the counter-clockwise circulation of the paleo-Tethys could possibly carry those fusulinacean species originally endemic to the South China plate northwards to the ocean regions adjacent to the Tarim plate. Nevertheless, this hypothesis should be tested by further paleontologic and stratigraphic studies.

Dynamic Mechanism of Formation of Dustpan Subsidence，Northern Jiangsu

CHEN An-ding

2001, 7(4): 408-418.

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Subei Basin is composed of several smal1 subbasin shaped like dustpan. Many authors had previously explained the origin of Subei Basin on the theory, of pull apart basin or rifting basin. However, seismic information suggests that wedges of the Palaeogene strata formed mainly through imbalance uplifting and erosion beside the sedimentary reason. In fact, Suhei Basin is a residual basin in the Palaeogene period. The tectonic phenomena happened in the Cenozoic are caused by both of the continuity of the Mesozoic tectonic processes and the complexity of Cenozoic stress field During the end of Indosinian to middle Yanshan movement, eastern China was only effected by Pacific-Kula plate, then the strata were deform ed strongly, and with the single di1ection of stress field, bearing the NW -NWW compression direction or the left-lateral shearing, lots of thrust-nappe tectonics were formed in eastern China. Since the Eocene the compression force caused by collision of India Plate to Eurasia has been added to this region. Subei Basin is in alter native-variable dualstic dynamic environment because of different move velocity for two plates. As the force source from India plate dominated, the force couple of right-lateral twist emerged and led to the reverse faults of early-middle Yanshan period to be reacted and reversed The sedimentation dominated in this region, while the raising dominated in western continental of China. But as the force source from Pacific Plate dominated, the couple force of left-lateral transpression appeared, then the whole uplifting of the basin occured, the slope and heave underwent erosion so that the dustpan structure got enhanced. Alternation of two force sources on the time and space completed a whole “fault subsidence-depression-uplift”, i.e. the sedimentary-erosion tectonic cycle.

Tectonic Setting of the Northern Margin of South China Sea

WU Shi-min, ZHOU Di, QIU Xue-lin

2001, 7(4): 419-426.

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There are different deformation characteristics between the east and west part of the number 1 fault in the northern margin of South China Sea(SCS). The east part includes the Beibuwan basin, Qiongdongnan basin, Zhujiangkou basin and Taixi basin, with NE-EW strike segment of normal faults and traverse fold. The west part includes Yinggehai basin, with NW strike transtensiona1 faults. Based on with the features of magmatics, subsidence, sedimentary fill, crust structure in the northern margin of SCS, the authors believe that the east part margin exist three relative tectonic active periods, i.e. 40—50, 28—30, 10—5Ma. They exhibited different dynamics characteristic respectively．The former two episodes are related to the break up processing of SCS. The third is nothing to do with it. The magmatics at the northern margin of SCS are not the correspond activity with the rifting of SCS. Therefore, the east part of the northern margin of SCS belongs to the non-volcanic passive margin according to its forming mechanism. The active factors are overlapped by the interaction of surrounding plates. The west part may be related to the collision of India-Tibet and it is not a part of the northern margin based on the formation mechanism.

Structure Restoration of Balancing Cross Section in Extension Area: An Example from the Huaifu Depression, North Jiangsu Basin

XUE Gang1, LU Hua-fu1, ZHU Cheng-hong2, BAO Hong-lin2

2001, 7(4): 427-434.

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Based on a review in geometric modes in extensional tectonics, the basic deformation structure models are discussed. In the light of study on the geometric models of hanging-wall, several mathematical approaches are presented to balance deformed structure. The square matrix method is applied in simulation of rigid-body rotation and shift. The algebra equations of two structura1 restoration methods are employed in restoration of rollover above listric normal fault. These expressions provide basis for deriving computer algorithms In this way, the particles of deformed layers in the cross section can be restored to their original positions. It is also feasible in simulation of layer deformation. A computer program was designed for structure analysis, and has been applied in the oil field in the Huaifu Depression, Noah Jiangsu Basin, East China Basic structure features of this basin was illustrated after the interpreted seismic profile of line Fs1420 was restored, and the tepo-tectonics history of sedimentary was also revealed From the restored cross sections of line Fs1420, it can be seen that fault F0 was apparently the main fault, and controlled the development of Huaifu Depression, North Jiangsu Basin. Fault F2, fault F3 and fault F6 actived in the same extensional tectonic regime with the main fault occurred from the beginning of the first stage of Pukou Formation (K2p1 )in Late Cretaceous to the Cenozoic Since the reflected surface in seismic section TgO as the based the Pukou Formation(K2P) can not be identified clearly, the characteristics of fault F1 was difficult to define. After detailed study, it is infered that it is emplaced in forth stage of Pukou Formation(K2p4). The synthetic fault F4 and the antithetic fault F5 were controlled by fault F3 and were emplaced in Cenozoic Fault F7, a later antithetic fault, was also emplaced in Cenozoic The total extention of Huaifu Depression was 6280 m since 97Ma and the individual episode extention values and the extentional rate are calculated respectively (see Table 1) From K2P to K2p4, the extentional rate increased from 0.133 m per Ka to 0.733 m per Ka. Then during the Cenozoic the extentional rate decreased to 0.024 m per Ka. Therefore, two different stage of extensional activities of Huaifu depression were presented. For the early stag e in Late Cretaceous the tectonic extension is strongly active and for the later stage during the Cenozoic that is relatively weak and slow.

Geochemistry of Basalitic Rocks in the Laoshan Mountain Area

ZHAO Guang-tao1, HAN Zong-zhu1, LUAN Guang-zhong1, XING Guang-fu2．CHEN Zuo-lin1

2001, 7(4): 435-443.

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The scattered outcrops of the Late Creraceous(95Ma), end Creraceous (69Ma), and the Oligocene(67-65Ma)basalitic rocks occur in the Laoshan Yanshanian granitite intrussives, eastern China. The rock types are alkaili-basalt, basanite and tholeiite, respectively. The alkai1i-basalt and basanite are all characterized by higher contents of LILE and LREE, with(La/Yb)N=25.5～46.6, depleted in Nb, Ta, Zr, Ti, and enriched in Ba, Rb, Th, as compared to those of the Cenozoic alkaili-basalt in North China The Sr, Nd isotopic ratios of basanite are 87Sr/86Sr=0.705517, Nd/ Nd= 0.572777. Both alkaiti-basalt and basanite should be derived by partial melting of an older mantle wedge that formed by the Early Mesozoic subduction of the Yangtze plate beneath the North China plate. Compared to alkaili-basalt and basanite, the tholeiite has lower contents of total trace elements, LILE and LREE, and with (La/Yb)N=4.7～6.4. Their typical ratios of trace elements axe similar to those of EM1-OIB 87Sr/88Sr=0.706054～0.706146; 143Nd/144Nd = 0.572387～0.512392. They should be originated by partia1 melting from the “metasome” -the lithospheric mantle metasomatised by the rising asthenospheric fluid. The intrusions of different kinds of basalts may reflect the dynamic process in the area of gradual crustal extension, thinning, and asthenospheric elevation from Late Creraceous to Eogene.

Diagenetic Illite K-Ar Age Analysis and Its Significance

WU Jing-wei1, CHEN Xiao-ming2, YANG Zhong-fang3;2

2001, 7(4): 444-448.

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The timing of hydrocarbon generation is of particular concern in resource exploration. When were the solid organic matters heated to form oil and gas? Because illite forms in rocks in response to heating in the same temperature range as oi1 formation, its K-Ar age is all important parameter. Illite in reservoir sedimentary rocks is a mixture of detrital and diagenetic components. Defining reliable diagenetic ages of illitization in sedimentary rocks still remains a formidable challenge because separation of the diagenetic component is impossible, even if it is carried out down to the grain size as small as

Study on Leaching of Potentially Hazardous Trace Elements froml Coa-Waste Rocks

LIU Gui-jian, YANG Ping-yue, PENG Zi-cheng, WU En-jiang, WANG Gui-liang

2001, 7(4): 449-457.

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In China coal accounts for 75% of the total consumption of primary energy. Trace elements in coal are important because of their close association with environmental issues and the health of plants, animals and human beings. Consideration must be given to essentiality, nonessentiality and toxicity that depend on concentrations, forms of existence of elements．pH and oxidation-reduction conditions, and other factors. There are many hazardous minor dements in coal-waste rocks. With the action d leaching by rain and water,some hazardous minor elements will be dissolved completely or partly and be separated from coal-waste rocks into water of soil environment. Consequently, they would pollute water quality, destroy soil function and influence ecology development and human health. Leaching is an important way of environment pollution while hazardous minor elements are leached out from coal-waste rocks and ashes. In this paper, based on the leaching experiments, leachable contents of hazardous minor elements from coal-waste rocks are studied in relation to their forms of occurrences and contents in coal-waste rocks, leaching times, leaching temperatures, and the pH values of the media. The higher temperature of leaching media and the longer leaching time, the higher leachable contents of hazardous minor elements. In the course of leaching, different hazardous minor elements are differently effected by pH values of leaching media.

The Wave Veloity Change Through the Mylonite in Southern Section of the Tancheng-Lujiang Fault and Its Geological Implications for Oil and Gas

LIU De-1iang1, YUAN Xue-cheng2, TAO Shi-zhen1, SHEN Xiu-zhi3

2001, 7(4): 458-465.

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For the inorganic-origin natural gas, especially the carbon dioxide gas, its accumulation in the deep-seated part of basin and inside mountain chain is related to cap rocks, which the tectonic decollement rifted rock (mylonite) is an ideal rock type．The ultrasonic method is optimum for detecting the, sealing effect of cap rock because it is effective, economic and convenient. The ultrasonic wave refers to the elastic wave propagating in continunm with its frequency over the hearing threshold value of human beings．The method is tenable theoretically, and is useful in study the anisotropy of rock’s wave velocity by means of ultrasonic wave, analyzing the wave velocity anisotropic body that shows oil and gas-bearing bed and sealing cover, and judging the migration direction of oil and gas. However, the study of wave velocity related to sea ling cover based on mylonite has not been reported so far. In this paper, the wave velocity of mylonite is detected and calculated. The result indicates that the wave velocity of mylonite is closely related to rock fabrics, tectonic stress field and accumulation-forming conditions. The wave velocity is negatively related to porosity(Vpz=5.96～ 0.98φ) and postively to sealing performance. The rock shows evident anisotropy, the minimum wave velocity direction indicating the sealing trend while the maxmum the favourable direction for migration of oil and gas.

Hydrocarbon Characteristics of Igneous Rock of the First Member of Kongdian Formation in Shenjiapu Area of Huanghua Depression, Hebei

ZHANG Shi-qi1, JI You-1iang1, SHI Zhan-zhong2

2001, 7(4): 466-474.

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We studied the factors of controlling the formation of igneous oil-bearing reservoir and analysis the law of oil-gas accommodation in Shenjiapu area of Huanghua Depression. In order to do so, according to interpretation of seismic sections and core analysed, drilling, logging and oil-testing data explanations to igneous rock, we had studied the distribution law and hydrocarbon characteristics of igneous rock of the first member of Kongdian Formation(Ek1)in the area, such as the property of petrography and geophysics, spatial distribution, reservoir characteristics and oil and gas bearing of igneous rock. The conclusions are as follows: (1) Shenjiapu area is divided into two parts by Kongxi fault. In the downthrow block effusive rock developed and in the uplifted wall intrusive rock developed. The distribution and thickness of effusive rock is larger than intrusive rock. (2) The igneous reservoir had undergone five diagenetic stages: cooling diagenesis, filling of chlorite, filling and replacement of calcite, forming of structure fracture and corrosion of cement. And during these stages two kinds of reservoir space, pore and fracture, were developed. (3) There are many igneous oil-bearing sequences and two kinds of oil and gas pools in the research area. The first one is oil and gas of volcanic rock in which the reservoir space of igneous rock was mainly composed of pore and fracture, and was developed in the first and second submember of Ek1 in the downthrow block of Korgxi fault. The second one is oil and gas of hypabyssal intrusive rock in which fracture was the main reservoir space, and was developed in the third and fourth submember of Ek1 in the uplifted wall of the fault. (4) The formation of igneous oil-bearing reservoir in the research area were controlled by the rock type of reservoir, modified degree of rock caused by the tectonic movement and the position of structural high.

Seal Characteristics of Eogene Mudstone Caprock in Kuche Depression and Its Improtance in Controlling Accumulation of 0il and Gas

FU Guang, WANG Peng-yang, FU Xiao-fei

2001, 7(4): 475-482.

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The Eogene mudstone caprock in Kuche Depression is very thick and distributed widely in the depression. It is of strong capillary seal ability, overpressure seal ability and weak restraining hydrocarbon concentration seal ability. The comprehensive seal ability of the Eogeneb mudstone caprock in Kelasu, Dongqiulitake and Yinan Structures is good, its comprehensive seal ability gradually become bad from north to south The distribution of the mudstone caprock controls the distributions of oil or gas in the Cretaceous system. The gas reservoirs distribute under good caprock, oil reservoirs distribute under middle caprock. The seal period of mudstone caprock of Eogene system is later than the period that a great deal of oil expelled from sourcerock of the Triassic and Jurassic system and is not favor able for a great deal of oil to accumulate. The seal period of mudstone caprock is earlier than the period that a great deal of gas expelled from sourcerock of the Triassic and Jurassic system and is favorable for a great deal of gas to accumulate.

State Equation of Groundwater Based on Artificial Neural Network

HAN Fei1, XUE Yu-qun1, ZHANG Yong-xiang2

2001, 7(4): 483-487.

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It is well known that the density of groundwater in geological environment is not invariable In general, groundwater temperature varies little and the solute concentration is not so high, the density of groundwater is close to a constant．In seawater intrusion ease, tota1 dissolved substance(TDS)of groundwater is leas than 35g/L, and the density of groundwater changes linearly with the solute concentration and its influence on movement of groundwater can not be neglected. With the occurrence of the problems such as brine water intrusion, heat storage in aquifer, exploitation of terrestrial heat and pumping brine water in deep aquifer, TDS of the groundwater is as high as l O00g/L and the temperature reaches 60℃ , and the range of variation of TDS is very extensive. For example, TDS can vary from 0.1g/L inland to 220g/L in coast in Laizhou Bay, and hydrogeochemical types of groundwater is complete, which involve fresh water, brackish water, salt water and brine water. Three states exist in relationships between the density and the TDS of groundwater, i.e., nearly constant in flash water, strongly nonlinear in brine water, and linea state in partially salted water. Moreover, the density of groundwater is influenced by the components of solute and the density may be different with the same TDS In the,south coast of Laizhou Bay, hydrogeochemical components vary complicatedly because they are influenced by many factors such as cation exchange, dissolution and sedimentation of mineral. Therefore, it is difficult to obtain a traditiona1 state equation which can completely satisfy conditions demonstrated above. We obtain the state equation of groundwater based on artificia1 neural network(ANN)by gathering every hydrogeochemical types of groundwater samples in the south coast of Laizhou Bay, gauging their density and TDS, by using neural network toolbox to design neural network model of back propagation in 3 layers, and then simulating the relationships between the density and the TDS of groundwater. It is shown that the equation based on ANN is a reasonable mapping between density and TDS of groundwater and it is straight forward in form and is easy to use. ANN has broad prospect in hydrogeological field because major geological environment in which groundwater exists and the variations of groundwater itself are very hard to understand fully. At present ANN is mainly applied in total evaluation and prediction of groundwater quality Applications of the neural network toolbox can simplify the design and exertion of ANN considerably, save time for programming and improve working efficiency, and thus provide more opportunity to popularize ANN.

Antarcrica GRV9927: A Possible Martian Meteorite

WANG He-nian1，WANG Ru-cheng1，LIN Cheng-yi2，ZHANG Fu-sheng2， ZHANG Wen-1an1

2001, 7(4): 488-488.

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GRV9927 meteorite from the Antarctica is composed of olivine and pyroxene. It is similar to ALHA77005 martian meteorite through igneous differentiation

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