Chief Editor:HOU Zengqian
Governing Body:China Association for Science and Technology
Organizer:Geological Society of China
start publication :1922
ISSN:ISSN 1000-9515
CN:CN 11-2001/P
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ZHU Dagang , ZHAO Xitao , MENG Xiangang , WU Zhonghai , WU Zhenhan , FENG Xiangyang , SHAO Zhaogang , LIU Qisheng , YANG MailingInstitute of Geomechanics , Chinese Academy of Geological Sciences , Beijing Institute of Geology , Geophysics , Chinese Academy of Sciences , Beijing Fei Zhenbi
2002, 76(3).
Abstract:Shorelines are widespread and lake deposits and lake geomorphology are well developed on the northern Tibetan Plateau. Through field observations of lacustrine deposits of Nam Co-the highest and largest Quaternary lake in Tibet, the authors found four-step shore terraces composed of sands and clays with well-developed horizontal bedding and 3-12 m, 15-22 m, 25-30 m and 35-45 m higher than the lake surface respectively, lacustrine deposits resting on the bedrocks and 60-150 m higher than the lake surface, and up to -50 levees composed of oblate lakeshore gravels. Moreover they found lacustrine and lakeshore deposits making up the terraces and levees on the bottoms of wide dividing valleys connecting Nam Co with the Rencoyuema, Rencogongma and Jiuru Co northwest of Nam Co (the valley bottoms are 20 m, 90 m and 60 m higher than the above-mentioned three lakes) and on slopes north of it, i.e. terraces II and III of Nam Co. Thus they confirm that Nam Co and Ring Co-Jiuru Co had connected with each other several times, i.e. formed a unified large lake several times, rather than had been different lakes connected only by river channels. From indications such as the distribution of the highest shoreline and lake deposits and geomorphology, the authors conclude that the total area of the old large lakes on the northern Tibetan Plateau is a few times larger than that of the modern lakes and that the last-stage old large lakes formed in the interglacial interval of the last glaciation.
LIU Junlai Department of Geology , Jilin University , Changchun , ChinaKlaus WEBERInstitute of Geology , Dynamics of the Lithosphere , University of Goettingen , Goettingen , Germany
2002, 76(3).
Abstract:Optical, cathodoluminescence and transmission electron microscope (TEM) analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclastic coarse-grained marbles from two fault zones, and a fractured mylonite. These fault rocks show similar microstructural characteristics and give clues to similar processes of rock deformation. They are characterized by the structural contrast between macroscopic cataclastic (brittle) and microscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e. deformation twins, kink bands and microfractures) are well preserved in the deformed grains in clasts or in primary rocks. The matrix materials are of extremely fine grains with diffusive features. Dislocation microstructures for co-existing brittle deformation and crystalline plasticity were revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformed clasts, while dislocation walls form in the transitions to the fine-grained
WU Shiguo Institute of Oceanology , Chinese Academy of Sciences , Nanhai Road , Qingdao , ChinaIzumi SAKAMOTO Japan Marine Science & Technology Center , Natsushima - , Yokusuka - , JapanXU JirenInstitute of Geology , Chinese Academy of Geological Sciences , Baiwanzhuang Road , Beijing , China , How Kin WONGInstitute of Geochemistry , Marine Chemistry , University of Hamburg , Bundesstrasse , D- Hamburg , Germany
2002, 76(3).
Abstract:Offshore active faults, especially those in the deep sea, are very difficult to study because of the water and sedimentary cover. To characterize the nature and geometry of offshore active faults, a combination of methods must be employed. Generally, seismic profiling is used to map these faults, but often only fault-related folds rather than fracture planes are imaged. Multi-beam swath bathymetry provides information on the structure and growth history of a fault because movements of an active fault are reflected in the bottom morphology. Submersible and deep-tow surveys allow direct observations of deformations on the seafloor (including fracture zones and microstructures). In the deep sea, linearly aligned cold seep communities provide indirect evidence for active faults and the spatial migration of their activities.The Western Sagami Bay fault (WSBF) in the western Sagami Bay off central Japan is an active fault that has been studied in detail using the above methods. The bottom morphology, fractured breccias directly observed and photographed, seismic profiles, as well as distribution and migration of cold seep communities provide evidence for the nature and geometry of the fault. Focal mechanism solutions of selected earthquakes in the western Sagami Bay during the period from 1900 to 1995 show that the maximum compression trends NW-SE and the minimum stress axis strikes NE-SW, a stress pattern indicating a left-lateral strike-slip fault.
SHU Liangshu , J. CHARVET , LU Huafu , S.C. LAURENT Department of Earth Sciences , State Key Laboratory of Metallization , NanjingUniversity , Nanjing , China UMR , CNRS FR , Departement des Sciences de la Terre , Universite d''''Orleans , Orleans , France
2002, 76(3).
Abstract:The Tianshan range could have been built by both late Early Paleozoic accretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture is marked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphic relics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanic arc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along with unconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation. The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductile shearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductile deformation, and the later deformation, a dextral strike-slip tectonic process, occurred during the Late Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably on pre-Carboniferous metamorphic and ductilely sheared rocks, implying the end of the early orogeny. The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by the second tectonic event, the Hercynian collision between the northern Tarim block and the southern Siberian block. Late Paleozoic granitic magmatism and superimposed structures overprinted this Early Paleozoic deformation belt. Results of geometric and kinematic studies suggest that the primary framework of the Southern-Central Tianshan belt, at least the eastern pan of the Tianshan belt, was built by these two phases of accretion events.
LIN Changsong , ZHANG Yanmei , LI Sitian , LIU Jingyan , TONG Zhigang , DING Xiaozhong , LI Xichen Department of Energy Resources , China University of Geosciences , Beijing Department of Computer Sciences , China University of Geosciences , Beijing Research Institute of Sedimentary Basin , Mineral Resources , China Universityof Geosciences , Wuhan Exploration , Development Research Centre , China National Offshore Oil Corp. , Gaobeidian
2002, 76(3).
Abstract:The stretching process of some Tertiary rift basins in eastern China is characterized by multiphase rifting. A multiple instantaneous uniform stretching model is proposed in this paper to simulate the formation of the basins as the rifting process cannot be accurately described by a simple (one episode) stretching model. The study shows that the multiphase stretching model, combined with the back-stripping technique, can be used to reconstruct the subsidence history and the stretching process of the lithosphere, and to evaluate the depth to the top of the asthenosphere and the deep thermal evolution of the basins. The calculated results obtained by applying the quantitative model to the episodic rifting process of the Tertiary Qiongdongnan and Yinggehai basins in the South China Sea are in agreement with geophysical data and geological observations. This provides a new method for quantitative evaluation of the geodynamic process of multiphase rifting occurring during the Tertiary in eastern China.
ZHANG Jianxin , YANG Jingsui , XU Zhiqin , WAN Yusheng , MENG Fancong , LI Haibing , SHI Rendeng , SONG Shuguang Institute of Geology , Chinese Academy of Geological Sciences , Beijing
2002, 76(3).
Abstract:Eclogites have been recently discovered in the Xitieshan area in the middle segment of the northern margin of the Qaidam basin. These eclogites, together with those recognized earlier in the Yuka area of the western segment of the northern margin of the Qaidam basin and in the Dulan area of the eastern segment of the northern margin of the Qaidam basin, form an eclogite belt with a length of 350 km. A comparison of the eclogites from the Yuka and Xitieshan areas suggests that they show different country rocks, microtextures, mineral assemblages, and especially, different peak temperatures, PT paths during decompression and isotopic features. Eclogites from the Yuka area bear evidence of prograde metamorphism, such as prograde mineral relics in garnet and growth zoning of garnet, and hairpin-shaped PT paths with coincidence of the baric and thermal peaks of metamorphism, which reflect rapid burial and uplift. Sm-Nd isotopic determination shows obvious Sm-Nd disequilibrium, and no isochron ages of Early Paleozoic metamorphism was obtained. On the contrary, the Xitieshan eclogite was subjected to metamorphism of higher eclogite-facies and post-eclogite-facies temperatures, showing an obvious granulite-facies overprint. A tentative PT path for the Xitieshan area suggests that the baric peak preceded the thermal culmination. Whole rock-gamet-omphacite Sm-Nd isotopic data give an isochron age in the Early Paleozoic. The differences between the two eclogites imply their different tectonic-thermal history during their burial and uplift.
YE Song , ZHANG Baoming , DI Jinru , YANG Mei , YE Delong China University of Geosciences , Wuhan , Hubei , China
2002, 76(3).
Abstract:This paper studies the hydrous facies of mantle-derived megacryst clinopyroxenes and pyroxenes of xeno-liths of pyroxenolite and spinel peridotite as well as garnet pyroxenolite in a kimberlitic lamprophyre pipe in Anyuan, Jiangxi, by Fourier Transform Infrared (FTIR). It explores the relationship between the water content of pyroxene on the one hand and its composition and source depths on the other hand. All the samples contain constitution water. Spectra of the clinopyroxene are dominated by two groups of bands: 3607-3630 cm-1 and 3522-3542 cm-1. Spectra of the orthopy-roxene are dominated by three groups of bands: 3410-3424 cm-1,3510-3516 cm-1 and 3560-3595 cm-1. The water content of the clinopyroxenes has a positive correlation with their FeO and Al2O3 contents. The source depths of mantle-derived clinopyroxene megacrysts, pyroxenolite, spinel peritotite and garnet pyroxenelite increase gradually in order. The Al2O3 and water contents of four pyroxenes have similar correlation with the source depths.
JIANG Yaohui , LING Hongfei , JIANG Shaoyong , ZHOU Xunruo , RUI Xingjian , YANG Wanzhi State Key Laboratory for Mineral Deposits Research , Department of Earth Sciences , Nanjing University , Nanjing Nanjing Institute of Geology , Mineral Resources , Nanjing China University of Geosciences , Beijing Xinjiang Geophysical , Geochemical Exploration Party , Changji
2002, 76(3).
Abstract:Taking the Himalayan granitoids around Kunjirap in the western Qinghai-Tibet plateau as an example, the authors present in this paper the characteristics of the granitoids rich in mantle-derived fluid components and discuss their rock-forming mechanism. The research results indicate that the rock assemblage of the studied granitoids involves diopside syenite-diopside granite-biotite (monzonitic) granite, consisting mainly of K-feldspar, oligoclase, quartz, iron-phlogolite, diopside and edenite. The rocks are rich in mantle-derived fluid components of volatiles including F, alkali metal elements such as K, Na, Rb, Sr and Ba, and radiogenic heat-producing elements such as U and Th. They were generated by the influx of mantle-derived fluids into the lower crust to give rise to partial melting during the lithosphere thinning in the Qinghai-Tibet plateau.
ZHANG Ronghua , HU Shumin , SU YanfengOpen Research Laboratory of Geochemical Kinetics , Institute of Mineral Resources , Chinese Academy of Geological Sciences , Baiwanzhuang Road , Beijing , China
2002, 76(3).
Abstract:This study reports the kinetic experimental results of albite in water and in KCI solution at 22 MPa in the temperature range of 25 to 400℃. Kinetic experiments have been carried out in an open flow-through reaction system (packed bed reactor). Albite dissolution is always incongruent in water at most temperatures, but becomes congruent at 300℃ (close to the critical point 374℃). At temperatures from 25 to 300℃, the incongruent dissolution of albite is reflected by the fact that sodium and aluminum are easily dissolved into water; from 300 to 400℃ it is reflected by silicon being more easily dissolved in water than Al and Na. Maximum albite dissolution rates in the flow hydrothermal systems have been repeatedly observed at 300℃, independent of flow rates.The kinetic experiments of albite dissolution in a KCl aqueous solution (0.1 mol KCl) indicate that the dissolution rate of albite increases with increasing temperature. Maximum silicon release rates of albite have been observed at 400℃, while ma
TANG Zhongli , BAI Yunlai , LI Zhilin Gansu Bureau of Geology , Mineral Exploration , Development , Hongxingxiang , Lanzhou , Gansu Province China University of Geosciences , Beijing
2002, 76(3).
Abstract:The geotectonic setting refers to the three-dimensional space and related events based on which a metallogenic system is formed and an ore-forming process takes place. This paper discusses the tectonic evolution of the southwestern margin of the North China paleocontinent and related geotectonic settings in which large or superlarge deposits are formed. Emphasis is put on the geodynamic conditions of the Jinchuan nickel-copper deposit, the Baiyin copper-polymetallic deposit and the Hanshan gold deposit. It is significant that the three deposits occur together as a "trinity" on the same paleocontinental margin. The Jinchuan nickel-copper deposit was formed during the early stage of rifting of the paleocontinental margin; the Baiyin copper-polymetallic deposit was formed during the splitting stage of a continental-margin arc. The continental-margin arc spitting resulted in an "island arc rift" in the early stage of evolution. The Hanshan gold deposit was formed within the Altun sinistral strike-slip fault system and its provenance is the "intraoceanic arc" volcanic rocks.
LI Changjiang , MA Tuhua , ZHU Xingsheng , WANG Guowu Zhejiang Institute of Geology , Mineral Resources , Hangzhou , Zhejiang Earth Science Department , Zhejiang University , Hangzhou , Zhejiang Zhejiang Bureau of Geology , Mineral Exploration , Development , Hangzhou , Zhejiang
2002, 76(3).
Abstract:Mineralization distributions are very heterogeneous in nature. As large or superlarge mineral deposits are quite rare whether in time or in space, it is difficult to detect all the largest mineral deposits in a region in a limited period of time owing to the restriction of technology and exploration degrees-this is called "not all discovered". However, all discovered large, especially superlarge, mineral deposits generally have a complete census in the geological literatures. On the other hand, not all discovered small mineral deposits are recorded in the geological literatures because for economic reasons people have not much interest in them-this is called "not all recorded". This practice often results in the observation truncations, that is, the data points near the two ends in an observable population, which is obtained by fitting a power law size-frequency distribution to discovered mineral deposits in a given region, show concave-down departure from the correlation line fitted. The authors suggest that the size and number of undiscovered deposits may be forecast by fitting a fractal size distribution to discovered mineral deposit sizes between the upper and lower truncation observations and then extrapolating the scale-independent area to deposit sizes larger than the upper truncation limit. Based on the statistical results obtained by the fractal size-frequency distributions of 394 discovered gold deposits with sizes greater than 21 Au in China and 83 known gold deposits with sizes over 0.3 t Au in the Jiaodong area of China, the authors forecast according to the present commercial standards for gold ores that the total resources of undiscovered gold deposits ranging in tonnage from 50 to 2000 t Au are more than 4500 t in China, and that in the Jiaodong area of China the total resources of potential gold deposits with sizes in the range of 30 to 650t Au are about 700t.
2002, 76(3).
Abstract:At the end of the Oligocene, the "long-range effect" of the India-Eurasia collision terminated the link between the Tarim basin and the Paiaeo-Mediterranean and the Tarim basin started a development of continental basin. A very thick continental sequence mainly of fluvial-lacustrine facies deposited in the western Tarim basin in the Neogene. This sequence, composed mainly of clastic rocks with intercalation of evaporites, and of varying thickness with maximum of 6050 m, is classified into the
WEI Lejun , ZHENG Mianping , LIU Xifang , CAI Keqin , NIE Zhen Institute of Mineral Resources , Chinese Academy of Geological Sciences , Beijing China University of Geosciences , Beijing Open Laboratory of Saline Lake Resources & Environment , Chinese Academy of Geological Sciences , Beijing Fei Zhenbi
2002, 76(3).
Abstract:The authors investigated lacustrine chemical sediments on terrace-I of Dong Co-a salt lake in the interior of the northern Tibetan Plateau and firstly discovered borax and a complete sedimentary section with five pure mirabilite beds. According to the sedimentary characteristics of rhythmic layering, palaeotemperatures for the formation of the cold-phase mineral-mirabilite-at the profiles and 14C dating, the authors applied the theory and method of comparative salinology in the study of the history of the palaeoclimate and palaeoenvironment of Dong Co in the early and middle Holocene and drew the conclusion that the salt lake had experienced the following climatic evolution: the warm and moist stage (>8470 a BP and possibly to 10500 a BP)→cold and dry stage (8470-8170 a BP)→warm and moist stage (8170-7590 a BP)→stage of repeated climatic oscillations (7590-7400 a BP, alternation of three dry oscillations and three moist oscillations in a generally cold climatic background)→cold and dry stage (7400-6
Chief Editor:HOU Zengqian
Governing Body:China Association for Science and Technology
Organizer:Geological Society of China
start publication :1922
ISSN:ISSN 1000-9515
CN:CN 11-2001/P