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Indian Ocean-MORB-type isotopic signature of Yushigou ophiolite in North Qilian Mountains and its implications

Science china earth {2. 2006年第6期49卷 561-572页

作者： HOU Qingye1,2. ZHAO Zhidan1,2. ZHANG Hongfei3. ZHANG Benren3.& CHEN Yuelong2.1. State Key Laboratory of Geological Processes and {3. resources,{2., Beijing 100083. china 2. School of earth Science and {3. resources,{2., Beijing 100083. china 3. Faculty of earth {12.,{2., Wuhan 43.074, china State Key Laboratory of Geological Processes and mineral resources China University of Geosciences Beijing China School of earth Science and mineral {2. China University of Geosciences Beijing China Faculty of earth sciences China University of Geosciences Wuhan China

In order to explore the disputed issue concerning the tectonic affinity ofthe ancient ocean mantle of North Qilian Mountains (NQM), geochemical and Sr, Nd, Pb isotopiccompositions of pillow basalts of the Yushigou Ophiolite (YSGO) suite from NQM have been analyzedsystematically. The pillow basalts exhibit tholeiitic characteristics, with flatchondrite-normalized REE patterns ((La/Yb)_N = 0.98—1.2.). They display no Nb, Ta, Zr, Hf negativeanomalies, and show MORB features in 2.b-Zr/4-Y and Ti/100-Zr-YX3.tectonic discrimination *** results indicate that the Yushigou ophiolite is most likely to be formed in a mid-ocean ridgeor mature back-arc basin. Their isotopic data show a relatively broad and enriched ^(87)Sr/^(86)Sr(0.70509 — 0.70700), restricted ^(143.Nd/^(144)Nd (0.512.55-0.512.78). Pb isotopes are in the rangeof ^(2.6)Pb/^(2.4)Pb (18.054-2..562., ^(2.7)Pb/^(2.4)Pb (15.53.-15.743. and ^(2.8)Pb/^(2.4)Pb(3..068-3..53.). These isotopic data imply that the basalts originated from the depleted mantle(DMM), with the involvement of enriched mantle components (mainly EMII). Geochemical comparisonsbetween the basalts in YSGO and the MORB-type basalts of ophiolite suites occurring in the knownancient Tethyan tectonic domain indicate that the ancient oceanic mantle represented by YSGO suiteforming in early Paleozoic in the North Qilian Moutains is very similar to the Tethyan mantle inboth trace elements and isotopic compositions. The North Qilian Mountains should be a part of theTethyan tectonic domain in early Paleozoic. This further implies that the Tethyan tectonic domaincan be deduced to early Paleozoic in the study area, which will be helpful to discussing thetectonic affinity and evolution of the North Qilian Mountains.

关键词： geochemistry, Indian Ocean-MORB-type isotopic signatures, Tethyan tectonic domain, Yushigou ophiolite, North Qilian Mountains.

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Science china earth {2. 2004年第10期47卷 896-911页

作者： ZHANG Changhou1,2. WU Ganguo1,2. WANG Genhou2. ZHANG Weijie2.& SONG Honglin2.1. Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology, china university of geosciences, Ministry of Education of china, Beijing {2. china 2. School of earth sciences and mineral {13., china university of geosciences, Beijing {2. china Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology China University of Geosciences Ministry of Education of China Beijing China School of earth sciences and {2. {3. China University of Geosciences Beijing China

The northwest trending tectonic belt in the middle part of the Mesozoic intraplate Yanshan Orogenic Belt, northeast Hebei Province, is composed of thrusts, extensional faults, strike-slip faults and syntectonic sedimentations as well. The northeastward basement-involved major thrusting deformation occurred between 174Ma and 168MaBP and was followed by an intrusion of the granitic plutonic rocks. As a part of the post-thrusting extensional deformations a northwest extending volcano-sedimentation system of Late Jurassic and Early Cretaceous formed in the southwest side of the belt. These volcano-sedimentary sequences are divided into Tuchengzi Formation, Zhangjiakou Formation, Yixian Formation and Jiufotang Formation re- spectively. They are characterized by southeastward migration as a result of the increasing down-dip slip displacement along the major extensional fault toward the southeast of the belt. The provenance area of the Jiufotang Formation north to it experienced southwestward thrusting during and after its later sedimentation. The thrusting in this stage resulted in the formation of an asymmetric footwall syncline with vergence to SW in the Jiufotang Formation in the NE side of the basin. Finally a dextral strike-slip deformation occurred along the NW tectonic belt. The striking tectono-geomorphological features and present seismic activities along this belt indicate that it has been being active since Cenozoic era and is still in the active state at present. This northwest extending tectonic belt was following the same direction and location as the existing fault systems within the basement as revealed by former geological and geophysical studies. So it is reasonable to infer the Mesozoic deformation along this belt to be a result of reactivation of the basement structures in a favorable tectonic stress field. The reactivation of basement struc- tures might be taken as one of the mechanisms of intraplate deformation and orogeny.

关键词： Yanshan Orogenic Belt, northwest extending tectonic complex, thrust system, geochronology.

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The role of aerial algae in the formation of the landscape of the Yunnan Stone Forest,Yunnan Province, china

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Science china earth {2. 2004年第9期47卷 846-864页

作者： TIAN Youping1,3. ZHANG Jie2. SONG Linhua1 & BAO Haosheng2.1. Institute of Geographic sciences and Natural {3. Research, Chinese Academy of sciences, Beijing 100101, china 2. Department of Geography, Nanjing university, Nanjing 2.0093. china 3. School of earth sciences and {3.,{13., Beijing 100083. china Institute of Geographic sciences and Natural resources Research Chinese Academy of Sciences Beijing China School of earth sciences and {2. China University of Geosciences Beijing China Department of Geography Nanjing University Nanjing China

Aerial algae on the surface of carbonate rocks at the Stone Forest, Shilin County, Yunnan Province, china, and their bioerosion were investigated in the field and studied in the laboratory in detail. Through the observation, identification and statistics of more than one hun- dred algal samples and rock samples with the optical microscopes (stereomicroscope, biological microscope) and the scanning electronic microscope (SEM), the relationships between erosional forms on the surface of the Stone Forest and algae and/or algal communities and the genetic mechanism for the formation of erosional forms were analyzed. It is suggested that aerial algae play an active role in bioerosive processes that may affect the formation of karst erosional forms. These effects include both direct and indirect ones. The direct effect is the initiative control (algal shape-controlling role) of algae on the formation of karst forms of various scales, mostly mi- cro-scale (3.) and minor-scale (10-3.10-1m) erosional forms. The algal shape-controlling roles can be divided into the algal individual shape-controlling role and the algal community shape-controlling role. The former mostly controls the formation of micro-scale erosional forms, while the latter mostly controls the formation of micro-scale and smaller minor-scale erosional forms. The indirect effect refers to the promoting role of algae in the formation of karst forms, which may affect the formation of karst forms of all types and scales. The bioerosion of algae accelerates the weathering process of the whole Stone Forest karst landforms.

关键词： aerial algae, bioerosion, the Stone Forest, Yunnan Province, china.

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Experimental remolding on the caprock's 3. strain field of the Indosinian-Yanshanian epoch in Tongling deposit concentrating area

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Science china earth {2. 2005年第7期48卷 863-874页

作者： DENG Jun1,HUANG Dinghua2.WANG Qingfei1,WAN Li1,SUN Zhongshi3.YANG Liqiang1 & GAO Bangfei1 1. State Key Laboratory of Geological Processes and mineral resources,{2. university of geosciences,Beijing 100083.{2. 2. Faculty of earth sciences,{2. university of geosciences,Wuhan 43.074,{2. 3. Department of earth sciences,Jilin university,Changchun 13.061,{2. State Key Laboratory of Geological Processes and mineral resources China University of Geosciences Beijing 100083 China Faculty of earth sciences China University of Geosciences Wuhan 430074 China Department of earth sciences Jilin University Changchun 130061 China

Based on field observations and rheology analysis, we perform one analogue experiment and remold the 3. structural frame of Tongling deposit concentrating area firstly. Then we disassemble and dialyze the 3. structures of the model using the methods of "slicing" and "stripping". A series of sliced planes vertical to the fold hinges show similar landscapes of that in the drill hole profiles. Meanwhile, layer stripping analysis indicates that the deformation features of each layer in the model are qualitatively analogical to those obtained from field observations. Through contrasting the 3. structure between the experimental model and the field phenomena, we verify the following 3. deformation features of the caprock in this area: (1) the Tongling area mainly consists of three series of NE S-typed fold groups; (2. in the uniform stress field, the incoherent folds universally develop in different positions, along different axes as well as in different strata; (3. the faults propagate upward which are mostly inter-bedded detachment faults, while the fold amplitudes decrease while going deeper; and (4) the folds and cleavages are highly developed in the Silurian System indicating that the deformation effect of the Indosin-ian-Yanshanian structural layer terminates at this layer, which suggests that the Silurian System is the crucial layer for the inversion between brittle and plastic deformation domains and the underlying strata are subject to the control of another deformation system with distinct properties.

关键词： Tongling deposit concentrating area Indosinian-Yanshanian epoch 3. structural frame of the caprock analogue experiment slicing and stripping analysis structural model.

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The species diversity of fusulinaceans and high-frequency sea-level changes in the Carboniferous-Permian boundary section at Xikou, Zhen'an County,Shaanxi Province, china

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Science china earth {2. 2006年第7期49卷 673-683页

作者： ZHANG Haijun1, WANG Xunlian2. DING Lin1, XIA Guoying3.& WANG Lei2.1. Institute of Tibetan Plateau Research, Chinese Academy of sciences, Beijing 100085, {3. 2. Faculty of {2. sciences and mineral resources, china university of geosciences, Beijing 100083. {3. 3. Tianjin Institute of Geology and mineral resources, Tianjin 3.0170, {3. Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China Faculty of earth sciences and {2. {3. China University of Geosciences Beijing China Tianjin Institute of Geology and mineral resources Tianjin China

The study on the interrelation between sea-level changes and biodiversity with its evolu-tion has great significance for understanding the impact of global changes on organic evolution and exploring the inherent laws of life-environment coevolution in geological history. In this paper, the stratigraphic distribution of fusulinacean fauna in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, is analyzed quantitatively, and the relationship between the species diversity of fusulinaceans and relative sea-level changes is discussed. As a whole, the spe-cies numbers of fusulinacean fauna experience a rapid increase and an obvious decline in Xikou, Zhen’an County, from the Late Carboniferous to the Early Permian. There is a significant increase in species diversity around the Carboniferous-Permian boundary, which is one of the biggest bio-events of the fusulinacean fauna, and represents the radiation of Pseudoschwagerininae subfamily in the studied area. Integrated fusulinacean species diversity into sequence stratigraphic framework, de-tailed study suggests that the species diversity of the fusulinaceans is closely related to its relative stratigraphic location, and is essentially controlled by the sea-level changes, especially by the high-frequency sea-level changes. Generally, the species diversity of fusulinaceans is low, and the number of first and last appearance datum is small in the lower unit of high-frequency depositional cycle formed during the quick rise of the sea level; whereas the species diversity of fusulinaceans is high, and the number of first and last appearance datum is large in the upper unit of high-frequency cycle formed during the slow fall of the sea level. Within the third-order depositional sequence, the species diversity of the fusulinaceans at the first flooding surfaces and the maximum flooding surfaces is low, and it increases upward. The fusulinacean species diversity is low within the transgressive syst

关键词： fusulinaceans, species diversity, high-frequency cyclothem, sequence stratigraphy, sea-level changes, Carboniferous-Permian boundary, Zhen'an, Shaanxi.

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Exsolution of ilmenite and Cr-Ti magnetite from olivine of garnet-wehrlite

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Science china earth {2. 2005年第9期48卷 1368-1376页

作者： LIU Xiangwen1,2. JIN Zhenmin1,3. QU Jing2.& WANG Lu2.1. State Key Laboratory of Geological Processes and {3. resources,{2., Wuhan 43.074, china 2. Graduate School of{2., Wuhan 43.074, china 3. Faculty of earth sciences,{2., Wuhan 43.074, china State Key Laboratory of Geological Processes and mineral resources China University of Geosciences Wuhan China Graduate School of china university of geosciences Wuhan China Faculty of earth sciences China University of Geosciences Wuhan China

Exsolution of rod-like ilmenite (Ilm) and Cr-Ti magnetite (Mt) have been found in olivine of garnet-wehrlite from the core of Chinese Continental sciences Drilling (CCSD). Their composition, morphology, crystal structure and their topotaxies with host olivine have been studied in detail by the transmission electron microscopy (TEM) and electron probe microanaly- sis (EPMA) technique. It shows that rod-like Ilm exsolution reported in this paper has similar characteristic with that of Alpe Arami olivine, while Cr-Ti magnetite exsolution mentioned in this paper has large discrepancy with chromite exsolution in Alpe Arami olivine. These observations suggest that both of the exsolutions found in this paper should be solid solution phases in β-olivine at their first period, then experiencing decomposition of solid solution and therefore forming Ilm and Cr-Ti magnetite exsolution with the pressure decreasing. So, this garnet-wehrlite perhaps had been ever located in mantle transition zone with a minimum depth of 3.0 km.

关键词： garnet-wehrlite, ilmenite, magnetite, exsolution, CCSD.

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Petrogenesis and dating of the Kangding complex,Sichuan Province

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Science china earth {2. 2005年第5期48卷 622-634页

作者： CHEN Yuelong 1 , LUO Zhaohua 1 , ZHAO Junxiang, LI Zhihong, ZHANG Hongfei & SONG Biao 3.1. Faculty of earth sciences and Natural {2.,{3., Beijing 100083. china 2. Faculty of earth sciences,{3., Wuhan 43.074, china 3. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological sciences, Beijing 10003., china Faculty of earth sciences and Natural {2. China University of Geosciences Beijing China Faculty of earth sciences China University of Geosciences Wuhan China Beijing SHRIMP Center Institute of Geology Chinese Academy of Geological Sciences Beijing China

An analysis of major and trace element geochemistry and SHRIMP U-Pb zircon dating of mafic, intermediate, and felsic rocks from the Mianning metamorphic complex of Si- chuan Province was conducted. One of our conclusions is that a majority of the zircons crystal- lized between 72. and 773.Ma in a magmatic regime. The complexes contain early to late Pa- leo-proterozoic relict zircons from ancient continental crust. The oldest age, 2.68 Ma, may rep- resent the basement of the Yangtze block. Overgrowth zircon rims and palingenetic zircons have been observed and dated, and are believed to have formed after crystallization, during Paleozoic and Mesozoic metamorphic-anatexis. We also conclude that depletion of Nb, Ta, HREE, in a spider-diagram normalized to primitive mantle and calc-alkaline association, implies that they formed in island-arc or under-plating settings.

关键词： Kangding complex, zircons, SHRIMP, tectonic setting.

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Pioneer organisms after F-F mass extinction in Dushan region,Guizhou Province,and their significance in establishing new ecosystem

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Science china earth {2. 2006年第5期49卷 449-460页

作者： WANG Yue1, 2. WANG Xunlian1 & SHI Xiaoying1 1. School of earth sciences and {2., china university of geosciences, Beijing 100083. china 2. School of {2. and Environment, Guizhou university, Guiyang 550003. china School of earth sciences and {2. China University of Geosciences Beijing China School of resources and Environment Guizhou University Guiyang China

After mass extinctions, most areas became “ecologically barren areas” lacking or even without ecosystem over an extensive region. Studying the pioneer organisms and the reconstruction process of a new ecosystem in the “ecologically barren area” is very important for revealing the evo- lution after bio-mass extinctions. In the Dushan region, Guizhou Province, china, the trace fossils appeared and flourished evidently earlier than body fossils after Frasnian-Famennian (F-F) mass extinction. The pioneer organisms and pathfinders in the “ecologically barren areas” are the trace-makers that are deposit-feeders with relatively simple structure and conformation on or near the deposit surface. The trace-makers have undergone an evolutionary process that their trace structures changed from simple to complex, and their living and moving areas and spaces enlarged from linear to planar and then to three-dimension spaces. Those characters show that the ability of the trace-makers to deposits and their efficiency of looking for food have been enhanced gradually and that those trace-makers constructed gradually a base for the new ecosystem. This process is similar to that of the trace fossils near the Precambrian-Cambrian boundary. In the Dushan area, only the recovery intervals have been identified for the Famennian body fossils, with no eminent radiation interval recognizable due to the Devonian-Carboniferous (C-D) mass ex- tinction. However, both the recovery and radiation intervals may be clearly recognized in the Famen- nian trace fossils based on their conformation and diversity. The evolution and diversification of the trace fossils in the “ecologically barren area” is considered to have played a role of necessary foun- dation for the recovery of body fossils in the ecological chain. With the gradual disappearance of the unfavourable environment factors resulting in the F-F mass extinction, a new ecosystem was reconstructed in the “ecologically barren area” through a three-

关键词： pioneer organisms, reconstruction of ecosystem, trace fossils, F-F mass extinction, Later Devonian, Dushan region, Guizhou Province, china.

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Transport network and flow mechanism of shallow ore-bearing magma in Tongling ore cluster area

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Science china earth {2. 2006年第4期49卷 397-407页

作者： DENG Jun1,2. WANG Qingfei1,2., HUANG Dinghua3., WAN Li4, YANG Liqiang1,2.& GAO Bangfei1,2.1. State Key Laboratory of Geological Processes and mineral resources,{2., Beijing 100083. china 2. Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, china university of Geo- sciences, Beijing 100083. china 3. Faculty of earth sciences,{2., Wuhan 43.074, china 4. School of Mathematics and Information Science, Guangzhou university, Guangzhou 510405, china State Key Laboratory of Geological Processes and mineral resources China University of Geosciences Beijing China Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education China University of Geosciences Beijing China Faculty of earth sciences China University of Geosciences Wuhan China School of Mathematics and Information Science Guangzhou University Guangzhou China

Abundant studies revealed that shallow intrusions of the Yanshanian epoch resulted in the mass mineralization of the Tongling region. Various evidences showed there existed a concealed magma chamber at ?10 km depth in the middle part of this region during Yanshanian epoch, from which the ore-forming magma was generated and then transported to the superficial layer. Yet the transport network and flow mechanism of the shallow ore-bearing magma, the key problem associ- ated with ore-forming process, was relatively little focused on. Integrate analysis of structural me- chanics, statistical fractal and geological facts suggested that NE trending high-angle fold-related thrust faults and the tessellated basement ones served as the main pathways for the shallow magma’s transporting, moreover, the saddle void spaces among adjacent strata in the folds upon this fault system provided the place for magma’s emplacement. So the folds in the upper part and faults in the lower part of the upper crust constituted the fluid’s transport and emplacement network. During the deformation of geologic body with multi-layer structure, the layers in the upper part tended to fold when received the jacking stress from the lower part, while the lower one inclined to fault undergoing loads of the upper part. And the producing probability of this structure assemblage was highly in- creased in the condition, such as in the Tongling area, that the mechanic rigidity of the lower layers was stronger than that of the upper ones. For the pre-existence of fluid-conducting network, the top magma with high volatile in the magma chamber transported rapidly to the superficial layer in dyking pattern, located in the void spaces of folds, filled and reconstructed them. The sudden drop of pres- sure caused the fluid unmixing from the magma and mass ore-forming elements concentration. Pulse activity of the dyking may be the principal reason why magmatic bodies in the Tongling area were spatially-temporally con

关键词： Tongling, structural network, magma intrusion, fractal, dyke.

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On the siltation of the middle Yangtze River

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Science china earth {2. 2004年第5期47卷 463-480页

作者： YIN Hongfu1, CHEN Guojin2. LI Chang抋n1 & WEI Yuan3.1. School of earth sciences,{2., Wuhan 43.074, china 2. Hydrogeological Team, Hubei Bureau of Geology and mineral resources, Jingzhou 43.100, china 3. Geological Survey of Jiangxi Province, Nanchang 3.02.1, china School of earth sciences China University of Geosciences Wuhan 430074 China Hydrogeological Team Hubei Bureau of Geol./Mineral Rsrc. Jingzhou 434100 China Geological Survey of Jiangxi Prov. Nanchang 330201 China

About 5.2.108 t/a of silts from the upper reach of the Yangtze River are transported through Yichang into the middle Yangtze River. The middle Yangtze itself and its tributaries yield ca. 0.8×108 t silts annually. Of this total 6×108 t/a input of silts, ca. 1.2.108 t/a are deposited within the river artery and lakes, while ca 4.83.108 t/a are at first transported into the lower reach through Datong, and then either deposited along the river and the Yangtze Delta, or output into the sea. Along the middle Yangtze River silting generally exceeds scouring, but the spatial and temporal distributions of scour-and-fill, as well as its distribution in the river valley transections, are uneven. Along the Yichang-Chenglingji and Jiujiang-Datong Segments of the middle Yangtze, scouring exceeds or equals silting. Silting mainly occurs along the Luoshan-Wuhan-Huangshi Segments with Wuhan as the pivotal point, as well as in the Dongting and Poyang Lakes. Even in these silting-dominated areas, there are times and parts of segments that scouring prevails. As to the transections, generally the river channel of main stream is scouring-dominated, forming V-shaped sections to a depth of 2.3. m or more, whereas the floodplains and bar islands are silting-dominated, forming wide and relatively high flats, which are often artificially transformed into protected embankments. Because the Jingjiang Levee separates the Jianghan Plain from Yangtze to the south, little has been deposited in that plain except a few sediments from the Han River—a tributary of the middle Yangtze. This factor plus the tectonic sag of that plain has made the altitude of plain surface several meters lower than that of the levee in most of the areas. Sil-tation along the Luoshan-Wuhan-Huangshi Segments has resulted in the elevation of flood level in this and upstream segments. River channel scouring plus floodplain silting have caused the transections of the middle Yangtze valley typically with deep channel and height

关键词： the middle Yangtze, scour-and-fill, siltation, silt utilization.

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