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Re-Os age for molybdenite from the Gangdese porphyry copper belt on Tibetan plateau: Implication for geody- namic setting and duration of the Cu mineralization

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Science china Earth Sciences 2004年第3期47卷 221-231页

作者： HOU Zengqian1. QU Xiaoming1. WANG Shuxian2, DU Andao2, GAO Yongfeng3 & HUANG Wei4.1. {1. of Mineral Resources, Chinese Academy of Geological Sciences, {1. 1.0037, china 2. National Center of Geoanalysis, Chinese Academy of Geological Sciences, {1. 1.0037, china 3. Shijiazhuang College of Economy, Shijiazhuang 056000, china 4. Xizang Bureau of geology and Mineral Resources, Lhasa 850000, china institute of Mineral Resources Chinese Academy of Geological Sci. Beijing 100037 China National Center of Geoanalysis Chinese Academy of Geological Sci. Beijing 100037 China Shijiazhuang College of Economy Shijiazhuang 056000 China Xizang Bureau of Geol./Mineral Rsrc. Lhasa 850000 China

The Gangdese porphyry copper belt consists of one large and five middle-small deposits in addition to dozens of ore-bearing porphyry bodies. The belt trends 350 km long along the EW-striking Gangdese batholith, and locally occurs as a string of beads extending about 50 km within the SN-trending rifting zones (grabens) on the Tibetan plateau. Monzonitic granite- porphyry and quartz monzonitic porphyry, as dominant host rocks, are shoshonitic and potassic calc-alkaline. Available dating data indicate that the ages of the shallow-level emplacement for these porphyries vary from 1. Ma to 1. Ma, which are identical to that of associated potassic calc-alkaline volcanic rocks (1.—1. Ma) and mafic dykes (1.—1. Ma). The timing and duration of Cu mineralization events are constrained by Re-Os ages for molybdenites from three porphyry copper deposits in the Gangdese porphyry copper belt. Five molybdenite samples from the Nanmu deposit yielded an 1.7Re-1.7Os isochron with a highly pre-cise age of (1.0}76?.22) Ma; six molybdenites from the Chongjiang deposit gave an isochron age of (1.0}04..1.) Ma. Re-Os model ages for two molybdenite samples from Lakang抏 deposit vary from 1..5 Ma to 1..6 Ma, which are basically identical to isochron ages mentioned above. All the thirteen samples from these three deposits yielded a linear array in the isochron diagram with a higher correlation coefficient of 0.9971. and an isochron age of (1.0}39?.22) Ma (1. error), suggesting an coeval event of the Cu mineralization and a shared source of ore materials for the Gangdese porphyry copper belt. Compared with the longer-lived felsic magmatic-hydrothermal system, the Cu mineralization is a relatively short event with duration of about 0.5 Ma, and usu-ally occurs in the later-stage of the complicate magmatic system. The emplacement age of the Gangdese porphyries indicates that they intruded after the rapid rising of the Gangdese Mountains at 21.23 Ma, and formed in a post-collision crustal ex-tension env

关键词： porphyry copper deposit, Re-Os age, Gangdese, Tibetan plateau.

Paleomagnetic study on orogenic belt:An example from Early Cretaceous volcanic rocks,Inner Mongolia,china

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Science china Earth Sciences 2004年第12期47卷 1127-1133页

作者： REN Shoumai 1.2 ,ZHU Rixiang 1.,HUANG Baochun 1.,ZHANG Fuqin 1.& WANG Hongqiang 1.1.institute of {1. and geophysics,Chinese Academy of Sciences,beijing {4.,china 2.Strategic Research Center for Oil and Natural Gas,The Ministry of Land and Resources of china,beijing 1.0034.china Strategic Research Center for Oil and Natural Gas The Ministry of Land and Resources of China Beijing China Chinese Academy of Sciences Institute of Geology and Geophysics Beijing China

We report paleomagnetic results for Early Cretaceous lava flows collected from the Suhongtu area of Inner Mongolia, the middle part of the Tianshan-Mongolia Fold Belt (TMFB). Rock-magnetic experiments for different lava flows indicate that the main magnetic mineral is pseudo-single-domain (PSD) magnetite. The characteristic high-temperature remanence com- ponent is isolated by thermal demagnetization temperature steps between 300°C and 585"C, which yields a mean direction of D = 23.6°, I=56.0° with α 95 = 2.3°. We interpret this high-temperature remanence component as primary magnetization based mainly upon the petrographic analysis, which shows that the shape of magnetite crystal is relatively rounded square or polygon without internal reflection and deuterogenous phenomenon. The correspond- ing pole of the high-temperature remanence component is at 71.1.N, 200.5°E with A 95 = 2.7°. This Early Cretaceous pole is in good agreement with those for Siberia, North china, and Inner Mongolia, suggesting that these continental blocks had already sutured together in the Early Cretaceous, which would further provide constraints on better understanding of the formation and evolution of the TMFB.

关键词： orogenic belt, paleomagnetism, Suhongtu of Inner Mongolia, Eurasia.

Kinematics and dynamics of the Mesozoic orogeny and late-orogenic extensional collapse in the Sino-Mongolian border areas

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Science china Earth Sciences 2005年第7期48卷 849-862页

作者： ZHENG Yadong 1.& WANG Tao2 1. Key Laboratory of Orogenic Belts and Crustal Evolution (Peking University), Ministry of Education, beijing 1.0871.{1. 2. institute of geology, Chinese Academy of Geological Sciences, beijing 1.0037,{1. Key Laboratory of Orogenic Belts and Crustal Evolution (Peking University) Ministry of Education Beijing 100871 China institute of {1. Chinese Academy of Geological Sciences Beijinq 100037 China

The Sino-Mongolian border areas underwent two important tectonic events during Mesozoic time after late Paleozoic orogeny: a late Triassic to earlier Jurassic contractional event that resulted in a large-scale south-vergent thrust during the orogeny and a late Jurassic-earlier Cretaceous extensional event in a north-south direction that formed a metamorphic core complex. The kinematic and dynamic analyses show that the thrust sheet moved southwards with a kinematic vorticity number of ca. -0.1. and sub-horizontal maximum compressive stress axis that belongs to a contraction-thickening shear. The upper plate of the late-orogenic detachment relatively moved in a 1.5°direction. The average kinematic vorticity in its earlier stage was 0.74.that belongs to simple shear dominated shearing and related to the maximum compressive stress axes dipping at ～66°, while the later average kinematic vorticity was ～0.55°that belongs to pure shear dominated shearing with sub-vertical maximum compressive stress axes. This suggests that the thrusting led to the crust thickened and the lower plate rocks that were originally located in the upper crust depressed through a brittle-ductile transition zone into the lower crust and became warmer. The heated rocks trended to uplift since their increasing volume and decreasing density while the loading of the upper-plate rocks increased due to the structural thickening. Under the combined effect of the loading and the thermal-uplifting, the ductile shear zone in between increased in its component of vertical pure shear. Once its pure-shear component exceeded its simple-shear one the ductile shear zone became an extension-thinned shear zone. This progressive transitional process reflects internal and essential temporal and spatial relationships: the extensional factor nucleated during the crust thickening by thrusting and increase of the extensional factor finally led to late-orogenic collapse.

关键词： Mesozoic thrusting,late-orogenic collapse,kinematic vorticity number,stress state.

Gas formation mechanism of marine carbonate source rocks in china

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Science china Earth Sciences 2005年第4期48卷 441-453页

作者： ZHAO Wenzhi1. WANG Zhaoyun1. HE Haiqing2, ZHANG Mingjie3, WANG Hongjun1. WANG Yunpeng4.& QIN Yong5 1. Research {1. of Petroleum Exploration & Development, Petro{1., beijing 1.0083, china 2. Petro{1. Exploration & Production, beijing 1.001., china 3. Department of geology, Lanzhou University, Lanzhou 730000, china 4. Guangzhou Geochemical {1., Chinese Academy of Sciences, Guangzhou 51.64., china 5. china University of Mining and Technology, Xuzhou 221.00, china Research institute of Petroleum Exploration & Development PetroChinaBeijin China Petrochina Exploration & Production Beijing China Department of geology Lanzhou University Lanzhou China Guangzhou Geochemical institute Chinese Academy of Sciences Guangzhou China china University of Mining and Technology Xuzhou China

By breaking through the conventional ideology on the study of gas-formation mechanism of source rocks which focused on merely the characteristics of source rocks them- selves, and based on the development and distribution characteristics of marine carbonate source rocks in the medium-to-bottom parts of the Chinese superimposed sedimentary basins as well as various processes in the course of gas generation and reservoir forming, the complex hydrocarbon-generating model of carbonates is established. Such a model concerns not only the “three-stage” gas formation characteristics of carbonates, but also the gas generation process due to a thermal cracking of oil and the re-generation process of gas from heated secondary organic matters during the gas-generation and reservoir-forming course. The high-quality hy- drocarbon generating matter of marine carbonate source rocks determined a high gas-oil ratio and tended to form paleo-oil-reservoirs, representing an enrichment process of organic matters. The thermal cracking of oil in palaeo-oil-reservoirs is an important means for the effective forma- tion of gas reservoirs. The secondary organic matters in carbonate reservoirs may regenerate gas after a secondary deep burial, thus becoming an effective gas source.

关键词： carbonate, three-stage hydrocarbon generation, inhibitive effect of maturity, oil-cracking gas, second-ary asphalt gas.

Reinterpretation of the Guangxian Orogeny

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Chinese Science Bulletin 2000年第13期45卷 1244-1248页

作者： WU Haoruoinstitute of {1. and geophysics, Chinese Academy of Sciences, beijing 1.002.,{4. institute of {1. and geophysics Chinese Academy of Sciences Beijing China

The Guangxian Orogeny, as an important concept on geology of South{1., was created 70 years ago. It is generally regarded as an erogenic movement caused by the convergence of the Cathaysian and Yangtze blocks at the end of Silurian. Based on the recent progress of the geological research on Guangxi and adjacent areas, western Guangxi and Liuzhou-Heshan area of central Guangxi may belong to a stable block of Early Paleozoic. The Guangxian Orogeny originated from the northward translation of the Yunkai Block on its south at the end of Cambrian, and formed the Damingshan-Dayaoshan fold belt between the two blocks. It was possibly related with the Late Pan-African Orogeny. The convergence of the Cathaysian and Yangtze blocks occurred in Late Ordovician to Early Silurian and mainly had effect on Hunan and Jiangxi provinces. The term 'Chongyu Orogeny' may be suitable for it. At the end of Silurian orogenic movement did not occur in this area.

关键词： South china tectonics Paleozoic Guangxian Orogeny Yunan Orogeny Chongyu Orogeny.

Carbon isotope ratios of C_(4. plants in loess areas of North{1.

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Science china Earth Sciences 2006年第1期49卷 97-102页

作者： WANG Guoan1.2,3, HAN Jiamao 2, ZHOU Liping3, XIONG Xiaogang4. TAN Ming2, WU Zhenhai5 & PENG Jun6 1. Department of Plant Nutrition,{1. Agricultural University, {1. 1.0094.{1. 2. institute of {4. and geophysics, Chinese Academy of Sciences, beijing 1.002.,{1. 3. College of Environmental Sciences, MOE Laboratory for Earth Surface Processes, Peking University, {1. 1.0871.{1. 4. institute of Botany, Chinese Academy of Sciences, {1. 1.0093,{1. 5. Northwest Sci-Tech University of Agriculture and Forestry, Yangling 71.1.0,{1. 6. Network Center,{1. Agricultural University, {1. 1.0094.{1. Department of Plant Nutrition China Agricultural University Beijing China institute of {1. and geophysics Chinese Academy of Sciences Beijing China College of Environmental Sciences MOE Laboratory for Earth Surface Processes Peking University Beijing China institute of Botany Chinese Academy of Sciences Beijing China Northwest Sci-Tech University of Agriculture and Forestry Yangling China Network Center China Agricultural University Beijing China

Carbon isotope ratios (δ^(1.)C) of 89 C_4.plant samples were determined fromthe loess area in North{1.. δ^(1.)C values vary between -1..5per thousand and -1.0}6per thousandwith a mean of -1..6per thousand. Along a precipitation gradient from the semi-moist area to thesemiarid area, then to the arid area, the δ^(1.)C values of C_4.plants show a slight decreasingtrend. The δ^(1.)C values of C_4.plants in the dry season are found lower than those in the wetseason. These trends are opposite to those observed for C_3 species.

关键词： C4 plants, carbon isotope ratios, loess area.

Modeling of 3-D terrain effect on MT field using BEM

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Chinese Science Bulletin 1997年第9期42卷 764-767页

作者： XU Shizhe, RUAN Baiyao, ZHOU Hui and CHEN Leshou1.institute of {1. and geophysics, Ocean University of Qingdao, Qingdao 266003, china 2. china University of Geosciences, beijing 1.0083, china institute of {1. and geophysics Ocean University of Qingdao Qingdao China Chi University of Geosciences Beijing China

THE modeling of 2-D terrain effect on magnetotelluric(MT)has been solved using finite ele-ment method(FEM)and boundary element method(BEM).This note uses BEM tosolve the *** solution of H_x- and E_x-polarization wave ... 详细信息

关键词： MT 3-D terrain boundary element method.

Comparison of eastern paleo-Tethyan ophiolites and its geodynamic significance--Evidence from Dur'ngoi ophiolite

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Science china Earth Sciences 2004年第4期47卷 378-384页

作者： CHEN Liang1.2, SUN Yong1.2, PEI Xianzhi2, Feng Tao2 & Zhang Guowei2 1. Open Laboratory of Continental Dynamics, Ministry of Education, Northwest University, Xi抋n 71.069, china 2. {1. of geology and geophysics, Chinese Academy of Sciences,{4., china Open Laboratory of Continental Dynamics Ministry of Education Northwest University Xi’an China institute of {1. and geophysics Chinese Academy of Sciences Beijing China

Nd-Pb isotopic geochemistry of metabasalt from Dur抧goi ophiolite, Qinghai Prov-ince, NW china reveals the presence of DMM mixing with EMII components in its upper mantle source, which is comparable with present Indian MORB. Comparisons indicate that the geo-chemistry, chronology and source characteristics of Dur抧goi ophiolite coincide with Pa-leo-tethyan ophiolites from 揝anjiang?area. Together with evidences from regional {1. in adjacent areas, this study proves that independent paleo-tethyan basins evolved contemporarily, the dynamics of which is attributed to the interaction of mantle plume with over-riding lithosphere.

关键词： ophiolite, Paleo-Tethys, DUPAL anomaly, Indosinian movement.

Paleomagnetic dating of the Cenjiawan Paleolithic site in the Nihewan Basin, northern china

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Science china Earth Sciences 2006年第3期49卷 295-303页

作者： WANG Hongqiang1.2, DENG Chenglong1. ZHU Rixiang1.& XIE Fei3 1. Paleomagnetism and Geochronology Laboratory (SKL-LE), institute of {1. and geophysics, Chinese Academy of Sci- ences, beijing 1.002.,{4. 2. School of the Earth Sciences and Resources,{4. University of Geosciences, beijing 1.0083,{4. 3. Hebei Province institute of Cultural Relics, Shijiazhuang 050000,{4. Paleomagnetism and Geochronology Laboratory (SKL-LE) Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China School of the Earth Sciences and Resources China University of Geosciences Beijing China Hebei Province institute of Cultural Relics Shijiazhuang China

Rock magnetic and magnetostratigraphic investigations on a lacustrine sequence in the Nihewan Basin, northern china, which bears the Cenjiawan Paleolithic site, indicate that the dominant magnetic mineral and remanence carrier contained in the sediments is magnetite. While hematite co-exists with magnetite in some portions of the Cenjiawan sequence, where characteristic remanent magnetizations are carried by both magnetite and hematite. Measurements of anisotropy of magnetic susceptibility confirm that the Cenjiawan sequence has preserved the original sedimentary features and is suitable for magnetostratigraphic study. Paleomagnetic results indicate that the Cenjiawan Paleolithic site is formed just posterior to the Punaruu normal event, which is dated at about 1.1.Ma. Combined with the paleomagnetic results of the Donggutuo, Xiaochangliang and Majuangou sections, it is concluded that early humans were occupying the Nihewan Basin around 1.6, 1.3 and 1.1.Ma. This integrated result is significant to understanding the ability of migration and adaptation to the envi- ronment of early humans.

关键词： Nihewan Basin, Early Pleistocene, Cenjiawan, Paleolithic site, paleomagnetism.