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    20 December 2010, Volume 16 Issue 4
    Comparison of Protolith Assemblages of Metamorphic Rocks in  the Dabie-Sulu Orogen and the Late Mesozoic Magmatic Rock Associations  in the Coastal Region of Zhejiang and Fujian Provinces: Implications for theNeoproterozoic Tectonic Setting of Northeastern Yangtze Block
    QIU Jian-sheng, HU Jian, LI Zhen, LIU Liang
    2010, 16(4):  413-425. 
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          The Dabie-Sulu orogenic belt is tectonically situated in the northeastern margin of the Yangtze Block. This belt is mostly underlain by granitic gneisses (over 80%), and minor eclogites occur as pods or layers within them. The protoliths of the granitic gneisses and eclogites correspond to acidic and basic igneous rocks, respectively, and both of them are of Neoproterozoic ages. In this paper, the protolith assemblages and geochemical characteristics of these metamorphic rocks are systematically compared with those of the Late Mesozoic igneous rock associations in the coastal area of Zhejiang and Fujian Provinces.

    Characteristics of Granitic Pegmatite with High-Purity Quartz in Spruce Pine   Region, USA and Altay Region of Xinjiang, China
    ZHANG Ye , CHEN Pei-rong
    2010, 16(4):  426-435. 
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    The alaskites/pegmatites from the Spruce Pine region of USA and the muscovite granites/pegmatites from the Altay region of Xinjiang, China, were comparatively studied. The pegmatites from both regions might be melt-vapor differentiation products of the peraluminous granitic magmas. The pegmatites from the Spruce Pine region with high-purity quartz were developed on the schist or gneiss background, whose major rock-forming minerals are rich in plagioclase, showing high Na/K ratios, high large-ion lithophile elements Sr and Ba contents, low high-field strength and rare earth elements contents, positive Eu anomalies,and low impurity elements contents in quartz. All these characteristics can be used as the discrimination criteria of high-purity quartz pegmatities. The Altay region of Xinjiang is abundant of pegmatites, and some samples studied showed the features which evidenced that the Altay pegmatite region has a perspective to find the gualified pegmatites with high-purity quartz.

    Zircon U-Pb Geochronology and Hf Isotopic Compositions of Hehuaping Granite Porphyry, Southern Hunan Province, and its Geological Significance
    ZHANG Rong-qing LU Jian-jun ZHU Jin-chu YAO Yuan
    2010, 16(4):  436-447. 
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    The Hehuaping granite porphyry  is  located  to  the southeast of Wangxianling granite and  there are cassiterite-sulfide type, porphyry type and altered fragmented-rock type tin deposits related to granite porphyry. Zircon LA-MC-ICP-MS U-Pb age for granite porphyry is 154~156 Ma, with a weighted mean age of (154.7±0.5) Ma (MSWD=0.085, n=21), which suggests an early Yanshanian emplacement. The  in situ Hf  isotope analysis reveals 176Hf/177Hf ratios  from 0.282403  to 0.282597,and ε Hf ( t )  from -2.84 to -10.14 (peak value around -6.5), and the two stage Hf model ages ( tDM2) ranging from 1.38 Ga to 1.84 Ga (peak value around 1.55 Ga),which indicates that its parental magma was derived from the mixed sources of the lower crust and mantle. Based
    on several age data of inherited zircons from the tin-bearing granites in the neighbouring Nanling Range, it can be concluded that
    the granitoids related to tin deposits were mainly products of remelting of the Mesoproterozoic basement rocks

    Rb-Sr Isochron Age Dating of the Bangpu Large-Scale Mo-Cu Polymetallic Deposit, Tibet and Its Geological Significance
    ZHOUXiong,WENChunqi,ZHANGXuequan,CAOShengyuan,WUPengyu,ZHOUYu,FEIGuangchun
    2010, 16(4):  448-456. 
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             The Bangpu Mo-Cu polymetallic deposit is one of the typical large-scale porphyry deposits which lies in the eastern Gangdese metallogenic belt, Tibet. Its major  ore elements are molybdenum and copper, and its accompanying elements are lead and zinc. A monzonite granite-porphyry whole-rock Rb-Sr isochron age of (13.88±0.38) Ma with MSWD=1.7 was obtained which represents the crystallization age of the rock. Furthermore, a pyrite Rb-Sr isochron age of (11.0±1.5) Ma with MSWD=3.5 was obtained for Mo and Cu bearing ores which represents the age of later episode of Mo-Cu mineralization. Combining with the zirconSHRIMP U-Pb age (13.9±0.3) Ma and laser micro-probe 40Ar-39Ar age (13.9±0.9) Ma, it is shown that the rock-forming and ore-forming ages are mutually consistent. The molybdenum and copper mineralization lasted about 3 Myrs. The inital 87Sr/ 86Sr valu(0.706538~0.709190) and mantle composition percentage (Pm) (4.03%~ 51.65%) indicate that the primary magma might be derived from the mantle, and emplaced in the Gangdese extensional setting 14 Myrs ago. The mantle magma was interacted with crustal dioritic magma and contaminated by crustal materials during its ascending process. But generally speaking, the magma source was mainly mantle-derived.

     

    Extensional Fault-Bend Folding in Urxun Sag, Hailaer Basin
    田继强,贾承造,段书府,李本亮,张荣虎,吴兴宁
    2010, 16(4):  457-464. 
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            Urxun Sag in the middle Hailaer Basin is a typical Meso-Cenozoic terrestrial half-graben. In this paper, we firstly illustrate the structural features and evolution of the Hailaer Basin and then analyze the structural geometric characteristics of the seismic reflection profile across the rifting-period prototype basin of the southern Urxun sub-sag. The kink-bands in the hanging-wall are proved to be extensional fault-bend folds. Thus further modeling about the rifting-period prototype basin of the southern Urxun sub-sag can be done to playback the development process of its rifting-period structure with the extensional fault-bend folding theory. The research shows that the evolution of the rifting-period prototype basin of the southern Urxun sub-sag can be divided into four phases: the pre-faulting phase, the initial faulting phase, the intense faulting phase and the stable faulting phase. In fact, its different evolutional phases have different sedimentary thicknesses, different folding styles and different horizontal extensions. Its total extension turns out to be 3.42 km.

    S-Wave Velocity Structures of the Crust and Uppermost Mantle, and Possion,s Ratios in Fujian Province
    HUANG Hui, MI Ning*, XU Ming-jie, WANG Liang-shu, LI Hua, YU Da-yong
    2010, 16(4):  465-474. 
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            In this paper, the receiver functions were obtained by analyzing the teleseismic P waveforms recorded by 12 broadband
    temporary and 8 permanent stations  in Fujian Province. By using  the H- k stacking method,  the average crustal  thicknesses and
    VP/VS  ratios were estimated. The S-wave velocity structures of 0-80 km were gained  through  the  linear  inversion method. The
    H-k stacking results show that the crustal thicknesses range from 28.4 to 32.8 km, decreasing from north to south and from inland
    to offshore of  the Fujian Province. Along  the NW-SE direction,  the Possion,s ratios can be separated  into several zones, and  the
    Possion,s ratios  in  the coastal area are higher  than  in  the  inland area. The crust can be divided  into  three  layers:  the upper,  the middle and the lower crust. Apparently, there are differences among the crustal structures. The low velocity layers of crust appear beneath many stations. The average S-wave velocity of  the uppermost mantle  is  lower  in  the coastal area  than  that  in  the  inland area. It may imply that a heat anomaly area occurs in the deep depth.

    Tectonic Characteristics and Numerical Stress Field Simulation in Indosinian -Early Yanshanian Stage, Lower Yangtze Region
    ZHUANG Jian-jian,YANG Feng-li, ZHAO Wen-fang
    2010, 16(4):  475-482. 
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             Based on  intensive  research on  the  tectonic deformation characteristics  in  Indosinian-Early Yanshanian stage  in
    the Lower Yangtze  region,  this paper has simulated  the  tectonic strain  rate and surface velocity  through  the “thin-shell”  finite
    element method. The modeling results  indicate  that  the area around  the  junction between Qinlin-Dabie Orogen and Tanlu  fault
    suffered intensively compressional effect, the eastern South Yellow Sea was a strongly tensional area, while the Sulu orogen and
    the Jiangshao  fault were  transpressional areas. The average strain rate of  the Lower Yangtze region was about 5.0×10-15/s ~1.0
    ×10-14/s and the surface velocity was probably about 50 mm/a. Controlled by this kind of tectonic stress field, the Lower Yangtze
    Block produced massive thrust nappe structures in a ramp style.

    Tectonic Modeling Constraints on Lithospheric Characteristics of the Qiongdongnan Basin
    WU Zhe , YANG Feng-li , WU Jian-xun
    2010, 16(4):  483-491. 
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            The Qiongdongnan basin  is an extensional basin  formed  in Late- Eocene.  In  this study, based on  the  flexure  isostasy
    principle  and flexural cantilever model, we utilize 2D structurcal simulation software and calculate the effective elastic thickness
    valuse (Te) and the extensional factors on 2D interpreted seismic profiles. The results show that the effective elastic thicknesses
    vary  in  the  range of 1-5 km, and  their optimum value  is 3 km. The extensional  factors change between 1.3 and 1.5, about 1.5
    for the post-rift period with forward modeling, and about 1.3 for the syn-rift period with inverse modeling. Finally, we discuss the
    possible influential factors of the activity of the Red River fault in the Cenozoic and the South China Sea spreading.

    Application of Fish Head Boudin Structure to Estimation of Competency of Adjacent Competent Layers
    LIN Yan-hao, ZENG Zuo-xun
    2010, 16(4):  492-497. 
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              The  initial  thicknesses of  the original  rock  layers can be  restored by various  fish head boudins. Furthermore, we
    can analyze the linear strain in Z and X axes of the strain ellipsoid of the original rocks by the layer thicknesses. In this article,
    a method  for estimating  the viscosity  ratios of adjacent competent  layers was derived  from  the Strain Differential Refraction
    Rheology Gauges. An application  trial was made  for  two specimens of  fish head boudins  from  the Tieshan area, Daye, Hubei
    province. We obtained the viscosity ratios of two adjacent fish head boudin hornfels layers in marble matrix, which are 3.07 and
    0.75, respectively.

    Standard Well for Quaternary Research and Its Geological Interpretation in Qinhuai River Valley of Nanjing Area
    XIONG Zhen,HOU Kang-ming,LI Qing-he,CHEN Jie
    2010, 16(4):  498-509. 
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           Based on data of systematic age sampling, Quaternary sediment  lithology and palynomorph assemblage analysis on the standard well  (N06S6)  for Quaternary  research  in Qinhuai River valley, a stratigraphic unit, Hanfu Formation since Late Pleistocene, was set up for Quaternary stratigraphy in the Qinhuai River valley. Five palynological assemblages were distinguished through an  intensive study on pollens and spores  from  the well, and  five stages  in  the evolution of vegetation and climate were
    correspondingly  reconstructed  for  the Late Quaternary  in  this area. The Quaternary paleoenvironment, paleoclimate and paleo-
    landform was also recovered in the area, which indicates that the  paleo-landform changed little and new tectonic movement during this time was weak in the study area.

    Sandstone Detrital Composition and Provenance Analysis of the Permian Longtan Formation in Southeastern Anhui Province
    DU Ye-long, LI Shuang-ying, KONG Wei-lun, WANG Song
    2010, 16(4):  510-517. 
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              Detrital composition analysis of  sandstone  is mainly used  to  study  the provenance of  sediments and  the  tectonic
    background evolution. The Longtan Formation  is one of  the major coal-bearing strata  in South China. The characteristics of
    sandstone detrital compositions of  the Permian Longtan Formation  in southeastern Anhui province show  that  the contents of
    monocrystal quart is mostly 25%-40%, and the polycrystal quart 30%-65%. The quart in the fine-grained sandstone usually has
    a corroded rim. The contents of feldspar show a great variation, mainly 5%-15% in the fine-grained sandstone and about 1% in
    the medium- to coarse-grained sandstone; Lithic fragments are mainly 15%-25% in the fine-grained sandstone and 10%-20% in
    the medium- to coarse-grained sandstone. The sandstone detrital compositions and provenance analysis indicate that the sandstone of  the Longtan Formation was derived  from  the mixed sources of  recycled orogen and subduction complex. Combining with  the  gravel characteristics and  the regional  tectonic setting,  it can be  inferred  that  the sources of  the Longtan Formation  in  the study area were mostly derived from the collision zone between the Cathaysia Plate and the Yangtze plate, namely the Jiangnan orogen

    Element Geochemistry of Lake Sediments from Sihu Lake in Guilin Karst  Wetland Region and Its Environmental Effect
    SHEN De-fu, LI Shi-jie, CAI De-suo, ZHANG Hong-liang,ZHAO Xiang-gui
    2010, 16(4):  518-527. 
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             Sedimentation rates and element concentrations  of core sediments from Sihu Lake are investigated and characteristics
    of element geochemistry and environmental change around  this  lake are discussed. By using principal component analysis,  the
    geochemical composition factors affecting the sediments of the cores are mainly four: the erosion factor, the watershed runoff and
    diagenesis factor, the regional background effect factor and the human activity effect factor. The latter two factors usually account
    for smaller proportions. However,  in recent years  the human  factor has rapidly numerical  increase because of quick  increase of
    phosphorus contents  in  lake sediments. On  the other hand, variations  in chemical elements obviously have periodic  feature:  the fourth period (0-4 cm, corresponding to 1987-2007), is mainly affected by human activities closely related with regional economic
    development. The other earlier  three periods  (4-20 cm, corresponding  to 1894-1987; 20-53 cm, corresponding  to 1703-1894;
    53-77 cm, corresponding to 1562-1703) were mainly controlled by climate change.

    Comparative Study of Geochemistry and Multivariate Data Analysis on Mixed Oils Accumulated in Ordovician Reservoir in Tahe Oilfield,Tarim Basin, NW China
    TAO Guo-liang, QIN Jian-zhong,TENGER, ZHANG Mei-zhen,FU Xiao-dong,LOU Zhang-hua
    2010, 16(4):  528-539. 
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             Quantificational discrimination of mixed oils is a hot concept and difficult point in petroleum geology and geochemistry research. This article shows a case study on Tahe oilfield, Tarim Basin, NW China. Comparative study of geochemistry and multivariate data analysis  indicate  that oils accumulated  in Ordovician  reservoir  in Tahe oilfield are characterized by multi-stage hydrocarbon generation and mixed sources. The early-stage generated oils were biodegraded,  thus  the  light hydrocarbons, alkanes, and regular steranes in present oils show features of later-stage generated oils. Quantitative data of tricyclic terpanes and hopanes with  little  influence of biodegradation were calculated  through Alternating Least Squares algorithm. The  results show that there were four end-member oils contributed to the mixed oils in this region. The end-members 1 and 2 indicate middle-upper Ordovician source  rocks, and  the end-members 3 and 4  indicate Cambrian source  rocks.  In  the main area of Tahe oilfield, oilsgenerated from the Cambrian source rocks were more than those from the middle-upper Ordovician source rocks. But in the area around the main area, the middle-upper Ordovician source rocks were the major contributors. For the whole oilfield, the Cambrian source rocks were more  important. This comparative research shows  that  the multivariate data analysis plays significant role  in calculating proportions of mixed oils and  identifying end-member oils. As an effective complement  to  traditional geochemistry study, multivariate data analysis is worthy to be popularized

    Study on Reservoir Properties and Effect of Syndepositional Faults in the Shanghe Oilfield
    LI Zun-zhi,YANG Zhi-Jun, WANG Si-wen,LI Ya-hui,JI You-liang,KANG Yun
    2010, 16(4):  540-547. 
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            The Shanghe oilfield presents obviously stepping distribution of multi-ordered  tectonic belts and multi-level slope belts  from north  to south, and clastic  reservoir properties also have apparent  regular pattern due  to  the structural  features. By means of analyzing a  large amount of data of  reservoir properties, combined with structure  research,  it  is considered  that  the reservoir properties of  the same stratum  in  the Shanghe oilfield are getting gradually worse and worse  from  the Shang 1 area, through the Shang 2 area and the Shang 3 area up to the Shang 4 area in the direction  from north to south. But within the same area,  the  reservoir properties are getting worse and worse with  increasing burial depth. The boundary  faults of  the Shanghe oil field are primarily syndepositional faults, and the stratum depths of different blocks are thickened from north to south because of syndepositional growth faulting. Consequently, the variation of formation thicknesses controlled by synsedimentary fault activity is
    the main influential factor of the reservior property differences for the same stratum in different areas of the Shanghe oilfield.

    Provenance Analysis of Late Triassic Sediments in the Southern Ordos Basin
    ZHU Zong-liang,LI Wen-hou,LI Ke-yong, CHEN Quan-hong, GUO Yan-qin
    2010, 16(4):  547-555. 
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           The source  rocks of  the Late Triassic  in  the southern Ordos basin are mainly  the Archaean highly metamorphosed schists and gneisses, and the Sinian to Paleozoic shallow marine clastic rocks and carbonates. Affected by different sources, the light and heavy mineral assemblages have different features in various areas of a sedimentation system. In the western Zhenyuan-Jingchuan area, quartz content of sandstone  is  relatively high, and  the  lithic debris  is mainly  the sedimentary  rocks. To  the
    southeast, in the Tongchuan-Yaoxian area, feldspar and debris of igneous and metamorphic rocks are gradually increased. In the
    southern region of  the basin,  the heavy mineral assemblage  is of zircon +  tourmaline + garnet  type, controlled by sedimentation
    channel net. There are mainly  four distribution areas  in heavy mineral association:  the Huanxian-Zhenyuan-Jingchuan area in  the west  is characterized by garnet + zircon +  tourmaline +  leucoxene assemblage;  the Changwu-Ningxian area  in  the south is characterized by zircon +  tourmaline +  leucoxene + garnet assemblage;  the Huangling-Tongchuan area  in  the southeast  is
    characterized by garnet + zircon + leucoxene assemblage; and the Fuxian-Yan,an area in the northeast is characterized by garnet
    + zircon + magnetite assemblage. They respectively correspond  to their own ancestral rivers and sedimentary diffusion areas. In
    the Fuxian-Yan,an area,  the REE patterns and geochemical characteristics of  theYanchang Formation are nearly similar withthe Archean and Early Proterozoic metamorphic rocks  to  the northeast of  the basin. In  the Zhenyuan-Jingchuan area,  the REE
    patterns of  the Yanchang Formation sandstones are nearly similar  to  the metamorphic  rocks  to  the southwest of  the basin. This is certainly genetically  related. Consequently,  it can be  inferred  that  the structural evolution process of  the southwestern and northeastern areas of the basin was different.