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Experimental remolding on the caprock's 3D 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,china university of Geo{2.,Beijing 100083,china 2. faculty of earth sciences,china university of Geo{2.,wuhan 43.074,china 3. Department of earth {2.,Jilin university,Changchun 130061,china State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences Beijing 100083 China faculty of earth {2. 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 3D structural frame of Tongling deposit concentrating area firstly. Then we disassemble and dialyze the 3D 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 3D structure between the experimental model and the field phenomena, we verify the following 3D 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 3D structural frame of the caprock analogue experiment slicing and stripping analysis structural model.

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 Mineral Resources, china university of Geo{2., wuhan 43.074, china 2. Graduate School of china university of Geo{2., wuhan 43.074, china 3. faculty of earth {2., china university of Geo{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 Geo{2. Wuhan China faculty of earth {2. 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 300 km.

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

Anatexis in Himalayan crust:Evidence from geochemical and chronological investigations of Higher Himalayan Crystallines

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Science china earth {2. 2005年第9期48卷 1347-1356页

作者： YANG Xiaosong1, JIN Zhenmin2.& MA Jin1 1. State Key Laboratory of earthquake Dynamics, Institute of Geology, china earthquake Administration, Beijing 10002., china 2. faculty of earth sciences, china university of Geosciences, wuhan 43.074, china State Key Laboratory of earthquake Dynamics Institute of Geology China Earthquake Administration Beijing China faculty of earth {2. China University of Geosciences Wuhan China

Migmatization in Higher Himalayan Crystallines (HHC) results from anatexis. The widely distributed migmatites in HHC are an important clue to investigate the relationship be- tween anatexis and the origins of Higher Himalayan leucogranites (HHL), and to understand the effect of anatexis on crustal evolution during the post-collision period. We studied in detail the chemical features of three basic constituent parts of the migmatites, i.e. leucosome, mesosome and melanosome, and determined the K-Ar ages of leucosomes. Our studies indicate that type-I leucosome is the product of crystallization of melt generated by partial melting of mesosome at source region, but type-II leucosome and HHL probably underwent crystallization differentiation of plagioclase during melt aggregation and migration. The age of 2..67 Ma of Type-I leucosome, which is a little older than the beginning of MCT movement, indicates that anatexis may have played an important role in the formation of MCT. That the ages of type-II leucosome (ranging from 14.82.to 18.37 Ma) are consistent with that of HHL provides new chronological evidence for the relationship between migmatization and HHL. We obtained a very young age of 6.2. Ma of Type-II leucosome that provides new time constraint on magma activity in the central segment of Higher Himalayas.

关键词： Higher Himalayan Crystallines, migmatite, anatexis, leucosome, K-Ar age.

earthquake-controlled event deposits and its tectonic significance from the Middle Permian Wandrawandian Siltstone in the Sydney Basin, Australia

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Science china earth {2. 2005年第9期48卷 1337-1346页

作者： DU Yuansheng1, G. R. Shi1,2.& GONG Yiming1 1. faculty of earth {2., china university of Geo{2., wuhan 43.074, china 2. School of Ecology and Environment, Deakin university, Victoria 312., Australia faculty of earth {2. China University of Geosciences Wuhan China School of Ecology and Environment Deakin University Victoria Australia

The Sydney-Bowen basin in eastern Australia is an elongate back arc-converted foreland basin system situated between the Lachlan Fold Belt in the west and the New England Fold Belt in the east. The Middle Permian Wandrawandian Siltstone at Warden Head near Ulla- dulla in the southern Sydney Basin is dominated by fossiliferous siltstone and mudstone, with a large amount of dropstones and minor pebbly sandstone beds. Two general types of deposits are recognized from the siltstone unit in view of the timing and mechanism of formation. One is rep- resented by the primary deposits from offshore to subtidal environments with abundant drop- stones of glacial marine origin. The second type is distinguished by secondary, soft-sediment deformational deposits and structures, and comprises three layers of mudstone dykes of seismic origin. In the latter type, metre scale, laterally extensive syn-depositional slump deformation structures occur in the middle part of the Wandrawandian Siltstone. The deformation structures vary in morphology and pattern, including large-scale complex-type folds, flexural stratification, concave-up structures, faulting of small displacements accompanied by folding and brecciation. The slumps and associated syn-sedimentary structures are attributed to penecontemporaneous deformations of soft sediments (mostly silty mud) formed as a result of mass movement of un- consolidated and/or semi-consolidated substrate following an earthquake event. The occurrence of the earthquake event deposits supports the current view that the Sydney Basin was located in a back-arc setting near the New England magmatic arc on an active continental margin during the Middle Permian.

关键词： Permian, seismites, earthquake, tectonics, Sydney Basin, Australia.

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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 Geo{2., Ministry of Education of china, Beijing 100083, china 2. School of earth {2. and Mineral Resources, china university of Geo{2., Beijing 100083, 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 Mineral Resources 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.

Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone,Tibet and its tectonic implications

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Science china earth {2. 2006年第4期49卷 348-357页

作者： ZHU Jie1,2. DU Yuansheng1, LIU Zaoxue2. FENG Qinglai1, TIAN Wangxue2. LI Jinping2.& WANG Changping2.1. faculty of earth {2.,china university of Geology, wuhan 43.074, china 2. Hubei Institute of Regional Geology Survey, wuhan 430034, china faculty of earth {2. China University of Geology Wuhan China Hubei Institute of Regional Geology Survey Wuhan China

Three radiolarian fauna, aged as the Middle-Late Triassic, Late Jurassic-Early Creta- ceous and Cretaceous radiolarian fauna, have been recognised in the radiolarian cherts from the middle sector of the Yarlung Zangbo suture zone, southern Tibet, china. The average contents of SiO2.in the radiolarian cherts of the Middle-Late Triassic and Late Jurassic-Early Cretaceous are 90.2.% and 92.58% respectively, with average ratios of Al/(Al+Fe+Mn) as 0.75 and 0.74 respectively, the average ratios of MnO/TiO2.as 0.36 and 1.2., the average ratios of Ce/Ce* as 1.15 and 1.03, and the average ratios of LaN/CeN as 0.85 and 0.93. These geochemical features indicate that both of them are biogenic, deposited in a continental margin basin. The SiO2.content of the Early Cretaceous radiolarian chert is 94.12., with the ratio of Al/(Al+Fe+Mn) as 0.59, ratio of MnO/TiO2.as 4.30, ratio of Ce/Ce* as 0.60, ratio of LaN/CeN as 1.59, which imply that the chert is biogenic and was deposited in a pelagic basin. The Middle-Late Triassic association of the radiolarian chert and turbidites as well as their geochemical characteristics indicates the existence of a strong rifting marginal basin in the belt of the Yarlung Zangbo River then. The association of radiolarian chert and bedded basalt indicate an initial Tethyan ocean basin in southern Tibet during the Late Jurassic-Early Cretaceous. The early Cretaceous radiolarian chert coexisting with pillow basalt in top of the ophiolite suite represents sediments from the oceanic Tethyan basin.

关键词： radiolarian chert, sedimentary geochemistry, Mesozoic, Yarlung Zangbo suture zone, Tibet.

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 {2. and Natural Resources, china university of Geo{2., Beijing 100083, china 2. faculty of earth sciences, china university of Geo{2., wuhan 43.074, china 3. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological {2., Beijing 100037, china faculty of earth {2. and Natural Resources China University of Geosciences Beijing China faculty of earth {2. 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.

Evolutionary patterns of Productida (Brachiopoda) morphology during the Permian in South china

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Science china earth {2. 2008年第11期51卷 1589-1600页

作者： ZHANG Yang1 & HE WeiHong1,2.1 faculty of earth {2., china university of Geo{2., wuhan 43.074, china 2.Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, china university of Geo{2., wuhan 43.074, china faculty of earth {2. China University of Geosciences Wuhan China Key Laboratory of Biogeology and Environmental Geology of Ministry of Education China University of Geosciences Wuhan China

The evolutionary patterns of Productida (brachiopod) morphology throughout the Permian show that while the percentage proportion of Productida (brachiopod) with strongly concentric and radial ornamentation declined from the Cisuralian to the Guadalupian, and then increased towards the Changhsingian via Wuchiapingian, the percentage proportion of Productida (brachiopod) with fine concentric and radial ornamentation distinctly increased from the Cisuralian to the Guadalupian, slightly declined towards the Wuchiapingian, and then increased towards the Changhsingian. From the Cisuralian to the Changhsingian, the percentage proportion of brachiopods with spinose ornamentation shows a persistent declining trend. The shell size generally indicates a miniaturization trend at species level during the Wuchiapingian to Changhsingian (including the transitional bed). These evolutionary patterns of brachiopod ornamentation and size are possibly related to the anoxia, food shortage, sea-level fluctuation, and change of substrate in the Permian (including the Permian-Triassic transitional interval) in South china.

关键词： brachiopod ornamentation size Permian South china

Experimental study of ore gabbro liquid immiscibility

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Science china earth {2. 2005年第4期48卷 496-505页

作者： SANG Zunan1,2. XIA Bin1, ZHOU Yongsheng3 & JIN Zhenmin4 1. Guangzhou Institute of Geochemistry, Chinese Academy of sciences, Guangzhou 510640, china 2. {2. university, {2. 430072. china 3. Institute of Geology, china Seismological Bureau, Beijing 10002., china 4. faculty of earth sciences, china university of Geosciences, wuhan 43.074, china Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou China wuhan university Wuhan China Institute of Geology China Seismological Bureau Beijing China faculty of earth {2. China University of Geosciences Wuhan China

In this paper, the authors present the results of a preliminary experimental study on partial melting of fine-grained gabbro, Panzhihua, Sichuan Province, china. Experiments were conducted under (confining) pressure ranging from 450 to 500 MPa and temperature of 900— 12.0℃. The results show that the initial melt is distributed along grain boundaries and triple junctions. Liquid immiscibility phenomena are noted in the melt with two compositional different melt phases, i.e. matrix and sphere phases. The matrix phase is relatively rich in Si, Al and K, and is depleted in Mg, Fe, Ca, Na and Ti, whereas the sphere phase shows opposite trends. The calculation of the melt free energy indicates that the liquid immiscibility is governed by the rule of thermodynamics, as the liquid immiscibility would result in the decrease in free energy of the melt system. The field relationships suggest that the liquid immiscibility may have played an important role in the generation of ore magma of Panzhihua V-Ti magnetite ore deposit. This study thus provides experimental constraints on the mechanism of the formation of V-Ti magnetite deposite.

关键词： partial melting, experimental study, gabbro, liquid immiscibility, ore formation mechanism.