Table of Content

20 March 2005, Volume 11 Issue 1

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Article

New Progress in Studying the Large Igneous Provinces

WANG De-zi, ZHOU Jin-cheng

2005, 11(1):  1-8. 

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Large lgneous Provinces(LIPs)are referred as continuous and voluminous magamatic rock formations consisted of mafic and felsic rocks. Included as mafic LIPS's are continental flood basalts, passive volcanic margin and oceanic plateau basalts, giant dyke swarms and large layered intrusions, Mafic LIPs are generally to have a mantle plume origin and not directly related to convergent plate boundaries. Felsic LIPs are mainly composed of acidic and acidic-intermediate ignimbrite and genetically relater granites. The occurrence of felsic LIPs is considered to be related to underplating of basaltic magma and extension of lithosphere. Further studies on mantle dynamics related with LIPs, the relationship between occurrence of LIPs and continental accretion, breakup, mass extinction as well as metallogenesis are envisaged in the future.

Generation and Evolution of Basaltic Magmas：Some Basic Concepts and a New View onthe Origin of Mesozoic-Cenozoic Basaltic Volcanism in Eastern China

Yaoling Niu

2005, 11(1):  9-46. 

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Some basic concepts of basaltic magma generation and evolution are discussed in the context of global tectonics．These concepts need better understanding before invoking elusive possibilities in igneous petrogenesis on all scales and in all tectonic environments．A hypothesis for the Mesozoic lithosphere thinning and Mesozoic—Cenozoic basaltic volcanism in eastern China is presented．This hypothesis is consistent with observations and complies with basic physics．While the eastern China volcanism can be defined as“intra-plate”volcanism．it is in fact a special consequence of plate tectonics．The Mesozoic lithosphere thinning in eastern China is best explained by a process that“transformed”the deep portion of the lithosphere into convective asthenosphere by hydration．The water that did so may come from dehydration of subducted Pacific(or predecessor)oceanic lithosphere that is presently lying horizontally in the transition zone beneath eastern Chinese continent as detected by seismic tomographic models．The Mesozoic volcanism may be genetically associated with the lithospheric thinning because the basaltic source is ancient isotopically enriched (ENd<0) lithosphere-being convened to the asthenosphere．The NNE-SSW Great Gradient Line(GGL) marked by the sharp altitude，gravity anomaly，crustal thickness，and mantle seismic velocity changes from the plateau west to the hilly plains of Eastern China is an expression of variation in lithospheric thickness from probably >150～200 km beneath the plateaus in the west to the thin，probably<80 km，beneath eastern China．The “remote”western Pacific subduction systems induce asthenospheric flow from beneath eastern China towards the subduction zones，which，in turn，requires asthenospheric material replenishment from beneath the plateaus to the eastern China．As a result，such eastward asthenospheric flow experiences an upwelling and decompression(from beneath thickened to thined lithosphere)，which causes the flowing asthenosphere (e．g．，ENd>0)to partially melt and produce Cenozoic eastern China basaltic volcanism．Such volcanism ma y have actually begun at the end of the Mesozoic lithosphere thinning in the late Cretaceous．This simplistic concept is currently being substantiated with detailed petrologic and geochemical data．

Zircon SHRIMP U-Pb Age Dating of Garnet-Acmite Syenite：Constraints on the Hercynian-IndosinianTectonic Evolution of Hainan Island

XIE Cai-fu1 2, ZHU Jin-chu2, ZHAO Zi-jie1, DING Shi-jiang3, FU Tai-an1, LI Zhi-hong1, ZHANG Ye-ming1, XU De-ming1

2005, 11(1):  47-57. 

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We discovered some garnet-acmite syenite rocks in Sanya terrain at the southern margin of Hainan Island．The mineralogical and geochemical studies demonstrate that these rocks are silica-saturated and peralkaline，enriched in LILE(Rb，Th，U，K，Pb)and LREE，with relatively distinct Nb，Ta，Ti，Sr，Ba，Eu，P negative anomalies．The HREE contents are relatively high，without obvious differentiation．Their Sr，Nd and Pb isotopic compositions are similar to those of EM-Ⅱ lithospheric mantle．11 zircon SHRIMP analytical data give the 206Pb／238U age ranges of 237—251 Ma．with a weighted average of 244±7 Ma．The above—mentioned information indicates that the Sanya syenite rocks were formed by decompression-dehydration melting of enriched lithospheric mantle at a shallower depth(<60 km，which was in tern caused by Triassic delamination and asthenospheric upwelling．It is emphasized that during the Triassic，the Hainan island Was under a post-orogenic extension environment，being the continuous evolution of the Hercynian orogeny．It is not reasonable to divide the Triassic activity as an independent Indosinian orogeny．It is also proposed that the Sanya terrain Was placed to present site adjacent to middle Hainan terrain through a Late Permian large scale right-lateral slideslip along the Jiusuo—Lingshui deep fault．There exists a NE-trending Triassic alkali-rich igneous belt in SE Hainan Island．This belt probably extends to South China continent through Luoding of Guangdong Province to Mingxi of Fujiang Province．It is considered that the South China Was probably also under a post-orogenic environment during the Triassic.

Characteristics of Organic Mineralization and Organic Matter in the Fankou Pb-Zn Deposit,North Guangdong Province,South China

SU Jing-wen, HU Kai, LI Kuang

2005, 11(1):  58-66. 

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The organic matter associated with Fankou Pb-Zn deposit(Northern Guangdong province, southeastern China) has been studied by petrographic，organic petrology，elements analysis and gas chromatographic methods, The host rocks of the deposit are abundant in organic carbon ranging from 0.03％ to 0.4％ ．The vitrinite reflectances (R0) are determined as 1.92％-3.55％ ，mostly above 3.0％ ．It is suggested that the maturity of the organic matter is high and most of the organic matter has become bitumen．The character of saturated hydrocarbons，extracted from host rocks and ores (Pr and Ph)shows a marine-facies reduction condition．Gas chromatographic analytical results show that the 0rganic matter in orebody experienced thermolysis and thermal metamorphism，and thus the formed CH4 and kerogen acted as reducing agents to reduce sulfate to sulfide hydrogen，which was favorable for precipitation of metal sulfides． In addition，the occurrence of pyrite in granular and “strawberry" form indicates the effect of bacteria and micro-algae during early sedimentation．

Recent Progress in Study of Metamorphic Core Complexes

LOU Fa-sheng, SHU Liang-hu, WANG De-zi

2005, 11(1):  67-76. 

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The metamorphic core complex is an important rheologic pattern of continental extension．The metamorphic core complexes and extensional tectonics have been being a hot-point in the international continental dynamics study in recent 20 years．Based on a large number of recent publications and data，the latest research progress on the metamorphic core complexes is reviewed briefly；the basic features of geometry，kinematics，geochronology ale described roughly；the main characteristics of major detachment faults bordering metamorphic core complexes are analyzed in detail；the tectonic set-tings under which the metamorphic core complexes were formed and the metallogenesis related to metamorphic core complexes are introduced；and the distinguishing indicators of the metamorphic core complexes ale synthesized. Some debated problems are also discussed in this paper including (1) If an important crustal section necessarily be omitted for all the metamorphic core complexes or not? (2) During the development of metamorphic core complexes，whether the magmatism and deformation is caused by extensional tectonics，or the extensional tectonics is induced by magmatism? (3) the genetic mechanism of low-angle normal faults．By contrast with many metamorphic core complexes over the world，we suggest that a major omission of crustal section is not the most important and necessary condition constraining the metamorphic Core complexes．Further studies on the metamorphic core complexes and extensional tectonics will largely promote our understanding of continental rheology and dynamics

Study on the Relationship between SiO2／Al2O3 Ratios andOre-Bearing Capacity in Interstratified Oxidized Zone：Exemplified by Kujieertai and Wukuerqi Uranium Deposits

WANG Jin-ping1 2, MIN Mao-zhong1, CHEN Yue-hui3, PENG Xin-jian3

2005, 11(1):  77-84. 

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Based on the detailed subzone division for Kujiertai and Wukuerqi uranium deposits，this paper studies the migration regularities of major elements in various subzones of interstratified oxidized zone．Some major elements including SiO2 and A1203 appear relatively active during the interstratified oxidation．However．such phenomenon has not been traced enough previously in literature．Si has a migration out behavior and its contents in the host rocks regularly decrease with intensifying oxidation．On the contrary，the Al contents regularly increase with intensifying oxidation．The relationship between Si and A1 shows that different Si02／A1203 ratios can indicate if the interstratified oxidized zone is ore-bearing or ore-barren

Mechanisms of Adsorption of Heavy Metal Ions on Kaolinite and Their Solution as a Function of pH

Wu Hong-hai, LIU Pei-hong, ZHANG Qiu-yun, HE Guang-ping

2005, 11(1):  85-91. 

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The adsorption behavior of heavy metal ions(Cu2+and Pb2+)to kaolinite was examined and the kaolinite dissolution was conducted in batch experiments as a function of pH and ion strength(electrolyte concentration)．The pHPNZPC of kaolinite in NaNO3 was determined as 5.2，but the aluminol groups(>A1OH)were deportonated at pH >6.5．The adsorption experimental results showed that the modes in adsorption of Cu(Ⅱ) and Pb(II) ions onto kaolinite were quite different from that to quartz．The adsorption mechanisms could be well interpreted in terra of two interfacial adsorption modes：all ion-exchange and a surface complexation coexisting with the adsorption processes of Cu(II) and Pb(II) in the case of kaolinite．However，only single surface complexation for quartz was detected．The succession of adsorption models of Cu(II)and Pb(II)to the kaolinite with increasing pH is as follows：(1)The adsorption isotherms at pH<6.5 could be elucidated mainly by ion-exchange at the permanently-charged site on the silanol faces，suggesting that ion-exchange model was major contributor to the adsorption of Cu(II) and Pb(II) adsorbed to kaolinite．Being affected by both the aluminum ion dissolved from kaolinite and the ion strength(too high)under condition of acidic pH(<4)，the sorption percentage of heavy metal ions to kaolinite was very low；(2)An adsorption plateau around pH=5～6 characterizes adsorption edges of Cu(II) and Pb(II) ions，because the kaolinite crystal edges almost carried neutral charge in this pH value；(3)Besides the ion exchange model，the surface complexation model in which the Cu(II) and Pb(II) ions are complexed to aluminol and perhaps silanol groups that occur in particular at the kaolinite crystal edges，also regulates the adsorption behavior of Cu(II) and Pb(II) to kaolinite at pH>6.5．(4)In addition，the surface precipitation model becomes major contributor to the uptake ofthe Cu(II) and Pb(II) cations to the above-mentioned two minerals at higher pH；As a consequence of the reaction processes of protonation-deprotonation and dissolution at kaolinite-water interface regulated by pH，the medium pH controls the transport and the fate of Cu(II) and Pb(II)ions in soil and sedimentation environment． Finally the experimental adsorption results were described in this paper by the Physical Surface-Complexation Model of Sverjensky D A(1993)．

Eastward Extension of Dabie—Sulu Orogenic Belt and the Suture Zoneof the Plates：Determination of Tanlu—Yalujiang—Yanji Faults

ZHOU Jian-bo, LIU Jian-hui, ZHENG Chang-qing, LIU Peng-ju, SUN Jia-peng

2005, 11(1):  92-104. 

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According to the exposure markers of the low-grade metamorphic accretionary complex in the north margin of the Dabie—Sulu orogenic belt and the Triassic low-grade metamorphic accretionary complex in the eastern Jilin and Heilongjiang Provinces，we believe that the suture zone of the plate subduction in Dabie region is the Xinyang—Shucheng fault，and that in Sulu region is the Tanlu—Yalujiang fault．Meanwhile，the Sulu orogenic belt extends into eastern Jilin and Heilongiiang Provinces, and the eastward extension part of the tectonic suture zone between the No China plate and South China plate is the Tanlu—Yalujiang—Tumenjiang—Yanji faults．Based on the above discussion．we put forward a continuous subduction-accretionary model in east Asia since the Triassic：(1)A spot collision between South and No China plates took place at the southward extension part of North China plate in the Triassic．then the South China plate was transformed from spot collision into revolving amalgamation toward both sides which resulted in forming accretionary complex．(2)Following the Triassic collision，with Pacific plate subduction and continuous accumulation towards Eurasian plate in the Jurassic—Cenozoic，the huge accretionary complex belt was eventually formed ．

Discussion on the Extension Model for the Conjugate Continental Margin of South China Sea

WU Shi-min, YANG Tian, ZHOU Di, QIU Xue-lin, XIA Bin

2005, 11(1):  105-110. 

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Based on examining the seismic profiles distributed at the north and south margins of South China Sea，cobined with the tectonic analysis of its adjacent area，the authors pointed out that this region experienced two periods’extensions，i.e. the earlier simple shear and the later pure shear．The simple shear extension mainly occurred in Late Cretaceous-Early Paleogene，related to slab roll back of Pacific plate，decreasing Paleogene Pacific—Eurasia convergence rate and possible preexisting suture zone．Pure shear happened in response to the extensional slab pull forces from south ward subduction of the Paleo-South China Sea beneath Borneo during the Oligocene and Miocene

Study on Characteristics of Gravity Field and Crustal Deformation in Sichuan-Yunman Region

ZHONG Kai, XU Ming-jie, WANG Lang-shu, LIU Shao-wen, DING Zeng-yong

2005, 11(1):  111-117. 

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Moho depth distribution and crustal deformation pattern between different sub-blocks in Sichuan-Yunnan region are presented here based on the studies of the gravity field characteristics．Generally，Moho depth within study area decreases gradually from northwest to southeast．There is an obvious extensive crustal thickening in whole Sichuan—Yunnan rhombic block．According to the gravity characteristics，the Lijiang—Xiaojinhe fault is shown to be the southwestward extension of the Longmenshan fault；to the east of these faults，the gravity field and main structural orientation of the Middle Yunnan sub-block are consistent with those of the Yangtze block, indicating these faults and the Red River fault zone are the west boundary of Yangtze block．The 1st vertical derivative of Bouguer gravity data in Siehuan—Yunnan region is generally similar to the present-day crustal deformation pattern．The main structural orientation is NNW or nearly SN，representing the major structural orietation of a later tectonism; while it changes into nearly EW based on gravity horizontal direction derivative data after upward 45km

Study on Effective Passage System in Liangjialou Oil Field Dongying Depression

HAO Xue-feng1 2, CHEN Han-lin1, YANG Shu-feng1, ZHUO Qin-gong2, XIONG Wei2

2005, 11(1):  118-125. 

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As a important part of the reservoir mechanism research，not only the static description of the geological bodies，but also the dynamic attention of petroleum migration should be considered together in the passage system study．Based on the correlation between oil and source rocks，analysis of faults and sand bodies，and the analysis of oil accumulation history，this paper discusses passage system of Liangjialou oil field in Dongying sag．This paper suggests that the effective source-rocks in the upper part of the fourth stage，the middle and lower parts of the third stage of Shahejie Formation were connected with reservoir through synsedimentary faults, and the vertical migration was the major type of accumulation in Liangjialou oil field．The growth fault is the most important element in the passage system，and the accumulation stage is determined by the active stage of faults．The model of petroleum migration is controlled by the distribution of effective source rocks and the motion type of faults．

Foreland Basins,Their Types and Hydrocarbon Potential

ZHANG Bo1, ZHANG Jin-jiang1, YANG Wu-ling2, LIU Ming-li3

2005, 11(1):  126-136. 

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This paper reviews the previous and current research on foreland basins，including the concept，modes of tectonics-sedimentation，types，characteristics，and hydrocarbon bearing features．At the same time，the features and hydrocarbon potential of the rejuvenated foreland basins around intracontinental orogens in Mid-West China are discussed．Conclusions are as follows：① The rejuvenated foreland basins，juxtaposing with peripheral foreland basin and retro-arc foreland basins，should be considered as a main type of foreland basins；② The foreland basins，on the basis of their geodynamic environments，Can be subdivided into three fundamental types：the peripheral foreland basins ，retro-arc foreland basins and rejuvenated foreland basins．The former two types are the representative foreland basins, and the latter one is a rather unique type around introcontinental orogens in the Mid-West of China．③ Due to different regional background and evolutional processes of three types of foreland basins，individual styles of oil and gas system are developed inthese foreland basins

A Kinetic Study on Methane Carbon Isotopes of Natural Gas and Its Application：A Case Study of Kela-2 Gas Field in the Kuqa Depression,Tarim Basin

LI Xian-qing1 2, XIAO Xian-ming2, TANG Yong-chun3, XIAO Zhong-yao4, MI Jing-kui2, LIU De-han2, SHEN Jia-gui2

2005, 11(1):  137-144. 

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Based on thermal simulation experiment of closed gold tube system under the given pressure(50 MPa)and analysis of methane carbon isotopes with GC-IRMS isotope mass spectrography，combined with the kinetic modeling calculation by using the GOR-Isotope Kinetics software，this paper obtained the carbon isotopic kinetic parameters of methane generated from Triassic-Jurassic coal measures source rocks in the Kuqa depression，Tarim Basin．The average activation energies of Jurassic coal，Jurassic mudstone and Triassic mudstone samples selected from Well Yinan 2 were 227.90 kJ/mol，204.84 kJ/mol，230.63 kJ/mol，respectively．The kinetic modelling results of methane carbon isotopes were generally accorded with the laboratory pyrolysis data．It is demonstrated that the laboratory pyrolysis data could be extrapolated and applied to the actual geological condition by using the method of carbon isotope kinetics．Combined with the geological background，the source，maturity，and accumulation time of natural gas in Kela-2 gas field were further discussed．Natural gas of Kela-2 gas field was mainly derived from the Middle and Lower Jurassic coal-bearing source rocks，and belonged to the staged cumulative gas．The gas was chiefly accumulated in the last 5Ma，with its Ro value ranging from 1.3％ to 2.5％ ．On the basis of the above research．a kinetic model of natural gas migration and accumu1ation in Kela-2 gas field was established ．This kind of study may provide a new idea for natural gas quantitative assessmentand dynamic research．