Table of Content

20 June 2004, Volume 10 Issue 2

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Article

Pb-Nd-Sr Isotopic Study of the Middle Jurassic Basalts in Southern Jiangxi Province：Characteristics of Mantle Source and Tectonic Implication

ZHANG Bang-tong, CHEN Pei-rong, LING Hong-fei, KONG Xin-gong

2004, 10(2):  145-156. 

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The basalts of the Changpu Formation of the Yutian Group in the Longnan-Xunwu area of Southern Jianxi were formed in the Middle Jurassic Epoch with a Rb-Sr isochron age of 173-176 Ma，and are the basic endmenber of the bimodal volcanic rock assosiation．The Pb-Nd-Sr isotope compositions of basalts are as follows：enriched in radiogenic lead，(206Pb／204Pb)i= 17．872～18．653，(207Pb／204Pb)i=15.434 ～16.131，(208Pb／204Pb)i=37．837 ～39．194；intermediate initial Nd isotopic ratios，εNd(t)= -0.4+1.1；and distinctive high initial Sr isotopic ratios，ISr=0．70835～0．71115．On the Pb-Pb diagrams．the basalts are plotted above NHRL line and have obvious Dural anomaly：Δ7／4Pb=0．19～61．7(22．1 in average)；△8／4Pb=59．2～101．5(71．03 in averag)；ΔSr=80～111．5(91．5 in average)．The Sr-Nd，Sr-Pb，Nd-Pb，Pb-Pb relationships of basalts strongly suggest a mixing source of the depleted mid．ocean ridge basalt mantle endmenber(DMM)and with the EM II enriched mantle endmenber．According to double-variation and two-component(Sr-Nd)mixing equation，calculation shows that the depleted mantle endmember and the EMII enriched mantle endmember for rock-forming materials of southern Jiangxi basalts are 58％ 一64％ and 42％ 一36％ ．respectively．The E-W trending Middle Jurassic bimodal volcanic rock belt in East Nanling area implies a major extensional tectonic event during the Early Yianshanian period．On the basis of Sr-Nd-Pb isotope geochemical and tectonic features mentioned above，it is assumed that the endmember component of EM II of Mesozoic mantle souses in southern Jiangxi was derived from the Gondwanaland．

Ar-Ar Isotopic Ages of Jinman and Shuixie Copper Polymetallic Deposits in Yunnan Province，and Their Geological Implications

XU Xiao-chun, HUANG Zhen, XIE Qiao-qin, YUE Shu-cang, LIU Yin

2004, 10(2):  157-164. 

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Lanping basin of the northwestern Yunnan province is an important Cu，Ag，polymetallic mineralization-concentrated area in the western China．There are many large，middle and small scale Cu-polymetallic deposits located in three metallogenic belts of the basin．The metallogenic belt of the western border of the basin is characterized by enrichment in copper and controlled by Lancangjiang fault belt．

Sr and C Isotopic Correlation and the Age Boundary Determination for the Neoproterozoic in the Southern Liaoning and Northern Jiangsu- Northern Anhui Provinces

ZHENG Wen-wu1, YANG Jie-done2 3, HONG Tian-qiu1,TAO Xian-cong2,WANG Zong-zhe4

2004, 10(2):  165-178. 

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The host strata of the deposits in the metallogenic belt are Perimian system to Tertiary system which are mainly composed of elastic rock formation，volcanic rock formation and red，salty elastic rock formation．The occurrences of the ore bodies are mainly veins，networks and lens-shaped．In order to know the regional metallogenetic epoch and regularities，quartz from the major ore-forming stage of Jinman copper deposit and Shuixie copper (cobalt)deposit was analyzed by the 40Ar-39Ar fast-neutron activation dating technique．which gives well-defined plateau ages of 56．7±1．0Ma and 59．2±0．8Ma，respectively． Each isochron age is corresponding to the plateau age respectively within the range of error．The Ar-Ar ages represent the forming ages of quartz，i．e．，the forming ages of the ores of Jinman and Shuixie deposits．

Geochronology of Layered Intrusions in Cida and Taihe Districts，Panxi Area，Sichuan Province

LIU Hong-ying, XIA Bin, LIANG Hua-ying, ZHANG Yu-quan

2004, 10(2):  179-185. 

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Based on the research results of the isotopic geochronology on the mineralization and the magmatism of the Cu，Ag，polymetallic deposits in the western border and other parts ofthe Lanping basin，it is concluded that the isotopic ages of these two deposits are consistent with those of other deposits in the region，and the mineralization epoch is basically synchronous in regional mineralization of the basin．The copper，polymetallic deposits were formed in a unitary geodynamic background．The mineralization epoch of the deposits is the earlier stage of Himalayan orogeny．The formation of the deposits in the basin is constrained by the evolutionary geological events of the structure and thermal regime in the same time．

Petrological and Geochemical Studies on the Intermediate-Basic Volcanic Rocks from the Middle-South Part of the Da Hinggan Mountains

Lü Zhi-cheng1 2, DUAN Guo-zheng3, HAO Li-bo3, LI Dian-chao3, PAN Jun3, WU Feng-chang2

2004, 10(2):  186-198. 

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The petrogenesis and tectonic background of Mesozoic volcanic rocks from the middle-south part of the Da Hinggan Mountains are closely related to the late stage evolution of the Southem Mongolia-Da Hinggan Mountains orogenic belt and to the genesis of copper-polymetallic deposits．Based on detailed fieldwork，petrological and geochemical studies on volcanic rocks have been carried on．The results show that the volcanic rocks，including basaltic trachyte，trachyandesite，trachyte and dacite，belong to cale-alkaline series．In major elements they are enriched in Si02，Na20 and K20，and depleted in Fe203，FeO，MgO and CaO；and in trace elements they are enriched in lithophile elements，and depleted in siderophile elements and Nb，Ta，Ti etc．In REE patterns they are generally LREE enriched，(87Sr／86Sr)t ratios are 0．7045～0．7077，mostly 0．7045～0．7055，and most of εNd(t)values are positive．The results suggest that partial melting of upper mantle in different degrees Was the major mechanism for generation of the volcanic rocks in the middle-south part of the Da Hingan Mountains。and the volcanic rocks were developed in the tensional tectonic setting．The Mesozoic volcanic activity was a response to the extension caused by upwelling of mantle plume of asthenosphere during the post-orogenic period of the Tianshan-Da Hingan Mountains belt，to the post-orogenic extension background of the Inner Mongolia-Jihei orogenic belt，and to compression background caused by closure of Mongolia-Okhotsk residual ocean in a scissors form．

Adakitic Granites within the NE Jiangxi Ophiolites，South China Geochemical and Nd Isotopic Evidence

LI Wu-xian, LI Xian-hua

2004, 10(2):  199-208. 

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The geochemistry and Nd isotope compositions of Xiwan albite gmaites within NE jiangxi ophiolites were reported in this paper．The granites share some geochemical similarities with modem adakite，including high Al203(15％ ～17％)，Sr(383 x 10-6～920 x 10-6)，Sr／Y(166～444)and high εNd(t)values(+4．9～+6．0)．Compared with the typical adakites，these granites are lower in HREE(Yb：0．14×1O-6～0．21×10-6)，MREE(Sm=0．6 x 10-6～1．2 x 10-6)and Y(1．66 x 10-6～2．81 x 10-6)contents but higher in Na20／K20(12～37)and Na20／CaO(2．7～3．6)ratios．Geological and geochemical features suggest that they were generated by lower degree of partial melting of subducting spillitized oceanic crest at pressure high enough to stabilize garnet and amphibole but the plagioclase absent．The scenario is similar to the formation of the modem adakite in circum-Pacific margin．

Geochemical Characteristics for Siliceous Rocks of Different Ages in Northeastern Jiangxi and Their Geological Significance

WU xin-hua1, LOU Fa-sheng1, WANG Yu-jing2, SONG Zhi-rui1, YANG Qun2, DENG Guo-hui1, HUANG Zhi-zhong1, LING Lian-hai1

2004, 10(2):  209-216. 

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The siliceous rocks are widely developed in strata of different ages in the northeastern JianXi Province．Their Si02 contents are in the range of72．2％ ～97．19％ ，and their Si／Al ratios are 10．84～9321．The Si02 contents are well negatively correlated with A]2O3 contents．This implies that these rocks have a source with higher proportion of terrestrial muddy sediments．Some geochemical characteristics of these siliceous rocks ale shown below： AL2O3／( AL2O3+Fe203)=0．60～0．99，Ce／Ce =0．99～1．22，(La／Ce)N=0．91～1．83；V／Y<5．78，Ti／V>17．These characteristics indicate that they were formed in a tectonic environment of continental margin．There is no relation with the deep oceanic basins and／or mid-ocean ridges．Since the Paleozoic the tectonic environment of deep oceanic basins was not developed in this region．

A Discussion on Geochemical Characteristics and Genesis of Intrusions in Shizishan Orefield，Tongling area，Anhui Province

HUANG Shun-sheng1, XU Zhao-wen1, GU Lian-xing1, HUA Ming1, LU Xian-cai1, LU Jian-jun1, NIE Gui-ping2, ZHU Shi-peng2

2004, 10(2):  217-226. 

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Baimangshan，Qingshanjiao and Nanhongchong intrusions in the Shizishan orefield，Tongling area，Anhui province，are composed of pyroxene diorite，quartz diorite and granodiorite，respectively． They are predominantly calc-alkine，alkaline-rich，with higher Ba，Sr contents，and share the following similar characteristics with the high Ba-Sr granitoids：higher Ba，Sr and LREE and lower Y and HREE abundances，distinct Nb，Ta and Ti depletion，and absence of negative Sr and Eu anomalies．It is suggested that crystallization differentiation played an important role in evolution of magmas because they have covariant major elements．Fractionation of P-and Ti-bearing accessory minerals，such as apatite，ilmenite and titanite might result in a decrease of P and Ti abundances．The relative depletion in Y and HREE might be caused by hornblende and／or garnet retention，but not intermediate plagioclase in the source．Initial 87Sr／86Sr(0．7062～0．7101)and 143Nd／ 144Nd(0．5116～0．5121)ratios show EM I-type signature, and are negatively correlated．The regional switching from compression to extension in the early Cretaceous in a post-collisional setting might readily trigger a rapid rise of hot Ba-and Sr-enriched upper asthenosphere material and result in widespread melting of lower crust to generate voluminous magmas in the deep-seated magma chamber．

2-D Gravity Modeling and Integrated Interpretation of the Kuqa Foreland Basin，Northwest China

WANG Qin1 2, LU Hua-fu1, WANG Liang-shu1 , XU Ming-jie1, HU De-zhao1, JI Shao-cheng2

2004, 10(2):  227-238. 

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The intense deformation in the Kuqa foreland basin，northwest China，limited the seismic exploration and interpretation in this important gas field of China．This study is devoted to improving the reliability of predicting complex structures by 2-D gravity modeling and joint interpretation along 2 MT profiles and 3 seismic profiles across the Kuqa fold-and-thrust belt．The results indicate that fault-related Folding is the basic deformation style in this foreland basin．The development of detachment along the Eocene gypsum rocks and gypseous mudstones，and along the Jurassic and Triassic coal-bearing formation stratigraphically controlled the deformation patterns of fault-related folds，and resulted in change of relative positions of gas traps at depth with anticline crests on the surface．Overall，in the north，a Paleozoic wedge of Tianshan has embedded into the Mesozoic strata of northern tilted zone and caused increased gravity anomalies；in the south, the increased sedimentation depth of the Cenozoic rocks decreased the gravity anomalies，and the accumulation of the Eocene salt body should be accounted for the low gravity value．The relatively higher density of basement in the Baicheng depression probably reveals an early regional uplift associated with intrusive igneous activity and continued extension．The thrust propagated progressively from Tianshan to the Tarim basin，which implies enhanced N-S compression and crustal shortening since the Miocene as a remote structural response to the India-Eurasia collision．

New Comment on the Early Precambrian Tectono-Magmatic Subdivision and Evolution in the Western Shandong Block

HOU Gui-ting1, LI Jiang-hai1, JIN Ai-wen2, QIAN Xiang-lin1

2004, 10(2):  239-249. 

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The evolution of early Precambrian tectono-magmatic activities in the Western Shandong Block was studied by using the methods of field geology，petrology and geochronology. Two units can be subdivided：The TTG rocks in the west and gneissic adamellite in the east．The TTG rocks were the products of Late NeoArchean continental magmatic activity，and the geissoid adamellite rocks were the products of continental accretion activity after the 1TrG magmatic activity．The subdivision of tectono-magmatic units in the Western Shandong Block provided a good Precambrian tectonic section．The ductile transtensional zones between these two tectono-magmatic units show that the paleocrust was thickened by superimposition of these ductile transtensional zones．The Protemzoic sialic and diabase dike swarms extensively developed in these two units show that these units were joined together after the cratonization at the end of NeoArchean．This indicates that the Western Shandong Block Was a part of the brittle craton in the Proterozoic time．

Mesozoic—Cenozoic Tectonic Evolution of the Hefei Basin

CHEN Hai-yun1 2, SHU Liang-shu1, ZHANG Yun-yin2, LIN Chun-min1, LIU Guo-hong2, ZHAO Yan-yan1

2004, 10(2):  250-256. 

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The authors studied the tectonic evolution of Hefei Basin by using anintegrated analysis on the geological，geophysical and drilling data．Results show that Hefei Basin is a Mz-Cz residual basin generated by conjunct influence of Dabie Orogeny and Tanlu(Taneheng-Lujiang)Fault Zone．During the early stage of basin development，it was strongly affected by Dabie Orogeny，and during the middle and late stages of basin evolution，the affection of Tanlu faulting gradually became more important．Due to co-affection by the Dabie and the Tanlu tectonic systems，Hefei Basin experienced a series of development stages：the basement stage during the Indosinian event，the depression basin stage during the early-middie Juvassie，the foreland basin stage during the Late Jurassic，the strike-slip basin stage during the Early Cretaceous，the fault basin stage from the Late Cretaceous to the Paleogene，and the basin closure stage from the Neogene to Quaternary．

Investigation on the Salt Lake Source Rocks for Middle Shasi Column of Dongying Depression

ZHU Guang-you1, JIN Qiang2, DAI Jin-xing1, ZHANG Shui-chang1, ZHANG Lin-ye3, LI Jian1

2004, 10(2):  257-266. 

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Evaporite is well developed in the middle Shasi column of Shahejie Formation，Tertiary system in Dongying Depression，where the thickness of saliferous layers with mudstone exceeds 1000 m in the southern Shengtuo and central rift zone．Analysis of many samples and study on sedimentary system show that the lake basin was in an under-filling condition．A deep water evapofite formation model was established．The geochemical characteristics of dark gray mudstone and shale in evapofite layers record the sedimentary environment of salt lake．The high salt medium is beneficial to organic concentration and preservation．The gray mudstone and shale in middle Shasi column was a kind of high quality source rocks in Dongying Depression．

Research on the Properties and Origin of the Crude Oil from the Transition Zone of Southern Xingshugang District in Daqing Oil Field，Northeastern China

WANG Yu-ming, LI Shi-kui, HE Guang-yu, ZHU Yan, CHEN Han-lin, YANG Shu-feng

2004, 10(2):  267-274. 

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The crude 0il of the southern Xingshugang district in Daqing oil field is of lower density, 1ower viscidity，lower colloid，high wax and lower freezing point，and belongs to the typical light oil type．It also has higher saturated hydrocarbon content，overall hydrocarbon content and higher saturated to aromatic hydrocarbon ratio，which indicates the input of original algae．The carbon number distribution of normal alkanes shows a range from Cl5 to C39 with a peak at nC22 or nC23．Moreover，the whole oil and its family group show a feature of light carbon isotopes．The crude oil is very rich in steranes and contains a few 4-methyl steranes．The C27 and C29 sterane compound concentrations and the C28 sterane compound concentrations are low，and the distribution of ，C28 and C29 steranes is"L"shaped．The pentacyclic triterpanes in the crude oil ale also plentifu1．They are mainly hopanes，novel hopanes and gammaceranes． The oil-source rock correlation indicates that the crude oil has the similar carbon isotope compositions，and the similar steranes，terpanes distribution with the mudstone of the Lower Qingshankou Formation in Sanzhao sag，which suggests that the crude oil in the study area was derived from the Lower Qingshankou Formation in Sanzhao sag．

Study on Sea—Level Changes in the Platform Area of Southern Guizhou across Luodian Stage to Lengwu Stage(Permian)

LIU Jia-run, YANG Xiang-ning, SHI Gui-jun, SUN Li

2004, 10(2):  275-282. 

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Seven 3rd-order cycles of continuous sea--level changes from the late Luodian Stage to the Lengwu Stage(Permian)in the platform area of southern Guizhou Province are recognized based on the characteristics of sequence stratigraphy in the study area．The process of regional sea-level changes could be divided into two stages，of which the first stage includes 1st～3rd cycles characterized by lower rote of early rise；and the second stage includes 4th ～7th cycles characterized by higher rote of early rise．Among these cycles，early-rise rotes in the first cycle and the fourth cycle were the lowest and highest，respectively．Although the sea surface in the process of sea-level changes was always high up the shelf break，the last sea-level fall accompanied by the Dongwu crustal movement at the end of Lengwu Stage caused overall regression and exposure of the area．The study results show that the evolutionary pattern of fusulinacean foraminifera (Middle Permian)in this area might be related to above mentioned sea-level changes．

Occurrences and Implications of Aryl Isoprenoids Detected in the Crude Oils from Lunnan Oilfield，Tarim Basin，NW China

LU Hong, SUN Yong-ge, PENG Ping-an

2004, 10(2):  283-289. 

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Abundant 1-alkyl一2，3，6-trimethyl aryl isoprenoids were detected in the aromatic fraction of the Paleozoic crude oil samples from Lunnan Oilfield，Tarim Basin，NW China．These compounds were considered to be derived from β-cleavage of diaromatic carotenoid moieties mainly found in the chlorobiaceae family of photosynthetic sulfur bacteria and regarded as a biomarker that indicates a saline and strongly reducing sedimentary environment．It can be inferred that these biomarkers indicate prolific bacteria growth in a stratified water column at and below the oxic-anoxic boundary layer in depositional environment，which implied that contributions of first-class source rocks in a stratified water column and highly reducing sedimentary environment were underestimated in present exploration strategy in the Tarim Basin．Especially，the distribution of C15·3，4，5-isomer was surveyed in these oil samples to pursue its geochemical significance or application．Furthermore，the ratio of C15-3，4，5 isomer to C13-2，3，6 isomer(C15-3，4，5／Q3-2，3，6)was proposed and correlated with some typical geochemical parameters(such as Pr／Ph，Ga／C31H，Ts／Tm)．The results in this paper show that the ratios of C15-3，4，5／C13-2，3，6 have a systematic increase with these increasing parameter values．This indicates that，apart from being a biomarker of having a specific precursor and indicating hypersaline and highly reducing sedimentary facies，1-alkyl-trimethyl aryl isoprenoids can also have a significance in the determination of organic matter maturity．The above-mentioned discussion can help us better understand their distribution，thermal maturity effect，diagenetic and catagenetic transformation of isorenieratene．

Experiment on the Fracture Behaviour in Rocks

GE He-ping1 2, SUN Yan1, ZHU Wen-bin1, GUO Ji-chun1. LIU De-liang3, CHEN Xiang-yun4, WANG Feng, WEN Shi-hong

2004, 10(2):  290-296. 

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Fracture behavior，failure process and parameter determination of the rock specimens are the basis for research on the fissure fault structures．Experimental rock specimens were collected from the eastern Sichuan and northern Xinjiang provinces，and the stress isopleths to the rock specimens were calculated with a finite element method(FEM)for accurate determination．Based on the failure observation and curve comparison of rock specimens from the uniaxial and triaxial experiments，the fracture behavior and stress-strain of the rocks can be divided into four stages，the fissure pressure-airtightness stage，the elastic deformation stage，the microscopic split stage and the macroscopic fracture stage．Through the microscopic analysis of developing process of the rock split-fracture-smash from the uniaxial pressure experiment, it is found that the macroscopic fractures are mainly developed along the primitive hidden fissures and critical fissures，and formation of many new fisures mainly occurs in the macroscopic fracture stage．

In Situ Measured Data and Systematic Study of Pile Body Stress in Different Retaining Structures

LI Jun-cai1 2, LUO Guo-yu1, DAI Jia-dong2

2004, 10(2):  297-304. 

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Borehole cast-in-place concrete pile cantilever retaining structure and single-pivot mixed retaining structure are usually deep-foundation retaining structures．Borehole cast-in-place concrete pile multi-arch retaining structure is a new retaining structure．Based on the in situ measured data and discussion on pile body stress at certain deep-foundation pit excavation in Nanjing city，the magnitudes and distribution patterns of force acted on single retaining pile at different excavation depths in different retaining structures under same engineering geological and hydrogeological conditions，but in the same conditions of construction and cut down groundwater were obtained．Valuable information is provided in this paper for retaining structure design of pit excavation and extending use of borehole cast-in-place concrete pile multi-arch retaining structure．