Table of Content

20 September 2006, Volume 12 Issue 3

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Article

Neotectonic Evolution of the Peripheral Zones of the Ordos Basin and Geodynamic Setting

ZHANG Yue-qiao1, LIAO Chang-zhen2, SHI Wei3, HU Bo1

2006, 12(3):  285-297. 

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based on satellite imagery interpretation, field structural measurements and morpho-tectonic analysis, this paper makes a brief synthesis on Cenozoic extensional history of the graben systems around the Ordos basin and delimits the lower bound of the initial age, 8 -9 Ma, of Neotectonic era in the peripheral zones of Ordos. Neotectonic evolution has been divided into 3 stages with distinct morpho-tectonic features. An early stage during the Latest Miocene to Early Pliocene was characterized by development of the Red clay basin and by initiation of the Shanxi graben system. The peripheral zones of the Ordos was dominated by transtension. A middle stage during the Late Pliocene and middle Pleistocene experienced multi tectonic events that were characterized by episodic compressive deformation along the SW margin, continued subsidence of the graben system along NW and SE margins, uplift of the Ordos basin and development of erosional valley and river terraces along the Jin-Shan deep incised valley of the Yellow River. The most recent neotectonic stage since the middle to Late Pleistocene was dominated by deformation of transpression and transtension in the peripheral zones of Ordos, with intensification of differential vertical motion and river incision. Fault activities during the neotectonic era include different combination of normal, sinistral and dextral strike-slip and reverse faulting. The Ordos block itself rotates around vertical axis, which was accommodated by normal faulting and crustal extension along the graben system. The episodic evolution of neotectonics in the Ordos regions has been dynamically related to fast northward growth and episodic eastward extrusion of Tibetan Plateau during the Late Cenozoic time

The Basement of Baryan Har Basin Is A Part of Western Yangtze Platform： Evidence from Granites

LEI Yu-hong1,2, MA Chang-qian1, WANG Guo-can1

2006, 12(3):  298-309. 

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The Zhajia pluton, emplaced in the Triassic Baryan Har sedimentary basin on the northeastern margin of the Tibet-Qinghai Plateau, consists of high-K calc-alkaline biotite granites. Mafic microgranular enclaves with magmatic textures are also present in the pluton. The granites are characterized by enriched LREE and LILE, and depleted HREE and HFSE. They have moderate negative Eu anomaly （0.5 -0.7）, low end （t）（ -3.5 - -6.2）and moderate initial （87Sr/86Sr） ratios （0.7088 -0. 7090）, and their depleted mantle model ages （tDM） range from 1.1 to 1.3 Ga, while mafic enclaves have lower SiO2 contents, lower end （t） （ - 4. 7 - - 6. 1 ）, higher initial （^87Sr/^86Sr） ratios （0. 7084 -0.7124） and older tDM （1.4 Ga） than the host granites. It is suggested that the early Jurassic Zhajia pluton was formed in post-collisional setting, and granitic magma of the pluton was generated by par- tial melting of the lower crust as a result of the intrusion of mantle-derived magma. The sources of granitic magma might be the mixture of Precambrian Kuhai complex and Wanbaogou group occurring in Kunlun orogenic belt. It seems that there is a Middle Proterozoic basement beneath the Baryan Har sedimentary basin, and the basement is a part of the Western Yangtze platform

Geochemical Characteristics and Genesis of Dioritic Enclaves in Lisong Granite, NE Guangxi Province

YANG Ce, ZHU Jin-chu, ZHANG Pei-hua,XlE Cai-fu

2006, 12(3):  310-318. 

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The dioritic enclaves are widely distributed in the Lisong granite. An integrated field and laboratory study on the colours, shapes, textures, structures, compositions, mineralogy and petrology of the enclaves indicates that they are products of rapid crystallization from the silicate melt. The major elements analytical data show a trend characterized by a linear correlation between rock-forming elements. In trace elements, both the dioritic enclaves and hosting granite are enriched in LILEs and HFSEs. Based on the zircon saturation temperature and hornblende geobarometer estimation, the crystallization temperature and pressure of enclaves and hosting granite are very close, in the range of 793 - 824 ℃ and 3.5 - 5. 1 Kb, respectively. The petrological and isotopic features indicate that the Lisong enclaves and hosting granite were basically crystallized at the same time, but with different crust-mantle proportions and different sources. All these integrated data demonstrate that the Lisong enclaves are remnants of magma mingling.

Geochemistry of Mesozoic Mafic-Intermediate Volcanic Rocks and Its Constraints on Lithospheric Characteristics

LI Xiao-yong1,2, LI Chao-wen2, FAN Li-yong2

2006, 12(3):  319-327. 

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The Mesozoic volcanic rocks in Yanshan area comprise a wide spectrum of rock types including calc-alkaline, high-K calc-alkaline and shoshonitic lava series. All these rocks show strong LREE, LILE enrichment and HFSE depletion as well as moderately enriched Sr-Nd isotopic compositions, which are different from the mafic volcanic rocks within North China craton and from Xingmeng Orogen. The Yanshan volcanic rocks show transitional geochemical and isotopic signatures when compared to the Mesozoic counterparts in the adjacent cratonic area and orogenic belts, e. g., La/Nb, （Nb/La）N, （Hf/Sm）N ratios and end values, indicating that the melting mantle source of these rocks was modified by the subducted Paleo-Asian Ocean Plate on the basis of inheriting characters of EMI mantle within North China craton. Similar to lithospheric thinning and replacement mechanism, subductionrelated metasomatism of Paleo-Asian Ocean Plate played an important role during lithospheric thinning and evolution beneath Yanshan area, which is different from lithospheric thinning and replacement mechanism within North China craton

Sequence-Stratigraphic Framework and Its Forming Background of Palaeogeography for the Middle Cambrian of the Upper-Yangtze Region

MEI Ming-xiang1,2, ZHANG Hai1,2, MENG Xiao-qing1,2, CHEN Yong-hong1,2

2006, 12(3):  328-342. 

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In the Upper-Yangtze region, especially in the Guizhou Province and its adjacent areas, the Middle Cambrian is well developed and is marked by a succession from small-amount limestones to large-amount dolomites. In the shallow intra-platform setting of the northwestern part of the study area, the middle Cambrian is made up by both the thin muddy and sandy dolomites with trilobite fossils of the Douposi Formation and the thick dolomites lacking fossils of the Loushanguan Group. In the deep-water setting of the southeastern part of the study area, the Middle Cambrian includes the Duliujiang Formation and the lower part of the Yangjiawan Formation that are constituted by black shales, muddy shales, muddy limestones and breccia limestones. In the transitional region, the middle Cambrian can be divided into Kaili and Jialao Formations marked by muddy shales and muddy limestones. Both the regularly temporal succession of sediments and the spatially distributional pattern of sedimentary facies form a particular sequence-stratigraphic framework that contains three third-order sequences. This sequence-stratigraphic framework not only demonstrates two types of facies-changing surfaces and two types of diachronisms in the stratigraphic records but also means a regular deepening-shoaling process of sedimentary environment controlled by cycles of the third-order sea-level changes. Series of panel diagrams of sequence-stratigraphic framework and corresponding maps of lithofacies and palaeogeography can overally illustrate the temporal evolution succession of sediments and spatial distributional pattern of sedimentary facies for the third-order sequences, and can demonstrate the forming palaeogeographic setting for the third-order sequences. More interestingly, the large-scale transgression after a large-scale regression at the turn from the early to the middle Cambrian apparently resulted in expansion of the ecological space. With this ecological expanding two famous biota＇s that are named as ＂the Taijiang Biota＂ in the end of the early Cambrian and ＂the Kaili Biota＂ of the initial stage of the middle Cambrian are formed in the deeper background of sedimentary environment. These two famous biota＇s represent another biological explosion after the biological explosion in the early stage of the early Cambrian represented by both ＂the Small-Shelly Biota＂ of the initial stage of the early Cambrian and ＂the Chengjiang Biota＂ of the early of the Early Cambrian. Therefore, together with the genetic relationship between the mass-extinction event the genetic relationship between the biodiversity event and the transgression become an important problem that needs to be studied in the future

Development Features of Triassic Strata and Analysis of Original Sedimentary Pattern in North China

PENG Zhao-meng, WU Zhi-ping

2006, 12(3):  343-352. 

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Based on the study on characteristics of vertical development and lateral distribution of Triassic in North China, and with the analysis of lithological characteristics, changes of strata thickness, strata contact relationships, as well as the research about the denuded thickness of strata, the influence of the Indosinian movement exerted on the sedimentation of North China during Triassic was analysed, and the original sedimentary pattern in North China during this period was studied and discussed. The research shows that there was a large-scale sedimentary basin inside the North China Plate during Early and Middle Triassic. It inherited the structural pattern and sedimentary characteristics of the Late Hercynian, and mottled sediments of fluvial-lacustrine facies developed. Beginning from the Late Triassic and caused by the Indosinian orogeny, the strata in the east of North China were uplifted and the Lower and Middle Triassic were denuded. In some areas, the Paleozoic was also denuded, and the intermountain basins were developed only in restricted areas. There still was a basin with sediments of fluvial-lacustrine facies under warm and humid climate in the southeast of North China, but its scale became smaller

Pb Isotopic Compositions and Evolution of Garnet from Bixiling Eclogite by a Stepwise-Leaching Technique

LI Quan-zhong1,XIE Zhi1,2, CHEN Jiang-feng1,GAO Tian-shan1,QIAN Hui1

2006, 12(3):  353-364. 

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After many studies on geochronology, geochemistry and petrology of the eclogite from Bixiling have been done, its formation and metamorphic history are well known now. However, little work about elements and isotopes changes during the UHP metamorphism was conducted. The garnet Pb isotopes from Bxiling eclogites were studied by the stepwise-leaching technique in this paper. The Pb isotopic compositions obtained by different individual steps are various; However, the evolution trends of Pb isotopic compositions of different garnets and different progresses are almost consistent. The Pb-Pb ＂isochron＂ ages are about 3 billion years ,which are different from the ages of protolith formation and UHP metamorphism obtained by precursors. Although the ages perhaps have no geologic significance, the results of stepwise-leaching may reflect that Pb isotopic compositions of the eclogite from Bixiling are mixture of materials from mantle and upper crust. In brief, the protolith of the eclogite was originated from mantle materials, and during rapid exhumation after the Triassic collison, the eclogites were matesomatized by the hydrous fluid with the upper crust Pb isotopic compositions.

Zircon Ages of the Haizhou Group in the Southern Part of the Sulu Ultrahigh Pressure Orogenic Belt and Geological Significances

WANG Xiu-li1, LI Xiang-hui1,2, CHEN Fu-kun1,3, LI Qiu-li1, GUO Jing-hui2

2006, 12(3):  365-374. 

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Constraints of age and isotopic compositions on the metamorphic rock units exposed in the southern part of the Dabie-Sulu ultrahigh pressure orogenic belt are essential for the study of regional stratigraphic comparison and further for understanding tectonic process and evolution of this orogen. In this study, Nd isotopic compositions and ages of detrital zircon of schists from the Haizhou Group in the southern part of the Sulu terrain are presented. Detrital zircon gains of three schist samples collected from the Yuntai Formation of the upper Haizhou Group yielded ages clustering around 740 to 800 Ma. Initial εnd （800 Ma） values and two-stage depleted-mantle Nd modal ages of the schist samples range from - 12.8 to - 8.8 and from 2.1 to 2.4 Ga. These ages and isotopic characteristics of the Yuntai schists are similar to those of paragneisses exposed in the Susong area of the Dabie Mountains and indicate a relatively single sedimentary source. Combined with a regional stratigraphic comparison, ages of the detrital zircons can place a constraint of Neoproerozoic age, later than about 740 Ma, for the deposition time of the Yuntai Formation. The sedimentary material was likely originated from Neoproterozoic magmatic rocks having an affinity of the Yangtze block.

Discussion on K-Ar Dating of K-feldspar

GAO Jing-jing, LIU Yu-lin

2006, 12(3):  375-377. 

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K-feldspar, a ubiquitous mineral in igneous and metamorphic rocks, has long been used in K-Ar dating. However, a number of problems exist in K-Ar dating of K-feldspar. For example, K-feldspar usually yields younger ages than the co-existed minerals such as biotite. K-feldspar may also yield older ages in some cases. It is suggested that incomplete extraction of radiogenic argon from K-feldspar is one of the main reasons that leads to a younger age. Several solutions have been put forward to resolve the problem, but none of them has been successfully used in experiments. K-feldspar has low closure temperature （about 130 -150℃ ）, which can easily cause radiogenic argon lose; In addition, radiogenic argon from the wall rock as excess argon may also enter the K- feldspar. The low temperature K-feldspar （such as adularia ） shows capability to maintain various amounts of radiogenic argon which is related to their textures. The content of radiogenic argon in adularia is decreased with the increase of their triclinities. In summary, the applicabilities of K-feldspars from different geological environments are various in K-Ar dating. K-feldspars （such as micro cline and perthite） from intrusive rocks can not be used in K-Ar dating, while those （sanidine and anorthoclase） from extrusive rocks are very good ones, and the low temperature K-feldspars （adularia） can be used in dating conditionally

Analytical Method of Oxygen Isotope Compositions in Sulphates

WAN De-fang1,2, LI Yan-he1,2

2006, 12(3):  378-383. 

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Sulfates are a sort of ordinary minerals in the supergene and endogenetic geological environment. They are among the few minerals that show mass independent fractionation of oxygen isotopes. The oxygen isotopic compositions and mass independent fractionation of sulfates can provide useful information for their formation conditions, reveal special processes that can not be acquired by element concentration or single isotope ratio measurements. This is a frontier and hot topic for isotope geochemistry study in the world. Because analytical techniques of oxygen isotopes in sulfates are very complicated, this method was not established until now in China. A traditional BrF5 fluorination method for oxygen isotope measurement of BaSO4 was established recently in our lab. The separation and purification processes for BaSO4 from sulfate-bearing samples are described in this paper. The BrF5 experimental equipment, purification technique of reagent BrF5, O2 extraction preparation from sulfates and oxygen isotope measurement are introduced. The oxygen isotope compositions of an international standard of BaSO4 NBS-127, and a chemical reagent of BaSO4 were repeatedly measured. The δ^18OV-SMOW values of NBS-127 are 9.20 ± 0. 11‰ , which is the same as the published standard values. The δ^18OV-SMOW values of the chemical reagent BaSO4 are 14.64 ±0.13%o. The analysis precision of oxygen isotope ratios of BaSO4 is up to 0.13%o （1σ） , and better than 0.15 - 0.29%o （ 1 σ） reported by Wasserman （ 1992 ）.

Analytical Approaches of Carbonate δ^13 C and δ^18 O Values in Enamel Hydroxylapatite from Mammals

LI Yu-mei1,2,LIU Tung-sheng2,HONG Ye-tang3,ZHU Yong-xuan3,DONG Li-min3, PENG Jian-hua3, HAN Jia-mao2,WAN Guo-jiang3

2006, 12(3):  384-387. 

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The carbon and oxygen isotope compositions of enamel carbonate hydroxylapatite from mammalian fossils are used to reconstruct paleoenvironment. δ^13C values are indicators for diets and δ^18O values are indicators for water sources of mammals. Commonly, carbonate hydroxylapatites are reacted with pure phosphoric acid at 25 - 90℃ for 10 minutes to 3 days to liberate CO2 gas for analysis. In this study, 23 experiments were performed at diverse reaction temperatures, reaction times or pretreatments. Enamel, dentin and chalk from fossils and enamel from modern equids were collected and 23 δ^13C and δ^18O values were compared. HAC-H2O2-HAC or HC1-H2O2-HAC is more effective than HCl-H2O2-NaHSO4 or HCl-H2O2-Na2B4O7to purify carbonate hydroxylapatites, and high temperature such as 70℃ is more advisable than low temperature, especially for δ^13℃ values

Analytical Method of Chlorine Isotopic Composition in the Marine Sediment Porewaters

LI Yan-ping1,2,JIANG Shao-yong1,2,YANG Tao1,2, PU Wei1,2

2006, 12(3):  388-391. 

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A simple technique using three step cation-exchanges （Ba-type, H-type, and Cs-type）was used to enrich and purify CI from the sediment porewater samples. The recovery of CI is better than 99.6%. After purification, the ^37CI/^35CI ratios of porewater samples were measured using positive ion thermal ionization mass spectrometry based on the measurement of Cs2Cl^＋ ion with graphite load. The measured results for both the NaCI standard and one porewater sample show that the method has high stability and high precision （0.09 -0.13‰）. Initial results for porewater sampled from the South China Sea reveal significant -δ^37 Cl variation, and it may have great implications for further gas hydrate exploration in the area

Assessment of Interferences in Cu Isotope Ratio Measurements Using Multiple-Collector Inductively Coupled Plasma Source Mass Spectrometry

CAI Jun-jun, ZHU Xiang-Kun, TANG Suo-han, LI Shi-zhen, HE Xue-xian

2006, 12(3):  392-397. 

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Multiple-collector inductively coupled plasma source mass spectrometry （MC-ICP-MS） is a relatively new technique for high precision copper isotopic ratio measurements. However, potential interferences may exist in the measurements of ^65Cu/^63Cu ratios. Assessment of the interferences and effects of Cu concentration on the analyses of Cu isotope compositions using MC-ICPMS is presented here. The problem is first investigated by measuring the abundances of Na in the samples to be able to conclude that the isobaric interference of these polyatomic ions is negligible in this study. Secondly, by assuming that there is no interfering signal at mass 63, the anticipated effect of interference at mass 63 on 665 Cu measurement is modeled. The modeling result shows that even the interfering signal is very small, its effect on the ε^65 Cu value can still be between sample and standard is large. Thirdly, by comparison significant when the difference in Cu concentrations of the modeling results and actual measurements, it has been shown that the isobaric interference on mass 63 is negligible. Fourthly, the results of actual measurements show that the true 65 Cu value can be obtained if the Cu concentration of a sample solution is within the range of 0.5 - 4.0 times of that of the standard. Fifthly, the possibility of matrix effects on measured ^65Cu/^63Cu ratios has been investigated. Of primary concern in this study are the effects of Fe and Co contents on the measured ^65 CU/^63 Cu ratio. This has been examined using synthetic mixtures with Fe：Cu and Co：Cu molar ratios ranging from 0.1 to 100, and 0.5 to 10, respectively. Results of these experiments show that there is no clear dependence of ^65Cu/^63Cu on Fe/Cu 〈 100, Co/Cu 〈 7 respectively under the working conditions. Finally, the results of repeated measurements over a period of ten months show that the ε^65 Cu value of the Romil Cu solution obtained from these analyses is 3.5 ±1 （2sd） relative to NBS standard

Separation of Some Elements Using AG MP-1 Anion Exchange Resin

TANG Suo-han,ZHU Xiang-kun

2006, 12(3):  398-403. 

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The anion exchange resin AG MP-1 is commonly used for the separation of Cu, Fe and Zn from other elements. Detailed experiments have been carried out to investigate the behaviour of matrix elements during the separation. The results demonstrate that Cu and Fe can be well separated from matrix elements （ including Cr and Ni） using 7 mol/L HCl, with exception of Co. The results of experiments using different acidities of HCl show that separation of Cu from Co can be achieved using 6 mol/L HCl, where Co is eluted prior to the elution of Cu. We therefore suggest using 6 mol/L HCl for Cu separation for samples with relative simple chemical compositions, such as sulphides, oxides and hydroxides. In this case, Cu can be well separated from Co and other elements, as these kinds of samples have low contents of Na, Ca, Mg and Al. For silicate samples with high Co contents, a twocolumn-precedure may be used to achieve total separation of Cu from matrix elements, i. e. , separation of Cu from the majority of matrix elements using 7 mol/L HCl, then separation of Cu from Co using 6 mol/L HCl, with the same column. Besides, the methods developed here may be used for separation of Ca and Mg from Fe, Cu, Zn and Co

An Engineering Slope Supporting Design Combined with Ecology Renewing

GAO Peng1,CHEN Zhen-zhou1,SHAO Chang-yun2, HE Qing-yu1, LIU Yu-hua1

2006, 12(3):  404-409. 

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Taking a slope in lava area in south Zhejiang Province as an example, the authors studied the slope vireseenee method in this paper. We calculated safety factor of slope covered by galvanized wire net. We also considered potential deficiency of stability when planting material ejecting method applied to high steep rock slope. We set up lattice on slope surface by considering vegetation slope surface having little effect in reinforcing slope surface. According to the ecological principle, we brought forward a slope support plan combined with slope surface vireseenee

Comment on《 Quantitative Analysis of X-ray Diffraction for Palygorskitewithin Attapulgite Clay》

LI Zhen1, YIN Lin1,2, XI0NG Fei3, HE Kun1, Zheng Yi-chun1

2006, 12(3):  410-412. 

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Xiong et al （2005）proposed the internal standard method for the clays. The original authors calculated the integral intensity of peaks by using the height. This method leads to the evident error presented in the internal standard quantitative analysis of attapulgite half peak width multiplied by peak curve. The contents in clay would be often higher than 100% when calculating with high purity attapulgite clay samples of palygorskite The peak areas are obtained by using software to integrating the intensity of peaks in current studies. The background in the text has been subtracted in all XRD patterns for discussion