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2003 Vol. 14, No. 2

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Kanfenggou UHP Metamorphic Fragment in Eastern Qinling Orogen and Its Relationship to Dabie-Sulu UHP and HP Metamorphic Belts, Central China
Shutian Suo, Zengqiu Zhong, Hanwen Zhou, Zhendong You
2003, 14(2): 95-102.

In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun North Qaidam North Qinling UHP metamorphic belt. The other is the Dabie Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite and microdiamond bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and collision belt between the Yangtze and Sino Korean cratons, occurred during the Paleozoic. On the other hand, the well constrained Dabie Sulu UHP and HP metamorphic belts occurred mainly during Triassic time (250-220 Ma), and were produced by the intracontinental deep subduction and collision within the Yangtze craton. The Kanfenggou UHP metamorphic fragment does not appear to link with the Dabie Sulu UHP and HP metamorphic belts along the orogen. There is no reason to assume the two UHP metamorphic belts as a single giant deep subduction and collision zone in the Central Orogenic Belt situated between the Yangtze and Sino Korean cratons. Therefore, any dynamic model for the orogen must account for the development of UHP metamorphic rocks belonging to the separate two tectonic belts of different age and tectono metamorphic history.

Sedimentary Facies Architectures of Third-Order Sequences from Early to Middle Triassic in Nanpanjiang Basin
Mingxiang Mei, Yongsheng Ma, Jun Deng, Jinhan Gao, Huijun Chen, Qingfen Meng, Donghai Li
2003, 14(2): 103-118.

There are complex and regular changes on sedimentary facies from the Early to the Middle Triassic in the Nanpanjiang basin. After the obvious drowned event of carbonate platforms in the transitional period between Permian and Triassic, carbonate platforms have evolved into the ramp type from the rimmed shelf type. The differentiation of sedimentary facies becomes clearer in space, which are marked by the changes from an attached platform to a turbidity basin and several isolated platforms in the basin. The striking characteristics are the development of oolitic banks on isolated platforms in Nanning and Jingxi and the reef and bank limestones in the margin of the attached platform in the Early Triassic. Despite the difference of the time span and the architecture of facies succession of third order sedimentary sequences, the process of the third order relative sea level changes reflected by the sedimentary facies succession of the third order sequences is generally synchronous. Therefore, six third order sequences could be discerned in the strata from the Early to the Middle Triassic in the Nanpanjiang basin. Using two types of facies changing surfaces and two types of diachronisms in stratigraphic records as the key elements, the sedimentary facies architectures of the third order sequences that represent sequence stratigraphic frameworks from the Early to the Middle Triassic in the Nanpanjiang basin could be constructed.

Raman Spectrum Study on Quartz Exsolution in Omphacite of Eclogite and Its Tectonic Significances
Lu Wang, Zhenmin Jin, Mouchun He
2003, 14(2): 119-126.

The studies on ultra microstructure characteristics of quartz exsolution in eclogite and coesite in UHP eclogite of several localities are done with the appliance of laser Raman spectroscopy and U stage. Research results show that the phase transformation of coesite quartz in garnet and/or omphacite is a continuous process. Topological relationship is present between quartz exsolution in omphacite and its host mineral which shows orientations of two long axes of quartz exsolution parallel to (100) and (-101) of omphacite. At present, some scholars suggest that the quartz exsolution in omphacite of eclogite is the evidence of UHP metamorphism. However, temperature and pressure condition and the exsolution mechanism of oriented needlelike quartz in omphacite still remain unclear. Therefore, further study should be enhanced on experimental research on exsolution mechanism of super silicate clinopyroxene, which could provide experimental quantitative constraint on quartz exsolution as UHP indicator.

Organic Geochemistry Characteristics in Ores and Host Rocks from Qixiashan Lead-Zinc Deposit, Nanjing, China
Shucheng Xie, Hongmei Wang, Jianqiu Guo, Bin Liang, Xiugao Zhou
2003, 14(2): 127-136.

Organic matter, associated with ores, host rocks, ore source rocks and present in fluid inclusions in the Qixiashan lead zinc polymetallic deposit hosted in Upper Carboniferous dolomites and limestones in East China, was systematically analyzed using Fourier transform infrared spectroscopy, gas chromatography (GC), GC/mass spectrometry and proton induced X-ray emission. The biomarker ratios of nC21--/nC22+-alkanes, C23-tricyclic/C30-hopane and the tricyclic terpane parameters including C21/C23, C19-20/C21-29 and C19-25/C26-29 can effectively discriminate ores from host rocks. Extractable organic matter present in fluid inclusions displays similarities to those enclosed in the ore source rocks in the biomarker ratios, suggesting that a proportion of organic matter was introduced into the deposit from the ore source strata. The presence of copper and zinc in stage Ⅱ pyrobitumen indicates that some metals may have been transported by an organic fluid or removed from an aqueous fluid by organic matter.

Petrographic of Northwestern Sudan
M Nafi, O M Abdullatif
2003, 14(2): 137-143.

The sedimentology of the Northwestern Sudan consists of lower, middle and upper cycles. The lower and upper cycles are composed of intercalated fluvial and shallow marine facies, whereas the middle cycle consists entirely of fluvial and glaciofluvial facies. The petrographic analysis shows that the lower and upper cycles consist of quartz and lithic arenite sandstones, whereas the middle cycle consists of arkosic and lithic arenite sandstones. The lower and upper cycle sandstones reflect derivation mainly from recycled orogens with minor contribution from craton interior provenances. However, the middle cycle sandstones indicate derivation from basement uplift, transitional and mainly recycled orogens provenances.

Assessment of Rock-Eval Tmax Data in Bambra-2 Well of Barrow Sub-basin, North West Shelf of Australia: A Case Study of Contaminated Rock-Eval Data
Sheng He, Kaiko Alex, Middleton Mike, Chunqing Jiang
2003, 14(2): 144-150.

The contamination of cuttings and side wall core (SWC) samples in the Bambra 2 well by drilling mud additives and natural hydrocarbons may cause Rock Eval Tmax (℃) data to be suspect, and affect its utility in the assessment of thermal maturity. The Rock Eval results of 284 cuttings samples, 31 side wall core samples and conventional core samples from the Jurassic Cretaceous sedimentary sequences in the Bambra 2 well are presented in this paper. Significantly lower Tmax values from cuttings samples compared with Tmax values from conventional core samples and solvent extracted SWC samples, from the deeper and higher maturity interval, are thought to have been caused by contamination by diesel and other drilling mud additives. The cuttings samples in the Barrow Group of Cretaceous may be contaminated by natural hydrocarbons, resulting their Tmax values to be 2-10 ℃ lower than a regularly increased Tmax trend from core samples. This study indicates that more reliable Rock Eval Tmax data are obtained from the conventional core samples and solvent extracted SWC samples. This study also indicates that the Tmax values from some SWC samples were also affected by free hydrocarbons, due to the use of diesel as a mud additive as well.

Measurements of 222Rn and 220Rn with a Large Size Collector of Radon Progeny
Qifan Wu, Wenyi Jia, Fang Fang, Jun Wang, Jianping Cheng, Guilin Liu, Li Zhu
2003, 14(2): 151-154.

Radon concentrations in high background radiation areas in the south are higher than those of others in China, especially 220Rn concentration is significantly high. Therefore, measurements of 222Rn and 220Rn concentrations should be carried out there. This paper introduces a large size collector of radon progeny and its applications. The collector is a sheet of polyvinyl chloride fiber with electrostatics of (-500 V)-(-700 V). Its size (60 mm in diameter) is larger than those of others (26 mm in diameter) that work with the same principle. The collector is more effective to adsorb radon progeny than most of others. The equipment of ZnS(Ag) Scintillation Counting System is available for large size collectors to detect radon progeny. Therefore, its sensitivity of measurement is higher than that of others. According to the different half lives of radon progeny, and based on both theory and experiments, a formula for discrimination and calculation of 222Rn and 220Rn concentrations is deduced. The 222Rn and 220Rn concentrations were surveyed with electrostatic collectors of radon progeny on the campus of commercial school and some other areas in Hainan, southern China. Neither 222Rn nor 220Rn concentration was found significantly high. However, several faults underground were delineated. The collector is also used to study radon transportation. Results indicate that radon changes regularly with date when it has transported for a certain distance. Velocities of radon migration in the four media are quite different. Radon migrates more quickly in vertical tube than in the horizontal tube.

Preliminary Study on Loess Slumping Hazard between Northern Shaanxi and Western Shanxi along the Line of West-East Gas Transportation Project
Guolin Liu, Shaoxiang Hu, Weizhi Lei, Yongshuang Zhang
2003, 14(2): 155-160.

The loess slumping hazard is a special type of slope failures in the northern area of loess plateau of China. The characteristics of paroxysm and high frequency of the hazard always lead to ruin of cave houses, as well as a high human casualties. The hazard is also seriously harmful to railways, highroads and long transporting pipelines. With the mechanisms of both landslide and falling, as well as the forming process of sliding followed by collapses, loess slumping is used to be treated as landslide or falling. Based on field investigations and lab analyses of the loess between Jingbian County of Shaanxi Province and Puxian County of Shanxi Province along the line of west east gas transportation project which is 300 km long, it is discovered that the hazards of loess slumping are controlled by the content of clay, which lead to their obvious regional properties: the area with a content of clay (< 0.005 mm) less than 10 %, called sand loess area, is a seriously developing area of slumping; the area with a content of clay between 10 % and 20 %, called typical loess area, is a medium developing area of slumping; the area with a content of clay more than 20 %, called clay loess area, is a non developing area of slumping. Based on research of the formation mechanism and formation conditions of the loess slumping hazards, some corresponding engineering countermeasures are suggested in this paper.

Artificial Neural Network Model for Discrimination of Stability of Ancient Landslide in Impounding Area of Three Gorges Project, China
Pinggen Zhou
2003, 14(2): 161-165.

The factors of geomorphology, geological setting, effect of ground water and environment dynamic factors (e.g. rainfall and artificial water recharge) should be integrated in the discrimination of the stability of the ancient landslide. As the criterion of landslide stability has been studied, the artificial neural network model was then applied to discriminate the stability of the ancient landslide in the impounding area of the Three Gorges project on the Yangtze River, China. The model has the property of self adaptive identifying and integrating complex qualitative factors and quantitative factors. The results of the artificial neural network model are coincided well with what were gained by classical limit equilibrium analysis (the Bishop method and Janbu method) and by other comprehensive discrimination methods.

Structural Earthquake Resistance Design Using Energy Method
Rongrong Hu
2003, 14(2): 166-168.

A summary of status of researches in the field of structural earthquake resistance design on energy concept is presented in three parts: earthquake input, demands on the structure and supplied capacity of the structure. A new approach is proposed for analysis of the seismic response and damage criteria based on the momentary input energy.

Research on Effect of SMA Damper in Passive Control
Gang Peng, Jian Fan, Li Li, Jiaxiang Tan
2003, 14(2): 169-174.

In this article, mechanics model of SMA center tension from damper is developed. According to the theory of Brinson constitutive model and thermodynamics first law, damper thermodynamics non linear equation has been developed. Dynamics non linear equation of frame structure under operation of SMA damper and its solution have been worked out; the software of seismic response analysis for frame structure and of damper characteristic analysis have been compiled with MATLAB software, and the examples have been computed with it. The result indicates that SMA damper has obvious damp characteristics and it can provide with obvious restraint effect for seismic response of frame structure. Decreasing rate of displacement and velocity on top of frame structure reaches 50 %-60 %. The result is in accordance with other pundits experimentation results, which indicates that the above methods are correct and useful.

Gravity Investigation in Area East of River Nile (Khartoum State)
M G Eldawi, A G Farwa
2003, 14(2): 175-181.

The purpose of the study is to investigate the subsurface geology of the area. For quantitative interpretation of the resulting Bouguer anomalies, borehole data are explored. This is done along several profiles obtained from software program G.model version 2.2 No.175. This program is based on two dimensional mass distribution. The interpretation reveals two basinal features filling depressions in the basement complex named as Abu Harira basin and Kabbashi basin. They are structurally related to Khartoum basin. As a result, a geological/structural map of the area in east of the Nile is produced. The basinal features in the study area are considered as parts of the central Sudan (Khartoum basin) that had been subjected to several tectonic events that resulted in the formation of several fracture systems associated with block subsidence and formation of these basins.

Experimental Study Optimizing Hole Cleaning-Cuttings Transport in Oil Drilling Engineering
A A Ibrahim, T A Musa
2003, 14(2): 182-189.

With a clear understanding of the drilling fluid techniques and the cutting taking mechanism, a new advanced model is set up for analyzing field data and quantitative forecast of cutting taking mechanism. Therefore, a number of values affecting the drilling rate and the hole cleaning are studied over a wide range of parameters. Drilling data obtained under high borehole pressure conditions are analyzed to determine the causes of the reduction in rate of penetration (ROP) as the borehole pressure increases, which in some cases is caused by the buildup of rock debris under the bit. The theoretical achievement and testing conclusions can be very instructional for horizontal well drilling. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. High viscosity muds are observed to provide better transport than low viscosity muds.