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2006 Vol. 17, No. 1

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Petrochemistry, Chronology and Tectonic Setting of Strong Peraluminous Anatectic Granitoids in Yunkai Orogenic Belt, Western Guangdong Province, China
Songbai Peng, Zhenmin Jin, Yunhua Liu, Jianming Fu, Longqing He, Minghai Cai, Yanbin Wang
2006, 17(1): 1-12.

Arguments persist on the genesis and ages for the banded-augen (rapakivi) anatectic granitoids (charnockite) extensively outcropped in the Yunkai (云开) region, western Guangdong (广东) Province. Their petrochemistry, SHRIMP dating, deformational and metamorphic structure were studied. The results show that most granitoids are A/CNK > 1.1, CaO /Na2O = 0.62-1.61 (average 0.94 > 0.3), Al2O3/TiO2 = 16.6-60.6 (average 23.68), depleted high field strong elements Ta, Nb, Zr, strong peraluminous high-K calcalkaline and calcalkaline granitoids in the post-collisional tectonic environment of a subduction-collision orogenic belt in an active-continental margin. The temperatures of charnockite and gneissic garnet-bearing biotite monzonitic granite are obviously higher than those of banded-augen (rapakivi) biotite monzonitic granite, and charnockite and gneissic garnet-bearing biotite monzonitic granite with the evolutional characteristics of A-type granites. The forming ages from banded-augen (rapakivi) biotite monzonitic granite to charnockite and gneissic garnet-bearing biotite monzonitic granite, whose crystallizing zircon SHRIMP ages are (465 ± 10) Ma, (467 ± 10) Ma, (435 ± 11) Ma and (413 ± 8) Ma, respectively, become younger. This shows that there was an oceaniccontinental subduction-collision and post-collisional extension-delamination-underplating between the Yangtze and Cathaysia plates during the Caledonian, and the granitoids experienced compressional uplift and extensional exhumation during the Indosinian. This provides important evidence of subduction collision of the Yangtze plate to the Cathaysia plate during the Caledonian in South China.

Lamprophyre or Lamproite Dyke in the SW Tarim Block? —Discussion on the Petrogenesis of These Rocks and Their Source Region
Fengmei Chai, Zhaochong Zhang, Jingwen Mao, Abudukadir Parat, Lijin Wang, Lianhui Dong, Huishou Ye, Li Chen, Rongfen Zheng
2006, 17(1): 13-24.

The mineralogical, petrological and geochemical studies on Keliyang(克里阳) potassic dykes have been carried out to understand their rock types, the petrogenesis and the nature of their mantle sources. They are potassic lamprophyre, not lamproites as the previous researchers believed. In this study, the whole-rock major and trace element compositions of another 6 lamproite dykes recently discovered are reported. Major elements were determined by X-ray fluorescence spectrometry(XRF)techniques, while REE and trace elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). They can be classified into phlogopite-diopside lamprophyre, leucite-diopside lamprophyre and granular carbonatite-bearing diopside lamprophyre on the basis of their mineral components. They are all characterized by relatively low SiO2(41.31% - 44.84%), TiO2(0.75% - 0.86%) and high MgO(7.30% - 11.33%), K2O(4.01% - 6.01%)concentrations with K2O/Na2O ratios of 2.77 12.49. In addition, they display enrichment in large-ion lithophile elements(LILEs, e.g., Rb, Sr, Ba)and LREE, but a relative depletion in high-field-strength elements(HFSEs, e.g., Nb, Ta, Zr, Hf and Ti). They display similar chondrite-normalized REE patterns with slight negative Eu anomalies (δEu= 0.64 - 0.82), and high initial 87Sr/86Sr ratios, which resemble those of high K/Ti and low-Ti potassic magmas formed in subduction-related settings. Consequently, we suggest that the parental magma was generated by partial melting of the phlogopite-amphibole-bearing garnet lherzolite within the lithospheric mantle that might have been metasomatized by a potassium-bearing fluid released from a subduction oceanic crust.

Petrography and Geochemistry of Peridotite Xenoliths from Hannuoba and Significance for Lithospheric Mantle Evolution
Chunmei Yu, Jianping Zheng, W L Griffin
2006, 17(1): 25-33.

The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba(汉诺坝),located on the north edge of the intra-North China orogenic belt,are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion,intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/fluid metasomatism as magnified by the trace elements of the clinopyroxenes from the Hannuoba lithospheric mantle.

Paleoenvironments Recorded in a New-Type Ferromanganese Crust from the East Philippine Sea
Zhaokai Xu, Anchun Li, Fuqing Jiang, Tiegang Li
2006, 17(1): 34-42.

We attempt to recover the paleoenvironments recorded in the accretion of a typical newtype hydrogenetic ferromanganese crust from the deep water areas of the East Philippine Sea. From detailed geochemical and U-series chronological studies, analysis of major and minor elements performed by X-ray fluorescence spectrometry(XRF)and inductively coupled plasma-mass spectrometer(ICP-MS), three major accretion periods and corresponding paleoenvironments can be ascertained. The first period is a faster accretion period in the terminal Late Miocene to the Early Pliocene with looser structure and higher volcanic detritus content, corresponding to the active Antarctic bottom waters and depressed temperature from the intermediate Middle Miocene to the Early Pliocene. The second period is a pulse of pelagic clay deposition at the Early to Middle Pliocene, reflecting the shrinkage of the Antarctic bottom waters and the global temperature elevation of this period. The third period is a slower accretion period from the Middle Pliocene, which indicates the more violent activity of Antarctic bottom waters once again and more depressed temperature than the first period, facilitating the accretion of a more compact and pure ferromanganese zone. The paleoceanographic histories of these studied areas had not been made clear in previous research.

Sandbox Experimental Study on the Influence of Rock Strength and Gravity on Formation of Thrusts
Chunguang Wei, Jianxun Zhou, Yudan He
2006, 17(1): 43-48.

A sandbox experiment model was designed to simulate how differences in rock strength and gravity between two blocks can influence the formation characteristics of thrusts. In the experiment the compression was from one direction with basement shortening and the initial surfaces of the model were oblique. The results show that if the initial surface was horizontal or the slope angle was smaller than 7°, the compression induced two groups of thrusts with opposite dip orientations. If the slope angle of the initial surface was greater than 7°, the compression induced only one group of thrusts with a dip orientation contrary to the original compression direction. This result is similar to the actual section of a collision zone between two continental blocks. By applying stress analysis, rock strength is shown to be an important factor in deformation. As other boundary conditions are changeless, it is the change of gravitational potential energy that leads to different deformation styles.

Distribution and Geochemical Implication of Aromatic Hydrocarbons across the Meishan Permian-Triassic Boundary
Xianyu Huang, Dan Jiao, Liqiang Lu, Junhua Huang, Shucheng Xie
2006, 17(1): 49-54.

Aromatic compounds extracted from sedimentary rocks can reflect environmental conditions, organic sources and maturity. The aromatics, identified in association with mass extinction in particular, would provide a signature assisting our understanding of the causes of the biotic crisis. Aromatic hydrocarbons were fractionated from the total lipid extracts of 37 samples taken from the Permian-Triassic boundary (beds 23 to 34) of section B at Meishan (煤山), Zhejiang (浙江) Province in South China. These aromatics were analyzed by using gas chromatography-mass spectrometry (GC-MS). Main compounds identified include naphthalene, phenanthrenes, fluorene, dibenzothiophene, dibenzofuran, fluoranthene, pyrene and some of their methyl homologues. The indices of methyl phenanthrene distribution fraction indicate the comparable maturity (within the oil window, 0.7%-1.0% of the mean vitrinite reflectance) of the organic matter throughout the whole profile analyzed. The ratio of dibenzothiophene to phenanthrene (DBT/PHN) varies generally at a comparable pace with lithology. Significantly, a gradual decrease of this ratio was observed within bed 24 limestone, which is probably due to the variation of sedimentary environment. This change is in line with the drop in the carbon isotope composition of carbonate, the loss of the Changhsingian reef ecosystem, and the decrease of cyanobacteria abundance within the bacteria population. The coincidence of these records suggests a close relation between the biotic crisis and marine environmental conditions, and these records clearly show the onset of the biotic crisis prior to event bed 25.

Petroleum Systems of Chagan Depression, Yingen-Ejinaqi Basin, Northwest China
Jiaren Ye, Xianghua Yang, Lianjin Wang
2006, 17(1): 55-64.

In order to further the course of petroleum exploration and development in the Chagan(查干) depression in the Yingen(银根)-Ejinaqi(额济纳旗) basin, Northwest China, the major characteristics of the petroleum systems were comprehensively analyzed, including the essential geological elements, processes, and oil characteristics. Petroleum system theory and quantitative simulation techniques were used. The dolomitic mudstone and shale of the Second Member of the Bayingebi(巴音戈壁) Formation are the major source rocks, with higher organic matter content and greater intensities of hydrocarbon generated and expelled. The sandstone in the First Member of the Suhongtu(苏红图) Formation is the main reservoir rock. The mudstone in the Second Member of the Suhongtu Formation is the most important seal. The crude oil discovered so far has a close relationship with the source rock in the Second Member of the Bayingebi Formation. There are three petroleum systems in the Chagan depression. The primary system is the Second Member of the Bayingebi Formation-the First Member of the Suhongtu Formation, which is the most important target for hydrocarbon exploration in the depression.

Applying the Dynamic Two-Step Method to Forecast Remaining Oil Distribution of Lower Series, Xiaermen Oilfield
Hong Zhou, Chuanyi Tang, Zenghui Li
2006, 17(1): 65-70.

The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of remaining oil. Logging data are required to accomplish this. However, many such projects cannot be completed. Since the old study of remaining oil distribution could not be quantified efficiently, the "dynamic two-step method" is presented. Firstly, the water cut of every flow unit in one well at one time is calculated according to the comprehensive water cut of a single well at one time. Secondly, the remaining oil saturation of the flow unit of the well at one time is calculated based on the water cut of the flow unit at a given time. The results show that "dynamic two-step method" has characteristics of simplicity and convenience, and is especially suitable for the study of remaining oil distribution at high water-cut stage. The distribution of remaining oil presented banding and potato form, remaining oil was relatively concentrated in faultage neighborhood and imperfect well netting position, and the net thickness of the place was great. This proposal can provide an effective way to forecast remaining oil distribution and enhance oil recovery, especially applied at the high water-cut stage.

GIS Based (W+-W-) Weight of Evidence Model and Its Application to Gold Resources Assessment in Abitibi, Canada
Zhijing Wang, Qiuming Cheng
2006, 17(1): 71-78.

The weight of evidence (WofE) model has been widely used for mineral potential mapping. During the conversion of a multiclass map into a binary map a lot of mineralization information is artificially added or lost because the generalization of the class within the cumulative distance interval to a linear feature is based on a maximum contrast, which matches a cumulative distance interval. Additionally, some categorical data evidence cannot be generated by this method because a maximum contrast does not exist. In this article, an alternative (W+-W-)-based WofE model is proposed. In this model, the " (W+-W-) greater than zero or not" is used as a criterion to reclassify the corresponding categorical class into a presence or absence class to convert a multiclass map into a binary map. This model can be applied to both categorical data and successive data. The latter can be operated as categorical data. The W+ and W- of the generated binary maps can be recalculated, and several binary maps can be integrated on the condition that the reclassified binary evidences are conditionally independent of each other. This method effectively reduces artificial data and both nominal and categorical data can be operated. A case study of gold potential mapping in the Abitibi area, Ontario, Canada, shows that the gold potential map by the (W+-W-) model displays a smaller potential area but a higher posterior probability (POP), whereas the potential map by the traditional (W+-W-) model exhibits a larger potential area but a lower POP.

Developing a Geological Management Information System: National Important Mining Zone Database
Renguang Zuo, Xinqing Wang, Qinglin Xia
2006, 17(1): 79-83, 94.

Geo-data is a foundation for the prediction and assessment of ore resources,so managing and making full use of those data,including geography database,geology database,mineral deposits database,aeromagnetics database,gravity database,geochemistry database and remote sensing database,is very significant. We developed national important mining zone database(NIMZDB) to manage 14 national important mining zone databases to support a new round prediction of ore deposit. We found that attention should be paid to the following issues: ① data accuracy: integrity,logic consistency,attribute,spatial and time accuracy; ② management of both attribute and spatial data in the same system; ③ transforming data between MapGIS and ArcGIS; ④ data sharing and security; ⑤ data searches that can query both attribute and spatial data. Accuracy of input data is guaranteed and the search,analysis and translation of data between MapGIS and ArcGIS has been made convenient via the development of a checking data module and a managing data module based on MapGIS and ArcGIS. Using ArcSDE,we based data sharing on a client/server system,and attribute and spatial data are also managed in the same system.

A Preliminary Study of the Solubility of Copper in Water Vapor at Elevated Temperatures and Pressures
Linbo Shang, Ruizhong Hu, Wenling Fan
2006, 17(1): 84-88.

In order to understand the capacity of water vapor to transport copper and its mechanism, using the solubility method, the solubility of copper in undersaturated water vapor was investigated experimentally at temperatures from 310 ℃ to 350 ℃ and pressures from 42×105 to 100×105 Pa. Results of these experiments show that the presence of water vapor increases the concentration of Cu in the gas. At a constant temperature, the solubility of copper increases with increasing water vapor pressure. Copper may exist as hydrated gaseous particles in the vapor phase, and the dissolution process can be described by the following reaction: CuClmsolid+nH2Ogas = CuClm· (H2O)ngas (m=1, 2). The hydration number decreases with increasing temperature, varying from ~6 at 310 ℃, to ~5 at 330 ℃, and ~4 at 350 ℃. The results show that interactions between gas-solvent H2O and copper will significantly enhance the dissolution and transport capacity of copper in the gas phase.

A Combined-Power Model for the Distribution of Axial Force in Shaft Anchor along Its Length
Jun Wei, Xiwu Zhou, Yu Zhu, Xin Luo
2006, 17(1): 89-94.

The theoretical results of axial force distribution models differ greatly from tests because of the complication of the rock type material. A three-parameter combined-power model is proposed by curves fitting the test data recorded from the pull tests on anchoring bars used in different engineering projects. Based on the comparison of the mechanical characteristics of shaft anchors and prestressed tendons, a two-parameter combined-power function model for prestressed tendons is proposed. The bounded length derived from the model and the suggested values of the parameters are also proposed. Compared with the Gaussian model, the three-parameter combined-power model is more precise and simple in expression. Results also suggest that the bounded length calculated from the average stress method is not safe enough.