2006 Vol. 17, No. 1
Arguments persist on the genesis and ages for the bandedaugen (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 highK calcalkaline and calcalkaline granitoids in the postcollisional tectonic environment of a subductioncollision orogenic belt in an activecontinental margin. The temperatures of charnockite and gneissic garnetbearing biotite monzonitic granite are obviously higher than those of bandedaugen (rapakivi) biotite monzonitic granite, and charnockite and gneissic garnetbearing biotite monzonitic granite with the evolutional characteristics of Atype granites. The forming ages from bandedaugen (rapakivi) biotite monzonitic
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 wholerock major and trace element compositions of another 6 lamproite dykes recently discovered are reported. Major elements were determined by Xray fluorescence spectrometry (XRF) techniques, while REE and trace elements were determined by inductively coupled plasma mass spectrometry (ICPMS). They can be classified into phlogopitediopside lamprophyre, leucitediopside lamprophyre and granular carbonatitebearing 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 larg
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 intraNorth China orogenic belt, are discussed based on the insitu LAMICPMS 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 modi
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 Useries chronological studies, analysis of major and minor elements performed by Xray fluorescence spectrometry (XRF) and inductively coupled plasmamass spectrometer (ICPMS), 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
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 PermianTriassic 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 chromatographymass spectrometry (GCMS). 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) var
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 t
dynamic twostep method, flow unit, quantitative forecast, remaining oil.
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
Geodata 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
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: CuClsolidm+nH2Ogas=CuClm?(H2O)gasn(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 gassolvent H2O and copper will significantly enhance the dissolution and transport capacity of copper in the gas phase.
The theoretical results of axial force distribution models differ greatly from tests because of the complication of the rock type material. A threeparameter combinedpower 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 twoparameter combinedpower 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 threeparameter combinedpower 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.
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.