Geochronological Study of Caledonian Granulite and High-Pressure Gneiss in the Dabie Mountains

Using the single-zircon evaporation technique and U-Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (" country rocks" of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443-455 Ma, which are essentially consistent with that of the Caledonian high-ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.     

The Characteristics of Spinels in Mantle-derivedXenoliths in Cenozoic Basalts from Eastern Chinaand Their Thermal States

The colours and chemical composition variations of 160 spinels in peridotite and pyroxenite xenoliths from Cenozoic basalts in eastern China and their petrogeneses have been studied in detail. The relationships between major elements of spinels are discussed. The equilibrium temperatures, pressures and oxygen fugacities of spinels and their coexisting olivines, orthopyroxenes and clinopyroxenes have been determined using the Brey-kohler' s T-P calculation methods (1990) and Ballhaus' fo2 calculation method (1991). The relationships betweenthe composition and the equilibrium temperatures, pressures or oxygen fugacities of spinels in peridotite xenoliths from the basalts and the stable field of the spinels in the upper mantle have been shown.     

Mechanism and Modes of Microbial Minerogenesis of Polymetallic Nodules on the Ocean Floor

This paper presents a quantitative analysis of the relations of the occurrence of polymetallic nodules with the geochemical actions of microbes in the seawater, pore water and sediments at the bottom of the eastern Pacific Ocean basin. Emphasis is laid on the relations of the activity intensity and biochemical transformation rate of aerobic bacteria (iron bacteria, Thiobacillus thioparus, halobacteria and manganese-oxidizing bacteria) and anaerobic bacteria (sulphate-reducing bacteria, denitrifying bacteria, Thiobacillus denitrificans) with mineralization. The experimental research on the migration and accumulation of ore-forming elements caused by microbial and chemical actions shows that the microbes have changed the conditions of oxidation and reduction in the system, and their effect on the element precipitation is much stronger than the chemical actions and accelerates the enrichment of Fe and Mn. It demonstrates that the microbes can change the environment to promote the accumulation of ore-formin     

Five-Stage Model of the Palaeozoic Crustal Evolution in Xinjiang

The great majority of the Palaeozoic orogenjc belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.     

Distribution Patterns of Pentacyclic TriterpenoidHydrocarbons in Low-Mature Source Rocksfrom Eastern China

Four typical distribution patterns of pentacyclic triterpenoid hydrocarbons (types A-D) are distinguished in the low-mature source rocks from eastern China. Type A has a relatively high content of pentacyclic triterpenes. It exists in immature sediments and the distribution and abundance of triterpenes vary with the maturity of the sediments. An unknown C30 triterpene (UCT2) has also been detected in very shallow sediments. This compound is very unstable and disappears rapidly with the increase of depth. Type B is characterized by a relatively high amount of 17α(H), 21β(H)-30-homohopane. This kind of distribution pattern is common in coals and terrestrial sediments of low maturity. Type C has a relatively high content of diahopane and neohopane series. The analysis shows that this distribution pattern may have an indirect relationship with the input of higher plants despite its microbial source. There are C30-unconfirmed triterpane (UCT2) and a relatively high content of C35 hopane in type D. The dist     

Accelerated Exhumation During the Cenozoic in the Dabie Mountains: Evidence from Fission-Track Ages

Zircon and apatite fission-track dating indicates that the exhumation of the Dabie Mountains tended to be accelerated in the Cenozoic and that the exhumation of the eastern Dabie Mountains was more and more intense from south to north, which is in accordance with the more and more intense dissection from south to north, as is reflected by the modern geomorphologic features of the Dabie Mountains. The accelerated exhumation during the Cenozoic was related to the high elevation of the Dabie Mountains resulting from Late Cretaceous-Palaeogene detachment faulting and subsequent fault-block uplift and subsidence. The average elevation at that time was at least about 660 m higher than that at the present. The intense exhumation lagged behind intense uplift.     

Reform of Carbonate Rock Subsurface by Crustose Lichens and Its Environmental Significance

Crustose lichens are distributed extensively in karst areas in Southern China. They can be found on the surface of carbonate rocks. Through biophysical and biochemical processes, crustose lichens reform the subsurface of carbonate rocks and in the meanwhile change their physical and chemical properties: (1) the mechanical strength decreases by 17.04° on average (up to 33.2° ); (2) the chemical solution surface area increases from 28.26% to 75.36% (lichen microholes considered only); and (3) the water-holding capacity is greatly improved. Comparative field experiments between biokarst samples underneath crustose lichens and fresh rock samples with the same composition and texture show that the corrosional rate of carbonate rocks of the former is 1.264-1.643 times higher than that of the latter. Crustose lichens are considered as an activator of the surface corrosion of carbonate rocks.     

A Simulation Study on the Evolution of Groundwater Circulation Systems in Cenozoic Basins of Northern China

Three Cenozoic basins-the Qaidam basin, the Weihe graben-type basin and the North China plain-which are different in climatic conditions, geological settings and run-off types, are selected for the study. Based on an analysis of background information of the transect along the middle-latitude region, studies of groundwater dynamics, geochemistry, simulation of water circulation of the main elements as well as isotopic chronology, the information on global changes is collected, the formation of groundwater circulation systems and their evolution under stacked impacts of natural conditions and human activities are discussed, and a correlation is made between the evolutionary features of the above systems in these basins since 25 ka B.P. All these have laid a good foundation for further generalizing the evolutionary model of land water in northern China.     

一种现代不对称波痕的成因特征及类比分析——以民和盆地红古城地区下白垩统第8岩组为例

本文以黄河边上现代不对称波痕的形成为例,结合民和盆地下白垩统第８岩组沉积环境进行类比分析,一改过去传统的“浅水”认识,而把它定为三角洲平原相沉积。因而不对称波痕不能作为某一种沉积环境,它可以广泛生成于不同的环境。因此应更多强调综合分析、类比分析、层序基本单元和体系域分析,使盆地岩石地层单位的古环境解释建立在可靠的理性基础上。     

遥感技术在南盘江地区油气烃类检测中的应用

应用陆地卫星 TM 资料对南盘江地区进行了烃类微渗漏蚀变信息检测研究。岩石土壤地球化学特征分析表明,该区不同程度地存在着“褪红”、“粘土矿化”、“碳酸盐矿化”等烃类蚀变异常现象。选择 FeO/Fe_2O_3作为褪红的成分因子;(K_2O+Na_2O+Al_2O_3)、(K_2O+Na_2O)/Al_2O_3、(K_2O+Na_2O+Al_2O_3)/S∶O_2和 K_2O/Na_2O 等作为粘土矿化的成分因子;CaO+MgO 和 CaO/MgO 作为碳酸盐矿化的成分因子。利用 TM1/TM3、TM1/TM4识别褪红蚀变信息,TM5/TM7、TM5/TM4用干识别粘土矿化和碳酸盐矿化蚀变信息。建立了地球化学—光谱—遥感图像三位一体的遥感找油气模式,根据油气遥感色调异常对南盘江地区进行了评价和分类。