Abstract:Abstract：The deficiencies in more than 50 national and regional geochemical mapping projects in the world carried out from 1973 to present are all analytical in character. The IGCP259 Project under the aegis of UNESCO＇s IGCP Program carried out from 1988 to 1992 aimed to standardize geochemical mapping methods used in the world. This project advances several analytical requirements for forthcoming geochemical mapping projects, which mainly include the following: 71 elements should be analyzed in the future mapping projects; the detection limits of trace and ultratrace elements must be lower than the corresponding crustal abundances and the Chinese GSD and Canadian STSD standard sample series should be used for the correlation of global data; the aim of the IGCP360 Project (Global Geochemical Mapping Project) is to use 5000 composite samples taken at very low sampling densities to cover the whole Earth＇s land surface. Besides social，political and economic problems, the main bottleneck is the difficulties to meet IGCP259 analytical requirements by many countries. The best way to solve this bottleneck is proposed in the present paper.

Abstract:Abstract: By the end of 2001, 21 large gas fields had been discovered in China, and their cumulative explored reserves of gas in place reached 17953×108 m3, taking up 59.80% of China＇s total gas reserves. Gas molecules are small, hard to be adsorbed and ready to diffuse. Large early-formed gas fields will lose their quantity and become small or medium-sized ones or even be depleted completely owing to long-continued gas diffusion, if no gas source replenishes the supply. Therefore, the formation of gas accumulations in the late stage is one of the fundamental conditions for the formation of large gas fields. Basins in China are polycyclic in nature. The tectonic cycle of succeeding basin usually reduces or damages the reserves and preservation conditions of gas accumulations in the preceding basins. So, the formation of gas accumulations in the late stage can avoid this defect and is favorable for the formation of large gas fields. The period of peak gas generation of large gas fields resulting from late-stage accumulation is synchronous or nearly synchronous with the period of accumulation, and their source and reservoir rocks are younger. Sometimes, the peak generation period is earlier than the period of accumulation and their source and reservoir rocks are older.

Abstract:Abstract: The Guanling biota is characterized by the occurrence of numerous well-preserved Late Triassic(Carnian) marine reptiles and crinoids with ammonoids, bivalves, conodonts, brachiopods, elasmobranch ichthyoliths and a few fossil fishes and plants. Such a rich, diversified and perfectly preserved paleontological assemblage is rarely encountered in the world and can be called, therefore, a unique Late Triassic“Fossillagerst?覿tte”in the world. Preliminary study indicates that the principal marine reptiles are ichthyosaurs: Qianichthyosaurus zhoui Li (1999), Cymbospondylus asiaticus Li et You (2002), Panjiangsaurus epicharis Chen et Cheng gen. et sp. nov., thalattosaurs: Anshunsaurus huangguoshuensis (Liu, 1999), Xinpusaurus suni (Yin et al., 2000), X. bamaolinensis sp. nov. Cheng et Liu, placodonts: Sinocymodus xinpuensis Li (2000) and some new unidentified taxa. The crinoids are dominated by Traumatocrinus hsui (Mu) (? =T. caudes (Dittmar,1866), ? =T. guanlingensis Yu et al. 2000) revised in the present paper. New discovery of Traumatocrinus attaching drifting wood fossils by anastomosing or articulated rootlets indicates that the taxa of crinoids are widespread in the world, depending on its pseudo-planktonic living style. Associated fossils comprise conodonts of the Metapolygnathus nodosus Zone redefined by Chen (in press), ammonoids of the Trachyceras multituberculatum Zone, bivalves of the Halobia-“Daonella” bifurcatus Assemblage Zone, brachiopods, Koninckina guizhouensis, K. zhengfengensis, and newly discovered fossil fishes, Asialepidotus sp. nov., shark scales and teeth, plants, Equisetites arenaceus, Ctenozamites sarrani etc. Comprehensive analysis of the above-mentioned various kinds of fossil suggests that the age of the Guanling biota should be Late Triassic early-middle Carnian. Detailed investigation and systematic exploration indicate that the Guanling biota is distributed mainly in the interval of 5-11 m above the base of the Lower Member of the Xiaowa Formation (former “Wayao Formation”) around Huangtutang, Xiaowa, Maowa, Bamaoling of Xinpu Township and Baiyan of Gangwu Township, Guanling County, covering an area of about 200 km2. Combined tectono-paleogeographic and eco-, sequence- and chemo-stratigraphic studies indicate that this rare biota was probably formed and developed in a particular “asylum” situated in the NW corner of the active shelf margin close to the relatively stagnated Nanpanjiang intracontinental rift basin. This basin was surrounded by the Sichuan-Yunnan-Guizhou-Guangxi old land on three sides during the earliest Late Triassic transgression, following the Middle Triassic Ladinian global regression. The anoxic and salted events, caused by subsequent Early-Middle Carnian maximum transgression and sedimentary organic surplus stockpiling, were probably the main causes for the mass extinction of this biota and formation of well-preserved taphococenosis.

Abstract:Abstract: Black shales have special lithological, paleontological and geochemical features, which are mainly represented by changes in faunal assemblage and abundance, an increase of organic carbon content and positive excursion of carbon stable isotopes. High surface water productivity is of paramount importance in organic matter deposition. Black shales were worldwide during the Mid Cretaceous and well marked the Cenomanian-Turonian transition. In southern Tibet, the extinction rates for planktonic foraminiferal species are 34%, and up to 50% for the benthos at the C/T boundary. A short positive δ13C excursion that shows a maximum value of 2.74‰ occurs at the top of the Cenomanian. The bioturbation almost disappeared; microburrows are pyritized; foraminiferal chambers are filled with pyrite microspherical clusters. Other geochemical indicators also show different degrees of anomalies. These features suggest that different degrees of oxygen-poor to oxygen-deficient states occurred in water layers at different depths of the ocean. The shales deposited simultaneously are the result of preservation of abundant organic carbon in the anoxic environment. The causes for the occurrence of this phenomenon are the influences of the sea-level rise and climatic change in the Mid Cretaceous. The changes of the conditions of the Tibetan Tethys Sea were markedly affected by the global and regional sea-level rises and the Mid Cretaceous black shale formed thus have the features consistent with those of the global shales.

Abstract:Abstract: This paper reports the results of a petrogeochemical study of lavas in lower Paleozoic back-arc basins in the Northern Qilian Mountains. The distribution of samples links regions of back-arc seafloor spreading to the north with regions farther south where a progression of island arc rifting styles occurred in the earliest stage of back-arc basin extension. Petrographic and geochemical characteristics of lavas reflect the change in style of extension, with typical back-arc basin basic lavas in the north passing southward to arc lavas. Glassy (devitrified now), minor-porphyritic basic lavas characterize regions of seafloor spreading. Felsic lavas and porphyritic basic lavas occur in the southern, island-arc rifting regions. Geochemically, mature arc portions (Y<20×10-6, TiO2<0.60%, Th/Yb>0.60) are distinguished from regions of back-arc spreading (Y>20×10-6, TiO2>1.0, Th/Yb<0.60). Samples show progressive marked changes in geochemical compositions, from back-arc basin basic lavas formed by seafloor spreading southward through lavas that increasingly resemble arc lavas to arc lavas that are indistinguishable from arc lavas encountered in the southernmost portion of the rift. These changes reflect the changes in the mechanism of mantle convection and processes of melt generation beneath the evolving back-arc basin in the Northern Qilian Mountains: from mantle downwelling beneath incipient island arc rifts caused by slab subduction to mantle upwelling beneath zones of back-arc seafloor spreading. The rift axis captured the arc magmatic flux in the early island arc rift stage, so that the lavas erupting from this part of the rift cannot be compositionally distinguished from arc lavas. As back-arc extension continued and the back-arc basin widened, the arc magmatic flux moved progressively away from the rift axis, finally generating a mid-ocean ridge-like decompression melting system-back-arc basin magmatic system.

Abstract:Abstract: The Pingyang gneissic trondhjemite is located in the vicinity of Pingyang Township, Fuping County, Hebei Province. Its country rocks are supracrustal rocks including migmatites and gneisses, stratigraphically equivalent to the lower part of the Fuping Group. The high-grade metamorphism, migmatization and anatexis have close spatial relationships in the Pingyang area, showing the ‘trinity’; thus the change from metamorphic rocks to granites show the gradational features with respect to systematic petrology, petrography and occurrence relationships. The metamorphosed supracrustal rocks and some inclusions in granites can not only be correlated with their equivalents in the surrounding areas but also show signs of modification by anatexis. Ample evidence indicates that the Pingyang gneissic trondhjemite is generally autochthonous anatectic trondhjemite, which has been displaced to some extent locally. The anatexis of metamorphosed supracrustal rocks in the Pingyang area progressed through the early stage characterized mainly by dissolution and recrystallization of minerals and the late stage when melting of some minerals predominated. The formation of the Pingyang gneissic trondhjemite represents the higher evolutionary stage of anatexis of metamorphosed supracrustal rocks of the Fuping Group-complex, which has great significance for the objective understanding of the composition and geological evolution of the Fuping Group-complex.

Abstract:Abstract: Fluid-geological mapping is a new method employed for geological investigation and mineral exploration. The first test of fluid-geological mapping in China was carried out in the Weishan-Yongping copper-gold-polymetallic mineralization district, Yunnan. The authors studied mineralization-controlling geological factors, characteristics of various major deposits (occurrences), ore fluid subsystems and its drainage area, salinities, homogenization temperatures, gas-liquid phase compositions of fluids, trace element contents and stable isotope features of ore fluids, and concentration centers of ore fluid systems in the mineralization district. The fluid-geological map shows the nature and state of ore fluids in the area and the basic characteristics of two ore fluid subsystems. The drainage area and seven concentration centers of the two ore fluid subsystems have been delineated. The distribution of these concentration centers essentially coincides with the distribution of the known mineralization occurrences, geochemical anomalies and favorable geological conditions; therefore they are thought to be an important basis for mineral exploration. This study suggests that fluid-geological mapping is an effective means for mineral exploration.

Abstract:Abstract: Volcanism has great significance not only for the formation of Fe and Cu-polymetallic deposits, but also for gold mineralization. The authors have deeply realized the great significance of volcanism in the formation of gold deposits through many years of work in areas of volcanic rocks and arrangement and analysis of geological data of large and superlarge gold deposits at home and abroad. This paper elucidates this understanding from the genetic types of gold deposits and their sizes and reserves and analyses of geological conditions of various types of gold deposits and preliminarily summarizes the problems meriting attention and indicators in gold prospecting with an attempt to improve gold prospecting in volcanic areas. The paper focuses on the internal relation between submarine volcanism and formation of gold deposits, while gold deposits related to terrestrial volcanism are scarcely discussed because they are more directly perceived.

Abstract:Abstract: The Xiashu loess in the Nanjing-Zhenjiang area records abundant information of the paleoclimatic change. The Xiashu loess, as a facies at the southern margin of eolian and dusty accumulations in northern China, occupies an important position in the study of the global environmental change. The authors systematically analyzed the Rb and Sr concentrations and magnetic susceptibility at the Laohushan section at 10 cm intervals. The results show that the Rb concentration and magnetic susceptibility may better indicate the variations in intensity of the East Asian monsoon and that the Rb/Sr ratio may server as a substitute proxy for chemical weathering of the Xiashu loess. The increase of the Rb/Sr ratio at the section from below upward is the result of intensification of chemical weathering over the last 120 ka.

Abstract:Abstract：Situated in the intersection area of the Loess Plateau and the northeastern margin of the Qinghai-Tibet Plateau, the Minhe loess is sensitive to the climate. Analysis of the CaCO3 and total organic carbon (TOC) contents in the 187-0.70 Ma interval of the Minhe loess shows that the content of CaCO3 in the Minhe loess ranges from 5.89 to 18.63%, averaging 11.41% and that the content of TOC is lower, ranging from 0.007% to 0.452% with an average of 0.88%. The CaCO3 content in the Minhe loess is notably higher than those in Lanzhou, Luochuan and Xi＇an, but the TOC content is much lower than those in the aforesaid areas. The variations of the CaCO3 and TOC contents in the Minhe loess indicate that the climate in the area had a trend of becoming cold and dry since 1.87 Ma BP. The variations of CaCO3 and TOC in loess as substitute proxies of climatic changes have certain limitations due to influences of complex sources and types of CaCO3, difficult sampling and differential comparisons among areas, as well as preservation conditions, sedimentation rates and “burial-effect” of TOC. At last, the paper points out that in actual applications the climatic proxies of CaCO3 and TOC in loess, especially loess in the northwestern part of the Loess Plateau, must be used together with other climatic proxies, and then correct paleoclimatic information can be extracted.

Abstract:Abstract：The prediction of preponderant minerogenic series in the eastern section of the Gangdise Mountains, Tibet, is a key problem that needs to be solved currently. The authors studied the provenance characteristics and relations between geochemical targets and minerogenic series, revealed the geochemical constraints of mineralization scale and calculated factors coupling coefficients for predicting potential resources. It can be concluded that four different minerogenic series are concentrated in the eastern section of the Gangdise Mountains.