摘要:

AbstractOn the basis of exhaustive researches on the facies sequences and depositional evolutionary process of various depositional systems, the genetic stratigraphic framework of the extensional rifted oceanic basin, which has undergone strong structural destruction, has been reconstructed by means of dynamic genetic stratigraphic analysis. Five depositional episodes have been distinguished from various isochronous stratigraphic boundaries and stratigraphic sequences with the three‐dimensional structure of each depositional episode analysed in detail. The tectonic paleogeographic environment corresponding to different stages of each depositional episode has been reconstructed for individual depositional system tracts. And the evolution history of this rifted basin has been divided into four stages: initial rifting and oceanization of continental crust, stretching and spreading of the basin, subduction and basin differentiation, and convergence and collision. A NNE‐trending intracontinental soft collision suture was left after the closing of the ba

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004001.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractLocated at the southern margin of the South China plate, the Youjiang basin is a closely related to the NW ‐ and NE ‐ trending syndepositional faults in respect to the configuration and structure of the basin. The evolution of the Youjiang basin progressed through two stages. In the Hercynian period, the opening of the Ailaoshan‐Honghe ocean basin gave rise to a number of NW ‐ trending rift belts in the Youjiang area. During this period, deep ‐ water sediments were dominant and the basin was possesed of the characteristics of the rift system of passive continental margins. In the early Indosinian after the Dongwu movement, the circum ‐ Pacific tectonism led to a major change in the configuration and structure of the basin. In the meantime, the Ailaoshan ocean basin began to be subducted towards the northeast, thus causing the basin to be split and expand again, and then the basin developed into the stage of the back ‐ arc basin. At the end of the Indosinian period, the basin gradually closed from east to west, thus ending up the history of development of the Youjiang basin. In the various developmental stages, sediments in the basin, also limited by the Dongwu movement, were formed by superposition of sedimentation systems with different features, and a typical two‐layered structure, which consisted of starved and compensated sediments, also occurred in the early stage. Likewise, volcanic activity in the basin involved two stages. Basin volcanic rocks of alkali and alkali ‐ calcic series, which were controlled by NW ‐ trending faults, occurred in the early stage, and basic and intermediate ‐ acid volcanic rocks of calc‐alkali and calcic series, which were controlled by NW ‐ and NE ‐ trending faults. From the above it follows that the Youjiang basin was formed by the combined action of the Palaeotethys and

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004002.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractBedded cherts occurring in the Early Permian Gufeng Formation in the Lower Yangtze region, eastern China, are nearly 20‐80 m in thickness and contain varying amounts of radiolarians and sponge spicules. There are three types of section for the Gufeng Formation: chert, carbonate and chert ‐ carbonate mixing types. Bedded cherts mainly occur in the first and third types of section. The depocentres of silica are marked by some small (not larger than a few thousand square kilometres in area) rhombic or elliptic hollows and their formation was controlled by faults. Argillaceous volcanic rocks in cherts occur as numerous thin layers. Bedded cherts are characterized by higher Fe and lower Al contents, enrichment in such trace elements as As, Sb, Bi, Ga, Au, Ag and Cr, lower total REE abundance, negative Ce anomaly and varying degrees of HREE enrichment. These characteristics are important evidence for hydrothermal cherts. Minor amounts of substances of non ‐ hydrothermal origin are mixed in the cherts. The temperatures of sea water range approximately from a few tens of degrees to over 160°C. during the deposition of siliceous sed

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004003.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractThe authors studied the biomarkers (alkanes) of eight iron ore samples from Nianpanshan and Dabaodui of Pangjiabao and Longguan, Xuanhua, Hebei. These samples have higher nC15‐ nC20contents, with main peaks at nC16, nC17and nC18, and contain abundant pristane and phytane. These results indicate that iron stromatolite and iron oncolites in orebodies are sedimentary structures of algal origin. Sedimentary iron accumulation mainly results from activity of blue algae. This study provides new valuable evidence for the origin of Xuanlong ‐ type iron depos

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004004.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractIn recent years, a considerable amount of microscopic spherules have been found in concentrates recovered from some stratabound gold deposits occurring in Middle‐Upper Triassic turbidite series in northwestern Sichuan. Study indicates that these spherules are cosmic dust. It is the first time that cosmic dust of extraterrestrial origin has been found in hydrothermal gold deposits in China.The spherules are steel‐grey in colour and show metallic luster. Their grain size is commonly less than 100 μm. According to their composition, they belong to chromium ‐ rich iron cosmic dust. The spherules have complex and diverse microscopic structures and textures, i.e. they show a very distinct Widmanstāten structure.The variation of cosmic dust content in gold deposits exhibits a positive correlation with the mineralization intensities and hydrothermal alteration. Such a relation indicates that the ore substances may transport not only mechanically but also may chemically in hydrothermal so

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004005.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractThe basalt terrain of the Neogene Huangguoshan and Guiwu Formations of eastern Anhui on the east side of the Tancheng ‐ Lujiang fault belt is one of a few Cenozoic basalt terrains in eastern China for which detailed geochemical study has not been conducted. This paper reports the abundances of major elements and more than 20 trace elements (including REE) of 22 samples and the Nd, Sr and Pb isotopic compositions of 11 samples from the eastern Anhui basalt terrain, thus more or less systematically revealing the geochemical characteristics of this continental basalt suite. The paper discusses the origin of the basalt suite and the character and process of its mantle source. The basalt suite was derived from a heterogeneous continental lithospheric mantle with end members characteristic of the EMI‐type oceanic basalt mantle, which was affected by mantle metasomatism (or enrichment of trace elements) and was characterized by a multi‐stage evolution under open condi

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004006.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractSystematic experimental studies on partial melting and subsolidus equilibration of three reconstituted spinel ‐ peridotites have been carried out at temperatures ranging from 1000 to 1380°C. and pressures of 1.0 and 1.5 GPa: The results show: (1) during partial melting, Mg# [=Mg/(Mg+Fe)]and Cr# [=Cr/ (Cr+Al)]of spinel increase with an increase in degrees of melting; (2) during subsolidus equilibration, with increasing temperatures, Mg# of spinel increases but Cr# of spinel remains almost unchanged in dunite and increases slightly in lherzolite and harzburgite. The negative and quasi ‐ linear Mg# ‐ Cr# correlation of spinel represents an isotherm of total non ‐ equilibrium. The same results have been obtained by means of mathematical modelling. It is also proved by Mg# ‐ Cr# correlation of spinel in natural peridotites. As a result of the spinel subsolidus equilibration, only variation of Cr# of spinel is limited, and then Cr# of spinel can be used to estimate the relative degree of melting undergone by host rocks. The bigger Cr# of spinel is, the higher the degree of melting will be. By contrast, during crystallization magma, Mg# and Cr# of spinel decrease with decreasing temperatures. Likewise, Cr# of spinel in basalts may be used to indicate the feature of Cr2O3/Al2O3of magma, and the compositional zoning of spinel may be used to study the evolution of magma (cooling rate and cont

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004007.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY

摘要:

AbstractThe authors have detailedly and systematically studied the carbon isotopic composition of Early Proterozoic carbonate rocks. Samples which are all dolomicrite were taken from the Jianancun, Daguandong and Huaiyincun Formations of the Hutuo Group in Wutai County Shanxi Province, North China. A total of 209 samples were analysed for their carbon isotope compositions, and the mean sampling interval was 6.9 m. Carbon isotope analysis clearly shows δ13C shifts at the boundary between the Jian'ancun Formation and Daguandong Formation and near the boundary between the Daguandong Formation and Huaiyincun Formation. Like carbon isotope shifts at the Cretaceous ‐ Tertiary, Permian ‐ Triassic and Precambrian ‐ Cambrian boundaries, the discovery of δ13C shifts in the Early Proterozoic has important significance in further studies on Early Proterozoic biotic evolution, regional and global stratigraphic correlation, and carbon geochemical

ISSN:1000-9515    

DOI:10.1111/j.1755-6724.1995.mp8004008.x

出版商:Geological Publishing House    

年代:1995

数据来源: WILEY