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Gao Y.-J.,Wuhan University | Gao Y.-J.,Chengdu Institute of Geology and Mineral Resource | Ling W.-L.,Wuhan University | Qiu X.-F.,Wuhan University | And 2 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2011

Element Ce shows variable valences in the nature, which accounts for the decoupling between La-Ce and Sm-Nd isotopic system. In addition to a radiometric application, the La-Ce system thus sheds new light on a set of studies such as crust recycling in mantle components, oxidation events during outer sphere evolution of the Earth and metallogenesis. This paper consists of two parts. The first part summarizes the application status of the La-Ce system, its analytical problem faced as well as developing trends in experimental technique and geological application. The second half describes a new chemical procedure for La-Ce separation and purification. Analytical results for some USGS standards and some gabbroic rocks from the Neoproterozoic Huangling complex, interior of the Yangtze craton, are also reported. Source

Wang Z.,Chengdu University of Technology | Zhao D.,Tohoku University | Wang J.,Chengdu Institute of Geology and Mineral Resource
Journal of Geophysical Research: Solid Earth | Year: 2010

To understand the deep structure and seismogenesis in the north-south seismic zone (NSSZ) in southwest China, we collected a large number of P and S wave arrival time data from both local earthquakes and teleseismic events to invert simultaneously for the three-dimensional P and S wave velocity (Vp, Vs) structures in the crust and upper mantle. The obtained Vp and Vs models are generally coherent with each other from the crust to the mantle transition zone. The NSSZ is characterized by strong structural heterogeneities from the mountainous areas of southeastern Tibet to the Yangtze Platform. Low-Vp and low-Vs anomalies are generally imaged in the upper crust under the Sichuan basin, showing good agreement with the surface geological features that the foreland basin contains primarily Mesozoic and Paleozoic sedimentary rocks with a thickness of several kilometers. The deep part of the Yangtze Platform is characterized by a cratonic lithospheric body dipping southwestward down to 400 km depth beneath the southeastern margin of the Tibetan Plateau, in sharp contrast to low-velocity anomalies in the upper mantle beneath the Songpan-Ganzi Fold System and the Northwest Qiangtang Block. At depths of the lower crust and uppermost mantle, a layer with low Vp and low Vs (1%-2%) is revealed under a region west of the Yangtze Platform, which may reflect the ductile flow in the lower crust. Our results indicate that the seismotectonics in the NSSZ is affected significantly by the ductile flow in the lower crust and strong heterogeneities in the upper mantle under southwest China in addition to the dominant role of the India-Asia collision. Copyright 2010 by the American Geophysical Union. Source

Zhu W.G.,Chinese Academy of science | Zhong H.,Chinese Academy of science | Wang L.Q.,Chengdu Institute of Geology and Mineral Resource | De He F.,Chinese Academy of science | And 3 more authors.
Acta Petrologica Sinica | Year: 2011

SIMS U-Pb zircon ages for rhyolite porphyries, and geochemical and Nd isotopic data are reported for rhyolite porphyries and the related basalts from the Songjiapo Formation of the Minle copper deposit of Yunnan Province, SW China. The aims are to constrain the origin and petrogenesis of these rocks. The basalts are commonly high in Fe 2O 3 , Al 2O 3 and Na 2O contents. In the Harker diagrams, MgO, CaO and P 2O 5 contents of the basalts decrease with increasing SiO 2 contents. These rocks with high ε Nd(t) values (+2.9 - +3.5), are characterized by relatively low total REE contents (50.1 X 10 -6 - 60.6 X 10 -6) with relatively flat REE patterns in the chondrite-normalized diagram and with slightly negative Nb-Ta and positive Sr anomalies in the primitive-normalized spidergram. The parental magma for the basalts exhibits affinity with a sub-alkaline basaltic magma generated by melting of a depleted, plagioclase-rich and garnet-free mantle source in the spinel field. It is suggested that the basalts originated by fractional crystallization of the parental magma plus varying degrees of crustal contamination. Cameca SIMS zircon U-Pb dating indicates that the rhyolite porphyries were emplaced at 234.8 ±2.4Ma. These rocks have high SiO 2, ( Na 2O + K 2O) and Al 2O 3 contents compared with the normal rhyolites, and are enriched in LREE and show relatively flat HREE patterns with slightly negative Eu anomalies in the chondrite-normalized diagram and significantly negative Nb-Ta, Sr, P and Ti anomalies in the primitive mantle-normalized spidergrams. The rhyolite porphyries display geochemical characteristics of I-type granites and exhibit variably initial ε Nd(t) values ranging from -1.9 to -0.51. The parental magma for these rocks exhibits affinity with a mildly alkaline intermediate to felsic magma, which was probably generated by partial melting of the regional Mesoproterozoic to Neoproterozoic mafic to intermediate lower crust and thereafter mixed with small amounts of the Middle Triassic basaltic magmas. The rhyolite porphyries were then formed by extensive crystal fractionation of the mildly alkaline magma. The basalts and the rhyolite porphyries from the Minle copper deposit display the characteristics of are volcanic rocks, which possibly formed in a late-collisonal to post-collisional environment. Source

Li D.,CAS Chengdu Institute of Mountain Hazards and Environment | Li D.,University of Chinese Academy of Sciences | He S.,CAS Chengdu Institute of Mountain Hazards and Environment | Ni H.,Chengdu Institute of Geology and Mineral Resource | Li J.,Traffic Survey Design Research Institute
2010 2nd Conference on Environmental Science and Information Application Technology, ESIAT 2010 | Year: 2010

The rainfall conditions research is one of the hot issues about landslide study,Facts show that there is a significant rainfall when the landslide occurred.However, the lag is significant,in this paper, we analyze the model of the landslide on rainfall conditions, based on the results of domestic and foreign scholars in the past three decades.domestic and foreign scholars in the past three decades,I propose some problems and give related recommendations. Problems include: (1) the reliability of rainfall conditions; (2)the contribution of effective rainfall on landslide issues; (3) the determination of the effective rainfall days. Relevant recommendations of the study mainly refers to rainfall research should be closely linked with the formation mechanism,Landslide types and environmental background. ©2010 IEEE. Source

Lin L.,Chengdu University of Technology | Zhu L.,Chengdu University of Technology | Pang Y.,Chengdu University of Technology | Sha J.,CAS Nanjing Institute of Geology and Palaeontology | And 3 more authors.
Science China Earth Sciences | Year: 2011

The Yidun Island Arc in the Three Rivers (Jinsha River, Lancang River, Nujiang River) region of southwestern China is one of the most important Kuroko-type volcanogenic massive sulfide deposits (VMS) in China. Intra-arc rifting of Yidun Island occurred during the Late Carnian-Norian when VMS deposits such as the Gacun Pb-Zn-Cu deposit were formed. A bivalve fauna was found in fine-grained tuffaceous slate and in mineralized tuffaceous siltstone containing very high contents of Pb (45.01-103.37 ppm) and Zn (135.78-300.03 ppm) of the upper Tumugou Formation in the Changtai-Gacun volcanic-sedimentary rift basin. Stratigraphically, the bivalve-bearing beds are equivalents of the Gacun Pb-Zn-Cu deposits. The diversity of this bivalve fauna is very low. It consists mainly of the thin-shelled, epibyssate suspension-feeding bivalves Pergamidia eumenea and Parapergamidia changtaiensis, the burrowing large, elongated, suspension-feeding Trigonodus keuperinus and Unionites? sp., and occasional specimens of the endobyssate suspension-feeding Trigonodus? sp. and the deep burrowing suspension-feeding Pleuromya markiamensis. Individuals of the first four taxa are so abundant that the specimens are sometimes concentrated in shell beds, probably indicating a gregarious habit. This bivalve fauna is associated with internal moulds of cylindrical, slightly conical tubes most likely produced by a worm-shaped organism. Composition, morphology, diversity, and high abundance of this fauna, chemical features of the surrounding sediment, and the tectonic setting all suggest that this bivalve fauna lived in a deep-water environment in or around a hydrothermal vent system. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg. Source

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