The pre-Mesozoic metamorphic belt runs parallel to the Day Nui Con Voi - Red River shear zone in Vietnam to the south. The belt is mainly composed of hornblende gneisses, amphibolite lenses and mica-schists. Five hornblendes from a gneiss and an amphibolite were analyzed chemically and chronologically by Electron Probe Micro Analysis (EPMA) and 40Ar/39Ar methods. EPMA analyses show that hornblendes in the gneiss and the amphibolite have significant amount of edenite component and similar average composition. However, the recalculated Fe3+ content is significantly heterogeneous in a thin section while total Fe is nearly the same among the analyses. The rim of each crystal is higher in Fe3+/(Fe3+ + Fe2+) than the core. These chemical and petrological features suggest that the hornblendes have suffered significant oxidation, in particular, largely in the gneiss.
40Ar/39Ar analyses showed that the gneiss has a significant variation of plateau ages (2089±14, 1977±19 and 1873±13 Ma) among three hornblende grains, whereas the amphibolite gives the same plateau ages (2056±14 and 2044±21 Ma) for two grains. All grains of both samples have excess ages in the first few fractions at low temperatures and partial-loss ages between the excess and plateau spectra. The Ca/K ratios indicate some disturbed phases for the lower temperature spectra but the partial-loss ages are also derived from hornblende phase. These facts suggest that hornblende in the gneiss has experienced partial argon loss by oxidation and/or thermally activated argon diffusion process. However, the gneiss and the associated amphibolite have preserved the early Proterozoic tectono-metamorphic event in the hornblende crystals except for their rims, giving new evidence for the early Proterozoic event within the pre-Mesozoic metamorphic belt (northern Vietnam) south of the Red River shear zone in Indochina. 相似文献
An original reinforced concrete(RC) column and four strengthened specimens, two with RC jackets and two with wing walls, were tested in this study. The original column specimen was designed to comply with older(pre-1999) design standards so that the usual detailing defi ciencies in existing school buildings in Taiwan could be simulated. Two different structural details were chosen to fabricate the full-scale specimens for each retrofi tting technique. The study confi rmed that either RC jacketing or the installation of wing walls with two different structural details can effectively improve the stiffness and strength of an existing column. RC jacketing shows a better improvement in energy dissipation and ductility when compared to the columns with wing walls installed. This is because the two RC jacketed columns experienced a fl exural failure, while a shear failure was found in the two columns with the wing walls installed, and thus led to a drastic decrease of the maximum lateral strengths and ductility. Since many factors may affect the installation of a post-installed anchor, it is better to use standard hooks to replace post-installed anchors in some specifi c points when using RC jacketing or installing wing walls. 相似文献
Efficiency of the modern network of seismological observations in Vietnam is estimated, and an optimal design of planning
network, consisted of 14 seismic stations is proposed. At the same sensitivity of network, but with a less number of stations,
the new network would enable to determine hypocenter parameters in a more precise at a more uniform distribution of errating
band within observation area. 相似文献
Groundwater pollution by arsenic is a major health threat in suburban areas of Hanoi, Vietnam. The present study evaluates the effect of the sedimentary environments of the Pleistocene and Holocene deposits, and the recharge systems, on the groundwater arsenic pollution in Hanoi suburbs distant from the Red River. At two study sites (Linh Dam and Tai Mo communes), undisturbed soil cores identified a Pleistocene confined aquifer (PCA) and Holocene unconfined aquifer (HUA) as major aquifers, and Holocene estuarine and deltaic sediments as an aquitard layer between the two aquifers. The Holocene estuarine sediments (approximately 25–40 m depth, 9.6–4.8 cal ka BP) contained notably high concentrations of arsenic and organic matter, both likely to have been accumulated by mangroves during the Holocene sea-level highstand. The pore waters in these particular sediments exhibited elevated levels of arsenic and dissolved organic carbon. Arsenic in groundwater was higher in the PCA (25–94 μg/L) than in the HUA (5.2–42 μg/L), in both the monitoring wells and neighboring household tubewells. Elevated arsenic concentration in the PCA groundwater was likely due to vertical infiltration through the arsenic-rich and organic-matter-rich overlying Holocene estuarine sediments, caused by massive groundwater abstraction from the PCA. Countermeasures to prevent arsenic pollution of the PCA groundwater may include seeking alternative water resources, reducing water consumption, and/or appropriate choice of aquifers for groundwater supply. 相似文献
Photochemical reaction pathways in Titan's atmosphere were investigated by irradiation of the individual components and the mixture containing nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene. The quantum yields for the loss of the reactants and the formation of products were determined. Photolysis of ethylene yields mainly saturated compounds (ethane, propane, and butane) while photolysis of acetylene yields the same saturated compounds as well as ethylene and diacetylene. Irradiation of cyanoacetylene yields mainly hydrogen cyanide and small amounts of acetonitrile. When an amount of methane corresponding to its mixing ratio on Titan was added to these mixtures the quantum yields for the loss of reactants decreased and the quantum yields for hydrocarbon formation increased indicative of a hydrogen atom abstraction from methane by the photochemically generated radicals. GC/MS analysis of the products formed by irradiation of mixtures of all these gases generated over 120 compounds which were mainly aliphatic hydrocarbons containing double and triple bonds along with much smaller amounts of aromatic compounds like benzene, toluene and phenylacetylene. The reaction pathways were investigated by the use of 13C acetylene in these gas mixtures. No polycyclic aromatic compounds were detected. Vapor pressures of these compounds under conditions present in Titan's atmosphere were calculated. The low molecular weight compounds likely to be present in the atmosphere and aerosols of Titan as a result of photochemical processes are proposed. 相似文献