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61.
新疆阿尔泰蒙库铁矿床的成矿流体及成矿作用 总被引:30,自引:8,他引:22
蒙库大型铁矿床赋存于上志留统—下泥盆统康布铁堡组变质火山-沉积岩系中,容矿岩石为石榴子石矽卡岩、变粒岩、浅粒岩和大理岩。矿体总体顺层分布,空间上与矽卡岩密切相关。研究表明,矽卡岩期石榴子石以发育玻璃质熔融包裹体、流体熔融包裹体和流体包裹体为特征,晚期矽卡岩阶段矿物中发育液相包裹体,变质期矿物中主要发育液相包裹体和含子矿物包裹体。矽卡岩期熔融包裹体的均一温度为1100℃,早期矽卡岩阶段流体包裹体均一温度变化于193~499℃,在450℃、350℃和230℃出现峰值。中期矽卡岩阶段均一温度变化于236~550℃,峰值为350℃。区域变质期均一温度介于132~513℃,在350℃、230℃和190℃出现峰值。流体包裹体的盐度w(NaCleq)介于1.23%~60.31%,流体密度变化于0.60~1.16g/cm3。石榴子石、石英和方解石的δ18OSMOW变化于0.2‰~8.4‰,δ18OH2O介于-5.1‰~5.33‰,δD为-127‰~-81‰,表明矽卡岩期成矿流体主要是岩浆水,混合少量大气降水;变质期流体主要为大气降水,为混合变质水。方解石δ13CPDB变化于-6.1‰~-2.3‰,表明流体中碳来自深部或地幔。成矿时代为早泥盆世早期(略晚于404~400Ma),成矿作用与矽卡岩的退化变质作用有关。 相似文献
62.
Impact of land use covers upon karst processes in a typical Fengcong depression system of Nongla, Guangxi, China 总被引:2,自引:0,他引:2
Cheng Zhang Jianguo Pei Yunqiu Xie Jianhua Cao Lanling Wang 《Environmental Geology》2008,55(8):1621-1626
The direction and intensity of karst processes can be deeply affected by soil physical and chemical variations which were
resulted from land use. Taking Nongla Fengcong depression area, Mashan County, Guangxi as an example, authors discussed the
impact of land use on karst processes based on the data of field limestone tablet. The results showed that the corrosional
rates at varied soil depth are quite different. Corrosional rate in woodland and orchard is mostly bigger than 20 mg/a, which
is much higher than that in tilled land and shrub. Generally, corrosional rate decreased from orchard, woodland, tilled land,
fallow land and shrub successively, in which soil organic matter (OM) and soil pH are two major controlling factors: corrosion
process is controlled remarkably by soil OM in woodland and orchard. The higher the organic matter content is and the less
the pH value is, the higher the corrosional rate is. Owing to lower organic matter content, the corrosional rate is mainly
affected by soil CO2 in tilled land and shrub. 相似文献
63.
The uptake and release of trace metals (Cu, Ni, Zn, Cd, and Co) in estuaries are studied using river and sea end-member waters
and suspended particulate matter (SPM) collected from the Changjiang Estuary, China. The kinetics of adsorption and desorption
were studied in terms of environmental factors (pH, SPM loading, and salinity) and metal concentrations. The uptake of the
metals studied onto SPM occurred mostly within 10 h and reached an asymptotic value within 40 h in the Changjiang Estuary.
As low pH river water flows into the high pH seawater and the water become more alkaline as it approaches to the seaside of
estuary, metals adsorb more on SPM in higher pH water, thus, particulate phase transport of metal become increasingly important
in the seaward side of the estuary. The percentage of adsorption recovery and the distribution coefficients for trace metals
remained to be relatively invariable and a significant reduction only occurred in very high concentrations of metals (>0.1 mg L−1). The general effect of salinity on metal behavior was to decrease the degree of adsorption of Cu, Zn, Cd, Co, and Ni onto
SPM but to increase their adsorption equilibrium pH. The adsorption–desorption kinetics of trace metals were further investigated
using Kurbatov adsorption model. The model appears to be most useful for the metals showing the conservative behavior during
mixing of river and seawater in the estuary. Our work demonstrates that dissolved concentration of trace metals in estuary
can be modeled based on the metal concentration in SPM, pH and salinity using a Kurbatov adsorption model assuming the natural
SPM as a simple surfaced molecule. 相似文献
64.
Natural radioactivity in sediment of Wei River,China 总被引:1,自引:0,他引:1
The concentrations of natural radionuclides in sediment of Wei River of China were measured using γ-ray spectrometry with
the aim of estimating the radiation hazard as establishing a database for radioactivity levels of river sediment of China.
The activity concentrations of 226Ra, 232Th and 40K in sediment samples ranged from 10.4 to 39.9 Bq kg−1, 15.3 to 54.8 Bq kg−1 and 514.8 to 1,175.5 Bq kg−1, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities
of Chinese soil and Shaanxi soil. Radium equivalent activity (Raeq), external hazard index (H
ex) and representative level index (I
γr) were calculated for the samples to assess the radiation hazards arising due to the use of these sediment samples in the
construction of dwellings. All the sediment samples have Raeq lower than the limit of 370 Bq kg−1, H
ex less than unity and I
γr close to 1 Bq kg−1. The overall mean outdoor terrestrial gamma dose rate is 64.8 nGy h−1 and the corresponding outdoor annual effective dose is 0.079 mSv. None of the studied location is considered a radiological
risk and sediment can be safely used in construction. 相似文献
65.
Application of MODFLOW and geographic information system to groundwater flow simulation in North China Plain, China 总被引:2,自引:0,他引:2
Shiqin Wang Jingli Shao Xianfang Song Yongbo Zhang Zhibin Huo Xiaoyuan Zhou 《Environmental Geology》2008,55(7):1449-1462
MODFLOW is a groundwater modeling program. It can be compiled and remedied according to the practical applications. Because
of its structure and fixed data format, MODFLOW can be integrated with Geographic Information Systems (GIS) technology for
water resource management. The North China Plain (NCP), which is the politic, economic and cultural center of China, is facing
with water resources shortage and water pollution. Groundwater is the main water resource for industrial, agricultural and
domestic usage. It is necessary to evaluate the groundwater resources of the NCP as an entire aquifer system. With the development
of computer and internet information technology it is also necessary to integrate the groundwater model with the GIS technology.
Because the geological and hydrogeological data in the NCP was mainly in MAPGIS format, the powerful function of GIS of disposing
of and analyzing spatial data and computer languages such as Visual C and Visual Basic were used to define the relationship
between the original data and model data. After analyzing the geological and hydrogeological conditions of the NCP, the groundwater
flow numerical simulation modeling was constructed with MODFLOW. On the basis of GIS, a dynamic evaluation system for groundwater
resources under the internet circumstance was completed. During the process of constructing the groundwater model, a water
budget was analyzed, which showed a negative budget in the NCP. The simulation period was from 1 January 2002 to 31 December
2003. During this period, the total recharge of the groundwater system was 49,374 × 106 m3 and the total discharge was 56,530 × 106 m3 the budget deficit was −7,156 × 106 m3. In this integrated system, the original data including graphs and attribution data could be stored in the database. When
the process of evaluating and predicting groundwater flow was started, these data were transformed into files that the core
program of MODFLOW could read. The calculated water level and drawdown could be displayed and reviewed online. 相似文献
66.
Gamma activity from the naturally occurring radionuclides namely, 226Ra, 232Th, the primordial radionuclide 40K was measured in the soil of Cuihua Mountain National Geological Park, China using γ-ray spectrometry technique. The mean
activity of 226Ra, 232Th and 40K were found to be 27.2 ± 6.5, 43.9 ± 6.2 and 653.1 ± 127.6 Bq kg−1, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities
of Chinese soil. The radium equivalent activity, the air absorbed dose rate, the annual effective dose rate, and the external
hazard index were evaluated and compared with the internationally approved values. All the soil samples have Raeq lower than the limit of 370 Bq kg−1 and H
ex less than unity. The overall mean outdoor terrestrial gamma dose rate is 66.3 nGy h−1 and the corresponding outdoor annual effective dose is 0.081 mSv. 相似文献
67.
Yuan-Bao Wu Shan Gao Hong-Fei Zhang Sai-Hong Yang Wen-Fang Jiao Yong-Sheng Liu Hong-Lin Yuan 《Contributions to Mineralogy and Petrology》2008,155(1):123-133
The Hong’an area (western Dabie Mountains) is the westernmost terrane in the Qinling-Dabie-Sulu orogen that preserves UHP
eclogites. The ages of the UHP metamorphism have not been well constrained, and thus hinder our understanding of the tectonic
evolution of this area. LA-ICPMS U–Pb age, trace element and Hf isotope compositions of zircons of a granitic gneiss and an
eclogite from the Xinxian UHP unit in the Hong’an area were analyzed to constrain the age of the UHP metamorphism. Most zircons
are unzoned or show sector zoning. They have low trace element concentrations, without significant negative Eu anomalies.
These metamorphic zircons can be further subdivided into two groups according to their U–Pb ages, and trace element and Lu–Hf
isotope compositions. One group with an average age of 239 ± 2 Ma show relatively high and variable HREE contents (527 ≥ LuN ≥ 14) and 176Lu/177Hf ratios (0.00008–0.000931), indicating their growth prior to a great deal of garnet growth in the late stage of continental
subduction. The other group yields an average age of 227 ± 2 Ma, and shows consistent low HREE contents and 176Lu/177Hf ratios, suggesting their growth with concurrent garnet crystallization and/or recrystallization. These two groups of age
are taken as recording the time of prograde HP to UHP and retrograde UHP–HP stages, respectively. A few cores have high Th/U
ratios, high trace element contents, and a clear negative Eu anomaly. These features support a magmatic origin of these zircon
cores. The upper intercept ages of 771 ± 86 and 752 ± 70 Ma for the granitic gneiss and eclogite, respectively, indicate that
their protoliths probably formed as a bimodal suite in rifting zones in the northern margin of the Yangtze Block. Young Hf
model ages (T
DM1) of magmatic cores indicate juvenile (mantle-derived) materials were involved in their protolith formation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
68.
Hydrogen sulfide (H2S) is known to catalyze thermochemical sulfate reduction (TSR) by hydrocarbons (HC), but the reaction mechanism remains unclear. To understand the mechanism of this catalytic reaction, a series of isothermal gold-tube hydrous pyrolysis experiments were conducted at 330 °C for 24 h under a constant confining pressure of 24.1 MPa. The reactants used were saturated HC (sulfur-free) and CaSO4 in the presence of variable H2S partial pressures at three different pH conditions. The experimental results showed that the in-situ pH of the aqueous solution (herein, in-situ pH refers to the calculated pH of aqueous solution under the experimental conditions) can significantly affect the rate of the TSR reaction. A substantial increase in the TSR reaction rate was recorded with a decrease in the in-situ pH value of the aqueous solution involved. A positive correlation between the rate of TSR and the initial partial pressure of H2S occurred under acidic conditions (at pH ∼3-3.5). However, sulfate reduction at pH ∼5.0 was undetectable even at high initial H2S concentrations. To investigate whether the reaction of H2S(aq) and occurs at pH ∼3, an additional series of isothermal hydrous pyrolysis experiments was conducted with CaSO4 and variable H2S partial pressures in the absence of HC at the same experimental temperature and pressure conditions. CaSO4 reduction was not measurable in the absence of paraffin even with high H2S pressure and acidic conditions. These experimental observations indicate that the formation of organosulfur intermediates from H2S reacting with hydrocarbons may play a significant role in sulfate reduction under our experimental conditions rather than the formation of elemental sulfur from H2S reacting with sulfate as has been suggested previously (Toland W. G. (1960) Oxidation of organic compounds with aqueous sulphate. J. Am. Chem. Soc.82, 1911-1916).Quantification of labile organosulfur compounds (LSC), such as thiols and sulfides, was performed on the products of the reaction of H2S and HC from a series of gold-tube non-isothermal hydrous pyrolysis experiments conducted at about pH 3 from 300 to 370 °C and a 0.1-°C/h heating rate. Incorporation of sulfur into HC resulted in an appreciable amount of thiol and sulfide formation. The rate of LSC formation positively correlated with the initial H2S pressure. Thus, we propose that the LSC produced from H2S reaction with HC are most likely the reactive intermediates for H2S initiation of sulfate reduction. We further propose a three-step reaction scheme of sulfate reduction by HC under reservoir conditions, and discuss the geological implications of our experimental findings with regard to the effect of formation water and oil chemistry, in particular LSC content. 相似文献
69.
Wenchuan Earthquake: Way of thinking is changed 总被引:9,自引:0,他引:9
Yong Chen Li Li Juan Li Gang Li 《《幕》》2008,31(4):374-377
On 12 May, 2008, at 14:28:04 local time, an Ms 8.0 earthquake struck the Wenchuan County, Sichuan Province, in southwest China (Figure 1). This quake left about 70,000 people dead, 18,000 missing and over 370,000 injured. In the 75 days after the main shock, 20,000 aftershocks were recorded, which included 241 with Ms≥4.0, 205 with 4.0≤M≤4.9, 30 with 5.0≤Ms≤5.9, and 6 with Ms≥6.0. The largest aftershock took place 13 days after the main shock, in Qingchuan County, 110 km northeast of the epicenter of the quake (Chen, 2008). The losses from the quaketriggered geological disasters accounted for over a third of the total quake losses, which is extremely rare in the history of earthquake disasters. Secondary disasters, such as landslides, rockslides, landfalls, debris flows, etc., were widely distributed. Large numbers of buildings collapsed, including ones with steel reinforcing in the area of the epicenter. Infrastructure was badly damaged. In many areas, communications, and power and water supplies were cut off. The earthquake left over 35 large quake-dammed lakes, which threatened further disasters in the catchment areas. 相似文献
70.
A U–Pb sensitive high‐resolution ion microprobe (SHRIMP) age of 654.5 ± 3.8 Ma from an ash bed immediately below the Nantuo Formation in South China provides the lowest age constraint for the Nantuo glaciation, which has been correlated with the global ‘Marinoan’ glaciation. A U–Pb SHRIMP age of 636.3 ± 4.9 Ma from a fallout tuff within the basal layer of the Nantuo Formation, along with the existing age of 635.2 ± 0.6 Ma from its overlying Doushantuo cap carbonate, suggests that the traditionally defined Nantuo Formation may have been deposited in a short time period at the end of the Nantuo glaciation. In combination with available ages globally, the data support a relatively short duration and rapid termination of ‘Marinoan’ glaciations. 相似文献