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61.
Trace and RE element geochemistry and genesis have been studied with respect to ferromanganese nodules from the sediments of the Pacific, Atlantic and Indian oceans. 相似文献
62.
Ni Xiang-bin Jiang Yao-tiao Chen Zai-zhang Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277
We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae. 相似文献
63.
Xie-Yan Song Hua-Wen Qi Paul T. Robinson Mei-Fu Zhou Zhi-Min Cao Lie-Meng Chen 《Lithos》2008,100(1-4):93-111
The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO2 contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high Nd (t) values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P2O5 (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low Nd (t) values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume. 相似文献
64.
高、低煤阶煤层气藏地质特征及控气作用差异性研究 总被引:4,自引:0,他引:4
高、低煤阶煤层气地质特征及控气作用差异性是研究煤层气富集成藏的重要组成部分,是煤层气勘探开发理论研究过程中重要的基础性研究领域之一。本文以中国沁水、阜新盆地和美国粉河盆地等典型的含气盆地为例,探讨了高、低煤阶煤层气的储层物性差异,分析了构造控气和水文地质控气作用的差异性。研究表明,高煤阶气藏含气量高,CH4百分含量高,δ13C1值大于-38.75‰,储层渗透率变化小,储层改造难,构造热事件对煤层气的生成、富集贡献大,持续的水动力使气藏遭到破坏,且破坏幅度大,现今地下水格局对气藏的形成具有一定的影响;低煤阶气藏含气量低,CH4百分含量低,δ13C1值大于-49.11‰,储层渗透率变化大,储层易改造,煤热演化史及煤阶影响着煤层气的生成、富集,在煤层气生成过程中活跃的水动力是甲烷生成的主要的水文地质条件之一,但持续的水动力使气藏遭到破坏,且破坏幅度小,而合适的地层水矿化度则是低煤阶煤层气生成的重要条件,地下水格局对气藏的调整和改造起到决定性的影响。 相似文献
65.
Zi-Fu Zhao Yong-Fei Zheng Chun-Sheng Wei Fu-Kun Chen Xiaoming Liu Fu-Yuan Wu 《Chemical Geology》2008,253(3-4):222-242
The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative εHf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive εHf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ18O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ18O rocks. North Dabie shares the same age of Neoproterozoic low δ18O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower. 相似文献
66.
A detailed characterization of the site is crucial to designing an efficient method of managing the risks associated with
tailings from abandoned mines. Therefore, samples collected from various depths within tailings in Guryong mine, Korea, were
analyzed for their chemical, physical and mineralogical characteristics. All samples of the Guryong tailings had acid-generating
potential. However, in the oxidation zone, the net acid generation (NAG) was low (30 kg H2SO4 t−1) although the acid neutralization potential (ANP) was less than zero. The ANP values in the unoxidation zone were higher
(> −56.0 kg CaCO3 t−1) than in the other zones. As a result, the amount of alkali ions that are needed to neutralize the acid needs to be considered.
In this experiment G3, G4 and G6 drill cores containing fine tailings particles near the unoxidation zone were observed to
contain calcite (CaCO3) with acid-neutralizing capacity. A low pH (2−4) in the oxidation zone of the tailings changed to a neutral pH in the unoxidation
zone of the tailings. These results suggest that the acid-neutralizing capacity of the tailings was controlled by particle
and mineral composition of tailings. 相似文献
67.
Zhou Haiyan Zhou Xun Chai Rui Yu Lan Liu Chunhui Li Liangping 《Environmental Geology》2008,53(7):1483-1489
Thermal groundwater occurs in bedrock aquifers consisting of the dolomite of the Wumishan Group of the Jixianin System and
the Cambrian carbonate in the Xiaotangshan geothermal field near the northern margin of the North China Plain, China. The
hot water in the geothermal field of basin-type discharges partly in the form of the Xiaotangshan hot spring under natural
conditions. The hot water has TDS of less than 600 mg/L and is of Na·Ca-HCO3 type. The geothermal water receives recharge from precipitation in the mountain area with elevation of about 500 m above
sea level to the north of the spring. Thermal groundwater flows slowly south and southeast through a deep circulation with
a residence time of 224 years estimated with the Ra–Rn method. The Xiaotangshan hot spring dried up in the middle of the 1980s
owing to the increasing withdrawal of the hot water in the geothermal field in the past decades. The water level of the geothermal
system still falls continually at an annual average rate of about 2 m, although water temperature changes very little, indicating
that the recharge of such a geothermal system of basin-type is limited. Over-exploitation has a dramatic impact on the geothermal
system, and reduction in exploitation and reinjection are required for the sustainable usage of the hot water. 相似文献
68.
Response of groundwater chemistry to water deliveries in the lower reaches of Tarim River,Northwest China 总被引:2,自引:0,他引:2
Yongjin Chen Kefa Zhou Yaning Chen Weihong Li Jiazhen Liu Tao Wang 《Environmental Geology》2008,53(6):1365-1373
In this paper, we analysed the monitored data from nine groundwater-monitoring transects in the lower reaches of Tarim River
during the five times of stream water deliveries to the river transect where the stream flow ceased. The results showed that
the groundwater depth in the lower reaches of Tarim River rose from −9.30 m before the conveyances to −8.17 and −6.50 m after
the first and second conveyances, −5.81 and −6.00 m after the third and fourth the conveyance, and −4.73 m after the fifth.
The horizontal extent of groundwater recharge was gradually enlarged along both sides of the channel of conveyance, i.e.,
from 250 m in width after the first conveyance to 1,050 m away from the channel after the fourth delivery. With the rising
groundwater level, the concentrations of major anions Cl−, SO42− and cations Ca2+, Mg2+, Na+, as well as total dissolved solids (TDS) in groundwater underwent a significant change. The spatial variations in groundwater
chemistry indicated that the groundwater chemistry at the transect near Daxihaizi Reservoir changed earlier than that farther
from it. In the same transect, the chemical variations were earlier in the monitoring well close to watercourse than that
farther away from the stream. In general, the concentration of the major ions and TDS at each monitoring well increased remarkably
when the water delivery started, and decreased with the continued water delivery, and then increased once again at the end
of the study period. Hence, the whole study period may be divided into three stages: the initial stage, the intermediate stage
and the later stage. According to the three stages of groundwater chemistry reaction to water delivery and the relationships
between groundwater chemical properties and groundwater depths, we educe that under the situation of water delivery, the optimum
groundwater depth in the lower reaches of the Tarim River should be −5 m. 相似文献
69.
For the assessment of shallow landslides triggered by rainfall, the physically based model coupling the infinite slope stability
analysis with the hydrological modeling in nearly saturated soil has commonly been used due to its simplicity. However, in
that model the rainfall infiltration in unsaturated soil could not be reliably simulated because a linear diffusion-type Richards’
equation rather than the complete Richards’ equation was used. In addition, the effect of matric suction on the shear strength
of soil was not actually considered. Therefore, except the shallow landslide in saturated soil due to groundwater table rise,
the shallow landslide induced by the loss in unsaturated shear strength due to the dissipation of matric suction could not
be reliably assessed. In this study, a physically based model capable of assessing shallow landslides in variably saturated
soils is developed by adopting the complete Richards’ equation with the effect of slope angle in the rainfall infiltration
modeling and using the extended Mohr–Coulomb failure criterion to describe the unsaturated shear strength in the soil failure
modeling. The influence of rainfall intensity and duration on shallow landslide is investigated using the developed model.
The result shows that the rainfall intensity and duration seem to have similar influence on shallow landslides respectively
triggered by the increase of positive pore water pressure in saturated soil and induced by the dissipation of matric suction
in unsaturated soil. The rainfall duration threshold decreases with the increase in rainfall intensity, but remains constant
for large rainfall intensity. 相似文献
70.
Shear strength characterization of municipal solid waste at the Suzhou landfill, China 总被引:5,自引:0,他引:5
The current practice of slope stability analysis for a municipal solid waste (MSW) landfill usually overlooks the dependence of waste properties on the fill age or embedment depth. Changes in shear strength of MSW as a function of fill age were investigated by performing field and laboratory studies on the Suzhou landfill in China. The field study included sampling from five boreholes advanced to the bottom of the landfill, cone penetration tests and monitoring of pore fluid pressures. Twenty-six borehole samples representative of different fill ages (0 to 13 years) were used to perform drained triaxial compression tests. The field and laboratory study showed that the waste body in the landfill can be sub-divided into several strata corresponding to different ranges of fill age. Each of the waste strata has individual composition and shear strength characteristics. The triaxial test results showed that the MSW samples exhibited a strain-hardening and contractive behavior. As the fill age of the waste increased from 1.7 years to 11 years, the cohesion mobilized at a strain level of 10% was found to decrease from 23.3 kPa to 0 kPa, and the mobilized friction angle at the same strain level increasing from 9.9° to 26°. For a confinement stress level greater than 50 kPa, the shear strength of the recently-placed MSW seemed to be lower than that of the older MSW. This behavior was consistent with the cone penetration test results. The field measurement of pore pressures revealed a perched leachate mound above an intermediate cover of soils and a substantial leachate mound near the bottom of the landfill. The measurements of shear strength properties and pore pressures were utilized to assess the slope stability of the Suzhou landfill. 相似文献