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991.
992.
The Gushan deposit is one of the typical magnetite–apatite deposits associated with dioritic porphyries in the Lower Yangtze River Valley belt of the eastern Yangtze craton. The origin of this deposit is still uncertain and remains a controversial issue. Divergent opinions are centered on whether the iron deposits are magmatic or hydrothermal in origin. However, our field observations and mineralogical studies, combined with previous published petrological and geochemical features strongly suggest that the main ore bodies in the Gushan magnetite–apatite deposit are magmatic. Specific evidence includes the existence of gas bubbles, tubes, and miarolitic and amygdaloidal structures, melt flow banding structure and the presence of “ore breccia”. New electron microprobe analyses of the pyroxene phenocrysts of the dioritic porphyry genetically associated with the Gushan magnetite–apatite deposit show that the Fe contents in the evolving magma dramatically decrease, and then gradually increase. Because there is no evidence of mafic magma recharge, this scenario (decreasing Fe) could be plausibly interpreted by Fe-rich melts separated from Fe-poor silicate melts, i.e., liquid immiscibility was triggered by minor addition of phosphorus by crustal contamination. The occurrence of massive iron ore bodies can be satisfactorily explained by the immiscible Fe-rich melt with enormous volatile contents was driven to the top of the magma chamber due to the low density. The hot and volatile-rich iron ore magma was injected along fractures and spaces between the dioritic intrusions and wall-rocks, and led to an explosion near the surface, resulting in the immediate fragmentation of the roof of the intrusion and wall-rocks, forming brecciated ores. Moreover, other types of ores can be considered as a result of post-magmatic hydrothermal activities. Our proposed metallogenic model involving the Kiruna-type mineralization is consistent with the observed phenomenon in the Gushan deposit. 相似文献
993.
Hou Zengqian Li Zhenqing Qu Xiaoming Gao Yongfeng Hua Lichen Zheng Mianping Li Shengrong Yuan Wanming 《中国科学D辑(英文版)》2001,44(1):35
There is no final conclusion yet on the uplifting mechanism and epoch of the Tibetan Plateau, which is a hot point of the geological research. This paper discusses the epoch and scales of the hydrothermal activities based on the ESR ages of hot-spring sediments. The ESR ages show that hydrothermal activities mainly happened in four periods: 50×104a, 50×104–47×104, 40×104–35×104, 27×104–20×104 and 10×104—0 aB.P. This conclusion is supported by the geophysical data and the inner plateau and surrounding sediments. Through analyzing the constraints of the deep restraint mechanism and uplift tensile function of the plateau, the uplifting processes of the Tibetan Plateau since 50×104a B.P. is elucidated. 相似文献
994.
The Ordos Basin, the second largest sedimentary basin in China, contains the broad distribution of natural gas types. So far, several giant gas fields have been discovered in the Upper and Lower Paleozoic in this basin, each having over 1000×108m3 of proven gas reserves, and several gas pools have also been discovered in the Mesozoic. This paper collected the data of natural gases and elucidated the geochemical characteristics of gases from different reservoirs, and then discussed their origin. For hydrocarbons preserved in the Upper Paleozoic, the elevated δ 13C values of methane, ethane and propane indicate that the gases would be mainly coal-formed gases; the singular reversal in the stable carbon isotopes of gaseous alkanes suggests the mixed gases from humic sources with different maturity. In the Lower Paleozoic, the δ 13C1 values are mostly similar with those in the Upper Paleozoic, but the δ 13C2 and δ 13C3 values are slightly lighter, suggesting that the gases would be mixing of coal-type gases as a main member and oil-type gases. There are multiple reversals in carbon isotopes for gaseous alkanes, especially abnormal reversal for methane and ethane (i.e. δ 13C1>δ 13C2), inferring that gases would be mixed between high-mature coal-formed gases and oil-type gases. In the Mesozoic, the δ 13C values for gaseous alkanes are enriched in 12C, indicating that the gases are mainly derived from sapropelic sources; the carbon isotopic reversal for propane and butane in the Mesozoic is caused by microbial oxidation and mixing of gases from sapropelic sources with different maturity. In contrast to the Upper Paleozoic gases, the Mesozoic gases are characterized by heavier carbon isotopes of iso-butane than normal butane, which may be caused by gases generated from different kerogen types. Finally, according to δ 13C1-R 0 relationship and extremely low total organic carbon contents, the Low Paleozoic gases would not be generated from the Ordovician source as a main gas source, bycontrast, the Upper Paleozoic source as a main gas source is contributed to the Lower Paleozoic gases. 相似文献
995.
Jingwei Hou Xingang Fan Rentao Liu 《International journal of geographical information science》2016,30(12):2462-2485
The optimal spatial allocation of irrigation water under uncertainty has become a serious concern because of irrigation water shortage and uncertain factors that affect irrigation water allocation. In this study, an optimal multi-objective model for irrigation water allocation under uncertainty is developed to maximise the economic benefit of crops and minimise the operation cost and water deficit of crop irrigation. The original and optimal plantation structure, irrigation mode and soil water content are acquired through geospatial technology. A bilayer nested optimisation (BLNO) algorithm is designed to produce multiple individuals of design vectors using an ant colony neural network algorithm for an outer optimisation. Meanwhile, a continuous adaptive ant colony (CAAC) algorithm is used for inner optimisation to calculate the interval values of the uncertain model. The crop distribution and irrigation mode are obtained to parameterise the planting area and the water demand of each crop and each block in the multi-objective model. This model is then solved and analysed. Compared to the optimal schemes obtained from an inexact two-stage fuzzy-stochastic programming and the CAAC, respectively, BLNO can effectively and efficiently solve the optimal spatial allocation of irrigation water under uncertainty. This method can spatially maximise the economic benefit of crops and minimise the operation cost and water deficit of crop irrigation using lower and upper bound maps whilst visually obtaining the exact crop type, reasonable irrigation method and precise water demand for each block and for the entire irrigated area. 相似文献
996.
Regional Ecological Risk Assessment of Soil Heavy Metals in Pearl River Delta Economic Zone Based on Different Land Uses 总被引:1,自引:0,他引:1
Based on the results of regional eco-geochemical survey in Pearl River Delta Economic Zone and the local land use patterns, two conventional risk assessment models are introduced to evaluate the ecological risk of eight heavy metals in the topsoil (0~20 cm) of Pearl River Delta. The spatial distribution characteristics of risk caused by metals in the region were characterized by GIS. Results show that As、Cd、Cu and Hg in the topsoil are the primary heavy metals posing risk to the Pearl River Delta while Cr and Zn are negligible. Meanwhile, 23.89% of soil samples have a hazard index of more than 1 which suggests that it is likely to cause chronic diseases in the region. The soils with high hazard index are mainly distributed in the Quaternary area. 37.22% of soil samples have a negligible chronic risk level, of which the spatial distribution is consistent with granite area. Moreover, the spatial distribution of carcinogenic risk is similar to chronic risk, where 25.68% of samples exceed the cancer risk index (1×10-4) recommended by USEPA. Furthermore, the evaluation results presented at administrative units indicate that there are both higher chronic and cancer risk in Panyu and Nansha district where more attentions should be paid to. 相似文献
997.
A vertical 2-D water–mud numerical model is developed for estimating the rate of mud mass transport under wave action. A nonlinear semi-empirical rheology model featured by remarkable hysteresis loops in the relationships of the shear stress versus both the shear strain and the rate of shear strain of mud is applied to this water–mud model. A logarithmic grid in the vertical direction is employed for numerical treatment, which increases the resolution of the flow in the neighborhood of both sides of the interface. Model verifications are given through comparisons between the calculated and the measured mud mass transport velocities as well as wave height changes. 相似文献
998.
塔里木板块西北缘沉积地层的研究,对于恢复南天山洋的演化过程有重要意义。文中利用岩石地球化学的手段,对新疆阿合奇地区志留系砂岩进行物源和构造背景分析。研究表明,阿合奇地区志留系砂岩样品的SiO2含量范围变化较大,为61.97%~93.91%,平均含量为76.76%;稀土元素球粒陨石标准化配分型式为右倾型,(La/Yb)N值较高,δEu值较低,Ce异常不明显。中-顶志留统塔塔埃尔塔格组砂岩的成熟度高于下志留统柯坪塔格组。地球化学物源分析图解和大地构造背景判别表明: 研究区沉积物源区逐渐由活动型向稳定型转换,下志留统部分沉积物来自于火成岩物源区,具有主动大陆边缘和大陆岛弧性质;中-顶志留统沉积物全部来自于成熟大陆的石英岩沉积物源区。结合广泛分布的奥陶系-志留系平行不整合,认为晚奥陶世研究区为活动大陆边缘,南天山洋盆向南俯冲到塔里木板块之下;早志留世,向南俯冲结束,研究区大地构造背景开始由活动大陆边缘向稳定的被动大陆边缘转换,来自活动型物源区的沉积物逐渐减少,稳定型物源区的碎屑物质逐渐增多;中-末志留世,研究区构造背景完全转变为被动大陆边缘,碎屑物质全部来自于稳定型物源区。上述成果表明,南天山洋的演化过程中确实存在双向俯冲。 相似文献
999.
Internal solitary waves (ISWs) are common mesoscale dynamic processes in the ocean that are spread throughout the world’s oceans. The South China Sea (SCS), Western Pacific (WPAC) and Indian Ocean (EIND) (SCS-WPAC-EIND) are areas where ISWs frequently occur. In particular, in the northern part of the South China Sea, Sulu Sea, Celebes Sea, Andaman Sea, Lombok Strait and northeastern part of Taiwan Island, ISWs exist almost year-round. Remote sensing is an important technique to carry out investigations and research on ISWs on a large scale. In particular, optical sensors represented by the Moderate Resolution Imaging Spectroradiometer (MODIS) can observe ISWs for a long time and on a large scale, while SAR sensors such as Sentinel-1 A/B can compensate for the deficiencies in optical sensors and comprehensively observe ISWs. Based on many years of remote sensing surveys of ISWs, this paper uses MODIS and Sentinel-1 satellite remote sensing images of more than 70 000 scenes from 2010 to 2020 to carry out survey studies of ISWs in the SCS-WPAC-EIND. The survey systematically gives the temporal and spatial distribution characteristics of ISWs in the SCS-WPAC-EIND and focuses on the analysis of the ISW characteristics in main areas in the SCS-WPAC-EIND, thereby providing basic data for further research on ISWs. 相似文献
1000.