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排序方式: 共有162条查询结果,搜索用时 31 毫秒
31.
Study of the major Asian rivers discharge to the ocean reveals variations of their water discharges and sediment loads.and local characteristics of river sediment concentrations.On the basis of this,the Asian rivers fall into three regions,including Eurasia Arctic,East Asia,Southeast and South Asia Regions.The Eurasia Arctic Region is characterized by the lowest sediment concentration and load,while the East Asia Region is of the highest sediment concentration and higher sediment load,and the South-East and South Asia Region yields Higher Sediment concentration and highest sediment load. The sediment loads of these regions are mainly controlled by climate,geomorphology and tectonic activity.The Eurasia Arctc rivers with large basin areas and water discharge,drain low relief which consists of tundra sediment,thus causing the lowest sediment load.The East Asia rivers with small basin areas and lowest water discharges,drain extensive loess plateau,and transport most erodible loess material,which results in highest sediment concentration.The SE and South Asia rivers originating from the Tibet Plateau have large basin areas and the largest water discharges because of the Summer Monsoon and high rainfall influence,causing the highest sediment load.In Asia,tectonic motion of the Tibet Plateau Plays an important role.Those large rivers originating from the Tibet Plateau trasport about 50% of the world river sediment load to ocean annually,forming large estuaries and deltas,and consequently exerting a great influence on sedimentation in the coastal zone and shelves.  相似文献   
32.
长江口南北支二维氯度数学模型   总被引:3,自引:0,他引:3  
枯水大潮期间,长江口北支向南支倒灌盐水,使南支河段和黄浦江水质恶化。,多年来这一问题为各界所重视。本文采用二维数学模型模拟了南北支水流和氯度的变化。数学模型经验证以后,计算了封堵北支方案,分析了工程前后含氯度变化情况。封堵北支后,切断了北支向南支倒灌盐水的来源,南支河段含氯度大幅度下降,数模计算反映了北支倒灌盐水在南支河段中的重要作用  相似文献   
33.
崖13-1气田陵三段是河控与潮控的辫状三角洲,主要储层沉积微相为分流河道、水下分流河道、河口坝、远砂坝及席状砂,其中河口坝的储层物性比分流河道和水下分流河道微相好,席状砂与远砂坝的物性相对较差,而各类正韵律河道与反韵律的砂坝决定了各垂向流动单元储层韵律特征。气田内的隔夹层与不同规模的海泛面相关,隔层以前三角洲泥为主,分布稳定,而夹层以分流间湾与水下分流间湾泥为主,分布较局限。结合沉积微相分布、储层非均质性及断层的分布,可以把气田区分为两个大区及6个流动单元,而南II、南III区仍可有较好的储层,但由于构造上处于低部位,含气前景还需进一步论证。  相似文献   
34.
http://www.sciencedirect.com/science/article/pii/S1674987110000034   总被引:5,自引:1,他引:4  
<正>We synthesize significant recent results on the deep structure and origin of the active volcanoes in mainland China.Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge,whereas the intraplate magmatism in China has different origins.The active volcanoes in Northeast China(such as the Changbai and Wuda-lianchi) are caused by hot upwelling in the big mantle wedge(BMW) above the stagnant slab in the mantle transition zone and deep slab dehydration as well.The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate(or Indian plate). The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs' deep subduction in the east and the Indian slab's deep subduction in the west down to the lower mantle.The stagnant slab finally collapses down to the bottom of the mantle,which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab—plume interactions.  相似文献   
35.
艾比湖近期入湖水量及其变化   总被引:4,自引:2,他引:4  
1988年对文比湖进行环湖考察,结果表明艾比湖入湖地表径流来自博尔塔拉河和精河.从1988年6月~1993年12月设站观测两河入湖水量,1989~1993年平均入湖水量4.64×108m3,其中博尔塔拉河入湖水量3.31×108m3,占71.3%;精河为1.33×108m3,占28.7%.在观测的五年中,水量多年变化不大,总入湖水量最大水年与最小水年信比为1.6.两河入湖水量的年内分配不同,博尔塔拉河入湖水量集中在冬季,其原因是博尔塔拉各地有三个断陷盆地,形成三个地下水库,对径流进行调节,使下游丰水期滞后半年.精河入湖水量集中在夏季.两河入湖水量丰、枯水期相互错开,使总太湖水量年内分配均匀.  相似文献   
36.
 The subduction of hydrated oceanic lithosphere potentially transports large volumes of water into the upper mantle; however, despite its potential importance, fluid–rock interaction during high-pressure metamorphism is relatively poorly understood. The stable isotope and major element geochemistry of Pennine ophiolite rocks from Italy and Switzerland that were metamorphosed at high pressures are similar to that of unmetamorphosed ophiolites, suggesting that they interacted with little pervasive fluid during high-pressure metamorphism. Cover sediments also have oxygen isotope ratios within the expected range of their protoliths. In the rocks that escaped late greenschist-facies retrogression, different styles of sub-ocean-floor alteration may be identified using oxygen isotopes, petrology, and major or trace element geochemistry. Within the basalts, zones that have undergone high- and low-temperature sub-ocean-floor alteration as well as relatively unaltered rocks can be distinguished. Serpentinites have δ18O and δ2H values that suggest that they were formed by hydration on or below the ocean floor. The development of high-pressure metamorphic mineralogies in metagabbros occurred preferentially in zones that underwent sub-ocean-floor alteration and which contained hydrated, fine-grained, reactive assemblages. Given that the transformation of blueschist-facies metabasic rocks to eclogite-facies assemblages involves the breakdown of hydrous minerals (e.g. lawsonite, zoisite, and glaucophane), and will thus liberate considerable volumes of fluids, metamorphic fluid flow must have been strongly channelled. High-pressure (quartz+calcite±omphacite±glaucophane±titanoclinohumite) veins that cut the ophiolite rocks represent one possible channel; however, stable isotope and major element data suggest that they were not formed from large volumes of exotic fluids. Fluids were more likely channelled along faults and shear zones that were active during high-pressure metamorphism. Such strong fluid channelling may cause fluids to migrate toward the accretionary wedge, especially along the slab–mantle interface, which is probably a major shear zone. This may preclude all but a small fraction of the fluids entering the mantle wedge to flux melting. Additionally, because fluids probably interact with relatively small volumes of rock in the channels, they cannot "scavenge" elements from the subducting slab efficiently. Received: 28 January 1999 / Accepted: 2 February 1999  相似文献   
37.
亚暴事件中磁尾多重等离子体团的数值研究(Ⅱ)   总被引:1,自引:0,他引:1       下载免费PDF全文
以宁静磁尾平衡解为初态,本文考虑介质的可压缩性,对GEOTAIL卫星于亚暴事件中,观测到多重等离子体团与高能离子爆相对应之特征作模拟研究.数值结果表明:重复形成的等离子体团是高温、高密度区,揭示了等离子体团与高能离子爆──对应的动力学原因.本文的模拟结果还表明:大尺度等离子体团的地向运动,与X中性点的尾向迁移及地向流动增强相对应,而上述现象与驱动入流沿着边界的分布形态(即电场E的分布)有关.  相似文献   
38.
Mechanical properties of high porosity chalks are strongly dependent on the type of fluid in the pores. Dry chalk is considerably stronger than water-saturated chalk, and this phenomenon is often referred to as the water-weakening effect. To address the problem of chalk–fluid interactions, several series of tests have been performed with glycol and high concentration brines as saturating fluids. Glycol is a fluid that in many aspects resembles oil, except that glycol is miscible with water. Glycol-saturated chalk turns out to have properties very similar to oil-saturated chalk. Compared to dry chalk, both oil and glycol make the chalk somewhat weaker, but this weakening effect is much less than with water. Several series of tests with brines with high concentrations of calcium chloride or sodium chloride show that the water-weakening effect is considerably reduced in high ionic strength solutions. Most tests were performed as quasi-hydrostatic tests, with a constant stress ratio of 0.9. In such tests, the yield point marks the onset of accelerated pore collapse, and the yield value is close to the hydrostatic yield stress. In addition to these compressive tests, a series of Brazilian tests were performed, revealing the same trend. The variations in mechanical strength have been correlated with the activity of water in the brines. Within the experimental accuracy of the compressive tests, there is a linear trend between reduction of water activity and the corresponding increase in strength. This leads to the hypothesis that the water activity may be a key parameter in the water-weakening mechanism. But this conclusion also indicates that water weakening may be a special case of general chalk–fluid interactions where the degree of weakening depends on the strength of adsorption of the fluid molecules to the calcite surfaces.  相似文献   
39.
孙波 《山东地质》2008,(7):57-58
张马屯铁矿为一夕卡岩型磁铁矿床,水文地质条件极其复杂,单一的防治水方法难以达到采矿生产的要求。在长期探索矿山防治水的基础上,采用同水平疏干法对张马屯铁矿地下水脉管式径流进行试验,取得了完全疏干的效果,为深井大水矿山探索出一条综合治理的途径。  相似文献   
40.
《地学前缘(英文版)》2020,11(3):989-998
Regions of slow strain often produce swarm-like sequences, characterized by the lack of a clear mainshock-aftershock pattern. The comprehension of their underlying physical mechanisms is challenging and still debated. We used seismic recordings from the last Pollino swarm (2010–2014) and nearby to separate and map seismic scattering (from P peak-delays) and absorption (from late-time coda-wave attenuation) at different frequencies in the Pollino range and surroundings. High-scattering and high-absorption anomalies are markers of a fluid-filled fracture volume extending from SE to NW (1.5–6 ​Hz) across the range. With increasing frequency, these anomalies approximately cover the area where the strongest earthquakes occurred from the sixteenth century until 1998. In our interpretation, the NW fracture propagation ends where carbonates of the Lucanian Apennines begin, as marked by a high-scattering and low-absorption area. At the highest frequency (12 ​Hz) the anomalies widen southward in the middle of the range, consistently marking the faults active during the recent Pollino swarm. Our results suggest that fracture healing has closed small-scale fractures across the SE faults that were active in the past centuries, and that the propagation of fluids may have played a crucial role in triggering the 2010–2014 Pollino swarm. Assuming that the fluid propagation ended at the carbonates barrier in the NW direction, fractures opened new paths to the South, favoring the nucleation of the last Pollino swarm. Indeed, the recently active faults in the middle of the seismogenic volume are marked by a high-scattering and high-absorption footprints. Our work provides evidence that attenuation parameters may track shape and dynamics of fluid-filled fracture networks in fault areas.  相似文献   
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