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排序方式: 共有263条查询结果,搜索用时 15 毫秒
1.
Yu Kuang-ming Zhang Jiachang Zhou Jiabao Professor Senior Engineer The River Harbour Department Nanjing Hydraulic Research Institute Nanjing Senior Engineer The River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1991,(4)
An empirical formula for estimating the overtopping discharge of wind-waves on a smooth-impermeable-simple slope dyke is derived through model tests in this paper, it can be adopted by related design departments in the determination of the crest elevation of the dyke. 相似文献
2.
桩式离岸堤保滩促淤工程消浪效果试验研究 总被引:9,自引:0,他引:9
在上海奉贤南北港保滩促淤工程中,采用了一种新型结构型式-桩式离岸堤,并通过物理模式试验进行了桩式离岸堤消浪效果研究。针对离岸堤通常建于近岸水区破波带的特点,重点研究水深,堤高以及堤身结构对波浪衰减的影响,同时对桩式离岸堤堤后水域的波浪底流速 分析探讨。研究结果表明,桩式离岸堤不仅具有良好的消浪效果。而且可在较大范围内改变波态,即由引起水体剧烈紊动的破波转变为浅水推进波,从而有效地改善海滩上的动力条件,促进海滩免受侵蚀,是一种具有广泛应用前景和新型保滩促淤结构。 相似文献
3.
湘东北中生代基性岩脉岩石地球化学及构造意义 总被引:8,自引:1,他引:8
湘东北中生代发育以辉绿岩类和煌斑岩类为代表的基性岩脉,属陆内拉斑玄武岩系,部分煌斑岩属于碱性系列。岩石富集LREE,δEu负异常不明显,其形成主要受软流圈地幔部分熔融作用制约。煌斑岩类微量元素总体上具有洋岛玄武岩(OIB)岩浆源区特征,富集Nd、P、Cs而K、Rb、Sr、U、Th等富集程度不明显,Ta、Nb略有富集。辉绿岩类表现出Ta、Nb、Ti亏损,但LILE并不富集,反映地壳混染程度的增强。基性岩脉形成于陆内拉张带的构造环境,岩浆活动未受到中生代大洋板块俯冲的影响。基性岩脉在时、空及物质组成上与湘东南玄武质岩石基本一致,属于整个湘东南岩石圈拉张-减薄带的一部分。 相似文献
4.
The intramontane basins of the Betic Cordilleras (SE Spain) formed subsequent to the main phase of orogenic deformation during the middle Miocene in a close genetic relation to the Trans-Alboran Shear zone. Left lateral movements along a local branch (Carboneras fault zone, CF; strike NE–SW) of this zone played a major role in controlling the formation and dynamics of the Nijar-Carboneras Basin. To the south of the fault, a major phase of strike-slip faulting is recorded during the late Tortonian. The expression of this event is the Brèche Rouge de Carboneras (BRC), which seals a deep denudational surface on top of dislocated fault blocks formed by volcanics of the Cabo de Gata complex and early Tortonian shallow marine calcarenite. The sedimentary facies of this widely distributed unit in the Carboneras-Subbasin mirror the submarine topography and the distribution of the fault zones. Along strike-slip fault zones, autoclastic breccias and neptunian dikes preferentially oriented NW–SE and NE–SW occur, which are interpreted to represent the near-surface expression of the faults. Red limestone forms the groundmass of the autoclastic breccia and infills of neptunian dikes, which exhibit multiple phases of opening of fissures, gravitational sedimentary infill, lithification, and renewed creation of cracks. Steep relief, probably along fault scarps, was mantled by epiclastic volcanic conglomerate with a red carbonate matrix. Well-lithified coarse skeletal limestone rich in planktonic foraminifera formed pavements along sediment starved rocky surfaces in deep water. Laterally, within topographic depressions, the pavement limestone grades into thick accumulations of skeletal rudstone composed of fragmented azooxanthellate corals and stylasterid hydrozoans, which were concentrated by powerful bottom currents and gravitiy flows. Within the shallow water zone of dip slope ramps, cross-bedded calcarenite and calcirudite formed. Based on textures, fabrics and biota, rocks of the BRC were grouped into nine genetic lithofacies which document cryptic, deep-aphotic and shallow-photic environments typical of a sediment starved extensional basin. 相似文献
5.
Sm/Nd isotopic age determination showed that Xiongshan dike swarm was at 585.7 Ma ± 30 Ma. The trace element geochemistry
and Sr/Nd/Pb isotope gemhemistry studies indicate that the dike swarm was products of back-arc basin spreading ridge and the
magma originated from the depleted mantle region which was metasomatized by LILE-rich liquids/melts derived from subduction
slab.
Project supported by the National Natural Science Foundation of China. 相似文献
6.
综合论述了潟湖潮汐通道口门之流速、断面面积、通道长度、延时角和饱满系数之间的关系,以及沿岸漂沙对口门的影响。对不同类型的潟湖潮汐通道,提出了中潮位射流导流堤、口门复式断面和通道分汊等治理方法及其通道口门相关尺度的具体计算。 相似文献
7.
8.
It is well established that Cretaceous magmatism in the South China Block (SCB) is related to the Paleo-Pacific subduction. However, the starting time and the associated deep crust-mantle processes are still debatable. Mafic dike swarms carry important information on the deep earth (including mantle) geodynamics and geochemical evolution. In the Jiangnan Orogen (South China), there is no information on whether the Mesozoic magmatic activities in this region are also directly related to the Pacific subduction or not. In this study, we present detailed zircon U-Pb geochronological, whole-rock element and Sr-Nd isotope data for Early Cretaceous Tuanshanbei dolerite dikes, and provide new constraints on the condition of the lithospheric mantle and mantle dynamics of the SCB during that time. LA-ICP-MS zircon U-Pb dating suggests that this dolerite erupted in the Early Cretaceous (~145 Ma). All samples have alkaline geochemical affinities with K2O + Na2O = 3.11–4.04 wt%, K2O/Na2O = 0.50–0.72, and Mg# = 62.24–65.13. They are enriched in LILE but depleted in HFSE with higher initial 87Sr/86Sr ratio (0.706896–0.714743) and lower εNd(t) (?2.61 to ?1.67). They have high Nb/U, Nb/La, La/Sm and Rb/Sr, and low La/Nb, La/Ta, Ce/Pb, Ba/Rb, Tb/Yb and Gd/Yb ratios. Such geochemical signatures suggest that the fractional crystallization is obvious but crustal contamination play a negligible role during magmatic evolution. Tuanshanbei dolerite were most likely derived from low-degree (2%–5%) partial melting of a phlogopite-bearing mantle material consisted of ~85% spinel peridotite and ~15% garnet peridotite previously metasomatized by asthenosphere-derived fluids/melts with minor subduction-derived fluids/melts. Slab-rollback generally lead to the upwelling of the hot asthenosphere. The upwelling of asthenosphere consuming the lithospheric mantle by thermo-mechanical-chemical erosion. The lithospheric mantle may have partially melted due to the heating by the upwelling asthenosphere and lithospheric extension. It is inferred that the Tuanshanbei dolerite might be associated with the initial slab rollback and corresponding lithospheric extension occurred potentially at ca. 145 Ma. 相似文献
9.
《China Geology》2021,4(1):56-66
The timing of the initial Indo-Asian collision is a subject of debate for a long time. Besides, the magmatic trace of the collisional process is also unclear. In the present study, the authors report Early Eocene leucocratic sill/dike swarms in the northern edge of the Nymo intrusive complex of the Gangdese belt, southern Tibet. The Nymo intrusive complex was emplaced at ca. 50 –47 Ma and surrounded by the metamorphosed Jurassic-aged Bima Formation volcano-sedimentary sequence along its northern side. At outcrops, the leucocratic sills/dikes intruded along or truncated the deformed foliations of the host Bima Formation, which has been subject to high-temperature amphibolite-facies metamorphism at ca. 50 –47 Ma. Detailed cathodoluminescence image analyses reveal that the zircon grains of the leucocratic sills/dikes have core-mantle textures. The cores yield the Jurassic ages comparable to the protolith ages of the Bima Formation. In contrast, the mantles of zircon grains yield weighted mean ages of ca. 49–47 Ma, representing the crystallization timing of these leucocratic sills/dikes. The coeval ages for the Nymo intrusive complex, the high-temperature metamorphism, and the leucocratic sills/dikes indicate that a close relationship exists among them. The authors tentatively suggest that these leucocratic sills/dikes were generated from partial melting of the Jurassic-aged Bima Formation volcanic rocks, triggered by the high heat from the magma chamber of the Nymo intrusive complex. This Early Eocene tectono-thermal event of coeval magmatism, metamorphism and partial melting was most likely formed during the Indo-Asian collisional setting.©2021 China Geology Editorial Office. 相似文献
10.
A Least-squares Window Curves Method for Interpretation of Magnetic Anomalies Caused by Dipping Dikes 总被引:1,自引:0,他引:1
E. M. Abdelrahman E. R. Abo-Ezz K. S. Soliman T. M. El-Araby K. S. Essa 《Pure and Applied Geophysics》2007,164(5):1027-1044
We have developed a least-squares method to determine simultaneously the depth and the width of a buried thick dipping dike
from residualized magnetic data using filters of successive window lengths. The method involves using a relationship between
the depth and the half-width of the source and a combination of windowed observations. The relationship represents a family
of curves (window curves). For a fixed window length, the depth is determined for each half-width value by solving one nonlinear
equation of the form f (z) = 0 using the least-squares method. The computed depths are plotted against the width values representing a continuous curve.
The solution for the depth and the width of the buried dike is read at the common intersection of the window curves. The method
involves using a dike model convolved with the same moving average filter as applied to the observed data. As a result, this
method can be applied to residuals as well as to measured magnetic data. Procedures are also formulated to estimate the amplitude
coefficient and the index parameter. The method is applied to theoretical data with and without random errors. The validity
of the method is tested on airborne magnetic data from Canada and on a vertical component magnetic anomaly from Turkey. In
all cases examined, the model parameters obtained are in good agreement with the actual ones and with those given in the published
literature. 相似文献