A study of the effect of local scour on the flow field near the spur dike

The flow field near a spur dike such as down flow and horseshoe vortex system(HVS)are susceptible to the topographic changes in the local scouring process,resulting in variation of the sediment transport with time.In this study,large eddy simulations with fixed-bed at different scouring stages were conducted to investigate the changes in flow field.The results imply that the bed deformation leads to an increase in flow rate per unit area,which represent the capability of sediment transportation by water,in the scour hole.Moreover,the intensity of turbulent kinetic energy and bimodal motion near the sand bed induced by the HVS were also varied.However,the peak moments between the two sediment transport mechanisms were different.Hence,understanding the complex feedback mechanism between topography and flow field is essential for the local scour problem.

Geochemical Characteristics and Genesis of the Luxi-Xianrenzhang Diabase Dikes in Xiazhuang Uranium Orefield, Northern Guangdong Province

The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, depletion in Zr and Hf, and basically no depletion in Nb and Ta and no Eu anomaly. They are similar to intraplate basalt in terms of trace element characteristics. They have high εNd（t） values （3.6-4.9）, initial ^87Sr/^86Sr ratios （0.70530-70641） and δ^18O values and Dupal anomaly of Pb isotope compositions. Their Sr-Nd, Pb-Sr, Pb-Nd and Pb-Pb isotopes plot between DMM and EMII, with Pb similar to EMII, Nd relatively close to DMM and Sr in between. This profile suggests that the diabase dikes studied were derived from partial melting of a mantle source that had been subjected to metasomatism by fluids originated from a subduction zone under a tectonic environment of crustal extension and lithosphere thinning in the late Yanshanian.

K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China: Implications for Crustal Extension

Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province. Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively.

Risk Analysis and Assessment of Overtopping Concerning Sea Dikes in the Case of Storm Surge

Risk analysis and assessment relating coastal structures has been one of the hot topics in the area of coastal protection recently. In this paper, from three aspects of joint return period of multiple loads, dike failure rate and dike continuous risk prevention respectively, three new risk analysis methods concerning overtopping of sea dikes are developed. It is worth noting that the factors of storm surge which leads to overtopping are also considered in the three methods. In order to verify and estimate the effectiveness and reliability of the newly developed methods, quantified mutual information is adopted. By means of case testing, it can be found that different prior variables might be selected dividedly, according to the requirement of special engineering application or the dominance of loads. Based on the selection of prior variables, the correlating risk analysis method can be successfully applied to practical engineering.

Ordovician Granitoids and Silurian Mafic Dikes in the Western Kunlun Orogen, Northwest China:Implications for Evolution of the Proto-Tethys

The western Kunlun orogen in the northwest Tibet Plateau is related to subduction and collision of Proto-and Paleo-Tethys from early Paleozoic to early Mesozoic. This paper presents new LA-ICPMS zircon U-Pb ages and Lu-Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes of two Ordovician granitoid plutons(466–455 Ma) and their Silurian mafic dikes(～436 Ma) in the western Kunlun orogen. These granitoids show peraluminous high-K calcalkaline characteristics, with(^(87)Sr/^(86)Sr)_i value of 0.7129–0.7224, ε_(Nd)(t) values of -9.3 to -7.0 and zircon ε_(Hf)(t) values of -17.3 to -0.2, indicating that they were formed by partial melting of ancient lower-crust(metaigneous rocks mixed with metasedimentary rocks) with some mantle materials in response to subduction of the Proto-Tethyan Ocean and following collision. The Silurian mafic dikes were considered to have been derived from a low degree of partial melting of primary mafic magma. These mafic dikes show initial ^(87)Sr/^(86)Sr ratios of 0.7101–0.7152 and ε_(Nd)(t) values of -3.8 to -3.4 and zircon ε_(Hf)(t) values of -8.8 to -4.9, indicating that they were derived from enriched mantle in response to post-collisional slab break-off. Combined with regional geology, our new data provide valuable insight into late evolution of the Proto-Tethys.

LA-ICP-MS U-Pb Zircon Geochronology of Basic Dikes within Maxianshan Rock Group in the Central Qilian Orogenic Belt and Its Tectonic Implications

A large number of basic dikes, which indicate an important tectonic-magmatic event in the eastern part of the Central Qilian （祁连） orogenic belt, were found from Maxianshan （马衔山） rock group, Yongjing （永靖） county, Gansu （甘肃） Province, China. According to the research on the characteristics of geology and petrology, the basic dike swarms, widely intruded in Maxianshan rock group, are divided into two phases by the authors. U-Pb isotope of zircons from the basic dikes above two phases is separately determined by LA-ICP-MS in the Key Laboratory of Continental Dynamics of Northwest University, China and the causes of formation of the zircons are studied using CL images. The formation age of the earlier phase of metagabbro dikes is （441.1±1.4） Ma （corresponding to the early stage of Early Silurian）, and the age of the main metamorphic period is （414.3±1.2） Ma （corresponding to the early stage of Early Devonian）. The formation age of the later phase of diabase dike swarms is （434±1.0） Ma （corresponding to the late stage of Early Silurian）. The cap- tured-zircons from diabase dike swarms saved some information of material interfusion by Maxianshan rock group （^207pb/206pb apparent ages are （2 325±3）-（2 573 ±6） Ma）, and some zircons from diabase dike swarms also saved impacted information by tectonic thermal event during the late period of Caledonian movement （^206pb/^238U apparent ages are （400±2）-（429±2） Ma）. By combining the results of the related studies, the basic dikes within Maxianshan rock group were considered to be formed in the transfer period, from subductional orogeny towards collisional orogeny, which represents geological records of NW-SE extension during regional NE-SW towards intense compression in the Central Qilian block.

Geodynamics of Dikes in North of Saveh

Dikes can be divided into sheeted, feeder, cone and swarm types based on the origin and the formation. A group of dikes that are formed in dense in a relatively broad zone influenced by a particular tectonic regime are referred to as swarm dikes. Swarm dikes have numerous applications such as locating mantle plume centers, determining areas of longstanding tensions and detection of deformation networks. The purpose of this article is classified swarm dikes of “North of Saveh” based on previous studies. In one study, swarm dikes are classified based on their initial geometry into five types of I, II, III, IV and V. According to this classification, our study has been shown that the dikes in north of Saveh are of type IV. In another study, the swarm dikes are classified into three types: parallel, large radial and small radial. According to the classification, our study has been shown that the dikes of North Saveh are parallel that have arisen by tensions caused by the collision of the Arabian plate and the Central Iran plate. In addition to original tensions in the region, local faults have been effective on the arrangement and the establishment of dikes.

Geochronology and Geochemistry of Mafic Dikes from Hainan Island and Tectonic Implications

In the present study, the major and trace element compositions, as well as Sr, Nd isotopic compositions and K-Ar age data in mafic dikes from Hainan Island, China, have been analyzed. Whole-rock K-Ar dating yielded a magmatic duration of 61-98 Ma for mafic dikes. Mafic dikes have a very high concentration of incompatible elements, for example, Ba, Rb, Sr, K, rare earth elements, and especially light rare earth elements （LREE）, and negative anomalies of Nb, Ta, and Ti in the normalized trace element patterns. The initial 87Sr/86Sr ratios and εSr（t） of the mafic dikes are 0.70634- 0.71193 and ＋27.7 to ＋112.2, respectively. In the 87Sr/86Sr versus εNd（t） diagram, the Hainan Island mafic dikes plot between fields for depleted mantle and enriched mantle type 2. All these characteristics show that the mantle （source region） of mafic dikes in this area experienced metasomatism by fluids relatively enriched in LREE and large ion lithophUe elements. The genesis of Hainan Island mafic dikes is explained as a result of the mixing of asthenospheric mantle with lithospheric mantle that experienced metasomatism by the subduction of the Pacific Plate. This is different from the Hainan Island Cenozoic basalts mainly derived from depleted asthenospheric mantle, and possibly, minor metasomatised lithospheric mantle. This study suggests that the Mesozoic and Cenozoic lithospheric revolutions in Hainan Island can be divided into three stages： （1） the compression orogenesis stage before 98 Ma. The dominant factor during this stage is the subduction of the ancient Pacific Plate beneath this area. The lithospheric mantle changed into enriched mantle type 2 by metasomatism; （2） the thinning and extension stage during 61-98 Ma. The dominant factor during this stage is that the asthenospheric mantle invaded and corroded the lithospheric mantle; and （3） the large-scale thinning and extension stage after 61 Ma. The large-scale asthenospheric upwelling results in the strong erupting of Cenozoic basalts, large-scale thinning of the lithosphere, the southward translating and counterclockwise rotating of Hainan Island, and the opening of the South China Sea.

A Possible Mechanism to Thin Lithosphere of the North China Craton: Insights from Cretaceous Mafic Dikes in the Jiaodong Pensinsula

The North China Craton(NCC)is a classic case of the destruction of an ancient craton,in that it records the loss of more than 100 km of ancient refractory lithospheric mantle during the Mesozoic(e.g.,Menzies et al.,1993).This

Petrology and Geochemistry of Dikes in the North of Saveh in Iran

Dikes in the north of Saveh are located in a region with an area of approximately 200 square kilometers, in a distance of approximately 100 kilometers south of Tehran. Dikes mentioned in terms of petrological composition, are divided into two categories: alkaline and intermediate to acidic. Alkaline dikes include: andesitic basalt and andesite and intermediate to acidic dikes include: trachyte and trachyandesite. In terms of geochemical, dikes in the north of Saveh have a dual nature of alkaline and calc-alkaline. Both groups are derived from more enrichment source than primitive mantle. Despite similarity of pattern of both groups, varieties of alkaline having less silica, in the elements Sr, Ti, Nb and Ta show more enrichment and in the elements Hf, Rb, Th, K show less enrichment than varieties of calc-alkaline.

Chemical and Sr-Nd compositions and ^(40)Ar/^(39)Ar ages of NW-trending dolerite dikes of Burkina Faso: Evidence for a Mesoproterozoic magmatism in the West African Craton

The Paleoproterozoic basement of the northeastern part of the Leo-Man craton is intruded by generally NW-trending dikes. These regional scale dikes extend over 1000 km in Burkina Faso, Mali and Niger. We present chemical and Sr-Nd isotope compositions, as well as 40 Ar/39 Ar ages of these dikes with the following strikes N98°-N112°, and N114°-N124° in NE Burkina Faso. Field relationships show that the dikes are posterior to all other rock types dated between 2.26 Ga and 2.0 Ga. Chemical data indicate that the dikes are continental flood basalts and composed of low-Ti(TiO2 ≤ 2 wt.%) sub-alkaline basalts and andesites. They exhibit a minor negative Europium anomaly(0.86-0.99) and slightly fractionated REE patterns((La/Yb)_N= 2.5-9.1; Yb_N = 9.5-19.9). The ratios of Th/Ta(1.3-11.4) and Ce/Pb(5.2-58.5)suggest a varying crustal assimilation of the dike magmas during ascent in the continental crust for all studied samples. Calculated P-T conditions indicate that the magma reached temperatures of 1285 ℃(calculated from olivine compositions) and pressures of 6.9 kbar(calculated for pyroxene minerals).Calculated initial 87 Sr/86 Sr(0.70040-0.70260) and ε_(Nd)(t)=+2.1 to-3.5 at 1575 Ma,also point to a crustal contamination with the most primitive samples showing T_(DM) values of 1946 Ma and 2154 Ma. The low values of La/Ba(<0.2) and Nb/La(<1.0), contrast with the low Th/Nb(<0.9), and suggest a lithospheric mantle or subduction-modified mantle as possible source for the dikes. Sr-Nd data, Mg# and NbTa-Zr-Y-Th-Tb-Yb compositions further suggest that the most primitive samples were emplaced in a none orogenic setting and their magmas were subjected to variable crustal contaminations. Literature and the present whole rock 40 Ar/39 Ar age determinations show that the dikes were emplaced during a widespread Mesoproterozoic magmatism between 1.6 Ga and 1.2 Ga, and were affected by a thermal event causing the argon systematics resetting, best constrained by the date of sample KK1(1236 ± 20 Ma,^(40)Ar/^(36)Ar = 294 ±13, MSWD = 2.2). Contemporaneous 1590-1570 Ma extensive magmatism is reported in other crustal blocks in Baltica(Sveconorw-Goth, svecofennian) NW Laurentia(Slave craton, Yukon),and Australia(Gawler craton), and together with the 1575 studied dikes, are related to the breakup of the supercontinent Nuna.

A Study on the Relations Between Ultrabasic Dikes and Fine Disseminated Gold Deposits in Southwestern Guizhou Province as Exemplified by Zimudang Large-Sized Gold Deposit

The relations between ultrabasic rocks and gold deposits in time, space and genesisare discussed in this paper. The research results show that the ore-forming materials of the golddeposits is characteristic of crust-mantle mixing. The formation of the gold deposits is relatedwith the activity of juvenile fluids along with the intrusion of ultrabasic dikes. The ascendingjuvenile fluids not only offered Part of the gold, water and mineralizers for gold ndneralhation,but also promoted the remobilization, defortion and enrichment of gold in crustal sediments.

Overtopping Discharge of Wind-Waves on Simple Slope Dikes

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.

Graben on the Lunar Nearside: Do Dikes Lie Beneath?

On the Moon,tectonic structures are concentrated on the nearside,spatially associated with the maria(e.g.,Watters and Johnson,2010),or basalt-filled impact structures.Lunar graben(or rilles)are long,narrow troughs up to

A Neoarchean Subduction Polarity Reversal Event in the North China Craton: Evidence from 2.5 Ga Mafic Dikes and Coeval Granites

Fabrics of an Archean mélange belt in the Zanhuang Complex of the North China Craton(NCC)were intruded by mafic dikes and a granite pluton(Deng et al.,2013;Wang et al.,2013).Igneous zircons from an undefomed

2.7-Ga-old mafic dike in the Trans-North China Orogen of the North China Craton and its tectonic significance

We studied an Archean mafic dike in the TransNorth China Orogen of the North China Craton, which has a magmatic age of 2701 ± 83 Ma and is currently the oldest mafic dike in the North China Craton. Such an old dike is extremely rare in the world. The presence of mafic dikes indicates that the North China Craton was in a tensional tectonic environment at 2.7 Ga. Geochemical characteristics reveal that this mafic dike belongs to continental tholeiitic basalt. Results from Hf isotope analysis reveal that the mafic dike originates from a depleted mantle. The plate assembly in the North China landmass was realized during the Archean era(2.7 Ga), and a thick and stable continental crust was formed. Therefore, the first cratonization of the North China Craton was completed before 2.7 Ga. The intrusion of the 2.7-Ga-old mafic dike from the deep lithospheric mantle of the continent indicates that the North China Craton has undergone a period of extensional tectonic activity. This event marks a significant extensional event that occurred after the cratonization of the North China Craton.

Modelling Estimation of the Available Rainwater Resource in Gbedji-Kotovi Clay Area for Supplying Dikes and Dams

Floods and flows data are useful for dimensioning of dikes and dams which often include evacuation devices that regulate flows to ensure the volumes of water. The objective of this study is to estimate the available water resource in the village of Gbédji-Kotovi, located in the watershed of Couffo river in Benin by using sequentially, the HBV (Hydrologiska Byrans Vattenbalansavdelning) and GR4J (Rural Engineering model with 4 daily parameters) climate models. Hydrographs of water levels are simulated according to the calibration period (1994-1999) different from the validation one (1982-1988). Considering the Nash-Sutcliffe model Efficiency coefficient (NSE), the performance of GR4J model during calibration is slightly higher than the performance of the HBV model, while during the validation, the contrary is noticed. The annual rainfall average simulated is 1117.7 mm/year while the average observed is 1104.6 mm/year over the period 1981-2005. By 2050, on one hand, the annual flow rate values will vary from -19.2 to -11.9%, while the actual evapotranspiration will vary between 0.5 and -5.8;on another hand, the potential evapotranspiration and the annual precipitation remain constant. An average flow of 187 millions m3/year for annual average water depth of 1094 mm is obtained at Lanta rain station, which covers an area of 1664.47 km2, while this flow enabled an average flow of 327.5 millons m3/year to be obtained at the virtual station of our study area of 2908.15 km2. The flow rates corresponding to the return periods of 10, 25 and 50 years vary from 5.51 to 12.67 m3/s at the outlet of the virtual station;while those at the outlet of Lanta station vary from 3.6 to 6.6 m3/s. However, the simulated water quantiles cannot be fully mobilized;because of the uses, they undergo upstream and downstream. Thus, Gbédji-Kotovi locality requires the implementation of an integrated water resource management strategy that includes the construction of dikes and dams.

鄱阳湖区某典型圩堤堤基管涌发展过程试验研究

堤基管涌是造成鄱阳湖区圩堤险情乃至溃决的最主要原因之一,从机理上研究并揭示鄱阳湖区圩堤堤基管涌的致灾机制,对于应对管涌险情、科学开展应急抢险具有重要意义。基于鄱阳湖区某圩堤典型堤基结构,采用堤基原型土和自行设计制作的模型槽开展管涌物理模型试验,完整模拟了原型多层复杂堤基管涌发生、发展及致溃的全过程。结合试验现象对管涌发生和发展过程中的水力条件、堤基破坏机理和土体颗粒侵蚀速度等展开分析。研究结果表明,鄱阳湖区圩堤堤基结构中管涌破坏集中于下伏砂层,在渗透压的作用下上覆弱透水层被渗流击穿,于砂层与上覆层的接触面形成管涌通道后加速土体颗粒的侵蚀,最终导致堤基溃决;鄱阳湖区某典型圩堤堤基中夹于黏土层中的壤土层无法起到强弱透水层间过渡层的作用,土体颗粒侵蚀规律与无壤土过渡层的堤基结构相类似,形成表面管涌出口和堤基开裂的土体颗粒累计侵蚀量增长速率均低于0.1 g/s;该圩堤发生管涌的堤基平均总体临界水平坡降约为0.1。

二元堤基结构堤防管涌机理模型试验

为了科学解释二元堤基结构堤防管涌致灾机制并揭示其形成、演化过程和致溃规律,在考虑堤基强、弱透水层之间壤土过渡层作用的基础上,通过室内模型试验完整地模拟了二元堤基管涌从单个泡泉发展至管涌群并最终造成堤基塌陷溃决的全过程。试验结果表明:上部黏土及壤土层在渗流的顶托作用下向上隆起并在堤基内部产生层间水平渗漏通道,导致发生潜层砂沸,最终向上发展为表面砂沸的渗透破坏;二元堤基结构管涌发展可分为裂缝发展、潜层破坏、上覆层破坏、管涌通道上溯、堤基破坏和堤基溃决6个发展阶段;表面砂沸由潜层砂沸发展而来,潜层砂沸是由于土层内竖向坡降所引起的渗流力大于上部土体浮容重时造成的土层结构破坏所致,临界竖向坡降处于0.9~1之间;壤土层的存在会加快堤后自由边界区域管涌群的发展速度,但可以延缓管涌通道的上溯,对堤基具有保护作用。

透水丁坝孔型对坝体附近水流特性影响研究

为深入探讨透水丁坝透水孔型对其附近水流特性的影响,通过室内高精度水槽试验,采用三维声学多普勒流速仪对矩形、方圆形和椭圆形三种透水孔型下丁坝附近水流流速进行测量,获得不同透水孔型影响下的丁坝附近水流流速和紊动强度分布特征。结果表明,坝后水流流速波动和紊动强度明显大于坝前,透水丁坝对近坝区水流影响较大,距丁坝越远,流速均匀性越好,紊动强度越小。透水丁坝的缓流效果与透水孔型密切相关,矩形透水孔的坝后缓流率为35.4%,缓流效果较好,方圆形透水孔次之,椭圆形最小,研究结果可为丁坝的透水孔型选择提供指导和参考。