舟山东港新城溃堤洪水演进数值模拟          下载免费PDF全文

黄潘阳  来向华  季有俊  胡涛骏  王友忠 《海洋学研究》2017,35(4):61-68

台风会引起风暴增水和强浪。围填海工程建于软土地基上,海堤易产生不规则沉降,在台风引起的强浪作用下有可能发生溃堤,海水在高水位下大量涌入围区,引发灾难。针对溃坝的急变流特性,基于Delft3D Open Source,采用一种基于经典交错网格的改进型数值方法(其水流扩展流动数值近似算法符合动量守恒,而水流收缩流动数值近似则满足伯努利方程),建立了舟山东港新城溃堤洪水演进模型,并计算了最大可能风暴增水条件下溃堤洪水在东港新城的演进过程。结果表明,围区内的地形形势对洪水的演进及最终分布起了决定性作用,当溃口出现在不同位置时,影响范围和程度不一样。东港南部由于地势较低,且没有大型的吸纳洪水的人工湖,当附近出现50 m宽的溃口时,近乎整个南部区域都会受到海水的影响;而北部由于地势相对较高,影响有限。  相似文献   

The ~AD1315 Tarawera and Waiotapu eruptions, New Zealand: contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system?     

Ian A. Nairn  Jeffrey W. Hedenquist  Pilar Villamor  Kelvin R. Berryman  Phil A. Shane 《Bulletin of Volcanology》2005,67(2):186-193

A series of large hydrothermal eruptions occurred across the Waiotapu geothermal field at about the same (prehistoric) time as the ~AD1315 Kaharoa rhyolite magmatic eruptions from Tarawera volcano vents, 10–20 km distant. Triggering of the Waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent Ngapouri Fault. The Kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the Tarawera volcano. A ~1000 t/day pulse of CO₂ gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from Waiotapu geothermal wells. This CO₂ pulse is most readily sourced from basalt intruded at depth, and although not precisely dated, it appears to be associated with the Waiotapu hydrothermal eruptions. We infer that the hydrothermal eruptions at Waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at Tarawera. This dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km-long fissure that formed across the Tarawera region in AD1886. Fault ruptures that occurred in the Waiotapu area in association with both the AD1886 and ~AD1315 eruptions are considered to be a result, rather than a cause, of the dike intrusion processes.Editorial responsibility: J. Donnelly-Nolan  相似文献   

40Ar–39Ar age and geochemistry of subduction-related mafic dikes in northern Tibet,China: petrogenesis and tectonic implications     

《International Geology Review》2012,54(1):57-73

The early Permian Xiaomiao mafic dike swarm in the East Kunlun orogenic belt (EKOB) provides an excellent opportunity to study the petrogenesis of such swarms developed in supra-subduction zone environments, and to investigate the early plate tectonic history of the Palaeo-Tethyan Ocean. Hornblende ⁴⁰Ar–³⁹Ar dating results indicate that the mafic dikes formed in the early Permian (277.76 ± 2.72 Ma). The Xiaomiao mafic hypabyssals have the following compositional range: SiO₂ = 46.55–55.75%, MgO = 2.80–7.38%, Mg^# = 36–61, and (Na₂O + K₂O) = 2.87–4.95%. Chemically, they display calc-alkali affinities, ranging in composition from gabbro to gabbroic diorite. All analysed dikes are enriched in light rare earth elements and large-ion lithophile elements (e.g. Rb and Ba), but are depleted in heavy rare earth elements and high field strength elements (e.g. Nb, Ta, and Ti). Their I_Sr and ?_Nd(t) values range from 0.707 to 0.715 and –2.60 to +2.91, respectively. They are geochemically similar to subduction-related basaltic rocks (e.g. island arc basalt), but differ from E-MORB and N-MORB. Petrographic and major element data reveal that fractional crystallizations of clinopyroxene, olivine, hornblende, and Fe–Ti oxides may have occurred during magma evolution, but that crustal contamination was minor. Based on geochemical and Sr–Nd isotopic bulk-rock compositions, we suggest that the mafic dikes were likely generated by 10–20% partial melting of a spinel + minor garnet lherzolite mantle source metasomatized by subducted, slab-derived fluids, and minor sediments. Based on our results, we propose that the early evolution of the Palaeo-Tethyan Ocean involved the spreading and initial subduction of the Carboniferous to early Permian ocean basin followed by late Permian subduction, which generated the magmatic arc.  相似文献   

Secular evolution of the lithospheric mantle beneath the eastern North China craton: evidence from peridotitic xenoliths from Late Cretaceous mafic rocks in the Jiaodong region,east-central China     

《International Geology Review》2012,54(2):182-211

The Mesozoic lithospheric mantle beneath the North China craton remains poorly constrained relative to its Palaeozoic and Cenozoic counterparts due to a lack of mantle xenoliths in volcanic rocks. Available data show that the Mesozoic lithospheric mantle was distinctive in terms of its major, trace element, and isotopic compositions. The recent discovery of mantle peridotitic xenoliths in Late Cretaceous mafic rocks in the Jiaodong region provides an opportunity to further quantify the nature and secular evolution of the Mesozoic lithospheric mantle beneath the region. These peridotitic xenoliths are all spinel-facies nodules and two groups, high-Mg# and low-Mg# types, can be distinguished based on textural and mineralogical features. High-Mg# peridotites have inequigranular textures, high Mg# (up to 92.2) in olivines, and high Cr# (up to 55) in spinels. Clinopyroxenes in the high-Mg# peridotites are generally LREE-enriched ((La/Yb)_N>1) with variable REE concentrations, and have enriched Sr–Nd isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0.7046–0.7087; ¹⁴³Nd/¹⁴⁴Nd = 0.5121–0.5126). We suggest that the high-Mg# peridotites are fragments of the Archaean and/or Proterozoic lithospheric mantle that underwent extensive interaction with both carbonatitic and silicate melts prior to or during Mesozoic time. The low-Mg# peridotites are equigranular, are typified by low Mg# ( < 90) in olivines, and by low Cr# ( < 12) in spinels. Clinopyroxenes from low-Mg# peridotites have low REE abundances (ΣREE = 12 ppm), LREE-depleted REE patterns ((La/Yb)_N < 1), and depleted Sr–Nd isotopic features, in contrast to the high-Mg# peridotites. These geochemical characteristics suggest that the low-Mg# peridotites represent samples from the newly accreted lithospheric mantle. Combined with the data of mantle xenoliths from the Junan and Daxizhuang areas, a highly heterogeneous, secular evolution of the lithosphere is inferred for the region in Late Cretaceous time.  相似文献   

Zircon U–Pb age and Sr–Nd–Hf isotopic constraints on the age and origin of Triassic mafic dikes,Dalian area,Northeast China     

《International Geology Review》2012,54(2):249-262

Post-orogenic mafic rocks from Northeast China consist of swarms of dolerite dikes. We report a new U–Pb zircon age, as well as whole-rock geochemical and Sr–Nd–Hf isotopic data. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon analysis yielded an age of 210.3 ± 1.5 million years (i.e. Triassic) for these mafic dikes. Most Dalian mafic rocks exhibit low K₂O + Na₂O contents, and span the border between alkaline and calc-alkaline rock associations in the total alkali–silica diagram. The investigated dikes are also characterized by relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios (0.7061–0.7067) and negative ?_Nd (t) (?4.7 to??4.3) and ?_Hf (t) values (?4.1 to??1.1), implying that they were derived from an enriched lithospheric mantle source. The mafic dikes are characterized by relatively low MgO (4.65–5.44 wt.%), Mg^# (41–44), and compatible element content [such as Cr (89.9–125 ppm) and Ni (56.7–72.2 ppm)], which are the features of an evolved mafic magma. No evidence supports the idea that the mafic rocks were affected by significant assimilation or crustal contamination during emplacement. We conclude that the dolerites formed in a post-orogenic extensional setting, related to lithospheric delamination or ‘collapse’ of the Central Asian Orogenic Belt (CAOB), also termed the Xingmeng Orogenic Belt in China.  相似文献   

Zircon SIMS U-Pb Age,Hf and O Isotopes of Mafic Dikes,Southwest Fujian Province     

Zhang Wenhui  Wang Cuizhi  Li Xiaomin  Liu Wenyuan 《地球科学进展》2016,31(3):320-334

The study in this paper determined whole rock major and trace elements, zircon U-Pb age and Hf, O isotopes of 5 mafic dikes in the southwestern Fujian province. The 5 dikes are mainly diabase and the whole rock SiO₂ content are between 45%~53%. Most zircons of the mafic dikes display obvious oscillatory zoning and fan-shaped zoning, and have the typical magmatic zircon crystallization characteristics. Zircon U-Pb age is dispersed with 96~2 400 Ma range. In addition to the minimum age (96~142 Ma) which might be the age of the formation of dikes, the remaining are captured zircon. The captured zircon age was mainly distributed in 4 groups: Early Proterozoic (2 467~1 796 Ma); Middle and late Proterozoic (1 343~647 Ma); Silurian to late Triassic Epoch (427~225 Ma); and Late Jurassic (159~140 Ma). Hf-O isotope shows that the early Proterozoic zircon was derived from the mantle of the homogeneous chondrite reservoir, and the others show magmatic mixing characteristics between depleted mantle and crust. Zircon’s ε_Hf(t) and δ¹⁸O of the early Late Cretaceous clearly show the mixing trend of depleted mantle and crustal magma. The peak of zircon Hf two-stage depleted mantle model age T_DM2 was mainly distributed in the 1.6~1.9 Ga. The Early Proterozoic mafic crust might be the main source for latter granite.  相似文献   

Evaluation of transtension and transpression within contractional fault steps: Comparing kinematic and mechanical models to field data     

《Journal of Structural Geology》2014

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华北陆块早元古代基性岩墙群及其构造意义   总被引：1，自引：0，他引：1  

王岳军  彭头平  范蔚茗  赵国春  喻晓冰 《矿物岩石地球化学通报》2007,26(1):1-9

华北陆块中部带的晋冀蒙地区早元古代未变形变质基性岩脉形成于1781~1765 Ma。东部陆块鲁西地区早元古代类似的基性岩脉形成时间约为1841 Ma。中部带基性岩脉依据其FeOt含量、(Nb/La)N和(Th/Nb)N值的差异能划分为组1、组2和组3三类。它们的元素-同位素组成变化表明,组1样品起源于再循环大陆玄武质组分参与的交代岩石圈地幔,组2样品源于交代富铁岩石圈地幔与MORB组分的混杂源区,组3样品则是受辉长质组分混染的、经俯冲改造而成的岩石圈地幔产物。相反,鲁西地区基性岩脉亏损HFSE,具MORB型钕同位素组成。上述地球化学特征支持华北陆块中部带约1780 Ma的基性岩脉与早期俯冲碰撞作用的关系密切,而东部陆块约1840 Ma基性岩脉类似于弧后盆地构造背景产物。  相似文献