Temporal evolution of the Mariana arc during rifting of the Mariana Trough traced through the volcaniclastic record   总被引：1，自引：0，他引：1  

PeterD.  Clift & Jongman  Lee 《Island Arc》1998,7(3):496-512

The sedimentary sequences that accumulate around volcanic arcs may be used to reconstruct the history of volcanism provided the degree of along-margin sediment transport is modest, and that reworking of old sedimentary or volcanic sequences does not contribute substantially to the sediment record. In the Mariana arc, the rare earth and trace element compositions of ash layers sampled by Deep Sea Drilling Project (DSDP) site 451 on the West Mariana Ridge, and sites 458 and 459 on the Mariana Forearc, were used to reconstruct the evolution of the arc volcanic front during rifting of the Mariana Trough. Ion microprobe analysis of individual glass shards from the sediments shows that the glasses have slightly light rare earth element (LREE)-enriched compositions, and trace element compositions typical of arc tholeiites. The B/Be ratio is a measure of the involvement of subducted sediment in petrogenesis, and is unaffected by fractional crystallization. This ratio is variable over the period of rifting, increasing up-section at site 451 and reaching a maximum in sediments dated at 3–4 Ma, ∼ 3–4 million years after rifting began. This may reflect increased sediment subduction during early rifting and roll-back of the Pacific lithosphere. Parallel trends are not seen in the enrichment of incompatible high field strength (HFSE), large ion lithophile (LILE) or rare earth elements (REE), suggesting that flux from the subducting slab alone does not control the degree of melting. Re-establishment of arc volcanism on the trench side of the basin at ca 3 Ma resulted in volcanism with relative enrichment in incompatible REE, HFSE and LILE, although these became more depleted with time, possibly due to melt extraction from the mantle source as it passed under the developing back-arc spreading axis, prior to melting under the volcanic front.  相似文献   

高桩码头锈蚀破损面板残余承载力评估方法   总被引：6，自引：0，他引：6  

刘富强  竺存宏等 《海洋工程》2001,19(1):45-50

高桩码头长期工作在具有腐蚀介质的潮湿环境中，因钢筋的锈蚀会使构件表面砼胀裂而破损，目前我国大部分的高桩码头进入了锈蚀破损的高峰期。通过研究指出：以往国内外用构件蚀破损表面积大小或顺筋裂缝大小的标准来确定维修方案的方法是不正确的。根据一般构件为等截面，而沿跨度分布的弯矩不均匀的事实，指出构件在控制断面以外的部位强度有富裕，允许钢筋适当的锈蚀仍能满足设计强度的新见解。提出了锈蚀破损面板的强度安全性评估准则、强度因子新概念及其具体计算式，可以量化评估犭蚀破损面板的残余承载力，为科学制定锈蚀破损面板的维修方案提供参考，在保证码头结构安全的同时，大大节省维修费用。  相似文献   

无梁板结构的边界元法分析     

冯正农  夏世群  王亮 《中国海洋大学学报(自然科学版)》1992,(2)

利用边界元法对无梁板结构进行较为全面的分析,纠正了以往计算中的某些错误结果。  相似文献   

基础底板注浆防渗技术研究及应用     

史金星  杨刚  姜谙南 《探矿工程》2008,35(1):44-47

部分采用片筏基础的建筑,当其地下室基础底板处于地下水水位以下时,由于勘察、设计、施工或其他诸如自然灾害等因素导致基础底板发生渗水现象[1].经过认真分析研究及工程应用,针对此种工程事故提出了一种创新施工方法,即采用两次注浆防渗技术进行整治,效果较好.并提供一个工程实例以供参考.  相似文献   

Degradation and Mechanism of the Mechanics and Durability of Reinforced Concrete Slab in A Marine Environment     

吴胜兴  刘冠国  卞汉兵  吕维波  蒋建华 《海洋工程》2016,(2):257-270

An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete (RC) slab at different ages in a marine environment. Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab. In the first stage, cracks appear. In the second stage, cracks develop from the edges to the middle of the slab. In the third stage, longitudinal and transverse corrosion-induced cracks coexist. The corrosion ratio of reinforcements nonlinearly increases with the age, and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established. The flexural capacity of the corroded RC slab nonlinearly decreases with the age, and the model for the bearing capacity factor of the corroded RC slab is established. The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio. Finally, the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.  相似文献   

班公湖-怒江缝合带中段东巧地区早白垩世岩浆作用——对大洋演化和地壳增厚的指示   总被引：1，自引：0，他引：1  

强巴扎西  吴浩  格桑旺堆  次仁欧珠  巴桑顿珠  琼达  女达娃 《地质通报》2016,35(5):648-666

对班公湖-怒江缝合带内的岩浆作用进行LA-ICP-MS锆石U-Pb测年和地球化学分析,在辉绿岩中获得138.7±1.0Ma的~(206)Pb/~(238)U年龄加权平均值,在流纹岩中获得了110.4±0.4Ma的谐和年龄,表明区内岩浆作用具有2期成因。地球化学研究认为,辉绿岩是地幔熔融的产物,花岗闪长岩为岩石圈地幔熔融的产物,而流纹岩显示2类不同的岩石地球化学特征,低Sr流纹岩为古老岩石圈地幔熔体经历分离结晶作用的产物,高Sr流纹岩具有埃达克岩的特征,为增厚下地壳熔融的产物。综合已有的研究,早白垩世岩浆作用在缝合带两侧均有展布,其中早期岩浆岩为班公湖-怒江洋双向俯冲的产物,末期岩浆岩是碰撞后俯冲洋壳前缘断离形成的。早白垩世班公湖-怒江洋经历了双向俯冲到大洋闭合的演化过程,并在早白垩世末期发生了俯冲洋壳的断离事件。同时,高Sr流纹岩的发现表明,早白垩世末期班公湖-怒江缝合带已经发生了明显的地壳增厚作用。  相似文献   

The Plankogel detachment of the Eastern Alps: petrological evidence for an orogen‐scale extraction fault          下载免费PDF全文

S. Schorn  K. Stüwe 《Journal of Metamorphic Geology》2016,34(2):147-166

The so‐called Plankogel detachment is an east‐west trending, south‐dipping low‐angle structure that juxtaposes the high‐P rocks of the eclogite type locality of the eastern European Alps against amphibolite facies rocks to the south. It occurs in both the Saualpe and Koralpe Complex in eastern Austria. During Cretaceous intracontinental subduction, the footwall and the hangingwall units of the Plankogel detachment were buried to different crustal levels as inferred by pseudosection modelling and conventional thermobarometry: ~23–24 kbar and 640–690 °C for the eclogite facies units in the footwall of the detachment and ~12–14 kbar and 550–580 °C for the amphibolite facies metapelites in the hangingwall. Despite the different peak metamorphic conditions, both sides of the detachment display a common overprint at conditions of ~10 kbar and 580–650 °C. From this, we infer a two‐stage exhumation process and suggest that this two‐stage process is best interpreted tectonically in terms of slab extraction during Eoalpine subduction. The first stage of exhumation occurred due to the downward (southward) extraction of a lithospheric slab that was localized in the trace of the Plankogel detachment. The later stage, however, is attributed to more regional erosion‐ or extension‐driven processes. Since the Plankogel detachment is geometrically related to a crustal‐scale shear zone further north (the Plattengneiss shear zone), we suggest that both structures are part of the same extraction fault system along which the syn‐collisional exhumation of the Eoalpine high‐P units of the Eastern Alps occurred. The suggested model is consistent with both the mylonitic texture of the Plattengneiss shear zone and the overall ambiguous shear sense indicators present in the entire region.  相似文献   

流变变形对高面板堆石坝面板脱空的影响分析   总被引：8，自引：3，他引：5  

张丙印  师瑞锋 《岩土力学》2004,25(8):1179-1184

面板堆石坝尤其是高面板堆石坝的运行实践表明,堆石的流变现象比较显著。采用基于直接约束算法的接触力学分析方法模拟了混凝土面板和堆石体之间的接触关系。考虑堆石体的流变特性,并结合天生桥一级面板堆石坝的现场观测结 果,对高面板堆石坝中的面板脱空问题进行了有限元计算分析,研究了坝体流变变形对面板脱空和垫层亏坡问题的影响。  相似文献   

Late Cretaceous subduction initiation and Palaeocene–Eocene slab breakoff magmatism in South-Central Anatolia,Turkey     

《International Geology Review》2012,54(1):66-87

The Late Cretaceous Alihoca ophiolite in the Inner Tauride suture zone (ITSZ) of South-Central Turkey represents part of a single ophiolitic thrust sheet that originated from the Inner Tauride ocean. The ophiolite contains upper mantle peridotites, cumulate wehrlites, layered-to-isotropic gabbros, and microgabbroic-to-doleritic dikes. An ophiolitic mélange beneath the Alihoca ophiolite includes blocks of limestone, peridotite, dolerite, basalt, and deep-sea sedimentary rocks (radiolarite, chert) in a matrix comprising sheared serpentinite and mudstone. Isotropic gabbro and dolerite dike rocks show enrichment in Sr, K, Rb, Ba, and Th (LILE) and depletion of Ta, Nb, Zr, Ti, and Y (HFSE), indicating an island arc tholeiite (IAT) affinity. Relatively younger dolerite rocks display low TiO₂ (<0.5 wt.%) contents, concave REE profiles with low HREE concentrations, and high LREE values, typical of boninitic affinities. The Alihoca ophiolite, hence, displays an IAT to boninitic geochemical progression in its magmatic evolution, reminiscent of many other Tethyan ophiolites in the region. It represents the remnant of a forearc oceanic crust, which developed during the early stages of subduction within the Inner Tauride ocean. Volcanic, volcano-sedimentary, and sedimentary rocks of the Uluk??la–Çamard? basin north of the ITSZ disconformably overlie the mafic-ultramafic rocks of the Alihoca ophiolite. Pillowed and massive lavas of the latest Cretaceous–Palaeocene Uluk??la Formation have alkaline basalt-to-basaltic andesite compositions, displaying relatively enriched LILE and LREE patterns with negative Nb and Ta anomalies. These geochemical features suggest that magmas of the Uluk??la–Çamard? volcanic rocks formed from partial melting of a metasomatized lithospheric mantle. This melting event was triggered by the influx of asthenospheric heat through a slab breakoff-induced window in the downgoing Tethyan oceanic lithosphere.  相似文献   

Geochemistry and petrogenesis of an adakitic quartz-monzonitic porphyry stock and related cross-cutting dike suites,Kighal, northwest Iran     

《International Geology Review》2012,54(9):1126-1144

A late Oligocene–early Miocene quartz-monzonitic porphyry stock intrudes upper Eocene andesitic-latitic lava flows, producing Cu–Mo mineralization and hydrothermal alteration zones in the Kighal area, northwest Iran. Numerous cross-cutting dikes of various compositions, ranging from quartz-diorite to granodiorite and microdiorite, branch off from three later-stage barren sub-volcanic bodies, and intrude the porphyry stock. Both the stock and comagmatic dikes display I-type, magnesian, calc-alkaline to high-K calc-alkaline signatures and metaluminous to peraluminous geochemical characters, being emplaced within an active continental margin setting. Analysed samples display the typical geochemical characteristics of adakites. Moreover, rare earth elements exhibit a fractionated pattern with low heavy rare earth element concentrations. The general trend in an La/Yb–Yb diagram shows that partial melting, rather than fractional crystallization, was the dominant process of magma generation. Based on the compositional classification of modern adakites, the studied rocks are of high-SiO₂ adakite type. They were generated through low degrees of high-pressure partial melting of subducted rutile- and amphibole-bearing eclogitic Neo-Tethyan oceanic slab. The descending slab underwent break-off, leaving behind a residue rich in garnet + amphibole ± rutile, lacking significant plagioclase. Interaction of the slab-derived magma with the mantle-wedge peridotite is also evident.  相似文献