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   

Nature and growth rate of the Northern Izu–Bonin (Ogasawara) arc crust and their implications for continental crust formation     

ASAHIKO  TAIRA  SANEATSU  SAITO  KAN  AOIKE  SUMITO  MORITA  HIDEKAZU  TOKUYAMA  KIYOSHI  SUYEHIRO  NARUMI  TAKAHASHI  MASANAO  SHINOHARA  SCHOICHI  KIYOKAWA  JIRO  NAKA & ADAM  KLAUS 《Island Arc》1998,7(3):395-407

The bulk composition of the continental crust throughout geological history is thought by most previous workers to be andesitic. This assumption of an andesitic bulk composition led to an early hypothesis by 72 ) that the continental crust was created by arc magmatism. This hypothesis for the origin of continental crust was challenged by several authors because: (i) the mean rate of arc crust addition obtained by 50 ) is too small to account for some certain phases of rapid crustal growth; and (ii) the bulk composition of ocean island arcs, the main contributor to the Archean and early Proterozoic crust, is basaltic rather than andesitic ( 4 ; 49 ). New data from the Northern Izu–Bonin arc are presented here which support the 72 ) hypothesis for the origin of the continental crust by andesitic arc magma. A geological interpretation of P wave crustal structure obtained from the Northern Izu–Bonin arc by 66 ) indicates that the arc crust has four distinctive lithologic layers: from top to bottom: (i) a 0.5–2-km-thick layer of basic to intermediate volcaniclastic, lava and hemipelagite (layer A); (ii) a 2–5-km-thick basic to intermediate volcaniclastics, lavas and intrusive layer (layer B); (iii) a 2–7-km-thick layer of felsic (tonalitic) rocks (layer C); and (iv) a 4–7-km-thick layer of mafic igneous rocks (layer D). The chemical composition of the upper and middle part of the northern Izu–Bonin arc is estimated to be similar to the average continental crust by 73 ). The rate of igneous addition of the Northern Izu–Bonin arc since its initial 45-Ma magmatism was calculated as 80 km³/km per million years. This rate of addition is considered to be a reasonable estimate for all arcs in the western Pacific. Using this rate, the global rate of crustal growth is estimated to be 2.96 km³/year which exceeds the average rate of crustal growth since the formation of the Earth (1.76 km³/year). Based on this estimate of continental growth and the previously documented sediment subduction and tectonic erosion rate (1.8 km³/year, 24 ), several examples of growth curves of the continental crust are presented here. These growth curves suggest that at least 50% of the present volume of the continental crust can be explained by arc magmatism. This conclusion indicates that arc magmatism is the most important contributor to the formation of continental crust, especially at the upper crustal level.  相似文献   

Utilization and sustainable development of island mountains in China     

张耀光  杨荫凯 《中国地理科学(英文版)》1998,8(1):58-66

ＵＴＩＬＩＺＡＴＩＯＮＡＮＤＳＵＳＴＡＩＮＡＢＬＥＤＥＶＥＬＯＰＭＥＮＴＯＦＩＳＬＡＮＤＭＯＵＮＴＡＩＮＳＩＮＣＨＩＮＡ①ＺｈａｎｇＹａｏｇｕａｎｇ（张耀光）ＹａｎｇＹｉｎｋａｉ（杨荫凯）ＩｎｓｔｉｔｕｔｅｏｆＭａｒｉｎｅＲｅｓｏｕｒｃｅｓ,Ｌｉａｏ...  相似文献   

中国北方海岛县经济区及其划分的初步研究^*   总被引：7，自引：2，他引：5  

张耀光 《地理研究》1998,17(3):289-288

在我国海岛县经济类型(或类型区)划分的基础上,划分出我国海岛经济区的框架,以我国北方海岛县经济区为重点,探讨海岛经济区的划分方法,提出发展方向与对策。  相似文献   

广州城市气候资源与被动蒸发冷却技术的应用   总被引：2，自引：0，他引：2  

孟庆林  李建成  汪志舞  陶杰  蔡宁 《热带地理》1998,18(2):168-171

城市热岛效应是城市的病态气候现象,潜在的危害极大。从广州的亚热带城市气候资源水平出发,讨论了应用城市气候资源的自我调节机制改善城市热环境的方法,目的在于减弱广州的城市热岛效应。广州地区利用被动蒸发冷却技术可获得建筑屋面的最大差为１０℃,平均温差为５℃。分析认为,广州地区因为具有完整的气候要素,具备依靠被动蒸发冷却技术实现城市非绿地地表面被动降温的自然条件。文中还提出了广州城市资源应用研究方向的５项  相似文献   

基于FY-3B/VIRR数据的济南市城市热岛效应与影响因素分析          下载免费PDF全文

王晗  李峰  王吴  秦泉  赵彤 《山东气象》2021,41(2):126-137

热岛效应是城市发展过程中的热点社会问题之一。研究以济南为例,基于 FY－3B/VIRR数 据,应用改进型 Becker和 Li “分裂窗” 算法获得遥感地表温度数据;采用热岛强度指数与热岛比例指数,定量分析济南市2013—2020年城市热岛效应的时空变化特征;从自然与社会经济角度,采用灰色关联度分析法,定量评价城市热环境的影响因素对城市热岛效应变化的贡献度。结果表明：1）改进型 Becker和 Li “分裂窗” 算法在济南市有较好应用,与国家级地面气象观测站 “0 cm地表温度” 实测数据线性拟合决定系数 R2 为 0.89。2）热岛区域面积年际变化呈现先增加后减小逐渐平稳的变化趋势,冷岛区域变化特征与热岛区域明显相反。3）夏季热岛区域面积（35.3%）最大,秋季（22.5%）次之,春（11.5%）、冬（10.6%）两季基本持平。4）热岛空间格局以城镇聚合轴为主导驱动,呈现 “点－线” 式空间结构特点。5）热岛比例指数总体呈现下降趋势,2013 年（0.22）与 2014 年（0.24）属较轻热岛年份。6）总人口数与归一化植被指数是影响济南城市热岛效应的主要因素。研究对于加强济南市地表热环境的监测与评价,指导城市规划与生态城市建设具有一定意义。  相似文献   

Development of a Multi-Layer Urban Canopy Model for the Analysis of Energy Consumption in a Big City: Structure of the Urban Canopy Model and its Basic Performance   总被引：4，自引：0，他引：4  

Hiroaki?KondoEmail author  Yutaka?Genchi  Yukihiro?Kikegawa  Yukitaka?Ohashi  Hiroshi?Yoshikado  Hiroshi?Komiyama 《Boundary-Layer Meteorology》2005,116(3):395-421

A multilayer one-dimensional canopy model was developed to analyze the relationship between urban warming and the increase in energy consumption in a big city. The canopy model, which consists of one-dimensional diffusion equations with a drag force, has three major parameters: building width, distance between buildings, and vertical floor density distribution, which is the distribution of a ratio of the number of the buildings that are taller than some level to all the buildings in the area under consideration. In addition, a simplified radiative process in the canopy is introduced. Both the drag force of the buildings and the radiative process depend on the floor density distribution. The thermal characteristics of an urban canopy including the effects of anthropogenic heat are very complicated. Therefore, the focus of this research is mainly on the basic performance of an urban canopy without anthropogenic heat. First, the basic thermal characteristics of the urban canopy alone were investigated. The canopy model was then connected with a three-dimensional mesoscale meteorological model, and on-line calculations were performed for 10 and 11 August, 2002 in Tokyo, Japan. The temperature near the ground surface at the bottom of the canopy was considerably improved by the calculation with the canopy model. However, a small difference remained between the calculation and the observation for minimum temperature. Deceleration of the wind was well reproduced for the velocity at the top of the building by the calculation with the canopy model, in which the floor density distribution was considered.  相似文献   

Morphological and structural analysis in the Anaga offshore massif, Canary Islands: fractures and debris avalanches relationships     

P. Llanes  A. Muñoz  A. Muñoz-Martín  J. Acosta  P. Herranz  A. Carbó  C. Palomo 《Marine Geophysical Researches》2003,24(1-2):91-112

As part of the ‘National Hydrographic and Oceanographic Research Plan for the Spanish Exclusive Economic Zone’, multibeam bathymetry and seismic reflection profiles were obtained in the Canary Islands aboard the R/V Hespérides. The submarine flanks of the Anaga offshore extension of Tenerife Island are here studied to analyze its geomorphology. In the north sector of the Anaga submarine massif, the extension of the Anaga Debris Avalanche has been mapped for the first time, and a volume of 36 km³ was calculated. The relationship between the Anaga and Orotava Debris Avalanches is also described. Faulting has been recognized as a key process for the occurrence of debris avalanches and the growth of volcanic lineaments. Moreover, faulting affects previous structures and the channelling of debris flows. Structural analysis shows the typical radial pattern of an oceanic island. In addition, a NE-SW dominant direction of faulting was obtained, consistent with the Tenerife Island structural trend seen in the Anaga Massif and Cordillera Dorsal. NW-SE and E-W are two other main trends seen in the area. Special interest is manifest in two long faults: ‘Santa Cruz Fault’ bounds the southern edge of Anaga offshore Massif with a length of 50 km and a direction that changes from NE-SW to almost E-W. The Güimar Debris Avalanche was probably channeled by this fault. The ‘Guayotá Fault’ was recognized in several seismic profiles with a N-S direction that changes towards NW-SE at its southern end. This fault affects the more recent sediments with a vertical offset of 25–30 m, along 60~km. It has been interpreted as a transpressive strike-slip fault.ZEE Working Group**F. Carrillo^a, C. Maté^a, M. Ballesteros^b, M. Vaquero^b, J. Martín-Dávilla^c and J.A. Marín^caInstituto Hidrográfico de la Marina. Cádiz^bInstituto Español de Oceanografía. Madrid.^cReal Observatorio de la Armada. S. Fernando, Cádiz.  相似文献   

近44年来滦河口障壁岛演变过程及其影响因素研究——以唐山市龙岛为例     

程林  田海兰  刘西汉  王艳霞 《海洋科学》2020,44(6):22-30

为掌握滦河口障壁岛的演变特征、为海岛保护与适度利用提供数据支撑，以唐山市龙岛为例，基于RS及GIS技术，分析了近44年来障壁岛的演变特征，并探讨了影响海岛演变的主要因素。分析显示，近44年来海岛面积和长度分别呈减少和增加的趋势，海岛质心位置向西南偏西方向迁移，海岛外海一侧岸线不断后退，平均后退速率达7.37 m/a，其中1978—1984年、1996—2003年、2008—2013年及2018—2019年海岛侵蚀后退明显。研究认为，由于滦河口的自然迁移，河流输沙减少，受沿岸输沙特征影响，海岛主体部分侵蚀而两端沙嘴处堆积，海岛自然状态下已出现5~6 m/a的侵蚀。航道整治挖岛及景区建设挖岛导致近年来海岸典型断面平均后退速率达到研究期内最大值14.27 m/a，海岛长度也出现明显减少，是影响海岛演变的首要因素。滦河流域大型水库的修建使滦河输沙急剧减少，海岛岸线侵蚀加剧、海岛面积明显减少，是研究时段内影响海岛演变的次要原因。风暴潮是影响海岛演变的主要的突发性因素，尤其是2018年内短期内密集过境的台风，造成海岛岸线典型断面平均后退达10.25 m。当前，海岛的保护与适度利用要遵循海岛演变特征，严格禁止不必要的挖岛采砂，并采取海滩修复、构筑透水潜堤等工程措施对重点功能区海岸线加以防护。  相似文献   

Diagnoses of vertical transport in a three-dimensional finite element model of the tidal circulation around an island     

Laurent White  Eric Deleersnijder   《Estuarine, Coastal and Shelf Science》2007,74(4):655

A three-dimensional finite element model is used to investigate the formation of shallow-water eddies in the wake of Rattray Island (Great Barrier Reef, Australia). Field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides. The water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments up to the sea surface. We first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport. The water age is defined as the time elapsed since particles of water left the sea bottom, where the age is prescribed to be zero. Two versions of this diagnosis are considered. Although the model predicts upwelling within the eddies, it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies. As mesh resolution increases, this upwelling does not intensify. However, strong upwelling is then resolved off the island's tips, which is confirmed by the results obtained with the age. This study also shows that the finite element method, together with unstructured meshes, performs well for representing three-dimensional flow past an island.  相似文献