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991.
http://www.sciencedirect.com/science/article/pii/S1674987111001083   总被引:2,自引:1,他引:2  
Stable carbon isotope geochemistry provides important information for the recognition of fundamental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elaboration of models for the global carbon cycle.Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon(organic matter,mantle,or carbonates) and help to constrain the fluid history and the mechanisms involved in graphite deposition.Graphite precipitation in fluid-deposited occurrences results from CO2- and/or CH4-bearing aqueous fluids.Fluid flow can be considered as both a closed(without replenishment of the fluid) or an open system(with renewal of the fluid by successive fluid batches).In closed systems,carbon isotope systematics in graphite is mainly governed by Rayleigh precipitation and/or by changes in temperature affecting the fractionation factor between fluid and graphite.Such processes result in zoned graphite crystals or in successive graphite generations showing,in both cases, isotopic variation towards progressive l3C or 12C enrichment(depending upon the dominant carbon phase in the fluid.CO2 or CH4,respectively).In open systems,in which carbon is episodically introduced along the fracture systems,the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of 5’ C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.  相似文献   
992.
A number of geological studies have already been conducted on the Zambales Ophiolite Complex (ZOC), a north-south trending complete ophiolite sequence exposed in the western portion of Central Luzon, Philippines. Previous works recognized the ZOC as being made up of two blocks, the Acoje and the Coto, acting as an arc-back arc pair sometime during the Eocene.  相似文献   
993.
There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan-Maowen, Beichuan-Yingxiu and Pengxian-Guanxian faults, terrace offsets, scarps, fault-controlled saddles, dextral shutter ridges, dextral channel offsets, graben, shatter belts, and pull-apart basins. Electron spin resonance (ESR) and thermoluminescence(TL) ages were obtained using silty sand taken from below the surface of the sediments. According to these data, we calculated the rates of thrusting and strike-slip, and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike-slipping less than 1.46 mm/a. The Longmen Shan is a zone of NNE-trending dextral shear with slip-dip ratio of 6:1-1.3:1. From NW to SE, the thrust component becomes smaller, whereas the strike-slip component becomes larger.  相似文献   
994.
稀有气体是地球流体源区信息的有效示踪剂.利用热熔融法对山东地区幔源巨晶、包体全岩及其单矿物以及寄主玄武岩等幔源样品中稀有气体的测试表明,不同类型样品具有明显不同的稀有气体同位素组成,特别是He同位素比值差异明显.巨晶和包体单矿物中的n(3He)/ n(4He)值分别为0.87~11.31Ra、0.911 ~10.11Ra,均值分别为6.1Ra和3.73Ra,主体介于地幔一大气一地壳源区之间;包体全岩中n(3He)/ n(4He)值0.19 ~ 2.30Ra(均值为1.05 Ra),且均低于相应单矿物中该比值;而玄武岩中n(3He)/ n(4He)值全为10-8数量级,与地壳均值无异.各类幔源样品中n(4Ar)/n(36 Ar)值无明显差异,介于296.4~864.3,高于大气但远低于典型地幔值.所获有限数据中,不同类型样品中n(2Ne)/n(2Ne)值均高于大气,具幔源特征,其中包体全岩及其单矿物n(2Ne)/n(22Ne)值分别为10.19 ~12.42和10.55~11.80,无明显差异;玄武岩中该值介于11.07~13.10,总体高于包体全岩及其单矿物.上述比值特征的差异反映了不同类型幔源样品各自不同的成因和演化特征:巨晶和包体单矿物中的轻稀有气体同位素组成主要反映了由于古板块俯冲所导致的岩浆源区地幔一大气/地壳的昆合特征,个别样品中可能存在宇宙成因3He;除单矿物中所体现的源区混合特征外,包体全岩还存在放射成因4He;而玄武岩在喷出地表后丢失大量地幔稀有气体信息,其同位素组成主要体现了放射成因4He的影响.  相似文献   
995.
卫星雷达联合重构大尺度流域降水场   总被引:6,自引:8,他引:6  
给出了一种用GMS-5卫星估计3h降水的方法,并利用地面测雨雷达和卡尔曼滤波器提取误差因子,用于在雷达探测范围以外校准卫星估计的降水,从而获得大尺度流域的(淮河流域)降水分布。在史灌河子流域的比较试验表明:卫星雷达联合重构的降水场具有比卫星估计降水更高的精度,3h降水估计的相对误差从31%下降到13%,和地面降水场的相关系数也有明显提高。  相似文献   
996.
以新疆第一次(2000年)和第二次(2011年)湿地资源调查中相同的347块湿地为研究对象,利用3S技术,对CBERS、SPOT5和LandsatTM遥感数据进行调查监测,并结合野外实地验证,比较分析新疆湿地资源的时空变化状况及其原因。结果表明,新疆湿地总面积呈减少的趋势,其中河流湿地和沼泽湿地面积增加,分别增加29162 hm2和17130 hm2,湖泊湿地和人工湿地面积减少,分别减少126618 hm2和19391 hm2;各湿地型中,永久性河流、草本沼泽、森林沼泽和季节性咸水沼泽面积有所增加,洪泛平原、内陆盐沼、永久性 淡水湖、季节性淡水湖、季节性咸水湖和库塘湿地面积减少。新疆湿地面积总变化率-7%,各湿地类型中,面积变化率最大的是湖泊湿地(18%),呈减少趋势;最小的是沼泽湿地(5%),呈增加趋势。湿地面积变化的主要原因是气候变化和人类活动。  相似文献   
997.
<正>While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-t...  相似文献   
998.
一、引言研究自动观测系统的算法要从“在观测中我们希望得到什么?”来开始。很明显,联邦气象手册第一部分(FMH~#1)的地面航空观测指南是立足于人工观测员的能力和局限性。虽然人工观测员是“万能”的,但他们受所选定的观测场地的限制(气象台地点不总是天气现象发生的地点)。而且对状况变化的反应能力由于其它任务及人体固有的缺陷(例如:夜间的视觉适应)而受到限制。美国天气局于1946年沿着佛罗里达Keys建立起三个自动气象站,用以探测逼近台站的飓风,从而迈出了自动观测的第一步。Stone详细描述了国家天气局(NWS)对观测的客观部分实行自动化所作的努力。其中包  相似文献   
999.
International trade in fishery commodities reached US 58.2 billion dollars in 2002, a 5% improvement relative to 2000 and a 45% increase over 1992 levels. Within this global trade, developing countries registered a net trade surplus of US 17.4 billion dollars in 2002 and accounted for almost 50% by value and 55% of fish exports by volume. This globalization of fish trade, coupled with technological developments in food production, handling, processing and distribution, and the increasing awareness and demand of consumers for safe and high quality food have put food safety and quality assurance high in public awareness and a priority for many governments. Consequently, many countries have tightened food safety controls, imposing additional costs and requirements on imports. As early as 1980, there was an international drive towards adopting preventative HACCP-based safety and quality systems. More recently, there has been a growing awareness of the importance of an integrated, multidisciplinary approach to food safety and quality throughout the entire food chain. Implementation of this approach requires an enabling policy and regulatory environment at national and international levels with clearly defined rules and standards, establishment of appropriate food control systems and programmes at national and local levels, and provision of appropriate training and capacity building. This paper discusses the international framework for fish safety and quality, with particular emphasis on the United Nation's Food and Agricultural Organization's (FAO) strategy to promote international harmonization and capacity building.  相似文献   
1000.
Radiocarbon levels were recorded in Fucus vesiculosus samples collected on a monthly basis over a three-year period at a site on the east coast of Ireland. The resulting data was analysed using a numerical model which estimates the transit times from the Sellafield plant to the sampling location, and the mean availability time of 14C in seaweed. With the inclusion of a model parameter allowing for seasonal variability in uptake by the Fucus, good correlation was observed between the predicted and measured concentrations. Future temporal trends of 14C Fucus concentrations along the eastern Irish coastline were modelled with the application of three possible prospective discharge scenarios, predicting 14C Fucus concentrations to reduce to ambient background levels within 2.5-years of discharges being set to zero. Such projections may prove helpful in assessing the consequences of discharge management and policy making in the context of the OSPAR convention.  相似文献   
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