大别山双河超高压变质矿物O同位素平衡及其对Sm-Nd和Rb-Sr等时线年龄有效性的制约     

赵子福郑永飞  李曙光龚冰 《岩石学报》2005,21(4):1243-1254

对于变质岩 Sm-Nd 和 Rh-Sr 同位素年代学来说,其中一个重要问题是等时线矿物之间在一特定的变质事件过程中是否达到并在随后保持同位素平衡。矿物 O 同位素地质测温也是如此。由于许多情况下 Nd、Sr 和 O 在变质矿物中的扩散速率具有可比性,变质矿物之间 O 同位素平衡状况能够为矿物 Sm-Nd 和 Rb-Sr 内部等时线定年结果的有效性提供制约。为了验证其适用性,本文对大别造山带双河超高压榴辉岩和片麻岩 Sm-Nd 和 Rh-Sr 等时线矿物进行了 O 同位素地质测温。尽管Sm-Nd 等时线给出一致的三叠纪年龄(213～238Ma),同一样品 Rb-Sr 等时线却给出侏罗纪年龄(171～174Ma)。片麻岩、榴辉岩和榴闪岩矿物对 O 同位素测温得到600～720℃和420～550℃两组温度,分别对应于约225±5Ma 榴辉岩相变质和约 175±5Ma 角闪岩相退变质条件下停止同位素扩散交换的温度。同一样品三叠纪 Sm-Nd 等时线年龄的保存、侏罗纪 Rh-Sr 等时线年龄的出现以及有规律的 O 同位素温度,表明在角闪岩相退变质过程中,Sr 和 O 在含水矿物(如黑云母和角闪石)中的扩散速率在手标本尺度上比石榴石 Nd 和多硅白云母 Sr 的扩散速率快。在退变质作用过程中,等时线矿物之间的初始同位素比值均一化速率主要受扩散速率慢的矿物控制,而矿物等时线时钟的启动主要受具有高母/子体比值的矿物控制。只有当高母/子体比值矿物具有快的放射成因同位素扩散速率时,才能够应用合理的矿物等时线确定变质再造的时间。  相似文献   

温度变化对夏季降温耗能的影响   总被引：12，自引：1，他引：12       下载免费PDF全文

陈峪  叶殿秀 《应用气象学报》2005,16(Z1):97-104

该文采用降温度日数作为评估夏季降温耗能的指标 ,分析了我国夏季降温度日分布和长期变化特征。温度与降温耗能相关分析表明 ,两者相关密切 ,相关程度随气温升高而增加 ;降温耗能的 1℃效应量 ,北方大于南方。文章最后 ,利用气温距平与降温度日变率建立了夏季降温耗能评估模型。  相似文献   

中国化肥利用率的区域分异   总被引：77，自引：2，他引：77  

陈同斌  曾希柏  胡清秀 《地理学报》2002,57(5):531-538

据全国各县近10年的化肥施用量和粮食产量数据，并从不同年份单位播种面积粮食产量和肥料施用量的变化，求出相应不施肥产量和通过施肥可能达到的最高产量，并以上述结果为基础计算出该地区化肥利用率，研究结果表明：当前我国化肥施用的地区差异明显，施用量较集中范围是180－270kg/hm^2和90－180kg/hm^2，部分地区的化肥施用已经过量；单位化肥的粮食产出率主要集中在10－30kg/kg，化肥利用率大多集中在15％－35％，且与化肥施用量有关，按地区统计，高施肥量区化肥施用明显过量，平均达339kg/hm^2，是全国平均用量（262kg/hm^2)的1．29倍，中施肥量区单位面积化肥平均施用量为252kg/hm^2，略低于全国平均水平，低施肥量区则仅为178kg/hm^2，是全国平均的67．8％，我国单位化肥的生产效率及化肥利用率均以低施肥量区最高，分别为17．5kg/kg和39．8％，中施肥量区为13．7和36。  相似文献   

改进的灰色模型在中国能源消费及其CO2排放预测中的研究   总被引：5，自引：1，他引：5  

穆海林  董旭辉  王伟  SAKAMOTO K  TONOOKA Y  周伟生  宁亚东 《中国沙漠》2002,22(2):141-149

中国高速的经济发展导致了快速的能源消费和地球温暖化气体的排放量。本文应用灰色理论建立了中国的终端能源消费量的动态预测模型，同时应用等维递补及带有马尔科夫链符号估计的残差修正，对原始模型进行了改进。后验检验的结果证明了改进的预测模型具有较高的计算精度。预测结果表明，两种经济发展情况（高速及低速）下，从2000年到2030年期间的终端能源消费量的平均增长率将分别达到3．06％和2．18％，2030年CO2 的排放量将分别达到2000年的 2． 15及 1．60倍。其中工业及居民生活的能源消费量的增加速度快于其他部门。这表明了中国将要加快其工业化及都市化的进程．终端消费中，煤炭的消费量所占的比例将要逐年减少，而电力的比例则将逐年增大。  相似文献   

污水渗滤土地处理系统中的复氧方式及效果   总被引：24，自引：0，他引：24  

何江涛  张达政  陈鸿汉  汤鸣皋 《水文地质工程地质》2003,30(1):103-106,109

复氧是困扰人工快渗、构造湿地等污水渗滤土地处理系统已久的问题。国际上目前采用的方法主要有3种：一是采用干湿交替的工作方式进行系统复氧，一是设置通气管对系统内部进行复氧，再一是利用植物的根系对系统内部进行复氧。研究结果表明，干湿交替的工作方式对系统的复氧条件有明显改善，而小水力负荷周期的工作方式对系统的复氧更为有效。通气管的设置通常与间歇性布水工作方式相结合，其效果通常要明显好于单纯采用干湿交替的工作方式。植物根系对系统的复氧，常因植物不同类型面具有不同的氧传输能力，植物根茎所能到达的范围往往决定了系统有效处理部位的大小。  相似文献   

Enhanced red fluorescence emission in the oxygen minimum zone of the Arabian Sea     

Wiebke Breves  Rüdiger Heuermann  Rainer Reuter 《Ocean Dynamics》2003,53(2):86-97

 Depth profiles of fluorescence at several excitation and emission wavelengths were measured along with CTD data during the cruise So119 of RV Sonne in the Arabian Sea from 12 May to 10 June 1997. In addition to chlorophyll fluorescence from phytoplankton in the near-surface layer, the profiles in the oxygen minimum region well below the euphotic zone show enhanced red fluorescence. Red fluorescence intensity is inversely related to the oxygen concentration in intermediate and deep waters. A relationship to characteristic water masses of the region cannot be found in the data, and this holds also with chemical data such as DOC. Absorbance spectra of water samples taken in the oxygen minimum zone show an absorption band at 420 nm wavelength with about 50 nm bandwidth, much weaker than gelbstoff absorbance in the same wavelength range. The absorption band remains stable after sample filtration with 0.45 μm glass fibre filters. Hence, the size of the absorbing matter is in the range of dissolved molecules or particles much smaller than 1 μm. Fluorescence spectra of unfiltered samples with 420 nm excitation show a weak emission band at 600 nm and a more pronounced one at 660 nm wavelength. The trailing edge of the 660 nm band falls into the range of chlorophyll emission, thus giving rise to the observed depth profiles of red fluorescence in the oxygen minimum zone. Red fluorescence measured on samples remain stable during a few hours after sampling even in the presence of oxygen. It is not detectable after several weeks of sample storage in the dark and cannot be reproduced even after depletion of dissolved oxygen. Received: 22 May 2002 / Accepted: 18 February 2003 Responsible Editor: Andreas Oschlies Acknowledgements. This work was supported by a grant from the Federal Minister of Education and Technology, Bonn, within the frame work of the JGOFS Arabian Sea program. We are grateful to the captain and the crew of RV Sonne for their support. We are indebted to Mrs. Kirsten Neumann from the Institute of Marine Chemistry and Biogeochemistry of the University of Hamburg for providing the oxygen data, and to Mr. Nikolai Delling from the same institute for making the DOC and chlorophyll data available to us.  相似文献   

西北四省(区)2000年的水资源足迹   总被引：78，自引：4，他引：78  

龙爱华  徐中民  张志强 《冰川冻土》2003,25(6):692-700

水资源足迹是如实反映人类对水资源消费利用的新概念,能深刻揭示社会经济系统对水资源的消费,为干旱缺水地区水资源科学管理提供了一个新视角.提出了水资源足迹的概念和衡量方法,引进了虚拟水概念,简要介绍了产品虚拟水计算方法,并以新疆、青海、甘肃和陕西为例,计算分析了2000年各省水资源足迹.结果表明,2000年西北四省(区)总的水足迹是为613.3×108m3,人均水足迹为712.3m3·人-1·a-1和1952L·人-1·d-1,高于统计的水资源利用量.以虚拟水概念为基础的水资源足迹更真实地衡量了社会经济系统对水资源的消费利用状况,为解决区域水资源短缺和创新水资源管理体制提供了新思路,产品形式的虚拟水贸易是平衡水资源赤字、维持区域水安全的有效工具.  相似文献   

Food-web manipulation of drinking water reservoirs with salmonids: vertical distribution of prey and predator     

Robert J. Radke  Uwe KahlJürgen Benndorf 《Limnologica》2003,33(2):92-98

In a novel biomanipulation experiment salmonids were used as a tool to improve water quality. The manipulation was initiated in spring 2000 as a response to non-point sources of phosphorus in a drinking water reservoir in Saxony, Germany. Salmonids (brown trout, Salmo trutta forma lacustris) were chosen as predators as the reservoir has a large hypolimnic water body and surface temperatures rarely exceed 20 °C. The vertical distributions of prey fish and brown trout were analysed with a fleet of vertical gill nets set in the pelagic zone of the reservoir. Consumption of brown trout was estimated by means of a bioenergetic model and the diet analyses of the trout. While the dominant planktivore (roach, Rutilus rutilus) was caught almost exclusively in the epilimnion during the stratification period trout were caught mainly below a depth of 10 m. Diet analysis revealed that the trout performed vertical migrations to consume food in the epilimnic layer, as an important food component were adult terrestrial and aquatic insects. The amount of fish in the food increased strongly with the size of the brown trout. The consumption estimate suggested that the trout had consumed 2-3% of the total roach stock during the study period (May-November 2000) of the first year of biomanipulation. We conclude that in general salmonids are suitable for food-web manipulation in deep reservoirs, but the stocked fish should be as large as possible (> 300 mm) and the proportion of large trout (> 500 mm) should be as high as possible.  相似文献   

Oxygen isotope composition and geothermometry of granulite to greenschist facies metamorphic rocks: a study from the Neoproterozoic collision-related nappe system, south of São Francisco Craton, SE Brazil     

Maria da Glria M. Garcia  Mrio C. Campos Neto  Anthony E. Fallick 《Journal of South American Earth Sciences》2003,15(8):871-883

Oxygen isotope studies were carried out across units of a Neoproterozoic nappe system, south of São Francisco Craton. A temperature decrease toward the base of the system is found, consistent with a previously recognized inverted metamorphic pattern. The tectonic contact of the basal unit and the reworked southern São Francisco craton show a steep temperature gradient, suggesting that low temperature thrusting acted as the dominant tectonic process. The contrasts between the δ¹⁸O values of the Três Pontas-Varginha and Carmo da Cachoeira nappes and the differences among the samples and minerals are consistent with the preservation of sedimentary isotopic composition during metamorphism. The small differences in the δ¹⁸O values between the undeformed and the deformed calc-silicate samples (1.6‰) suggest that the δ¹⁸O value of mylonitization fluids was close to that which equilibrated with the metamorphic assemblage. The distinct δ¹⁸O values of metapelitic and calc-silicate samples and the great temperature difference from one type to the other indicate that no large-scale fluid interaction processes occurred during metamorphism. Oxygen isotopic estimations of both Três Pontas-Varginha undeformed rocks and Carmo da Cachoeira unaltered equivalents indicate δ¹⁸O values of up to 18‰. Comparison between these values and those from the ‘basement’ orthogneisses (8.3–8.5‰) indicates the latter are not sources for the metapelites.  相似文献   

A biogenic-silica δO record of climatic change during the last glacial–interglacial transition in southwestern Alaska     

Feng Sheng Hu  Aldo Shemesh 《Quaternary Research》2003,59(3):379-385

Despite growing evidence for environmental oscillations during the last glacial–interglacial transition from high latitude, terrestrial sites of the North Pacific rim, oxygen-isotopic records of these oscillations remain sparse. The lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen-isotopic analysis. We report here the first record of oxygen-isotopic composition in diatom silica (δ¹⁸O_Si) from a lake in that region. δ¹⁸O_Si increases gradually from 19.0 to 23.5‰ between 12,340 and 11,000 ¹⁴C yr B.P., reflecting marked climatic warming at the end of the last glaciation. Around 11,000 ¹⁴C yr B.P., δ¹⁸O_Si decreases by 1.7‰, suggesting a temperature decrease of 3.5–8.9 °C at the onset of the Younger Dryas (YD) in southwestern Alaska. Climatic recovery began ca. 10,740 ¹⁴C yr B.P., as inferred from the increase of δ¹⁸O_Si to a maximum of 23.9‰ near the end of the YD. Our data reveal that a YD climatic reversal in southwestern coastal areas of Alaska occurred, but the YD climate did not return to full-glacial conditions.  相似文献