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71.
分析了西北水资源的特点,就生态环境用水、生态环境治理以及植树造林与沙漠治理等西部开发中的突出问题提出了一些认识。指出:西北开发必须以水为度,充分考虑区域水资源的承载能力;保护和改善西北地区生态环境的基本途径是偿还已被人类逐步夺占而本该属于自然生态系统的那一部分水源。 相似文献
72.
Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments 总被引:8,自引:7,他引:8
This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and 206Pb/207Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the 206Pb/207Pb ratio in unpolluted background sediments in Sweden was > 1.3, while that of lead from pollution, derived from ores and coal, was < 1.2. The sediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period. The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain. 相似文献
73.
74.
高峰100号矿体硫、铅同位素特征 总被引:1,自引:0,他引:1
李蘅 《矿物岩石地球化学通报》2001,20(4):334-336
10 0号矿体的成矿物理化学环境为 :成矿温度 30 0± 30℃ ;成矿压力为 84.2× 10 5Pa ;LogfO2 =- 30 .4~- 35 .6 ,LogfCO2 =- 2 .5 5~ +0 .36 ,LogfS2 =- 8.3~ - 11.0 ,pH =4.2~ 4.9。同位素的分析结果 :硫化物的硫同位素为 6 4‰~ 12 .3‰ ,δ3 4 SΣS 值为 6 6~ 13 8;2 0 6Pb 2 0 4Pb值为 17 4 91~ 18 96 0 ,2 0 7Pb 2 0 4Pb值为 15 5 39~15 940 ,2 0 8Pb 2 0 4Pb值为 37 95 7~ 39 4 90。表明 10 0号矿体的硫源是混合硫 ,铅源是两种异常铅混合的结果。 相似文献
75.
76.
Concentrations of Pb, Cd, Cu and Zn have been measured using improved ultraclean procedures in a succession of twenty six snow samples integrating a 40 yr time sequence from 1940 to 1980 which were collected from the walls of a 6 m deep pit at stake D 55 in Adelie Land, East Antarctica. Measured concentrations, which are among the lowest ones ever measured in Antarctic snows, are found not to have significantly increased during the investigated time period, with the possible exception of Pb for which there might have been a significant increase after the mid 1960's. For this last metal, measured concentrations in the 1940's are about 6-fold higher than in Antarctic Holocene ice several thousand years old, which indicates that a large fraction of the anthropogenic increase for Pb probably occurred before the 1940's. 相似文献
77.
山门银矿铅同位素地质特征及地质意义 总被引:2,自引:0,他引:2
山门银矿铅同位素地质特征的研究结果表明,矿石铅为年轻、稳定的正常铅,成矿时代为燕山晚期;黄莺屯组地层及岩浆岩系列岩石铅为弱异常铅。从铅同位素组成及源区特征值看,矿石铅与岩浆岩岩石铅为同源的壳幔混合铅,表明成矿物质来自深源,并与燕山期岩浆活动密切相关。铅构造模式应属太平洋西岸岛弧铅。 相似文献
78.
大降坪黄铁矿床是产于云开隆起中段偏北震旦系海相碎屑岩-细碎屑岩中的层状硫化物矿床,矿床成因和海底喷气热水沉积作用有关,局部经受了后期热液的叠加改造。黄铁矿的δ~(34)S值在-25.55‰—+21.07‰之间,与矿石及黄铁矿中的有机碳含量呈反比。从条带状细粒黄铁矿到块状粗粒黄铁矿,亦即从南到北,硫同位素组成从富轻硫变为富重硫。条带状矿石的铅同位素组成与矿体围岩一致,为富放射成因上地壳源铅,块状矿石铅同位素组成较均一,三组铅同位素比值较条带状矿石略低,为原始沉积的矿石铅与热液带来基底混合岩铅的混合铅。 相似文献
79.
秦岭勉略带中鞍子山蛇绿杂岩的地球化学:——古洋壳碎片的证据及意义 总被引:15,自引:3,他引:12
鞍子山蛇绿杂岩位于秦岭勉略带东段,它由蛇纹石化变质橄榄岩和MORB型变质镁铁质岩组成。蛇纹石化变质橄榄岩主要是方辉橄榄岩和少量二辉橄榄岩,表了古洋幔的上部岩石;变质镁铁质岩为斜长角闪岩,其原岩是基性火成岩类,它多以亏损LREE元素和具有很高的^143Nd/^144Nd值为特征,类似于现代洋壳中的洋中脊玄武岩(MORB),代表了古洋壳的残余部分。这表明鞍子山晕绿杂岩是勉略混杂岩带中又一个典型的蛇绿岩 相似文献
80.