青海某地第三纪红色碎屑岩层中发现金矿物   总被引：1，自引：0，他引：1  

马生明  王俊祥 《黄金地质》1998,4(2):58-61

第三纪红色碎屑岩层在青海分布广泛。长期以来,由于它特征的地理地质条件,在这一层位中寻找金属矿床的工作不受重视,至今未见在该层位中发现金属矿（化）的文献报导。但在一些地区的第三纪红色碎屑岩层中有化探金异常。在某地Ａｕ异常浓集区所进行的化探查证工作初步揭示了Ａｕ异常的形成是由于次生富集作用引起的,并在水系重砂样品中首次发现金矿物颗粒,从而为地质工作者重新认识这个金属矿的“不毛之地”提供了确凿证据。  相似文献   

历史时期关中地区气候变化的初步研究   总被引：79，自引：6，他引：73       下载免费PDF全文

朱士光  王元林  呼林贵 《第四纪研究》1998,18(1):1-11

关中地区地理位置特殊,是中华民族的一个重要发祥地,历史时期气候曾发生多次明显的变化。通过对这一地区考古发掘、抱粉分析研究成果以及丰富的史籍文献、地方志等资料的收集、整理、分析,划分出全新世早期寒冷、全新世中期暖湿、西周冷干、春秋至西汉前期暖润、西汉后期至北朝凉干、隋和唐前中期暖润、唐后期至北宋凉干、金前期温干、金后期和元凉干、明清冷干等10个气候变化阶段,从而建立起该地区历史时期完整的气候变化序列。  相似文献   

火山活动与构造气候旋回   总被引：5，自引：2，他引：3       下载免费PDF全文

刘嘉麒  郭正府 《第四纪研究》1998,18(3):222-228

火山活动是一种重要的地质现象,它的发生总是与构造运动相关联,构造运动有强有弱,持续时间有长有短,具有旋目性,火山活动同样也具有旋回性。大规模的火山喷发往往会对气候变化产生影响,而影响的程度取决于火山所处的位置和喷发的性质及程度。强烈的火山喷发将造成局部地区乃至全球气温下降,由此人们推测火山喷发多发生在冰期,然而统计资料表明,绝大多数火山喷发发生在间冰期,此时的构造运动也比较活跃,而在冰期时很少有火山喷发。至于火山喷发后在短时间内造成的降温与长时间的冰期不能相提并论。火山活动有旋回性,它影响的气候变化也具备有旋回性,这是构造气候旋回的一种表现形式。  相似文献   

川西石棉地区田湾与扁路岗岩体的锆石U-Pb定年   总被引：7，自引：0，他引：7  

郭建强  游再平    杨军  沈渭洲  徐士进  王汝成 《矿物岩石》1998,(1)

对扬子板块西缘石棉地区田湾闪长岩体与扁路岗花岗岩体开展了精细的单颗粒锆石Ｕ－Ｐｂ年代学研究。测试结果表明,田湾岩体中锆石的结晶年龄为８２３Ｍａ±１２Ｍａ,扁路岗岩体中锆石的结晶年龄为８７６Ｍａ±４０Ｍａ,表明石棉地区与扬子板块西缘其他地区一样,晋宁期岩浆活动也是相当强烈的。  相似文献   

准四年周期的北半球夏季遥相关与东亚夏季风环流的相互关系   总被引：3，自引：3，他引：0  

谭言科  何金海 《南京气象学院学报》1998,21(1):70-79

利用ＮＭＣ的２００ｈＰａ和８５０ｈＰａ风场资料研究了北半球夏季遥相关和东亚夏季风异常环流在准４年时间尺度上的相互关系。研究发现当北半球夏季出现积雪强迫型遥相关时,东亚－西太平洋地区既存在异常纬向环流,也存在异常经向环流;而当出现东亚太平洋型遥相关时,东亚－西太平洋地区以异常纬向环流为主。分析还发现源于北太平洋的异常涡旋在向南传播的过程中,先取西南路径,在到达菲律宾东部以后折向东南。  相似文献   

对流层高层偏北气流在梅雨暴雨中的作用   总被引：11，自引：0，他引：11  

翟国庆 《气象学报》1998,56(1):68-76

文中对江淮梅雨暴雨过程中的高低空流场特征及物理过程进行分析．结果表明：对流层上部青藏高原东侧常有高空偏北大风轴汇入南亚东风急流中．在这支强北风轴北端发现高空辐散和辐散的增长．亦即有利于低层辐合上升的持续、发展和加强;表明了低层西南急流与高空青藏高压东侧的偏北强风轴之间的次级环流圈,有利于梅雨暴雨的持续．  相似文献   

Flood frequency analysis of Turkey using L‐moments method     

Neslihan Seckin  Tefaruk Haktanir  Recep Yurtal 《水文研究》2011,25(22):3499-3505

The index flood procedure coupled with the L‐moments method is applied to the annual flood peaks data taken at all stream‐gauging stations in Turkey having at least 15‐year‐long records. First, screening of the data is done based on the discordancy measure (D_i) in terms of the L‐moments. Homogeneity of the total geographical area of Turkey is tested using the L‐moments based heterogeneity measure, H, computed on 500 simulations generated using the four parameter Kappa distribution. The L‐moments analysis of the recorded annual flood peaks data at 543 gauged sites indicates that Turkey as a whole is hydrologically heterogeneous, and 45 of 543 gauged sites are discordant which are discarded from further analyses. The catchment areas of these 543 sites vary from 9·9 to 75121 km² and their mean annual peak floods vary from 1·72 to 3739·5 m³ s^?1. The probability distributions used in the analyses, whose parameters are computed by the L‐moments method are the general extreme values (GEV), generalized logistic (GLO), generalized normal (GNO), Pearson type III (PE3), generalized Pareto (GPA), and five‐parameter Wakeby (WAK). Based on the L‐moment ratio diagrams and the |Z_dist|‐statistic criteria, the GEV distribution is identified as the robust distribution for the study area (498 gauged sites). Hence, for estimation of flood magnitudes of various return periods in Turkey, a regional flood frequency relationship is developed using the GEV distribution. Next, the quantiles computed at all of 543 gauged sites by the GEV and the Wakeby distributions are compared with the observed values of the same probability based on two criteria, mean absolute relative error and determination coefficient. Results of these comparisons indicate that both distributions of GEV and Wakeby, whose parameters are computed by the L‐moments method, are adequate in predicting quantile estimates. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

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何晓业  何晓红 《大地测量与地球动力学》2007,27(2):122-124

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Relationship of Arctic sea ice and Northern Hemispheric 500 hPa Polar vortices     

References： 《极地研究(英文版)》2007,18(1):73-83

Using the NCEP/NCAR reanalysis monthly 500 hPa height data on a 2.5 latitude-longitude grid and 1°×1° sea ice data,the polar vortex area,intensity index and arctic sea ice area index are calculated respectively,and the meridional distribution,period variation and the abrupts in the long range trend are analyzed to study their relationship.The results show that the meridional distribution of sea ice and polar vortex h-ave distinctive difference,the relative positions of them are different in the eastern and western hemispheres,and exept they have periods of 4 months,quasi half year,quasi year,4-5 years and 10 years commonly,and each of them has its own respective variation as well.The sea ice area is decreasing apparently since 1980's,so is the polar vortex area,but their abrupt changge time are different totally.The area of sea ice and polar vortex has prominent positive correlation,but the relationship of sea ice intensity,polar vortex intensity,polar vortex area is complicated.  相似文献   

White dwarf + red dwarf binary systems and the period gap of cataclysmic variables     

N. F. Vojkhanskaja 《Astrophysics》2007,50(3):351-361

Cataclysmic variables (CV) and pre-cataclysmic binaries (PCB) are discussed. The main difference between them (accretion or its absence) is shown to be a consequence of the evolutionary process and the properties of their progenitors. Both types of system have a bimodal distribution of their periods, but the extrema are in counterphase. Luminosity-effective temperature diagrams for the primary components are used to show that both systems have approximately the same age, which conflicts with the notion of PCBs as precursors of CVs. Calculations of the maximum distance between components for which the system remains stable show that CVs have passed this limit, while PCBs maintain their stability during this evolution. It is suggested that, after ejecting a common shell, future CVs immediately become semi-detached systems. It this is so, then there must be cataclysmic variables which are the central stars of planetary nebulae. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 427–439 (August 2007).  相似文献