北祁连玉石沟蛇绿岩形成于晚震旦世的SHRIMP年龄证据   总被引：45，自引：5，他引：45  

史仁灯  杨经绥  吴才来  J.WOODEN 《地质学报》2004,78(5):649-657

玉石沟蛇绿岩位于青藏高原东北缘的北祁连山中部 ,由地幔橄榄岩、堆晶辉长岩、辉绿岩、枕状熔岩以及夹杂在其中的硅质岩组成。地幔橄榄岩主要是方辉橄榄岩 ,其主要氧化物成分较为单一 ,具 L REE富集、Eu亏损的 U形 REE配分模式 ,亏损强不相容元素 ;枕状熔岩具典型 MORB特征 ,在构造判别图解上位于 MORB和 IAT区域 ,指示蛇绿岩可能形成于类似于洋中脊的构造环境 ,并受到火山弧岩浆作用的影响。堆晶辉长岩具明显的 Eu正异常 ,其锆石离子探针 (SHRIMP) 2 0 6 Pb/2 38U加权平均年龄为 5 5 0± 17Ma,Th/U值为 0 .5 3～ 1.85 ,大于0 .2 3,为岩浆成因锆石 ,其年龄代表辉长岩的成岩时代 ,推断玉石沟蛇绿岩形成于晚震旦世。  相似文献   

Study of charge structure and radiation characteristic of intracloud discharge in thunderstorms of Qinghai-Tibet Plateau     

Yijun Zhagn  Wansheng Dong  Yang Zhao  Guangshu Zhang  Hongfa Zhang  Chengpin Chen  Tong Zhang 《中国科学D辑(英文版)》2004,47(1):108-114

The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges. A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection.  相似文献   

Impact of permafrost change on the Qinghai-Tibet Railroad engineering     

Qingbai Wu  Guodong Cheng  Wei Ma 《中国科学D辑(英文版)》2004,47(1):122-130

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The application of auto-temperature-controlled ventilation embankment in Qinghai-Tibet Railway     

Qihao Yu  Guodong Cheng  Fujun Niu 《中国科学D辑(英文版)》2004,47(1):168-176

Auto-temperature-controlled ventilation embankment is an effective engineering measure for “cooling roadbed”. Practice proves that this new method can sufficiently make use of natural cold energy. It has the advantages of higher efficiency, better cooling effect and feasibility in engineering practice, and wider application in various environment, etc. And also, it is comparatively cheap in project cost. Through practice in the field for half a year, the testing results show that, with the application of auto-temperature-controlled system, the artificial permafrost table has been raised by 65 cm. The artificial permafrost table was basically at the embankment bottom, and the action of freeze-thaw circle on engineering stability was effectively avoided. In the month with highest ground temperature, in the scope with 1–4 m in depth, including the majority of the embankment and the upper part in the original seasonal layer, the ground temperature decreased by 0.7°C. Through thermal flux calculation in the original seasonal layer, in the month with the maximum thermal flux coming into permafrost, it is found that the thermal flux reduces nearly by half. Coming into the cooling period for nearly a month, the ground temperature in entire auto-temperature-controlled embankment is close to zero, and the foundation is at negative temperature. But in a large region in the embankment and foundation the ground temperature was over 0°C and varied from 0°C to0.39°C in ordinary ventilation embankment.  相似文献   

Carbon isotopic studies of individual lipids in organisms from the Nansha sea area, China   总被引：2，自引：0，他引：2  

DUAN Yi    SONG Jinming & ZHANG Hui . Lanzhou Institute of Geology  Chinese Academy of Sciences  Lanzhou  China  . School of Geology  Lanzhou University  Lanzhou  China  . Institute of Oceanology  Chinese Academy of Sciences  Qingdao  China 《中国科学D辑(英文版)》2004,47(7):593-598

Sediments contain abundant lipid compounds in general, which are used as biomarker compounds to study organic matter sources and reconstruct the pa-laeoenvironments[1—7]. However, lipid compounds in sediments are generally a mixture of various genetic components so that it is difficult to correctly decouple their biological sources only by the results of bio-chemical researches. Carbon isotopic studies of indi-vidual sedimentary lipid compounds can discover their genetic information, which pr…  相似文献   

~(40)Ar/~(39)Ar dating of shear deformation of the Xianshuihe fault zone in west Sichuan and its tectonic significance   总被引：6，自引：1，他引：6  

ZHANG Yueqiao  CHEN Wen  & YANG Nong . Institute of Geomechanics  Chinese Academy of Geological Sciences  Beijing  China  . Institute of Geology  Chinese Academy of Geological Sciences  Beijing  China  . Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China 《中国科学D辑(英文版)》2004,47(9)

TheNW-SEstrikingXianshuihefaultzoneslicesthesoutheasternTibetanPlateauandconnectssoutheastwardwiththeAnninghe-Zemuhe-Xiaojiangfaultzone,whichformahuge,activesinistralstrike-slipfaultzone(fig.1).ThisfaultzoneisanimportantseismicfaultineastTibet[1-5].EarthquakegeologystudiesandoffsetpatternsofyounggeologicalfeatureshaveshownthatlateQuaternarysinistralsliprateoftheXianshuihefaultzonereaches13mm/a[1,2].TheXianshuhefaultzoneconsistsoftwomainbranches,theDaofufaultbranchinthewestandtheXianshuih…  相似文献   

A comparative study on the illite crystallinity and the clay mineral reflectance spectral index for subdividing the very low-grade metamorphic belt along the Lizhou-Hekou geological section in the Youjiang sedimentary basin, Guangxi, China     

YAN Shouxun Laboratory of Remote Sensing Information Sciences  Institute of Remote Sensing Applications  Chinese Academy of Sciences  Beijing  China 《中国科学D辑(英文版)》2004,47(9)

To examine the application potential of hyperspectral remote sensing techniques in classifying very low-grade metamorphic belts, the composition of clay minerals and the cyrstallinity of illite from mudstones were measured using XRD and VIS-SWIR (400-2500 nm) reflectance spectroscopy. Based on the illite cyrstallinity, Kubler Index (KI), the Early Triassic LuoLou Group and the Middle Triassic lower Baifeng Formation were classified as the lower Epizone with KI△2θ° ranging from 0.22 to 0.25, the upper Baifeng Formation as upper anchizone with KI△2θ°ranging from 0.26 to 0.33, and the Hekou Formation as lower anchizone with KI△2θ° ranging from 0.38 to 0.40. According to a KI△2θ° value of 0.43, it is possible that there may exist a local diagenetic zone in the upper strata. The illite cyrstallinity Kubler index and the metamorphic grade increase from the bottom to the top of the stratigraphic sequence. The metamorphic grade boundaries nearly match the stratigraphic boundaries, indicating a burial metamorphism nature for the stratigraphic sequence. From the bottom to the top of the sequence, the spectral absorption band center of clay minerals from fresh rocks is around 2200 nm. The absorption band centers change towards shorter wavelengths: the Luolou Group being at 2220 nm, the Baifeng Formation at 2217-2213 nm, the lower member of the Hekou Formation at 2214-2206 nm, and the upper member of the Hekou Formation at 2205-2197 nm. The spectral absorption band center of illite shows the same change pattern. These results indicate that very low-grade metamorphic belts can be subdivided using spectral indices of clay minerals, which are measured by using field portable spectroradiometers. However, it may not work well with satellite and airborne sensors.  相似文献   

The Rotational Structure along the Eastern Segment of the Altyn Tagh Fault and Its Implications in Dynamics     

Wang Ping 《中国地震研究》2004,18(4):327-336

As a result of the left-lateral strike-slipping of the Altyn Tagh fault in Neotectonic period, a contra-rotational structure, namely the Zhaobishan vortex structure, has developed at the juncture of the main Altyn Tagh fault and the northern fringe fault of the Qilian Mountains.Preliminary analysis on the deformation and evolution of the Zhaobishan vortex structure. In combination with the previous data, suggests that the tectonic transform between the Altyn Tagh fault and the northern fringe fault of the Qilian Mountains attributes to the deformation of the rotational structure. The existence of a series of rotational structures along the Altyn Tagh fault and on the northeastern edge of the Qinghai-Xizang(Tibet) plateau indicate that as the substance in the northern Qinghal-Xizang (Tibet) plateau moves clockwise around the eastern tectonic knot of the Himalayas, rotational structures become the principal mode on the northern marginal zone of the Plateau of transforming and absorbing tectonic deformation.  相似文献   

湖南汛期降水异常的时空分布特征研究   总被引：16，自引：5，他引：16  

刘会玉  林振山  张明阳 《热带气象学报》2004,20(4):409-418

利用湖南19个测站23年(1959～2001年)4～9月的降水量资料，用EOF、REOF、小波分析对湖南汛期降水的特征场分布、分区特征、周期性和突变性等时空分布特征进行了诊断研究。研究结果表明：EOF分析得到的前三个典型场可以很好的反映湖南汛期降水空间分布的异常结构，即具有整体一致的空间结构，南北相反的空间结构，中部和周围地区相反变化的空间结构。旋转后的前6个空间模态可以较好地代表湖南汛期降水的6个异常敏感区：湘北、湘中、湘南、湘东南、湘西、湘东北。利用小波分析方法研究湖南汛期降水的周期性及其突变性发现，湖南汛期降水存在着明显的3年、7年和23年的特征时间尺度和周期性振荡；并且在今后相当长的一段时间内，湖南汛期的降水将逐年减少，并将转入干旱时期。  相似文献   

热带西太平洋热状况年代际和年际变化特征分析   总被引：3，自引：0，他引：3  

李丽平  王盘兴  何金海  王东晓 《热带气象学报》2004,20(5):472-482

采用谐波分析和EOF分析方法,对比研究了暖池区域表层热状况(海表温度距平SST'表征)和浅层热状况(热含量距平HS'和次表层海温距平ST'表征)在1月和7月的年代际、年际尺度时空特征.分析结果表明:⑴不同季节的年代际、年际尺度SST'和HS'都存在两个显著模态,HS'1月的年代际、年际尺度结构最简单,而SST'7月的年代际和1月年际结构最复杂;⑵ 1970年代末和1980年代初发生的年代际跃变HS'晚于SST', 且SST'(HS')呈增温(减少)趋势;⑶ HS'的年际异常与ENSO关系密切,而SST'与ENSO关系不显著.  相似文献