锂同位素分馏机制讨论   总被引：7，自引：0，他引：7  

汤艳杰  张宏福  英基丰 《地球科学》2009,34(1):43-55

作为一种新兴的稳定同位素示踪工具, 锂同位素地球化学的研究近年来受到了国际地学界日益广泛的关注.其应用领域涵盖了从地表到地幔的流体与矿物之间的相互作用.在地表风化作用过程中, 轻锂同位素(6Li) 优先进入固体相, 而7Li则进入流体相, 因而地表风化作用淋滤出了岩石中的重锂, 致使河水具有重的锂同位素组成, 河水又将重锂同位素组分补给海洋, 洋壳的低温蚀变作用使得海水的锂同位素组成进一步变重.在俯冲带, 由于俯冲板片释放的流体具有重锂同位素组成的特征, 它们上升并交代上覆的地幔楔和相邻的地幔, 使得地幔楔的锂同位素组成变重.同时, 深俯冲的板片由于脱水而具有较轻的锂同位素组成, 它们在地幔中可能形成一个局部轻锂的地幔储源.影响地幔橄榄岩锂同位素分馏的因素主要有3个方面: 温度、扩散机制以及外来熔体的反应.由于高温下地幔矿物之间的锂同位素分馏很小, 而单纯的扩散分馏机制不能够很好的解释我国华北汉诺坝地区地幔橄榄岩中矿物之间的锂同位素分馏.因此, 具有轻锂同位素组成的熔体与橄榄岩之间的反应是上述现象的一个合理解释.需要指出的是, 在橄榄岩-熔体反应的过程中, 锂同位素的扩散作用也对地幔矿物之间的同位素分馏有一定的贡献.   相似文献   

青藏高原现今高分辨率地壳运动特征   总被引：2，自引：0，他引：2  

方颖  江在森  张晶  武艳强 《地球科学》2009,34(3):399-404

利用GPS资料, 采用最小二乘配置和小波技术分析了青藏高原的地壳运动特征, 对该区地壳运动强度和涡旋运动进行了定量分析.结果显示, 青藏高原地壳运动强度沿喀喇昆仑断裂、玛尼-玉树-鲜水河-小江的弧型构造带, 自西向东递减.川滇菱形块体显示出北强南弱、西强东弱的特点, 东边界形成明显的分界线, 而西边界并不明显; 青藏高原存在3个涡旋分区: 顺时针旋转的拉萨、羌塘及川滇中西部地区, 亚东-谷露断裂以东的区域为其涡旋高值区; 逆时针旋转的柴达木地块及其以北的地区, 西昆仑断裂与阿尔金断裂之间为其高值区; 逆时针旋转的青藏高原与华南地块的边界带, 龙门山与安宁河的拐角处为其高值区.   相似文献   

黔东南地区褶皱构造样式及其断层突破模式   总被引：3，自引：0，他引：3  

崔敏  汤良杰  郭彤楼  宁飞  田海芹  胡东风 《地球科学》2009,34(6):907-913

黔东南地区发育隔槽式褶皱组合和逆冲断层.通过对褶皱和地层的平面展布、断层的产状和性质以及滑脱层的分析, 结合典型地震剖面解释和平衡剖面恢复, 对黔东南地区构造特征及其成因进行了探讨.结果表明, 隔槽式褶皱的发育不仅与滑脱深度和剥蚀差异有关, 而且与逆冲断层的推覆距离、逆冲断层的产状、断坪断坡长度比、断层突破方式和多层次滑脱等方面存在着密切联系.结合区域构造演化和推覆距离的制约, 建立了黔东南地区的隔槽式褶皱构造样式的几何学和运动学模型, 确定其主要影响因素是断坪断坡长度比较小、多种方式断层突破和多层次滑脱.   相似文献   

Quantitative analysis of soil pores under natural vegetation successions on the Loess Plateau     

ZHAO ShiWei  ZHAO YongGang  & WU JinShui State Key Laboratory of Soil Erosion  Dryl  Farming on the Loess Plateau 《中国科学:地球科学(英文版)》2010,(4)

Soil pore is a key attribute of the soil structure that affects soil reservoir under natural vegetation recovery on the Loess Plateau.This study is to quantitatively analyze soil pore parameters,measured with Computed Tomography(CT) at 15-57 mm depths under five different vegetation succession stages using a concept of substituting space for time in the Ziwuling Forest Region of the Loess Plateau.The results showed that the soil pore parameters,such as pore number,porosity,circularity,and fractal dimension,...  相似文献   

Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts     

JIA ShiXu  ZHANG XianKang  ZHAO JinRen  WANG FuYun  ZHANG ChengKe  XU ZhaoFan  PAN JiShun  LIU Zhi  PAN SuZhen & SUN GuoWei Geophysical Exploration Center  China Earthquake Administration  Zhengzhou  China 《中国科学:地球科学(英文版)》2010,(2)

Songpan-Garze massif is located at the turning position of tectonics from the nearly west-east direction to the nearly north-south direction in the northeastern margin of Tibetan Plateau,with Zoigê basin in the centre of the massif.In this paper,we build a crustal structure model of Zoigê basin and its surrounding folded orogenic belts using the deep seismic sounding data in this region.We also discuss structures and properties of the basement in Zoigê basin,tectonic relations between Zoigê upland basin and its surrounding folded orogenic belts,crustal deformation and thickening in the northeastern margin of Tibetan Plateau,and decoupling and relaxing processes in the crust.The results indicate that a special "Mesozoic basement" is formed of Triassic rocks with high density (2.65-2.75 g/cm3) and high velocity (5.6 km/s) in Zoigê basin.Songpan-Garze tectonic massif was transformed into two types of tectonic units with different crustal structures,i.e.,relatively stable Zoigê upland basin and active folded orogenic belts around the basin,in the course of the crustal material of Tibetan Plateau flowing eastward and obstructed by surrounding stable blocks.The thickening of the crust in the northeastern margin of Tibetan Plateau mainly occurred in the mid and lower crust,and the structure characterized by low velocities and multiple reflectors obviously appears in the folded orogenic belts around Zoigê basin.It implies that the mid and lower crust underwent a strong tectonic deformation in the folded orogenic areas.The thickness of the crust is about 50 km in Zoigê basin and the folded orogenic belts at the both southern and northern sides of Zoigê basin.The "Mountain root" cannot be identified.It is inferred that during the later orogenic period the eastwards flowing deep materials moved clockwise along the relatively relaxing southern side around the eastern tectonic knot under the obstructing of surrounding rigid massifs,and it resulted in the strong stretching action of the folded orogenic belts around Zoigê basin.  相似文献   

SHRIMP U-Pb dating and Hf isotopic analyses of Middle Ordovician meta-cumulate gabbro in central Qiangtang, northern Tibetan Plateau   总被引：5，自引：0，他引：5  

ZHAI QingGuo WANG Jun  LI Cai & SU Li Institute of Geology  Chinese Academy of Geological Sciences  Beijing  China  College of Earth Sciences  Jilin University  Changchun  The Geological Laboratory Center  State Key Laboratory of Geological Processes  Mineral Resources  China University of Geo- sciences  Beijing 《中国科学:地球科学(英文版)》2010,(5)

Metabasites consisting of metamorphic ultra-mafic rocks, cumulate gabbro, gabbro (diabase), basalt, and plagiogranite are exposed at the Taoxinghu area in central Qiangtang, northern Tibetan Plateau. Zircon SHRIMP U-Pb dating for the cumulate gabbro yields a weighted mean age of 467±4 Ma, which is the oldest and most reliable magmatic age in this area. Zircon 176Hf/177Hf ratios range from 0.282615 to 0.282657, with εHf(t) values of 5.02±0.28, indicating that the cumulate gabbro was mainly derived from the depleted mantle. In addition, geochemical data of metabasites suggest that they have similar characteristics to those in the mid-ocean ridge basalts (MORB). The Taoxinghu metabasites may represent the fragment of Early Paleozoic ophiolite in the "Central Uplift" of the Qiangtang, northern Tibetan Plateau.  相似文献   

Statistics of gravity wave spectra in the troposphere and lower stratosphere over Beijing     

YUAN Wei    XU JiYao  WU YongFu    CHEN HongBin & BIAN JianChun State Key Laboratory of Space Weather  Center for Space Science  Applied Research  Chinese Academy of Sciences  Beijing  China  Graduate University of the Chinese Academy of Sciences  Beijing  School of Electronic Information  Wuhan University  Wuhan  LAGEO 《中国科学:地球科学(英文版)》2010,(1)

We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67-8.02 km and 13.57-19.92 km altitude ranges and compare them with linear saturation model.Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude.The observed variability is not consistent wit...  相似文献   

Distribution,formation and evolution of sand ridges on the East China Sea shelf     

WU ZiYin      JIN XiangLong  CAO ZhenYi  LI JiaBiao  ZHENG YuLong  & SHANG JiHong  Key Laboratory of Submarine Geosciences  State Oceanic Administration  Hangzhou  China  Second Institute of Oceanography 《中国科学:地球科学(英文版)》2010,(1)

Based on the integrated results of multiple data types including MBES (Multi-Beam Echo Sounding) and historical topography maps,the LSR (Linear Sand Ridges) on the ECS (East China Sea) shelf are identified,divided into subareas,and classified.The distribution of sand ridge crests is also established.The strikes of the LSR on the ECS shelf fall in a normal distribution with the center point being 155° azimuth with additional peak points at 125°,130°,140°,and 180° azimuth.The distribution of the ECS shelf san...  相似文献   

Retrieving crop leaf area index by assimilation of MODIS data into a crop growth model     

WANG DongWei      WANG JinDi  & LIANG ShunLin State Key Laboratory of Remote Sensing Science  Jointly Sponsored by Beijing Normal University 《中国科学:地球科学(英文版)》2010,(5)

Leaf area index (LAI) is an important parameter in monitoring crop growth. One of the methods for retrieving LAI from remotely sensed observations is through inversion of canopy reflectance models. Many model inversion methods fail to account for variable LAI values at different crop growth stages. In this research, we use the crop growth model to describe the LAI changes with crop growth, and consider a priori LAI values at different crop growth stages as constraint information. The key approach of this re...  相似文献   

我国典型海洋型冰川区高海拔区输出水量变化对气候变暖的响应   总被引：2，自引：0，他引：2  

李宗省  何元庆  温煜华  庞洪喜  贾文雄  和献中  蒲焘 《地球科学》2010,35(1):43-50

通过丽江盆地气象水文观测资料研究发现: 冰雪消融加剧、融水增加, 漾弓江流域径流量明显上升; 高海拔冰雪区消融期提前, 春季径流增加明显; 高海拔冰雪区的径流输出对漾弓江流域水量平衡的贡献量逐年增加, 体现了全球气候变暖背景下高海拔冰雪区对整个流域水循环的重要性.对海螺沟流域实测气象水文资料的分析也表明, 气候变暖背景下, 该流域冰雪区水量输出也逐年上升.两流域高海拔区输出水量的剧烈增加, 明显响应了气候变暖, 表明了流域水循环的加速, 这必然将对区域的发展和资源开发产生重要影响.   相似文献