Neoproterozoic metamorphism and deformation at the southeastern margin of the East European Craton,Uralides, Russia     

U.?A.?GlasmacherEmail author  W.?Bauer  N.?Clauer  V.?N.?Puchkov 《International Journal of Earth Sciences》2004,93(5):921-944

The eastern margin of the East European Craton (EEC) has a long lasting geological record of Precambrian age. Archaean and Proterozoic strata are exposed in the western fold-and-thrust belt of the Uralides and are known from drill cores and geophysical data below the Palaeozoic cover in the Uralides and its western foredeep. In the southern Uralides, sedimentary, metamorphic and magmatic rocks of Riphean and Vendian age occur in the Bashkirian Mega-anticlinorium (BMA) and the Beloretzk Terrane. In the eastern part of the BMA (Yamantau anticlinorium) and the Beloretzk Terrane, K-Ar ages of the <2-µm-size fraction of phyllites (potassic white mica) and slates (illite) give evidence for a complex pre-Uralian metamorphic and deformational history of the Precambrian basement at the southeastern margin of the EEC. Interpretation of the K-Ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade. In the Yamantau anticlinorium, the greenschist-facies metamorphism of the Mesoproterozoic siliciclastic rocks is of Early Neoproterozoic origin (about 970 Ma) and the S1 cleavage formation of Late Neoproterozoic (about 550 Ma). The second wide-spaced cleavage is of Uralian origin. In the central and western part of the BMA, the diagenetic to incipient metamorphic grade developed in Late Neoproterozoic time. In post-Uralian time, Proterozoic siliciclastic rocks with a cleavage of Uralian age have not been exhumed to the surface of the BMA. Late Neoproterozoic thrusts and faults within the eastern margin of the EEC are reactivated during the Uralian deformation.  相似文献   

Exhumation History of a Garnet Pyroxenite-bearing Mantle Section from a Continent-Ocean Transition (Northern Apennine Ophiolites, Italy)   总被引：3，自引：0，他引：3  

MONTANINI  A.; TRIBUZIO  R.; ANCZKIEWICZ  R. 《Journal of Petrology》2006,47(10):1943-1971

Garnet clinopyroxenite and garnet websterite layers occur locallywithin mantle peridotite bodies from the External Liguride Jurassicophiolites (Northern Apennines, Italy). These ophiolites werederived from an ocean–continent transition similar tothe present-day western Iberian margin. The garnet clinopyroxenitesare mafic rocks with a primary mineral assemblage of pyrope-richgarnet + sodic Al-augite (Na₂O 2·5 wt %, Al₂O₃ 12·5wt %), with accessory graphite, Fe–Ni sulphides and rutile.Decompression caused Na-rich plagioclase (An_50–45) exsolutionin clinopyroxene porphyroclasts and extensive development ofsymplectites composed of secondary orthopyroxene + plagioclase(An_85–72) + Al-spinel ± clinopyroxene ±ilmenite at the interface between garnet and primary clinopyroxene.Further decompression is recorded by the development of an olivine+ plagioclase-bearing assemblage, locally under syn-kinematicconditions, at the expense of two-pyroxenes + Al-spinel. Mg-richgarnet has been also found in the websterite layers, which arecommonly characterized by the occurrence of symplectites madeof orthopyroxene + Al-spinel ± clinopyroxene. The enclosingperidotites are Ti-amphibole-bearing lherzolites with a fertilegeochemical signature and a widespread plagioclase-facies myloniticfoliation, which preserve in places a spinel tectonite fabric.Lu–Hf and Sm–Nd mineral isochrons (220 ±13 Ma and 186.0 ± 1·8 Ma, respectively) have beenobtained from a garnet clinopyroxenite layer and interpretedas cooling ages. Geothermobarometric estimates for the high-pressureequilibration have yielded T 1100°C and P 2·8 GPa.The early decompression was associated with moderate cooling,corresponding to T 950°, and development of a spinel tectonitefabric in the lherzolites. Further decompression associatedwith plagioclase–olivine growth in both peridotites andpyroxenites was nearly isothermal. The shallow evolution occurredunder a brittle regime and led to the superposition of hornblendeto serpentine veining stages. The garnet pyroxenite-bearingmantle from the External Liguride ophiolites represents a raretectonic sampling of deep levels of subcontinental lithosphereexhumed in an oceanic setting. The exhumation was probably accomplishedthrough a two-step process that started during Late Palaeozoiccontinental extension. The low-pressure portion of the exhumationpath, probably including also the plagioclase mylonitic shearzones, was related to the Mesozoic (Triassic to Jurassic) riftingthat led to continental break-up. In Jurassic times, the studiedmantle sequence became involved in an extensional detachmentprocess that resulted in sea-floor denudation. KEY WORDS: garnet pyroxenite; ophiolite; non-volcanic margin; mantle exhumation; Sm–Nd and Lu–Hf geochronology  相似文献   

天山北坡城市群空间组织形态的识别研究   总被引：1，自引：0，他引：1       下载免费PDF全文

季珏  高晓路 《干旱区地理》2012,35(4):687-694

 正确认识天山北坡城市群的空间组织结构以及空间发展形态,对于完善绿洲城市群的发展理论和规划具有重要意义。以天山北坡城市群为研究对象,通过资源环境承载力的分析,总结出未来城市群发展面临的客观制约因素;通过中心性分析、断裂点理论修正的Voronoi多边形等方法识别出城市群的中心城市及各自的辐射范围城市;通过引力模型识别出城市之间的社会经济联系强度。据此,利用多维尺度分析的方法,可视化地展现了天山北坡城市群发展的空间组织形态。经调查了解：（1）乌鲁木齐市与克拉玛依市是未来城市群发展的两个中心城市,五家渠市、阜康市、昌吉市、石河子市周边目前属于乌鲁木齐市的辐射范围城市,奎屯市,乌苏市属于克拉玛依市的辐射范围城市;（2）城市群内部的城市之间的联系比较松散,特别是两个中心城市之间联系较弱;（3）城市群的空间发展形态为串珠式,是一种特殊的走廊式空间形态。  相似文献   

一次阻塞型华北对流性暴雨过程的诊断分析和数值模拟     

姜学恭  李夏子  李彰俊  云静波 《高原气象》2012,31(5):1283-1293

利用常规和地面加密气象观测资料、卫星云图、NCEP再分析资料及中尺度模式MM5,对2006年7月23日一次阻塞型华北暴雨过程进行了诊断分析和数值模拟。结果表明,此次暴雨过程发生在以东西伯利亚阻塞高压为典型特征的大尺度鞍型场的背景下,宽广的低压区及高、低空急流次级环流为中尺度对流系统(MCS)的发生、发展提供了适宜的环境和动力强迫;700hPa和850hPa天气尺度的偏西水汽输送和低涡北侧的偏东水汽输送改善了环北京地区的水汽条件,暴雨发生前850hPa中尺度西南水汽输送对北京暴雨的发生有直接影响;MM5模式再现了导致MCS的形成及演变过程;中-β尺度MCS是这次暴雨的直接触发系统,其水平尺度约为0.5个经距,垂直方向由地面伸展到300hPa左右,具有典型的暖心结构,辐合、辐散中心分别位于900hPa和400hPa;MCS北侧强垂直次级环流为强对流的产生创造了有利条件。同时,MCS南侧相当位温的强梯度高能区及该区域的不稳定能量输送也是暴雨发生的重要条件。  相似文献   

近50a华北暴雨研究主要进展     

张文龙  崔晓鹏 《湖北气象》2012,31(4)

在我国加快实现气象业务现代化进程及2012年7月21日北京出现特大暴雨洪涝灾害的背景下,较为系统地回顾总结了近50 a华北暴雨的主要研究进展,其内容涉及大尺度环流形势及其分型、中低纬度系统相互作用、水汽输送、高低空急流、直接造成暴雨的中尺度系统、复杂地形以及下垫面、气候学特征等诸多方面。对这些研究成果的梳理,旨在加深对华北暴雨的理解和认识,加强华北暴雨研究,提高华北暴雨的预报水平。提出在继续开展大尺度系统发展演变研究的同时,有必要借助新型观测和数值模拟手段,有针对性地开展华北暴雨β（γ）中尺度系统细致研究,以期更清楚地揭示华北暴雨中尺度系统的三维结构特征、发生发展机理。  相似文献   

AN OBSERVATIONAL STUDY ON DISTRIBUTION OF PRECIPITATION ASSOCIATED WITH LANDFALLING TROPICAL CYCLONES AFFECTING CHINA     

舒守娟  许音  宋金杰  喻自凤 《热带气象学报(英文版)》2012,18(3):275-283

In order to provide an operational reference for tropical cyclone precipitation forecast,this study investigates the spatial distributions of precipitation associated with landfalling tropical cyclones(TCs) affecting China using Geostationary Meteorological Satellite 5(GMS5)-TBB dataset.All named TCs formed over the western North Pacific that made direct landfall over China during the period 2001-2009 are included in this study.Based on the GMS5-TBB data,this paper reveals that in general there are four types of distribution of precipitation related to landfalling TCs affecting China.(a) the South-West Type in which there is a precipitation maximum to the southwestern quadrant of TC;(b) the Symmetrical South Type in which the rainfall is more pronounced to the south side of TC in the inner core while there is a symmetrical rainfall distribution in the outer band region;(c) the South Type,in which the rainfall maxima is more pronounced to the south of TC;and(d) the North Type,in which the rainfall maxima is more pronounced to the north of TC.Analyses of the relationship between precipitation distributions and intensity of landfalling TCs show that for intensifying TCs,both the maximum and the coverage area of the precipitation in TCs increase with the increase of TC intensity over northern Jiangsu province and southern Taiwan Strait,while decreasing over Beibu Gulf and the sea area of Changjiang River estuary.For all TCs,the center of the torrential rain in TC shifts toward the TC center as the intensity of TC increases.This finding is consistent with many previous studies.The possible influences of storm motion and vertical wind shear on the observed precipitation asymmetries are also examined.Results show that the environmental vertical wind shear is an important factor contributing to the large downshear rainfall asymmetry,especially when a TC makes landfall on the south and east China coasts.These results are also consistent with previous observational and numerical studies.  相似文献   

北大西洋涛动位相转换的数值研究   总被引：1，自引：0，他引：1  

李忠燕  罗德海 《大气科学》2012,36(2):374-384

借助一个非线性准地转正压模型,模拟了基本西风气流的强弱、不同空间分布的天气尺度扰动涡对北大西洋涛动(NAO)位相转换的作用,以及大尺度双波地形对其的影响.通过一系列的对比试验发现,适当弱的基本西风气流有利于下游系统西退使NAO由正(负)位相转换为负(正)位相;振幅强、活动范围大的天气尺度扰动波是NAO由负位相转换为正位...  相似文献   

Possible Impact of the Summer North Atlantic Oscillation on Extreme Hot Events in China          下载免费PDF全文

SUN Jian-Qi 《大气和海洋科学快报》2012,5(3):231-234

This paper reveals that the summer North Atlantic Oscillation (SNAO) is closely related to the extreme hot event (EHE) variability in China during the period of 1979 2009, with a positive-phase (negative-phase) SNAO corresponding to less (more) EHEs in northern China. The summer circulation anomalies associated with the SNAO give further confirmation of the above relationship. In a positive-phase (negative-phase) SNAO year, there is an anomalous cyclone (anticyclone) over central East Asia, which can increase (decrease) the total cloud cover over this region. Such changes of the total cloud cover can then decrease (increase) the solar radiation reaching the surface, which is consequently unfavorable (favorable) to the formation of EHEs over northern China.  相似文献   

城市化对华北地区最高, 最低气温和日较差变化趋势的影响   总被引：31，自引：4，他引：27       下载免费PDF全文

周雅清  任国玉 《高原气象》2009,28(5):1158-1166

利用华北地区255个一般站和国家基本、 基准站1961\_2000年的实测资料, 经过质量检验和均一性订正后, 将所有台站根据人口和台站地理位置分为5个类别, 分析了这5个类别台站和国家基本、 基准站地面平均气温、 最高、 最低气温的年和季节变化趋势以及城市化影响。结果表明： 华北全部台站的年平均气温、 最高、 最低气温均呈增加趋势, 且以最低气温上升最为明显, 导致年平均日较差呈现明显下降。就城市化影响而言, 平均气温、 最低气温变化趋势中城市热岛效应加强因素的影响明显, 但城市化对最高气温趋势影响微弱, 个别台站和季节甚至可能造成降温。在国家基本、 基准站观测的年平均气温和年平均最低气温上升趋势中, 城市化造成的增温分别为0.11℃·(10a)-1和0.20℃·(10a)-1, 对全部增温的贡献率分别达39.3%和52.6%。各类台站的四季平均气温和最低气温序列中城市化影响均造成增温。城市化增温以冬季为最大, 夏季最小。城市化还导致乡村站以外的各类台站日较差减小, 近40年华北地区国家基本、 基准站年平均和秋、 冬季平均气温日较差明显下降均由城市化影响造成的。  相似文献   

西太平洋副热带高压对华北地区降水蒸发差的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

孙卫国  程炳岩  郭渠 《高原气象》2009,28(5):1167-1174

采用小波相关和交叉小波变换等方法, 分析了西太平洋副热带高压脊线和北界位置变化对华北地区降水蒸发差的影响。结果表明, 2000年以来华北区南部的水资源短缺问题有所缓解, 但以北京为中心的华北区东北部仍处于持续缺水期; 华北地区降水蒸发差与副热带高压脊线及北界位置变化相关密切, 存在年际和年代际尺度的显著相关振荡, 与副热带高压脊线的年代际尺度相关凝聚性最强; 时域中年际尺度相关存在局部化特征, 年代际尺度相关具有阶段性。分析认为, 2000年以来副热带高压脊线和北界位置偏北并维持反气旋型环流, 有利于水汽向华北输送, 使得华北降水增多, 是近年来华北中南部降水蒸发差增大的主要原因; 而东亚季风减弱不利于西南气流的水汽输送, 以及蒙古高原显著增暖导致蒸发增大等因素, 使得华北东北部仍处于持续缺水期。  相似文献