Paleomagnetic dating of the Cenjiawan Paleolithic site in the Nihewan Basin, northern China     

WANG Hongqiang  DENG Chenglong  ZHU Rixiang  XIE Fei 《中国科学D辑(英文版)》2006,49(3):295-303

It draws much attention of scientists how early hu- mans occupy and adapt to the rigorous climate and environment at high northern latitudes in East Asia after they stepped out of Africa, passed West Asia and finally arrived in East Asia[1-4]. Reliable age determi- nations of Paleolithic sites from northeastern Asia not only help to find out the earliest occupation of early humans in this region, but also relate to the founda- tion of the overall framework of human origin and migration[1-8]…  相似文献   

松潘—阿坝地块三叠系古地磁结果及运动学意义     

何登发  庄忠海  马永生 《现代地质》2007,21(3):556-563

迄今为止,位于扬子地块的西北缘,夹持于扬子、华北、塔里木和羌塘—昌都地块之间呈倒三角形构造区块的巴颜喀拉褶皱带尚未有构造古地磁研究成果报导。为配合该区油气勘查与油气资源评价,并对构造区块定位提供定量数据,开展了松潘—阿坝地块的古地磁研究。采样区集中在西秦岭构造区南亚带(摩天岭和若尔盖)、中亚带(洮河)和巴颜喀拉构造区的马尔康复向斜带(巴颜喀拉褶皱区)4个微地块。采样地层单元主要为三叠系。共采集57个采点,376块岩心标本。通过对岩石样品测试数据的分析和计算,获得洮河、巴颜喀拉、摩天岭和若尔盖(后两者夹于前两者之间)4个微地块古地磁极极点位置:经度为191.4°E~202.9°E,纬度为49.5°N~58.5°N。洮河和巴颜喀拉两微地块在晚三叠世的古纬度同为26.2°N,表明晚三叠世这4个被断裂相隔的微地块已构成一个统一的较大的地块。洮河和巴颜喀拉地块在三叠纪时的古纬度变化分别从早三叠世的13.4°N和11.3°N向北移动到晚三叠世的26.2°N,同时在北向移动过程中从早三叠世至晚三叠世分别发生了约40°和16°的逆时针旋转。  相似文献   

华北与西伯利亚地块碰撞时代的古地磁分析——兼论苏鲁-大别超高压变质作用的构造起因   总被引：4，自引：2，他引：4  

李朋武  高锐  管烨  李秋生 《地球学报》2007,28(3):234-252

对华北和西伯利亚地块进行了古纬度和纬度运移量的对比分析,结合古生物地理、同位素年代学等地质数据,确定了两地块的运动特征,相应地,确定了位于两地块间中亚洋盆最终闭合时代,并与苏鲁-大别山地区的超高压变质岩的峰期变质时代进行了对比.结果表明:①西伯利亚地块于晚泥盆世开始快速向北漂移,分隔华北和西伯利亚地块的中亚洋在晚泥盆世至晚石炭世期间已经存在;②早二叠世西伯利亚地块开始快速向南漂移,并于二叠纪末期(～250 Ma)和华北地块发生碰撞;③早二叠世,中亚洋纬度宽度约39°;④苏鲁-大别山地区的超高压变质岩的形成  相似文献   

毛北榴辉岩古地磁及岩石磁学初探     

孟小红  余钦范  郭友钊  周姚秀 《地球科学》2007,32(4):533-539

对中国大陆科学钻探孔区——江苏省东海县毛北地区的55块榴辉岩样品进行了古地磁研究,并从中抽样测试了等温剩磁、磁滞迴线、磁组构、热磁化率以及电子探针和镜下分析,结果表明,毛北榴辉岩有两组稳定的剩磁,即反向磁化和正向磁化,稳定剩磁方向分别为:D=94.3°,I=-29.1°和D=273.7°,I=15.4°,携带正向磁化与携带反向磁化样品的磁化强度和密度变化很大;毛北榴辉岩的磁各向异性度非常弱,最小轴方向很难确定;等温剩磁和磁滞迴线显示磁铁矿可能是毛北榴辉岩的主要载磁矿物,且在以Mr/Ms和Hcr/Hc的对数为纵、横坐标的图上落在视单畴(PSD)区域.根据磁性特征,对毛北榴辉岩的磁性载体成因、剩磁获得机制及构造意义进行了讨论.  相似文献   

滇池晚更新世末期以来湖积环境分析     

周建民  田升平  夏学惠  东野脉兴  张灼 《化工矿产地质》2002,24(3):129-135

通过对滇池湖心区晚更新世末期以来的沉积剖面、沉积物及其化学组合、古地磁特征及孢粉组合的研究,初步确定了滇池上更新统与全新统的分界,认为自晚更新世末期以来,滇池一直维持着稳定的湖相沉积。晚更新世末期,滇池处于温凉偏于的相对浅水环境。全新世早期气候逐渐转暖,湿度渐增,湖水面积扩大且渐深,至全新世中期,气候变得温暖湿润,湖水面积进一步扩大变深。全新世晚期滇池气候又变得温凉偏干、处于湖水面积缩小的浅水环境。  相似文献   

秦岭二叠纪古海洋再造   总被引：3，自引：2，他引：3       下载免费PDF全文

杨逢清  王治平 《地球科学》1995,20(6):641-647

  相似文献   

扬子地块泥盆纪—石炭纪古地磁新结果及其古地地理意义   总被引：15，自引：1，他引：15  

张世红  朱鸿等 《地质学报》2001,75(3):303-313

本文通过对扬子地块西南缘贵州独山－平塘地区泥盆－石炭纪316块定向岩心样品的系统退磁处理，揭示出晚侏罗世、新生代两期重磁化成.73个岩心样品，分布在早一中泥盆世（17个）、晚泥盆世（25个）、早石炭世（24个）和中－晚石炭世（7个）4个统计单元，得到了最可能的原生剩磁。结合已有的古地磁数据，修订了扬子地块极移曲,纯利 移曲线拟合的结果表明，扬子地块在早古生代是冈瓦那大陆的组成部分，与印度－喜马拉雅－澳大利亚地区临近。晚泥盆世、冈瓦那大陆发生大规模顺时针旋转，扬子地块开始与之分离。  相似文献   

Paleomagnetism and Cyclostratigraphy of the Middle Ordovician Krivolutsky Suite,Krivaya Luka Section,Southern Siberian Platform: Record of Non-Synchronous NRM-Components or a Non-Axial Geomagnetic Field?     

Rodionov  V.P.  Dekkers  M.J.  Khramov  A.N.  Gurevich  E.L.  Krijgsman  W.  Duermeijer  C.E.  Heslop  D. 《Studia Geophysica et Geodaetica》2003,47(2):255-274

The Middle Ordovician Volginsky and Kirensky fossil zones were sampled in the Krivaya Luka section (Krivolutsky suite) that outcrops along the Lena river in Siberia. The Volginsky and Kirensky zones are coeval to the Llandeilo in the global geologic time scale. The Krivaya Luka section consists of siltstones, clays, sandstones, and limestones, and displays a remarkably distinct sedimentary cyclicity, especially in its reddish middle part.Stepwise thermal demagnetization yields three NRM components. Component A, isolated in the 100—250°C interval can be either normal or reversed. The normal A-component has a direction close to recent local magnetic field. The reversed A-component directions are scattered around a direction close to that of the lower Triassic Siberian traps. Component B has unblocking temperatures that range from 400 to 500°C and is represented mainly by normal polarity directions. The B-component, isolated from rocks of the middle part of the section is of a normal polarity with D = 176.5°, I = 30.0° and a North pole position at 16.2°S, 111.3°E. The other parts of the section are characterized by intermediate B-directions, which resulted possibly by partially overlapping A- and C-components. The highest temperature dual-polarity component C was isolated in the 550—670°C interval, resulting in the detection of two complete polarity zones and three magnetic reversals. The C-component is characterized by the following mean directions: for the reversed component D = 335.7°, I = 6.9°, and for the normal component D = 188.6°, I = 28.0°, which is very close to the normal polarity directions of the B-component. The corresponding paleomagnetic North pole for reversed polarity rocks is 32.6°S, 137°E, which is typical of Middle Ordovician rocks from Siberia – the mean pole for Llanvirn-Llandeilo is 30°S, 136°E (cf. Smethurst et al., 1998) – whereas for normal polarity rocks the pole position 17.2°S, 99.1°E is markedly different. Nevertheless, we assume that the C-component records the ancient geomagnetic field of Ordovician times, even though it does not pass the reversals test. This could be explained by overlapping NRM unblocking temperature spectra for the B and C components. In this case, the paleomagnetic pole positions should be interpreted with some caution.In addition, the section was logged and sampled in detail for cyclostratigraphic purposes. Spectral analysis in the depth domain using the high-field susceptibility as input parameter showed that the observed cyclicity is most likely orbitally forced. Detected spectral peaks (significant at the 95% confidence level) were close to the expected positions of the periodicities of precession, obliquity and eccentricity for the Ordovician. Consequently, the average sediment accumulation rate is estimated at 3.5 cm/kyr. Extrapolating this sedimentation rate yields a total duration of at least 1 Myr for the Volginsky fossil zone and 1.2 Myr for the entire Krivaya Luka section.  相似文献   

青藏高原拉萨地块西段三叠纪古地磁结果及其构造意义   总被引：1，自引：0，他引：1  

程鑫  周亚楠  郭强  侯宝宁  吴汉宁 《地质通报》2015,34(203):306-317

报道拉萨地块西段三叠纪古地磁研究的初步结果。古地磁样品来自措勤县敌布错北缘新发现的海相三叠纪地层,共采集6个采点67块独立定向样品。岩石磁学实验表明,样品中含有大量中低矫顽力中等阻挡温度的磁性矿物和一定量的磁铁矿。于4个采点的47块样品中分离出现代地磁场的低温粘滞剩磁（分量A）,在6个采点66块样品中获得白垩纪的次生剩磁分量（分量B）,5个采点28块样品获得高温特征剩磁分量（分量C）。分量C仅可在少数以磁铁矿为主要载磁矿物的样品高温区间（525~585℃）获得,可通过标准褶皱检验,为岩石形成时期的原生剩磁信息。计算得出拉萨地块三叠纪的古地磁极位置：φρ=17.4°N、λρ=205.9°E、（dp=6.7,dm=3.7）,该结果表明拉萨地块三叠纪处于南纬中低纬度地区。结合羌塘古地磁结果推测,羌北地块与拉萨地块之间班公湖—怒江缝合带所代表的特提斯洋盆可能在早三叠世打开,早三叠世—晚三叠世期间快速扩张并推动羌北地块快速北移,促使了羌北地块与欧亚大陆南缘的拼合。  相似文献   

Tectonic implications of paleomagnetic data from upper Cretaceous sediments in the Oyubari area, central Hokkaido, Japan     

Machiko  Tamaki  Yasuto  Itoh 《Island Arc》2008,17(2):270-284

Abstract   Paleomagnetic studies provide constraints on the geometric configuration of the eastern Eurasian margin on geological time scales. Characteristic remanent magnetization components were isolated from eight sites by progressive demagnetization executed on samples from 25 sites in the Oyubari area, central Hokkaido where the Late Cretaceous Yezo Group is distributed. After tilt-correction, all sites show normal polarity site-mean directions, and well-clustered directions pass a positive fold test and a correlation test. Planktonic foraminifera indicate an age range of Cenomanian to Turonian, and the studied section is correlated to the geomagnetic polarity chron C34n. Reliable formation-mean directions that have been corrected for post-depositional shallowing (D = 7.5°, I = 65.9°, α₉₅ = 6.6°) are characterized by inclination data indicative of no significant latitudinal translation since the Late Cretaceous. Central Hokkaido has, therefore, been situated adjacent to easternmost Mongolia including Sikhote Alin around the present latitude since the Late Cretaceous. Declination data require significant differential rotation between Hokkaido and the eastern Asian margin, which may be indicative of rearrangement of crustal blocks along the continental margin.  相似文献