佳木斯地体晚侏罗世－白垩纪古地磁研究及其构造意义     

张世红  杨惠心 《吉林大学学报(地球科学版)》1996,(2)

对佳木斯地体盖层鸡西群和桦山群１９８个标本的古地磁研究，确定了该地体晚侏罗世和白垩纪的古磁极位置（６３．４Ｎ，７１．ＯＥ，Ａ９５＝６．１和７２．２Ｎ，７３．７Ｅ，Ａ９５＝３．６）和古地理纬度（５２．５Ｎ和５２．６Ｎ）。白垩纪以后，佳木斯地体相对于松辽地体又有大幅度的位移。  相似文献   

Shallow bias of paleomagnetic inclinations in the Paleozoic and Precambrian     

D.V. Kent  M.A. Smethurst 《Earth and Planetary Science Letters》1998,160(3-4):391-402

An updated analysis of the global paleomagnetic database shows that the frequency distributions of paleomagnetic inclinations for the Cenozoic and Mesozoic eras (younger than 250 Ma) are compatible with a random geographical sampling of a time-averaged geomagnetic field that closely resembles that of a geocentric axial dipole. In contrast, the frequency distributions of paleomagnetic inclinations for the Paleozoic and Precambrian eras (prior to 250 Ma) are over-represented by shallow inclinations. After discounting obvious secondary causes for the bias, such as from data averaging, sedimentary inclination error, inhomogeneous lithological distributions, and tropical remagnetization, we show that the anomalous inclination distributions for the Paleozoic and Precambrian can be explained by a geomagnetic field source model which includes a relatively modest (25%) contribution to the axial dipole from a zonal octupole field and an arbitrary zonal quadrupolar contribution. The apparent change by around 250 Ma to a much more axial dipolar field geometry might be due to the stabilization of the geodynamo from growth of the inner core to some critical threshold size, a gross speculation which would imply that either the threshold size was rather large or the inner core nucleated rather late in Earth history. Alternatively, if a geocentric axial dipole model is assumed or can eventually be demonstrated independently, the anomalous inclination distributions for the Paleozoic and Precambrian may reflect a tendency of continental lithosphere to be cycled into the equatorial belt, perhaps because geoid highs associated with long-term continental aggregates influence true polar wander.  相似文献   

华南地块的地极移动曲线及其地质意义   总被引：12，自引：1，他引：12       下载免费PDF全文

林金录 《地质科学》1987,(4):306-315

结合最近获得的古地磁数据,作者重新计算编制了华南地块的地极移动曲线,进而讨论了华南和华北地块在早古生代的地理位置,二者最后拼合的时代,以及华南地块和欧亚大陆北部两条极移曲线之间的系统偏差等问题。  相似文献   

东秦岭造山带古地磁研究的初步结果   总被引：3，自引：1，他引：3  

刘育燕  森永速男 《地球科学》1992,17(1):79-86

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Magnetic,paleomagnetic and palynologic studies of Paleolithic depositions of the Akhshtyrskaya cave (Russia)     

Genrietta A. Pospelova  Elżbieta Król  Galina M. Levkovskaya  Jadwiga Kruczyk  Magdalena Kądziałko-Hofmokl  Sergey A. Kulakov 《Acta Geophysica》2007,55(4):619-639

The paper presents the results of experimental rock-magnetic, paleomagnetic and palynologic study of Paleolithic sediments sampled along two profiles in the Akhshtyrskaya cave, situated in the vicinity of Black Sea shore. In the upper part of profiles, some magnetite was observed; in the middle and lower parts, strongly oxidized non-stoichiometric magnetite and hematite prevail. Thin maghemite covers on the surface of fine magnetite grains are present in the majority of specimens. Natural remanence has one characteristic component (CHRM), mostly of chemical origin, although in few specimens containing magnetite it may be sedimentary. Directions of CHRM obtained by standard paleomagnetic methods revealed anomalous pattern only in layer 3/2, which is slightly older than the overlying layer 3/1 whose age was established as (35±2)×10³ years BP by the U-Th method. This suggests that this paleomagnetic anomaly (PMA) can be correlated with Kargapolovo excursion dated on about (45−39)×10³ years BP. In the remaining overlying and underlying layers, directions of CHRM are grouped around the present geomagnetic field. Depth distributions of scalar magnetic parameters generally coincide with the lithological division of the profiles. Palynologic study revealed the presence of 22 pollen zones. Five thermomers separated with colder periods were found in the middle and lower parts of profile. The non-magnetite composition of magnetic fraction of the majority of studied sediments — oxidized nonstoichiometric magnetite and hematite — resulted in the lack of correlations between paleoclimatic and scalar magnetic characteristics.  相似文献   

新近系谢家阶层型剖面古地磁年代学研究   总被引：9，自引：1，他引：9  

武力超  岳乐平  王建其  F.Heller  邓涛 《地层学杂志》2006,30(1):50-53

古地磁测量表明,中国新近系谢家阶界线层型剖面——西宁盆地谢家剖面共记录了18个正极性段与17个负极性段,与标准极性柱中C5Bn.2n—C7n.1n之间的极性带能很好的对应。剖面中谢家组的年龄为17.32—21.58Ma,谢家哺乳动物群的年龄约为21Ma,相当于MN2中期。  相似文献   

Paleomagnetism of a pyroclastic flow deposit and its correlative widespread tephra in central Japan: Possible tectonic rotation since the late Pleistocene   总被引：1，自引：0，他引：1  

Yasuto Itoh  Haruo Kimura 《Island Arc》2004,13(1):110-118

Abstract The late Pleistocene Kamitakara Pyroclastic Flow Deposit (KPFD) and its correlative Kasamori (Ks22) Tephra in central Japan are found to preserve stable thermoremanent magnetization (TRM) and detrital remanent magnetization (DRM), respectively. Untilted site‐mean declinations of the KPFD are characterized by a fairly large scatter with easterly deflection, while those of the Ks22 show significantly smaller deflections. Because northerly paleomagnetic directions consistently characterize shallow marine sediments intercalating the Ks22 layer, the directional discordance is not attributed to different acquisition timing between TRM and DRM, but is probably due to a recent tectonic rotation in central Japan. Large scatter in TRM declinations of the KPFD implies that a number of right‐lateral active faults around the depositional area of the pyroclastic flow raised differential rotation of crustal blocks in central Japan, even during the late Pleistocene.  相似文献   

New paleomagnetic and magnetic fabric results for Early Cretaceous rocks from the Turpan intramontane basin,east Tianshan,northwest China     

HUANG Baochun  WANG Yongcheng &ZHU Rixiang Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China 《中国科学D辑(英文版)》2004,47(6):540-550

~~New paleomagnetic and magnetic fabric results for Early Cretaceous rocks from the Turpan intramontane basin,east Tianshan,northwest China~~  相似文献   

Meridional equatorial electrojet current in the American sector     

R. G. Rastogi 《Annales Geophysicae》1999,17(2):220-230

Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when H is negative, Y also becomes negative. Thus, the diurnal variation of Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.  相似文献   

华南地区古地磁研究初步成果及其地质意义   总被引：4，自引：0，他引：4  

张惠民  赵风清  王富福  张文治 《安徽地质》1994,(Z1)

依据２０００余个热退磁样品，经计算获得极点６０余个，可以构成代表华南地区不同块体的视极移轨迹５条，并与已知的华北和扬子两地块的极移轨迹进行对比，结合地质构造特征，在研究区内划分出扬子、华夏两个地块和江南、怀玉山－越北两个地体。同时本文还对有关的地层对比和各地块间的演化关系作了分析讨论。  相似文献