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扬子地块湖北兴山-秭归剖面古生界至中生界构造古地磁研究 总被引：7，自引：0，他引：7
对扬子地块北部地区的湖北兴山 秭归剖面寒武系至中生界进行了构造古地磁学研究 .对岩石标本剩磁载体和剩磁稳定性的分析以及褶皱检验和倒转检验的结果表明 ,从 82 5个岩芯 ( 84个采样点 ,代表古生界至侏罗系 )分离出的高温特征分量代表了原生剩磁分量 ,从而得到这一地区古生代至侏罗纪几个地质时代的古地磁极位置 ,补充了中国扬子地块古地磁极移曲线的基本数据 . 相似文献
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系统研究了河西走廊火烧沟组陆相红层200个采点岩石的热退磁行为和17个代表性样品的岩石磁学特征,结果表明有102个采点可以分离出A、B、C三个剩磁分量,有82个采点只有一个分量(C分量),16个采点只能分离出A、B分量.A、B分量分别由针铁矿和磁赤铁矿携带,C分量在砂岩中由磁铁矿携带,在泥质砂岩和泥岩中由磁铁矿和赤铁矿共同携带.A、B分量剩磁方向随机分布,不能获得置信水平的古地磁平均方向,为次生剩磁.它们的存在并不影响岩石原生剩磁的分离,也不影响原生剩磁信号的稳定性和获得的古地磁数据的可靠性.16个砂岩采点中不能分离出C分量,是由于后生的赤铁矿彻底改变了由磁铁矿携带的原生剩磁组分,在高密度采样的情况下剔除这些采点并不影响古地磁极性柱的构建和解释. 相似文献
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通过对滇西兰坪盆地白垩系地层的古地磁采样和室内退磁研究,揭示出一组高温特征分量,９５％正倒转检验和９９％置信度下的正褶皱检验,说明这组高温分量很可能代表岩石形成时的原生剩磁．对比国际标准地磁极性年表,发现南新组与阿尔比期、赛诺曼期和土仑期相当,而虎头寺组则相当于晚白垩世的三冬期和康尼阿克期．与中国东部的白垩纪古地磁数据比较．进一步证实了晚白垩世华南与印度支那地块存在明显的纬度差,这一事实说明了印度支那地块在印度板块与欧亚板块的碰撞及进一步挤压下,印度支那地块在早第三纪沿红河大断裂走滑千余公里,并伴随着１５ －２０ 的顺时针旋转． 相似文献
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塔里木盆地南缘中一新生代火山岩古地磁新结果 总被引：2，自引：0，他引：2
近年从塔里木盆地南缘获取的火山岩古地磁研究成果,古地磁资料表明,塔里木盆地南缘的构造格局基本定型于早更新世,并初步探讨了这些新资料的大地构造意义. 相似文献
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对山西交城早三叠世刘家沟组红色砂岩的岩石磁学和系统热退磁研究表明, 一方面高矫顽力的赤铁矿为高温特征剩磁载体. 另一方面, 绝大多数样品的系统热退磁表现为室温至100/200℃之间的粘滞剩磁和250~500℃之间的中温分量及500~680℃之间的高温分量. 中温分量在99%置信范围内有负褶皱检验结果, 且其地理坐标下的平均方向所对应的古地磁极位置在95%置信范围内与华北地块中晚侏罗世古地磁参考极一致, 表明其很可能为燕山期获得的重磁化分量. 高温分量具有双极性和c级分类倒转检验结果, 且在99%置信范围内通过了褶皱检验, 表明其最可能代表岩石形成时的特征剩磁. 高温分量所对应的古地磁极位置与前人在鄂尔多斯盆地早三叠世古地磁极之间的差异, 可能意味着山西交城地区在早三叠世之后相对于鄂尔多斯盆地发生了一定的局部旋转运动. 这一局部旋转运动很可能与作为山西与鄂尔多斯两个构造单元分界的离石大断裂和位于采样地区东南侧, 中新生代仍在活动的交城大断裂的活动有关. 相似文献
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本文是对秦岭丹凤县桃花铺郭家沟剖面和商县三十里铺剖面丹凤群蛇绿岩标本的古地磁学研究结果.逐步热退磁和剩磁方向主分量分析表明,60％以上的标本含有可明显区分的3个剩磁组分.另外的约30％-40％的标本,尽管它们具有很高的天然剩磁强度,在150-200℃时,其剩磁强度即衰减50％以上,且显示出不稳定的方向.两种不同的磁性表现与不同的岩石组成和结构有关,特别是与岩石的结晶程度有关.经对3个剩磁组分成因的分析及与变质变形关系的研究,表明高温剩磁组分是原生.由高温剩磁组分得到丹凤群古地磁极位置为43.0°N,274.5°E,古纬度值为12.0°S.比较丹凤群的古地磁极位置和华北扬子块体古地磁极移曲线,发现它们之间存在显著差异,这表明丹凤群在古生代不从属于华北或扬子块体,而是一个独立的地体,很可能是秦岭古洋壳的残片,从而给丹凤群蛇绿岩赋予新的大地构造含义. 相似文献
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Abstract Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90° clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminiferal zone of N.8: 16.6–15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40–50°) probably occurred at ca 15 Ma in association with the rapid rotation of Southwest Japan. The remainder (50-40°) continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems to have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate. 相似文献
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I. V. Golovanova K. N. Danukalov V. I. Kozlov V. N. Puchkov V. E. Pavlov Y. Gallet N. M. Levashova G. S. Sirota R. R. Khairullin M. L. Bazhenov 《Izvestiya Physics of the Solid Earth》2011,47(7):623-635
We have carried out paleomagnetic studies of the Upper Vendian sedimentary rocks from the Bashkirian Meganticlinorium (Southern
Ural). The rocks were sampled at three localities spread over more than 100 km. Totally, more than 300 samples were collected
from about 40 sampling sites. Stepwise thermal demagnetization up to 700°C revealed a stable component of magnetization of
either polarity in 25 sites. The fold test and the reversal test for this component are positive, which is usually regarded
as a sound argument in favor of the primary origin of magnetization. However, the Basu paleomagnetic pole (longitude 187.3°E,
latitude 1.1°N) is located near the Late Ordovician-Early Silurian segment of the apparent polar wander path for Baltica,
which might indicate a Paleozoic remagnetization of Vendian rocks. In this work we analyze different interpretations of the
obtained results and evaluate the reliability of the Late Riphean and Vendian paleomagnetic data for Baltica. 相似文献
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V. G. Bakhmutov V. Ya. Yevzerov V. V. Kolka 《Izvestiya Physics of the Solid Earth》2009,45(7):567-582
The genesis, varve, and paleomagnetic informativeness of glaciolacustrine sediments are considered based on paleomagnetic and lithological studies. The magnetic properties of varved clays from periglacial basins have been considered using the sedimentological model of formation of varved clays as products of glacial turbidity currents, which explains the differences in the magnetic characteristics and degree of paleomagnetic informativeness of these clays. The distal zone sediments (formed due to precipitation from glacial turbidity currents, suspension, and sometimes along the periphery of the proximal zone) are most successfully used to study secular variations. The possible errors of the secular variation records in varved clays and such errors in estimating annual bedding of these clays have been analyzed. It has been indicated that information about the composition, concentration, and magnetic fraction size should be completed with detailed lithological studies, which make it possible to reconstruct the character of clastic material income into a basin and to decipher a paleomagnetic record. An analysis of the magnetic susceptibility anisotropy parameters and the magnetization formation in a sediment makes it possible to take into account disturbances caused by the sedimentation process and, thereby, to detect a pure geomagnetic signal 相似文献
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选择伊朗中部、南部及西北部地区的近２０条晚元古代－早古生代完整地层剖面，系统采集Ｓｏｌｔａｎｉｅｈ组、Ｂａｒｕｔ组、Ｚａｉｇｕｎ组、Ｌａｌｕｎ组及Ｍｉｌａ组古地磁样品９６０件．经测试和对比获得结论：Ｓｏｌｔａｎｉｅｈ组记录的地磁极性带为反向，Ｂａｒｕｔ组－Ｌａｌｕｎ组为正向，Ｍｉｌａ组又为反向．此成果完全可与国际地质科学联合会（ＩＵＯＳ）１９８９年建立的全球地层极性柱中相应时代的极性带对比．计算得出５个地层组的古地磁南极位置．古地磁研究表明，晚元古代－早古生代伊朗全境均属稳定地块，处于赤道南侧约１６°的低纬度区．此期间似无大幅度转动和纬度变化． 相似文献
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Santiago Hincapié-Gómez Agustín Cardona Giovanny Jiménez Gaspar Monsalve León Ramírez-Hoyos Germán Bayona 《Studia Geophysica et Geodaetica》2018,62(3):485-511
The reconstruction of the tectonic evolution of the oceanic crust, including the recognition of ancient oceanic plumes and the differentiation between multiple and single oceanic arcs, relies on the paleogeographic analysis of accreted oceanic fragments found in orogenic belts. Here we present paleomagnetic and gravity data from Cretaceous oceanic basaltic and gabbroic rocks, the continental metamorphic basement, and their associated cover from northwestern Colombia. Based on regional scale tectonic reconstructions and geochemical constraints, such rocks have been interpreted as remnants of an oceanic large igneous province formed in southern latitudes, which was accreted to the sialic continental margin during the Late Cretaceous. Gravity analyses suggest the existence of a coherent high density segment separated by major suture zones from a lower density material related to the continental crust and/or thick sedimentary sequences trapped during collision. A characteristic paleomagnetic direction in Early and Late Cretaceous oceanic volcano-plutonic rocks, revealing a southeastern declination (D) and a negative inclination (I), may be interpreted in two different ways: (1a primary magnetization (tilt-corrected direction D = 130.3°, I = -23.3°, k = 23.4, α95 = 26.4°), suggesting clockwise rotation around 130°, and magnetization acquired in southern latitudes (range of 4°S to 21°S); or (2) a remagnetization event during a reverse interval of the Earth’s magnetic field in the Cenozoic (in situ direction D = 128.7°, I = -6.2°, k = 23.1, α95 = 26.1°), suggesting a counter-clockwise rotation around 50°. The first scenario seems more plausible, as it is consistent with previous paleomagnetic studies at other localities; it is compatible with a southern paleogeography for this block, and when integrated with other regional geological and paleomagnetic studies, supports a southern Pacific origin of a major oceanic block, formed as a part of a broader Cretaceous plateau that may have extended south or southwest of Galapagos. After its initial accretion, this block was subsequently fragmented due to the oblique SW-NE approach to the continental margin during the Late Cretaceous. 相似文献
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T.H TorsvikAuthor Vitae R Van der VooAuthor VitaeT.F RedfieldAuthor Vitae 《Earth and Planetary Science Letters》2002,202(2):185-200
The fixity of hotspots and mantle plume locations has long been axiomatic. If the assumption of fixed hotspots is granted, ‘absolute’ plate motions and movements of the spin axis with respect to the hotspot framework, defined by some as True Polar Wander (TPW), can be determined. However, this assumption can be tested by paleomagnetic data, and such tests are gradually raising some doubts about the fixity of hotspots. The result is that discrepancies between Cretaceous and Tertiary hotspot and paleomagnetic reference frames are now beginning to be interpreted as the result of plume drift within a convective mantle. In the Indo-Atlantic, hotspots have remained relatively stationary with respect to the spin axis for the last 95 million yr. However, the Pacific hotspots, notably Hawaii, appear to have undergone large-scale southward drift with respect to the spin axis during the Early Tertiary. Global paleomagnetic data do not indicate that any TPW occurred during the Late Cretaceous or Tertiary. Although the Early Cretaceous paleomagnetic and hotspot frames for the Indo-Atlantic realm can be interpreted as slow TPW, direct estimates of paleolatitude and hotspot motion, in particular the Kerguelen hotspot, challenge TPW as a global phenomenon. At present, we consider that the large Early Cretaceous discrepancy between hotspot and paleomagnetic data is best explained by southward drift of the Atlantic hotspots prior to ∼95 Ma. 相似文献
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Robert M. Negrini Kenneth L. Verosub Jonathan O. Davis 《Earth and Planetary Science Letters》1988,87(1-2)
A 400,000 year record of the paleomagnetic field has been acquired from 22 meters of middle to late Pleistocene fine-grained sediments from Summer Lake in south-central Oregon and Double Hot Springs in northwestern Nevada. The stratigraphy is based on 55 tephra layers, nine of which have been correlated with tephra layers from other localities on the basis of their distinct major- and trace-element geochemistry and their distinct petrography. The paleomagnetic samples carry a strong and stable magnetization that does not appear to have been affected by the inclination error commonly associated with the magnetization of sediments. The samples have accurately recorded the declination and inclination of the geomagnetic field at or near the time of deposition except for errors arising from rotations of discrete blocks of sediment predominantly about vertical axes. Errors introduced by this type of rotation were corrected by using paleomagnetic directions associated with correlated tephra layers. The Summer Lake paleomagnetic record suggests that secular variations occurred throughout the middle and late Pleistocene often maintaining the same waveform through several oscillations. The amplitudes of these variations were similar to those of Holocene variations, and the periods ranged from 15,000 years to greater than 100,000 years. 相似文献
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R. V. Veselovskiy A. A. Arzamastsev L. I. Demina A. V. Travin S. B. Botsyun 《Izvestiya Physics of the Solid Earth》2013,49(4):526-547
The new paleomagnetic data on forty dikes and two intrusive plutons of Devonian age located in different parts of the Kola Peninsula, which have not been previously covered by systematic paleomagnetic studies, are reported. We describe the results of the rock magnetic, petrographic, and microprobe investigations of the Devonian dikes and present their isotopic ages (40Ar/39Ar, stepwise heating). Within the studied area, almost all the Devonian dikes, metamorphic Archaean-Proterozoic complexes of the Fennoscandian Shield, and Proterozoic dikes have undergone low-temperature hydrothermal-metasomatic alteration, which resulted in the formation of new magnetic minerals with a secondary (chemical) component of magnetization. The comparison of the paleomagnetic poles indicates the Early Jurassic age of the secondary component. We suggest that regional remagnetization event was caused by endogenic activity genetically related to the formation of the Barents Sea trap province 200–170 Ma ago. On the basis of the obtained data, the preliminary Devonian paleomagnetic pole of the East European Platform is determined. 相似文献
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古地磁数据的可靠性问题,迄今已成为古地磁学进一步发展的关键所在。早在1964年Irving首次提出了数据可靠性的最低判据。当时绝大部分数据为天然剩磁测试结果（至1963年所搜集的554个数据中,经磁清洗的仅占12％）,因此,该判据强调一致性及野外检验。随着磁清洗技术的不断完善和广泛应用(1964-1970年新增的812个数据 相似文献