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1.
本文报道塔里木地块阿克苏—柯坪—巴楚地区奥陶纪古地磁研究新结果.对采自44个采点的灰岩、泥灰岩及泥质砂岩样品的系统岩石磁学和古地磁学研究表明,所有样品可分成两组：第一类样品以赤铁矿和少量磁铁矿为主要载磁矿物,该类样品通常可分离出特征剩磁组分A;第二类样品以磁铁矿为主要载磁矿物,系统退磁揭示出这类样品中存在特征剩磁组分B.特征剩磁组分A分布于绝大多数奥陶纪样品中,具有双极性,但褶皱检验结果为负,推测其可能为新生代重磁化.特征剩磁组分B仅能从少部分中晚奥陶世样品中分离出,但褶皱检验结果为正,且其所对应古地磁极位置（40.7°S,183.3°E,dp/dm=4.8°/6.9°）与塔里木地块古生代中期以来的古地磁极位置显著差别,表明其很可能为岩石形成时期所获得的原生剩磁.古地磁结果表明塔里木地块中晚奥陶世位于南半球中低纬度地区,很可能与扬子地块一起位于冈瓦纳古大陆的边缘;中晚奥陶世之后,塔里木地块通过大幅度北向漂移和顺时针旋转,逐步与冈瓦纳大陆分离、并越过古赤道;至晚石炭世,塔里木地块已到达古亚洲洋构造域的南缘. 相似文献
2.
通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质. 相似文献
3.
通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质. 相似文献
4.
重磁化碳酸盐岩中磁性矿物相变特征分析 总被引：3，自引：0，他引：3
通过光学显微镜鉴定和电子探针元素特征X射线像分析与化学成分定量分析 ,对已进行过岩石磁学实验研究的 10个华北地块早古生界重磁化碳酸盐岩样品进行了磁性矿物相变特征分析 .在部分样品中发现了通过交代黄铁矿形成的、不含Ti的次生磁铁矿 ,它们可能就是重磁化剩磁的主要携磁矿物 .在其中 4个样品所含的磁铁矿中还发现了黄铁矿交代残余 ,这为确认磁性矿物相变现象提供了有力的证据 ,并为如何识别与重磁化相关的次生磁铁矿提供了鉴别标志 .在此基础上 ,进一步探讨了重磁化的形成机制 相似文献
5.
拉萨地块是研究班公湖—怒江特提斯洋和雅鲁藏布江特提斯洋演化过程的关键,但印度—亚洲大陆的碰撞可能导致拉萨地块遭受不同程度的重磁化影响,为寻找理想地层进行古地磁研究,本文对拉萨地块中二叠世洛巴堆组砂岩、火山岩及灰岩样品进行详细的岩石磁学研究,以确定各类岩石是否具备记录原生剩磁信息的能力．结果表明砂岩样品中主要载磁矿物为磁黄铁矿,火山岩及灰岩样品中主要为磁铁矿或赤铁矿．结合区域地质资料和部分样品退磁实验,本文认为砂岩样品可能遭受林子宗群火山和岩浆活动所提供的区域热扰动影响,记录了古近系重磁化信息;火山岩和灰岩样品可能记录了岩石形成时期的原生剩磁信息,有望从中获得可靠古地磁数据． 相似文献
6.
四川旺苍早三叠世古地磁学结果及其大地构造学意义 总被引：4，自引：0，他引：4
对四川北部旺苍地区(32.14°106.17°)早三叠世地层进行了古地磁学和岩石磁学研究,其结果表明剩磁载磁矿物主要为磁铁矿,另有少量赤铁矿.采样地层岩石高温剩磁分量(D=45.1°,I=18.0°,a_(95)5. 9°),通过褶皱及倒转检验,表明认岩石中获得的高温分量为原生分量.由原生分量求得扬子地块早三叠世虚地磁极为:42.5°N,214.6°E(d_(p)=3.2,d_m=6.1),古纬度为9.2°.认为,华北与扬子地块在自早三叠世期间已基本拼合,现有古地磁结果支持秦岭造山带为陆内造山作用的结果 相似文献
7.
本文对四川北部旺苍-南江地区晚侏罗世蓬莱镇组进行了较为详细的岩石磁学和古地磁学研究．逐步热退磁揭示出蓬莱镇组岩石所携带的剩磁由两个分量组成,其中低温组分（次生剩磁）的解阻温度低于420℃;高温组分（特征分量）可通过褶皱及倒转检验,由此求得磁偏角和磁倾角分别为18．4°和29．3°（构造校正后）,95％置信回（α95）为8．5°,对应的古地磁极经纬度分别为236．4°E和66．6°N．基于古地磁结果,并结合已有的地质证据,提出根据古地磁学确定的扬子地块晚侏罗世古纬度偏低的原因可能是由真极移造成的． 相似文献
8.
扬子地块中寒武世古地磁新结果 总被引：8，自引：0，他引：8
对采自四川北部旺苍-南江地区(32.14°N,106.17°E)中寒武世陡坡寺组12个采点的120块定向标本进行的系统岩石磁学和古地磁学研究表明:紫红色细砂岩的剩磁方向表现为单分量(D=29.3°, I=-19.4°,k=283.7,α95=7.3°),所对应的古地磁极位置(39.5°N,247.3°E,置信椭圆为:dp=4.0°,dm=7.6°)与扬子地块晚二叠世极位置基本重合.红色泥岩的剩磁方向由两个组分携带,其中低温剩磁分量在地理坐标下与现代地磁场方向基本一致;高温剩磁分量(D=129.1°, I=23.6°,k=44.6,α95=7.8°)可通过褶皱检验,对应的古地磁极位置为39.5°S,185.1°E,(置信椭圆为:dp=4.4°,dm=8.3°),我们认为扬子地块在中寒武世处在南半球低纬度地区. 相似文献
9.
华北盆地南缘早古生代岩石系统的岩石磁学研究表明,其岩石中的磁性矿物组合相当复杂,重磁化时代可分为晚二叠/早三叠世和早、晚白垩世2个大的阶段.焦作剖面具有原生剩磁和次生剩磁岩石共生的特征,以及细致的岩石磁学分析表明,未重磁化和重磁化岩石两者间磁铁矿颗粒度大小存在明显区别,这暗示了热粘滞剩磁是重磁化的重要原因之一,而济源和登封剖面不仅岩石遭受完全的重磁化,而且广泛发育早白垩时期形成的磁黄铁矿,磁黄铁矿形成则暗示着造山热液的渗透作用. 相似文献
10.
泥盆纪时期各板块的古地理重建缺乏可靠古地磁数据,以至于古特提斯洋在泥盆纪的演化过程存在争议,而高质量的古地磁数据定量限定板块的古纬度位置是解决上述问题的关键.本文对北羌塘地块早泥盆世平沙沟组灰岩进行了古地磁学研究,提供了一个较为可靠的古地磁数据.镜下观察及岩石磁学实验结果表明平沙沟组灰岩样品中的主要载磁矿物为磁铁矿和赤铁矿,并且没有重磁化的特征.系统热退磁与混合退磁实验结果表明,样品的天然剩磁强度较低,从54块样品中获得了较为集中的特征剩磁分量,在样品水平下的平均方向为Dg=358.5°,Ig=22.8°,kg=17.7,α95=4.6°,Ds=8.8°,Is=-0.9°,ks=18.1,α95=4.5°,通过了C级倒转检验,对应的古地磁极为λp=54.8°N,φp=251.2°E,(dp/dm=2.3°/4.5°),这一极位置与石炭纪以来可靠的古地磁极位置存在差异,很... 相似文献
11.
Belén Oliva-Urcia Emilio L. Pueyo Juan C. Larrasoaña 《Earth and Planetary Science Letters》2008,265(3-4):525-534
New paleomagnetic analyses of Triassic, Cretaceous and Eocene strata in the south-central Pyrenees show evidence for a widespread remagnetization, located along the southern border of the Axial Zone, the Internal Sierras, and the northern part of the Jaca-Pamplona basin. This remagnetization, always reversed in polarity, was acquired after an extensive period of Late Eocene–Early Oligocene folding and tilting in the area, and affects limestones, sandstones, marls and red beds. In addition, a characteristic prefolding component was identified in 30% of Upper Cretaceous and Triassic red beds. These results, together with a revaluation of previously published paleomagnetic data from the central Pyrenees, indicate that the spatial distribution of the postfolding remagnetization coincides with that of a domain of pressure solution cleavage. A relationship between the intensity of the remagnetization and the characteristic (prefolding component) with respect to the density of cleavage surfaces, leads us to propose a mechanism for the remagnetization related to the development of pressure solution cleavage that is framed within the tectonic evolution of the central Pyrenees. Partial dissolution of rock under tectonic compression leads to the liberation and subsequent accumulation of insoluble minerals in cleavage planes. Magnetic grains are part of the relatively insoluble residue, and they reorient in the presence of the ambient field after they are freed during dissolution of the rock matrix. Chemical reequilibrium (dissolution and/or neoformation of magnetic carriers) during this process cannot be excluded. The remagnetization mechanism we propose can help to explain widespread remagnetizations in low to moderately deformed rocks without the need of large-scale migration of orogenic fluids. 相似文献
12.
The opinions vary on the secondary remagnetization mechanisms of carbonate rocks. The prevalent interpretations of magnetic remanences are either chemical in origin that invoked the large-scale migration of orogenic fluids. or thermoviscous magnetization involved burial diagenetic processes. The paleomagnetic study carried out in northwestern part of Henan Province (north of the Qinling orogenic belt) reveals that 90% of carbonate rocks have suffered from the secondary remagnetization. On the basis of rock magnetic experiments, the assemblage of the magnetic minerals, remanent carriers and its formation process, and the possible mechanisms of remagnetization in these carbonate rocks are discussed. 相似文献
13.
14.
R. V. Veselovskiy A. A. Arzamastsev V. A. Tselmovich A. M. Fetisova E. P. Kulakova 《Izvestiya Physics of the Solid Earth》2017,53(6):898-907
Based on the results of the preliminary paleomagnetic investigation of 57 Precambrian dikes of the Kola Peninsula, in 31 of them a stable monopolar component of natural remanent magnetization (NRM) is revealed (D = 353.2°, I = 53.0°, K = 58, and α95 = 3.4°). The peculiarities of the distribution of this magnetization component within the Kola Peninsula and the rock magnetic characteristics of the dikes in which this component is isolated suggest its secondary nature and relate the mechanism and formation time to the remagnetization processes which took place in the northwest of Fennoscandia about 1.8 billion years ago during the Svecofennian orogeny. The corresponding geomagnetic pole of Fennoscandia has the coordinates Plat = 54.5°, Plong = 224.0°, and A95 = 3.9° and is located in the immediate vicinity of the known Paleoproterozoic (1.9–1.7 Ga) poles of Baltica (Khramov et al., 1997; Veikkolainen et al., 2014). 相似文献
15.
Marta Neres Pedro F. Silva Moha Ikenne Sofia Martins Ahmid Hafid João Mata Francisco Almeida Nasrrddine Youbi Moulay A. Boumehdi 《Studia Geophysica et Geodaetica》2016,60(4):700-730
No paleomagnetic data exist for Paleo-Mesoproterozoic times of the West African Craton (WAC). Therefore, paleogeographic reconstructions for such old geological times are difficult to constrain. Gaps on the sedimentary record and intense remagnetizations are the major problems that paleomagnetic studies come across. Recent geochronological results for dyke swarms that intrude several Proterozoic inliers of WAC in the Anti-Atlas Belt (southern Morocco) revealed ages between Paleoproterozoic and early Neoproterozoic, opening for the first time a window of opportunity to conduct paleomagnetic studies and tentatively infer about the paleoposition of WAC during Proterozoic. On this scope we conducted a paleomagnetic study on seven Proterozoic dykes of the Iguerda inlier. The meaning of the obtained paleomagnetic directions was evaluated by rock magnetic and mineral analyses, complemented by petrographic observations. Our samples record the presence of a complex history of remagnetization, mostly assigned to several Phanerozoic thermal/chemical events, in particular to the late stages of Pan African orogeny (s.l.), to the Late Carboniferous Variscan orogeny, and even to more recent events. The recognized remagnetization processes are related to widespread metamorphic events under greenschist facies followed by low-temperature oxidation, both responsible for the formation of new magnetic phases, like magnetite and hematite. These events obliterated the primary (magmatic) thermo-remanent magnetization and promoted multiple remagnetizations of the dykes, thermally and chemically. For only one dyke the presence of primary magnetization is possible to infer, though not to confirm, and would place WAC at an equatorial position around 1750 Ma. 相似文献
16.
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
17.
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
18.
Although paleomagnetic study of the Early Paleozoic for the North China Block (NCB) has witnessed rapid progress since the 1980s, significant difference in the results can be found from the widespread areas in North China. Besides the paleomagnetic techniques used in the laboratories, the difference of these Paleozoic poles could also be due to the early and late Mesozoic remagnetization in the eastern part of China. It is therefore necessary to carry out systematic paleomagnetic and rock magnetic studies for the Early Paleozoic rocks in the NCB. The remagnetizarion re-sults from the northwestern part of Henan Province are reported, and related geological implications are discussed. 相似文献
19.
为研究四川攀西（攀枝花-西昌）地区大陆演化,在该区及邻区采集了中生代岩石标本。用热退磁和交变场退磁方法对59个采点的619块样品做了磁清洗处理。古地磁结果满足褶皱检验,对精度参数K小于10的采点或有后期重磁化的样品未纳入统计处理。 古地磁结果表明,攀西断隆、凉山断陷、断凹属扬子地块的西缘,早三叠世时位于北纬13°左右,至今北移了千余公里,上三叠纪后北移速度明显减慢;其西邻盐源断陷自早三叠世以来南移数百公里,无论古纬度或古方位与东邻地块的结果有较明显差异。 相似文献