共查询到20条相似文献，搜索用时 93 毫秒
1.
《Acta Geochimica》2015,(2)
Mn-Zn ferrite powders were produced from low-grade manganese ore(LMO) via the chemical coprecipitation method combined with the ceramic method,after the LMO was leached in sulfuric acid and the obtained solution was purified.The effect of the pH on the magnetic properties of Mn-Zn ferrite was investigated by the varying pH of the co-precipitation system.The crystal structure and phases of the samples were characterized by X-ray diffraction and infrared spectrum,respectively.The magnetic measurements were carried out on a vibrating sample magnetometer.The optimal sample was obtained with a saturation magnetization of 55.02 emu/g,a coercivity of 8.20 G and a remanent magnetization of1.71 emu/g when pH is 7.5. 相似文献
2.
The REM(AF) method is a new tool for the analysis of the origin and alternating field demagnetization coercivity spectra of
the remanent magnetization. We applied this method on precambrian Gila diabase sheets from Arizona in order to identify the
high coercivity magnetic carrier, and on artificially shocked Rowley Regis basalt from UK in order to analyze the effect of
the shock on the natural remanent magnetization.
In the Gila diabase the high coercivity magnetic component was identified to be most likely represented by the acicular magnetite
(increase in the efficiency ratio in the high coercivity region).
In the Rowley Regis basalt, the REM(AF) analysis revealed that comparing to NRM, the shock produced a different distribution
of the AF demagnetization coercivity spectra due to the occurrence of the Shock Remanent Magnetization. 相似文献
3.
Tectonic rotations during the Chile Ridge collision and obduction of the Taitao ophiolite (southern Chile) 总被引：2，自引：0，他引：2
Abstract The < 6 Ma young Taitao ophiolite, exposed at the westernmost promontory of the Taitao Peninsula, is located approximately 40 km southeast of the Chile triple junction and consists of a complete sequence of oceanic lithosphere. Systematic sampling for paleomagnetic study was performed to understand the complex obduction processes of the ophiolite onto the forearc of the South American Plate. Two representative demagnetization paths of remanent magnetization vectors were observed. One is characterized by stable univectorial demagnetization paths and was observed in volcaniclastic rocks and dyke complexes. Orientations of their remanent magnetization vectors indicate various degrees of counterclockwise rotations. The other is characterized by multivectorial demagnetization paths and was observed in the plutonic units (gabbros and ultramafic rocks). From these, two distinct stable remanent magnetization vectors were isolated; one has high coercivity and the other has low coercivity along the demagnetization paths with little influence of viscous magnetizations. This suggests that the complex deformation history involved at least two rotational events. The clockwise rotation, inferred from high coercivity remanent magnetization vectors, was attributed to a ridge collision event and the counterclockwise rotation, inferred from the low coercivity remanent magnetization vectors, was attributed to an accommodation phase into the South American forearc during obduction and final emplacement of the ophiolite. Folds developed during this period. Paleomagnetic restorations of the internal structures of the plutonic units and dyke complexes suggest that they probably originated in a mid‐oceanic ridge environment near a transform fault. The counterclockwise rotation of the plutonic and dyke complex units during the obduction generated tectonic gaps between these and the basement. The volcaniclastic rocks must have been deposited at nearly their present location, filling the tectonic gaps, as less effect of tectonic rotation was identified on these rocks. 相似文献
4.
Bertha Aguilar Reyes Francisco Bautista Avto Goguitchaichvili Juan Julio Morales Contreras Julie Battu Patricia Quintana Owen Claire Carvallo 《Geofísica Internacional》2013,52(2):121-133
In this work, we investigate the correlation between some magnetic parameters and the level of contamination by heavy metals in urban soils from Morelia city, western Mexico. The magnetic study was carried out on 98 urban soils samples belonging to distinct land uses. Most of analyzed samples contain ferrimagnetic minerals as the responsible for magnetization, most probably corresponding to the titanomagnetites/ titanomaghemites solid solutions. This is inferred from the susceptibility vs. temperature measurements and the isothermal remanent magnetization (IRM) experiments. These measurements also indicate that most of samples are almost completely saturated before 300 mT. Additionally, the S-200 values (S-200 = IRM-200/ SIRM, where IRM-200= Back-field of 200 mT after magnetic saturation) are between 0.7 and 1.0, characteristic of low coercivity magnetic minerals. The averaged saturation isothermal remanent magnetization (SIRM) curves can be used as an indicator of pollution level, as these curves show different saturation values according to the level of contamination by heavy metals: Cu, Ni, Cr and Sr. These associations of (titano)magnetite with heavy metals were observed by Scanning Electron Microscope revealing some complex aggregates rather than commonly detected spherules. 相似文献
5.
K.A. Hoffman J.R. Baker S.K. Banerjee 《Physics of the Earth and Planetary Interiors》1979,20(2-4):317-323
A single-heating procedure is presented which makes possible the determination of two partially independent values of paleofield intensity for a given sample, one serving as a check to the other. The approach combines data required for Shaw-type and “ARM-method” determinations and in so doing furnishes a value of the ratio of TRM to ARM acquisition efficiency (f′) corrected for any physicochemical alteration to the magnetic carriers which may have occurred during laboratory heating.
Applicability of the Shaw-method to Fe-bearing samples is favorably demonstrated through simulated paleointensity determinations conducted on synthetic samples containing multi-domain grains. Moreover, coercivity spectra corresponding to anhysteretic remanent magnetization (ARM) are found to be considerably more sensitive to thermally induced alteration when compared with those corresponding to thermoremanent magnetization (TRM).
The combined Shaw-ARM procedure was successfully applied to lunar basalt sample 10017,135 rendering a paleointensity of 0.82 ± 0.11 Oe. The Thellier-Thellier method, however, was not able to provide a meaningful determination on the neighboring chip (number 136). These apparently conflicting findings may be explained by one or more of the following possible interpretations: (1) multiple step-wise heatings cause considerably more damage to the carriers of remanence than does a single-heating procedure; (2) the rock possesses extreme variability in magnetic properties from one sub-sample to the other; (3) the natural remanent magnetization in this lunar basalt is not a simple TRM. 相似文献
6.
7.
Bertha Aguilar Reyes Francisco Bautista Avto Goguitchaichvili Ofelia Morton 《Studia Geophysica et Geodaetica》2011,55(2):377-388
This paper focuses on the study of the correlation between magnetic parameters with the level of contamination by heavy metals
in urban soils. We report a magnetic investigation of urban soil samples from Merida, state of Yucatan, Southern Mexico. It
appears that most of our samples contain ferrimagnetic minerals as the magnetic carriers, probably coming from the titanomagnetites/titanomaghemites
series. This is inferred by the acquisition of isothermal remanent magnetization, which shows that most of samples are almost
completely saturated at about 200 mT. The S−200 value (factor characterizing stability of remanent magnetization) is between 0.8 and 1.0, characteristic of ferrimagnetic
minerals. The susceptibility vs. temperature measurements also point to some titanomaghemites and titanomagnetites as probable
responsible for magnetization. On the other hand, measurements of magnetic susceptibility at high and low frequencies helped
us to determine the high content of superparamagnetic grains in the majority of the samples, although not all of these showed
high values of magnetic susceptibility. We found that the most contaminated samples by Pb and Zn showed the higher saturation
isothermal remanent magnetization values, whereas the higher values in magnetic susceptibility correspond to samples contaminated
by Cr. Finally, we noted that a high level in Sr decreases the magnetic susceptibility. 相似文献
8.
《Physics of the Earth and Planetary Interiors》1992,70(3-4):194-200
Thermal remanent magnetization (TRM) and anhysteretic remanent magnetization (ARM) components were imposed on natural rock samples. The artificial laboratory components had different directions and the blocking temperature and/or coercivity spectra were overlapping. Two methods, principal component analysis (PCA) by Kirschvink and analytical modelling of demagnetization data (by Stupavsky and Symons, S&S) were used to resolve these components. The PCA technique calculated lines fitted to the demagnetization path with ASD = 10° (angular standard deviation), and the S&S method used four types of intensity decay curves for calculated components.
Both methods (PCA and S&S) resolved perfectly the one-component case. The two- or three-component case results strongly depended on spectra overlapping, and on the angles between component directions and magnetic minerals in samples. Principal component analysis gave more reliable results for separated spectra of TRM and thermally cleaned samples, whereas the S&S technique was more efficient for the case of strong spectra overlapping of ARM components and the alternative current field (AF) demagnetization method. Remarkable anisotropy of RM was observed which influences the results for the haematite-bearing samples. 相似文献
9.
单畴磁铁矿颗粒是地质样品中最重要的磁性载体,其稳定性一直备受关注.为了认识有机质对纳米级磁铁矿颗粒热稳定性的影响,本文对比研究了趋磁细菌AMB-1合成的单畴磁铁矿分别在全细胞中和经去胞提纯后的纯化磁小体中的热磁性质,以及热处理后样品的磁滞参数和低温磁性的变化.发现仅有磁小体膜包裹的纯化磁小体中单畴磁铁矿热稳定性极强,而全细胞中的单畴磁铁矿加热过程中发生了显著的热变化:磁铁矿在约270℃即开始转化,400℃以前几乎完全被有机质还原为顺磁性物质;同时在400℃以前,有机质的还原作用与有机质热分解引起磁小体链的坍塌,共同导致了样品矫顽力(Bc)、剩磁矫顽力(Bcr)和剩磁比(Mrs/Ms)的减小,以及矫顽力比(Bcr/Bc)的增加. 我们的实验结果清楚地表明,当地质样品中含有较多有机质组分并受热事件影响时,其中的单畴磁铁矿难以得到保存. 相似文献
10.
A. L. Piskarev Ch. Heunemann A. A. Makar’ev A. M. Makar’eva V. Bachtadse M. Aleksyutin 《Izvestiya Physics of the Solid Earth》2009,45(2):150-166
A combined study of magnetic parameters of basalt and andesite samples is performed in the framework of geological investigations of the Franz Josef Land at the paleomagnetic laboratory of Munich University. The study included the determination of the coercivity, saturation magnetization, Curie points, natural remanent magnetization (NRM), and magnetic susceptibility and the examination of ferromagnetic minerals with a microscope. Data on the chemical composition of rocks are obtained for all samples, and radiological ages are determined for the majority of rocks.Thermomagnetic curves of samples are subdivided into four types depending on the composition of ferromagnetic NRM carriers.The data obtained point to multiple changes in the predominant composition of igneous rocks. Each stage of magmatism is characterized by a specific type of the ferromagnetic component in the rocks and, therefore, magnetomineralogical investigations can be used for differentiation and correlation of the igneous rocks. 相似文献
11.
The remanent magnetization of ‘basement’ volcanics from Madeira define three different axes of magnetization, each having a dual-polarity build-up. The suggested oldest of these components, with declination 302 and inclination +4, is assigned to the late Lower Cretaceous and is thought to reflect the age of the early volcanism of the island. Subsequent magnetization overprints seem to have occurred in the Late Cretaceous/Early Tertiary (minor) and in Neogene times, respectively. The latter magnetization, which is strongly developed, was most likely impressed during the extensive volcanism that swept the island in post-Late Miocene. The palaeomagnetic evidence for a Cretaceous origin of Madeira is supported by the finding of Lower-Middle Cretaceous tuff layers in DSDP site 136 which is located only 160 km north of the island. The inferred palaeomagnetic structure of the ‘basement’ rocks of Madeira is similar to that found in the old volcanic complexes of other east central Atlantic islands. 相似文献
12.
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
13.
Carlos A. Vasquez Facundo F. Sapienza Agustín Somacal Sabrina Y. Fazzito 《Studia Geophysica et Geodaetica》2018,62(2):339-351
A phenomenological model based on a linear relationship between the magnetic coercivity field and the reciprocal of the grain diameter is applied to explain the anhysteretic remanent magnetization (ARM) imparted to artificial samples with different concentrations of a very well characterized magnetite powder. By analyses of scanning electron microscopy images, the spherically shaped single domain synthetic magnetite is found to follow a lognormal grain size distribution with ~86 nm of mean diameter. The proposed model, fitted to ARM measurements up to a peak alternating field of 100 mT, yields a very good agreement. The coercivity behaviour predicted by micromagnetism theory disagrees with the experimental results of this work. A likely explanation for the discrepancy is that the magnetite particles, which consist of a mixture of grains in coherent rotation and curling modes, produce similar observations as domain processes. 相似文献
14.
镇江大港下蜀黄土剖面多个层位的磁化率出现异常降低,导致与北方黄土的磁化率记录难以对比.为探讨磁化率异常降低的原因,我们在大港钻探ZK孔获取了岩芯.在10个具代表性的层位采样并测量了其等温剩磁获得曲线.通过基于期望最大化算法的计算程序（Irmunmix V2.2）,定量分析了样品的磁性矫顽力组分（magnetic coercivity component）.结果显示这10个样品可大致分成3类,第一类不含中磁组分,第二类含有较少的中磁组分,第三类则含较多的中磁组分.矫顽力组分的含量与样品中铁锰结核的含量密切相关.铁锰结核含量高的样品,中磁组分、硬磁组分含量也高,而软磁组分含量低,与此对应的是这类样品的磁化率低.表明在铁锰结核的形成过程中,原始的软磁组分被溶解,而产生新的中磁组分、硬磁组分,这个次生变化过程导致样品磁化率异常降低.铁锰结核含量高的样品,经历过较强的还原作用,因此ZK剖面磁化率异常降低是还原作用的结果,可能是某时期降水量增大所致. 相似文献
15.
S. K. Gribov A. V. Dolotov V. P. Shcherbakov 《Izvestiya Physics of the Solid Earth》2017,53(2):274-292
The results of the experimental studies on creating chemical and partial thermal remanent magnetizations (or their combination), which are imparted at the initial stage of the laboratory process of the oxidation of primary magmatic titanomagnetites (Tmts) contained in the rock, are presented. For creating chemical remanent magnetization, the samples of recently erupted Kamchatka basalts were subjected to 200-h annealing in air in the temperature interval from 400 to 500°С under the action of the magnetic field on the order of the Earth’s magnetic field. After creation of this magnetization, the laboratory modeling of the Thellier–Coe and Wilson–Burakov paleointensity determination procedures was conducted on these samples. It is shown that when the primary magnetization is chemical, created at the initial stage of oxidation, and the paleointensity determined by these techniques is underestimated by 15–20% relative to its true values. 相似文献
16.
M. A. Irurzun C. S. G. Gogorza A. M. Sinito M. A. E. Chaparro H. Nuñez J. M. Lirio 《Studia Geophysica et Geodaetica》2008,52(2):157-172
We present results of paleomagnetic and sedimentological studies carried out on three cores Lmor1, Lmo98-1, Lmor98-2 from
bottom sediments of Lake Moreno (south-western Argentina), and integrate them with data from our previous studies. Measurements
of directions (declination D and inclination I) and mass specific intensity of natural remanent magnetization (NRM intensity),
magnetic susceptibility (specific, χ and volumetric, κ), isothermal remanent magnetization (IRM), saturation of isothermal
remanent magnetization (SIRM), and back field remanent coercivity (B0CR) were performed. The stability of the NRM was investigated using alternating-field demagnetization. The results show that
these sediments meet the criteria required to construct a reliable paleomagnetic record. The cores were correlated very well
based on magnetic parameters, such as χ and NRM intensity, as well as with lithological features. Tephra layers were identified
from the lithological profiles and magnetic susceptibility logs. We obtained the D and I logs of the characteristic remanent
magnetization for the cores as a function of shortened depth. The data from the three cores were combined to form a composite
record using the Fisher method. A comparison between stacked inclination and declination records of Lake Moreno and those
obtained in previous works on Lake Escondido and Lake El Trébol shows good agreement. This agreement made it possible to transform
the stacked curves into time series spanning the interval 12–20 kyr. The results obtained improved our knowledge of SV and
the behaviour of the geomagnetic field and also allowed us to determine the range of past inclination variations from −70°
to −45° for the southern hemisphere, where data are scarce. 相似文献
17.
Marta Chlupá?ová Franti?ek Hrouda Daniel Ni?ňansky Václav Procházka Zdeňka Petáková Franti?ek Laufek 《Studia Geophysica et Geodaetica》2012,56(3):803-825
Frequency-dependent magnetic susceptibility, its anisotropy (AMS), its temperature variation, natural remanent magnetization and time-dependent isothermal remanent magnetization as well as M?ssbauer spectroscopy of a small collection of Celtic and Mediaeval graphitic pottery from Southern Bohemia were investigated. The mineral composition of the pottery is dominated by fragments of quartz, accompanied mainly by various silicates from granitoids and paragneisses, or by calcite, within the plastic component being probably illite but also graphite. No ferrimagnetic minerals were found in optical microscope, among Fe-oxides only limonite was observed, even though the bulk susceptibility of the pottery varies in the orders of 10?4 to 10?2 [SI]. This may indicate presence of ferromagnetic particles in the ultrafine (superparamagnetic, SP) state, which is confirmed by frequency-dependent susceptibility ranging from 3% to almost 16%. The low temperature susceptibility vs. temperature curves are only moderately sloped, showing the Verwey transition only in one case. The high temperature curves mostly show presence of two magnetic phases, maghemite and magnetite. Cooling curves show distinctly lower susceptibilities than the heating curves indicating instability of the assemblage of ferrimagnetic minerals, particularly in temperatures slightly under 700 °C. M?ssbauer spectroscopy confirmed the results of the frequency-dependent susceptibility, showing the increase of ferrimagnetic sextets in the spectra measured at 4.2K, likely indicating maghemite as the distinct ferrimagnetic phase. The frequency-dependent AMS indicates preferred orientation of SP1,16 particles, coaxiality between SP1,16 grain AMS and whole specimen AMS indicate that all grains, ultrafine and coarser ones, were oriented by the same process, i.e. copying the pottery structure created during wheel-turning. 相似文献
18.
Tsutomu Sueishi Takaharu Sato Naoto Kawai Kazuo Kobayashi 《Physics of the Earth and Planetary Interiors》1979,19(1):1-11
Two short geomagnetic episodes in the middle Matuyama epoch have been identified within thin (4.3-mm) sections of two deep-sea calcareous sediment cores taken in the western equatorial Pacific. Both cores are correlated by magnetostratigraphic and micropaleontological methods. Magnetic stability and paleomagnetic reliability are tested by alternating field demagnetization of natural remanent magnetization as well as by the ratios of intensities of anhysteretic remanent magnetization to those of saturation isothermal remanent magnetization. One episode is dated to be 1.06 m.y. BP. The other is identified to be about 1.94 m.y. BP, which is presumably in agreement with the Reunion event. Both episodes seem to be accompanied by conspicuous drops in field intensity. Possible correlation of field intensity with biological productivity in the ocean is also postulated from the present paleomagnetic results. 相似文献
19.
Ruth Thomas 《Surveys in Geophysics》1983,5(4):381-393
Most of the traditional methods of determining the intensity of the ancient geomagnetic field from archaeological materials utilized thermal demagnetization of the natural remanent magnetization (NRM) and of the laboratory induced thermoremanent magnetization (TRM). When applied rigorously these methods are foolproof. They are, however, very time consuming and the number of samples with which they can be used is limited. Attempts to speed up these traditional methods have generally led to the use of subjective criteria in assessing the reliability of the results and archaeomagnetic research has recently been concentrated on extending the range of samples to which the method can be applied. Through the use of alternating field, rather than thermal, demagnetization of NRM and TRM it has become possible to apply corrections for alteration occurring during laboratory firing of the archaeological samples and develop objective criteria of reliability. Recent research has shown that it may be possible to determine archaeointensities the laboratory redeposition of lake sediments. 相似文献
20.
我国西北地区出露大量富含哺乳动物化石的"第三纪红层",探明这些地层的岩石磁学特征对进一步开展磁性地层、环境磁学和古气候学研究具有重要意义.本文对青藏高原东北缘兰州盆地渐新世地层进行了详细的岩石磁学研究,分别确定了咸水河组下部砂岩和泥岩中磁性矿物含量、种类及其在加热过程中的转变;并结合X射线衍射,漫反射光谱和粒度分析等非磁学手段,揭示了磁性矿物种类与沉积环境的关系.结果表明,剖面底部和顶部的砂岩为河道沉积,磁性矿物含量较低,主要为高矫顽力的赤铁矿和针铁矿;中部泥岩为湖相沉积,指示了一个相对稳定的静水沉积环境,其磁性矿物含量比砂岩要高,不仅含有高矫顽力的赤铁矿和针铁矿,也含有低矫顽力的磁铁矿.在岩石磁学和环境磁学结果的基础上,结合野外考察和古生物证据,我们推测兰州盆地在晚渐新世为半湿润半干旱的气候条件,这为赤铁矿的生成提供了有利条件,导致盆地中富含赤铁矿的红色泥岩广泛发育. 相似文献