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1.
Summary A magnetic study of metabasic dykes of pre-Cambrian age in Gomoh has been done. 9 magnetic profiles have been taken with Schmidt vertical force variometer. Direction and intensity of NRM have been determined for 25 oriented samples with an astatic magnetometer. Magnetic susceptibility of the samples has been determined. The magnetic profiles have been interpreted by considering both natural remanence and susceptibility of the rock samples. The remanent magnetic directions have two groups, one corresponding to the northern hemisphere and the other to the southern hemisphere. The corresponding latitudes of the place would then be 34°N and 42°S. It is suggested here that metamorphism of the basic rocks of this area took place during two distinct geologic epochs, one when India was in northern hemisphere and the other when in southern hemisphere, presuming that continental drift has taken place. 相似文献
2.
在磁化磁场为恒定磁场（无定向磁力仪─-Ａ）与１０ｋＨｚ交变磁场（ＭｉｎｉｓｅＰ旋转磁力仪─-Ｍ）的两种情况下，作岩样比测时发现，后者测得的主磁化率值кＭ较小，而且沿磁性叶理面方向ｆ的主磁化率值кｍａｘ与кｉｎｔ比沿其法线方向ｎ上的кｉｎｔ减少得更多．作者以涡流磁滞机构对磁性载体材料的“磁屏蔽”作用发生了各向异性的影响来解释此现象；并推测磁化率各向异性存在频散现象． 相似文献
3.
Mike Jackson 《Pure and Applied Geophysics》1991,136(1):1-28
The magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low-field magnetic susceptibility (AMS). However, alternative methods based on remanent magnetization (measured in the absence of a magnetic field) rather than induced magnetization (measured in the applied field) have distinct advantages for certain geological applications. This is particularly true for; (1) adjunct studies in paleomagnetism, in order to assess the fidelity with which a natural remanence records the paleofield orientation; (2) studies of weakly magnetic or weakly deformed rocks, for which susceptibility anisotropy is very difficult to measure precisely; and (3) quantitative applications such as strain estimation. The fundamental differences between susceptibility and remanence (and their respective anisotropies) are due to several factors: (1) susceptibility arises from all of the minerals present in a sample, whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals; (2) ferromagnetic minerals are generally more anisotropic than para- and diamagnetic minerals; (3) for ferromagnetic minerals, remanence is inevitably more anisotropic than susceptibility; and (4) a number of common minerals, including single-domain magnetites, possess an inverse anisotropy of susceptibility, i.e., they tend to have minimum susceptibility parallel to the long axis of an individual particle; remanence is immune to this phenomenon. As a consequence of all these factors, remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample.Contribution number 9102 of the Institute for Rock Magnetism, University of Minnesota. 相似文献
4.
Magnetostatic interaction between a single magnetized particle and a surrounding shell of ulvöspinel
R.J. Veitch 《Physics of the Earth and Planetary Interiors》1980,23(3):215-221
The magnetic moment of a sample, consisting of a spherical ulvöspinel shell and one of several magnetic inclusions, has been measured below the ulvöspinel Curie point. The sample could be dismantled at low temperatures and the moment of the shell measured separately. Adequate agreement between these results and remanence measurements on pieces of ulvöspinel is found if some assumptions are made about local interactions inside the material. 相似文献
5.
陕西交道全新世黄土-黑垆土磁化率的CBD研究 总被引：16，自引：7，他引：9
根据黄士高原中部交道剖面全新世黄土－黑垆土剖面的非磁滞磁化率和ＣＢＤ提取前后的磁化率、频率磁化率以及热磁分析结果,分析了磁性矿物的种类和磁畴状态,讨论了古土壤的磁化率增强,指出ＣＢＤ技术强有力的支持古土壤磁化率增强的土壤成因观点．虽然ＣＢＤ能非常有效地溶解土壤成因的磁赤铁矿,但并不是完全选择性地溶解土壤成因的磁铁矿颗粒．此外,通过对样品ＣＢＤ处理前后磁化率数据的分析,从土壤化学角度为黄土的风成说提供了新证据。 相似文献
6.
The advent of cryogenic magnetometers with which remanence can be measured at high sensitivity statically permits continuous thermal demagnetization and, in principle, a continuous version of the classic stepwise method of intensity determination. In the technique we have initially tried a field is trapped in the superconducting shield of the magnetometer throughout the experiment. The sample is then thermally cycled over progressively higher temperature ranges so that the incremental acquisition of partial thermoremanence (PTRM) and loss of the natural remanence (NRM) of the sample can be compared. In control experiments we have found that bad intensity estimates arise because the presence of the field causes difficulty in reliable separation of remanent and induced moments. A better approach is to heat and cool the sample in the required fields outside of the magnetometer and to insert it into the magnetometer only for the measurement of remanence. In this way it will be possible to cycle the sample to progressively higher temperatures and measure at elevated temperatures without cooling to room temperature, but one will measure remanence directly in zero field. 相似文献
7.
Débora C. Marié Marcos A. E. Chaparro Claudia S. G. Gogorza Ana Navas Ana M. Sinito 《Studia Geophysica et Geodaetica》2010,54(1):135-152
In this work, we carried out a preliminary study of traffic-derived pollutants from primary sources (vehicles), and on roads
(paved area), road borders and surroundings areas. The study is focussed on the identification, distribution and concentration
of pollutants and magnetic carriers. Magnetic parameters and their analyses suggest that the magnetic signal of vehicle-derived
emissions is controlled by a magnetite-like phase. Magnetic grain size estimations reveal the presence of fine particles (0.1–5
μm) that can be inhaled and therefore are dangerous to human health. Magnetic susceptibility results (about 175 × 10−5 SI) show a higher magnetic concentration — magnetic enhancement — in the central area of the tollbooth line that is related
to higher traffic. In addition, magnetic susceptibility was computed on several roadside soils along a length of 120 km and
used to generate a 2-D contour map, which shows higher magnetic values (100–200 10−5 SI) near the edge of the road. The observed distribution of magnetic values indicates that magnetic particles emitted by
vehicles are accumulated and mainly concentrated within a distance of several meters (1–2 m) from the edge of the road. In
consequence, the magnetic susceptibility parameter seems to be a suitable indicator of traffic-related pollution. Non-magnetic
studies show an enrichment of some trace elements, such as Ba, Cr, Cu, Zn and Pb, that are associated with traffic pollution.
Furthermore, statistical correlations between the content of toxic trace metals and magnetic variables support the use of
magnetic parameters as potential proxies for traffic-related pollution in this study area. 相似文献
8.
Summary The dolerite dyke of post-lower Gondwana age reported earlier by the authors [5]2) has been taken for detailed magnetic study. Seven magnetic traverses have been taken across the dyke using Schmidt vertical force variometer. Negative anomalies varying from 1400 to 2200 gammas have been observed. Magnetic susceptibility of samples from the dyke has been determined on both cores and crushed material, using the Model MS-3 susceptibility bridge. The average susceptibility of 20 samples has been found to be 1930x10–6 C.G.S. units. Direction and intensity of remanence on 10 oriented samples have been determined by an Astatic magnetometer. The average intensity of remanence has been found to be 3.13x10–3 C.G.S. units and the average direction has a declination of 323° and inclination-68° (up dip). The Koenigsberger ratio varies from 1.6 to 5.6. The high negative magnetic anomalies have been explained in terms of remance-that more than 80% of the anomaly is due to remance and that negative anomalies are due to negative inclination of remanent direction of the rocks. The magnetic direction for the dyke gave the position for Dhanbad as 51° south latitude in Jurassic period. This is in conformity with the deductions made by other workers from the palaeomagnetic studies of the Deccan and Rajmahal traps. The virtual geomagnetic pole in Jurassic period as deduced from the palaeomagnetism of the dyke has a position of latitude 8 1/2°N and longitude 71°W, in the southern Carribean. On palaeomagnetic evidence this dyke has been correlated with Rajmahal traps of eastern Bihar. 相似文献
9.
The KLY-4S Kappabridge and KLF-4A Magnetic Susceptibility Meter enable automated measurement of susceptibility variation with
field in the ranges of 2–450 A/m and 5–300 A/m (in effective values), respectively. Unfortunately, the measurement accuracy
decreases with decreasing field and it is not easy to decide whether the susceptibility variation at the lowest fields is
natural phenomenon or results from measuring errors. To overcome this problem, the accuracies of both the above instruments
were investigated experimentally using artificial specimens (mixture of pure magnetite and plaster of Paris) with variable
susceptibilities ranging from 1 × 10−5 to 5 × 10−2. The complete curve of the field variation of susceptibility of each specimen was measured 10 times and the relative error
was calculated for each field.
In the KLY-4S Kappabridge, in specimens with susceptibilities higher than 100 × 10−6, the relative errors are lower than 3% in all fields and lower than 1% in the fields stronger than 10 A/m. In the KLF-4A
Magnetic Susceptibility Meter, in relatively strongly magnetic specimens with susceptibilities 5 × 10−4 to 5 × 10−2, the relative error is less than 1.5% in the entire field range. While the former instrument is convenient for investigating
almost all rock types, the latter instrument is convenient for measuring moderately and strongly magnetic specimens.
To facilitate work with field variation of susceptibility curves, showing variable accuracies with field, the programme FieldVar
was written. One of its options is plotting the measured data with corresponding field-variable error bars. In this way, a
tool is offered for interpreting such susceptibility changes that are sound and reasonable from the point of view of measuring
accuracy. 相似文献
10.
结合岩石磁学、磁化率各向异性度与区域构造分析了西秦岭温泉岩体的侵位机制及意义.温泉岩体的样品的平均磁化率km值总体很大,岩石磁学表明对于磁化率较低的样品,顺磁性矿物（如黑云母等）对磁化率的贡献较大,而少量铁磁性矿物（如磁铁矿等）可能作为剩磁载体.对于磁化率较高的样品,其主要载磁矿物为磁铁矿;花岗岩样品的校正磁化率各向异性度PJ总体小于1.2,显示了岩体为流动磁组构的特征,磁化率椭球体形态参数T总体大于0,扁率E总体大于1,以压扁椭球体为主;岩体的磁面理同磁线理相比更为发育,样品的磁面理普遍表现出围绕岩体边界分布的特点,且倾角较陡;而在岩体内部磁线理与磁面理分布相对散乱,定向性差,这一特征说明温泉岩体的磁组构主要由侵位时的侧向挤压作用形成的;虽然岩体的磁组构特征总体显示了N-NEE和SW向的挤压作用,但岩体侵位时由商丹缝合带闭合所产生的垂直于缝合带方向的挤压作用已相对较弱.本文认为,温泉岩体侵位时是一种弱挤压环境,或者是一种相对稳定的环境甚至可能是一种相对引张的背景,这与温泉岩体形成于后碰撞环境,秦岭造山带已演化至后碰撞拆沉作用发生的伸展阶段所反映的区域构造背景是一致的. 相似文献
11.
C. Aubourg J.P. Pozzi D. Janots L. Sahraoui 《Earth and Planetary Science Letters》2008,272(1-2):172-180
Thermal effects related to burial and hydrothermal alteration leads to chemical remanent magnetization (CRM). We present an experimental study of CRM production by heating claystones at 95 °C. A vertical magnetic field of 2 mT was applied to the claystones during heating and the evolution of the remanence during heating in air is monitored intermittently for up to four months. Solid fragments (9 to 26 g) of claystones are included in a Teflon holder that is placed in the oven under a controlled atmosphere. Newly formed grains acquire a CRM and a thermoviscous magnetization (TVRM), both being parallel to the applied magnetic field. CRM is related to the amount of newly formed grains that pass the critical volume during the reaction. To measure the acquired remanence, the claystones are first cooled in a zero magnetic field and then measured using a 2G SQUID magnetometer.In the frame of the research programme on the feasibility of radioactive waste disposal in a deep geological formation, we investigate the magnetic transformation of Mont Terri Lower Dogger claystones (Switzerland) due to thermal imprinting at 95 °C. We simulate the dehydration that occurs in the walls of galleries after excavation when interstitial water evaporates and rehydration when the galleries are refilled allowing water to move towards dehydrated zones. During dehydration, the remanence gains one order of magnitude at the beginning of the experiment and then it follows a linear rate of 0.23 ± 0.07 mA m− 1/day between 3 and 14 days. The magnetic susceptibility increases by a few percent. The increase of the remanence and of the magnetic susceptibility stops after 15 days. Mass monitoring indicates that interstitial water evaporates when remanence and magnetic susceptibility stabilizes. During rehydration, the remanence increases again whilst magnetic susceptibility drops by a few percent. After 20 days, the remanence during rehydration follows a rate of 0.42 ± 0.15 mA m− 1/day. By contrast, when rehydration takes place later, after 66 days, the rate is much lower (0.09 ± 0.04 mA m− 1/day). Low temperature investigation of magnetic properties indicates an initial magnetic assemblage of magnetite and pyrrhotite. Newly formed magnetite and hematite carry the remanence. We propose that magnetite is formed at the expense of pyrite. Hematite results from the progressive oxidation of newly formed magnetite. Our results suggest the possibility that any claystones that pass the oil window can be remagnetized due to the unique action of temperature. 相似文献
12.
The high-amplitude wide magnetic anomaly that covers a large area of the north-eastern – central Adriatic Sea in the Croatian offshore is ∼100 km wide and extends NW–SE for ∼350 km. The anomaly is located between the Dinarides and Apennines chains, in an interesting geodynamic scenario. The presence of intruded gabbroid rocks in the Croatian archipelago also contributes to making this intriguing and still not extensively investigated anomaly potentially significant to the geologic and geophysical context in which it is located. In this work, we model the Bouguer and magnetic anomalies across the Adriatic Sea. The 2D geophysical modeling was produced across four cross sections considering surface heat flow data to calculate the Curie depth. The magnetic susceptibilities and densities used for the synthetic bodies are in agreement with the literature and with those derived by previous models. The results suggest the presence of an uplifted magnetized basement with high magnetic susceptibility (0.075 SI units) to be the main contributor to the observed magnetic anomaly. This magnetic susceptibility is interpreted as representative of a gabbroid-intruded basement. The high-susceptibility basement is in lateral continuity with a relatively low susceptibility basement (0.025–0.038 SI units). The results of the geophysical modeling are compared with a conceptual geological model realized from the integration of surface, well and geophysical data, the latter concerning seismic, tomographic, magnetic and gravimetric anomalies and heat flow data. These data have been merged in an integrated data-base using MOVE software, and the geophysical modeling was performed using GM-SYS. The comparison allowed to confirm the hypothesis that the magnetic anomaly is related to the basement and to its position in the complex geodynamic evolution of the Apennines–Adriatic–Dinarides system. 相似文献
13.
The frequency-dependent anisotropy of magnetic susceptibility (AMS) can be most easily determined through subtracting directional susceptibilities measured at two operating frequencies along each of the measuring directions and the differences subsequently processed using standard methods for AMS computation. The effect of the measurement precision on the accuracy of the determination of the frequency-dependent AMS is investigated through mathematical simulation of the measurement process using the statistical theory of measuring the AMS of rocks. The accuracy of the AMS determination is presented in terms of the errors in determining the principal susceptibilities and principal directions. By modelling the measuring errors, the limits are discovered for the investigation of the frequency-dependent AMS. The modelling shows extremely high requirements for measurement accuracy met by the most sensitive instruments, only. 相似文献
14.
Detailed bathymetric and magnetic data, complemented by nine dredge stations, define the eastern and western limits of a belt of high-amplitude magnetic anomalies associated with the Galapagos hot spot. The hypothesis of “magnetic telechemistry” was tested and locally confirmed. High amplitudes correspond to high remanence, susceptibility, FeOT, TiO2, and presumably titanomagnetite concentration. The average remanence of surface samples in the high-amplitude zone is 0.027 emu/cm3 (range, 0.009–0.085 emu/cm3), about 4 times that of the normal-amplitude zone. Magnetic amplitudes are only 2–2.5 times higher, however. If the greater TiO2/FeOT ratio of high-amplitude zone basalts also characterizes the titanomagnetites, remanence in the high-amplitude zone may fall off more rapidly with depth in the crust as a result of reheating. Alternatively, small pillows of high remanence are more common than larger pillows at the top of the high-amplitude zone crust; FeTi basalt may also be concentrated in the upper part of the crust. Anomaly amplitudes are highest at the ends of the zone, particularly in the east. As asthenosphere crystal slushes presumably flow away from the Galapagos plume, progressive crystal fractionation may enrich residual magmas in FeOT and TiO2. The Galapagos FeTi zone terminates abruptly against transform fractures at both ends, perhaps because subaxial flow is dammed at the transforms. The FeTi-producing crystal slushes have advanced east and west at speeds up to 10 cm/yr since they first appeared at the spreading axis at least 6.6 m.y. B.P. Their progressive advance was connected with the progressive southward jumps of the spreading axis east of the Galapagos hot spot, and northward jumps to the west. 相似文献
15.
Summary Conditions are given under which two thick plates, differing in dip, apparent susceptibility, and remanence, will produce similar magnetic anomalies. From these conditions correction formulae are developed. Using these formulae the dip and susceptibility of a plate with remanent magnetization can be obtained from those of non-remanent plate. An interpretation procedure is suggested where the magnetic anomaly is first interpreted by means of a plate without remanence, dip and apparent susceptibility are then estimated by using the correction formulae developed. Thickness, position and depth of the plate are unaffected by the remanence correction procedure. The procedure is independent of the field component measured. 相似文献
16.
对杭州城区四个不同功能区块土壤进行了系统的环境磁学测定,结果表明城市土壤的磁化率平均值为128×10-8m3·kg-1,频率磁化率平均值3.6%(样品数=182),城市土壤呈现明显的磁性增强. 城市土壤的磁化率与频率磁化率呈极显著指数负相关,表明城市土壤磁性增强明显区别于自然成土过程引起的以超顺磁性(SP)颗粒为主的表土磁性增强机理. 统计分析表明,城市土壤磁化率与软剩磁和饱和等温剩磁(SIRM)呈显著直线正相关,说明亚铁磁性矿物是城市土壤剩余磁性的主要载体. 综合等温剩磁获得曲线、热磁曲线、磁滞回线等岩石磁学测定和SEM/EDX分析,城市土壤的磁性矿物以磁铁矿和赤铁矿为主,磁性矿物以假单畴-多畴（PSD-MD）颗粒存在,粒度明显大于成土过程形成的磁性颗粒,这些磁性颗粒主要来自燃料燃烧、汽车尾气等环境污染物. 因此,城市土壤磁测可作为城市土壤污染监测、污染空间分布和污染物来源判断的新手段. 相似文献
17.
P. Vallabh Sharma 《Pure and Applied Geophysics》1976,114(2):195-206
Summary Measurements of bulk magnetic properties, including the natural remanent magnetization (NRM), susceptibility and the Königsberger ratio, on over 250 samples of Tertiary basalts from Disko and Nûgssuaq, West Greenland are reported.The NRM intensities in basalts (geometric mean value 3.3 A/m in SI units) were on average three to four times as large as the induced magnetization intensities. The susceptibilities (geometric mean value 2.1×10–2 SI units) were much more uniform than the NRM intensities. In the majority of samples, the NRM was predominantly of reverse (R) polarity, but samples from a few sites showed a remanence of normal (N) polarity.The NRM of both polarity classes (N, R) was very stable against alternating field (AF) demagnetization with median destructive fields of the order of 20,000–30,000 A/m (250–350 Oe), comparable to those for many stable continental and oceanic basalts. The viscous remanence intensity, as studied by storage tests on some specimens, was found to be an insignificant fraction of the original NRM, except in few cases.The low field hysteresis loops (Rayleigh loops) were studied for some specimens. A qualitative association was noted between wide hysteresis loop and relatively low AF stability, but no correlation was apparent between the loop type and the Königsberger ratio (Q
n) of a specimen.Contribution no. 6 Institute of Geophysics, University of Copenhagen. 相似文献
18.
《Physics of the Earth and Planetary Interiors》2002,129(1-2):173-179
Grain sizes in the range (10−4 to 10−1 mm) are common in some rocks. Because thermal and/or chemical remanent magnetization of hematite in this range approaches intensities of single domain (SD) magnetite, careful exploration of this transition, may serve to develop new applications in rock magnetism that relate to magnetic anomaly source identification, and various paleomagnetic and grain size-dependent investigations.Grain size-dependent magnetic behavior of hematite reveals a SD–multidomain (MD) transition at 0.1 mm. This transition is recognized by variation in magnetic coercivity and susceptibility and is related to an anomaly in remanence recovery when cycling through the Morin transition. The coercivity decrease with increasing grain size occurs much more gradually above 0.1 mm than below this value. Magnetic susceptibility of the grains smaller than 0.1 mm has negligible dependence on the amplitude of the applied alternating magnetic field. For the larger grains a new amplitude-dependent susceptibility component is observed. The grain size of 0.1 mm is also associated with loss of most of the remanence when cycling through the Morin transition. This behavior is ascribed to a transition from the metastable SD to the MD magnetic state. The increase in magnetized volume causes the demagnetizing energy to destabilize the SD state, resulting in a transition where the demagnetizing energy is reduced by nucleation of the domain wall for grains larger than 0.1 mm. The 0.1 mm transition has no significant effect on shape of the temperature-dependent coercivity and saturation magnetization. 相似文献
19.
J. K. Eyre 《Studia Geophysica et Geodaetica》1996,40(3):234-242
Summary High resolution isothermal remanent magnetisation (IRM) acquisition was performed on forty-one Chinese loess samples with
the aim of investigating the effects of weathering on the remanence carrying mineralogy. Magnetic susceptibility was taken
as a measure of the degree of weathering. This is a valid assumption based on previous studies which have demonstrated a close
relationship between climate and magnetic susceptibility in the Chinese loess. Detailed analysis, based on fitting accumulative
log-gaussian curves to IRM acquisition data, reveals up to four distinct coercivity components. The remanences of the two
harder coercivity components are found to be almost independent of magnetic susceptibility. On the other hand, the remanences
of the two softer coercivity components are found to be positively correlated with magnetic susceptibility. Most probably
the two harder components are associated with detrital iron-oxides in the primary dustfall, whereas the softer components
were created during pedogenesis. 相似文献
20.
Graham Borradaile John Mothersill Don Tarling Craig Alford 《Earth and Planetary Science Letters》1986,76(3-4)
Magnetic susceptibility and its anisotropy in the Borrowdale Volcanic slates at Kentmere in the English Lake District are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite-ripidolite composition. In units of 10−6 cgs/g, the principal susceptibilities for the slates are 9.61; 9.42; 8.69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11.57; 11.22 and 9.15. Because the magnetic susceptibility is carried by a tightly packed, matrix-forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility. 相似文献