Magnetic parameters and variations in the composition of igneous rocks of the Franz Josef Land archipelago

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.     

On the theory of depositional remanent magnetization in sediments

Summary A more precise solution of equation, describing process of orientation of isometric ferromagnetic particles at their deposition in liquid under influence of external homogeneous magnetic field is presented. It is shown, that this moreprecise investigation of the problem doesn't lead to qualitative new results for describing processes of particles orientation, than that given byT. Nagata.     

Anisotropy of magnetic remanence: A brief review of mineralogical sources,physical origins,and geological applications,and comparison with susceptibility anisotropy

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.     

Ferrospinels and petromagnetism of Siberian traps: A case study of traps drilled by the Norilsk borehole

Magnetic characteristics and compositions of ferromagnetic species of trap samples from the Norilsk borehole are studied; the borehole penetrated the complete section of a trappean rock sequence (nearly 3 km) represented by eight magmatic formations. The lowest (Ivakinskian) formation consists of rocks of the subalkalic type, and the remaining formations generally belong to the tholeiitic series. Primary ferromagnetic phases are represented by titanomagnetites with various ulvospinel concentrations in a solid solution. Three modes characterized by TiO₂ concentrations of 14.6, 18, and 23.9 wt % are revealed. The Ivakinskian rocks are most magnetized, and magnetization is low in core samples from depths of 1700–2500 m. Various magnetic characteristics have polymodal distributions of their values. Plateau basalt samples of the Ivakinskian Formation from other regions of Siberia, the Lory Plateau (Armenia), and Kamchatka are additionally studied. On the whole, titanomagnetites of plateau basalts were crystallized under the quartz-fayalite-magnetite (QFM) buffer conditions.     

Assessment of soils pollution extent in surroundings of ironworks based on magnetic analysis

This paper reports on magnetic and magnetomineralogical studies of soils influenced by ironworks activity. Researches were conducted in five areas, of which Ostrowiec Świętokrzyski ironworks area is described in detail. A map of magnetic susceptibility was created based on field measurements and samples taken from soil profile were analyzed in laboratory. Measurements of magnetic susceptibility in two frequency ranges, anhysteretic remanent magnetization, isothermal remanent magnetization thermomagnetic and geochemical analysis were carried out. SEM was used to identify ferromagnetic fractions. As a result the horizontal and vertical extent of heavy metals pollution was established.     

Estimation of depth and magnetization of magnetic sources from magnetic data: The linearized continuous inverse problem for 21/2D structures

The estimation of the depth to the top and bottom of a magnetic source from magnetic data defines a nonlinear inverse problem, while the evaluation of the distribution of magnetization determines a linear inverse problem. In this paper, these interpretation problems are resolved in the continuous case of 2_1/2D magnetized bodies with lateral magnetization variations. A formulation of the magnetic problem accounting for different directions of remanent and total magnetization vectors and including a more general definition of apparent susceptibility is presented. Differences between 2D and 2_1/2D formulations are stressed, as regards the anomaly amplitude, shape and zero-level.In order to utilize well-known continuous linear inverse methods, Fréchet derivatives of the data functionals with respect to the depth of the source top and bottom, are analytically described. Thus, using the spectral expansion inverse method (Parker, 1977) and linearizing the problem at several steps of an iterative process, the source depth is obtained within a few iterations, although the starting model is distant from the final solution. The interpretation of an anomaly in the Italian region shows the usefulness of the method.     

On the theory of depositional remanent magnetization in sediments: Influence of fluid motion upon the magnetic orientation of sediments

Summary It has examined the influence of fluid laminar motion upon the magnetic orientation of ferromagnetic particles with different form: sphere, rod-like, disk-like, ellipsoid. It is shown, that the inclination error depends on the form and the magnitude of particles, on the value of their remanent magnetization and on the size of vertical velocity gradient of the fluid.     

Remanent magnetization of andesitic and dacitic pumice from the 1985 eruption of Nevado del Ruiz (Colombia) reversed due to self-reversal

The natural remanent magnetization of andesitic pumice emitted during the 1985 eruption of the Nevado del Ruiz volcano (Colombia) has a direction opposite to the present geomagnetic field. The self-reversing mechanism can be re-activated in the laboratory during cycles of heating and subsequent cooling in air and zero magnetic field. Laboratory-produced thermoremanent magnetization is dominated by the same self-reversal process in fields up to several mT. Microchemical, optical and Curie temperature analyses indicate that the ferromagnetic minerals are members of the magnetite-ulvöspinel and hematite-ilmenite series with average compositions of Fe_2.73Ti_0.27O₄ and Fe_1.38Ti_0.62O₃, respectively. In analogy with the magnetic behaviour of synthetically grown antiferromagnetic-ferromagnetic FeMn-FeNi films, the self-reversal can probably be interpreted in terms of an exchange field acting between a Ti-poor canted antiferromagnetic and a Ti-rich ferrimagnetic phase in the hemoilmenite grains.     

On the interpretation of paleomagnetic data on moraines

Some methods of the interpretation and application of paleomagnetic data for the stratigraphic separation and correlation of Neopleistocene moraines, as well as the factors affecting the degree of ordering of magnetic moments of ferromagnetic particles in a moraine, are considered. A refined interpretation of the well-known Ryabushkin-Pevzner model of moraine magnetization is proposed. It is shown that the way of using an occasional coincidence of the direction of long axes of fragments with the direction of magnetization vectors, which is stated in some publications, has no grounds for its application for the stratigraphic separation of moraines related to the Dnieper and Moscow glaciations. However, it cannot be ruled out that this phenomenon may be used for the investigation of processes of glacial lithogenesis.     

Studies on reaction kinetics in magnetic oxide minerals

Summary Reactions within spinel-type oxides are examined by consideration of (i) the law of mass-action and its limits, (ii) the structural field situation (Mössbaufr) and the (high- or low-) spin state, (iii) the cation site preferences. The conditions for electron transport, cation and vacancy diffusion during oxidation are determined. Effects of defect diffusion on domain-wall mobility and ordering processes during thermal influences are discussed.     

地球基本磁场的形成与变化的探讨

本文在铁磁体假说的基础上,探讨地球基本磁场的形成与变化的原因.地球的偶极磁场是由于地球的回转和内核中特殊的磁化环境,使内核中心形成的饱和磁化的永磁球体（即磁核）产生的,磁核的大小和温度负相关.地球的非偶极磁场,由外核内几个可确定的磁偶极子产生,这些磁偶极子,是外核中液态金属的流动,切割磁核的磁场而产生的涡流形成的.     

Some anomalous features in rock magnetism

Summary In the course of thermal demagnetization of igneous rocks, the author observed that in a few cases there was a rise in the intensity of magnetization with a rise in temperature and this was observed with all types of formations with normal and inverse polarizations. The increase of intensity with rise in temperature took place at various temperatures ranging from 150°C to 550°C. The results are discussed in the light of modern theories and the author concludes that the interaction of different ferromagnetic constituents with different Curie points is the probable cause of the anomalous features.     

Coherency of rupture and seismic spectrum

In considering the seismic spectrum, one of the methods to incorporate irregularity of fault motion statistically is to introduce the concept of coherency of fracture. In a classic paper,Aki (1967) investigated the scaling law of seismic spectrum on the basis of a statistical model in which an exponentially decaying function is fitted to the autocorrelation function of the dislocation velocity. It is found, however, thatAki's model does not necessarily express irregular fault motion, but corresponds to a smooth dislocation. We show that an analytical function of dislocation velocity gives the same autocorrelation function and the same seismic spectrum as those ofAki's model. In actual fault motion, there is considerable evidence which indicates that the dislocation is not continuous and smooth over the whole fault plane, but is often segmented in several parts. In order to take into consideration this feature we introduce a generalized autocorrelation function of the dislocation velocity in which many coherent fractures smaller than the size of the fault dimension are included. It is shown that the more small-scale coherent fractures, the larger the seismic wave energy in the high frequency range.Kanamori andAllen (1986) showed that a large ratio of seismic wave energy relative to the seismic moment means a large effective stress drop. On the other hand, it is well known that when a fault plane is segmented in several parts, stress drop becomes large (e.g.,Madariaga, 1979;Rudnicki andKanamori, 1981). These two results are fused in our model, because we find that large seismic wave energy is obtained when the fault motion includes small-scale fractures.Kanamori andAllen (1986) also showed that there is a tendency for earthquakes with long repeat times to have a large effective stress drop. Our model implies that a fracture corresponding to earthquakes with long recurrence intervals is more complex, and the strength is large, as also suggested byCao andAki (1986) using a numerical simulation. It should be noted that to the zeroth order, an approximate scaling relation is observed among earthquakes, which means that a large earthquake consists of a relatively large-scale coherent fracture. This fact seems to suggest that the condition of occurrence of a large earthquake is related to the maturing of a source region in which a large coherent fracture becomes feasible.     

Thermal regime of the Earth's outer core

Summary First an introduction into the dynamo problem and the core paradox is given. A novel theory of the volume dependence of Grüneisen's parameter is used for calculating the adiabatic temperatures on the assumption that the melting temperature of the material is reached at the boundary between the inner and outer cores of the Earth (IOB). On this condition, thermal convectionthroughout the outer core is impossible according to the melting-point curves ofKennedy andHiggins (1973) andLiu (1975), whereas it is permitted by that ofLeppaluoto (1972),Boschi (1975), andStacey (1977). Various possibilities of solving the core paradox are described.Mitt. d. ZIPE Nr. 682.     

Ueber Anwendungen einer Formel zur Berechnung des Vertikal-gradienten der Schwere

Summary A formula is derived, which allows to calculate the vertical gradient of gravity from gravity anomalies with consideration of the whole gravitational field of the earth. It is shown that the formula given byEvjen for a plane surface in practical cases is nearly always sufficient. The accuracy of calculation is to be checked with regard to the geophysical applications. Two examples give an idea of the variations of the vertical gradient at the earth's surface. FurthermoreEvjen's method of direct structural calculation by means of the vertical gradient is discussed.

---

Résumé On déduit une formule qui permet de calculer, par rapport au champ total de gravité de la Terre, le gradient vertical de la pesanteur résultant des anomalies gravimétriques. Il s'en suit que la formule donnée parEvjen pour une surface plate est presque toujours suffisante dans les cas pratiques. On examine la précision du calcul à l'égard des applications géophysiques. Deux examples nous donnent une idée des variations du gradient vertical sur la surface de la Terre. Enfin on discute la méthode d'Evjen de calculer directement la structure a l'aide du gradient vertical.

     

Magnetic hysteresis in the F.M.R. spectra of fine-grained spherical iron: Possible evidence for a new carrier of hard remanence in lunar soils and rocks

Magnetic hysteresis effects have been observed in ferromagnetic resonance (FMR) spectra obtained at 9 and 16 GHz for certain simulated lunar glasses which were reduced by H₂ in the melt and rapidly quenched. Transmission electron microscopy has revealed that these samples contained spherical particles in the size range ～0.01–0.5 μm. FMR spectra obtained at 35 GHz (applied field ～ 12.5 kOe) exhibited a line shape characteristic of spherical, single-domain (SD) iron particles with no hysteresis. Computer simulations of the latter spectra confirmed that the average deviation from sphericity must be ?3% and that (2K₁/M_s) ≈ + 600 Oe for the precipitated magnetic phases. The principal features of the spectra obtained at all three frequencies have been explained on the basis of a simple theoretical treatment for spherical iron particles which have 2 domains in applied fields ?7 kOe, but become saturated at higher fields. Isothermal remanent magnetization (IRM) of these samples has been studied by both FMR and standard static techniques; the mean coercive force measured by the former (～4 kOe) contrasts with the mean value determined by the latter (～550 Oe). Apparently, FMR singles out and even amplifies the contributions of two-domain particles (which are magnetically hard), while the static measurement is more sensitive to the average of all particles present. The intensity of the FMR hysteresis of typical lunar soils is found to be ～1% of the total FMR intensity. In spite of this seemingly small value, two-domain iron particles may be important carriers of natural remanent magnetization (NMR) in certain lunar rocks.     

Propagation of the radiofrequency ground wave transient over a finitely conducting plane earth

Summary The introduction of precision radio navigation systems employing pulse techniques and the ever increasing interest in spherics have stimulated considerable interest in the propagation of the ground wave transient over the surface of the earth. The theory of the propagation of a transient radio frequency ground wave over a finitely conducting plane earth is presented for the particular case of theNorton surface wave by a consideration of a wave, interrupted abruptly at one point in time (t=0), a wave interrupted abruptly at two points in time (t=0,T ₂) and a wave interrupted at one point in time followed by an exponential decay. The first case is illustrated by several numerical examples of a cosine current wave applied to a vertical electric dipole source. It is apparent that the method of the inverse aplace transform for the particular cases considered yields some simple mathematical formulas.     

Free non-radial vibrations of the earth

Summary Earthquake shear waves with period around 12.2 min have been lately reported byM. Båth (1958), who suggests that these might be due to torsional vibrations of the whole mantle on some axis through the centre of the earth. An attempt has been made here to put forward a theory which accounts for such vibrations. The general elastokinetic equation for a heterogeneous isotropic medium is solved for a free spherical shell overlying a liquid core, and the solution is investigated for the first two modes. The frequency equation is solved for a shell and the limiting cases of a full sphere and an infinitely thin shell. Application is then made for various approximate mantle models, and periods are found which are in fair agreement with the observed. It is then shown that if the rigidity of the core is taken into consideration a closer agreement with the observed might be attained.

---

Zusammenfassung Seismische Transversalwellen mit einer Periode von rund 12.2 min sind neulich vonM. Båth (1958) beobachtet worden, der vermutet, dass sie Torsionsschwingungen des ganzen Erdmantels um eine Achse durch das Erdzentrum sind. Ein Versuch wird hier gemacht eine Theorie für solche Schwingungen zu entwickeln. Die allgemeine elastokinetische Gleichung für ein heterogenes, isotropisches Medium wird für eine freie, sphärische Schale über einem flüssigen Kern gelöst, und die Lösung wird für die zwei ersten Schwingungsformen untersucht. Die Frequenzgleichung wird für eine Schale und für die Grenzfälle einer ganzen Sphäre und einer unendlich dünnen Schale gelöst. Die Lösungen werden dann auf verschiedene, approximative Mantel-Modellen angewendet, und Perioden werden gefunden, die ziemlich gute Übereinstimmung mit der beobachteten Periode zeigen. Es wird danach gezeigt, dass, falls die Righeit des Erdkerns in Betracht gezogen wird, eine noch bessere Übereinstimmung mit der beobachteten Periode erreicht wird.

---

---

This research was supported by Eng.Herbert E. Linden of Beverly Hills, California.     

Gravitational coagulation of charged cloud drops in turbulent flow

Summary Gravitational coagulation of particles in turbulent flow is investigated with respect to the electrostatic forces. As turbulence mixes particle trajectories at large distances, its account reduces the consideration of drawing particles together till some definite distance. Taking into account hydrodynamical forces of interaction, series converging faster thanHocking's one and their more exact values are obtained. For electrostatic forces series with better convergence are also obtained. Equations of moment were solved numerically on electronic computer BESM-2. Results of collection efficiency computation are given.     

L’effetto di parete nelle camere di ionizzazione

Riassunto Vengono dedotte le formule teoriche per il calcolo dell’effetto di parete nelle camere di ionizzazione per la misura della radioattività, prendendo in considerazione sia il caso della parete piana che il caso della parete cilindrica. Si applicano le formule dedotte al calcolo dell’effetto di parete nella camera di ionizzazione annessa all’apparecchio dellaSchmidt, aīla quale, essendo di piccole dimensioni nei confronti delrange della particella α, non sono applicabili le formule già note delDuane (empirica) e delDeij (approssimata) e si confrontano i risultati che si ottengono con le tre formule. Si accenna all’estensione del metodo applicato allo scopo di pervenire ad una relazione analitica che consenta di dedurre l’effetto di parete, note le dimensioni della camera

---

Summary Theoretical formulas for the calculation of the wall effect in the ionisation chambers for the determination of radioactivity are deduced, taking in consideration both the cases of plane and of the cylindrical wall. The formulas obtained are applied to the calculation of the wall effect in the ionisation chamber annexed toSchmidt’s instrument; chamber to whom, because of its smallness with respect to α particles’s range the empirical formula ofDuane and the approximate formula ofDeij are not applicable and we compare the results obtained making use of each of the three formulas. The extension of the method to the aim of obtaining an analytical relation enabling to deduce the wall effect from the chamber’s dimensions is indicated.

---

---

Prof.Pio Vittozzi, Istituto di Fisica Terrestre dell’Università diNapoli.