Direct determination of the natural remanent magnetization effect in a hole drilled in layered ground from magnetic field and susceptibility logs

Geophysics ◽  
1992 ◽  
Vol 57 (7) ◽  
pp. 872-884 ◽  
Author(s):  
Guy Desvignes ◽  
Véronique Barthes ◽  
Alain Tabbagh
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Direct Determination ◽  
Theoretical Models ◽  
Natural Remanent Magnetization ◽  
Case Examples ◽  
Joint Interpretation ◽  
The Fourier Transform ◽  
Layered Ground

A new method as presented, allows the joint interpretation of both electromagnetic (EM) and magnetic logs in layered ground, based on the fact that the susceptibility responses for these two measurements are linear. Thus we can make use of the classical properties of the Fourier transform to extract from these two signals the magnetic field due to remanent magnetization. Theoretical models show that for a sufficient sample step this remanent magnetization can be recovered, even if the Koenigsberger ratio is of the order of 0.2 and if the thickness of the magnetized layer is of the order of 1 m. The results for two case examples in a sedimentary context are also shown. Despite the difficulties due to experimental procedures, we show that the amplitude of the extracted information is significant in these two cases, even if its variations are somewhat structureless and cannot be easily explained by the geology.

Direct Determination of the Velocity of Vortices in High-Tc Superconductors by a Non-Equilibrium Method

1998 ◽  
Vol 12 (29n31) ◽  
pp. 3288-3291
Author(s):  
I. Kirschner ◽  
R. Laiho ◽  
A. C. Bódi ◽  
E. Lähderanta ◽  
I. Vajda
Keyword(s):  
Magnetic Field ◽  
Temperature Gradient ◽  
Vortex Motion ◽  
Direct Determination ◽  
Field Investigation ◽  
High Tc Superconductors ◽  
High Tc ◽  
Pinning Centers ◽  
Non Equilibrium

As is shown, thermally assisted vortex motion can come into being in high-T c superconductors due to the applied temperature gradient. Its behavior strongly depends on the local and global microstructure of the samples, moreover on the temperature and magnetic field. Investigation of the density, size and intensity of the pinning centers of specimens leads to the conclusion that the higher homogeneity immediately weakens and the lower one strenghtens the pinning, thus the former promotes and the latter impedes the vortex motion. The non-equilibrium experimental technique together with a.c. susceptibility measurements render possible the direct determination of the velocity of vortices. Depending on the actual microstructural state of samples it has the values between 6 × 10-2 mm/s and 18 × 10-2 mm/s in the case of Y-Ba-Cu-O specimens investigated.

Evidence of Single-Domain Magnetite in the Michikamau Anorthosite

1971 ◽  
Vol 8 (3) ◽  
pp. 361-370 ◽  
Author(s):  
G. S. Murthy ◽  
M. E. Evans ◽  
D. I. Gough
Keyword(s):  
Remanent Magnetization ◽  
Theoretical Models ◽  
Natural Remanent Magnetization ◽  
Single Domain ◽  
Isothermal Remanent Magnetization ◽  
Mineral Separation ◽  
Domain Configuration ◽  
Plagioclase Felspar ◽  
Magnetite Particles ◽  
Theoretical Evidence

The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretical models of grains elongated along [111] and [110] axes are used to show that magnetite needles can exist in stable single-domain configuration in the size and shape ranges of the needles observed in the Michikamau anorthosite. There is thus considerable experimental and theoretical evidence for the conclusion that the stable remanent magnetization of the Michikamau anorthosite is carried by fine single–domain needles of magnetite in the plagioclase felspar.

IN‐SITU DETERMINATION OF THE REMANENT MAGNETIC VECTOR OF TWO‐DIMENSIONAL TABULAR BODIES

Geophysics ◽  
1966 ◽  
Vol 31 (5) ◽  
pp. 949-962 ◽  
Author(s):  
H. P. Ross ◽  
P. M. Lavin
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Potential Fields ◽  
Small Samples ◽  
Magnetic Survey ◽  
Two Dimensional ◽  
Magnetic Vector ◽  
Gravity And Magnetic

Recent studies have shown that many rocks of the earth’s crust have a substantial component of remanent magnetization. Extensive sampling is required to determine adequately the remanent vector from small samples. A field technique has been developed (and tested on model data) for the in‐situ determination of the resultant (induced+remanent) magnetic vector of bulk volumes of rock, using a combined analysis of the gravity and magnetic fields of a disturbing body (Poisson’s Theorem). The potential fields are sampled adequately at a limited expenditure of time and effort in the field by utilizing the geometry of two‐dimensional bodies. The major limitation to the analysis is the removal of regional gradients and the estimation of the base levels of anomalies. Combined gravity and magnetic surveys were conducted over six diabase bodies in the Triassic Basin of Pennsylvania. The results of these surveys indicate a resultant direction of magnetization given approximately by: declination 2° W, inclination 41 degrees below the horizon. The corresponding direction of natural remanent magnetization has a declination of 1° W and an inclination of 28 degrees. The ratio of remanent to induced magnetization for the diabase is approximately two. These results have been used to provide a better interpretation of magnetic survey data over a magnetite deposit in the Triassic Basin.

Anisotropy of out-of-phase magnetic susceptibility: an approach for magnetic subfabrics determination

2021 ◽  
Author(s):  
Cláudia Cruz ◽  
Helena Sant'Ovaia ◽  
William McCarthy ◽  
Fernando Noronha
Keyword(s):  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Shape Parameter ◽  
Direct Determination ◽  
Anhysteretic Remanent Magnetization ◽  
The Matrix ◽  
Low K ◽  
Permanent Magnetization ◽  
Bulk Response

<p>The Anisotropy of Magnetic Susceptibility (AMS) represents the contribution of all minerals in rock samples (paramagnetic, diamagnetic, and/or ferromagnetic minerals). An intermediate AMS tensor may be recorded in rocks where a composite fabric is present, due to the presence of both paramagnetic and ferromagnetic minerals, being possible to be resolved into two distinct subfabrics using techniques as out-of-phase AMS (opAMS). The magnetic susceptibility measured in alternating field can be resolved into in-phase and out-of-phase components. In-phase AMS (ipAMS) measures the bulk response of all minerals in a sample however, opAMS is only sensitive to selected ferromagnetic minerals such as hematite, titanomagnetite, and ultrafine magnetite. The opAMS can be harnessed as a tool for direct determination of magnetic subfabrics defined by ferromagnetic minerals. This work focuses on three Portuguese plutons: Lamas de Olo, Lavadores-Madalena, and Santa Eulália. The preliminary results show that magnetic susceptibility is lower in opAMS, the degree of magnetic anisotropy is much higher in opAMS and the ellipsoid shape parameter has no significant differences in opAMS or ipAMS. The ipAMS and opAMS tensors are in general coaxial, pointing out that standard AMS fabric is parallel to the subfabric of minerals like hematite, titanomagnetite, and ultrafine magnetite. Two sites from Lamas de Olo Pluton with low in-phase magnetic susceptibility (ipK<sub>m</sub>) values were also measured, showing two different scenarios: (i) the coaxially is present in one site, pointing out the presence of minerals like hematite (after magnetite) but with the same orientation as the matrix; (ii) different orientation of K<sub>1</sub> and K<sub>3</sub> in ipAMS and opAMS suggesting the presence of a ferromagnetic oxide like hematite (after magnetite) but with a different orientation from the paramagnetic minerals. Nevertheless, it should be noted that in samples with low K<sub>m</sub> values, the presence of ferromagnetic minerals is scarce (or absent) and the opAMS has minor accuracy (the associated error is greater). The opAMS findings attain similar results to the anisotropy of anhysteretic remanent magnetization (AARM) studies, once both are related to the presence of ferromagnetic minerals, and their magnetic properties. However, the opAMS does not require the permanent magnetization of samples and is measured simultaneously with the ipAMS. With further works, a larger number of samples will be measured to accomplish more information, and AARM measurements will be performed on the same samples to compare the ipAMS, opAMS, and AARM tensors.</p><p>Acknowledgements: This work was funded by the Fundação para a Ciência e a Tecnologia (FCT) under UIDB/04683/2020 project.</p>

Rock magnetism as a tool for investigating the use of archaeological artefacts from baked clay

2021 ◽  
Author(s):  
Evdokia Tema ◽  
Enzo Ferrara ◽  
Lorenzo Zamboni ◽  
Marica Venturino ◽  
Margherita Reboldi ◽  
...  
Keyword(s):  
Iron Age ◽  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Magnetic Behavior ◽  
Archaeological Site ◽  
Natural Remanent Magnetization ◽  
Rock Magnetic Properties ◽  
Ring Shape ◽  
Magnetic Analysis

<p>Even though multidisciplinary approaches applied to the investigation of archaeological findings are widely used, the use of rock magnetic properties is still poorly exploited in the determination of the use of ancient artefacts. In this study, we present the results of a combined archaeological, morphological and magnetic analyses applied on the ring-shape clay artefacts found at the archaeological site of Villa del Foro, in Northern Italy. The materials studied are dated between the sixth and the first half of fifth century BC and are found in large quantities in different trenches of the archaeological excavation. To investigate their thermal history and to exploit their possible use as kiln supports, cooking stands, or loom weights, we have investigated their natural remanent magnetization (NRM) and the magnetic mineralogy changes occurred during laboratory heating. Magnetic analysis used for the determination of the firing temperatures show thermal stability up to 500-600 <sup>o </sup>C, while further laboratory heating at 700 <sup>o </sup>C introduces magnetic alteration. Thermal demagnetization of the samples generally shows a strong and stable thermal remanent magnetization. In few cases, a clear secondary component is present, suggesting partial re-heating or displacement at temperatures ranging from 200 <sup>o</sup>C to 450 °C. Such secondary magnetic component can be indicative of a secondary heating or of a displacement of the rings from their initial firing position while still hot. Even though the studied rings belong to casually different morphological typologies, no connection among type and magnetic behavior was observed, suggesting that the ring’s morphology does not define neither their production conditions nor the final use of the artefacts. The estimated firing temperatures of around 600-700 <sup>o</sup>C are compatible with the heating of the rings during their manufacture rather than related to cooking activities. In combination with the archaeological evidence and the morphological analysis it is thus suggested that the rings were used as weight looms and baked only during their production procedures. Such a pilot study can be used as reference for the identification of similar objects found in Italy and Europe during the Iron Age and confirms the great potential of rock magnetic analysis in the investigation of the technology and use of ancient baked clays.</p>

Viscosité magnétique potentielle, aimantation détritique et viscosité réelle d'un sédiment lacustre quaternaire

1987 ◽  
Vol 24 (9) ◽  
pp. 1903-1912 ◽  
Author(s):  
Daniel Biquand ◽  
François Sémah
Keyword(s):  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Viscosity Index ◽  
Natural Remanent Magnetization ◽  
Blocking Temperature ◽  
Magnetic Viscosity ◽  
Paleomagnetic Study ◽  
Temperature Spectra

The magnetic viscosity of sediments, as indicated by thermal demagnetization of natural remanent magnetization (NRM), depends on two main parameters: (i) the specific magnetic viscosity of the material and (ii) the efficiency of the primary magnetization process. In an attempt to determine the relative importance of these two variables, we studied a Lower Pleistocene lacustrine sequence bearing a primary reversed detrital remanent magnetization (DRM).Using natural samples and small cores made of crushed sediment, our study is based on the thermodynamic theory of rock magnetism developed by L. Néel, who established an equivalence between time and temperature, that is, between viscous remanent (VRM) and thermoremanent (TRM) magnetization processes. The determination of the blocking temperature spectra from 20 to 152 °C allows us to calculate the maximum theoretical VRM acquired in situ at each horizon, while the detailed thermal study of the NRM permits an appraisal of the DRM quality. This leads us to define a geological viscosity index, which accounts, in a rather convincing manner, for the behaviour of the samples observed during the classical paleomagnetic study. For the section studied, it appears that the variations of this index are closely correlated with the efficiency of the DRM acquisition process.

Sign in / Sign up

Export Citation Format

Share Document