Natural Remanent Magnetization Of Rocks Research Articles

Susceptibility and remanent magnetization inversion of magnetic data with a priori information of the Köenigsberger ratio

SUMMARY Magnetic susceptibility and natural remanent magnetization of rocks are useful parameters to study geological structures and geodynamic processes. Traditional widely used algorithms for the inversion of magnetic data can recover the distribution of the apparent susceptibility or total magnetization intensity, but do not provide information on the remanent magnetization. In this paper, we propose a framework to directly invert for the magnetic susceptibility and the natural remanent magnetization vector using surface or airborne magnetic data, assuming that the Köenigsberger ratio of the rock is known or approximately deducible. The susceptibility and remanence are computed using two different approaches: (1) the susceptibility, intensity, and direction of the remanent magnetization are continuously recovered for each discretized cell and (2) the remanence direction is assumed to be uniform in each subzone and is iteratively computed as discrete values. Both processes are implemented using the preconditioned conjugate gradient algorithm. The method is tested on three synthetic models and one field data set from the Zaohuohexi iron-ore deposit, Qinghai Province, northwest China. The results of the continuous inversion show the trend of the remanent magnetization directions, while the discrete inversion yields more specific values. This inversion framework can determine the source bodies’ geometry and position, and also provide superposed and comprehensive information on the natural remanent magnetization, which may be useful to investigate geological bodies bearing stable primary remanent magnetization.

Haematite pigmentation events and palaeomagnetic recording: implications from the Pilbara Print Stone, Western Australia

SUMMARY Haematite pigment is a common constituent of sedimentary rocks, but its contribution to the natural remanent magnetization of rocks is poorly understood. Here, we describe magnetic properties of two distinct pigment types that produce a characteristic decorative ‘print stone’ foundinthe ∼2.5GaMount McRae ShaleFormation,Hamersley Province,WesternAustralia. Distinct magnetic remanence directions observed in the Print Stone can be correlated to each pigment type. By comparison with the Australian apparent polar wander path, the remanence carried by uniformly distributed pigment can be dated to ∼15–25 Ma, while two age options, the Mesoproterozoic (∼1.5 Ga) or the middle Carboniferous (∼320–310 Ma), are permissible for the remanence carried by the pigment responsible for the distinctive ‘newsprint’ pattern. Magnetic properties and demagnetization characteristics of the different pigment types overlap significantly, and thus are not predictive of the dominant remanence carrier. Magnetic characteristics of the uniformly distributed pigment vary significantly on short spatial scales. Strong local control on pigment formation raises the possibility that a primary remanent magnetization may survive locally in pockets within sedimentary red bed formations.

Analysis of the natural remanent magnetization of rocks by measuring the efficiency ratio through alternating field demagnetization spectra

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.

Possibilities of remote estimation of the natural remanent magnetization of rocks in the zones of geomagnetic field reversal

The possibilities of the remote estimation of the distribution character of the rock natural remanent magnetization in the zones of geomagnetic field reversal are considered. The Faraday effect—rotation of the signal polarization plane in the magnetic field—is used for this purpose in the process of radar impulse sounding of the magnetic field.

Laser magnetometer measurement of the natural remanent magnetization of rocks

The ability of a laser magnetometer to measure the natural remanent magnetization of rocks is experimentally investigated. It is shown that the performance of such a magnetometer permits the rapid measurement of rock magnetizations of less than 1 A m−1 in a laboratory without the need of any magnetic shielding or cryogenic facilities. Moreover, the laser magnetometer is experimentally shown to be able to measure the distribution of magnetization in spatially inhomogeneous samples.

Magnetism of the Earth's Crust and the Earth's Interior: ABSTRACT

Power spectrum analyses of the geomagnetic field over the earth's surface show that the field fluctuations of wave lengths shorter than about a thousand kilometers are connected mostly with the geological structure of the earth's crust. Possible interpretations of the relation between geological structure and the surface geomagnetic anomalies are demonstrated by referring to fairly detailed maps of geology, geomagnetic anomaly, and Bouger anomaly of the gravity field over Japan Islands as well as magnetic properties of various rocks. Special attention is drawn to the absolute importance of natural remanent magnetization of rocks for this kind of interpretation. It seems likely that geomagnetic anomalies of wave lengths from several hundred kilometers to several thousand kilometers are related to the distribution of continents, to the variation of thickness of the earth's crust, and to the undulation of isothermal surfaces in the earth's upper mantle. Geomagnetic field fluctuations of larger scale seem to be attributable to the electric eddy currents just beneath the surface of the earth's core. End_of_Article - Last_Page 354------------

Anisotropy of Susceptibility and the Natural Remanent Magnetization of Some Welsh Slates

IN order to investigate the effect of the deformation associated with mountain building upon the aniso-tropy of susceptibility and the natural remanent magnetization of rocks, approximately a hundred specimens were prepared for measurement from some fifty samples of Lower Palaeozoic Welsh slates cleaved during the Caledonian orogeny. The anisotropy in fields of less than two œrsted was determined with a transformer bridge1 and the natural remanent magnetization with an astatic magnetometer. The results showed that the cleavage is a plane of high susceptibility, and that the remanent vector is parallel to it. In some of the slates it appears that the direction of natural remanent magnetization has been controlled by the anisotropic susceptibility, and in others that the pattern of anisotropy and the natural remanent magnetization have been aligned with the cleavage independently. I am indebted to Dr. J. C. Belshe and Dr. R. W. Girdler, with whose help the susceptibility work was begun.