David W. Strangway

Magnetic fields of the solar nebula as recorded in chondrules from the Allende meteorite

Abstract The natural remanent magnetization (NRM) in individual chondrules from the Allende meteorite was measured. These had previously been oriented relative to each other. The NRM directions of the chondrules are not initially random, but they become scattered after either alternating field (AF) or thermal demagnetization. The NRM is less stable than anhysteretic remanent magnetization (ARM) against AF-demagnetization. The bulk of the NRM in the matrix is erased by 300°C. For the larger chondrules it is erased by 550°C, but for the smaller chondrules and the white inclusion a substantial decrease in NRM occurs by 350°C leaving about 20% up to 600°C. The behavior of the laboratory-induced ARM and the NRM under alternating field demagnetization suggest that the NRM of the chondrules consists of at least two components of TRM. One is a high-temperature component which was acquired when the individual chondrules were cooled through the Curie temperature and before they were assembled into the Allende meteorite. The other is a low-temperature component which was probably acquired in a field of about 1 Oe when the meteorite experienced thermal metamorphism or during the assembly of the meteorite.

DIELECTRIC PROPERTIES OF DRY, GEOLOGIC MATERIALS

A detailed investigation of the dielectric properties of powdered and solid dry rocks in the frequency range of 50 hz to 2 mhz has revealed the following general characteristics: 1) All dry rocks, powdered and solid, show an increase in both the dielectric constant and the loss tangent as frequency decreases and as temperature increases. This dispersion is believed to be due to polarization associated with charge buildup at grain boundaries or at grain imperfections. 2) Dry powdered rocks often show a thermally‐activated relaxation peak with a typical Debye‐relaxation character. This is due to the presence of pyroxene and biotite and may be associated with other minerals. The relaxation peak is not seen in solid rocks, where it is hidden by the low‐frequency dispersion. 3) At high frequencies, the loss tangent approaches a constant value which is frequency independent. This behavior is observed in many dielectrics and may be the result of a distribution of relaxation times.

RADIO INTERFEROMETRY DEPTH SOUNDING: PART II—EXPERIMENTAL RESULTS

In such highly resistive geologic environments as ice sheets, salt layers, and the moon’s surface, radio waves penetrate with little attenuation. The field strengths about a transmitting antenna placed on the surface of such an environment exhibit interference maxima and minima which are indicative of the in‐situ electrical properties and the presence of subsurface layering. Experimental results from an analog scale model and from field tests on two glaciers are interpreted on the basis of the theoretical results of Part I. If the upper layer is thick, the pattern is very simple and the dielectric constant of the layer can be easily determined. An upper bound on the loss tangent can be estimated. For thin layers, the depth can be determined if the loss tangent is less than about 0.10, and a crude estimate of scattering can be made.

The magnetic fields of the terrestrial planets

Abstract A single model for the terrestrial planets based upon the structure inferred for the lunar interior is developed, which subdivides them according to size. It is probable that planetary bodies smaller than the moon have never melted but they could still carry a memory of an early intense solar-system field. The magnetic fields of Mercury, Mars and Venus can be explained in terms of a crustal remanence which is a memory of a primitive internal or external field. The earths present field, on the other hand, is due to an active internal dynamo.

INTERPRETATION OF THE MAGNETIC ANOMALIES OVER SOME PRECAMBRIAN DIKES

In this paper, some examples of the influence of the remanent magnetism of rocks on magnetic fields are presented. In the study, a series of dikes were investigated since, in this case, the geometry is simple and the fields can be calculated with some precision. A large number of samples were collected and the remanent magnetization and susceptibility measured. Using this information the expected curves for ground vertical component magnetic profiles and airborne magnetic profiles were computed. These were then compared with the actual observed profiles. A good correlation was found when both remanent and induced magnetization were considered. In determining the remanent magnetization intensity, samples that had unusually high Q values were rejected because these probably represented local effects due to lightning strikes. In addition, the mean value of the magnetization was determined by taking into account the scatter of directions of the measured NRM’s. The agreement between observed and computed data ...

Superconducting second-gradient spinner magnetometer

Abstract The application of a superconducting second-gradient spinner magnetometer to paleomagnetism and rock magnetism is described. The use of a spinner permits the measurement of the magnetic remanence and the magnetic susceptibility anisotropy with a high sensitivity. A furnace for carrying out continuous thermal experiments has been developed and applications described.

A geophysicist’s advice to a university student for the year 2000

As president of the University of British Columbia, I was privileged to live in one of the most beautiful homes on the west coast with a full view out to the Pacific Ocean and to Vancouver Island. Each summer, my wife and I entertained a group of 40 or so high school students. They studied at UBC for a month and then scattered to summer jobs across Canada before returning home to complete high school. Each year, as the students arrived for dinner, some would ask, “What does it take to live in a house like this?”