Some characteristic magnetic properties of lunar materials

One of the typical magnetic characteristics of lunar materials is the composition of their ferromagnetic constituent. Lunar breccias often contain kamacite (less than 7 weight per cent of Ni content) as well as almost pure metallic iron. Metallic ferromagnetics in most igneous rocks are almost pure iron, but the kamacite phase also has been found in some Apollo 15 igneous rocks. It seems likely therefore the metallic ferromagnetics in the lunar crust are more or less similar to those in chondrites.Another typical magnetic characteristic of lunar materials is the presence of a considerable amount of superparamagnetically fine particles of metallic iron. A higher relative content of such fine iron particles results in a higher value of the ratio of magnetic susceptibility (o) to saturation magnetization (I _s), a smaller ratio of the coercive force (H _c) to remanence coercive force (H _RC), and an extremely higher ratio of the viscous component (I _v) to the stable one (I _s) of the remanent magnetization.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.     

Coercivity maxima at low temperatures

Recent measurements have shown that the magnetic coercive forces of some Apollo lunar samples show an un-expected decrease with decreasing temperature at cryogenic temperatures. This behavior can be explained quantitatively in terms of a model which considers additive contributions from a soft, reversible magnetic phase and from a harder, hysteretic magnetic phase.     

Anisotropic magnetic susceptibility of rocks under mechanical stresses

Summary The magnetic susceptibility of a rock under a uniaxial compression () decreases along the axis of compression and increases along the direction perpendicular to the axis, with an increase of . Thus, the magnetic susceptibility of a compressed rock becomes anisotropic.The decrease of longitudinal susceptibility,K (), and the increase of transverse susceptibility,K (), are theoretically derived from a model of rock which assumes the uniaxial anisotropy and the isotropic magnetostriction of magnetic minerals in rocks and a random orientation of the minerals. Results show thatK () decreases toward zero whereasK () increases and approaches a finite asymptotic value with an increase of , and –(/)K () is twice as large as /K () for small values of . These results are in good agreement with experimental data.

---

Zusammenfassung Die magnetische Suszeptibilität eines Steines unter zunehmender uniachsigen Druckspannung () nimmt ab längs der Achse der Druckspannung und nimmt zu längs der Richtung senkrecht der Achse. Somit wird die magnetische Suszeptibilität des gedrückten Steines anisotrop.Die Abnahme der longitudinalen Suszeptibilität,K (), und die Zunahme der transversalen Suszeptibilität,K (), werden theoretisch von einem Modell eines Steines hergeleitet, das die uniachsige Anisotropie, die isotrope Magnetostriktion, und eine nichtbevorzugte Orientierung der magnetischen Minerals im Stein annimmt. Die Ergebnisse zeigen, dass mit einer Zunahme des ,K () gegen Null abnimmt, währendK () zunimmt und sich einem begrenzten asymtotitschen Wert nähert und, dass für kleine Werte des , –(/)K () zweimal so gross wie /K () ist. Diese Ergebnisse stimmen gut mit den Versuchangaben überein.

     

Piezo-remanent magnetization of lunar rocks

Summary Characteristics of the piezo-remanent magnetization (PRM) of lunar rocks are particularly interesting in comparison with the PRM of terrestrial rocks, because ferromagnetic constituents in lunar materials are metallic iron grains whose average magnetostriction coefficient is negative. Experimentally observed characteristics of the PRM of lunar rocks are substantially the same as those of the PRM of terrestrial rocks and magnetites, in which is positive. These experimental results indicate that the acquisition mechanism of PRM is due to a non-linear superposition of the magnetoelastic pressure upon the magnetostatic pressure on both sides of the 90° domain walls in ferromagnetic particles, as suggested by Nagata and Carleton.

---

Zusammenfassung Die Eigenschaften der piezo-remanenten Magnetisierung (PRM) der Mondgesteine sind besonders interessant im Vergleich mit der PRM der Erdgesteine, weil die ferromagnetischen Bestandteile der Mondmaterien die metallischen Eisenkörnchen sind, derer durchschnittliche Magnetostriktion-Koeffizient negativ ist. Die experimentelle gemessenen Eigenschaften von PRM der Mondgesteine sind wesentlich dieselbe der Erdgesteine und Magnetite, derer positive ist. Solche experimentaren Ergebnisse zeigen an, dass die Erwerbung von PRM durch eine nonlineare Übereinanderwirkung des magnetoelastischen Druckes und des magnetostatischen Druckes gegen die beiden Seiten der 90° Gebietwände der ferromagnetischen Teilchen ist, wie Nagata und Carleton vorgeschlagen haben.

     

Melting relations of peridotite and the density crossover in planetary mantles

Melting relations of primitive peridotite were studied up to 25 GPa. The change of the liquidus phase from olivine to majorite occurs at 16 GPa. We confirmed the density crossover of the FeO-rich peridotite melt and the equilibrium olivine (Fo₉₀) at 7 GPa. Sinking of equilibrium olivine (Fo₉₅) in the primitive peridotite melt was observed up to 10 GPa. The compression curves of FeO-rich peridotitic and komatiite melts reported in this and earlier work suggest that the density crossover in the Earth's mantle will be located at 11–12 GPa at 2000°C, consistent with an previous estimation by C.B. Agee and D. Walker.

The density crossover can play a key role in the Moon and the terrestrial planets, such as the Earth, Venus and Mars. Majorite and some fraction of melt could have separated from the ascending diapir and sunk downwards at the depths below the density crossover. This process could have produced a garnet-rich transition zone in the Earth's mantle. The density crossover may exist in the FeO-rich lunar mantle at around the center of the Moon. The density crossover which exists at the depth of 600 km in the Martian mantle plays a key role in producing a fractionated mantle, which is the source the parent magmas of the SNC meteorites.     

End wall effects in experiments on water intrusion along the interface between two homogeneous layers

End wall effect puts an inherent limitation on tank experiments, especially when the problems in a stratified fluid are dealt with. During experiments involving horizontal intrusion along the interface between two homogeneous layers, a curious phenomenon was found, i.e., the tip of the intruding water wedge continues to extend for a short time after supply is stopped, but then it begins to retreat in the cases of relatively high Reynolds numbers. The cause of this retreat of the wedge was investigated and was shown to be attributable to the initial disturbance generated near the mouth of the feeder at the start of water supply which propagates along the interface layer and reflects at the end of the tank as a bulge of the interface layer. The retreat of the intruding wedge would not occur in a sufficiently long tank, and so the cause of the retreat can be considered as one kind of end wall effect in a tank.     

Numerical study of the behavior of heated water discharged into the ocean

The effect of the earth's rotation on the behavior of heated water discharged from gigantic nuclear power plants was investigated numerically. It is shown that the effect is significant even for the existing scale of discharge. Horizontal spreading of the heated water is suppressed in offshoreward and northward directions (when heated water is discharged in an eastward direction from a westfacing coast in the northern hemisphere), but accelerated in the southward direction, and the shape of the formed warm water region becomes asymmetric. In this paper, several calculations were done using exaggerated Coriolis parameters (f) in order to demonstrate the effect of the earth's rotation. An increase off enhances above effect, but the situation of the inner region of the produced warm water mass is much different from that in the outer region near its margin. The southward expansion of surface isothermal contours in the inner region increases with an increase inf, but those in the outer region do not. This results in an increase of the sharpness of the front which is generated near the southern edge of the warm water region. We have not found simple parameters which describe the temperature and velocity distributions in the warm water mass produced.     

Cold water areas in the vicinity of the shoal,Kokushô-sone

By using data obtained at about 120 XBT stations, cold water regions in the vicinity of the shoal, Kokushô-sone (30°00N, 128°30E), which is located in the current zone of the Kuroshio in the East China Sea, were investigated.The temperature cross-sections obtained were compared with corresponding cross-sections obtained from the four former cruises which were already reported. On the present cruise forced upwelling area was found along the south slope of the shoal, instead of the north slope as was found on the former cruises.The area of the cold water region found along the south slope tends to decrease with decrease in depth, and at depths shallower than 250 m the cold water region extends northward passing the shoal. The area at a depth of 400 m is comparable to that of the shoal itself, and is about 35 km².Physical parameters and their scales which seem to be related to the dynamics near the shoal are given in the Appendix.