摘要:

With the use of the excitation functions for26Al‐producing reactions measured by us, the rates of26Al production in interplanetary targets (lunar rocks 10017 and 12002 and cosmic dust) by solar‐flare particles have been calculated. The same calculations have also been made for53Mn with the estimated excitation functions. The energy spectrum of solar protons averaged over the 1956–1966 solar cycle was used as a guide for the unknown flux over the last few million years with the assumption that the ratio of H/He was 6. It is shown that the half‐value of the average flux reproduces rather well the observed depth profiles of these nuclides in the lunar rocks and the observed limit of26Al in marine sediment. A slight discrepancy between the calculated and the observed pattern of53Mn at the top surface of lunar rocks is discussed in terms of surface erosion and other effects. The present calculations are compared with earli

ISSN:0148-0227    

DOI:10.1029/JB077i023p04281

年代:1972

数据来源: WILEY

摘要:

We propose that the average diffuse component of lunar radar echoes results from the cumulative effect of multiple scattering within the ejecta blanket of fresh young craters. Using a multiple‐scattering polarization computer program, we compare our model with a variety of observations of the diffuse component and find a general agreement between the two. We show that multiple scattering makes a significant contribution to the partial depolarization of incident completely polarized radar signals, although single scattering may also be important. Mean indices of refraction of 1.3 and 1.6 are inferred for the ejecta blanket at wavelengths of 3.8 and 23 cm, respectively. These values are consistent with measurements made on an Apollo 11 fine sample and indicate an increasing density with depth below the surface. We hypothesize that the difference between the diffuse reflectivities of mare and highland areas is due chiefly to differences between the microwave absorption properties of rocks and dust in the two regions. If that is so, radar maps, properly prepared to display such differences, can serve as geological maps of the mineral or minerals (perhaps ilmenite) that are the principal microwave absorber

ISSN:0148-0227    

DOI:10.1029/JB077i023p04289

年代:1972

数据来源: WILEY

摘要:

As a simulation of erosion processes on the lunar surface, impact craters were formed in dust targets by 2‐ to 5‐/μm‐diameter polystyrene spheres with velocities between 2.5 and 12 km/sec. For weakly cohesive, thick targets of basalt dust with a maximum grain size comparable to the projectile diameter, the craters had an average projectile‐to‐diameter diameter ratio of 25, and the displaced mass was 3 orders of magnitude greater than the projectile mass. The ratio of the displaced mass to the kinetic energy of the projectile was about 0.1 μg/μJ. These ratios decreased as the cohesiveness of the dust grains was increased. For grain sizes an order of magnitude larger, the craters were not well defined, but the ratios were about the same. No detectable raised rim was produced by ejecta or uplift of the surface in any of these cases. In a simulation of the effect of a dust covering on lunar rocks, a layer of cohesive, fine‐grained basalt dust with a thickness nearly twice the projectile diameter protected a glass substrate from damage, but an area about 50 times the cross‐sectional area of the projectile was cleared of all but a few grains. Impact damage was produced in glass under a thinner dust layer. The results are useful in studies of mixing of the fine fraction of the lunar regolith and shielding of dust‐coated lunar rock surfaces under bombardment

ISSN:0148-0227    

DOI:10.1029/JB077i023p04304

年代:1972

数据来源: WILEY

摘要:

The principle of isotope thermometry is that isotope ratios are temperature dependent. It is proposed that isotopic ratios in bio‐organic material may have independent temperature coefficients, so that, by measuring ratios for several elements, e.g., hydrogen, carbon, and oxygen, it may be possible to show that a temperature change occurred. Assuming that cellulose is formed almost at equilibrium, temperature coefficients for C, H, and O are computed and found to be of measurable size. The coefficients computed for13C/12C and D/H agree with measured values. Thus indications are that temperature changes in past climates can be measured in old tree rings by using this principle of multiple thermometer

ISSN:0148-0227    

DOI:10.1029/JB077i023p04310

年代:1972

数据来源: WILEY

摘要:

A simple earth model consistent with the current physical and petrological theories of the mantle is constructed. The density of different layers is estimated in different ways, depending on the relative reliability in the seismic velocities in the layers. In the upper mantle, where the representative seismic velocities are somewhat uncertain, velocities and density are calculated from a petrological model; D. H. Green and A. E. Ringwood's (1967) model is taken as a convenient starting point. In the transition zone whereVPalone is reliable, Birch's empirical relation betweenVPand density is used to estimate density. In the lower mantle where bothVPandVSare reliable, an empirical relation between the bulk sound velocity and density is used to estimate density. Adams and Williamson's relation is used in the core. The various properties of this model, such as mass, moment of inertia, travel times, periods of free oscillations, and velocities of the surface waves, are calculated and compared with the observations. With the provision of a low‐velocity zone in the upper mantle, this model satisfies the observations within the widely accepted uncertaintie

ISSN:0148-0227    

DOI:10.1029/JB077i023p04318

年代:1972

数据来源: WILEY

摘要:

Typical samples of ship accelerations are used to examine errors in gravity measurement at sea. Ships experience large vertical (heave) accelerations that must be filtered out in order to obtain accurate measurements from a gravimeter mounted on a stabilized platform. Four heave filters designed to reduce such accelerations to<1 mgal while not affecting the gravity signals are examined. The off‐leveling that depends on the erection loop of the gyro was also determined for most of the gyrostabilized platforms in use. Fourier analysis of sway and surge acceleration recorded aboard RVVemaand RVRobert D. Conradwere used in the determinatio

ISSN:0148-0227    

DOI:10.1029/JB077i023p04330

年代:1972

数据来源: WILEY

摘要:

A method is presented that permits marine magnetic anomaly profiles from all parts of the world to be stacked for the purpose of enhancing coherent small anomalies due to short geomagnetic polarity events. In general, the shape of a profile depends not only on the sequence of normally and reversely magnetized magnetic prisms that constitute the source, but also on the following five angles: the declination and inclination of the regional field; the declination and inclination of the magnetization; and the azimuth of the magnetic stripes. Our method transforms a measured anomaly to a second anomaly which would have been produced by an identical source with vertical magnetization and vertical regional field. The method uses Fourier transform and linear systems theory and employs filters with a flat spectral response, so that no information is lost at short wavelengths. No assumptions are made about the true depth or shape of the source: this may be any two‐dimensional body or bodies in which the direction of magnetization is constant and the intensity varies arbitrarily. A preliminary application of the method to marine profiles from the East Pacific rise has yielded encouraging result

ISSN:0148-0227    

DOI:10.1029/JB077i023p04339

年代:1972

数据来源: WILEY

摘要:

Textural evidence, clinopyroxene fabric, and mineral assemblages of eclogite nodules from the kimberlite‐bearing breccia pipes of the east Colorado plateau are consistent with an origin by metamorphic recrystallization of predominantly basic igneous rocks. The eclogites are divided into three fabric groups exhibiting linear, planar, and random fabrics. Clinopyroxenes follow similar orientation rules as amphiboles in metamorphosed crustal tectonites. Partial recrystallization of olivine and extensive postcrystalline strain in the pyroxenes of the lherzolites and the websterites are believed to be due to a modification of the original fabric under crustal conditions. The inferred structural history of the ultramafic nodules puts various constraints on petrologic models attempting to explain their origi

ISSN:0148-0227    

DOI:10.1029/JB077i023p04350

年代:1972

数据来源: WILEY

摘要:

Microwave radiometric field observations were conducted at wavelengths of 21, 2.8, and 0.95 cm to determine the microwave penetration depth of a number of sands and gravels as a function of particle size and moisture content. Observations of a reflecting plate covered with varying thicknesses of test material exhibit a pronounced oscillatory behavior that is consistent with established electromagnetic theory for plane‐parallel layered mediums. Utilization of this interference effect is proposed as a microwave radiometric technique for determining the bulk electrical properties of geologic materials, snow, ice, and other materials readily adapted to layering experiments. Extension of the technique could lead to a method for remotely determining layer thickness in certain naturally layered systems such as sea ic

ISSN:0148-0227    

DOI:10.1029/JB077i023p04366

年代:1972

数据来源: WILEY

摘要:

The elasticity of high‐pressure mantle phases can be characterized by using data for crystal‐chemically similar compounds. The single‐crystal elastic constants are determined as a function of pressure and temperature for pleonaste spinel (Mg0.75Fe0.36Al1.90O4) and at room conditions for hercynite spinel (FeAl2O4). The bulk modulus increases from 1.95 Mb for MgAl2O4to 2.10 Mb for FeAl2O4. The pressure derivative of the shear constantCS= (C11−C12)/2 is slightly negative for pleonaste. Low or negative values of the pressure derivatives of shear constants are characteristic of the spinel structure and imply a low kinetic barrier to phase transformations and diffusion. Compressional and shear velocities of the spinel phase of olivine are estimated as a function of mean atomic weight by using the pleonaste and hercynite data. In comparison with a velocity and density model of the earth's mantle, the compressional velocity data indicate an increase in mean atomic weight across the transition zone, whereas the shear velocity data indicate no i

ISSN:0148-0227    

DOI:10.1029/JB077i023p04379

年代:1972

数据来源: WILEY