摘要:

The spatial distribution of elements in tektites from Indochina and Czechoslovakia and in certain terrestrial materials has been studied by charged particle activation analysis and β autoradiography in an attempt to throw light on the mode of formation of tektites. Tektites from both of these strewn fields, as well as volcanic glass from the island of Melos, show homogeneous distributions within the accuracy of the experiment. On the other hand, impactites from Ries crater in Germany and Lake Bosumtwi in Ghana (and, even more, a granite used for comparative purposes) show considerable inhomogeneity of elemental distribution. The conclusions drawn from these observations are discussed in this paper

ISSN:0148-0227    

DOI:10.1029/JB078i008p01245

年代:1973

数据来源: WILEY

摘要:

The effect on seismic transmission of phase transitions in which the transformation of one solid to another involves a change in density is analyzed theoretically. Stress exerted by the seismic wave is assumed to transform a minute amount of material at a rate proportional to the local stress relative to the transformation value. The analysis shows that such transitions, even though the amount of material affected is very small, can have an appreciable effect on velocities and attenuation if the regions transforming are in the shape of thin planar areas. The effect is negligible for regions with more equant dimensions. The hydrostatic component of the response is found to be that of a standard linear solid; the response in shear is more complicated but can be approximated as a standard linear solid also. The characteristic frequency of the transition from nickel olivine to nickel spinel is found to be 0.01 Hz at 1000°C and 0.001 Hz at 900°C. The ratio of compressional wave velocity to shear wave velocity at frequencies when this mechanism is operative is lower than normal, whereas the ratio is higher than normal when grain boundary sliding occur

ISSN:0148-0227    

DOI:10.1029/JB078i008p01253

年代:1973

数据来源: WILEY

摘要:

The single‐crystal elastic constants are determined as a function of pressure and temperature for rutile structure germanium dioxide (GeO2). The data are qualitatively similar to those of rutile TiO2measured by Manghnani (1969). The compressibility in thecdirection is less than one‐half that in theadirection, the pressure derivative of the shear constantCs= (C11−C12)/2 is negative, and the pressure derivative of the bulk modulus ∂K/∂Phas a relatively high value of about 6.2. The high ∂K/∂Pvalues for rutile GeO2and rutile TiO2are not consistent with the Slater or Dugdale‐MacDonald equations relating ∂K/∂Pto the Grüneisen parameter. The ∂K/∂Pfor stishovite (which has the rutile structure) is probably high also. According to an elastic strain energy theory, the negative shear modulus derivative implies that the kinetic barrier to diffusion decreases with increasing pressure. Kinetic data on the quartz GeO2→ rutile GeO2transformation appear to support the a

ISSN:0148-0227    

DOI:10.1029/JB078i008p01262

年代:1973

数据来源: WILEY

摘要:

New shock compression data to 340 kb for single‐crystal orthoclase (along (001)) demonstrate the onset of a shock‐induced phase change at ∼115 kb. Along the Hugoniot a mixed‐phase region extends to ∼300 kb, above which the data are believed to correspond to the properties of a high‐pressure phase having the hollandite structure (zero pressure density of 3.84 g/cm3) reported by Ringwood et al. If the hollandite value for the zero pressure density is used, the zero pressure bulk modulus of this phase is approximately 2

ISSN:0148-0227    

DOI:10.1029/JB078i008p01274

年代:1973

数据来源: WILEY

摘要:

Thirteen new strontium isotopic analyses are presented for volcanic rocks from St. Vincent and St. Lucia, adjacent islands in the Lesser Antilles. Basalts and basaltic andesites from St. Vincent all have87Sr/86Sr ratios very close to 0.7040. This suggests that these rocks probably were derived from the mantle with minimal crustal contamination. An andesite and a rhyolite from St. Lucia also have87Sr/86Sr ratios close to 0.7040 and may represent differentiation products of such magmas. However, several andesites and dacites of the Qualibou volcano on St. Lucia have87Sr/86Sr ratios of 0.708–0.709. Such high ratios seem best explained by a hypothesis of anatexis of subducted marine sediments to produce these magmas. Magmas in which the87Sr/86Sr ratios are close to 0.705 may represent cases in which the strontium from marine sediments is present but subordinate to either mantle‐derived strontium or strontium from the basaltic layer of the oceanic crust or, alternatively, may reflect the larger amounts of continental detritus in the subduction zone off the southern part of the

ISSN:0148-0227    

DOI:10.1029/JB078i008p01279

年代:1973

数据来源: WILEY

摘要:

Formal analytic solutions to a class of problems of downward continuation of potential fields into a homogeneous semi‐infinite solid are given. The solid contains stationary sources below a fixed depth, and the potential field in the source‐free slab is derived on the basis of given boundary values of the field and its vertical derivative. The results are expressed in terms of infinite series that lead to meaningful results when the boundary data are given as bounded band‐limited func

ISSN:0148-0227    

DOI:10.1029/JB078i008p01288

年代:1973

数据来源: WILEY

摘要:

The velocity of compressional waves in a limestone is determined up to 25 kb. Two phase transitions occur in this range of pressure. The first (at about 15 kb) is associated with a pronounced and continuous decrease in velocity and a marked increase in attenuation; the second (at 23 kb) is associated with a discontinuous jump in velocity and no appreciable change in attenuation. The velocity of shear waves is determined up to 15 kb; a decrease in velocity similar to that in thePvelocity appears at about this pressure. Poisson's ratio computed from the velocity data drops from 0.29 at 13 kb to 0.19 at 15 kb. A detailed study of strain up to 21.5 kb reveals no discontinuous change in volume and suggests that on a macroscopic scale the first transition is a high‐order phase transition. Using data from the velocity measurement and the strain measurement, we estimated the characteristic time for the first transition to be about 0.05 μsec. Not enough data are available to estimate the characteristic time for the second transition, but it must be very much longer. Inside the earth a phase transition with a characteristic time of about or less than 0.1–1 sec may affect the propagation of seismic waves in much the same way as the first calcite transition affects the propagation of the ultrasonic waves and thus result in a pronounced decrease in velocity and a marked increase in attenuation. The decrease in Poisson's ratio may serve as a criterion for differentiating phase transitions from other possible causes for low‐velocity

ISSN:0148-0227    

DOI:10.1029/JB078i008p01293

年代:1973

数据来源: WILEY

摘要:

Analyses coupling in‐material stress and particle velocity gage measurements with the equations of hydrodynamic flow are presently used for determining stress‐volume paths during transient one‐dimensional plane wave propagation in solids. In this work a method is described that allows analysis of attenuating experimental wave profiles of arbitrary shape in spherically symmetric flow. The method is applied to radial stress and particle velocity data for spherically divergent wave propagation in Westerly granite. The resulting relations among pressure, volume, and deviatoric stress are compared and are found to be consistent with other available data on Westerly granite. It is concluded that the analysis promises to be a useful tool for relating observed wave structure to physical processes occurring in the material and for developing better constitutive relations to predict the transient dynamic behavior of mat

ISSN:0148-0227    

DOI:10.1029/JB078i008p01299

年代:1973

数据来源: WILEY

摘要:

Cosmic ray spallation produced3He,21Ne,22Ne, and38Ar have been measured as a function of depth in three mutually perpendicular cores (56, 51, and 21 cm) taken from the ∼120‐kg L chondrite found near Keyes, Oklahoma. The data obtained represent the first experimental determination of the depth variation in the production rates of these cosmogenic nuclides in a single stone meteorite. Fifteen samples across the 56‐cm core showed maximum concentration changes of 14%3He, 28%21Ne, 19%3He/21Ne, and 5%22Ne/21Ne. The 51‐cm core showed somewhat smaller concentration changes. All three cores are characterized by increasing production of3He and21Ne concentrations and decreasing3He/21Ne and22Ne/21Ne ratios with depth. A relatively broad maximum in the spallation production of3He and21Ne occurs at a depth of>20 cm. The ranges of3He/21Ne and22Ne/21Ne ratios observed in Keyes (5.7–4.8 and 1.14–1.08, respectively) are typical of the irradiation hardness experienced by many ordinary chondrites and imply shielding of 5–35 cm. These ratios are not as depth sensitive as21Ne production rates for chondrites but offer a possible means for making relative shielding corrections to calculated noble gas

ISSN:0148-0227    

DOI:10.1029/JB078i008p01308

年代:1973

数据来源: WILEY

摘要:

Means for the continuous monitoring of seismic phase velocity to precision finer than one part in 104have been used to detect in situ periodic velocity variations apparently related to solid earth tides. The magnitude of the velocity change implies that the elastic moduli of crustal rock are much more stress sensitive in situ at shallow depths than in laboratory tests on small rock samples.

ISSN:0148-0227    

DOI:10.1029/JB078i008p01319

年代:1973

数据来源: WILEY