摘要:

Measurements were made of22Na,26Al,54Mn, and60Co produced by cosmic rays in five samples of the Allende C3 meteorite and in one specimen of Murchison (C2);46Sc,48V,51Cr and57Co were also measured in several of these samples. Comparison of observed Allende60Co activities with calculated neutron‐capture production rates yields a depth scale for Allende that appears unambiguous to about 30‐cm depth. Using this scale, the production of26Al is constant (±10%) to a depth in excess of 30 cm,22Na activity increases ∼30% from near the surface of Allende to 20‐ to 30‐cm depth, and54Mn production increases ∼50% over the same depth range. The46Sc/54Mn activity ratio is constant at 0.059 ± 0.005 from 8 to 20 cm. Murchison's26Al activity yields a cosmic‐ray‐exposure age

ISSN:0148-0227    

DOI:10.1029/JB077i026p04905

年代:1972

数据来源: WILEY

摘要:

Present gravimetric algorithms that approximate the Vening Meinesz equations do not take into account in any detailed way the random nature of the anomalies, deflections, and gravimeter errors. A new algorithm based on the criterion of minimizing the mean‐square error between the true and calculated deflections is derived. The improved performance of the statistical algorithm compared with the deterministic algorithms is demonstrated. The approach advanced here can easily be extended to more general cases of calculating undulations, anomalies, and deflections from a variety of measurement

ISSN:0148-0227    

DOI:10.1029/JB077i026p04912

年代:1972

数据来源: WILEY

摘要:

Shock‐wave, static‐compression (X ray), ultrasonic, thermal expansion, and thermodynamic data are simultaneously inverted to determine the equations of state of stishovite and a coesitelike SiO2phase. All the stishovite data except the thermal expansion data are satisfied by a Mie‐Grüneisen‐type equation of state having a zero pressure bulk modulusKof about 3.50 ± 0.1 Mb, a pressure derivativedK/dPof 3.3 ± 1, and a Grüneisen parameter, initially 1.25 ± 0.1, that decreases slowly with compression. The volume coefficient of thermal expansion at ambient conditions is found to be 13 ± 1 × 10−6/°K, in comparison with 16.4 ± 1.3 measured by Weaver. Some Hugoniot data of Trunin et al. for very porous quartz have densities very close to the density of coesite. However, a calculation of the coesite‐stishovite phase line shows that the coesitelike phase persists to about twice the predicted transition pressure at 10,000°K. It is suggested that the discrepancy can be explained if this phase is interpreted as a liquid of

ISSN:0148-0227    

DOI:10.1029/JB077i026p04920

年代:1972

数据来源: WILEY

摘要:

An X‐ray‐diffraction study under pressure has shown that BaO, which has the NaCl‐type structure at standard temperature and pressure, transforms to a tetragonal structure witha= 4.459 ± 0.008 A,c= 3.606 ± 0.006 A, andZ= 2 at 92 ± 3 kb and 23 ± 3 °C. At 140 ± 5 kb, it transforms to the tetragonal PH4I‐type structure (space group P4/nmm). At 180 kb, the BaO in this structure hasa= 4.397 ± 0.007 A,c= 3.196 ± 0.005 A,Z= 2, andu= 0.40. These two phase changes are reversible, and the volume changes at the transitions are approximately 5% and 7%, respectively. Using F. Birch's equation of state with an assumed value of 6 for (∂KT/∂P)T, the initial isothermal bulk modulusK0has been calculated to be 0.69 ± 0.03 Mb for the phase with the NaCl‐type structure. The axial ratiosc/afor the high‐pressure phases of BaO appear to be independent of pressure w

ISSN:0148-0227    

DOI:10.1029/JB077i026p04934

年代:1972

数据来源: WILEY

摘要:

Recent ultrasonic measurements performed on hot‐pressed polycrystalline materials as a function of pressure and temperature simultaneously indicate that the interiors of the specimens may not be strain free. Residual strain arising from the fabrication process produces an anisotropic effect separate from any anisotropy that may arise simply from relative grain orientations that may or may not be randomized. Internal strain has a significant effect on measurements of the bulk modulus and particularly of its pressure derivative. The effect of residual porosity and permeability on the pressure derivative of the bulk modulus is also examine

ISSN:0148-0227    

DOI:10.1029/JB077i026p04938

年代:1972

数据来源: WILEY

摘要:

The Maxwell equations are written and discussed in the frequency domain for a medium exhibiting electrical polarization at radio and lower frequencies, in the range of linearity between current density and electric‐field intensity. A complex function of frequency is proposed for the conductivity, which is able to describe all the families of available experimental curves for rock samples in the natural state, showing the effect of polarization. Such a function is a constitutive relation for the polarizable medium in the frequency domain. The concept of ‘abnormal’ dielectric constant for rocks is discussed in the context of the physical mechanisms responsible for the effect of electrical polarization at radio frequencies and below. Such a concept, always possible theoretically, only introduces confusion in the understanding of the basic physical mechanisms involved. As an alternative the extensive use of the concept of a total current complex conductivity is sugg

ISSN:0148-0227    

DOI:10.1029/JB077i026p04945

年代:1972

数据来源: WILEY

摘要:

A time domain electromagnetic sounding technique was used to study variations in ground conductivity in the summit area of Kilauea volcano on the Island of Hawaii. The survey indicated the presence of a boundary between two zones with different resistivities at depths ranging from 900 to 2000 meters. In the upper zone the observed resistivity was 10–30 ohm m, whereas the resistivity in the lower zone was approximately 2 ohm m. A striking feature of the results of the survey is a mound of material with a resistivity of 2 ohm m within 900 meters of the surface near the southern end of the Kilauea caldera. The area of the mound is also the center of ground deformation believed to be associated with a magma chamber at a depth of several kilometers as well as with a concentration of shallow earthquake epicenter

ISSN:0148-0227    

DOI:10.1029/JB077i026p04957

年代:1972

数据来源: WILEY

摘要:

Mutual relationships of mobile lithospheric plates define two distinct tectonic environments each characterized by diagnostic magmatism. A compressional environment occurs at loci of plate convergence; quartz‐ and hypersthene‐normative intermediate, acid and basic members of the calc‐alkaline orogenic suite are emplaced above a dipping seismic zone. A tensional environment occurs mainly at loci of plate divergence, areas characterized by networks of deep fractures, offset by transform faults. Products of nonorogenic magmatism typically consist of abundant tholeiitic or alkali olivine basalt, possibly accompanied by rhyolite, trachyte, or phonolite (or plutonic equivalents); intermediate compositions are volumetrically insignificant. On a differentiation index versus frequency plot, orogenic suites define one maximum, nonorogenic suites two maximums. Orogenic rocks show no iron enrichment; nonorogenic suites do. Recognition of older igneous associations as orogenic or nonorogenic by employing chemical and mineralogical criteria can lead to inferences about tectonic environments during emplacement. Such criteria may provide a unique insight into regional tectonic evolution very difficult to deduce from structural investigations

ISSN:0148-0227    

DOI:10.1029/JB077i026p04966

年代:1972

数据来源: WILEY

摘要:

An array of six strainmeters was used to determine a least‐squares regional strain field in southern Nevada. The deformation occurs in several distinct episodes over the 8‐month interval analyzed. In each episode the directions of principal axes remain NW and NE, and the deformation is almost entirely pure shear. The end of each episode is marked by an abrupt reversal in the direction of compression and extension. Local, instrumental, and weather effects seem to be ruled out, and tectonic stresses remain the most likely explanation for the observed deformation. Substantial strain accumulation and relaxation appear to occur here without any manifestation in the form of earthqua

ISSN:0148-0227    

DOI:10.1029/JB077i026p04976

年代:1972

数据来源: WILEY

摘要:

Previous paleomagnetic studies of Jurassic rocks have not given concordant results and have led to the conclusion that the Jurassic pole position was possibly close to the present geographic pole. To test that supposition, the Kayenta, Carmel, Entrada, and Summerville formations were sampled from the extensive Jurassic sedimentary sequence in eastern Utah. The Lower and Upper Jurassic Kayenta and Summerville formations gave very similar magnetization directions. However, the Middle to Upper and Upper Jurassic Carmel and Entrada formations proved to be paleomagnetically unstable, and no reliable pole positions could be calculated. Poles calculated from two localities in the Kayenta formation and from the Summerville formation are 98°E, 59°N and 84°E, 59°N (Lower Jurassic) and 86°E, 70°N (Upper Jurassic, Oxfordian); thus they show a lack of major movement of the North American continent before Upper Jurassic (upper Oxfordian) time. Comparison with published Lower Cretaceous pole positions (135–100 m.y. in age) indicates that the 30 degrees of arc movement in the North American polar‐wander curve (from the Upper Jurassic to the Lower Cretaceous pole positions) occurred in approximately 30 m.y. Thus the major portion of the spreading in the North Atlantic between Africa and North America did not occur until uppermost Jurassic‐Lower Cretaceous times, making this period one of rapid sea‐floor spreading compared to that of the

ISSN:0148-0227    

DOI:10.1029/JB077i026p04981

年代:1972

数据来源: WILEY