Seismic studies of low-velocity layers and horizontal inhomogeneities within the crust and upper mantle on the territory of the U.S.S.R.

Recent seismological studies of low-velocity layers in the U.S.S.R. have led to the development of new methods of investigation. The most important results obtained are presented in this paper. Several new techniques of record treatment and advanced computer programs make it possible to solve two-dimensional problems of seismic wave propagation in complex media and to outline zones of velocity inversion in the crust and mantle of many regions in the U.S.S.R.Zones of this type seem to occur only locally and are typical of some particular geostructures. Lateral inhomogeneities are also found to be closely related to geological features. Their depths sometimes can reach 300–400 km.     

Structure of the crust in the conterminous United States

On the basis of the newest interpretations of all sufficiently long seismic profiles, a contour map of the Mohorovi?i? discontinuity for the conterminous United States is compiled. Differences from earlier interpretations are discussed.     

Zoning in garnets—Diffusion models

When reference frames and diffusing components are properly selected, the flux equations for diffusion of the major components in natural garnets may often be approximated by: J DC. In such cases it is shown that, for reasonable diffusion coefficients and boundary conditions, observed zoning profiles in natural garnets may be explained with pure diffusion models. These models allow for original inhomogeneities in the host rock and may be used to explain why single hand specimens may show such a variety of zoning profiles within a single mineral species.     

Mechanics of growth of some laccolithic intrusions in the Henry mountains, Utah, I: Field observations, Gilbert's model, physical properties and flow of the magma

The shapes of sills and laccolithic intrusions and associated host rock deformation were studied at several locations on the flanks of the Henry Mountains. Diorite sills range from 0.5 to 10 m in thickness, are less than 1 km² in areal extent, and have blunt terminations. The laccolithic intrusions range from 10 to 200 m in thickness, and from 1 to 3 km² in areal extent. The host rock, principally sandstone and shale, is deformed along closely spaced cataclastic shear planes. This deformation is concentrated at contacts, especially near sill terminations and over laccolith peripheries. The diorite contains plagioclase phenocrysts which are usually sheared in a thin zone adjacent to each contact. Field observations suggest that sills are the forerunners of laccolithic intrusions which form only after magma has spread far enough laterally (greater than about 1 km² in the Henry Mountains) to gain leverage to bend the overburden upward. Further injection of magma results in laccolithic peripheries or terminations with one of three distinct cross-sectional forms: (1) blunt termination of the diorite accompanied by bending and minor faulting of the host rock; (2) termination at a peripheral diorite dike cutting upward across the host rock; or (3) abrupt termination of the diorite against a nearly vertical fault zone.In order to study some of the processes of sill and laccolith intrusion, mechanical models for the driving pressure, physical properties, and flow behavior of the diorite magma are derived and discussed. A static driving pressure (equal to the difference between total magma pressure and lithostatic pressure) of up to 700 bar is estimated. The rheological behavior of the magma in the Henry Mountains is unknown. However, flow behavior is calculated assuming three of the more common models for fluids: Newtonian viscous, pseudoplastic, and Bingham. Suspended crystals probably contributed to the finite strength of the magma (estimated to be at least 10³ dyn/cm² for the Henry Mountains magma) which enables it to support dense zenoliths and also fixes maximum limits on the lengths of sills or dikes. Pressure in magma flowing along tabular intrusions of uniform thickness drops linearly in the flow direction for all three rheological materials. Thickening of tabular intrusions tends to make the pressure drop less rapidly, but pressure drops more rapidly in the tapered region near a termination. Pressure distributions under these and other conditions are derived in order to use them in the models of host rock deformation presented in Part II.     

High temperature mass spectrometric gas-release studies of Hawaiian volcanic glass: Pele's tears

The identification of gaseous molecular species and mechanisms of their release from glassy lava have been investigated with a high temperature mass spectrometer. Using Pele's tears as representative of quenched liquids of Hawaiian tholeiitic basalts, it was found that volatiles are released at low temperatures by a rate-limiting diffusion mechanism and, at temperatures in the softening range of the glass, by bursting of bubbles trapped near the vaporizing surface of the sphere-like particles.Gases released by bursting gave pressure surges and were found to be water vapor, CO₂ and CO. Those released principally by diffusion, and in some cases generated by thermal degradation and further reaction with the sample, include H₂, O₂, N₂, S₂, H₂S, SO₂, SO₃, COS, HCl, HF and NH₃. Average mole percent compositions of the volatiles H₂O, CO₂ and SO₂ relative to the total gas released were found to be 95 per cent, 3·5 per cent and 1 per cent, respectively. Minor concentrations of organic constituents, previously unobserved in volcanic gas analyses, were also found. Fragmentation patterns and gas release behavior suggest that these are derived from a mixture of low-molecular weight saturated and unsaturated acyclic hydrocarbons (C₁-C₄).     

Interactions of biogenic opal,sediment and seawater in the Central Equatorial Pacific

The solution rate of biogenic opal in near-surface sediments in the Central Equatorial Pacific is three to eight orders of magnitude lower than similar acid-cleaned samples. Iron, magnesium and calcium aluminosilicates may be the minerals which are forming on the surface of the opal and reducing its solution rate. The scale height of the system studied suggests that diffusive and not advective processes are primarily responsible for the removal of dissolved silica in sediments. Solution budget calculations for this area suggest that 90–99 per cent of the biogenic opal produced in surface waters dissolves before reaching the sediment-water interface; an additional amount dissolves within the sediment and diffuses into bottom waters leaving 0.05–0.15 per cent of the original amount of opal produced by organisms in the sedimentary record. The relative solution potential of the upper 1000 m of the water column varies by more than an order of magnitude from the Antarctic to Equator and may have a pronounced effect on the accumulation rate of biogenic opal in underlying sediments.     

Distribution and diagenesis of organic compounds in JOIDES sediment from Gulf of Mexico and western Atlantic

Fifteen sediment samples were studied from five drill sites recovered by the ‘Glomar Challenger’ on Legs I and IV in the Gulf of Mexico and western Atlantic. This study concentrated on compounds derived from biogenic precursors, namely: (1) hydrocarbons, (2) fatty acids, (3) pigments and (4) amino acids.Carbon isotope (δC¹³) data (values < ? 26%, relative to PDB), long-chain n-alkyl hydrocarbons ( ?C₂₇7) with odd carbon numbered molecules dominating even carbon numbered species, and presence of perylene proved useful as possible indicators for terrigenous contributions to the organic matter in some samples. Apparently land-derived organic matter can be transported for distances over 1000 km into the ocean and their source still recognized.The study was primarily designed to investigate: (i) the sources of the organic matter present in the sediment, (ii) their stability with time of accumulation and (iii) the conditions necessary for in situ formation of new compounds.     

Oxygen and bulk element abundances in Luna 20 fines

Abundances of O, Si, Al and Mn have been determined in Luna 20 fines sample 22001,9 by instrumental neutron activation analysis. The abundances of O, Si and Al are among the highest we have observed in lunar samples and reflect a highlands origin for much of this regolith sample. The Luna 20 abundances reported here most closely resemble those we have determined in four samples of two Apollo 16 fines, rock 14310, and a clast from breccia 15459. The Luna 20 $\text{O}\text{Si}$ ratio of 1.96 ± 0.05 is similar to that in most other lunar samples, but the $\text{Al}\text{Si}$ ratio of 0.532 ± 0.024 is exceeded only by our data on the Apollo 16 fines. This $\text{Al}\text{Si}$ ratio is in agreement with the value of 0.55 ± 0.06 determined by the remote X-ray fluorescence experiment for the highlands between Mare Crisium and Mare Smythii which lie near the Luna 20 site (Adleret al., 1972).     

Perylene and its geochemical significance

Perylene was found in a variety of marine sediments, in a shale and in peat. It is suggested that its precursors arise predominantly from land organisms and are carried into oceanic traps along with detrital minerals. When rates of deposition are fast, and reducing conditions are established within the sediment, biogenic pigment precursors of perylene are converted to the polycyclic aromatic hydrocarbon, which is then stabilized by π-bonding with metals and protected from degradation.     

Subsurface electric fields of a grounded cable of finite length for both frequency and time domain

Summary The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations.