Factors controlling the noble gas abundance patterns of deep-sea basalts     

Jack Dymond  Lewis Hogan 《Earth and Planetary Science Letters》1978,38(1):117-128

A number of processes may modify the noble gas composition of silicate liquids so that the composition of noble gases observed in glassy margins of deep-sea basalts is not that of the upper mantle. Differential solubility enhances the light noble gases relative to the heavier gases; however, we demonstrate that the observed abundance pattern cannot be attributed to solubility of noble gases with atmospheric proportions. Partial melting and fractional crystallization increase the noble gas content of all species relative to mantle concentrations, but do not fractionate their relative abundances. Noble gases may be lost from an ascending magma in various ways, the most important, however, may be exclusion of gas from crystals forming at the time of solidification, which is shown to result in marked loss of gas from the basalt. Small amounts of low-temperature alteration of solidified basalt can produce dramatic changes in the noble gas abundance pattern, since the adsorption coefficients for the different noble gas favor uptake of heavy species relative to the light species. Atmospheric contamination can account for observed variations in the ⁴⁰Ar/³⁶Ar ratio of oceanic basalts. The degree of crystallinity of glassy margins of deep-sea basalts may control the helium abundance of these samples; however, the uniform ³He/⁴He values reported apparently reflect a relatively constant proportion of radiogenic and primordial helium in the mantle.  相似文献   

Uptake of radioactivity by marine sediments and implications for monitoring metal pollutants     

J.A Hetherington  B.R Harvey 《Marine pollution bulletin》1978,9(4):102-106

The value of studying artificially-produced radionuclides in the marine environment is discussed in the wider context of monitoring sediments for other metal pollutants. Differences in the dispersion of selected radionuclides discharged from the same known source are used to illustrate the sort of changes in phase or speciation which must occur with other metal pollutants, but which cannot be demonstrated directly because of the multiplicity of sources. Various chemical and physical procedures are discussed which can be applied to a study of heavy metal associations with marine sediments, as are questions such as the existence, or otherwise, of mechanisms for the slow release of adsorbed material from the buried sediment back into the water column. Suggestions are made as to how radionuclide studies may be helpful in answering questions such as these, which are considered to be vital for the meaningful interpretation of sediment analyses.  相似文献   

Metal accumulation rates in the Southeast Pacific and the origin of metalliferous sediments     

Jack Dymond  H.H. Veeh 《Earth and Planetary Science Letters》1975,28(1):13-22

Metal accumulation rates over the East Pacific Rise and Bauer Deep rule out normal authigenic precipitation of iron and manganese as the major mechanism of enrichment to the metalliferous sediments. A hydrothermal source located along the East Pacific Rise is compatible with the transition metal and aluminum accumulation rates. For the Bauer Deep the accumulation rate data suggest either that metal-bearing phases are being transported from the rise to the protected basins of the deep or that a second hydrothermal source exists within the Bauer Deep. A major portion of the minor elements being deposited in the Bauer Deep could result from authigenic precipitation, thus accounting for their distinctive chemical composition.  相似文献   

A study of the Rima Sirsalis lunar magnetic anomaly     

L.J. Srnka  J.L. Hoyt  J.V.S. Harvey  J.E. McCoy 《Physics of the Earth and Planetary Interiors》1979,20(2-4):281-290

The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10⁻³ G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10⁻⁵ – 10⁻⁴ G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length.  相似文献   

The realm of the terrestrial planets: Zdenek Kopal,institute of physics, 1978, 224 pp. £7.50     

Jack B. Hartung 《Geochimica et cosmochimica acta》1979,43(10):1701

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Pelagic tar off Georgia and Florida in relation to physical processes     

Camille Cordes  Larry Atkinson  Richard Lee  Jack Blanton 《Marine pollution bulletin》1980,11(11):315-317

Following the Ixtoc I oil rig blowout in Campeche Bay we hypothesized that resulting tarballs should eventually appear in the Gulf Stream off Gerogia and that because of dynamic barriers in the innershelf little would reach nearshore areas. To test these hypotheses, surface tows to collect floating tar were taken off the coasts of Georgia and Florida in October and December, 1979.No tar was found within 40 km of the shore. All samples more than 40 km offshore contained some tar. The mean concentration was 0.82 mg m^?2 with a range of 0.01–5.6 mg m^?2. Closely spaced sampling showed extreme variation but trends were consistent. Perylene was the most abundant compound in the tarballs.  相似文献   

Stranded tar on Florida beaches: September 1979–October 1980     

G.C. Romero  G.R. Harvey  D.K. Atwood 《Marine pollution bulletin》1981,12(8):280-284

Amounts of tar stranded on Florida beaches were determined periodically over one year (September 1979–October 1980). Results show that tar fouling of southeast Florida beaches is an order of magnitude greater than the rest of the state. This may result from the extensive ship traffic in the Straits of Florida. There is no evidence that any Florida beaches received increased amounts of tar as a result of the 1979 Ixtoc-1 blowout in the southern Bay of Campeche. There is also no evidence that the amounts of tar on southeast Florida beaches have increased over amounts measured in API studies conducted in 1958 and 1971.  相似文献   

Geochronology and petrochemistry of Easter and Sala y Gomez Islands: implications for the origin of the Sala y Gomez Ridge     

James G. Clark  Jack Dymond 《Journal of Volcanology and Geothermal Research》1977,2(1):29-48

Easter and Sala y Gomez Islands lie along the Sala y Gomez Ridge, a broad zone of high topography and scattered seamounts extending east-southeast from the East Pacific Rise. K-Ar ages and major element abundances of volcanic rocks from these islands are used to test the fixed melting spot hypothesis for the origin of this feature. Poike volcano, the oldest center on Easter Island, was constructed in two episodes, occurring at 2.5 and 0.9 m.y. ago. Eruptive activity on Sala y Gomez was nearly contemporaneous with the earliest volcanism on Easter Island. No migration of volcanism with time is apparent along the Sala y Gomez Ridge. Basaltic rocks from Easter Island have tholeiitic affinities, while those dredged from the base of Sala y Gomez belong to an alkali olivine basalt series. Differences in basalt chemistry suggest that the volcanic rocks from the two islands formed from magmas that equilibrated at different pressures, and a model is presented which relates the character of the erupted liquids to magma segregation at the base of a progressively thickening lithosphere. The islands and seamounts comprising the Sala y Gomez Ridge do not fall on a small circle about the Nazca-mantle pole of absolute motion. Available evidence, therefore, does not support a fixed melting spot origin for Easter Island, Sala y Gomez, and the Sala y Gomez Ridge. Rather, it appears that the Sala y Gomez Ridge formed along a leaky fracture zone, and in response to a major re-orientation of spreading centers in this area.  相似文献   

Velocity profiles and bed shear stress over various bed configurations in a river bend     

John S. Bridge  Jack Jarvis 《地球表面变化过程与地形》1977,2(4):281-294

Vertical velocity profiles measured over various bed configurations (plane beds, ripples, and dunes) in. the meandering River South Esk, Glen Clova, Scotland are presented on semilogarithmic paper. Local bed shear stress and roughness height are calculated from the lowermost parts of the profiles using the Karman-Prandtl law of the wall; these parameters, and the geometrical properties of the profiles, are related to the various bed configurations. A graphical model is used to identify profiles developed on specific regions of dune geometry, in order to discriminate those profiles that define bed shear effective in transporting sediment over dunes. An assessment is made of the errors involved in estimating local mean velocity from extrapolating the law of the wall to the water surface. A Darcy-Weisbach friction coefficient is related to bed configuration and local stream power.  相似文献   

The lower symmetric regime and its transition to waves in rotating annulus convection     

Jack A.C. Kaiser 《Dynamics of Atmospheres and Oceans》1977,1(4):323-343

Measurements of the temperature and zonal velocity fields which develop in a rotating annulus of fluid with an upper surface, differentially heated from the inner to outer cylinder, are described for the lower symmetric regime (small radial temperature differences). The temperature field is essentially conductive for moderate to large rotation rates, Ω (>1.0 sec⁻¹). The zonal velocity field is poorly approximated by the thermal wind equation.Measurements of the transition to waves from the lower symmetric regime at very large rotation rates are presented for positive and negative radial temperature differences. They suggest that the centrifugal buoyancy force and the free surface curvature may be important factors for the lower symmetric-wave transition at large Ω. By varying the stratification of the fluid over a range of 10³ independently of the radial temperature difference, Δr_wT, it is conclusively shown that several theories are correct in predicting that the lower symmetric transition is independent of the stratification at small Δr_wT > 0 for large enough Ω.  相似文献