Uranium and boron distributions in some oceanic ultramafic rocks     

M.G. Seitz  S.R. Hart 《Earth and Planetary Science Letters》1973,21(1):97-107

From mica fission-track maps the serpentinized and weathered portions of four ultramafic rocks from oceanic ridge systems contained 0.5 to 2.4 ppm U compared to only 2.5 ppb in clinopyroxene, 0.6 ppb in chromite and less than 7.0 ppb in olivine. Orthopyroxene grains contained 0.4 ppb U which is three orders of magnitude lower than had previously been reported.Long thin tracks from (n, α) reactions with boron were recorded in cellulose nitrate plastic and were counted like fission tracks. The track density from boron was 2×10⁴ times higher than that from uranium fission alone. Boron in serpentine was variable on a 50-μm scale attaining 155 ppm concentrations. Orthopyroxene grains, in contrast, had maximum concentrations of 0.8 ppm.Most of the uranium and boron in the rocks is believed to have been introduced during serpentinization. From known crystal-melt partitioning ratios the uranium and boron distributions are consistent with the ultramafic rocks being cumulates or residues from partial melting events.  相似文献   

Foraminiferal evidence for the age of the Cambridge Greensand     

M.B. Hart 《Proceedings of the Geologists' Association. Geologists' Association》1973,84(1):65-82

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Particle track record in Apollo 15 deep core from 54 to 80 cm depths     

R.L. Fleischer  H.R. Hart 《Earth and Planetary Science Letters》1973,18(3):420-426

Particle track measurements have been made in nearly 500 individual grains from 13 levels in the 54–80 cm depth range of the Apollo 15 deep core. They reveal a wide range of track densities at all depths and some systematic variations within layers, indicating that both predepositional mixing and subsequent layering are present and that separate sub-layers exist within larger regions where no sub-layers are visible. Minimum track densities are inferred to be useful measures of maximum residence times for undisturbed layers. Using the observed minimum track densities we conclude that the average deposition rate in this section of soil column was ≥ 0.4 cm/million years.  相似文献   

Stepwise mass extinctions: the case for the Late Cenomanian event     

Malcolm B. Hart  Paul N. Leary 《地学学报》1991,3(2):142-147

The various extinctions of marine taxa in the Late Cenomanian can be shown as conforming to the 'step-wise extinction' model. The order of such extinctions is, however, compatible with the presence of an expanded oxygen minimum zone in the world ocean. The occurrence of iridium anomalies at this level in the succession may, however, indicate a volcanogenic control on the global environment. Detailed time-analysis of the Late Cenomanian event has been used to produce a correlation of some key successions.  相似文献   

The dynamics of explosion and its use. Developments in civil engineering, 1, Josef Henrych (Ed.), Elsevier,Amsterdam (1979), 558 pp., U.S. $107.25, Dfl 220.00     

Malcolm Mellor 《Engineering Geology》1981,17(3):204-207

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A three-dimensional numerical model of particulate transport for coastal waters     

Malcolm L. Spaulding  Daniel Pavish 《Continental Shelf Research》1984,3(1):55-67

A Lagrangian marker particle in Eulerian finite difference cell solution to the three-dimensional incompressible mass transport equation was developed for predicting particulate transport in coastal and estuarine waters. Special features of the solution procedure include a finite difference grid network which translates horizontally and vertically with the mean particle motion and expands with the dispersive growth of the marker particle cloud. The cartesian vertical coordinate of the three-dimensional mass transport equation has been transformed, using instantaneous water column depth to allow adaptation to flow situations with a temporally and spatially varying bottom topography and free surface. Results from this model for turbulent diffusion and advection of a uniform plug flow of sediment in an unbounded uniform flow field with various sediment settling velocities were in excellent agreement with the corresponding analytic solutions. Using current information from a two-dimensional vertically averaged hydrodynamic's model, the model was utilized to predict the long term diffusion and advection of dilute neutrally and negatively buoyant suspended sediment clouds resulting from a hypothetical instantaneous release of dredge spoil waste at Brown's Ledge in Rhode Island Sound.  相似文献   

An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer   总被引：2，自引：27，他引：2  

Robert J. Beare  Malcolm K. Macvean  Albert A. M. Holtslag  Joan Cuxart  Igor Esau  Jean-Christophe Golaz  Maria A. Jimenez  Marat Khairoutdinov  Branko Kosovic  David Lewellen  Thomas S. Lund  Julie K. Lundquist  Anne Mccabe  Arnold F. Moene  Yign Noh  Siegfried Raasch  Peter Sullivan 《Boundary-Layer Meteorology》2006,118(2):247-272

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.  相似文献   

Trace Metal Solid State Speciation in Aerosols of the Northern Levantine Basin,East Mediterranean   总被引：3，自引：0，他引：3  

Mustafa Koçak  Nilgun Kubilay  Barak Herut  Malcolm Nimmo 《Journal of Atmospheric Chemistry》2007,56(3):239-257

An established three stage sequential leach scheme was applied to a series of selected high volume aerosol samples (n = 35) collected from the Turkish Eastern Mediterranean coastline (Erdemli). Samples were selected according to their air mass back trajectory history to reflect the contrasting mixtures of aerosol material present in the Eastern Mediterranean marine aerosol. Two populations were adopted, those samples which were classed as “anthropogenic” and those which were “Saharan” dominated aerosol populations. Applying the three stage leach it was possible to define the proportion for each of the considered metals (Al, Fe, Cu, Pb, Cd, Zn and Mn) present in the (a) “exchangeable” (b) “carbonate / oxide” and (c) “refractory” phases, representing novel solid state aerosol speciation data for this marine system. Clear trends were established, conforming with data from previous studies with mainly crustal derived metals (Al and Fe) being present in the refractory phases (Al > 88%; Fe > 84%) and those influenced by anthropogenic sources being dominating in the exchangeable phase, although for these metals the variability was comparatively high (12–64%; 19–85%; 40–100% for Zn, Pb and Cd, respectively). For the majority, greater exchangeable fractions were present the lower the crustal source contribution to the aerosol population, whereas the “refractory” fraction exhibited contrasting behaviour. This was illustrated by the novel application of the mixing diagram, presenting each of the three speciation stages against the corresponding percent anthropogenic contribution to each collected sample. Zn, Pb and Cd all illustrated progressive decrease in the percent exchangeable with increasing crustal contribution to the aerosol population. The percent exchangeable was discussed in terms of its use to represent the upper limit of the bioavailable fraction of metal associated with the aerosol, post deposition. The mixing diagram approach enabled the prediction of the residual fractions for Cd, Pb and Zn (41 ± 4%; 62 ± 4% and 82 ± 5%, respectively,) in Saharan end-member material.  相似文献   

Blast vibration analysis     

Malcolm Mellor 《Engineering Geology》1981,17(4):285-286

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A general mixing equation with applications to Icelandic basalts   总被引：4，自引：0，他引：4  

Charles H. Langmuir  Robert D. Vocke  Gilbert N. Hanson  Stanley R. Hart 《Earth and Planetary Science Letters》1978,37(3):380-392

The mixing equation applied by Vollmer [1] to Pb and Sr isotope ratios is shown to be a general equation applicable to consideration of element and isotope ratios. The mixing equation is hyperbolic and has the form:Ax + Bxy + Cy + D = 0where the coefficients are dependent on the type of plot considered: i.e. ratio-ratio, ratio-element, or element-element. Careful use of this equation permits testing whether mixing is a viable process, places constraints on end member compositions, allows distinction between mixing of sources and mixing of magmas, and should allow distinction between recent mixing and long-term evolution of sources.The available chemical data for postglacial basalts from Iceland and along the Reykjanes Ridge are not consistent with either mixing of magmas or simple mixing of an enriched ocean island source with a depleted ocean ridge source. If the available analyses for basalts are representative of the source regions, the data are consistent with at least two models neither of which can be properly tested with the available data.(1) There are two separate mixing trends: one beneath Iceland with the alkali basalt source and a depleted Iceland source as end members; the second along the Reykjanes Ridge with a heterogeneous ocean ridge basalt source and a source similar to that for intermediate basalts on Iceland as end members. The depleted Iceland source and the depleted ocean ridge source are not the same.(2) The chemistry of the basalts is not determined by mixing. Instead the basalts are derived from a multiplicity of sources with a similar history which have been isolated for hundreds of millions of years.  相似文献