The ages of the lunar maria and the filling of the mare basins

The age discrepancy between lunar highlands and mare is examined in terms of a hydrostatic head model incorporating an impact crater being fed continuously from depth with basaltic magma. It is shown that if the age difference is attributed to the filling time of the impact basin, the dimensions of the volcanic feeder conduits are of the order of a few metres.     

Numerical modelling of stratified flow: a spectral approach

A numerical formulation is developed to solve the three-dimensional hydrodynamic equations which describe flow in a stratified sea.Arbitrary continuous physically realistic variations of density and eddy viscosity can be included in the model, which is sufficiently flexible to be applicable to sea areas of any horizontal extent and depth. A continuous current profile from sea surface to sea bed, is computed with the model. A method for expanding computed current profiles in terms of vertical modes is proposed and the contribution of these modes to the current profiles is considered.The time variation of the wind-induced circulation of a stratified lake in response to a suddenly imposed and maintained wind stress is examined. Calculations show that the wind-driven surface current is modulated by the internal seiche motion of the lake.     

Estimating the Surface Wind Speed Over Drifting Pack Ice from Surface Weather Charts

Routine surface wind speed data, vital for the study of drifting pack ice, are not available for the polar oceans. Over sea, it has been demonstrated by Hasse that estimates of surface wind speed may be obtained from the geostrophic wind speed using linear formulae. Comparing estimated with observed data for six sites in Canada, it is found that the formulae may also be applied to obtain estimates of surface wind speed over pack ice.     

Thickness and thermal history of continental crust and root zones

The survival to the present of the Archean nuclei of Precambrian shields requires special explanation if, as seems likely, the rate of heat flow out of the earth was two or three times greater in the late Archean (2.5 b.y. ago) than at present, since such a high heat flux would have melted the base of the Archean crust. It is proposed that there must have existed beneath stable continental crust a root zone (or lithosphere, or tectosphere) at least 200 km thick which has acted as a thermal buffer between the crust and the convecting mantle; this is virtually the same model as has been proposed to explain the present distribution of heat flow between continents and oceans. The strong temperature dependence of silicate rheology insures that the mantle temperature at the base of the root zone was no more than about 150°C higher in the late Archean than at present; the greater Archean heat flux would have been removed mainly through faster sea-floor spreading. To have survived, the root zone must be mechanically and chemically distinct from the rest of the mantle, and its formation was probably intimately related to the differentiation and stabilization of the continental crust.     

Homogeneity and constitution of the earth''s lower mantle and outer core

The lower mantle and outer core of the recent “parametric earth model” (PEM), in which the velocity and density distributions in these regions are both smooth and consistent with the Adams-Williamson equation, are extrapolated to zero pressure using fourth-order finite-strain relations, and the results are compared with recent experimental data on relevant materials. The fourth-order term is found to significantly improve the fits to the model. The lower-mantle velocities are found to be significantly higher than those expected for mixtures of MgO, FeO and SiO₂ of olivine or pyroxene compositions. It is concluded that a slightly denser phase assemblage, with a low FeO content (roughly 5 mole%) is required to explain these results. This Fe content is not significantly different from that in the upper mantle. These results imply that no compositional or thermal constraints on whole-mantle convection can be resolved. The extrapolation of the outer core is well-determined, and the results are consistent with a mixture of Fe and a small proportion of a lighter element.     

Experimental data at 3 kbars pressure on parental magma to the Bushveld Complex

Experimental studies, mainly under 3 kbars pressure, have been undertaken on representative samples to determine if any of these compositions could be parental magma to the Bushveld Complex. One such composition, with 12.5% MgO, Mg/(Mg + Fe) of 0.72 and quartz-normative, crystallizes olivine, Fo₈₈, as liquidus mineral, at about 1,300° C, followed at only slightly lower temperature by orthopyroxene at 3 kbars pressure. There is a temperature drop of over 100° C before the appearance of plagioclase and finally clinopyroxene. This crystallization sequence is in excellent agreement with the observed sequence in the lower part of the Bushveld Complex.Results at higher pressures show that this composition cannot be a partial melt from mantle peridotite because olivine is replaced by orthopyroxene as the liquidus mineral at lower crustal pressures. A combination of olivine fractionation and contamination was probably involved in the early evolution of this magma.Experimental data on the other compositions show that they are not suitable as parental magma to the lowest portion of the complex. However, the data are used to construct phase diagrams within the basalt tetrahedron at 3 kbars pressure, which are of relevance to the crystallization of basic magmas in the upper crust.Research undertaken at the Grant Institute of Geology, University of Edinburgh, Scotland     

Temperature-dependent physiological response of Carcinus maenas exposed to copper

The effect of temperature on the heart rate (fH) of Carcinus maenas exposed to a sublethal nominal concentration (0.5 mg l(-1)) of copper is reported. Adult, intermoult males (4 cm carapace width) were collected from Stavanger Fjord (Norway) in August (seawater TEMPERATURE=17 degrees C) and maintained in the laboratory (fed ad libitum) at 5, 15 and 25 degrees C for 7 days. Following this holding period, crabs were exposed to waterborne copper at the same temperature. After 3 days of exposure, individual fH was measured using the non-invasive Computer Aided Physiological MONitoring system (CAPMON) method. Copper-exposed individuals demonstrated significantly increased fH compared with controls at 5 and 25 degrees C (P<0.01). It is inferred that physiological function in C. maenas may be more vulnerable to copper contamination at seasonal temperature extremes (5 and 25 degrees C) than at the 'standard' test temperature (15 degrees C). Additionally, cardiac arrest observed at 5 degrees C is interpreted as a physiological response to limit copper uptake while the erratic fH in the 25 degrees C group reflected enhanced copper toxicity.     

Contents Volume 15

Volume Contents

Contents Volume 15