Age and origin of early Proterozoic dolerite dykes in South-West Greenland

Samples of three dolerite dykes from South-West Greenland give a pooled weighted mean Rb-Sr whole-rock isochron age of 2,130±65 Ma. Initial ⁸⁷Sr/⁸⁶Sr ratios are 0.70155±0.00018 for one of the dykes (Naujat) and 0.70277±0.00012 for the other two (Torssut and Akinaq). A fourth dyke (Qaqarssuaq) did not yield an isochron. Torssut samples have significantly lower initial ²⁰⁷Pb/²⁰⁴Pb ratios than samples from the Naujat dyke, indicating that the Torssut dyke has been affected by crustal contamination. Samples of the dykes vary widely in chemical composition because of an uneven distribution of different primocryst phases throughout the dykes, and because of variable degrees of fractionation of the magma. For two of the dykes some constraints on the composition of the parent magma have been inferred from trace element data. Higher concentrations of K, Rb, Ba, Sr, Ce and perhaps Nb (at comparable levels of magmatic fractionation) in the dykes with higher Sr_i are probably related to crustal contamination of their parent magmas. Two of the dykes probably intruded from zoned magma chambers. The marginal zones of these dykes crystallised from a strongly fractionated magma, whereas the centres of the dykes consist of more primitive material with large proportions of olivine and plagioclase primocrysts. The central part of Torssut is less strongly contaminated with crustal Pb than the border zones. A more detailed analysis of the Pb-isotopic composition in the Torssut dyke shows that contaminant lead must have been derived from rocks in the deeper crust considerably older than the late Archaean gneisses which occur at the surface.     

Aircraft and ship observations of the mean structure of the marine boundary layer over the Arabian Sea during MONEX 79

Analysis of the mean wind, equivalent potential temperature and virtual potential temperature profiles observed by the National Center for Atmospheric Research (NCAR) Electra aircraft and obtained from dropwindsondes and ship-launched radiosondes were made in conjunction with synoptic observations to study the structure of the monsoon boundary layer over the Arabian Sea during MONEX 79. Comparison of mean profiles indicates the monsoon boundary layer to be much different from the trade wind boundary layer. Results confirm the existence of a boundary-layer jet known as East African or Somali Jet. Regions of multiple cloud layers at roughly the height of the capping inversion layer were associated with the jet. Regions in which a more well-mixed layer was observed showed a jet structure depressed in height. A free-jet surface-layer model appears to describe the mean wind structure of this jet observed during the present study and by others. An approximate balance of forces was found in the monsoon boundary layer between friction, advective acceleration, Coriolis and pressure gradient forces. Friction and advective acceleration terms were significant in the lower levels of the boundary layer. Forces in a typical trade wind boundary layer were found to be approximately one order of magnitude smaller than those observed in the monsoon boundary layer.     

Recruitment of Mytilus edulis L. in the Thames estuary,with evidence for differences in the time of maximal settling along the Connecticut shore

In the Thames Estuary at the eastern end of Long Island Sound, most mussels achieve maximal gonadal development during the summer and larval settlement occurs primarily during the fall. The timing of reproductive events is several months later than has been reported for other populations of mussels in Long Island Sound but corresponds to that of mussels inhabiting the south shore of Long Island. The data support the growing body of evidence which indicates that temperature is not a major factor determining the reproductive period of this bivalve.     

An evaluation of rate equations for calcite precipitation kinetics at pCO2 less than 0.01 atm and pH greater than 8

We used a reproducible seeded growth technique with a pH-stat to study the kinetics of calcite precipitation at 25°C. We performed different experiments at initial Ca²⁺ and HCO₃^? concentrations ranging from 0.7–2 and 4–7 mmol L^?1, pH values ranging from 8.25 to 8.70, $\text{pCO}{}_2$ values ranging from 0.0006 to 0.01 atm, and ionic strengths ranging from 0.015 to 0.10 mol L^?1. With this experimental data set, we used initial rate measurements and integral methods to test several precipitation rate equations. Rate equations that possess a disequilibrium functional dependence, such as the BURTON et al. (1951) dislocation model, forms of the Davies and Jones (1955) model, and the model used by Reddy and Nancollas (1973), did not adequately describe the kinetics of calcite precipitation at pH greater than 8 and $\text{pCO}{}_2$ less than 0.01 atm. Rate equations that describe independent dissolution and precipitation mechanisms with elementary reactions, such as the equation presented by Plummeret al. (1978), and nancollas and Reddy (1971) were more successful. However, Plummer's model did not adequately describe the rate of all experiments due to the presence of an OH^? surface term in the precipitation rate equation. The elementary reaction of the Nancollas and Reddy model is written in terms of bulk Ca²⁺ and CO₃^? concentrations, and appears to be the most successful model which describes calcite precipitation at pH > 8 and $\text{pCO}{}_2\text{< 0.01}$ atm. The Nancollas and Reddy model, altered to account for varying ionic strengths, adequately described the rate of all experiments and yielded a precipitation rate constant of $\text{118.2 ± 13.9}$ dm⁶ mol^?1 m^?2 s^?1, with an apparent Arrhenius activation energy of 48.1 kJ mol^?1.     

Nature and culture in social science: the demarcation of domains of being in eighteenth century and modern discourses

Modern social science is concerned with policing the ‘boundary’ between nature and culture, with limiting and excluding phenomena which threaten to challenge its account of the social determination of the attributes of human beings. The paper argues that this boundary defence is an unusually touchy and difficult matter because social science has inherited an Enlightenment conception of man as ‘unique’. Human culture is regarded as different in quality from any possible form of animal association or attainment. At the same time as supporting this ontology it supposes the ‘boundary’ is in some sense a matter of empirical science, capable of specification by reference to evidence. We try to show the confusions these two contradictory circumstances produce by considering two debates: those concerning the possibility of ‘feral’ children and those concerning the uniqueness of language to human beings. It is demonstrated that the modern debates develop theories, issues and lines of dispute which appeared in the eighteenth century.     

Cathodoluminescence petrography of syntectonic quartz fibres

The cathodoluminescence of low grade metamorphic quartz is reported in the literature to be uniformly brown. This study describes an investigation of syntectonic quartz fibres from veins and pressure shadows contained in different carbonate units of the Helvetic Alps, Switzerland, and of Anglesey, U.K., with the Scanning Electron Microscope in the cathodoluminescence mode. The cathodoluminescence spectra measured show systematic variations between older and younger parts of the same fibre, and between fibres from different tectonic units. These variations can be related first to variations in the temperature of formation of the quartz fibres, and second to deformation-induced differences in the microstructure of the earlier formed parts of fibres during later imposed strains.     

The formation age of the Brachina meteorite

Nuclear particle tracks were studied in various phases from the Brachina meteorite, which was classified until recently as a chassignite. Fission tracks due to the decay of²⁴⁴Pu(T₁₂ = 82m.y.) were observed and indicate that Brachina formed ～ 4.5 b.y. ago in a parent body which was most probably asteroidal in size. Contrary to what has been previously suggested [7], there is no need to postulate a Martian origin for this meteorite. This conclusion is supported by independent evidence obtained by other groups.