Precise laboratory wavelengths of the Mg I and Mg II resonance transitions at 2853, 2803 and 2796 Å

Strong ultraviolet resonance transitions are observed routinely both in the Galactic interstellar medium and in quasar absorption systems. The quality of the astronomical spectroscopic data now available demands more precise laboratory rest wavelengths. Of particular interest is the accuracy with which one can constrain space–time variations in fundamental constants using quasar spectra. A recent analysis by Webb et al. of 25 quasar spectra using Mg and Fe transitions tentatively suggests that the fine-structure constant was smaller at earlier epochs. To permit a check on this result, and to allow further more extensive investigations, we have carried out a new determination of the laboratory wavelengths of Mg  i  2853 Å, Mg  II  2796 Å and Mg  II  2803 Å by high-resolution Fourier transform spectroscopy. Our results for Mg  II  2796 Å are consistent with the value measured independently by two other groups. To our knowledge, no previous measurements of comparable precision exist for Mg  I  2853 Å and Mg  II  2803 Å.     

Noble gases in the earth's mantle

The abundances and isotopic compositions of noble gases in two samples from ultramafic xenoliths in alkali basalt, a young kaersutitic amphibole separated from a peridotite xenolith from Dish Hill, California and an ancient whole-rock lherzolite xenolith from Baja California, are reported and compared with the results of analyses on other mantle samples. In addition to previously recognized excesses of ³He and ¹²⁹Xe, our results indicate that ambient gases in the mantle show a general enrichment of the lighter-mass nonradiogenic isotopes of Ar, Kr and Xe, and Ar with ⁴⁰Ar/³⁶Ar = 3 · 10².     

Trachyte shield volcanoes: a new volcanic form from South Turkana,Kenya

Seven Pliocene volcanoes, one of which is described in detail, occur in the northern part of the Kenya Rift. They have low-angle, shield like forms, and comprise lavas, pumice tuffs and ash-flow tuffs almost wholly of trachytic composition. Each volcano possesses a structurally complex source zone in which plugs, dykes and pumice tuffs are concentrated and in which clearly defined craters and calderas are uncommon. By contrast, the flank zones are stratiform with slopes of about 5° and are composed of lavas and ash-flow sheets erupted in a highly fluid condition. The volcanoes range up to 50 km in diameter and are elongated parallel to the general trend of the rift reflecting a tectonic control on the distribution of the vents and their products. This combination of morphological, structural and compositional features suggests that the volcanoes are of a type not described before. Notes on the petrography of the lavas are included and it is suggested that the trachytes are petrogenetically related to alkali basalts, compositionally similar to those which form the substrate to the trachyte volcanoes.     

Model systems for anatexis of pelitic rocks

Subsolidus and melting reactions involving calcic plagioclase in pelitic assemblages in the K-Na-Ca model system occur at higher temperatures than their K-Na counterparts. For the most calcic plagioclase compositions observed in high-grade pelitic rocks (An₂₅-An₄₀) the equilibria are rarely extended by more than 30 ° C above those in KA1O₂-NaAlO₂-Al₂O₃-SiO₂-H₂O, although all discontinuities in facies inferred for the K-Na system are continuously displaced when they involve Ca-bearing plagioclase. The maximum pressure-temperature overlap between muscovite dehydration and initial melting reactions occurs in the pressure range of 4–6 kbar between about 640 ° and 720 ° C. This provides optimum conditions for anatectic melt generation in felsic rocks of the appropriate compositions progressively metamorphosed in kyanite-sillimanite facies series. Progressive regional metamorphism at pressures of 2–4 kbar, corresponding to andalusite-sillimanite facies series, shows little overlap between muscovite dehydration and initial melting reactions. Consequently anatectic melt generation in andalusite-sillimanite facies series would require the participation of biotite in dehydration-melting reactions. Felsic intrusive rock in andalusite-sillimanite terranes could have risen upward from their anatectic sites in high grade kyanite-sillimanite facies series at depth. Many andalusite-sillimanite facies series terranes culminating in migmatites could represent upward movement of kyanite-sillimanite facies series rocks to shallower depths with uplift rates faster than cooling rates.     

A reinterpretation of the entrainment process in some laboratory experiments

Pollard et al. (1973) proposed a closure hypothesis for the entrainment process in the stress-mixed layer of a stratified fluid. Some laboratory experiments suitable for testing the hypothesis were carried out by Kantha et al. (1977) and by Kato and Phillips (1969). In the early period of each experiment, before side-wall friction becomes important, these experiments support the closure hypothesis, with a critical Froude number close to 1, perhaps F = 1.2 ± 0.2.     

Turbulence Measurements above a Pine Forest

Eddy fluxes of momentum, sensible and latent heat, and turbulence spectra measured over the Thetford Forest during 10 days in the Spring of 1973 are described. The measured total heat flux (H + λE) for 122 20-min periods agreed closely on average with independent estimates from an energy balance method. There was evidence that the energy balance data gave small systematic overestimates of available energy during the hours before noon, compensated by slight underestimates for the remainder of the day. A comparison of measured wind speeds and friction velocities in neutral stability confirmed the validity of the aerodynamic method for estimating momentum fluxes at heights of a few roughness lengths above the canopy. In stable conditions the log-linear wind profile $U=(u_{?t}/k)({? ln}((z-d)/z_{0})+←pha(z-d-z_{0})/L)$ with α = 3.4 ± 0.4 provided a good fit to the data. Spectra in unstable conditions were generally more sharply peaked than those measured by other workers over smoother terrain: differences were less marked in the case of vertical velocity in stable conditions. Temperature spectra in these stable conditions showed high energy at relatively low wavenumbers, and wT cospectra showed a cospectral gap; both of these results were associated with an intermittent sawtooth structure in the temperature fluctuations.     

Pollution records from sediments of three lakes in New York State

Sediment core segments from Sylvan Lake, Lake Champlain and Lake Canadarago were dated radiometrically with ²¹⁰Pb and ¹³⁷Cs. Their respective sedimentation rates were determined to be 0.11, 0.14 and 0.52 g cm^?2 yr^?1. For the two lakes of lower sedimentation the variations of selected elemental abundances as function of depth were analyzed. Two groupings were found: Al, K, Ti, Rb and Zr were correlated among themselves but reflected different variations in the input of terrigenous erosion material to the lakes. The Cu, Zn and Pb correlated among themselves showed similar depth dependence with increasing concentrations toward the top which can be attributed to cultural pollution. Recent ‘excess’ fluxes to the sediments above the natural contribution by clastic material were derived for the location of the cores, which for Cu, Zn and Pb amounted to 3.8, 24 and 16 μg cm^?2 yr^?1 respectively for Sylvan Lake and 4.9, 20 and 16 μg cm^?2 yr^?1 for Lake Champlain. The corresponding ²¹⁰Pb flux was 3.3 and 2.3 dpm cm^?2 yr^?1, respectively for the two lakes.Approximate residence times in the water column were obtained for trace metals at the Lake Champlain location. Short residence times estimated for Pb (< 0.15 yr) and Cu (< 0.4 yr) indicate fast removal, whereas those for Zn (1.0 ± 0.3 yr) and Cr (2.0 ± 0.5 yr) appeared to be dominated by the water residence time.     

Stable isotope studies of fluid inclusions in speleothems and their paleoclimatic significance

Fluid inclusions found trapped in speleothems (cave deposited travertine) are interpreted as samples of seepage water from which enclosing calcium carbonate was deposited. The inclusions are assumed to have preserved their D/H ratios since the time of deposition. Initial ¹⁸O/¹⁶O ratios can be inferred from δD because rain- and snow-derived seepage waters fall on the meteoric water line (δD = 8δ¹⁸O + 10). Estimates of temperature of deposition of the carbonate can be calculated from inclusion D/H ratios and δ¹⁸O of enclosing calcite in Pleistocene speleothems. For most speleothems investigated (0–200,000 yr old) δ¹⁸O of calcite appears to have decreased with increasing temperature of deposition indicating that the dominant cause of climate-dependent change in δ¹⁸O of calcite was the change in K_cw, the isotope fractionation equilibrium constant, with temperature; δ¹⁸O of meteoric precipitation generally increased with increasing temperature, but not sufficiently to compensate for the decrease in K_cw.