Effects of alteration on element distributions in archean tholeiites from the Barberton greenstone belt,South Africa

Major and trace element and modal analyses are presented for unaltered, epidotized, and carbonated tholeiite flows from the Barberton greenstone belt. Au, As, Sb, Sr, Fe⁺³, Ca, Br, Ga, and U are enriched and H₂O, Na, Mg, Fe⁺², K, Rb, Ba, Si, Ti, P, Ni, Cs, Zn, Nb, Cu, Zr, and Co are depleted during epidotization. CO₂, H₂O, Fe⁺², Ti, Zn, Y, Nb, Ga, Ta, and light REE are enriched and Na, Sr, Cr, Ba, Fe⁺³, Ca, Cs, Sb, Au, Mn, and U are depleted during carbonization-chloritization. The elements least affected by epidotization are Hf, Ta, Sc, Cr, Th, and REE; those least affected by carbonization-chloritization are Hf, Ni, Co, Zr, Th, and heavy REE. Both alteration processes can significantly change major element concentrations (and ratios) and hence caution should be used in distinguishing tholeiites from komatiites based on major elements alone. The amount of variation of many of the least mobile trace elements in the altered flows is approximately the same as allowed by magma model calculations. Hence, up to about 10% carbonization and 60% epidotization of tholeiite do not appreciably affect the interpretation of trace-element models for magma generation.     

Basic entrainment equations for the atmospheric boundary layer

The parameterization of penetrative convection and other cases of turbulent entrainment by the atmospheric boundary layer is reviewed in this paper. The conservation equations for a one-layer model of entrainment are straightforward; all modeling problems arise in the context of the parameterization of various terms in the budget of turbulent kinetic energy. There is no consensus in the literature on the parameterization of shear production and of dissipation. Unfortunately, field experiments are not sufficiently accurate to guide the selection of suitable hypotheses. Carefully designed laboratory experiments are needed to settle the problems that remain.This paper has also been presented as Invited Paper at the Second IAHR Symposium on Stratified Flows, Trondheim, Norway, June 24–27, 1980.Free University, Amsterdam, The Netherlands.     

High-Pressure crystal chemistry of spinel (MgAl2O4) and magnetite (Fe3O4): Comparisons with silicate spinels

High-pressure crystal structures and compressibilities have been determined by x-ray methods for MgAl₂O₄ spinel and its isomorph magnetite, Fe₃O₄. The measured bulk moduli, K, of spinel and magnetite (assuming K′=4) are 1.94±0.06 and 1.86±0.05 Mbar, respectively, in accord with previous ultrasonic determinations. The oxygen u parameter, the only variable atomic position coordinate in the spinel structure (Fd3m, Z=8), decreases with pressure in MgAl₂O₄, thus indicating that the magnesium tetrahedron is more compressible than the aluminum octahedron. In magnetite the u parameter is unchanged, and both tetrahedron and octahedron display the 1.9 Mbar bulk modulus characteristic of the entire crystal. This behavior contrasts with that of nickel silicate spinel (γ-Ni₂SiO₄), in which the u parameter increases with pressure because the silicon tetrahedron is relatively incompressible compared to the nickel octahedron.     

Environmental oxidation rate of manganese(II): bacterial catalysis

A simple mass balance for dissolved manganese(II) in waters containing low levels of oxygen in Saanich Inlet indicates that the residence time for Mn(II) removal to the solid phase is on the order of a few days. The average oxidation state of Mn in particulate material sampled from the region of Mn removal was 2.3–2.7, and electron micrographs revealed structures characteristic of bacterially formed Mn precipitates. Radiotracer experiments utilizing ⁵⁴Mn(II) indicated that removal of Mn from solution in the region of active uptake was substantially blocked by a poison mixture, demonstrating that Mn(II) binding to particulates is catalyzed by bacteria in this environment.     

Iron porphyrins in the Permian Kupferschiefer of the lower Rhine Basin, N.W. Germany

Immature samples of the Permian Kupferschiefer from the Lower Rhine Basin in N.W. Germany were analysed for tetrapyrrole pigment type and abundance. The sediment, thought to have been deposited in a marine regime with enhanced salinity, was found to contain high concentrations of metalloporphyrins. The porphyrins are complexed to nickel (Ni) and oxovanadium (V=0), but high abundances of iron (Fe) porphyrins were also detected using UV/visible spectroscopy and mass spectrometry. The presence in the latter of series of aetioporphyrins, cycloalkanoporphyrins, di-cycloalkanoporphyrins and benz-cycloalkanoporphyrins was confirmed by accurate mass measurements; HPLC co-injection of deoxophylloerythroetioporphyrin (C₃₂ DPEP) with the demetallated iron porphyrins indicated its presence in the sediment as an iron complex. The study provides the first evidence for the occurrence of Fe porphyrins in geological samples other than coals and lignites, and reports the highest concentrations in sedimentary organic matter to date.     

Hotspots in ambient noise caused by ice-edge eddies in the Greenland and Barents Seas

Mesoscale eddies are frequently observed in the Greenland and Barents Seas' marginal ice zone (MIZ). The objective of this study was to investigate the hypothesis that acoustic hotspots along the ice-edge region are due to mesoscale eddy currents interacting with the broken-up ice floes in the MIZ. To test this hypothesis, ambient-noise case studies were carried out during the MIZEX 85-87 and SIZEX 89 field experiments. In each experiment, ice-edge eddies were localized visually from aircraft and by use of satellite remote-sensing data obtained in near real time. Sonobuoys were, thereafter, deployed by fix-wing aircraft and helicopters in selected eddy areas. Ambient-noise data, recorded over several hours by aircraft, were analyzed estimating averaged ambient-noise levels at four selected frequencies: 40, 100, 315, and 1000 Hz. The analysis showed high mean levels and large gradients in ambient noise near ice-edge eddies and during strong wind and wave forcing against the ice edge. The conclusion of this study is that mapping of the ice edge and localization of mesoscale ocean processes using remote sensing from space will provide important input to ambient-noise prediction in the MIZ.     

Submerged cylinder wave energy device: theory and experiment

Linearized water wave theory is used to show that a submerged long circular cylinder suitably constrained by springs and dampers to make small harmonic oscillations, can be extremely efficient in absorbing the energy in an incident regular wave whose crests are parallel to the axis of the cylinder. Experimental results are described which confirm the theory for small amplitude waves and which suggest that the device can still be fairly efficient in waves of moderate amplitude.     

X-Ray Line Transfer in Plasmas with Large Velocity Gradients

An astrophysically relevant experiment is compared to the output of a multidimensional radiation transfer code in which populations and radiation are self-consistently treated. Experimental Al Ly α spectra obtained with a very high-resolution spectrometer are presented as quantitative evidence of dot plasma non-planar expansion. Analysis of these spectra using the code is performed, in particular examining the effects of velocity gradients in directions other than that of the primary expansion. These calculations are found to be in good agreement with the experimental results. Usage of the Ly α doublet as a planarity diagnostic is discussed.     

Optical Fiber Interferometers for Referencing Surface Benchmarks to Depth

—We have developed and operated optical fiber interferometers for monitoring displace ments within boreholes, as part of a program of crustal deformation measurement. These optical fiber strainmeters—a total of twelve instruments at two sites in southern California—were installed to sense the motion of the end-monuments of much longer baseline strainmeters and tiltmeters, allowing correction for any near-surface ground movement. One of the installations was specifically designed to investigate the distribution of deformation with depth, measuring over several borehole length-intervals from 5 m to 50 m. The displacements recorded over year-long time scales along these length intervals range up to 6 mm and show internal consistency and stability at the 50 μ m level. The use of these interferometers to provide correction signals for kilometer-scale crustal strain measurements has resulted in greatly improved records.