Vector magnetic fields in prominences

A preliminary discussion is presented of measurements of the polarization of the He i D₃ multiplet in a quiescent prominence, observed with a wavelength-scanning Stokes polarimeter. For a series of 43 observations in the same prominence, the linear polarization of the major component of D₃ lies primarily in the range 1 to 2% and of the wing component, the range 2 to 5%; the polarization vector angle lies primarily in the range 10–25° for the major component, and 25–35° for the other component. From a more limited data set, the polarization of both components is found to first increase as a function of height in the prominence, and then to decrease; the polarization angles of the major component vary in a random-like way with height, while the wing component shows a systematic change. The amount of polarization and the angle of polarization are governed by the Hanle effect. The collective effect of the group of lines at the peak of D₃ evidently has a different sensitivity to the Hanle effect than does the wing component, thus yielding at least four independent measurements - two polarizations and two angles. With some redundancy, the vector magnetic field can then be established using the detailed theory of the Hanle effect. Since the wing component of D₃ is a simple triplet, an initial estimate of the magnetic field strength and its horizontal orientation, 0, relative to the line of sight, is simply obtained. Examples of such calculations are presented.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation.     

Fluid inclusions in high-grade gneisses of the Kapuskasing structural zone,Ontario: metamorphic fluids and uplift/erosion path

Fluid inclusions in quartz grains from five samples of high-grade rocks (two paragneisses, an amphibolite, a mafic gneiss and a tonalite dike) from the 2.7 Ga Kapuskasing structural zone (KSZ), Ontario, were examined with petrographic, microthermometric and laser Raman techniques. Three types of fluid inclusions were observed: CO₂-rich, H₂O-rich and mixed CO₂-H₂O. CO₂-rich fluid inclusions are pseudosecondary or secondary in nature and are generally pure CO₂; a few contain varying amounts of CH₄·H₂O-rich fluid inclusions are secondary in nature, contain variable amounts of dissolved salts, and generally contain daughter crystals. Mixed CO₂-H₂O fluid inclusions occur where trails of H₂O-rich inclusions intersect trails of CO₂-rich inclusions. Isochores for high density (p=1.03 g/cm³) pseudosecondary, pure CO₂ inclusions intersect the lower pressure portion of the estimated P-T field for high-grade metamorphism, implying that pure CO₂ was the peak metamorphic fluid. The variable CH₄ content of CO₂ inclusions within graphite-bearing samples suggests that CH₄ was introduced locally after the formation of the CO₂ inclusions; however the origin of the CH₄ remains problematic. An aqueous fluid clearly penetrated the gneisses after the peak metamorphism (during uplift/erosion), forming secondary inclusions and contributing to the minor retrogressive hydration observed in these rocks. The presence of the pseudosecondary, high-density CO₂ inclusions in quartz crystals in the KSZ rocks constrains the uplift/ erosion path for the KSZ to one of simultaneous decrease in pressure and temperature.     

There is no horohalinicum

Species abundance declines to a minimum (the Artenminimum) between 5 and 8‰, not only in estuaries, but in all bodies of brackish water. Khlebovich (1968) examined published hydrochemical data for estuaries and concluded that sharp changes in the ionic composition of seawater diluted with fresh water occur at salinities below 5 to 8‰. He further argued that these ionic changes constitute a physico-chemical barrier between marine and freshwater faunas. Kinne (1971) gave the name “horohalinicum” to the segment of the salinity gradient between 8 and 5‰. We have re-examined the data used by Khlebovich (1968) and found that, in fact, while the ionic composition of diluted seawater changesslightly between 8 and 5‰, the changes in ionic ratios below 2‰ are much larger. Thus, the proposed physico-chemical barrier does not exist between 8 and 5‰; it cannot then explain the Artenminimum; and there is no basis for the horohalinicum concept of Kinne (1971). Two ecological explanations for the occurrence of the Artenminimum—a species-area effect and the stability-time hypothesis—are discussed and found to be inconsistent with published data on species distributions in brackish waters. The low species diversity of brackish water may be explained, in part, by two factors: few animals evolve those physiological mechanisms required for life in the variable habitat; and these species, which are very eurytopic, have low rates of speciation.     

Noble gas abundance patterns in deep-sea basalts — Primordial gases from the mantle

Rapidly cooled portions of eleven samples of mid-ocean ridge tholeiitic basalt pillows have noble gas abundance patterns which resemble the solar rare gas pattern rather than the noble gas pattern of the terrestrial atmosphere. We conclude that these samples contain primordial noble gases. In contrast, holocrystalline samples and a sample from the interior of a basalt pillow have noble gas abundance patterns which resemble the sea water pattern. Whereas the quenched glossy margins of basalt pillows record a non-atmospheric gas reservoir, these slowly cooled samples apparently have undergone exchange of their noble gases with those dissolved in sea water.     

Composition,physical properties and origin of sodic anorthites from the ejected plutonic blocks of the Soufrière Volcano,St. Vincent,West Indies

Three complete analyses and one partial analysis are recorded of unzoned sodic anorthites having compositions An_94,9, An_94,0, An_92,7 and An₉₂ (mol per cent). Although crystallising at a high temperature the K and Sr contents are low. X-ray parameters show the material to be in a relatively high structural state comparable with material from Japanese volcanics. Available data indicate small but real differences in optical parameters between sodic anorthites of volcanic and plutonic origin but this needs further clarification. Refractive indices and specific gravities of the analysed samples are also recorded. Anorthite (An₉₀-An₁₀₀) occurs widely as phenocrysts in basic lavas and as crystal ejecta in the calc-alkaline rock suites of the circumoceanic islands. Anorthite can be precipitated from sub-alkaline magmas under certain conditions and does not require the postulation of special magmas or of contamination. It is apparent that factors other than the normative feldspar composition of the magma determine the composition of the plagioclase precipitated. Evidence from experimental work on synthetic systems indicates that an increase in both hydrostatic pressure and water vapour pressure will influence the plagioclase composition but it is not possible to evaluate these effects fully at the present time. The occurrence of anorthite is interpreted as evidence of extensive crystal accumulation at depth from fractionating basic magmas in circumoceanic calc-alkaline suites.     

Circular meander pools

Aerial photographs led to the detection of a previously undescribed type of river meander. These features are characterized by nearly circular pools located at the apex of the bend and are widely distributed on small to medium sized coastal plain streams in the southeastern United States. Bathymetric evidence shows that the structure of meanders containing circular pools is distinctive. Field and laboratory evidence suggests that these features are formed by a short-lived countercurrent that develops during the flood cycle.