Ab initio calculations on (OH)4 defects in α-quartz

Ab initio total energy calculations based on a new optimized oxygen psuedopotential have been used to study the structures and relative energies of α-quartz, a partly (OH)₄ substituted version of the α-quartz structure, and interstitial water molecules in α-quartz. Hydrogen bonds formed from two hydroxyl groups of the (OH)₄ defects in the substituted α-quartz structure promote a stable structure for the defect α-quartz at low temperature. Comparable ab initio calculation of the energy of the interstitial water molecule in the quartz structure indicates that, energetically, the (OH)₄ defect is likely to be strongly favoured as a mode for the incorporation of water. Ab initio stress calculations confirm that the (OH)₄ defect in quartz has a large associated stress field which is likely to lead to segregation of these defects on supersaturation in wet quartz. The calculations indicate that segregation should occur in the plane (10 0) of the α-quartz structure.     

The Use of Close Range Photogrammetry for Studying Ice Accretion on Aerofoil Sections

This paper describes the use of photogrammetry to measure and quantify ice accretion on an aerofoil section. A series of stereoscopic photographs was taken during the ice accretion on the section in an icing tunnel. From measurements made on these photographs with a Kern (Leica) DSR 14 analytical photogrammetric plotter, a series of three dimensional models of the ice surfaces was constructed. The results of the project are discussed and possible improvements in the methodology are suggested.     

Genesis of the Archean–Paleoproterozoic Tabletop Domain,Rudall Province,and its endemic relationship to the West Australian Craton

The Tabletop Domain of the Rudall Province has been long thought an exotic entity to the West Australian Craton. Recent re-evaluation of this interpretation suggests otherwise, but is founded on limited data. This study presents the first comprehensive, integrated U–Pb geochronology and Hf-isotope analysis of igneous and metasedimentary rocks from the Tabletop Domain of the eastern Rudall Province. Field observations, geochronology and isotope results confirm an endemic relationship between the Tabletop Domain and the West Australian Craton (WAC), and show that the Tabletop Domain underwent a similar Archean–Paleoproterozoic history to the western Rudall Province. The central Tabletop Domain comprises Archean–Paleoproterozoic gneissic rocks with three main age components. Paleo–Neoarchean (ca 3400–2800 Ma) detritus is observed in metasedimentary rocks and was likely sourced from the East Pilbara Craton. Protoliths to mafic gneiss and metasedimentary rocks are interpreted to have been emplaced and deposited during the early Paleoproterozoic (ca 2400–2300 Ma), and exhibit age and isotopic affinities to the Capricorn Orogen basement (Glenburgh Terrane). Mid–late Paleoproterozoic mafic and felsic magmatism (ca 1880–1750 Ma) is assigned to the Kalkan Supersuite, which is exposed in the western Rudall Province. The Kalkan Supersuite provided the main source of detritus for mid–late Paleoproterozoic metasedimentary rocks in the Tabletop Domain. Similarities in the age and Hf-isotope compositions of detrital zircon from these metasedimentary rocks and Capricorn Orogeny basin sediments suggests that a regionally extensive, linked basin system may have spanned the northern WAC at this time. The Tabletop Domain records evidence for two metamorphic events. Mid–late Paleoproterozoic deformation (ca 1770–1750 Ma) was high-grade, regional and involved the development of gneissic fabrics. In contrast, early Mesoproterozoic (ca 1580 Ma) high-grade deformation was localised and associated with more widespread, late-stage, greenschist facies alteration. These new findings highlight that the Tabletop Domain experienced a much higher grade of deformation than previously assumed, with a Paleoproterozoic metamorphic history similar to that of the western Rudall Province.     

Sea-floor sediment distribution in the Gulf of Mexico

Carbonate content, smear-slide analysis and diffuse reflectance spectrophotometry were utilized to determine modern sediment composition and distribution throughout the Gulf of Mexico. In all, 186 core top and grab samples distributed throughout the Gulf were analyzed. Reflectance spectra were taken from thick smear slides from the near ultraviolet, through the visible, and into the near infrared. The first derivatives of the percent reflectance data were subjected to factor analysis producing factors that grouped covarying first-derivative wavelengths. Factors were interpreted by comparison to first-derivative curves for known sediment components and minerals. Interpretation was aided by the mapping of both calcium carbonate content and smear-slide sediment classes. The most easily interpreted factor solution was produced by analyzing only the visible region of the spectrum and extracting seven factors which explained 98% of the cumulative variance. These factors, in order of their relative importance, are interpreted as (1) marl and calcareous clay, (2) glauconite, (3) kaolinite, (4) organic matter, (5) phosphorite, (6) hematite, and (7) goethite. Some factor maps are consistent with known sources of fluvial sediment input; for example, kaolinite is deposited off rivers draining the southeastern US. Other factor maps are related to the origin of the material in the factor, glauconite, for example, being confined to low sedimentation regions of the outer shelf. The most unusual observation concerns the distribution of hematite, which appears to be transported from the rivers of south Texas, primarily the Rio Grande, across the shelf then eastward downslope along the base of the Sigsbee Escarpment. This eastward transport seems to be explainable only by transport in bottom currents flowing along the base of the Sigsbee Escarpment.     

Petrogenesis of ca 1.50 Ga granitic gneiss of the Coompana Block: filling the ‘magmatic gap’ of Mesoproterozoic Australia

The Coompana Block is an essentially unknown basement province that separates the Gawler Craton of South Australia from the Yilgarn Craton of Western Australia. Previously unstudied granitic gneiss intersected by deep drilling in the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. Granitic gneiss intersected at ～1500 m depth in Mallabie 1 diamond drillhole is metaluminous and dominantly granodioritic in composition. The granodiorites have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. U – Pb LA-ICPMS dating of magmatic zircons provides an age of 1505 ± 7 Ma, interpreted as the crystallisation age of the granite protolith. ? _Nd values are high with respect to exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The granitic gneiss is interpreted to be a fractionated melt of a mantle-derived parental melt. The tectonic environment into which the precursor granite was emplaced is not clear. One possibility is emplacement within an extensional environment. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the ‘Australian Mesoproterozoic magmatic gap’ of ca 1.50 – 1.35 Ga, and is a possible source for ca 1.50 detrital zircons found in sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province.     

The spatial extent of tephra deposition and environmental impacts from the 1912 Novarupta eruption

The eruption of Novarupta within the Katmai Volcanic Cluster, south-west Alaska, in June 1912 was the most voluminous eruption of the twentieth century but the distal distribution of tephra deposition is inadequately quantified. We present new syntheses of published tephrostratigraphic studies and a large quantity of previously un-investigated historical records. For the first time, we apply a geostatistical technique, indicator kriging, to integrate and interpolate such data. Our results show evidence for tephra deposition across much of Alaska, Yukon, the northern Pacific, western British Columbia and northwestern Washington. The most distal tephra deposition was observed around 2,500?km downwind from the volcano. Associated with tephra deposition are many accounts of acid deposition and consequent impacts on vegetation and human health. Kriging offers several advantages as a means to integrate and present such data. Future eruptions of a scale similar to the 1912 event have the potential to cause widespread disruption. Historical records of tephra deposition extend far beyond the limit of deposition constrained by tephrostratigraphic records. The distal portion of tephra fallout deposits is rarely adequately mapped by tephrostratigraphy alone; contemporaneous reports of fallout can provide important constraints on the extent of impacts following large explosive eruptions.     

Limnology of nine Westland beech forest lakes

Lakes in the beech (Nothofagus sp.) forest foothills between Greymouth and Hokitika, Westland, are characterised by amber‐coloured waters. Microbiological, biochemical, and chemical analyses of samples from nine such lakes during March 1976 indicate that they are unproductive. Microbial biomass was intensively investigated in heavily stained Lakes Haupiri and Lady and in least‐stained Lake Brunner. A combination of adenosine triphosphate assays, Utermöhl phytoplankton counts, and autoradiographic biomass determinations revealed a greater bacterial than algal biomass in heavily stained lakes, a highly unusual phenomenon which suggests that most of the production of organic matter was allochthonous. Autochthonous productivity was low, probably because biologically available phosphorus was very scarce and because discoloration reduced the transparency of the water. Hypqlimnetic oxygen depletion was slight during this period of maximum thermal stratification; decomposition of organic matter was apparently incomplete. Reactive phosphorus did not increase appreciably in partially deoxygenated hypolimnia. Much of the allochthonous organic matter originating from beech forests and their soils may be partially resistant to biodegradation.     

Long-slit optical spectroscopy of Large Magellanic Cloud radio supernova remnants

We use long-slit spectra from shocked regions of radio supernova remnants (SNRs) in the Large Magellanic Cloud to estimate electron density and derive an average 'metal' abundance of 10^−3.9 based on diagnostic line ratio plots. These simple diagnostics may be especially useful to determine abundances in more distant galaxies. Abundance values listed in this paper, in units of log(x/H) + 12, for nitrogen (7.3) and oxygen (8.2) agree with those reported in the literature. These estimates – which we assume to be dominated by the interstellar medium with little evolutionary interference – were obtained from spectral analysis of ∼50 per cent of known radio SNRs using the double beam spectrograph on the 2.3-m Advanced Technology Telescope at Siding Spring Observatory in Australia and the Cassegrain spectrograph on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory. We also found optical evidence of shocked regions near 2 of 20 radio SNR candidates (J053620−693136 and J053731−662740), strengthening their identification as true remnants.