Infrared and Raman spectroscopy studies of the α–β phase transition in cristobalite

Infrared and Raman spectra of cristobalite are presented as a function of temperature through the phase transition. The modes are assigned and the assignments compared to those of earlier workers. The compatibility of modes at the G-point of the a-phase with the X and G-points of the ß-phase is given. In the transition region of ca. 500–550 K, smooth changes in intensity, frequency and linewidths are seen in many modes, indicative of coexistence of a- and ß-forms.     

Extreme Ultraviolet Emission Lines of ca xv in Solar and Laboratory Spectra

New R-matrix calculations of electron impact excitation rates in Caxv are used to derive theoretical electron density diagnostic emission line intensity ratios involving 2s ²2p ²–2s2p ³ transitions, specifically R ₁=I(208.70 Å)/I(200.98 Å), R ₂=I(181.91 Å)/I(200.98 Å), and R ₃=I(215.38 Å)/I(200.98 Å), for a range of electron temperatures (T _e=10^6.4–10^6.8 K) and densities (N _e=10⁹–10¹³ cm^–3) appropriate to solar coronal plasmas. Electron densities deduced from the observed values of R ₁, R ₂, and R ₃ for several solar flares, measured from spectra obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, are found to be consistent. In addition, the derived electron densities are in excellent agreement with those determined from line ratios in Caxvi, which is formed at a similar electron temperature to Caxv. These results provide some experimental verification for the accuracy of the line ratio calculations, and hence the atomic data on which they are based. A set of eight theoretical Caxv line ratios involving 2s ²2p ²–2s2p ³ transitions in the wavelength range 140–216 Å are also found to be in good agreement with those measured from spectra of the TEXT tokamak plasma, for which the electron temperature and density have been independently determined. This provides additional support for the accuracy of the theoretical line ratios and atomic data.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Application of the luciferase cell culture bioassay for the detection of refined petroleum products

A luciferase cell culture-based bioassay, developed to detect 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity of halo-genated and polycyclic aromatic hydrocarbons, was optimized to detect refined petroleum products and to determine their relative inducing potency. Quality control standards from 32 refined products (gasolines and diesels, jet fuels, lubricating oils, fuel oils and weathered products) and three commercial products were evaluated. Induction equivalents (I-EQs) were determined by direct comparison of the EC50 and EC20 values (based on the median and 20% TCDD maximal response, respectively) from dose-response curves for each product to those obtained with TCDD. Most petroleum products were active in the luciferase bioassay, with those products composed of fractions produced later in the distillation process (i.e. fuel oils) inducing higher levels. Additionally, weathering of products reduced their induction potency. Based on the high I-EQ estimates of many products, biological effects associated with exposure may have been previously underestimated using other diagnostic methods.     

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2

We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.     

Which way to the Moon?

Andrew Ball and Ian Crawford report on NASA's planning for a return to the Moon, with some thoughts on opportunities open to the UK.     

Scale in structure and dynamics

Ian Main, Bruce Malamud, Chris Bean and John McCloskey summarize the presentations and lively debate at the British Geophysical Association's annual British Discussion Meeting on Scale-Invariance and Scale-Dependence in Earth Structure and Dynamics.     

Link between SSZ ophiolite formation, emplacement and arc inception, Northland, New Zealand: U–Pb SHRIMP constraints; Cenozoic SW Pacific tectonic implications

New U–Pb age-data from zircons separated from a Northland ophiolite gabbro yield a mean ²⁰⁶Pb/²³⁸U age of 31.6 ± 0.2 Ma, providing support for a recently determined 28.3 ± 0.2 Ma SHRIMP age of an associated plagiogranite and  29–26 Ma ⁴⁰Ar/³⁹Ar ages (n = 9) of basalts of the ophiolite. Elsewhere, Miocene arc-related calc-alkaline andesite dikes which intrude the ophiolitic rocks contain zircons which yield mean ²⁰⁶Pb/²³⁸U ages of 20.1 ± 0.2 and 19.8 ± 0.2 Ma. The ophiolite gabbro and the andesites both contain rare inherited zircons ranging from 122–104 Ma. The Early Cretaceous zircons in the arc andesites are interpreted as xenocrysts from the Mt. Camel basement terrane through which magmas of the Northland Miocene arc lavas erupted. The inherited zircons in the ophiolite gabbros suggest that a small fraction of this basement was introduced into the suboceanic mantle by subduction and mixed with mantle melts during ophiolite formation.

We postulate that the tholeiitic suite of the ophiolite represents the crustal segment of SSZ lithosphere (SSZL) generated in the southern South Fiji Basin (SFB) at a northeast-dipping subduction zone that was initiated at about 35 Ma. The subduction zone nucleated along a pre-existing transform boundary separating circa 45–20 Ma oceanic lithosphere to the north and west of the Northland Peninsula from nascent back arc basin lithosphere of the SFB. Construction of the SSZL propagated southward along the transform boundary as the SFB continued to unzip to the southeast. After subduction of a large portion of oceanic lithosphere by about 26 Ma and collision of the SSZL with New Zealand, compression between the Australian Plate and the Pacific Plate was taken up along a new southwest-dipping subduction zone behind the SSZL. Renewed volcanism began in the oceanic forearc at 25 Ma producing boninitic-like, SSZ and within-plate alkalic and calc-alkaline rocks. Rocks of these types temporally overlap ophiolite emplacement and subsequent Miocene continental arc construction.     

Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

Post-10 ka rhyolitic eruptions from the Haroharo linear vent zone, Okataina Volcanic Centre, have occurred from several simultaneously active vents spread over 12 km. Two of the three eruption episodes have tapped multiple compositionally distinct homogeneous magma batches. Three magmas totalling ~8 km³ were erupted during the 9.5 ka Rotoma episode. The most evolved Rotoma magma (SiO₂=76.5–77.9 wt%, Sr=96–112 ppm) erupted from a southeastern vent, and is characterised by a cummingtonite-dominant mineralogy, a temperature of 739±14°C, and fO₂ of NNO+0.52±0.11. The least evolved (SiO₂=75.0–76.4 wt%, Sr=128–138 ppm, orthopyroxene+ hornblende-dominant) Rotoma magma erupted from several vents, and was hotter (764±18°C) and more reduced (NNO+0.40±0.13). The ~11 km³ Whakatane episode occurred at 5.6 ka and also erupted three magmas, each from a separate vent. The most evolved (SiO₂=73.3–76.2 wt%, Sr=88–100 ppm) Whakatane magma erupted from the southwestern (Makatiti) vent and is cummingtonite-dominant, cool (745±11°C), and reduced (NNO+0.34±0.08). The least evolved (SiO₂=72.8–74.1 wt%, Sr=132–134 ppm) magma was erupted from the northeastern (Pararoa) vent and is characterised by an orthopyroxene+ hornblende-dominant mineralogy, temperature of 764±18°C, and fO₂ of NNO+0.40±0.13. Compositionally intermediate magmas were erupted during the Rotoma and Whakatane episodes are likely to be hybrids. A single ~13 km³ magma erupted during the intervening 8.1 ka Mamaku episode was relatively homogeneous in composition (SiO₂=76.1–76.8 wt%, Sr=104–112 ppm), temperature (736±18°C), and oxygen fugacity (NNO+0.19±0.12). Some of the vents tapped a single magma while others tapped several. Deposit stratigraphy suggests that the eruptions alternated between magmas, which were often simultaneously erupted from separate vents. Both effusive and explosive activity alternated, but was predominantly effusive (>75% erupted as lava domes and flows). The plumbing systems which fed the vents are inferred to be complex, with magma experiencing different conditions in the conduits. As the eruption of several magmas was essentially concurrent, the episodes were likely triggered by a common event such as magmatic intrusion or seismic disturbance.