Tracking meteoric infiltration into a magmatic-hydrothermal system: A cathodoluminescence, oxygen isotope and trace element study of quartz from Mt. Leyshon, Australia

The oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope-cathodoluminescence (SEM-CL) images and fluid inclusion properties to track fluid sources and hydrothermal processes in the Mt. Leyshon Au deposit, Australia. Oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections, using secondary isotope mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively, with SEM-CL images obtained before analysis for petrographic context. Over the 280 to 650 °C quartz precipitation range suggested by fluid inclusion microthermometry, δ¹⁸O_quartz varies from 0.0 to 14.4‰, corresponding to a wide range of equilibrium δ¹⁸O_fluid values, from-6.1 to 10.2‰ (vs. V-SMOW). The δ¹⁸O_quartz signature varies systematically among distinct SEM-CL quartz generations (both within and between samples), and can be correlated with variations in temperature and fluid composition, but is independent of intra-generational oscillatory zoning. In contrast, Al and Li concentrations correlate broadly with CL intensity in oscillatory quartz, whereas their concentration is unpredictable in sealed fractures and overgrowths. Concentrations of B, Mg, Na, P, Cl, K, Ti, Mn, Fe, Ge, and Sn are independent of Al, Li, and oscillatory CL features, but Ti correlates with quartz precipitation temperature. Although no systematic correlation between δ¹⁸O_quartz and trace element concentrations was found, complementary patterns exist in narrow overgrowths of low δ¹⁸O_quartz ( 0‰) and high Al (> 10,000 ppma). These quartz zones likely formed during the incursion of ¹⁸O-depleted meteoric water into the magmatically-dominated Mt. Leyshon hydrothermal system. We interpret the highest Al concentrations as the result of high quartz precipitation rates, triggered by depressurisation of the hydrothermal cell. The decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that (1) under most circumstances, temperature and fluid chemistry dominate δ¹⁸O_quartz, and (2) the trace element record, and in particular Al and Li, is influenced by the superimposed effects of quartz precipitation rate.     

Can Sea Fog be Inferred from Operational GEM Forecast Fields?

Three cases of widespread sea fog in Lunenburg Bay, Nova Scotia were used to evaluate the suitability of operational regional GEM forecast fields for inferring advection fog occurrences. Verification scores suggest that the objective analyses contain significant departures from observations that will affect model accuracy, given the sensitivity of fog condensation microphysics. Dew point depression (ES) scores show larger differences compared to temperature, with both influenced by surface characteristics. For objective analyses and GEM forecasts ES < 2 C seems to match fog satellite images better than the physical threshold ES ≤ 0 C. In addition the GEM forecasts show a general tendency towards drier conditions near the surface, therefore reconfiguring GEM to better represent condensation in the boundary layer is proposed.     

Pc5 pulsations associated with ring current proton drifts: Stare radar observations

Detailed properties of a Pc5 pulsation with large azimuthal wavenumber observed using the STARE radar have recently been reported. A further four examples of this type of pulsation are presented, and it is shown that their properties are generally similar to those of the first example. However, there are some differences, the most important being that the variation of azimuthal phase velocity with latitude is significantly different for different time intervals during individual events, so that a mean phase velocity for a given latitude cannot be defined.When mapped to the equatorial plane in a dipole geomagnetic field, the variation of azimuthal phase velocity with L resembles the gradient-curvature drift of energetic protons in only a few time intervals within the events. The results are interpreted in terms of current theories of drift and bounce resonance of energetic particles with hydromagnetic waves. It is found that no single theory explains all aspects of the observations.     

Distribution and covariance function of elevations on a cratered planetary surface

We derive the distribution and covariance function of elevations on a cratered planetary surface from a representation of the surface as the moving average of a random point process. It is assumed that an initially plane surface is excavated by primary impact craters with an inverse-power law size distribution. Crater rim height and rim-to-floor depth are assumed to be power functions of crater diameter. Crater shapes studied include rimless cylinders and paraboloidal bowls, and paraboloidal bowls with power-law external rims and ejecta blanket. The inverse-power law diameter distribution induces a positively skewed stable law elevation distribution, with heavy inverse-power law tails whose exponent (for small craters) is two smaller than the crater diameter distribution exponent. The covariance function (equivalently, power spectral density) is shown to be a power-law at moderate distances, whose exponent also depends on the parameters of the cratering process. Observations of lunar elevations and elevation spectral densities on a meter scale agree well with theory.This work summarizes and extends Bellcomm Technical Reports TR-68-340-3, 4, 5, which were supported by the National Aeronautics and Space Administration, Contract NASw-417.Now at Johns Hopkins University, Baltimore, Md.     

Telescope and instrument robotization at Dome C

This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain‐storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night‐time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000‐hour night at Dome C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multiple origins of xenoliths and xenocrysts in the Elephant Moraine 79001 Lithology A olivine‐phyric shergottite

Petrographic examination of the xenolith and xenocryst populations in the olivine‐phyric shergottite Elephant Moraine 79001 Lithology A shows more chemical heterogeneity than previously documented. Analyses of olivine grains in 18 megacrysts and in 4 lithic fragments show that these two populations either do not have the same source or that this source is heterogeneous in terms of its time–temperature history. Additionally, among the four lithic fragments analyzed, two are distinctive (1) one contains a major‐element‐equilibrated, euhedral olivine grain and (2) the second contains high‐magnesium pyroxene cores. Furthermore, two populations of ferroan olivine were identified (1) one more ferroan than any other reported in EET 79001 and (2) a slightly less ferroan, unequilibrated olivine, but with a restricted range in Mg#. We have also observed an equilibrated pyroxene grain associated with a zoned olivine megacryst. As a result, we recognize that the xenolith/xenocryst population does not represent the incorporation of a single xeno‐lithology into Lithology A, and propose that it be subdivided into a suite of seven identified lithologies, with the understanding that more are likely to be identified with further study. The abundance of Ca in olivine in the xeno‐lithologies suggests a set of crustal, rather than deep mantle, lithologies. Diffusion rates in olivine suggest that the lithologies were incorporated shortly before rapid cooling of the host magma, preserving preexisting mineral chemical zoning. These mineral chemical zones could have been preserved at lower crustal temperatures for up to 10s of Ka. Trace‐element studies of these distinct populations would be required to test whether they are related by igneous processes from a common source magma.