Project ELF electromagnetic compatibility assurance program--A status report

The U.S. Navy is presently planning an extremely low frequency (ELF) communications system to improve operational control and reduce the detection probability of its submarine fleet. An integral component of the shore-based ELF transmitting facility development activity is the Environmental Compatibility Assurance Program (ECAP) which was instituted by the Navy during the early stages of program concept development. The principal components of the ECAP include: electromagnetic compatibility, biological/ecological monitoring, and environmental documentation. The current activities being performed in association with each of these program elements are discussed. The necessary ECAP requirements for achieving a fully operational ELF facility are also reviewed.     

A field evaluation of plate and screen microlayer sampling techniques

Field studies of surface microlayer sampling methods involving simultaneous use of glass plates and two depths of screens have been conducted. Intercomparisons of the two methods are based upon thicknesses of sample and amounts of dissolved organic carbon, dissolved UV-absorbing phenolic materials, chlorophyll a, ATP and particulate organic carbon and nitrogen collected. Plate samples are always thinnest, and are influenced by wave state and bulkwater temperature. Amounts of materials collected generally follow sample thicknesses. Biases toward fractions of microlayer materials are not evident in either method. It was concluded that intercomparisons of data collected separately by the two methods is inadvisable.     

Lava lakes on Io: observations of Io's volcanic activity from Galileo NIMS during the 2001 fly-bys

Galileo's Near-Infrared Mapping Spectrometer (NIMS) obtained its final observations of Io during the spacecraft's fly-bys in August (I31) and October 2001 (I32). We present a summary of the observations and results from these last two fly-bys, focusing on the distribution of thermal emission from Io's many volcanic regions that give insights into the eruption styles of individual hot spots. We include a compilation of hot spot data obtained from Galileo, Voyager, and ground-based observations. At least 152 active volcanic centers are now known on Io, 104 of which were discovered or confirmed by Galileo observations, including 23 from the I31 and I32 Io fly-by observations presented here. We modify the classification scheme of Keszthelyi et al. (2001, J. Geophys. Res. 106 (E12) 33 025-33 052) of Io eruption styles to include three primary types: promethean (lava flow fields emplaced as compound pahoehoe flows with small plumes <200 km high originating from flow fronts), pillanian (violent eruptions generally accompanied by large outbursts, >200 km high plumes and rapidly-emplaced flow fields), and a new style we call “lokian” that includes all eruptions confined within paterae with or without associated plume eruptions). Thermal maps of active paterae from NIMS data reveal hot edges that are characteristic of lava lakes. Comparisons with terrestrial analogs show that Io's lava lakes have thermal properties consistent with relatively inactive lava lakes. The majority of activity on Io, based on locations and longevity of hot spots, appears to be of this third type. This finding has implications for how Io is being resurfaced as our results imply that eruptions of lava are predominantly confined within paterae, thus making it unlikely that resurfacing is done primarily by extensive lava flows. Our conclusion is consistent with the findings of Geissler et al. (2004, Icarus, this issue) that plume eruptions and deposits, rather than the eruption of copious amounts of effusive lavas, are responsible for Io's high resurfacing rates. The origin and longevity of islands within ionian lava lakes remains enigmatic.     

Chemical speciation and fate of tripolyphosphate after application to a calcareous soil

Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces.     

Origins of yttrium and rare earth element distributions in metamorphic garnet

Highly variable distributions of yttrium and rare earth elements (Y+REEs) are documented in pelitic garnet from the Picuris Mountains, New Mexico, and from Passo del Sole, Switzerland, and in mafic garnet from the Franciscan Complex, California. The wide variety of these Y+REE zoning patterns, and those described previously in other occurrences, imply diverse origins linked to differing degrees of mobility of these elements through the intergranular medium during garnet growth. In the Picuris Mountains, large, early‐nucleating crystals have radial profiles of Y+REE dominated by central peaks and annular maxima, in patterns that vary systematically with atomic number. Superimposed on these features are narrow spikes in HREEs and MREEs, located progressively rimward with decreasing atomic number. In contrast, profiles in small, late‐nucleating crystals contain only broad central maxima for all Y+REEs. In garnet from Passo del Sole, Y+REE zoning varies radically from sample to sample: in some rocks, crystals of all sizes display only central peaks for all Y+REEs; in others, profiles exhibit irregular fluctuations in Y+REE contents that match up with small‐scale patchy zoning in Y and Ca X‐ray maps. In the Franciscan Complex, Y+REE in garnet cores fluctuate unsystematically, but mantles and rims display concentric oscillatory zoning for both major elements and Y+REEs. Our interpretation of the complexity of Y+REE distributions in metamorphic garnet centres on the concept that these distributions vary primarily in response to the length scales over which these elements can equilibrate during garnet growth. Very short length scales of equilibration, due to low intergranular mobility, produce overprint zoning characterized by small‐scale irregularities. Higher but still restricted mobility yields diffusion‐controlled uptake, characterized by patterns of central peaks and annular maxima that vary with atomic number and are strongly influenced by T–t paths during garnet growth. Still greater mobility permits progressively greater, potentially rock‐wide, equilibration with major‐ and accessory‐phase assemblages, leading to mineralogical controls: an unchanging mineral assemblage during garnet growth produces bell‐shaped profiles resembling those produced by Rayleigh fractionation, whereas changes in major‐ and/or accessory‐phase assemblages produce profiles with distinct annuli and sharp discontinuities in concentration. The very high mobility associated with influxes of Y+REE‐bearing fluids can cause these element distributions to be dominated by factors external to the rock, yielding profiles characterized by abrupt shifts or oscillations that are not correlated to changes in mineral assemblages.     

Magnitudes of departures from equilibrium during regional metamorphism of porphyroblastic rocks

Numerical models of diffusion‐controlled nucleation and growth of garnet crystals, which successfully replicate diverse textures in 13 porphyroblastic rocks, yield quantitative estimates of the magnitudes of departures from equilibrium during crystallization. These estimates are derived from differences in chemical potential between subvolumes containing stable product assemblages and those containing persistent but metastable reactant assemblages. The magnitude of disequilibrium is evaluated in terms of the thermal overstepping, which is commonly referenced to the garnet‐in isograd; the reaction affinity in the intergranular fluid at the site and time of each nucleation event, and on average throughout the rock, and the ‘latent energy of reaction’ per unit volume, a measure of the average unreacted capacity of the bulk rock, which describes its overall metastability. Across all of the models, the first crystals nucleate after 5–67 °C of thermal overstepping (correspondingly, 0.7–5.8 kJ mol^?1 of 12‐oxygen garnet); the maximum reaction affinity averaged across the intergranular fluid is between 4.7 and 16.0 kJ mol^?1 of 12‐oxygen garnet; and the maximum latent energy of reaction ranges from 7.3 to 51.7 J cm^?3. These results demonstrate that impediments to crystallization significantly delay nucleation and retard reaction, with the consequence that nucleation of new crystals extends throughout nearly the entire crystallization interval. This potential for protracted reaction during prograde metamorphism, with reactions continuing to temperatures and pressures well beyond equilibrium conditions, suggests the likelihood of overstepping of multiple – possibly competing – reactions that can progress simultaneously. Isograds and ranges of stability for metamorphic assemblages along a metamorphic field gradient may therefore be significantly offset from the positions predicted from calculations based on equilibrium assumptions, which poses a substantial challenge to accurate interpretations of metamorphic conditions and processes.     

Artificial neural networks applied to mineral potential mapping for copper-gold mineralizations in the Carajás Mineral Province, Brazil

Motivated by recent successful results of artificial neural network modelling in a variety of problems related to the geosciences, we have applied a radial basis functional link net to a regional-scale mapping of the potential for Cu-Au mineralizations in the Carajás Mineral Province, northern Brazil. To derive the input feature vectors, we have used geological and both radiometric and magnetic geophysical data. A k -fold cross-validation method was employed in order to tune the parameters of the network and to select the best radial basis functional link net model amongst several others. Subsets of the available data set were used for training and validation and the estimated overall accuracy of the selected model is 91.7%. The plotting of a cumulative area versus favourability curve allowed us to define favourability zones of occurrences of Cu-Au mineralizations and to assess the efficiency and the predictive power of the model. A binary map showing high and low favourability sectors was produced for the study area as an end product that can be used to guide and support more detailed exploration efforts. Our results show that 4.18% of the study area has an extremely high potential to contain Cu-Au mineralizations, especially those of iron-oxide Cu-Au type, which are related to volcanic rocks and hydrothermal alteration.     

Chemical Separation of Tungsten and Other Trace Elements for TIMS Isotope Ratio Measurements Using Organic Acids

One requirement for isotope ratio measurement results with small measurement uncertainties is that the element of interest is effectively separated from the sample matrix. Efficient chemical separation of W from matrix components, especially Ti, can be challenging, particularly for large test portion masses (> 1 g). We present a new W separation procedure that takes advantage of the distinct complexation behaviour of Ti and W with citrate ligand in a moderately low pH, oxidising solution. This preparation procedure can reduce the Ti/W ratio of large (4–10 g) basaltic (i.e., high‐matrix) test portions by a factor of 10⁵, relative to their original compositions, in a two‐step separation procedure. The procedure additionally provides a separate, well‐purified Mo fraction. We show that optimal separation requires precise selection of reagent concentrations and sample load. The procedure was employed to determine the μ¹⁸²W composition of BHVO‐2 as ?6.7 ± 4.2 (2 standard deviation, 2s). The principles derived from this method may prove useful for chemical separation of other elements used for geochemical and cosmochemical applications given an appropriate selection of organic acid. Future successful applications of this method may reveal that the use of organic acids as procedural reagents is a currently under‐utilised tool for efficient chemical separation protocols.     

H2O and CO2 in kimberlitic fluid as recorded by diamonds and olivines in several Ekati Diamond Mine kimberlites,Northwest Territories,Canada

Surface dissolution features on diamonds and Fourier Transform Infra Red spectroscopy (FTIR) of phenocrystal and xenocrystal olivines from kimberlites contain a record of magmatic fluid in kimberlite magmas. We investigated composition and behavior of kimberlitic fluid and the effect of volatiles on the eruption style and geology of kimberlites using microdiamonds and olivine concentrates from six kimberlite pipes with different lithologies and the character of diamond resorption (Ekati Diamond Mine, Northwest Territories, Canada). The study showed a clear correlation between the resorption style of diamond population of the kimberlites and the type of infrared (IR) spectra of their olivines. Four kimberlites have high quality diamonds with smooth regular surface features and high H₂O content of the olivines indicating the presence of H₂O-rich fluid during the emplacement. Fast ascent rates of fluid-rich magma can explain explosive eruption and filling the pipes with volcaniclastic kimberlite facies. Conversely, Grizzly and Leslie kimberlites have diamonds with complex sharp features diminishing diamond quality and indicating loss of the fluid. The slower ascent rates and less explosive eruption of the fluid-free magmas produced kimberlite pipes filled with magmatic facies kimberlite. Distinctive peaks in olivine IR spectra at 3356 and 3327 cm^? 1 were found to correlate with the presence of hydrous magmatic fluid. Character of diamond morphology suggests that during the whole ascent of all six kimberlites, the magmatic fluid when present had a high H₂O:CO₂ ratio.     

Karhunen–Loève spectral analysis in multiresolution decomposition

In this work we develop a method for pinpointing the scales in a multiresolution decomposition where coherent structures appear. A sequence of images yielded from the wavelet multiresolution analysis of seismic signals are analyzed in the Karhunen–Loève (KL) space. Using KL decomposition we distinguish two coherent structures in the scale–images: the ground roll and the hyperbolic lines characteristic of geologic layers. Moreover, the KL spectrum also points out the high frequency noise. In this way the method allow us to split three energy mode regimes in the data and, as a consequence, to select the relevant geologic information. The method can be extended to other problems where coherent structures need to be recognized.