Permeability and pore-connectivity variation of pumices from a single pyroclastic flow eruption: Implications for partial fragmentation

The relationship between permeability and vesicularity in volcanic rocks has been used to infer the degassing behavior of hydrous magma. Recent data on natural samples from various eruptions show a wide variation, fitting a power–law relationship of the percolation models with low (< 30%) critical vesicularity (Ф_C). In this study, we present data on permeability and pore-connectivity of juvenile rhyolitic pumice clasts in a pyroclastic flow around Onikobe volcano, NE Japan, and investigate their relationship with vesicularity developed in a single eruption event. The permeability of the pumices having a relatively low abundance of microlites and microphenocrysts shows a trend increasing by 4 orders of magnitude (from 10^− 13.8 to 10^− 10.1 m²) in a high and narrow vesicularity range (from 72 to 80%). This trend intersects at a high angle with the fit to the permeability–vesicularity data in the previous studies that has a low Ф_C, and is located on the extension of the trend for the products of isotropic decompression experiments. The two-dimensional (2D) connectivities of pores for the pumices were also measured from thin sections. From the point of view of percolation theory, connectivity provides information about the probability of percolation. They showed a steep increase from ca. 0 to 0.7 in an almost similar vesicularity range, as compared to their permeabilities. We attribute the increase in 2D connectivity to the increasing amount of ruptured bubble walls, which might have provided less-tortuous paths through larger apertures for gas flow. This, in turn, would cause an effective increase in the permeability. Aggregates of bubble-wall-shaped glass shards were found in the pumices, and their amount and degree of welding are higher in the pumices that have a higher abundance of microlites and microphenocrysts. These pumices have relatively high permeability and 2D connectivity at low vesicularity, which is accounted for by the existence of large irregularly shaped pores. These textural characteristics suggest that a series of partial fragmentation processes, including local rupturing of bubble walls and subsequent foam-collapse with permeable gas flow, might have occurred before the ultimate bulk fragmentation, thus resulting in the increase in permeability. We suggest that the 2D connectivity of pores is a useful parameter to quantify the degree of fragmentation of bubble walls and has the potential for use to assess their permeability.     

Origin of the early Cenozoic belt boundary thrust and Izanagi–Pacific ridge subduction in the western Pacific margin

The belt boundary thrust within the Cretaceous–Neogene accretionary complex of the Shimanto Belt, southwestern Japan, extends for more than ~ 1 000 km along the Japanese islands. A common understanding of the origin of the thrust is that it is an out of sequence thrust as a result of continuous accretion since the late Cretaceous and there is a kinematic reason for its maintaining a critically tapered wedge. The timing of the accretion gap and thrusting, however, coincides with the collision of the Paleocene–early Eocene Izanagi–Pacific spreading ridges with the trench along the western Pacific margin, which has been recently re‐hypothesized as younger than the previous assumption with respect to the Kula‐Pacific ridge subduction during the late Cretaceous. The ridge subduction hypothesis provides a consistent explanation for the cessation of magmatic activity along the continental margin and the presence of an unconformity in the forearc basin. This is not only the case in southwestern Japan, but also along the more northern Asian margin in Hokkaido, Sakhalin, and Sikhote‐Alin. This Paleocene–early Eocene ridge subduction hypothesis is also consistent with recently acquired tomographic images beneath the Asian continent. The timing of the Izanagi–Pacific ridge subduction along the western Pacific margin allows for a revision of the classic hypothesis of a great reorganization of the Pacific Plate motion between ~ 47 Ma and 42 Ma, illustrated by the bend in the Hawaii–Emperor chain, because of the change in subduction torque balance and the Oligocene–Miocene back arc spreading after the ridge subduction in the western Pacific margin.     

Notes on Extended-Range Atmospheric Prediction in the Northern Hemisphere Winter

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Direct evidence for nitrogen isotope discrimination during sedimentation and early diagenesis in Lake Kasumigaura, Japan

Sediment core samples from the center of Lake Kasumigaura, Japan, were collected from 1979 to 2007 at intervals of 1 month to 5 yr. We evaluated the degree of modification in N isotope composition during sedimentation and diagenesis. We estimated the degree of isotope discrimination during diagenesis by comparing historical changes in N isotope composition of the surface sediment (top 2 cm) against the vertical profile of the isotope composition of sediment core samples (15 cm depth). The degree of ¹⁵N enrichment during sedimentation appeared to be significant under the preferential N decomposition that occurred in the periods with low C/N ratio values of suspended particulate organic matter. We documented ¹⁵N depletion in sediment deeper than approximately 3 cm during diagenesis. The contrasting directions of N isotope discrimination during sedimentation and diagenesis suggest changing mechanisms of isotopic shift across an oxidation-reduction boundary.     

Multi-technique comparison of troposphere zenith delays and gradients during CONT08

CONT08 was a 15 days campaign of continuous Very Long Baseline Interferometry (VLBI) sessions during the second half of August 2008 carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, VLBI estimates of troposphere zenith total delays (ZTD) and gradients during CONT08 were compared with those derived from observations with the Global Positioning System (GPS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and water vapor radiometers (WVR) co-located with the VLBI radio telescopes. Similar geophysical models were used for the analysis of the space geodetic data, whereas the parameterization for the least-squares adjustment of the space geodetic techniques was optimized for each technique. In addition to space geodetic techniques and WVR, ZTD and gradients from numerical weather models (NWM) were used from the European Centre for Medium-Range Weather Forecasts (ECMWF) (all sites), the Japan Meteorological Agency (JMA) and Cloud Resolving Storm Simulator (CReSS) (Tsukuba), and the High Resolution Limited Area Model (HIRLAM) (European sites). Biases, standard deviations, and correlation coefficients were computed between the troposphere estimates of the various techniques for all eleven CONT08 co-located sites. ZTD from space geodetic techniques generally agree at the sub-centimetre level during CONT08, and??as expected??the best agreement is found for intra-technique comparisons: between the Vienna VLBI Software and the combined IVS solutions as well as between the Center for Orbit Determination (CODE) solution and an IGS PPP time series; both intra-technique comparisons are with standard deviations of about 3?C6?mm. The best inter space geodetic technique agreement of ZTD during CONT08 is found between the combined IVS and the IGS solutions with a mean standard deviation of about 6?mm over all sites, whereas the agreement with numerical weather models is between 6 and 20?mm. The standard deviations are generally larger at low latitude sites because of higher humidity, and the latter is also the reason why the standard deviations are larger at northern hemisphere stations during CONT08 in comparison to CONT02 which was observed in October 2002. The assessment of the troposphere gradients from the different techniques is not as clear because of different time intervals, different estimation properties, or different observables. However, the best inter-technique agreement is found between the IVS combined gradients and the GPS solutions with standard deviations between 0.2 and 0.7?mm.     

Epithermal Gold Mineralization in the Trenggalek District,East Java,Indonesia

Gold‐mineralized quartz veins at the Trenggalek district of the Southern Mountains Range in East Java, Indonesia, are hosted by Oligo‐Miocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects (Dalangturu, Suruh, Jati, Gregah, Jombok, Salak, and Kojan) and the southern prospects (Sentul and Buluroto). The plugs are subalkaline tholeiitic basaltic‐andesite to calc‐alkaline andesite in composition. ⁴⁰Ar–³⁹Ar dating of a quartz‐adularia vein at the Dalangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone‐pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50 cm wide in the northern prospects and up to 3 m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag, Zn, Pb, and Cu contents in both the northern and southern prospects. The quartz veins at the Jati, Gregah, and Sentul prospects have relatively lower gold‐silver ratios (Ag/Au = 23.2) compared to those at the Kojan, Dalangturu, Salak, and Suruh prospects (Ag/Au = 66.8). The quartz veins at the Dalangturu prospect are relatively rich in base metal sulfides. Ag/(Au+Ag) ratios of electrum in the Dalangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore‐forming temperatures of 190–200°C and 220–230°C at the Sentul and Kojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore‐fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the Sentul and Kojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the Sentul prospect.     

Removal of lead from cathode ray tube funnel glass by chloride volatilization

Cathode ray tube funnel glass is an environmentally problematic relict of old television sets. In particular, landfilling of this material is strongly discouraged because of its high lead content. However, recovery of this toxic lead could prevent its release into the environment and allow its reuse. In this research, lead was separated from the glass matrix by a chloride volatilization process. Melting of the funnel glass together with CaCl₂ resulted in the volatilization of 80 % of lead at 1,000 °C. The use of NaCl as a chlorination agent yielded less volatile lead, while poly(vinyl chloride) and gaseous HCl proved to be ineffective chlorination agents. The differences in the chlorination agent efficiencies could be attributed to differences in the corresponding formation of silicates. Energy-dispersive X-ray spectroscopy showed that diffusion plays an important role in the volatilization of PbCl₂.     

Elasto‐plastic model for cement‐treated sand

This paper presents an elasto‐plastic model for non‐linear analyses of cement‐treated sand. Various laboratory tests were systematically carried out to investigate the pre‐peak and post‐peak behaviours of a cement‐treated sand. On the basis of these experimental results, the new model was built within the framework of a relatively simple elasto‐plastic theory. Two failure criteria are employed to express tensile and shear failure characteristics observed in the experimental results of the cement‐treated sand. The proposed model can describe strain‐hardening and strain‐softening responses under both failure modes. In the strain‐softening rules, the smeared crack concept is used, and a characteristic length is considered to avoid the issue of mesh‐size dependency. Since the failure criterion and strain‐hardening/softening rules are based on the experimental evidences, the model is relatively easy to understand and the parameters used in the model have clear physical meaning. The proposed model was applied to simulate the behaviour of cement‐treated sand in various laboratory tests, allowing for a reasonable comprehensive evaluation. It was demonstrated that the proposed model is suitable for describing both the tensile and shear failure behaviours of cement‐treated sand. Copyright © 2006 John Wiley & Sons, Ltd.     

Unsteady flows in Io’s atmosphere caused by condensation and sublimation during and after eclipse: Numerical study based on a model Boltzmann equation

The behavior of Io’s atmosphere during and after eclipse is investigated on the basis of kinetic theory. The atmosphere is mainly composed of sulfur dioxide (SO₂) gas, which condenses to or sublimates from the frost of SO₂ on the surface depending on the variation of surface temperature (～90–114 K). The atmosphere may also contain a noncondensable gas, such as sulfur monoxide (SO) or oxygen (O₂), as a minor component. In the present study, an accurate numerical analysis for a model Boltzmann equation by a finite-difference method is performed for a one-dimensional atmosphere, and the detailed structure of unsteady gas flows caused by the phase transition of SO₂ is clarified. For instance, the following scenario is obtained. The condensation of SO₂ on the surface, starting when eclipse begins, gives rise to a downward flow of the atmosphere. The falling atmosphere then bounces upward when colliding with the lower atmosphere but soon falls again. This process of falling and bounce back of the atmosphere repeats during the eclipse, resulting in a temporal oscillation of the macroscopic quantities, such as the velocity and temperature, at a fixed altitude. For a pure SO₂ atmosphere, the amplitude of the oscillation is large because of a fast downward flow, but the oscillation decays rapidly. In contrast, for a mixture, the downward flow is slow because the noncondensable gas adjacent to the surface hinders the condensation of SO₂. The oscillation in this case is weak but lasts much longer than in the case of pure SO₂. The present paper is complementary to the work by Moore et al. (Moore, C.H., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Stewart, B. [2009]. Icarus 201, 585–597) using the direct simulation Monte Carlo (DSMC) method.