Pressure responses of portlandite and H–D isotope effects on pressure-induced phase transitions

The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization) observed from the Raman and IR spectra of Ca(OH)₂ occurred at lower pressures than those of Ca(OD)₂. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns. X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e., packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines, even at pressures below the hydrostatic limit of the pressure medium.     

Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations

We conducted a detailed investigation of seismic activity from January 2011 to February 2013 along the Nankai trough off the Kii Peninsula, central Japan, by using data obtained from the DONET ocean-bottom observation network. The hypocenters are mostly within the subducting Philippine Sea (PHS) plate, although a few are along the plate boundary or in the sedimentary wedge below the Kumano forearc basin. The seismic activity can be separated into events above and below 20 km depth, which corresponds approximately to the Moho. The hypocenter distributions are distinctly different for these groups. The seismic activity in the oceanic crust can be further separated into three clusters. Most of the seismic activity recorded in our data represents aftershocks of the 2004 off the Kii Peninsula earthquakes (M _JMA = 7.1, 7.4, and 6.5), which occurred in the PHS plate. The hypocenter distribution in the oceanic crust correlates well with the location of the Paleo-Zenisu ridge, which is formed by a chain of seamounts that is subducting beneath the forearc basin. The hypocenters in the uppermost mantle are aligned on a plane dipping to the southeast, consistent with the existence of a thrust fault cutting through the lithosphere of the oceanic plate. The focal mechanisms of the earthquakes show that the axis of compressive stress in the PHS plate is oriented N–S, almost perpendicular to the direction of plate convergence, indicating a complex tectonic regime in this region. These results suggest that intraplate shortening may be occurring in the subducting oceanic plate.     

Formation mechanism of the Weddell Sea Polynya and the impact on the global abyssal ocean

An experiment using a global ocean–ice model with an interannual forcing data set was conducted to understand the variability in the Southern Ocean. A winter-persisting polynya in the Weddell Sea (the Weddell Polynya, WP) was simulated. The process of WP breaking out after no-WP years was explored using the successive WPs found in the late 1950s. The results suggested that the anomalously warm deep water, saline surface layer, and a cyclonic wind stress over the Maud polynya region in early winter are essential for the surface layer to be dense enough to trigger deep convections which maintain a winter-persisting polynya; also, the reanalyzed surface air temperature (SAT) over the observed polynya region is too high for an ocean–ice model’s bulk formula to yield sufficient upward heat fluxes to induce WP formation. Therefore the Weddell Polynya, a series of WPs observed from satellite in the mid-1970s, is reproduced by replacing the SAT with a climatological one. Subsequent to the successive WP events, density anomalies excited in the Weddell Sea propagate northward in the Atlantic deep basins. The Antarctic Circumpolar Current (ACC) is enhanced through the increased meridional density gradient. The enhanced ACC and its meandering over the abyssal ridges excite buoyancy anomalies near the bottom at the southwestern end of the South Pacific basin. The buoyancy signals propagate northward and eventually arrive in the northern North Pacific.     

Three‐dimensional structures and elemental distributions of Stardust impact tracks using synchrotron microtomography and X‐ray fluorescence analysis

Abstract— Three‐dimensional structures and elemental abundances of four impact tracks in silica aerogel keystones of Stardust samples from comet 81P/Wild 2 (bulbous track 67 and carrot‐type tracks 46, 47, and 68) were examined non‐destructively by synchrotron radiation‐based microtomography and X‐ray fluorescence analysis. Track features, such as lengths, volumes and width as a function of track depth, were obtained quantitatively by tomography. A bulbous portion was present near the track entrance even in carrot‐type tracks. Each impact of a cometary dust particle results in the particle disaggregated into small pieces that were widely distributed on the track walls as well as at its terminal. Fe, S, Ca, Ni, and eight minor elements are concentrated in the bulbous portion of track 68 as well as in terminal grains. It was confirmed that bulbous portions and thin tracks were formed by disaggregation of very fine fragile materials and relatively coarse crystalline particles, respectively. The almost constant ratio of whole Fe mass to track volume indicates that the track volume is almost proportional to the impact kinetic energy. The size of the original impactor was estimated from the absolute Fe mass by assuming its Fe content (CI) and bulk density. Relations between the track sizes normalized by the impactor size and impact conditions are roughly consistent with those of previous hypervelocity impact experiments.     

Use of similarity solutions for the problem of a wetting front — a question of unique representation

The use of similarity solutions for the problem of horizontal infiltration of water into a semi-infinite, dry and homogeneous porous medium is studied based upon some recent results of functional analysis. It is found that the so-called non-unique representation of reported experimental moisture profiles for this problem is not necessarily evidence against the validity of the extended Darcy's law for unsaturated flow through porous media.     

Particular solutions to the problem of horizontal flow of water and air through porous media near a water table

Particular solutions to the problem of horizontal flow of water and air through porous media near a water table are derived and regularity properties of the solutions are presented. It is found that a singularity occurs in the solutions at the water table and the water table can be interpreted as an acceleration wave of the nth order in terms of either air or water flow where n is a positive integer. Effects of air flow on water flow are discussed.     

Chemical variations of magmas at Izu-Oshima volcano,Japan: plagioclase-controlled and differentiated magmas

Systematic analyses of the major-element chemistry of products of several eruptions during syn-and post-caldera stages of Izu-Oshima volcano were compiled. Comparisons of the products of large-scale eruptions in 1338?, 1421? and 1777–1778, of intermediate-scale eruptions in 1950–1951 and 1986, and of small-scale eruptions in 1954, 1964 and 1974 clearly show the existence of two types of magmas. One is “plagioclase-controlled” and the other is “differentiated” magma (multimineral-controlled); i.e. the bulk chemistry of the first magma type is controlled by plagioclase addition or removal, while that of the second type is controlled by fractionation of plagioclase, orthopyroxene, clinopyroxene, and titanomagnetite. Eruptions of Izu-Oshima volcano have occurred at the summit and along the flanks. Summit eruptions tap only plagioclase-controlled magmas, while flank eruptions supply both magma types. It is considered unlikely that both magma types would coexist in the same magma chamber based on the petrology. In the case of the 1986 eruption, the flank magma was isolated sometime in the past from the summit magma chamber or central conduit, and formed small magma pockets, where further differentiation occurred due to relatively rapid cooling. In a period of quiescence prior to the 1986 eruption, new magma was supplied to the summit magma chamber, and the summit eruption began. The dike intrusion or fracturing around the small magma pockets triggered the flank eruption of the differentiated magma. This model can be applied to the large-scale flank eruption in 1338(?) which erupted differentiated magmas. In 1421(?), the flank eruption tapped plagioclase-controlled magma. In this case, the isolated magmas from the summit magma chamber directly penetrated the flank without differentiation.     

Variation of the distribution coefficients of rare earth elements in modern coral-lattices: species and site dependencies

Rare earth element (REE) concentrations in the carbonate lattice of four species of coral have been analyzed and compared with the dissolved REE in ambient seawaters. The corals were from two areas of different salinity, marine (34-34.5) and bay (33-34). The measurement of REE in coral was carried out with inductively coupled plasma mass spectrometry (ICP-MS) after meticulous washing of coral samples, digestion with acetic acid and preconcentration of REE. The concentrations of REE in the two ambient seawaters were quite different, being ten-times higher in the bay area and enriched in light REE. However, the average distribution coefficients (D’s) were almost identical in the two areas. Substantial distribution coefficient differences were observed among the four coral species and the magnitude of inter-species variation in D was also species-dependent. Theoretical calculations imply that pH variation could cause variations in D large enough to account for the small differences between the two areas.     

Deformation structures in shale bed indicate flow direction of overlying Miocene subaqueous pyroclastic flow

Thrusts, pinch-and-swell structures and undulations are present within a 2-m-thick layered shale bed of Miocene age that is overlain by a rhyolite subaqueous pyroclastic flow deposit 2–3 m thick. The deformation structures were caused by loading and lateral compression by the subaqueous pyroclastic flow, probably analogous to those observed in layered muds deformed by a sand mass advancing across them. Prominent thrusts strike east-west and dip south, and the crests of undulations strike east-west, indicating that the subaqeuous pyroclastic flow moved northward.     

Asymptotic behaviour of solutions to the problem of wetting fronts in one-dimensional,horizontal and infinite porous media

The asymptotic behavior of solutions to the problem of wetting fronts is studied in one-dimensional, horizontal and infinite porous media with the soil-water diffusivity proportional to some power of the water content. The uniqueness of the similarity solution for the problem is studied and the properties of this solution are presented. It is shown that the similarity solution is an asymptotic solution of a wide class of initial value problems of wetting fronts in the media. The use of the similarity solution is discussed for the experimental determination of the soil-water diffusivity.