Progressive changes in lithological association of the Sanbagawa metamorphic complex,Southwest Japan: Relict clinopyroxene and detrital zircon perspectives

The main tectono‐stratigraphic unit (Shirataki unit) of the Sanbagawa metamorphic complex in central Shikoku is characterized by abundant mafic schist layers that show the mid‐ocean ridge basalt (MORB) affinity. These MORB‐derived schist layers are absent in a southern (structurally lower) domain within the unit. Instead, sporadic occurrences of small metabasite lenses that contain relict igneous minerals (Ti‐rich augite and kaersutite) indicative of alkali basalt magmatism are newly recognized in the southern domain. Compositions of relict clinopyroxene in metabasalt are useful to identify the tectonic setting and origin of the protolith basalt, and those in each unit of the Sanbagawa metamorphic complex are presented. The metamorphic grade of the Shirataki unit generally increases structurally upwards in the southern side of the highest‐grade zone, and metamorphic zonation is subparallel to lithostratigraphic succession. The protolith assemblage of the Shirataki unit shows a distinct change from the southern low‐grade domain (lower Shirataki subunit) composed of terrigenous sedimentary rocks (mudstone and sandstone) with minor alkali basalt to the northern higher‐grade domain (upper Shirataki subunit) consisting of terrigenous and pelagic sedimentary rocks with abundant MORB. The youngest detrital zircon U–Pb ages (ca 95–90 Ma) suggest that both domains have Late Cretaceous depositional ages at the trench. Progressive peeling of oceanic plate stratigraphy during subduction can account for the observed change of lithological association in the Shirataki unit.     

Land transformation and pond sediment information

Five years of observations on sedimentation rates in two ponds located near transformed land areas in the Kobe district of central Japan have shown the relationship between sedimentation and development during land transformation. One of the ponds observed has artificial land transformation in its drainage area (KR), whereas the other does not (KN). The sedimentation rate in the pond without artificial land transformation is roughly proportional to the rainfall intensity, whereas in the pond with land transformation it is related to change in the transformed area as well as the rainfall intensity. The relative sedimentation rate (sedimentation rate divided by the catchment area and rainfall intensity) is also related to loss on ignition and grain density; large relative sedimentation rates correspond to low loss on ignition and high grain density, suggesting that these factors are very sensitive to land transformation. Changes in catchment factors, which indicate the topographical and hydrological conditions in the catchment area, are inversely proportional to change in the ratio of the reclaimed to the natural area; this is indicative of change in the erodibility of the surface material in the catchment area. © 1997 John Wiley & Sons, Ltd.     

Scoria cone formation through a violent Strombolian eruption: Irao Volcano, SW Japan

Scoria cones are common volcanic features and are thought to most commonly develop through the deposition of ballistics produced by gentle Strombolian eruptions and the outward sliding of talus. However, some historic scoria cones have been observed to form with phases of more energetic violent Strombolian eruptions (e.g., the 1943–1952 eruption of Parícutin, central Mexico; the 1975 eruption of Tolbachik, Kamchatka), maintaining volcanic plumes several kilometers in height, sometimes simultaneous with active effusive lava flows. Geologic evidence shows that violent Strombolian eruptions during cone formation may be more common than is generally perceived, and therefore it is important to obtain additional insights about such eruptions to better assess volcanic hazards. We studied Irao Volcano, the largest basaltic monogenetic volcano in the Abu Monogenetic Volcano Group, SW Japan. The geologic features of this volcano are consistent with a violent Strombolian eruption, including voluminous ash and fine lapilli beds (on order of 10^?1 km³ DRE) with simultaneous scoria cone formation and lava effusion from the base of the cone. The characteristics of the volcanic products suggest that the rate of magma ascent decreased gradually throughout the eruption and that less explosive Strombolian eruptions increased in frequency during the later stages of activity. During the eruption sequence, the chemical composition of the magma became more differentiated. A new K–Ar age determination for phlogopite crystallized within basalt dates the formation of Irao Volcano at 0.4?±?0.05 Ma.     

Full-scale dynamic testing of response-controlled buildings and their components: concepts,methods, and findings

A series of shake-table tests was conducted by inserting and replacing 4 different types of dampers, or by removing them in a full-scale 5-story steel frame building. The objective is to validate response-control technologies that are increasingly adopted for major Japanese buildings without being attested to-date by a major earthquake. Test results are briefly described, and good performance of the dampers and frame demonstrated. The concepts of the full-scale building tests and various contributions are discussed. The difficulty associated with full-scale dynamic testing is explained.     

Lunar gravity field determination using SELENE same-beam differential VLBI tracking data

A lunar gravity field model up to degree and order 100 in spherical harmonics, named SGM100i, has been determined from SELENE and historical tracking data, with an emphasis on using same-beam S-band differential VLBI data obtained in the SELENE mission between January 2008 and February 2009. Orbit consistency throughout the entire mission period of SELENE as determined from orbit overlaps for the two sub-satellites of SELENE involved in the VLBI tracking improved consistently from several hundreds of metres to several tens of metres by including differential VLBI data. Through orbits that are better determined, the gravity field model is also improved by including these data. Orbit determination performance for the new model shows improvements over earlier 100th degree and order models, especially for edge-on orbits over the deep far side. Lunar Prospector orbit determination shows an improvement of orbit consistency from 1-day predictions for 2-day arcs of 6 m in a total sense, with most improvement in the along and cross-track directions. Data fit for the types and satellites involved is also improved. Formal errors for the lower degrees are smaller, and the new model also shows increased correlations with topography over the far side. The estimated value for the lunar GM for this model equals 4902.80080±0.0009 km³/s² (10 sigma). The lunar degree 2 potential Love number k ₂ was also estimated, and has a value of 0.0255 ± 0.0016 (10 sigma as well).     

Detection and isolation of p-nitrophenol-lowering bacteria from intestine of marine fishes caught in Japanese waters

To determine the existence of p-nitrophenol (PNP)-lowering bacteria in intestine of Japanese coastal fish, the gastro-intestinal contents were incubated in Brain Heart Infusion (BHI) broth and minimal medium (MM) broths containing 1 mmol/L PNP at 30 °C for 7 days. Among 26 samples of 19 fish species, 17 samples showed a decrease in PNP of 0.5-0.8 mmol/L in BHI broth, but no decrease was shown in MM broth. Eighteen PNP-lowering bacterial strains were isolated from four fishes. All of the strains were identified as Lactococcus lactis subsp. lactis. Three L. lactis strains JS1-3 isolated from Japanese seabass Lateolabrax japonicus showed the highest PNP-lowering activity (0.44 mmol/L). Optimum temperature and pH for the growth and PNP decreasing corresponded with the marine environment. These results suggested that marine fishes have PNP decreasing bacteria in their intestine. These bacteria might protect host fish from toxicities of PNP and PNP related compounds.     

Mixing of magmatic CO2 into volcano groundwater flow at Aso volcano assessed combining carbon and water stable isotopes

To understand deep groundwater flow systems and their interaction with CO₂ emanated from magma at depth in a volcanic edifice, deep groundwater samples were collected from hot spring wells in the Aso volcanic area for hydrogen, oxygen and carbon isotope analyses and measurements of the stable carbon isotope ratios and concentrations of dissolved inorganic carbon (DIC). Relations between the stable carbon isotope ratio (δ¹³C_DIC) and DIC concentrations of the sampled waters show that magma-derived CO₂ mixed into the deep groundwater. Furthermore, groundwaters of deeper areas, except samples from fumarolic areas, show higher δ¹³C_DIC values. The waters' stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) reflect the meteoric-water origin of that region's deep groundwater. A negative correlation was found between the altitude of the well bottom and the altitude of groundwater recharge as calculated using the equation of the recharge-water line and δD value. This applies especially in the Aso-dani area, where deeper groundwater correlates with higher recharge. Groundwater recharged at high altitude has higher δ¹³C_DIC of than groundwater recharged at low altitude, strongly suggesting that magmatic CO₂ is present to a much greater degree in deeper groundwater. These results indicate that magmatic CO₂ mixes into deeper groundwater flowing nearer the magma conduit or chamber.     

Origin of the difference in the distribution behavior of tellurium and selenium in a soil-water system

The distribution behavior of tellurium (Te) between soil and water in a synthetic soil-water system was studied coupled with the speciation of Te both in soil and water phases by using X-ray absorption fine structure (XAFS) spectroscopy and a high-performance liquid chromatography connected to an ICP-MS (HPLC-ICP-MS), respectively. The results were compared with a similar data set for Se, which was simultaneously obtained in this study. The oxidation states and host phases of Te and Se in the soil samples were given by XAFS, while the oxidation states in water were given by HPLC-ICP-MS. It was found that both Te and Se in soil are mainly associated with Fe(III) hydroxides under oxic conditions. From the EXAFS analyses, the outer-sphere complex is important for the Se(VI) sorbed on Fe(III) hydroxides in soils, while Se(IV), Te(IV), and Te(VI) form inner-sphere complexes. Under reducing condition, it was found that Te(0) and Se(0) species were formed and that Se was more readily reduced to Se(0) than Te, as is predicted from their Eh-pH diagrams. The reduction process from hexavalent to zerovalent species was different between Se and Te, that is, the direct reduction from Se(VI) to Se(0) was observed for Se, while Te was reduced stepwise from Te(VI) to Te(0) via Te(IV). In terms of the distribution between soil and water, Se distribution to water was much higher than that of Te under wide redox conditions. For Se, selenate is the predominant species in water even under reducing condition due to the much higher solubility of Se(VI) than Se(IV). Furthermore, a much smaller distribution of Te in water was primarily due to the larger affinities of Te(IV) and Te(VI) to Fe(III) hydroxides than Se(VI), which originates from the formation of the inner-sphere complexes of Te(IV) and Te(VI) to Fe(III) hydroxides.     

Ostwald ripening of garnet in high P/T metamorphic rocks

This paper presents a theoretical formulation of Ostwald ripening of garnet and discusses the importance of the process during high pressure and low temperature (high P/T) metamorphism. The growth rate of garnet due to Ostwald ripening is formulated for the system consisting of minerals and an intergranular medium. Crystal size distribution (CSD) of garnets are examined and compared with the theoretical distribution for Ostwald ripening. Two types of CSDs are recognized. One is consistent with the theoretical prediction of size distribution while the other is wider than the theoretical distribution. The former CSD applies to samples in which garnets show homogeneous spatial distributions. The latter CSD applies to samples in which garnets show heterogeneous spatial distributions such as in clusters or layers. These relations suggest that the heterogeneity of spatial distributions results in a heterogeneity of concentration of garnet, causing the wide distributions. The mean diameter (dg) has a large variation in samples having narrow distributions. Ostwald ripening explains well the similar patterns of CSD in these samples with different dg because of a scaling law. Compositional profiles of garnets with different size are consistent with Ostwald ripening rather than nucleation and growth kinetics. This suggests that the CSDs result from Ostwald ripening. Magnitude of heating rate will determine which mechanism controls CSD. Nucleation and growth kinetics are dominant when heating rate is large. On the other hand, Ostwald ripening is dominant when heating rate is small. CSDs of garnets in high P/T metamorphic rocks are consistent with the latter case.