Petrology of green polished stone axes of the Jomon period from the Sannai-Maruyama site,Japan, investigating the origin of source rock

Numerous green polished stone axes have been excavated from the Sannai-Maruyama site, one of Japan's largest archeological sites in the Jomon period (5.9–4.2 cal kyr BP). The axes are composed of weakly metamorphosed fine-grained volcaniclastic rock having a peculiar texture that includes numerous acicular actinolites growing in random directions within a quartz and albite matrix. Cobbles of Aotora stone found along the Nukabira River, Biratori town, southern Hokkaido, are the most likely raw material for these stone axes. Aotora stones have alternate bands of a soft dark-green picritic layer and a hard SiO₂-rich pale-green layer. The pale-green layer has a texture similar to the stone axes. Basaltic and picritic volcanic rocks of the Sorachi-Yezo Belt occupy the area along the Shidoni River, a tributary of the Nukabira River. Volcaniclastic rocks similar in texture, mineralogy, and bulk rock compositions to the Aotora stone are exposed in the area. These rocks underwent metamorphism under the actinolite-pumpellyite facies conditions. Their protolith is submarine hyaloclastic rocks that are intercalated with laminated picrite detritus. The stone axes, pale-green layers of Aotora stone, and those of the volcaniclastic rocks of the Shidoni River area all have high SiO₂ (~ 55 wt%), Cr (~ 840 μg/g), and Ni (~ 370 μg/g). The rare earth element patterns with abundant light rare earth elements and depleted heavy rare earth elements of stone axes were also consistent with the pale-green layers of the outcrop. These pale-green layers, interleaved with dark-green layers of picritic detritus, were the likely source rock of the stone axes. The high SiO₂ content in the pale-green layer caused the crystallization of quartz and albite in the matrix, which resulted in high-quality raw material for making stone axes.     

A trial prediction of the values of some surface-layer turbulence constants using Schumann's method for promoting realizability

Based on a suggestion by Yamada (1986), values of the unknown constants in a particular second-order closure model are determined by applying Schumann's method (Schumann, 1977), using empirical data under neutral conditions. It is found that this closure model predicts favorably the Monin-Obukhov universal functions on both the stable and the unstable sides. It is likely that Schumann's method can be used as an expedient means of determining values of unknown model constants.     

Determination of rare earth elements,thorium and uranium in seaweed samples on the coast in Niigata Prefecture by inductively coupled plasma mass spectrometry

The determination of rare earth elements (REEs), Th and U in seaweeds of various species and in ambient surface seawater were performed by inductively coupled plasma mass spectrometry. The seaweeds and the seawater samples were collected at 10 different coastal areas of Niigata Prefecture in Japan twice a year (spring and autumn) in 2004 and 2005. Results showed that concentration of REEs in seaweed species from Niigata Prefecture were about 10³ times higher than those in seawater, and the enrichment factors of REEs were larger in heavy REE than light REE. A significant concentration difference of REEs, Th and U was found among species even in the same phylum. Undaria pinnatifida had the highest concentration of U. Considering that U. pinnatifida has low concentrations of REEs among typical brown algae, different REEs and U uptake mechanisms are suggested. The concentration of REEs, Th and U did not vary remarkably between sampling points and/or seasons.     

Electron microscopy of clinoenstatite from a boninite and a chondrite

Clinoenstatite crystals from a boninite and the Yamato-74191 chondrite have been studied with an analytical electron microscope. (100) twins and cracks perpendicular and parallel to the c axis are characteristic of their submicroscopic textures. The frequency in appearance along the c axis and widths of the cracks have been explained by the dimensional change of the c axis in the direct transformation of protoenstatite to clinoenstatite and by the cooling rate around the transformation temperature. The cracks in the crystals from the boninite are filled with fibrous crystals of talc, while those from the chondrite are open or filled with glass in which fine crystals of plagioclase are common.     

Timing of the cataclastic deformation along the Akaishi Tectonic Line,central Japan

This paper describes K-Ar ages of cataclasites and fault gouges from the Akaishi Tectonic Line (ATL), central Japan. Petrological and mineralogical features of these rocks are also examined. Based on the results, we test the hypothesis that the K-Ar ages of these rocks represent the age of hydrothermal alteration associated with the fault movement. Intensity of deformation and alteration increase passing from host rock into cataclasite and finally into fault gouge. This increase corresponds to an increase of the value of crystallinity index (Kübler index) of the micaceous minerals contained in these rocks. Furthermore, the degree of rejuvention of K-Ar ages of the micaceous minerals increases in the same sense. A correlation of K-Ar ages (plotted on the y axis) versus Kübler index (plotted on the x axis) yields a concave curve asymptotically parallel with the x axis at approximately 15 Ma. This curve is interpreted to represent the mode of decrease of the relative amounts of inherited argon in the K-Ar system of the micaceous minerals, corresponding to an increase in the intensity of deformation and alteration. Inclination of the curve becomes zero if all the inherited argon is lost from the K-Ar system of the micaceous minerals. Thus, it is concluded that the hydrothermal alteration occurred at approximately 15 Ma. The strike-slip basin along the ATL formed the middle Miocene. The K-Ar dating of ATL gouges indicates that the ATL was active simultaneously with formation of the strike-slip basin along its trace during the middle Miocene.     

A numerical model for far-field tsunamis and its application to predict damages done to aquaculture

The 1960 Chilean tsunami which traveled the Pacific Ocean and caused much damages to Japan is simulated from its generation to the terminal effects on coastal areas. In the computation of ocean propagation by the linear longwave theory, a new technique is introduced to keep the same accuracy as the linear Boussinesq equation and reduce the CPU time as well as the computer memory. In the coastal transformation computation, the energy dissipation due to sea-bottom scouring is suggested to be included, particularly in the case of long bays. To obtain accurate results, the current velocity requires finer spatial grids than the water surface elevation. Damage done to pearl culture rafts are explained in terms of the computed current velocity.     

Rare gases in a phlogopite nodule and a phlogopite-bearing peridotite in South African kimberlites

Rare gas isotopes in a phlogopite nodule and a phlogopite-bearing peridotite nodule in South African kimberlites were studied to examine the state of rare gases in the deep interior of the kimberlite region.Within the experimental error of 1 ～ 2%, rare gas isotopic compositions are atmospheric except for radiogenic⁴He and⁴⁰Ar. No excess¹²⁹Xe was observed.In phlogopite, Ne is more depleted, whereas the heavier rare gases are more enriched than the atmospheric rare gases relative to³⁶Ar.Together with other data these results suggest that the state of rare gases in the upper mantle of the South African kimberlite region might have been changed from the typical primitive mantle by a process such as mixing of crustal materials.     

Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.     

The superstructure of plagioclase feldspars

A modulation function representing the position and density of (Na, Ca) atoms in the superstructure of the e-plagioclase has been derived from the average structures of different plagioclase and a general modulation theory. Based on this function the superstructure of bytownite (An₇₃) has been studied with the single crystal X-ray method. The cell dimensions by Megaw's axes are a=7.946(3)A, b=67.09(2)A, c=12.236(4)A, α=39.03(1)°, β=45.63(1)° and γ=59.63(1)°. Z=18(Na, Ca) Al(Al, Si)Si₂O₈. The initial phase factor of the modulation function for bytownite has been obtained from the intensity data of the satellite reflections. This modulation function indicates a coherent small-scale alternation of the Na-rich and Ca-rich bands in the superstructure. This superstructure has been refined by applying the albite and anorthite structures to the Na-rich and Ca-rich bands, respectively. The change of the superstructure of the e-plagioclase due to the compositional change has been described based on the movements of the satellites in reciprocal space. The direction of the coherent small-scale intergrowth of the anorthite-like and albite-like bands is perpendicular to the t vector. The thickness of the intergrowth is 1/|t|. Both direction and thickness change regularly from An₇₅ to An₂₅.