IR active orientation of OH bending mode in topaz     

Keiji Shinoda  Nobuyuki Aikawa 《Physics and Chemistry of Minerals》1997,24(8):551-554

Infrared (IR) and nearinfrared (NIR) absorption spectra of hydrous and F-rich topazes were measured to assign an OH bending mode of topaz. Three absorption peaks at 1165, 3650, and 4803 cm⁻¹ are assigned to OH related absorption peaks. Since a peak at 4803 cm⁻¹ can be assigned to a combination mode of 1165 and 3650 cm⁻¹, the 1165 cm⁻¹ peak is harmonic with the 3650 cm⁻¹ peak. Polarized IR absorption spectra of (100), (010), and (001) planes of the hydrous topaz were measured to examine IR active orientation of the 1165 cm⁻¹ OH related mode. Three pleochroic distributions of the absorption peak at 1165 cm⁻¹ on (100), (010), and (001) planes indicate an active orientation of the 1165 cm⁻¹ OH related mode. The IR active orientation of the 1165 cm⁻¹ OH related mode in topaz is normal to the OH dipole. The orthogonality and harmonic combination mode indicate that the 1165 cm⁻¹ peak is OH bending mode. The active orientation of OH bending mode is polarized in the plane normal to the OH dipole. The polarization suggests that anisotropic thermal vibration of protons on the hydroxyl is maximum along the IR active orientation. Received: August 16, 1996 / Revised, accepted: April 20, 1997  相似文献   

U-Pb and Pb-Pb ages of zircons from basaltic eucrites: Implications for early basaltic volcanism on the eucrite parent body     

Keiji Misawa  Akira Yamaguchi  Hiroshi Kaiden 《Geochimica et cosmochimica acta》2005,69(24):5847-5861

We have undertaken petrologic and SHRIMP U-Th-Pb isotopic studies on zircons from basaltic eucrites (Yamato [Y]-75011, Y-792510, Asuka [A]-881388, A-881467 and Padvarninkai) with different thermal and shock histories. Eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites. Some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene, and typically have rounded to subrounded shapes due to recrystallization. Superchondritic Zr/Hf ratios of eucritic zircons indicate that they crystallized from incompatible element-rich melts after crystallization of ilmenite. Concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite Y-75011 are higher than those in metamorphosed eucrites.The U-Pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance. Radiogenic lead-loss up to 48% from zircons is observed in the shock-melted eucrite Padvarninkai. The ²⁰⁷Pb-²⁰⁶Pb ages of zircon in Y-75011 (4550 ± 9 Ma, n = 5) are nearly identical, within analytical uncertainty, to the ages of zircons from the metamorphosed eucrite Y-792510 (4545 ± 15 Ma, n = 13), the highly metamorphosed eucrites A-881388 (4555 ± 54 Ma, n = 5) and A-881467 (4558 ± 13 Ma, n = 8), and the shock-melted eucrite Padvarninkai (4555 ± 13 Ma, n = 18). The averaged ²⁰⁷Pb-²⁰⁶Pb age of zircon from five eucrites analyzed in this study is 4554 ± 7 Ma (95% confidence limits, n = 49), indistinguishable from the averaged U-Pb age (4552 ± 9 Ma) of the same samples. Because of the high closure temperature of lead in zircon (T_closure = ∼1050°C with a cooling rate of 0.2°C/yr), the ²⁰⁷Pb-²⁰⁶Pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas.This fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the Solar System history, 7-20 Ma after CAI formation (4567.2 ± 0.6 Ma), thus basaltic eucrites crystallized from parental magmas within a short interval following the differentiation of their parent body. The U-Pb ages of eucritic zircons are older than the U-Pb, Sm-Nd and Rb-Sr ages of some basaltic eucrites, which is consistent with differences in closure temperatures of each isotopic system, and suggests that thermal and shock metamorphism affected the isotopic systems of pyroxene, plagioclase and phosphates.  相似文献   

Anisotropic phase transition of rutile under shock compression     

Keiji Kusaba  Masae Kikuchi  Kiyoto Fukuoka  Yasuhiko Syono 《Physics and Chemistry of Minerals》1988,15(3):238-245

Shock recovery experiments for single crystal and powdered specimens of TiO₂ with the rutile structure were performed in the pressure range up to 72 GPa. Single crystal specimens were shocked parallel to [100], [110] and [001] directions. X-ray powder diffraction analysis showed that the amount of -PbO₂ type TiO₂ produced by shock-loading depended strongly on the shock propagation direction. The maximum yield (about 70%) was observed for shock loading to 36 GPa parallel to the [100] direction. In the [001] shock direction, the yield is much smaller than that of the [100] direction. This anisotropic yield was consistent with the observed anisotropy of the phase transition pressure in shock compression measurements. However, transformation to the -PbO₂ type cannot explain the large volume change observed above about 20 GPa. On the basis of the high pressure behavior of MnF₂, we assumed that the high pressure phase was either fluorite or distorted fluorite type and that the phase conversion to the -PbO₂ type was induced spontaneously in the pressure reduction process.We present a displacive mechanism of phase transition under shock compression from the rutile structure to the fluorite structure, in which the rutile [100] is shown to correspond to the fluorite [001] or [110] and the rutile [001] to the fluorite [110]. Direct evidence is obtained by examining the [100] shocked specimen by high resolution electron microscopy.  相似文献   

A primitive odobenine walrus of Early Pliocene age from Japan     

Hideo  Horikawa 《Island Arc》1994,3(4):309-328

Abstract The well preserved cranium of Protodobenus japonicus, a new genus and species of odobenine walrus, is from the lower part of the Tamugigawa Formation at Ooshima-mura, Higashi Kubiki-gun, Niigata Prefecture, central Japan. The lower part of the formation that yielded P. japonicus is Early Pliocene, dating approximately from 5.0 to 4.9 Ma. The skull of P. japonicus is generally shaped like that of the modern walrus, Odobenus rosmarus (Linnaeus, 1758), but is much more primitive, especially in the dentition. Protodobenus japonicus is derived from the Imagotariinae. It is similar to such primitive fossil walruses as Prorosmarus alleni from the Western Atlantic and Aivukus cedrosensis from Baja California, and has some similarities as well as significant differences from them. Protodobenus japonicus could have evolved directly into Odobenus in the North Pacific Ocean, and could have dispersed directly to the Arctic Ocean. This is contrary to the scenario proposed by Repenning and Tedford, in which primitive odobenids, like Aivukus cedrosensis, migrated to the Atlantic Ocean through the Central American Seaway and returned to the North Pacific Ocean as O rosmarus via the Arctic about 0.6 Ma. Regarding the first lower premolar of the living walrus, Fay concluded after studying fetal O. rosmarus that the first premolar (P₁) of the mandible is absent, and that the lower tooth row consists of: C₁ P₂, P₃, P₄. Protodobenus japonicus has in its mandible I _1-2 C₁ P₂, P₃, P₄, and this is the primitive pinniped formula. Pinnipeds typically lose the molars, not the anterior premolars, and the present author believes that the correct tooth formula for O rosmarus is C₁ P₁, P₂, P₃. Its skull, palate, and mandible suggest that P. japonicus had morphology pre-adapted to an early stage of benthic suction feeding, but it probably was unable to rely on that method of feeding. The discovery of P. japonicus demonstrates that the odobenine lineage (true walruses) goes back in time at least 5 Ma. Other more aberrant odobenine walruses, such as Aivukus and Prorosmarus, and pseudo-walruses of the subfamily Dusignathinae, are more distantly removed from the lineage leading to living walruses than has previously been suspected.  相似文献   

Reactions to define the biotite isograd in the Ryoke metamorphic belt,Kii Peninsula,Japan     

Ge-Fan Wang  Shohei Banno  Keiji Takeuchi 《Contributions to Mineralogy and Petrology》1986,93(1):9-17

Two types of biotite isograd are defined in the low-grade metamorphism of the Wazuka area, a Ryoke metamorphic terrain in the Kii Peninsula, Japan. The first, BI₁, is defined by the reaction of chlorite+K-feldspar= biotite+muscovite+quartz+H₂O that took place in psammitic rocks, and the second, BI₂, by the continuous reaction between muscovite, chlorite, biotite and quartz in pelitic rocks. The Fe/Mg ratios of the host rocks do not significantly affect the reactions. From the paragenesis of pelitic and psammitic metamorphic rocks, the following mineral zones were established for this low-pressure regional metamorphic terrain: chlorite, transitional, chlorite-biotite, biotite, and sillimanite. The celadonite content of muscovite solid solution in pelitic rocks decreases systematically with the grade of metamorphism from 38% in the chlorite zone to 11% in the biotite zone. Low pressure does not prohibit muscovite from showing the progressive change of composition, if only rocks with appropriate paragenesis are chosen. A qualitative phase diagram of the AKF system relevant to biotite formation suggests that the higher the pressure of metamorphism, the higher the celadonite content of muscovite at BI₁, which is confirmed by comparing the muscovites from the Barrovian and Ryoke metamorphism.  相似文献   

The influence of weathering on the geotechnical properties and slope angles of mudstone in the Mineoka earth-slide area,Japan   总被引：1，自引：0，他引：1  

Yukinori Matsukura  Keiji Mizuno 《地球表面变化过程与地形》1986,11(3):263-273

Three active earth-slide slopes of Tertiary mudstone were investigated: Slope 1 has an angle of 17 ?4°, Slope 2 of 12.9°, and Slope 3 of 11.6°. Infinite slope analysis indicated that the instability of these three slopes can be well explained by using the residual strength parameters of earth-slide soils near the sliding surface in conjunction with the highest ground water table. The residual angle of shearing resistance, ø'_r, plays an important role in the determination of slope angle because it differs greatly among slopes. Mineralogical studies and X-ray diffraction analyses were performed for the clay minerals included in the slope material. The results showed that illite and chlorite were found in Slope 1, and also in Slopes 2 and 3 together with interstratified illite/montmorillonite and montmorillonite. The degree of weathering is progressive in order of Slopes 1, 2 and 3. The alteration of clay minerals by weathering causes the reduction in ø'_r -values, i.e., 19.4° in Slope 1 (steep, less weathered) and 12.1-9.2° in Slopes 2 and 3 (gentle, much more weathered). This result indicates that the degree of weathering has a great influence on the value of ø'_r, which in turn determines the slope angle.  相似文献   

Radiation induced lattice defects in natural zircon (ZrSiO4) observed at atomic resolution     

Keiji Yada  Takayoshi Tanji  Ichiro Sunagawa 《Physics and Chemistry of Minerals》1987,14(3):197-204

Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO₂ thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated.  相似文献   

Dual publication     

Simon Wallis  Akira IshiwatariEditors-in-Chief  Keiji Takeuchi  Toshiaki TsunogaeExecutive Editors 《Island Arc》2007,16(2):211-211

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Quaternary vertical offset and average slip rate of the Nojima Fault on Awaji Island, Japan   总被引：5，自引：0，他引：5  

Akihiro Murata  Keiji Takemura  Takao Miyata  Aiming Lin 《Island Arc》2001,10(3-4):360-367

Abstract Drilling was carried out to penetrate the Nojima Fault where the surface rupture occurred associated with the 1995 Hyogo-ken Nanbu earthquake. Two 500 m boreholes were successfully drilled through the fault zone at a depth of 389.4 m. The drilling data show that the relative uplift of the south-east side of the Nojima Fault (south-west segment) was approximately 230 m. The Nojima branch fault, which branches from the Nojima Fault, is inferred to extend to the Asano Fault. From the structural contour map of basal unconformity of the Kobe Group, the vertical component of displacement of the Nojima branch–Asano Fault is estimated to be 260–310 m. Because the vertical component of displacement on the Nojima Fault of the north-east segment is a total of those of the Nojima Fault of the south-west segment and of the Nojima branch–Asano Fault, it is estimated to total to 490–540 m. From this, the average vertical component of the slip rate on the Nojima Fault is estimated to be 0.4–0.45 m/10³ years for the past 1.2 million years.  相似文献   

Crack-filling clays and weathered cracks in the DPRI 1800 m core near the Nojima Fault, Japan: Evidence for deep surface-water circulation near an active fault     

Shin-Ichi Uda  Aiming Lin  Keiji Takemura 《Island Arc》2001,10(3-4):439-446

Abstract Crack-filling clays and weathered cracks were observed in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m cores drilled from the Nojima Fault Zone, which was activated during the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). The crack-filling clays consist mainly of unconsolidated fine-grained materials that fill opening cracks with no shear textures. Most of the cracks observed in the DPRI 1800 m cores are yellow-brown to brown in color due to weathering. Powder X-ray diffraction analyses show that the crack-filling clays are composed mainly of clay minerals and carbonates such as siderite and calcite. Given that the top of the borehole is approximately 45 m above sea level, most of the core is far below the stable groundwater table. Hence, it is suggested that the crack-filling clays and weathered cracks in the cores taken at depths of 1800 m were formed by the flow of surface water down to the deep fractured zone of the Nojima Fault Zone during seismic faulting.  相似文献