古川 邦之

In this study, Raman spectra (3700–10 cm ^–1 ) and attenuated total reflection infrared–far-infrared (ATR-IR/FIR) spectra (4000–50 cm ^–1 ) including low-frequency region were measured for amorphous rocks, which were five types of obsidians whose formation ages and sources are different and pitchstone to clarify the differences in water content (free and bound water species), their Si–O bonds and possible linkage with a metal ion, and the mean atomic volume. In order to explore these points, we focused on infrared (IR) absorptions of hydroxyl (OH) groups that is observed in the 4000–3000 cm ^–1 region, those of Si–O bond that is identified in the 1300–850 cm ^–1 region and a Boson peak that appears in a low-frequency region of Raman spectra, respectively. IR absorption of Si–O stretching was detected for all samples and that of OH stretching and H–O–H bending was also detected in some rocks. Therefore, using IR spectroscopy was useful to discriminate each rock based on the water content and the environment of Si–O bonds. On the other hands, a Boson peak could be detected for the low-frequency region below 60 cm ^–1 of Raman spectra, which appears in amorphous solids. This study is the first finding that the Raman shift of Boson peak was different among similar natural glassy rocks from multiple sources and it means that the mean atomic volume of samples was different. In addition, sharp bands of Raman scattering which came from inorganic substances such as feldspar helped to identify ingredients in samples. As a results, we made clear that using both IR and Raman including low-frequency regions is effective to identify the same types of natural amorphous rocks.

Abstract To test the hypothesis that a Cretaceous hairpin turn is absent in the apparent polar wander path (APWP) of the inner arc of southwestern Japanese island (southwest Japan), we refined a mid-Cretaceous (100 Ma) paleomagnetic pole from southwest Japan. Red mudstone samples from the 100 Ma Hayama Formation were collected for paleomagnetic analysis from eight sites in the Hayama area in the central part of southwest Japan. A high-temperature remanent magnetization component carried by hematite was isolated from these sites and was found to be of primary mid-Cretaceous origin. The primary nature of the magnetization is supported by the detrital character of the magnetic carrier. The primary directions provided a paleomagnetic pole (35.0°N, 209.6°E, A₉₅ = 6.1°, N = 8), which represented southwest Japan at 100 Ma. This pole falls into a cluster of Cretaceous poles in southwest Japan. An APWP for southwest Japan between 110 and 70 Ma was updated to ascertain the stationarity of the pole positions for this region. Therefore, it is unlikely that the APWP for southwest Japan experienced a hairpin turn during the Cretaceous.

<p>岐阜県南部に分布する可児層群の最下部を占める蜂屋層は第一瀬戸内累層群東部で最も古い地層であり，主に非海成の火砕岩類からなる．蜂屋層最下部の栃洞溶結凝灰岩部層の溶結凝灰岩から分離したジルコンのレーザーアブレーションICP-MSによるU-Pb年代測定を行ったところ，²³⁸U-²⁰⁶Pb年代の加重平均として22.38±0.17Ma（2σ）が得られた．この年代は蜂屋層の堆積開始時期を拘束する．分析を行った溶結凝灰岩試料の蛍光X線分析による全岩主成分・微量元素組成を併せて報告する．</p>

先カルデラ火山活動期の噴火活動およびマグマ供給系を明らかにするため，カルデラ北西壁に分布する先阿蘇火山岩類の地質調査，全岩化学分析およびSr, Nd同位体比分析を行った．カルデラ北西壁は，主に安山岩溶岩から構成され，一部にデイサイト溶岩が分布する．これらの比較的穏やかな噴火様式からカルデラ噴火への噴火様式の変遷は，豊肥火山地域における地殻歪速度の減少に起因している可能性がある．また先阿蘇火山岩類の全岩化学組成は，カルデラ形成期以降の噴出物と大局的には類似している．このことは，先カルデラ火山活動期のマグマがカルデラ形成期と同じく，地殻物質の溶融により生成されたことを示唆する．一方で，Sr同位体比は先阿蘇火山岩類とカルデラ形成期の噴出物で異なる．つまり先カルデラ火山活動期とカルデラ形成期のマグマは，全岩化学組成は類似するが，同位体組成が異なる地殻を溶融することにより生成されたのかもしれない．

阿蘇火山直下のマグマ溜りの化学的進化を明らかにするため，先阿蘇火山岩類の岩石記載と全岩化学組成分析を行った．それら溶岩は，斑晶鉱物組合せと全岩化学組成の異なる8タイプに区分できる．液相濃集元素のモデル計算結果は，先阿蘇火山岩類が示す組成多様性が単純な分別結晶作用では導かれないことを示した．さらに，先阿蘇火山岩類とカルデラ形成期以降噴出物を比較した結果，特に安山岩～流紋岩の斑晶鉱物組合せ，量比に顕著な違いがみられること，前者が後者に比べてSiO₂含有量に対する液相濃集元素含有量が乏しい特徴があることが明らかになった．これらの結果は，先カルデラ火山活動期からカルデラ形成期の間に，安山岩～流紋岩マグマの起源物質化学組成や生成時の物理条件などに変化が生じたということを示唆している．

Planetary aerosol laboratory experiments for science education were carried out in a curriculum of Kyoto University. Our goal is to reproduce "the blue sunset" on Mars which are reported from NASA's Mars Pathfinder. In reproducing the rays scattered by Martian atmosphere (dust storm) in a laboratory, the number density of scattering particles has to be as large as possible. Three experiments were conducted in the air and water. Although we were not able to reproduce Martian blue sunset, we elucidated its spectrum. Converting this spectrum to a color in the RGB system, we obtained R = 114, G = 122, B = 192. Though the experiment, we proved that planetary aerosol laboratory experiments are significantly fruitful for science education as well as for science studies. We propose that researchers and lecturers should make active use of planetary aerosol laboratory experiments for science education.

阿蘇カルデラ内に分布する高野尾羽根流紋岩溶岩から得られた4本のボーリングコアの構造記載を行い, 内部構造の発達過程を議論した.高野尾羽根溶岩は上部の軽石質層と黒曜石層の互層, 中部の結晶質層, そして下部の黒曜石層の三層準からなる.この内部構造は流動時の冷却と脱ガス過程を経て形成されると考えられる.中部の結晶質層には, 周囲よりも結晶化し, 微細な空隙を多量に含む微細空隙部が存在している.この微細空隙部は, 溶岩の噴出直前あるいは直後に形成されたと考えられる.給源から離れたボーリングコアでは, 微細空隙部が流動により引き伸ばされ流紋岩溶岩に特徴的な縞状の流理構造を形成する.またその微細空隙部により規定される流理構造の傾斜角は, 結晶質層の上部ほど大きくなる傾向があり, ランプ構造を呈している.

The drilling core (501.9 m in depth) has been obtained from Okogashima Island located in southern margin of the Aira caldera at northern end of Kagoshima Bay in southern Kyushu. The core reveals detailed eruption history prior to the Aira pyroclastic eruptions about 25,000 years ago by descriptions of lithofacies and fissiontrack dating. The three types of lithofacies are identified in the drilling core. They are (1) 2-8 m in depth: pyroxene andesite; (2) 8-253.2 m in depth: the Okogashima rhyolite lava flow; (3) 253.2-501.9m in depth: pyroclastic materials. This study focuses mainly on pyroclastic materials, which have not been described yet. The pyroclastic materials in lower levels are composed mainly of tuffaceous sand with cross lamination, containing shell fossils. They also contain pumice-concentration zone and welded tuff, indicating explosive eruption. The pumice-concentration zone occurs in 326-340 m (unit A), 354-360 m (unit B), 425-427 m (unit D), 449-450 m (unit E), and 478-497 m (unit F), while the welded tuff occurs in 360-380 m (unit C). The fission-track ages of around 0.4 Ma from the units B and C indicate that the deposits were erupted prior to the Aira pyroclastic eruptions. Therefore, this drilling core shows that at least sixth pyroclastic eruptions are identified in southern margin of the caldera prior to the Aira pyroclastic eruptions.