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Volume 115, Issue 10
Displaying 1-8 of 8 articles from this issue
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Articles
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Kana Ozawa, Shigeru Takizawa2009 Volume 115 Issue 10 Pages 503-511
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSWe used transmission electron microscopy (TEM) to analyze amorphous material in pseudotachylyte from the Hatagawa Fault Zone (HFZ), Fukushima Prefecture. The pseudotachylyte matrix includes amorphous material with irregular shapes and uniform contrast in bright-field images. The appearance of this material in TEM images is distinct from that of amorphous material that occurs as nanoparticles in crush-origin pseudotachylyte from the Iida-Matsukawa Fault (IMF) in Nagano Prefecture. We also performed melting experiments of the host rock of the HFZ and low-speed shear tests of the host rock of the IMF pseudotachylyte, producing amorphous material in each experiment. The two pseudotachylytes have contrasting characteristics in TEM images. The present results suggest that the origins of various amorphous materials in pseudotachylyte can be distinguished based on their appearance in TEM images.View full abstractDownload PDF (2184K) -
Akio Nagatomo, Hidekazu Yoshida2009 Volume 115 Issue 10 Pages 512-527
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSUnderstanding the history of faulting is important in assessing the long-term hydrological, geochemical, and rock-mechanical behavior of a fault and related fracture zones. In particular, the characterization of faults and fracture systems is critical for the safe construction and operation of underground facilities such as structures for the storage of liquefied petroleum gas (LPG), high-level radioactive waste (HLW), and CO2. Here, we studied the Atera Fault, a well-known active fault in central Japan, as an analog to investigate faulting history and fracture systems with infilling minerals. To investigate the structural and mineralogical evolution of the Atera Fault, we carried out detailed mapping of faults and fracture systems in and around the fault, as well as microscopic observations, XRF analysis of fault rocks, and XRD analysis of infilling minerals within fractures. Our analysis of the microtexture and infilling minerals along the fault plane and in adjacent fractures reveals that the Atera Fault records the following three-stage faulting history: Stage I) the formation of cataclasite under relatively high confining pressure; Stage II) the circulation of high-temperature groundwater, resulting in hydrothermal alteration and the growth of infilling minerals within fractures (prehnite, actinolite, sericite, chlorite, and quartz); and Stage III) once the fault had been uplifted to close to the ground surface, the penetration of low-temperature oxidized rainwater to form iron oxyhydroxides in open fractures. Our results suggest that analyses based on faults and fracture systems with infilling minerals are an effective method in assessments of the long-term use of underground storage facilities.View full abstractDownload PDF (1473K) -
Shun Chiyonobu, Hayato Saruwatari, Tokiyuki Sato, Junichi Kabamoto, Ya ...2009 Volume 115 Issue 10 Pages 528-539
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSThe Chinen Formation in southern Okinawa-jima, southwestern Japan, is composed mainly of calcareous sandstone and siltstone, sandy limestone, and detrital limestone that represent the transitional lithofacies between siltstones of the upper Miocene to Pliocene Shimajiri Group and detrital to reefal limestones of the Pleistocene Ryukyu Group. The calcareous nannofossil biostratigraphy of the Chinen Formation and the Ryukyu Group in two drillcores from the Katsuren Peninsula were studied. Abundant specimens of the calcareous nannofossils, Gephyrocapsa caribbeanica and G. oceanica, whose biostratigraphic bases occurred at 1.73 Ma and 1.65 Ma, were recognized in the Chinen Formation and the Ryukyu Group in the two cores. The early Calabrian datum plane, the first occurrence of large specimens of Gephyrocapsa spp. (>6μm; 1.45 Ma), is situated in the Chinen Formation. Biostratigraphic correlation of the Shimajiri and Chinen Formations and the Ryukyu Group, compiled from selected boreholes and surface outcrops, indicates that the Chinen Formation on the Katsuren Peninsula and its environs is correlated with the late Gelasian to early Calabrian between >1.73 Ma and 1.21 Ma and that the deposition of the Ryukyu Group initiated in early Calabrian time between 1.45 Ma and 1.21 Ma.View full abstractDownload PDF (1359K)
Short Articles
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Shohei Tomiyoshi, Akira Takasu2009 Volume 115 Issue 10 Pages 540-543
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSThis is the first report of lawsonite in pelitic schists from the Kebara Formation, a tectonometamorphic unit exposed between the Sambagawa metamorphic belt and the Chichibu belt in western Kii Peninsula. Lawsonite and pumpellyite have previously been reported from basic schists in the Kebara Formation, suggesting high-P/T metamorphic conditions. The pelitic schists consist mainly of quartz, albite and chlorite along with minor carbonaceous matter and rare phengite, lawsonite, calcite and titanite. The mineral assemblage of the lawsonite-bearing pelitic schists is chlorite+phengite +lawsonite+albite+quartz. This assemblage is basically the same as that reported for lawsonite-bearing pelitic schists from the chlorite zone in the Sambagawa metamorphic belt, i.e. in the Ise area in eastern Kii Peninsula and in the Besshi nappe complex exposed along the Asemigawa River in central Shikoku. These various lawsonite-bearing pelitic schists probably experienced similar high-P/T metamorphic conditions suggesting that the entire Kebara Formation experienced similar high-P/T metamorphism to that of the chlorite zone in the Sambagawa belt.View full abstractDownload PDF (876K) -
Akira Furusawa, Chisato Nakamura2009 Volume 115 Issue 10 Pages 544-547
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSIn strongly weathered tephras, it is commonly the case that only quartz and opaque minerals remain unaltered. For example, the K-Tz tephra is distinguished by abundant quartz crystals. The identification of strongly weathered tephras is difficult because major-element analyses of volcanic glass are affected by weathering. Here, we propose a method of identifying weathered tephras based on major-element analyses of pristine glass inclusions preserved in quartz phenocrysts, and apply the method to identifying the K-Tz, Nr-N, and Kt-1 tephras.
We used energy-dispersive X-ray (EDX) techniques to analyze samples of the K-Tz tephra collected from a proximal location (Tanegashima, near Kikai caldera) and from three distal locations. The major-element compositions of glass inclusions are similar in all the K-Tz samples, but are distinct from those of the Nr-N and Kt-1 tephras.
Major-element analysis of quartz-hosted glass inclusions is a promising method in investigations of strongly weathered Quaternary tephras in Japan, such as K-Tz.View full abstractDownload PDF (511K) -
Hokuto Iwatani, Kenyu Murai, Toshiaki Irizuki, Hiroki Hayashi, Yuichir ...2009 Volume 115 Issue 10 Pages 548-551
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSA fossil egg case of Argonauta hians Lightfoot, 1786 was collected from the middle Pliocene Sado-wara Formation of the Miyazaki Group in Shintomi Town, Miyazaki Prefecture, southwest Japan. This is the second report of argonautid fossils from Pliocene formations in Japan and marks the earliest occurrence of living species of Argonautidae in the North Pacific region. Fossil planktonic foraminifers and calcareous nannofossils were examined to establish the biostratigraphy of the fossil-bearing sequence. The horizon yielding the specimen of A. hians corresponds to the planktonic foraminiferal zone N.21 and calcareous nannofossil zone CN12a (ca. 3.25–3.12 Ma).View full abstractDownload PDF (1691K)
Note
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Hiroyoshi Arai, Soichi Omori, Atsushi Miyashita2009 Volume 115 Issue 10 Pages 552-557
Published: 2009
Released on J-STAGE: May 29, 2010
JOURNAL FREE ACCESSGeological information is of little value in the absence of location data regarding the site where the observation was made. Topographic maps have traditionally been used for this purpose; however, this role has now been taken over by GPS receivers. The past decade has seen the development of compact and inexpensive GPS receivers, the so-called GPS loggers, which sequentially record positional data every 1–15 seconds. Such data can be linked with, for example, image files taken by a digital camera, using common time-stamp data. The geographic coordinates (latitude and longitude) of the site where the image was taken are embedded within the image file as metadata (i.e., a geotag). This paper introduces a geotagging system designed for use with a GPS logger and digital camera, and examines the accuracy and precision of positioning by GPS logger, as well as its application in geological surveys.View full abstractDownload PDF (872K)
Erratum
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Yoshihiro Kakizaki, Akihiro Kano2009 Volume 115 Issue 10 Pages 558
Published: October 15, 2009
Released on J-STAGE: November 27, 2013
JOURNAL FREE ACCESS
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