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| index | Vol. 49 | 1 | 2/3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | Japanese Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Nanometer-scale structures in a Mn-Mg-Fe Amphibole from Vittinki Group, Western Finland
Franco Mancini(Mineral and Fuel Resources Department, GSJ), Katsumi Marumo(Mineral and Fuel Resources Department, GSJ), Reijo Alviola(Geological Survey of Finland), Norihiko Kohyama(National Institute of Industrial Health), Brian Marshall(Department of Applied Geology, University of Technology, Sydney)
1998
vol. 49 (11) P. 551-569
14 figs., 4 tables
Keywords: Precambrian, Finland, metamorphism, manganese, minerals, chain silicates, transmission electron microscope, twinning
Abstract: Samples of Mn-Mg-Fe amphibole from regionally metamorphosed (T=650-700Ž, P=4-6 kbars) quartz-Mn-Mg-Fe amphibole veins intercalated with Mn-rich gneiss in the Vittinki Group, western Finland, have been studied by analytical transmission electron microscopy (ATEM). The results show that the Mn-Mg-Fe amphibole is exsolved on a submicroscopic scale and contains abundant lamellae of Mn-rich actinolitic amphibole, consistent with unmixing from an homogeneous amphibole upon cooling. The lamellae are coherently intergrown with the host and occur in two orientations, nearly parallel to (101) and (100) planes of the host, consistent with previously reported lamellar orientation for monoclinic amphiboles. Their exact orientation varies 11‹for theg100hset and 6‹for theg101hset, indicating exsolution over a large temperature range. Furthermore, theg100hlamellae have widths between 70 and 150 nm, whereas theg101hlamellae show a larger range, 150-700 nm, which do not correlate with the orientation and that presumably reflect local variations in the diffusivity of chemical elements.
@High resolution TEM images of the Mn-Mg-Fe amphibole show rareefaultsfwhich consist of triple-chain lamellae (5-10 nm, at most, in the b-direction), in a predominantly ordered double-chain host. In contrast, many Mn-Mg-Fe amphibole grains show topotactic replacement to talc as is evidenced by chemical compositions intermediate between amphibole and talc.
Seismic profiling of deep geological structure in the Osaka Bay area
Takanobu YOKOKURA(Geophysics Department, GSJ), Naomi KANO(Geophysics Department, GSJ), Kazuo YAMAGUCHI(Geophysics Department, GSJ), Teruki MIYAZAKI(Research Planning Office, GSJ), Takeshi IKAWA(R&D Department, JAPEX Geoscience Institute Inc.), Yohichi OHTA(R&D Department, JAPEX Geoscience Institute Inc.), Taku KAWANAKA(R&D Department, JAPEX Geoscience Institute Inc.) and Susumu ABE(R&D Department, JAPEX Geoscience Institute Inc.)
1998
vol. 49 (11) P. 571-590
10 figs., 1 table
Keywords: 1995 Hyogo-ken Nanbu Earthquake, seismic reflection method, Osaka Bay, active fault, Osaka-wan Fault, Osaka Group, Median Tectonic Line, deep structure, basement, airgun, streamer cable
Abstract: On January 17, 1995 the Kinki district, southwest Japan, was struck by a disastrous earthquake of magnitude 7.2, named as the 1995 Hyogo-ken Nanbu Earthquake. Around the epicentral region, no large earthquake had occurred since 1596 earthquake of magnitude 7.5. Geologically, however, it is well known that many active or inactive faults are densely distributed around this region. The basement structure in this region shows the following zonal arrangement from north to south: the Tanba zone (Paleozoic-Mesozoic sedimentary rocks), the Ryoke zone (Cretaceous gneissose granitic rocks), the Izumi zone (upper Cretaceous sedimentary rocks), the Median Tectonic Line, and the Sanbagawa zone (Jurassic-Cretaceous crystalline schists). The zonal arrangement was severely disturbed by late Cretaceous acidic volcanic activities, later granitic intrusions, and neotectonic activities. Such activities produced the complex geological setting: Rokko Mountains and Awaji Island have been uplifting and Osaka Bay has been subsiding. The uplifting areas mainly consist of late Cretaceous granitic rocks. Cretaceous acidic pyroclastic rocks are distributed in the mountainous region to the north of Rokko Mountains. These basement rocks are partly covered by the Kobe Group (Paleogene sediments) and the Iwaya Formation (early Miocene-middle Miocene sediments). The Osaka Group (Pliocene-Pleistocene soft sediments) is thickly distributed in the Osaka Bay and adjacent areas.
@In order to clarify deep structures of this geologically complex region, we conducted seismic surveys along 12 survey lines on land, in shallow water, and at sea which are about 260km long in total. In this paper we discuss the results of six survey lines located in the Osaka Bay area. Sources used were two airguns of about totally 700in3 (about 11l, or 1.1~10-2m3) at the pressure of 1800psi (about 120atm, or 1.2~107Pa). Receivers were 48-channel streamer cables of 12.5m interval. Sources were shot at standard intervals of 25m. Common-mid points were set at 12.5m intervals. The standard CMP fold number was 24. This region is one of the largest economical centers in Japan, and therefore many types of ships and boats are sailing densely. We had to use short streamer cables, which mean small number of channels or CMP folds. The lack of CMP folds sometimes cannot suppress many types of multiples in a seismic section.
@After overcoming many types of difficulties and applying many noise-suppression methods, we could get relatively clear images. The processing results indicate: 1) The basement depth of the Osaka Bay is deeper than 3000m at the eastern side of the Osaka-wan Fault. 2) The eastern part of the basement is monoclinically declined to the northwest. 3) There are a few inactive faults in the eastern part of the Osaka Bay, while there are many reverse faults in the western part. 4) Almost all of these faults in the western part extend to near surface or are accompanied by flexures in the Osaka Group and overlying layers, and they are considered to be active faults. 5)The Osaka-wan Fault extends to the northeast, and branches off in three directions. One of them is the Wada-misaki Fault, which may extend to the Kobe city area, and others to the north of the Rokko Island. 6) The Osaka-wan Fault produces a large vertical displacement in the basement which is more than 1000m at the midst of the Osaka Bay. 7) The vertical component of its average slip rate is about 0.5-0.6m/ky and is nearly constant since 1Ma. 8) The total length of the Osaka-wan Fault may reach to 40km. 9) The extension of the Suma Fault has been found at the mouth of Akashi Strait. 10) The extension of the Kariya Fault and two other new reverse faults have been found between Awaji Island and the Osaka-wan Fault. The two new faults make a depression zone along the Awaji Island. 11) As the regional stress in this area is of E-W compression, these faults may have large strike-slip components which cannot be estimated from seismic sections only. Particularly the Osaka-wan Fault may have the degree A of fault activity in consideration to its strike-slip component. 12) There are many faults off the east coast of the central Awaji Island. Their continuities are not known. 13) There is a small sedimentary basin surrounded by faults to the east of Tsuna-cho. 14)The basement rock around the southern coast of the Osaka Bay may be different from the granites in the northern part. 15)The Median Tectonic Line (MTL) has been clearly imaged in the south of Kitan Strait. 16) A synclinal structure of the Izumi Group has also been imaged in the north of the MTL. 17) There is no notable active fault in the south of the MTL.
Utilization of Geological Map of Japan 1:1,000,000 3rd Edition CD-ROM version with scientific visualization software -customization of IRIS Explorer modules for importing geological data and topographical data
Naoto Takeno(Geothermal Resources Department, GSJ)
1998
vol. 49 (11) P. 591-597
2 figs.
Keywords: scientific visualization, geological map, digital map, software
Abstract: SoftwaregReadGSJmap100Chwas written for reading geology data and fault data in Mesh map database of Geological Map of Japan 1:1,000,000 3rd Edition, CD-ROM Version (Geological Survey of Japan, 1995). With this software, we can draw three dimensional geological map, using commercial scientific visualization software IRIS Explorer. As topographical data, mesh data (elevation) CD-ROM version (Geographical Survey Institute, 1997a,b) were used,and a softwaregReadGSImeshChwas also written for reading these topographical CD-ROM data. Using the graphical user interface, these softwares work as modules in cooperation with bundled modules of IRIS Explorer, and enable us not only to present three dimensional image of topography and geology, but also to overlay the other earth science data on them. Softwares coded in this study are available from anonymous ftp site (URL=ftp://www.gsj.go.jp/ftp/g0442) of Geological Survey of Japan.
Data processing of X-ray CT scan image (1) -Prepare processing and 3D view
Xinglin LEI(Earthquake Research Department, GSJ)
1998
vol. 49 (11) P. 599-603
6 figs., 1 table
Keywords: X-ray CT, Tiff, Level correction
