Annual report for research on long-term stability of geological environment in FY2006

Nohara, Tsuyoshi; Umeda, Koji; Sasao, Eiji; Hanamuro, Takahiro; Saito, Tatsuo; Yasue, Kenichi; Niwa, Masakazu; Mashima, Hidehisa*; Shimada, Koji; Yamada, Kunimi; et al.

JAEA-Research 2008-062, 61 Pages, 2008/07

JAEA-Research-2008-062.pdf:39.02MB

The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. During fiscal year 2006, we carried out the following researches, to confirm existence of the phenomena that have influences on geological disposal system, and to develop the research techniques to reconstruct the history of these phenomena. For studies of active faulting and seismic activity, we reviewed the existing techniques to research past activities and distribution of active faults (migration, extension, development process of a deformation zone). For volcanological and geothermal studies, we extracted a technique for detecting crustal magma and/or geothermal fluid in deep underground using geophysical and geochemical data, and models assessing the likelihood of future volcanism and its influence on geological environment. For studies of uplift/denudation and climatic/sea-level change, we constructed conceptual models such as landform development model.

Genesis of high magnesium andesites from Nagasaki, Northwest Kyushu, Southwest Japan

Mashima, Hidehisa; Tajima, Toshihiko*

no journal, , 

High magnesium andesites (HMAs) with island arc geochemical signatures are distributed in Nagasaki, Northwest Kyushu, Southwest Japan. The genesis of the Nagasaki HMAs cannot be explained by current flux melting models for HMA magmas since mantle xenoliths from NW Kyushu suggests that the NW Kyushu mantle is anhydrous. Normative Jd+CaTs-Ol-Qz compositions of the HMAs suggest that they were separated from their source mantle at 0.5 GPa. This abnormally low pressure partial melting would have been caused by the large contrast of lithospheric strength between the land area composed of the Nagasaki metamorphic rocks and the sea area where sedimentary basins have been formed. The large contrast of lithospheric strength would have concentrated mantle upwelling at the boundary between the land and the sea areas. In the genesis of the Nagasaki HMA magmas, the subduction of the Philippine Sea plate would habe played not as the source of hydrous components but as the driving force of strike-slip tectonics in NW Kyushu.