The last lecture by the author was held at lecture room B202 of School of Science, Shizuoka University in the afternoon of 29th February 2008. The lecture consists of two parts, activities of Shizuoka University in Plate Tectonics revolution and understandings of Tokai Earthquake on Plate Tectonics.
Institute of Geosciences, Shizuoka University was the first institution in Japan with the course of Marine Geology, in which Plate Tectonics was nurtured. The institute has acted as a center in the Plate Tectonics revolution of Japan and world for the last 30 years. Especially, the institute was a key in the 1980s international project in the earth science, Dynamics and Evolution of Lithosphere Project, for the task group of collision in the South Fossa Magna, and working group on scientific drilling, and also submersible studies. The geologic and paleomagnetic studies verified the relation between collisional process in the South Fossa Magna and Plate Tectonics.
Tokai Earthquake is an earthquake expected along the subducting boundary of the Philippine Sea Plate. The subduction and collision of the Philippine Sea Plate observed with submersible “Shinkai 2000” at off-Matsuzaki along the Suruga Trough. The Suruga Trough connects at the south end to the Nankai Trough with reentering angle. The descending slab along the Plate boundary with reentering angle should be ruptured with breakage along the backside. The backside breakage appears as Zenisu, and the ruptures of descending slab are recognized as the discontinuities in the contours of hypocenter depth for the earthquakes along the Suruga Trough and Nankai Trough. Because the ruptures in the slab are correlated well with large scale topography, the large scale topography such as Ise Bay, Kii Peninsula, Shikoku Island and Kyushu Island, should be related to the descending slabs. One of the ruptures under the Ise Bay fits with the estimated rupture from Zenisu of the backside breakage. The depths of ruptured slabs represent descending of west slab under east slab. The overlapping of the slabs with descending should induce upward propagation of the top end of the rupture.
The collinding volcanics at off-Matsuzaki along the Suruga Trough axis is covered with shallow marine sandstone, which deposited also under the geologic situation of backside breakage as Zenisu. The rupture estimated from off-Matsuzaki backside breakage fits to the synclinal axis of descending slab. The synclinal form also represents overlapping with descending of west slab, and the rupture crossed the axis of the Izu Arc along the Kannawa Fault by the upward propagation which occurred as step out of the subduction plate boundary.
The slabs are related directly with the collisional process, and important for the forecasting of the Tokai Earthquake.
MAT-251 mass-spectrometer installed at Shizuoka University, donated by the Thermo-Quest Co. Ltd., was renovated for precise carbon and oxygen isotopic measurement of very small amount of carbon dioxide. We examined the fundamental properties of mass-spectrometer, such as isotopic shift of reservoir CO2 during capillary leak separation, pressure effect on isotopic ratio and the correction of data with international standard material. We obtained consistent results that match the precision and accuracy with that of MAT-250 at the same laboratory. An online carbonate extraction apparatus was installed to the Inlet system for carbonate minerals including dolomite, calcite and aragonite using oil bath circulation heating system, which can attain temperatures up to 100°C. We describe the operation manual for precise measurement of small amount of carbon dioxide, derived from carbonate minerals reacted with conc. phosphoric acid and organic materials or graphite combusted in quartz tube.
Synthetic quartz aggregates as a starting material for high-temperature / high-pressure deformation experiments were prepared using a high-temperature / high-pressure apparatus. Silica gel was prepared using a sol-gel method and subsequently dried and heated in air for three days at temperatures between 700 and 1000°C Various sets of the gels were then packed into Pt-Ni capsules with 0–2 wt% water and were sintered to form quartz aggregates at 800°C and 1 GPa for 5 hours. As a result, synthetic quartz aggregates with polygonal textures and very weak crystallographic preferred orientations were formed from a 1:4 mixture of two silica gels dried at 700°C and 1000°C, respectively.
An original computer software EATPAN was developed as a utility program for SEM-EBSD analysis of crystal orientation. It transforms original Euler-angle data into trends and plunges of crystal axes to depict crystal orientations as a more intuitive color map than have hitherto been available. It was designed for crystallographic studies of molluscan shell in which c-axes of aragonite crystals are preferably oriented. Hue and brightness of a color map displayed on the EATPAN interface represents trends of a-axes and plunges of c-axes, respectively.
Molluscan shell remains off Tokai region, Pacific coast of central Japan, are studied by using grab-samples collected from total 262 sites during the GH97 cruise (29th April to 20th May, 1997) and GA97 cruises (30th July to 17th August, 1997) organized by Geological Survey of Japan. Tokai region is one of the most tectonically active area, due to the collision
of the Izu-Bonin volcanic arc as well as the subduction of Philippine Sea Plate beneath the Honshu arc, and provides various submarine topography and sedimentary settings. The sampling points are located with 4.4 km intervals, covering throughout the area off Tokai region (Sagami Bay, the Izu-Shichito Islands, Suruga Bay, the Sea of Enshu and Enshu Trough), and range from 30 m to 3,455 m in bathymetrical depth. As a result, the total of 682 species (255 bivalves, 18 scaphopods, 402 gastropods, 7 polyplacophorans) were identified at generic or species level. This study makes clear species composition of molluscan thanatocoenosis at each sampling location, and provides systematic list of molluscs. These basic data make a contribution into reconstruction of sedimentary environment from fossil molluscan assemblages.