The search for ultrahigh-pressure metamorphic bodies and analysis of their structures in the Himalayas and the Japanese islands

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<Study of the Himalayan metamorphic belt>The geological survey and petrological study of the western part of the Himalayas reveals the tectonic setup of the Himalayan metamorphic belt (HMB). The ultrahigh-pressure metamorphic unit (including coesite-bearing rocks) is overlain and underlain by metamorphic units of common pressure-temperature conditions. Microscopic petrographical observations with "In-focus image integration system", which was equipped by this grant in 2004 and used for all microscopic observations in this study, reveal unusual occurrence of zircon in ultrahigh-pressure eclogite. The geochemical and geochronological studies of eclogites (under the Visiting Research Program of the Institute for Study of the Earth's Interior, Okayama University at Misasa) suggest that the origin of eclogites can be correlated with three generations of basaltic volcanic activity (zircon U-Pb ages of c. 267 Ma, c. 180.2 Ma and c. 114 Ma).<Study of the Luobusa ophiolite>The major part of the … More Luobusa ophiolite in the southern Tibet (north of the Himalayas) is mantle peridotite which includes ultrahigh-pressure indicating minerals such as diamond. The existing geological data combined with microscopic petrographical Dbservations reveal that the Luobusa ophiolite as a whole forms overturned imbricate structure.<Study of the Horoman peridotite body>The Horoman peridotite body in the southern part of central Hokkaido has been considered to be separated from the mantle during the formation of the Hidaka collision belt. Presence of high-pressure and high-temperature metamorphic rocks is expected in the vicinity of the peridotite body. Geological survey was carried out in and around the peridotite body. In the northeast, south and east sides of the peridotite body, the boundaries between peridotites and gneisses were located and deformation structures along the boundaries were analyzed. The boundaries between peridotites and sedimentary rocks were found at two locations in the western side of the peridotite body and deformation structures along the boundaries were analyzed. The results combined with microtectonic analysis of oriented samples suggest that the Horoman peridotite body thrust over the sedimentary rocks from the east to the west. Less