日時 ： ２００７年３月２日（金）17：00〜
場所 ： 愛媛大学理学部講義棟 １０１室
要 旨
U and Th have been since years subject to many studies about their abundance and distribution in the Earth, because of their special importance as radioactive heat sources. It is believed that almost half of the 44 TW heat flux recorded at the surface of the Earth comes from the radioactive decay of 238U, 235U and 232Th. It is also now quite well accepted that most of the U and Th in the Earth are deeply located in the mantle. During years, geochemistry has largely investigated the partitioning of U and Th in the mantle, however we still have no information about the mineralogical and elastic properties of the host phases of these elements. Our results from solid-solid experiments at HP-HT conditions support a (U,Th)-rich aluminous Ca-perovskite as the only silicate host of U and Th in the lower mantle, with the assumption that the mantle has a pyrolite composition. The existence of this perovskite is not incompatible with Earth's mantle mineral data. Some studies proposed that the major part of the radioactive elements in the Earth could be stored in deep reservoirs of primitive material, in the lowermost part of the lower mantle. The (U,Th)-bearing Ca-perovskite could therefore be the major host of U and Th in the Earth, as a part of this radiogenic reservoir. The mechanism of formation and the structure of the (U,Th)-rich Ca-perovskite are studied and correlated with ab initio calculations. The agreement of these results with recent models of mantle structure is discussed.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
