日時 ： ２００９年１１月２７日（金）※16：30～
場所 ： 愛媛大学総合研究棟Ⅰ 4F 共通会議室（理学部構内）
要 旨
Garnet is a key mineral to understand the geodynamics processes that occur across the mantle's transition zone. Because of its complex nature and as its composition might significantly vary in the mantle, it is difficult to fully understand the behavior of garnet as a function of pressure, temperature and chemical composition. Therefore several experimentalists investigated the HP-HT phase relations of garnet end-members. Unlike Mg- and Fe-rich garnets, the HP-HT behavior of Ca-rich garnets is still poorly constrained. To clarify the situation, we examinated the phase tranformations of Ca3Al2Si3O12 grossular garnet using Kawai-type multi-anvil apparatus coupled with in situ X-ray diffraction (XRD) at the synchrotron radiation facility SPring-8. Recovered samples were analyzed by a combination of micro-focused x-ray diffraction (μ-XRD) and transmission electron microscopy (TEM). Our results show a serie of transformations in the range of 15-25 GPa and 1200-2000 K that displayed some new insights: An orthorhombic Al-bearing CaSiO3 perovskite with a Ca3Al2Si3O12 bulk composition stable at HP-HT; A new high temperature phase assemblage of CaAl4Si2O11 CAS phase + two distinct populations of Al-bearing CaSiO3 perovskites (1.7 at% and 4.5 at% of Al). Chemical composition and structural properties of grossular garnet and its post-garnet phases are discussed in term of Ca- and Al-content and possible implications for the structure of the Earth's mantle transition zone.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
