Meeting room "Glova", 4 floor, Integrated Research Building
Abstract
Mg3Cr2Si3O12 knorringite garnet, the Cr end members of the pyrope garnet series, is an important component of garnet solid solutions in deep upper mantle (Irifune, 1982). However, previous studies on the stability field are still ambiguous. So, further investigations are needed to understand the extent of synthesis of knorringite and/or majorite substitution in knorringite as a function of pressure and temperature. In this study, phase stability, pressure and/or temperature dependence of majorite substitution in knorringite have been re-evaluated at pressures of 8-16 GPa and temperatures from 1200 °C to 1800 °C using a Kawai-type multi-anvil apparatus. To understand the stability field and pressure dependence of majorite substitution in knorringite, phase identification, lattice parameters and chemical compositions analysis were made using Micro-focus XRD, Raman spectroscopy and SEM. We found that no pure knorringite garnet was observed at P-T conditions up to 16 GPa and 1800 oC, suggesting that pure knorringite may not be stable. And knorringite is susceptible to majorite substitution at pressures above ~9 GPa, which is similar to that observed for pyrope at lower pressures (Ringwood 1967; Liu 1977). This behaviour of knorringite in this study is different from earlier results reported by Ringwood (1977), Irifune (1982) and Klemme (2004) etc. We also found that with increasing pressures from 9 GPa to 16GPa at 1600 °C, the contents of Cr2O3 in garnet and eskolaite decreased.
For inquiry：Taku Tsuchiya TEL:（089）927-8198
E-mail takut@sci.ehime-u.ac.jp
