Dr. Wei Du [Peking University, China]

Title: Excess volume, microstrain, and stability ofpyrope-grossular garnets

Time: 10:30-11:30AM, Monday December 26, 2016

Place: Conference Room C206, HPSTAR (Beijing)

Host: Dr. Jiuhua Chen

Abstract

Garnet is a major phase in Earth mantle modelssuch as pyrolite and piclogite (Irifune and Ringwood 1987, 1993) and garnetvolume fraction may increase to more than 40% in the Earth’s transition zone(410-660km) (Duffy and Anderson 1989). They are stable over a wide pressure andtemperature range and compatible with phases such as mica, pyroxene, andolivine, making them important candidates for geothermal barometers andthermometers. Knowledge of the effect of compositional change on the physicalproperties of garnet is essential for the correct interpretation of regionallateral variations in seismic velocity imaged by seismic tomography andgeodynamic studies of the continental lithosphere in terms of thermal andchemical properties. The garnet binary pyrope-grossular (Mg3Al2Si3O12-Ca3Al2Si3O12)provides an excellent solid-solution system for the study of non-ideal mixingbehavior, because of the large size difference between divalent Mg2+and Ca2+ (0.89 vs 1.12 in 8 coordination) (Shannon 1976). To clarify the disagreements amongthe literature studies and to further constrain the mixing properties of  pyrope-grossular garnet solutions, I haveperformed experimental studies on synthesized garnet solid solution by usingmulti-anvil device, comprehensive X-ray diffraction powered with synchrotronlight sources. Our new results show that the nonlinear compositional dependenceof thermo-compression may be related to the elastic structural strain caused bysubstitution of Mg and Ca. And the exsolution of pyrope-grossular garnet athigh pressure is confirmed by laboratory observation for the first time. I willdiscuss the details about the non-linear composition dependence of mixingproperties along pyrope-grossular garnet and their application.

Biography of the Speaker:

Wei Du performs experimental studies onminerals, rock samples, and meteorites by using multi anvil device and diamondanvil cell. She is interested in the mineral structures, mixing properties ofsolid solutions, element partitioning between solid phase and silicate liquidduring partial melting of rock samples from the Earth’s mantle, and planetaryformation and differentiation based on melting of meteorite samples at highpressure and high temperature.

Wei Du is a research fellow at School ofEarth and Space Sciences of Peking University. She comes back to PKU afterworking as a research scientist in Earth-Life Science Institute at TokyoInstitute of Technology, Ehime University Satellite in Japan. She receiveddegrees from Columbia University in the City of New York (Ph.D 2011, M.A. 2008)and Peking University (S.B.  2002, M.S.2005).