The 15th Global-COE International Frontier Seminar
January 14th, 2010, from 17:00, at the room#486 meeting room 4F

Let’s creep! – Part II
Prof. Yanbin Wang
Center for Advanced Radiation Sources, The University of Chicago
I would like to continue with the theme I discussed in Nov 2008, during my last visit to GRC, and reportprogress on investigations on high pressure rheological properties of mantle minerals conducted atGSECARS, using both the D-DIA and the high-pressure x-ray tomography microscope (HPXTM). I will
use four examples to demonstrate the importance of continuing developments addressing four criticalaspects of rheological studies. (1) In the study of polycrystalline “rocks” of olivine, I will show theimportance of using monochromatic diffraction and elasto-plastic self-consistent (EPSC) modeling to
examine changes in deformation mechanisms at various experimental conditions. One of the major issues
in diffraction-based rheology studies is how to link stresses derived from lattice planes to the macroscopic
stress in the bulk sample. EPSC modeling, based on the assumption that crystals deform by dislocation
glide only and with small total strain, provides great insights into deformation mechanisms, but cannot
provide a satisfactory solution to the stress issue. (2) Quasi-Laue diffraction on deformed single-crystals is
being developed to determine uniquely the full stress tensor. This is a new development and I will show ourpreliminary results on garnets. Single crystal creep studies at ambient pressure have been a critical part ofrheolgoical studies, the quasi-Laue technique has the potential to provide single-crystal deformation
information at high pressures. (3) Since the mantle is made of multiple phases, it is important to understandrheological behavior of individual phases in a deforming composite. I will show some preliminary results
on an analog lower mantle composite, which is produced by experimentally breaking down CaMgGeO4 (inolivine structure) into CaGeO3 perovskite and MgO. By comparing the behaviors of the two phases in thecomposite with those in single-phase samples (pure CaGeO3 perovskite and pure MgO), some physicalinsights can be gained as to how the composite should behave under modest axial strains (up to about 20 –30% in the D-DIA). (4) Large-strain deformation in composite is the norm in considering mantle rheology,
but quantitative studies in this area have been virtually non-existent. I will show some results on analog
materials obtained in the HPXTM, which provides an unique opportunity to directly view textural evolution
during large-strain deformation. From these observations, some important conclusions, although qualitative,
can be drawn regardinh composite rheological behavior and anisotropy due to the development of shapepreferred orientation. Finally, I will discuss the development of a large D-DIA, namely DDIA-30. A similar
instrument (MADONNA) is already operating at GRC. Many of the exciting developments for
MADONNA can be directly applied to DDIA-30, which is operated at an insertion-device beamline. With
this new instrumentation and collaboration with GRC colleagues, more significant progresses are expectedin the near future.

14 January 2010 17:00-18:00
Room486, meeting room 4F
Sogo-Kenkyu-to Bldg 1
Ehime University

Contact: T. Irifune
irifune@dpc.ehime-u.ac.jp
http://www.ehime-u.ac.jp/~grc