TY  - JOUR
A1  - Nishihara, Yu
A1  - Ohuchi, Tomohiro
A1  - Kawazoe, Takaaki
A1  - Spengler, Dirk
A1  - Tasaka, Miki
A1  - Kikegawa, Takumi
A1  - Suzuki, Akio
A1  - Ohtani, Eiji
T1  - Rheology of fine-grained forsterite aggregate at deep upper mantle conditions
JF  - Journal of geophysical research : Solid earth
KW  - high-pressure
KW  - olivine
KW  - rheology
KW  - upper mantle
Y1  - 2014
U6  - https://doi.org/10.1002/2013JB010473
SN  - 2169-9313
SN  - 2169-9356
VL  - 119
IS  - 1
SP  - 253
EP  - 273
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Ohuchi, Tomohiro
A1  - Nishihara, Yu
A1  - Kawazoe, Takaaki
A1  - Spengler, Dirk
A1  - Shiraishi, Rei
A1  - Suzuki, Akio
A1  - Kikegawa, Takumi
A1  - Ohtani, Eiji
T1  - Superplasticity in hydrous melt-bearing dunite Implications for shear localization in Earth's upper mantle
JF  - Earth & planetary science letters
N2  - Deformation experiments on hydrous melt-bearing dunite (olivine+4 vol% orthopyroxene+4 vol% clinopyroxene with less than 2.5 vol% of the melt phase) were conducted at pressures of 1.3-5.7 GPa and temperatures of 1270-1490 K in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth's upper mantle. The strain rate was proportional to steady-state creep strength to the 2.1 power, and the creep strength markedly increased with increase in grain size. Developments of the crystallographic preferred orientation of olivine and flattening of olivine grains were hardly observed even after 33-55% shortening of the samples. These observations show that grain boundary sliding (GBS) dominated the deformation of olivine (i.e., superplasticity). The creep strength of hydrous melt-bearing dunite was 2-5 times lower than that of melt-free dunite. The dependence of creep rate on melt fraction is known to be expressed empirically as (epsilon) over dot(phi) = (epsilon) over dot(0) exp(alpha phi), where alpha is a constant and phi is the melt fraction. The experimentally obtained value of alpha was in the range of 150-230, corresponding to 5-7 times the reported values for the olivine-basalt system at 0.3 GPa (i.e., creep strength of dunite was efficiently reduced by the hydrous melt). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions (i.e., peridotite shear zones in the upper mantle). Superplasticity induced by geological fluids would play an important role in the shear localization (and thus initiation of subduction) in the upper mantle.
KW  - olivine
KW  - hydrous melt
KW  - grain boundary sliding
KW  - superplasticity
KW  - shear localization
KW  - subduction
Y1  - 2012
U6  - https://doi.org/10.1016/j.epsl.2012.04.032
SN  - 0012-821X
VL  - 335
IS  - 12
SP  - 59
EP  - 71
PB  - Elsevier
CY  - Amsterdam
ER  -