SIT04-P01

Room:Convention Hall

Time:May 27 18:15-19:30

Iron concentration around dislocation in naturally deformed olivine
YAMAMOTO, Takafumi1∗ ; ANDO, Jun-ichi1 ; TOMIOKA, Naotaka2 ; ITO, Motoo2 ; MORISHITA, Tomoaki3 ;OHFUJI, Hiroaki4
1

Department of Earth and Planetary Systems Science, Hiroshima University, 2 Kochi Institute for Core Sample Research, Japan
Agency for Marine-Earth Science and Technology, 3 UniversitySchool of Natural System, Kanazawa University, 4 Geodynamics
Research Center, Ehime
The concentration of specific atom on dislocation core can be caused by pipe diffusion and Cottrell atmosphere. Both the phenomena are important for the property of materials including rocks and minerals. As an example of the former, Fe concentration
has been reported in the naturally deformed olivine (e.g. Plumper et al., 2011). Pipe diffusion is important for atomic migration
during various reactions in the Earth, such as metasomatism and serpentinization. On the other hand, Kitamura et al. (1986) andAndo et al. (2001) have reported Fe concentration in the mantle-derived olivine caused by Cottrell atmosphere. The Cottrell atmosphere strongly influences plasticity of materials in the low strain rate regime. Therefore, the discovery of Cottrell atmospherefrom the mantle-derived olivine indicates that the effect on the plasticity of olivine is important to understand mantle dynamics
under very low strain rate condition. However, the possibility of pipe diffusion cannnot be neglected completely to explain theobservations of Kitamura et al. (1986) and Ando et al. (2001). Here, we carried out more detailed chemical composition analysisof the mantle-derived olivine to assess whether the Fe concentration on dislocation core is a common phenomenon, and to clarify
the exact mechanism of the Fe concentration, i.e. Cottrell atmosphere or not.
We studied two types of peridotites, which are xenolith-type in basalt (Takashima, Megata, Kurose and Salt Lake) and alpinetype (Uenzaru and Horoman) by using EPMA and ATEM techniques. EPMA and ATEM analyses show Fe concentration at
dislocations in all the studied samples, which suggests that it is a common phenomenon in mantle peridotites. Fe-enrichment
at the rim of olivine grains and other major element concentration on dislocations, which are general features of pipe diffusion,cannot be observed. Therefore, the mechanism of Fe concentration on dislocation core in olivine grains is possibly derived byCottrell atmosphere, not pipe diffusion.
Ando et al. (2001) Nature, 414, 893; Kitamura et al. (1986) Proc. Japan Acad., 62, 149; Plumper et al. (2011), Contributions
to Mineralogy and Petrology, 163, 701.

Keywords: Cottrell atmosphere, olivine, dislocation

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SIT04-P02

Room:Convention Hall

Time:May 27 18:15-19:30

Fabrication of textured Fe-free and Fe-bearing olivine aggregates using colloidal processing under high magnetic field
KOIZUMI, Sanae1∗ ; SUZUKI, Tohru S.2 ; SAKKA, Yoshio2 ; HIRAGA, Takehiko1
1Earthquake Research Institute, University of Tokyo, 2 National Institute for Material Science

Crystallographic preferred orientation (CPO) of minerals is considered to be widely produced in the Earth’s interior. Dueto the presence of anisotropic physical properties such as elasticity, plasticity, electron conductivity and etc... of single crystal
minerals, their bulk rock properties can significantly be affected by the presence of CPO. To measure CPO effect on the bulkrock properties by room experiments, it is required to prepare polycrystalline materials with ideally controlled CPO.
Magnetic field was applied to fine-grained (∼120 nm) equigranular Fe-free and Fe-bearing olivine particles, which were dispersed in ethanol (solvent) with dispersant (polyethyleneimin). We expected the particles to align with respect to magnetic
direction due to their magnetic anisotropy. The aligned particles were gradually deposited on a solid-liquid separation filter
during ethanol drainage. The directions of magnetic field and particle deposition were parallel. The dried particles were thendensified isostatically at 200 MPa for 10 min and sintered using the alumina tube furnace with vacuum pump.
Highly dense (density of ≧ 99%) and fine grained (∼1 µm) samples with a-axis alignment for Fe-free and c-axis alignment
for Fe-bearing olivine to the magnetic direction were obtained. Such synthesized aggregates will allow us to measure CPO effecton the physical properties of olivine aggregate.

Keywords: crystallographic orientation, olivine

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SIT04-P03

Room:Convention Hall

Time:May 27 18:15-19:30

High pressure and high temperature deformation on lawsonite: Implication for low velocity layers in subduction zones
IIZUKA, Riko1∗ ; SOUSTELLE, Vincent2 ; MIYAJIMA, Nobuyoshi3 ; FROST, Daniel3 ; YAGI, Takehiko4
1Geodynamics Research Center, Ehime University, 2 Brown University, USA, 3 Bayerisches Geoinstitut, Bayreuth University,Germany, 4 Geochemical Research Center, The University of Tokyo
Low-velocity layers (LVLs) located in the upper portions of subducting slabs, are regions of lower seismic wave velocities thanthose in the surrounding mantles. LVLs apparently persist to depths of 100-250 km [1,2]. Hydrated mafic rocks provide a plausible explanation for the origin of LVLs and trench-parallel/normal S-wave fast polarization. Lawsonite (CaAl2 Si2 O7 (OH)2 ·H2 O),
which is stable at depths greater than serpentine minerals, is considered to be one of the prime candidate hydrous minerals thatcan be present deep in the cold subduction zones [3,4]. Single crystals of lawsonite have a high elastic anisotropy, suggestingthat the development of the crystallographic preferred orientations (CPOs) when it deformed might strongly affect the seismicproperties [5].
This study reports deformation experiments on lawsonite aggregates that were conducted at high pressure and high temperature corresponding to 150 km depth in the subduction zone, to investigate the development of CPOs and the seismic propertiesof lawsonite. Experiments were performed using a multi-anvil apparatus with six independently acting rams installed at Bayerisches Geoinstitut, Bayreuth University. The starting material consisted of fine-grained (<25 µm) natural lawsonite powder,which was loaded in a Pt capsule and annealed for >20 h at 5 GPa, between 500 and 800 ℃. The samples were then deformed
using pure or simple shear geometry at strain rates of 10−4 -10−6 s−1 and a finite strain of 0.3-1.0. Recovered samples wereanalyzed using a scanning electron microscope (SEM) coupled with an electron backscatter diffraction (EBSD) detector and atransmission electron microscope (TEM).
The deformed lawsonite aggregates display a porphyroclastic texture characterized by a bimodal grain size distribution. The
microstructures with dynamically recrystallized grains imply the evidence for the deformation through grain-boundary sliding
accommodated by diffusion creep due to the grain size reduction, whereas the porphyroclasts (20-50 µm in size) have undulose
extinction, deformation lamellae, irregular grain boundaries, and many sub-grain boundaries. The porphyroclasts also display aCPO characterized by a girdle distribution of the [100] axes in the shear plane with a maximum concentration close to the shear
direction. The [010] axes form a maximum subnormal to the shear plane. The microstructures and the occurrence of a CPO showthat the dominant deformation mechanism for the porphyroclasts is dislocation creep. These results of CPOs diverge from thoseof previous studies of natural lawsonite rocks [e.g., 6], which might result from differences in experimental or natural conditions.
TEM images show a variety of dislocations with a high density of {110} wedge-shaped mechanical twins. Lawsonite seems tohave numerous potential slip systems with [100](010) appearing to be the most dominant. The calculated anisotropies of theseismic wave velocities (AVp = 2% and AVs = 6%, respectively) are characterized by the fast propagation of P-wave is oriented
subnormal to [010] maxima of the deformed lawsonite aggregates and the polarization of the fastest S-wave is perpendicular to
the foliation. This indicates that lawsonite can contribute to the LVL observations and trench-normal S-wave splitting observed
at depth of >150 km in the cold subducting slab of northeastern Japan [7].
[1] Abers and Sarker Geophys. Res. Lett., 23, 1171-1174 (1996)[2] Abers, Earth Planet. Sci. Lett., 176, 323-330 (2000)[3] Schmidt and Poli, Earth Planet. Sci. Lett., 163, 361-379 (1998)[4] Connolly and Kerrick, Earth Planet. Sci. Lett., 204, 61-74 (2002)[5] Chantel et al., Earth Planet. Sci. Lett., 349-350, 116-125 (2012)[6] Kim et al., Phys. Earth Planet. Int., 222, 8-21 (2013)[7] Nakajima et al., Geophys. Res. Lett., 33, L05305 (2006)
Keywords: lawsonite, deformation, crystallographic preferred orientation, high pressure, subduction zone, low velocity layer

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SIT04-P04

Room:Convention Hall

Time:May 27 18:15-19:30

Calibration for stress measurement of Griggs-type high temperature and high pressure
deformation apparatus
KIDO, Masanori1∗ ; MUTO, Jun1 ; NAGAHAMA, Hiroyuki11Department of Earth Sciences, Tohoku University

1. Introduction
It is necessary to perform deformation experiments in appropriate temperature and pressure conditions equivalent to the insideof the earth to characterize rheological properties of rocks. There are several types of deformation apparatus using different
confining media such as gases, liquids or weak solids (e.g., Tullis and Tullis, 1986). Liquid medium apparatus has a disadvantagethat it cannot be used for temperatures above 500 ℃ because of prevention from alteration of oil. Gas medium apparatus has themost accurate stress measurements because of using internal force gauge. However, experiments are typically restricted to confining pressures less than 300 MPa. Solid medium apparatus can provide us high pressure (˜2.0 GPa) easily and safely. However,its stress measurements accuracy is low mainly because of frictions between the confining media and samples or loading piston(e.g., Tullis and Tullis, 1986).
Recently, comparison of stress measurements of Griggs-type apparatus with solid salt assemblies (SSA) and gas apparatus provide a calibration law for Griggs apparatus with SSA (Holyoke and Kronenberg, 2010). This calibration law allowed steady-state
stresses to be measured accurately to within ±30 MPa. However, it was not able to reproduce elastic, transient and post-yield
behaviors because the calibration law was obtained from the comparison of stresses measured only at 5% strain. Moreover,since the calibration was carried out in low confining pressure, influence of confining pressure to stress measurements of Griggs
apparatus is not clear. Calibration law for Griggs apparatus in various deformation conditions are required for revealing detailed
rheological properties of the lower crust and upper most mantle rocks. In this study, we derived a calibration law for stressmeasurements of Griggs apparatus by the master curve method.
2. Axial compression experiments and construction of master curves
Axial compression experiments were performed on high-purity metals (nickels and molybdenums) using a Griggs apparatus
with SSA. Experiments were performed in several conditions (confining pressures: ˜300 MPa, ˜1200 MPa, ˜1500 MPa, temperatures: 600 ℃, 700 ℃, 800 ℃, strain rates: 2×10−4 /s, 2×10−5 /s, 2×10−6 /s). Measured stresses were consistent withresults of the former study (Holyoke and Kronenberg, 2010) within ±30 MPa under the identical confining pressure of ˜300
MPa. Measured stresses tended to become higher with confining pressures. Logarithms of steady-state stresses almost linearly
increase with confining pressures in the range of this study. Obtained mechanical data were analyzed based on high temperature
viscoelastic constitutive law proposed by Shimamoto (1987). Then, a master curve which normalized temperatures strains andconfining pressures was constructed. A master curve from mechanical data (Holyoke and Kronenberg, 2010) using gas apparatus
was also constructed.
3. Derivation and application of a calibration law
Master curves were constructed from identical materials between Griggs and gas apparatuses under normalized temperatures,strains, and confining pressures. Therefore, it is considered that differences between both master curves are derived from distinction of various rheology components of two apparatuses. A calibration law for Griggs apparatus was derived from differences inboth master curves. Applying the calibration law to stress measurements of metals using Griggs apparatus with SSA, it became
possible to reproduce gas apparatus0s stresses not only at steady-state but also at elastic, transient and post-yield behaviors within
an error of ±30 MPa. Moreover, calibration can be extended to higher confining pressure up to 1500 MPa. When the calibration
law was also applied to the stresses of carbonate rock, although an error was at most ˜70 MPa, elastic to post-yield behaviors
could be reproduced.

Keywords: rheology, rock deformation experiment, solid medium deformation apparatus

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SIT04-P05

Room:Convention HallTime:May 27 18:15-19:30

Weak-beam dark-field TEM characterization of dislocations in wadsleyite deformed insimple shear at 18 GPa and 1800 K
KAWAZOE, Takaaki1∗ ; MIYAJIMA, Nobuyoshi1
1

Bayerisches Geoinstitut, University of Bayreuth

Characterization of dislocations in textured wadsleyite is important in understanding crystallographic preferred orientation(CPO) of wadsleyite and in turn seismic anisotropy at the mantle transition zone. A [001](010)-textured wadsleyite was recently
obtained by deformation experiments on wadsleyite in simple shear at 15-18 GPa and 1770-1870 K with a deformation-DIA
apparatus (Kawazoe et al., 2013; Ohuchi et al., 2014). However, [001] dislocations have been rarely reported in wadsleyite in
the literature (cf. Cordier, 2002). To reconcile the wadsleyite CPO pattern with its slip systems, dislocation microstructuresof the [001](010)-textured wadsleyite have been investigated in weak-beam dark-field imaging in a transmission electron microscope. 1/2<101>partial dislocations on the (010) plane are characterized with [100] dislocations on the (001) plane and1/2<111>dislocations forming {011} slip bands. The former partial dislocations are extended on the (010) stacking fault as a
glide configuration (i.e. Shockley-type stacking faults with 1/2<101>displacement vector). The [001] slip on the (010) plane
occurs by glide of the dissociated dislocations on a sub-oxygen close packing plane, which can play an important role to generate
the crystallographic preferred orientation patterns reported in water-poor deformation conditions (e.g., Kawazoe et al. 2013,
Ohuchi et al. 2014).
Keywords: wadsleyite, crystallographic preferred orientation, dislocation, seismic anisotropy, transmission electron microscopy,
deformation-DIA apparatus

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