Editorial Board (Oct. 2015)
Editor-in-Chief
Yasuo Ogawa, Tokyo Institute of Technology, Japan

Editorial Board
Yosuke Aoki, University of Tokyo, Japan
Stephen Bannister, GNS Science, New Zealand
Benjamin Fong Chao, Academia Sinica, Taiwan
Nobuo Geshi, Geological Survey of Japan, AIST,Japan
Lin-Ni Hau, National Central University, Taiwan
Hauke Hussmann, German Aerospace Center,
Germany
Alexey Kuvshinov, Institute for Geophysics,
Switzerland
Hiroo Kanamori, California Institute ofTechnology, U.S.A.
Kristine M. Larson, University of Colorado, U.S.A.
Takuto Maeda, University of Tokyo, Japan
Koji Matsumoto, National Astronomical
Observatory, Japan
Yasuhiro Nariyuki, University of Toyama, Japan

Nozomu Nishitani, Nagoya University, Japan
Azusa Nishizawa, Japan Coast Guard, Japan
Keiji Ohtsuki, Kobe University, Japan
Taku Ozawa, National Research Institute for Earth
Science and Disaster Prevention, Japan
Takeshi Sakanoi, Tohoku University, Japan
Martha Savage, Victoria University of Wellington,
New Zealand
Shanaka de Silva, Oregon State University, U.S.A.
Hiroshi Takenaka, Okayama University, Japan
Hiroaki Toh, Kyoto University, Japan
Yih-Min Wu, National Taiwan University, Taiwan
Zhongliang Wu, China Earthquake Administration,
China
Toshitsugu Yamazaki, University of Tokyo, Japan
Akimasa Yoshikawa, Kyushu University, Japan

Journal Scope
Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
The journal was launched in 1998 and has since published over 2700 articles. All of them are available forfree on SpringerLink:
http://link.springer.com/journal/40623
More information about the journal, its article collections, and the submission process is available on thejournal homepage:
http://www.earth-planets-space.com/
Submit your next research article to Earth, Planets and Space via:
https://www.editorialmanager.com/epsp
Yours sincerely,
Prof. Yasuo Ogawa
Editor-in-Chief, Earth, Planets and SpaceEarth, Planets and Space
Kawamoto et al. Earth, Planets and Space (2015) 67:46
DOI 10.1186/s40623-015-0209-z

PREFACEOpen AccessSpecial issue ‘Geofluid processes in subduction
zones and mantle dynamics’
Tatsuhiko Kawamoto1*, Junichi Nakajima2, Bruno Reynard3,4 and Hiroaki Toh5
Introduction
Almost all physico-chemical characteristics of earthforming materials are influenced by the presence of
H2O. As N. L. Bowen stated in 1928, H2O plays the roleof Maxwell’s demon - it does just what a petrologist may
wish it to do [p. 282, The evolution of the igneous rocks(Bowen 1928)]. In the following decades, this has been
proven to be the case not only in petrology but in every
field of solid Earth science.
H2O is the most abundant fluid in the Earth, except
for liquid iron alloys present in the outer core. Volcanoes emit magmas and volatiles, which include COH ±S ± N species, halogens (F, Cl, I, Br), rare gases (He, Ne,
Ar, Kr, Xe), fluid-mobile elements such as alkali elements (Li, Na, K, Rb, Cs), B, possibly Pb and U, and lesslikely Th. In the Earth’s interior, these volatile components exist as geofluids, affecting various phenomena
and acting as effective tracers for the respective phenomena. Seawater and atmosphere are geofluids thathave accumulated on the surface of the Earth, and they
hydrate and carbonate lithosphere through chemical reactions and depositions. Geofluids are released from
subducting lithospheres, migrate upward, and play vitalroles in various subduction-zone phenomena, such as
magma genesis (Kawamoto et al. 2012; Kimura andNakajima 2014), seismic activity (Mitsui and Hirahara
2009; Shiina et al. 2013), rock deformation (Katayama
et al. 2004; Hilairet et al. 2007), and electromagnetic response (Yoshino and Katsura 2013). Geofluids also affectmantle dynamics (Korenaga 2013; Reynard 2013), including global material circulation and chemical differentiation(Tatsumi 2005), and the transportation of mainly C-O-H
fluids into the Earth’s interior (Deschamps et al. 2013).
This special issue is a collection of 30 studies on such geofluid processes.

Fluids in the mantle wedge and crust originating fromthe subducting slab

Kusuda et al. (2014) report on the chemical compositionof non-volcanic hot springs in the forearc region of theSouthwest Japan arc. The forearc hot springs have beenstudied by means of aqueous chemistry for over 40 years(Kazahaya et al. 2014). By comparing the analyzed chemical composition of hot water with modeled compositionof dehydrated materials from downgoing oceanic crustal
materials, the authors conclude that the water originatesin the subducting oceanic plate (Matsumoto et al. 2003;
Kawamoto et al. 2013; Kazahaya et al. 2014). Within thesame forearc region in the Kii peninsula, Japan, Katoet al. (2014) report on an intensive non-volcanic seismic
swarm and estimate a fine-scale seismic velocity structure of the region. The results indicate the presence ofgeofluids such as partial melt or water beneath theswarm. Such fluids may potentially be released from thesubducting crust of the Philippine Sea plate.
In the near-trench area in the Northeast Japan arc, Togoet al. (2014) report on the isotopes of hydrogen/deuterium, oxygen, iodine, and chlorine, as well as tritium concentrations of deep groundwater. They propose that theseare derived from subducting sediments. Okamoto et al.
(2014) describe CH4-CO2-H2O fluid inclusions in quartz
veins from the Shimanto belt, a near-trench Tertiary accretionary prism in the Southwest Japan arc. Such fluids
may represent fluids degassed from crystallizing neartrench magmas generated during subduction of hot
oceanic lithosphere.
Mori et al. (2014) evaluate bleaching processes of pelite in serpentine mélanges by studying the chemicalcomposition of a bleached and unaltered sedimentaryrock at the reaction boundary between the surrounding
chlorite schist and metapelite. Regarding reactions thattake place inside subducting slabs, Zheng and Hermann(2014) summarize major and trace element features ofslab-derived fluids based on an analysis of high-pressure
and ultra-high-pressure metamorphic rocks. Koga et al.
(2014) demonstrate that vibrational spectroscopy can be* Correspondence: kawamoto@bep.vgs.kyoto-u.ac.jp1
Institute for Geothermal Sciences, Graduate School of Science, Kyoto
University, Beppu 874-0903, Japan
Full list of author information is available at the end of the article© 2015 Kawamoto et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly credited.

1Geofluid processes in subduction zones and mantle dynamics
Kawamoto et al. Earth, Planets and Space (2015) 67:46

Page 2 of 4

used to determine halogen content in Ti-clinohumite, ahigh-pressure hydrated phase formed from fluids produced by dehydration reactions in ultramafic rocks.
Within the deeper subducting slab, geofluids released
from the slab trigger the melting of the mantle wedge.
Ikemoto and Iwamori (2014) model trace element transport in volcanic rocks and show that disequilibriumtransport through channels likely plays an importantrole in element cycling in subduction zones. Such fluid
transport without further chemical changes is also seenin the hot springs in the forearc region that originatedfrom subducting slabs (Kusuda et al. 2014).
Hydrous melting of the mantle produces hydrous
magmas, leaving behind residual mantle minerals thathave distinct compositions compared to those formed
through anhydrous melting. Matsukage and Kawasaki(2014) compare the chemical composition of cratonic
garnet peridotites and experimental peridotite residue
under various H2O contents from 100- to 200-km depth.
The results suggest heterogeneity of H2O content in theupper mantle during the early history of the Earth andraise the question of how much H2O is present incurrent arc magmas. Hamada et al. (2014) describe differentiation processes of low-K tholeiite basaltic magma
having H2O content of 3 wt.% in a shallow magma
chamber at approximately 4-km depth and propose possible differentiation processes of the magma at deeper
crustal levels. Based on Ca/Na partitioning between
plagioclase and melt, Ushioda et al. (2014) estimate theH2O content in erupted basaltic magmas in the Northeast Japan and Izu arcs. According to their results, thefrontal volcanoes appear to have higher H2O content
than the rear-arc volcanoes.
Rose-Koga et al. (2014) report on the abundance of
H2O, CO2, F, Cl, and S and Pb isotopes in basaltic melt
inclusions in a frontal-arc volcano in the Northeast
Japan arc and discuss temperatures of slab surface andphase relationships of the dehydrating slab materials.
Kawamoto et al. (2014) conducted synchrotron X-ray
fluorescence (XRF) experiments to determine the effectsof salinity and pressure on partitioning of large-ion
lithophile elements such as Pb, Rb, and Sr between silicate melts and aqueous fluids. They propose a process of
separation of Cl-bearing supercritical fluids from theslab and their subsequent incorporation into hydrous
melts and saline fluids to explain the geochemical features of island arc basalts (Kawamoto et al. 2012).

controlling factors of seismogenic properties in suchmegathrusts. Shimizu (2014) proposes a rheological profile across the source area of the 2011 Tohoku earthquake and argues that the large tsunamigenic slip during
the Tohoku earthquake can be explained by a large gradient in fault strength on the up-dip side of the hypocenter.
Based on a long-term multiscale earthquake cycle simulation on a three-dimensional (3D) plate boundary model,
Ariyoshi et al. (2014) suggest that activation and quiescence of shallow, very low-frequency earthquakes following the 2011 Tohoku earthquake are closely associatedwith plate coupling perturbations resulting from the stressshadow effect of the Tohoku earthquake. By modeling theeffect of poroelastic rebound on surface deformation following the 2011 Tohoku earthquake, Hu et al. (2014)
show how the effect is restricted to the vicinity of the rupture area. They also show that the viscosity in the lower
crust beneath the volcanic front is several orders of magnitude lower than the surrounding areas.
Geofluids detected with magnetotelluric and seismic
observations

Kanda and Ogawa (2014) estimate a 3D distribution of
fluids and melts under the Northeast Japan arc using geomagnetic transfer functions. Their results suggest thepresence of a deep crustal conductor that may correspondeither to partial melts and/or high-salinity fluids. Ichihara
et al. (2014) present a 3D electrical resistivity model beneath the focal zone of the 2008 Iwate-Miyagi Nairiku
earthquake that shows a shallow conductive zone beneath
the Kitakami Lowland and several conductive patches beneath active volcanic areas. Yoshida et al. (2014) determined pore fluid pressure distribution in the focal regionof the above earthquake and suggest that geofluids supplied from the mantle wedge have contributed to the generation of high pore pressures and to the lowering offrictional strengths of seismic faults in this region. Ogawa
et al. (2014) conducted a densely distributed magnetotelluric survey around the Naruko Volcano in Northeast
Japan and produced a shallow resistivity model of the
Quaternary volcano. They found a southward-dipping,sub-vertical conductor that may imply the presence ofgeofluids just below the volcano. Okada et al. (2014) foundseismic low-velocity zones beneath the same volcano andin the aftershock region of the 2008 Iwate-Miyagi Nairiku
earthquake, both of which can be attributed to the presence of geofluids. The former, having a diameter of 10 to
20 km, resides in the lower crust. Kosuga (2014) observed
the migration of seismicity for a seismic cluster near theMoriyoshi volcano in the Northeast Japan arc and identifies distinct seismic scatters above low-frequency earthquakes in the lower crust. He argues that the observed
migration is associated with geofluids supplied from theuppermost mantle.

The 2011 Tohoku-oki earthquake: friction, strength, andpost-seismic deformation

Den Hartog et al. (2014) evaluate an experimental physical model of phyllosilicate-rich fault gouges in themegathrust. The results imply that water-assisted thermally activated quartz deformation is one of the major

2Earth, Planets and Space
Kawamoto et al. Earth, Planets and Space (2015) 67:46

Page 3 of 4

Shiina et al. (2014) show that hydrated mineralogy
alone cannot sufficiently explain the low velocities observed in the subducting crust beneath Hokkaido, suggesting that fluids may coexist with hydrated rocks
down to 80-km depth. Nakajima (2014) provides evidence of the presence of high-attenuation areas in a
serpentinized mantle wedge using seismological tomography. These areas are associated with low seismic activity that may be explained by deformation of weak
serpentine. Based on numerical simulation, Kirby et al.
(2014) suggest that the serpentinized mantle was formed
through plate subduction during the Mesozoic andPaleogene that has been sufficiently heated over time, releasing water into the crust over much of the history of
the San Andreas Fault system. Kuwatani et al. (2014) apply
the Markov random field model to the observed seismic
velocity models in the mantle wedge of the Northeast
Japan arc and estimate the porosity and pore shapes ofrocks. There is a significant difference in the calculated
porosity and aspect ratio of geofluids between the forearc
side and the volcanic front.
A frontier letter by Pommier (2014) describes how
electromagnetic and seismic methods can complement
each other in providing information about the storage of
fluids in subduction systems. She implies a possible correlation between electrical conductivity and seismic wave
attenuation anomalies in the mantle wedge. Jung et al.
(2014) studied seismic anisotropy of two fluid-induced
peridotite samples collected from wall rock and mylonite
fabrics and find that seismic anisotropy becomes significantly weaker as the percentage of mylonite increases.
Ishikawa and Matsumoto (2014) measure Vp for quartz
aggregate at PT conditions of the middle crust andquantify the effect of pore fluids on Vp. The results
show that even a small amount of fluids (0.4 to 1.0 wt.%)
reduces Vp by 3% to 4%. Shimojuku et al. (2014) reporton the experimental results of conductivity measurementof saline-fluid-bearing rocks. Their set of data will behighly instrumental in distinguishing between magmas
and saline fluids and also in determining their possible
volumes and geometry based on comparison with the observed conductivity data in subduction zones.

Claude Bernard Lyon 1, 43 Bd du 11 Novembre 1918, F-69622 Villeurbanne,
Cedex, France. 5Data Analysis Center for Geomagnetism and Space
Magnetism, Graduate School of Science, Kyoto University, Kyoto 606-8502,
Japan.
Received: 25 February 2015 Accepted: 25 February 2015

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Kawamoto T, Yoshikawa M, Kumagai Y, Mirabueno MHT, Okuno M, Kobayashi T(2013) Mantle wedge infiltrated with saline fluids from dehydration anddecarbonation of subducting slab. Proc Natl Acad Sci U S A 110:9663–9668
Kawamoto T, Mibe K, Bureau H, Reguer S, Mocuta C, Kubsky S, Thiaudiere D, Ono
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Acknowledgements
We are deeply grateful to the many referees who have given their time andprovided us with valuable suggestions. This special issue on geofluids was
initially conceived by core members including Drs. Toru Matsuzawa, Yasuo
Ogawa, Tetsu Kogiso, Michihiko Nakamura, and Hikaru Iwamori during the2009 to 2014 Geofluids project lead by Dr. Eiichi Takahashi. We appreciate
their efforts. We would also like to express our thanks to our colleagues who
submitted their cutting-edge work to this special issue.
Author details
1
Institute for Geothermal Sciences, Graduate School of Science, Kyoto
University, Beppu 874-0903, Japan. 2Research Center for Prediction ofEarthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku
University, Sendai 980-8578, Japan. 3Ecole Normale Supérieure de Lyon, Site
Monod, 15 parvis René Descartes, BP7000, Lyon F-69342, France. 4Université

3

Geofluid processes in subduction zones and mantle dynamics
Kawamoto et al. Earth, Planets and Space (2015) 67:46

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Korenaga J (2013) Initiation and evolution of plate tectonics on Earth: theories
and observations. Ann Rev Earth Planet Sci 41(1):117–151
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geofluid reservoir. Earth Planets Space 66(1):77
Kusuda C, Iwamori H, Nakamura H, Kazahaya K, Morikawa N (2014) Arima hot
spring waters as a deep-seated brine from subducting slab. Earth Planets
Space 66(1):119
Kuwatani T, Nagata K, Okada M, Toriumi M (2014) Markov random field modelingfor mapping geofluid distributions from seismic velocity structures. Earth
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fluids. Earth Planets Space 66(1):93

4

Earth, Planets and SpaceFRONTIER LETTER

Open Access

Geophysical assessment of migration and storage conditions of fluids
in subduction zones
Anne Pommier
Earth, Planets and Space 2014, 66:38 doi:10.1186/1880-5981-66-38
Received: 3 February 2014, Accepted: 14 May 2014, Published: 23 May 2014

Abstract
By enhancing mass transfer and energy release, the cycle of volatiles and melt is a major component of subduction.
Investigating this fluid cycle is therefore critical to understand the past and current activity of subduction zones. Fluids cansignificantly affect rock electrical conductivity and elastic parameters that are measured using electromagnetic and seismic
methods, respectively. This letter emphasizes how these geophysical methods complement each other to provide information
about the storage of fluids in subduction systems. By compiling electromagnetic and seismic results from various subduction
zones, a possible correlation between electrical conductivity and seismic wave attenuation anomalies in the mantle wedge isobserved, consistent with fluid accumulation. A possible relationship between geophysical properties and the slab age is alsosuggested, whereas no significant trend is observed between electrical conductivity or seismic wave attenuation andestimates of water flux in the mantle wedge. These field-based relationships require further constrains, emphasizing the needfor new measurements in the laboratory.
A)

0
200

40

SERP

0

Depth (km)

50

60

0

AM

CH

L

100

AMPH
CHL

800

PH

AMPH

ponding melt? 1000
hydrous mantle?

SE

1200

RP

5 to
>10
vol.
<
%m
LAW 5 vo
elt
l.%
me
lt

CL

D

CHL

150

SE

RP

200

12

00

10

00

800

Figure 1

Corresponding author: Anne Pommier, apommier@asu.edu

FRONTIER LETTER

Open Access

The roles of quartz and water in controlling unstable slip in
phyllosilicate-rich megathrust fault gouges
Sabine AM den Hartog*, Demian M Saffer and Christopher J Spiers
Earth, Planets and Space 2014, 66:78 doi:10.1186/1880-5981-66-78
Received: 11 February 2014, Accepted: 18 July 2014, Published: 28 July 2014

Abstract

Friction coefficient

A recent microphysical model for the steady-state frictional behaviour of wet illite/quartz gouges in subduction megathrust settings
predicts that velocity-weakening in the seismogenic zone results from a competition between shear-induced dilatation andcompaction involving water-assisted, thermally activated deformation (pressure solution) of quartz clasts. While this model issupported by experimental data, proof that quartz and water are a requirement for velocity-weakening is lacking. Here, we report on
shearing experiments on water-saturated (near-)pure illite and dry 65/35 illite/quartz gouges, deformed at P-T conditions near thosein situ at seismogenic depths along subduction megathrusts. We used low sliding velocities relevant to earthquake nucleation andslow slip events (1 to 100 μm/s). Previous experiments on wet illite/quartz gouges under the same conditions documented three
regimes of slip stability, with velocity-strengthening at 150°C to 250°C and 400°C to 500°C, and velocity-weakening at 250°C to 400°C.
In the present study, wet illite gouge exhibited similar three-regime behaviour, but with
1.0
velocity-neutral rather than velocity-weakening behaviour at the intermediate
0.9
temperatures. Dry illite/quartz gouge exhibited near velocity-neutral behaviour at all
10
100
0.8
temperatures investigated. These results confirm that water-assisted, thermally activated0.7
10
1
quartz deformation is a key process in the velocity-weakening behaviour at intermediate
0.6
10
100
0.5
temperatures in wet illite/quartz gouges and support the existing microphysical model.
10
0.4
The implication of this model is that seismogenesis occurs under conditions where creep
0.3
by thermally activated quartz deformation is fast enough to moderate ‘brittle’ dilatation to
wet ill-qtz, 200°C
0.2
wet ill-qtz, 500°C
remain at subcritical porosity values but too slow to allow ductile shear of clasts.
wet ill, 500°C
0.1

Keywords: Quartz; Water; Pressure solution; Velocity-weakening; Subduction zone
seismicity; Illite friction; Brittle-ductile transition

dry ill-qtz, 500°C

0.0
0

10

20

Displacement (mm)Figure 1*Corresponding author: Sabine AM den Hartog, s.denhartog@psu.edu
5

30

40

50

Geofluid processes in subduction zones and mantle dynamics

FRONTIER LETTER

Open Access

Geochemistry of continental subduction-zone fluids
Yong-Fei Zheng* and Joerg Hermann
Earth, Planets and Space 2014, 66:93 doi:10.1186/1880-5981-66-93
Received: 11 December 2013, Accepted: 29 July 2014, Published: 18 August 2014

Abstract
The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous
silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure(UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily
derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdownof hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous
minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic
rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element
abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus
conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which
exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks andmultiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophileelements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion ofhigh field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating theircrystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts withthe mantle wedge peridotite leads to modal metasomatism with the generation of new mineralphases as well as cryptic metasomatism that is only manifested by the enrichment of fluidmobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic
mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and theiradjacent active continental margins. The study of such metasomatic processes and products isof great importance to understanding of the mass transfer at the slab-mantle interface insubduction channels. Therefore, the property and behavior of subduction-zone fluids are a key
for understanding of the crust-mantle interaction at convergent plate margins.

Keywords: Water; Subduction factory; Metamorphic fluids; Anatectic melts; Major
elements; Trace elements

Figure 1*Corresponding author: Yong-Fei Zheng, yfzheng@ustc.edu.cn

FULL PAPER 

Open Access

Seismic attenuation beneath Kanto, Japan: evidence for highattenuation in the serpentinized subducting mantle
Junichi Nakajima
Earth, Planets and Space 2014, 66:12 doi:10.1186/1880-5981-66-12
Received: 9 December 2013, Accepted: 25 March 2014, Published: 16 April 2014

Abstract

ion

zat

tini

pen

Ser

The three-dimensional (3-D) P-wave attenuation (Qp−1) structure beneath Kanto, Japan, is estimated by using a large number ofwaveform data. Corner frequencies of earthquakes are initially calculated from spectral ratios of S-coda waves, followed by aninversion to simultaneously determine attenuation terms and frequency-dependent site amplification factors. The attenuation
terms are then inverted for estimation of the 3-D Qp−1 structure. The obtained results show that seismic attenuation is highly
heterogeneous, and pronounced high-attenuation areas are located in the continental
139˚
140˚
141˚
142˚
lower crust and mantle of the Philippine Sea slab. Seismic activity is very low in the high37˚(b)attenuation lower crust, which is most likely attributable to ductile deformation facilitated
1921(M7.0)
by fluids supplied from the underlying Philippine Sea slab. The high-attenuation area in
the Philippine Sea slab represents the serpentinized mantle, and two M ~ 7 earthquakes
are documented to have occurred along the western boundary of this area. Interplate
36˚earthquakes on the Pacific slab are absent in areas overlain by the serpentinized Philippine
Sea slab, which is likely due to the low viscosity of serpentine promoting continuous
1987
ductile deformation rather than brittle failures along the plate boundary.
(M6.7)

Keywords: Serpentine; Intermediate-depth earthquakes; Interplate earthquakes; Fluids;

35˚Ductile deformation; Dehydration

Figure 1

34˚

4.00

4.25

Figure 1

Corresponding author: Junichi Nakajima, nakajima@aob.gp.tohoku.ac.jp
6

4.50

4.75

S-wave velocity (km/s)

Earth, Planets and Space

FULL PAPER 

Open AccessPolybaric crystallization differentiation of H2O-saturated island arc low-K
tholeiite magmas: a case study of the Izu-Oshima volcano in the Izu arc
Morihisa Hamada*, Yuko Okayama, Takayuki Kaneko, Atsushi Yasuda and Toshitsugu Fujii
Earth, Planets and Space 2014, 66:15 doi:10.1186/1880-5981-66-15
Received: 24 September 2013, Accepted: 24 March 2014, Published: 22 April 2014

Abstract
Island arc low-K tholeiites are basaltic magmas erupting from frontal arc volcanoes of juvenile arcs associated with thesubduction of old and cold plates. We investigated the origins of geochemical variation in volcanic rocks having multiple
phase saturated liquid compositions from the Izu-Oshima volcano in the northern Izu arc. The geochemical variations in theliquids fall between two endmember trends, namely higher- and lower-Al/Si trends. Polybaric differentiation of H2O-saturated
melts between a 4-km-deep magma chamber and degassed melts near the surface should be responsible for the observed
variation in the liquids.

Keywords: Island arc low-K tholeiite; Volcanic front; Ca-rich plagioclase;

Senzu Group
Older Oshima Group
Yonger Oshima Group

Experimental petrology; Izu-Oshima volcano

FeO*/MgO

5

(b)

4
3
2
1
50

TH
CA

52

54
56
SiO2 (wt %)58

60

Figure 1*Corresponding author: Morihisa Hamada, mhamada@jamstec.go.jp

FULL PAPER 

Open Access

Characterization of olivine fabrics and mylonite in the presence of
fluid and implications for seismic anisotropy and shear localization
Sejin Jung, Haemyeong Jung* and Håkon Austrheim
Earth, Planets and Space 2014, 66:46 doi:10.1186/1880-5981-66-46
Received: 15 November 2013, Accepted: 1 May 2014, Published: 2 June 2014

Abstract
The Lindås Nappe, Bergen Arc, is located in western Norway and displays two high-grade metamorphic structures. A Precambrian
granulite facies foliation is transected by Caledonian fluid-induced eclogite-facies shear zones and pseudotachylytes. To understandhow a superimposed tectonic event may influence olivine fabric and change seismic anisotropy, two lenses of spinel lherzolite werestudied by scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) techniques. The granulite foliation of
the surrounding anorthosite complex is displayed in ultramafic lenses as a modal variation in olivine, pyroxenes, and spinel, and theCaledonian eclogite-facies structure in the surrounding anorthosite gabbro is represented by thin (<1 cm) garnet-bearing
ultramylonite zones. The olivine fabrics in the spinel bearing assemblage were E-type and B-type and a combination of A- and B-typelattice preferred orientations (LPOs). There was a change in olivine fabric from a combination of A- and B-type LPOs in the spinelbearing assemblage to B- and E-type LPOs in the garnet lherzolite mylonite zones. Fourier
(A)
N
(B)
transform infrared (FTIR) spectroscopy analyses reveal that the water content of olivine in
mylonite is much higher (approximately 600 ppm H/Si) than that in spinel lherzoliteLindås(approximately 350 ppm H/Si), indicating that water caused the difference in olivine fabric.
Nappe
Fabric strength of olivine gets weaker as the grain size reduced, and as a result, calculated
Hundskjeften area
seismic properties for the two deformation stages reveal that P- and S-velocity
anisotropies are significantly weaker in the mylonite. Microtextures and LPO data indicate
2 kmthat the deformation mechanism changed from dominant dislocation creep in spinel
Eclogite shear zone
>80% eclogitizedpyroxenite
lherzolite to dislocation creep accompanied by grain-boundary sliding in mylonite. Shear
Eclogite breccia>40% eclogitized
localization in the mylonite appears to be originated from the grain size reduction through
Granulite(1) enhanced dynamic recrystallization of olivine in the presence of water and (2) Zener<40% eclogitizedpinning of clinopyroxene or (3) by ultracomminution during the pseudotachylyte stage.
Holsnøy Island

BergenFigure 1*Corresponding author: Haemyeong Jung, hjung@snu.ac.kr
7

Geofluid processes in subduction zones and mantle dynamics

FULL PAPER 

Open Access

A trial derivation of seismic plate coupling by focusing on the activityof shallow slow earthquakes
Keisuke Ariyoshi*, Toru Matsuzawa, Ryota Hino, Akira Hasegawa, Takane Hori, Ryoko Nakata and Yoshiyuki Kaneda
Earth, Planets and Space 2014, 66:55 doi:10.1186/1880-5981-66-55
Received: 16 January 2014, Accepted: 28 May 2014, Published: 16 June 2014

Abstract
To understand the effect of plate coupling on very low-frequency event (VLFE) activity resulting from megathrustearthquakes, we performed long-term multiscale earthquake cycle simulations (including a megathrust earthquake and slow
earthquakes) on a 3-D subduction plate boundary model, based on a rate- and state-dependent friction law. Our simulationsuggests that quiescence of shallow VLFEs off Miyagi may be explained by the location in the shallow central part of the 2011
Tohoku earthquake because of the locally strong coupling, while observed activation of
VLFEs off Iwate (northern part of Tohoku district), Fukushima (southern part of Tohoku
district), and Ibaraki (northern part of Kanto district) is explained by the location on thepossible activationof VLF events
outer rim. The area and duration of the quiescence off Miyagi may be a new clue toIwate
evaluate the potential for plate coupling strong enough to cause the next megathrustearthquake.
Miyagi
140˚

142˚

144˚

40˚

38˚

dependent friction law; Superhydrostatic pressure38˚

VLF eventquiescence ?
Fukushima
50
40

36˚

VLF events
Ibaraki activated by M9 ?

30
20
10
0

140˚

142˚

Coseismic slip (m)Keywords: Subduction plate boundary; Megathrust earthquake; Rate- and state-

40˚

36˚

144˚

Figure 1*Corresponding author: Keisuke Ariyoshi, ariyoshi@jamstec.go.jp

FULL PAPER 

Open Access

Large-ion lithophile elements delivered by saline fluids to the sub-arc
mantleTatsuhiko Kawamoto*, Kenji Mibe, Hélène Bureau, Solenn Reguer, Cristian Mocuta, Stefan Kubsky,
Dominique Thiaudière, Shigeaki Ono and Tetsu Kogiso
Earth, Planets and Space 2014, 66:61 doi:10.1186/1880-5981-66-61
Received: 19 January 2014, Accepted: 14 June 2014, Published: 27 June 2014

Abstract
Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/or supercritical fluids fromthe subducting slab to the sub-arc mantle. Partitioning of large-ion lithophile elements between aqueous fluids and melts is
crucial as these two liquid phases are present in the sub-arc pressure-temperature conditions. Using a micro-focused
synchrotron X-ray beam, in situ X-ray fluorescence (XRF) spectra were obtained from aqueous fluids and haplogranite or
jadeite melts at 0.3 to 1.3 GPa and 730°C to 830°C under varied concentrations of (Na, K)Cl (0 to 25 wt.%). Partition coefficients
fluid/melt
between the aqueous fluids and melts were calculated for Pb, Rb, and Sr (DPb,
Rb, Sr ). There was a positive correlation between
fluid/melt
fluid/melt
DPb,
Rb, Sr values and pressure, as well as DPb, Rb, Sr values and salinity. As compared to the saline fluids with 25 wt.% (Na, K)Cl, theCl-free aqueous fluids can only dissolve one tenth (Pb, Rb) to one fifth (Sr) of the amount of large-ion lithophile elements
fluid/meltvalues were greater than unity, which iswhen they coexist with the melts. In the systems with 13 to 25 wt.% (Na, K)Cl, DPb,
Rb
indicative of the capacity of such highly saline fluids to effectively transfer Pb and Rb.
Enrichment of large-ion lithophile elements such as Pb and Rb in arc basalts relative
to mid-oceanic ridge basalts (MORB) has been attributed to mantle source
fertilization by aqueous fluids from dehydrating oceanic plates. Such aqueous fluids
are likely to contain Cl, although the amount remains to be quantified.

Keywords: Subduction zone magmatism; Mantle wedge; Water; H2O; Brine; Traceelement; Chlorine

Figure 1*Corresponding author: Tatsuhiko Kawamoto, kawamoto@bep.vgs.kyoto-u.ac.jp
8Earth, Planets and Space

FULL PAPER 

Open AccessA large mantle water source for the northern San Andreas fault
system: a ghost of subduction past
Stephen H Kirby*, Kelin Wang and Thomas M Brocher
Earth, Planets and Space 2014, 66:67 doi:10.1186/1880-5981-66-67
Received: 14 December 2013, Accepted: 20 May 2014, Published: 7 July 2014

Abstract
Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest, USA iscold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to thesouth in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with thecreation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25
Ma by serpentine dehydration into the crust above. This deep, long-term water source could
facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad
region above the wedge. Moreover, the location and breadth of the water release from this model
gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely
plays a role in the occurrence of non-volcanic tremor (NVT) that has been reported along the SAFS
in central California. This process of water release from mantle depths could also mobilize mantle
serpentinite from the wedge above the dehydration front, permitting upward emplacement ofserpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected fromtectonically emplaced serpentinite blocks along the SAFS show mineralogical and structuralevidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also leadto tectonic mobility along other plate boundaries that succeed subduction, such as othercontinental transforms, collision zones, or along present-day subduction zones where spreading
centers are subducting.

Keywords: Serpentinite; Antigorite; Lizardite; Chrysotile; Ophiolite; Mantle water; San

Andreas Fault System; Subduction; California Coast Ranges; Non-volcanic tremor

Figure 1*Corresponding author: Stephen H Kirby, skirby@usgs.gov

FULL PAPER 

Open AccessRheological profile across the NE Japan interplate megathrust in
the source region of the 2011 Mw9.0 Tohoku-oki earthquake
Ichiko Shimizu
Earth, Planets and Space 2014, 66:73 doi:10.1186/1880-5981-66-73
Received: 30 November 2013, Accepted: 25 June 2014, Published: 18 July 2014

Abstract

Jap

an

Tre

nch

TO

HO

KU

A strength profile across the NE Japan interplate megathrust was constructed in the source region of the 2011 Tohoku-oki
earthquake (Mw9.0) using friction, fracturing, and ductile flow data of the oceanic crustal materials obtained from laboratory
experiments. The depth-dependent changes in pressure, temperature, and pore fluid pressure were incorporated into amodel. The large tsunamigenic slips during the M9 event can be explained by a large gradient in fault strength on the up-dip
side of the M9 hypocenter, which was located 17 to 18 km beneath sea level. A large stressdrop (approximately 80 MPa) induced by the collapse of a subducted seamount possibly
139
140
141
142
143
144E
41N
41N
triggered the M9 earthquake. In the deep (>35 km) part of the thrust fault, where M7-class
Miyagi-oki earthquakes have repeatedly occurred, plastic deformation occurs in siliceous
40
rocks but not in gabbroic rocks. Thus, the asperity associated with the M7-class earthquakes 40
Iwa
was most likely a gabbroic body, such as a broken seamount, surrounded by siliceous
39
39
sedimentary rocks. The conditionally stable nature of the surrounding region can be
1981
1978
78
Miy
explained by the frictional behavior of wet quartz in the brittle-ductile transition zone. In
38
38
2005
200
5
contrast to the deep M7-class asperity, the M9 asperity (i.e., a region that was strongly
2011
coupled before the M9 Tohoku-oki earthquake) extended to a large area of the plate
Fuk
37
37
interface because shear strength is relatively insensitive to lithological variation at
Ibaintermediate depths. However, the along-arc extension of the M9 asperity was constrained
36
36
Tokyo
by fluid-rich regions on the plate interface.

Keywords: Fault strength; Rheology; Friction; Pore pressure; Seamount; Interplate
earthquake

100 km
35

35
139

140

141

142

Figure 1

Corresponding author: Ichiko Shimizu, ichiko@eps.s.u-tokyo.ac.jp
9

143

144E

Geofluid processes in subduction zones and mantle dynamics

FULL PAPER 

Open Access

Seismic activity near the Moriyoshi-zan volcano in Akita Prefecture,northeastern Japan: implications for geofluid migration anda midcrustal geofluid reservoir
Masahiro Kosuga
Earth, Planets and Space 2014, 66:77 doi:10.1186/1880-5981-66-77
Received: 22 November 2013, Accepted: 15 July 2014, Published: 25 July 2014

Abstract
The 2011 off the Pacific coast of Tohoku (Tohoku-oki) earthquake caused increased seismicity in many inland areas in Japan. A seismic
cluster north of the Moriyoshi-zan volcano in Akita prefecture, Tohoku District, is of interest in light of the contribution of geofluids toseismic activity. We observed a seismic cluster characterized by the migration of seismicity and reflected/scattered phases. We
relocated hypocenters of the cluster using data from temporal observations and the hypoDD location technique, which significantly
increased the hypocentral accuracy. We interpreted a complex spatiotemporal variation of seismicity in the cluster as the migration ofpore fluid pressure from multiple pressure sources. The hydraulic diffusivity of the cluster was in the range of 0.01 to 0.7 m2/s andincreased with time, implying that the migration of hypocenters accelerated after a pathway for fluids was formed by fracturing of thewall rock during the initial stage of seismic activity. A prominent feature of the seismograms is a reflected/scattered phase observed
at stations around the volcano. We regard the phase as S-to-S scattered waves andestimated the location of the scatterers using a back-projection method. The scatterers areinferred to be located about 5 km northwest of the Moriyoshi-zan volcano, at an
approximate depth of 13 km. The Moriyoshi-zan area is one of the source areas of deep
low-frequency earthquakes that have been interpreted as events generated by the
migration of geofluids. The depth of the scatterers is close to the upper limit of the depth
at which low-frequency earthquakes occur. Thus, we interpret the observed scatterers to
be a reservoir of geofluid that came from the uppermost mantle accompanying
contemporaneous low-frequency earthquakes.

Keywords: The 2011 off the Pacific coast of Tohoku earthquake; Triggered
seismicity; Hypocenter migration; Scattering, Geofluid

Figure 1

Corresponding author: Masahiro Kosuga, mkos@cc.hirosaki-u.ac.jp

FULL PAPER 

Open Access

Volatile (F and Cl) concentrations in Iwate olivine-hosted melt
inclusions indicating low-temperature subduction
Estelle F Rose-Koga*, Kenneth T Koga, Morihisa Hamada, Thomas Hélouis, Martin J Whitehouseand Nobumichi Shimizu
Earth, Planets and Space 2014, 66:81 doi:10.1186/1880-5981-66-81
Received: 25 November 2013, Accepted: 11 July 2014, Published: 1 August 2014

Abstract
Investigation of olivine-hosted melt inclusions provides information about the abundance of volatile elements that are often
lost during subaerial eruptions of lavas. We have measured the abundances of H2O, CO2, F, Cl, and S as well as Pb isotopes in 29
melt inclusions in the scoria of the 1686 eruption of the Iwate volcano, a frontal-arc volcano in the northeast Japan arc. Pb
Isotope compositions identify that Iwate magma is derived from a mixture of depleted mantle, subducted basalt, andsediment. Systematics of F in comparison to MORB and other arc magma indicates that (1) the slab surface temperature mustbe among the lowest on Earth and (2) hydrous minerals, such as amphibole, humites, and/or mica, must be present as residual
phases during the dehydration of the slab.

wt% Na2O + K2O

10
8
6

Phonotephrite
Tephritebasanite

4
2

CH

JAPAN
SEA

Iwate
38ºN

Basaltic
trachyandesite

Basalt

144ºE

JAPAN TR
EN

138ºE
42ºN

Basaltic
Andesite
Andesite Dacite

Picrobasalt

037 41 45 49 53 57 61 65 69 73 77

wt% SiO2
as a function of K O and Na*Corresponding author: Estelle F Rose-Koga, e.koga@opgc.univ-bpclermont.fr
10

Figure 1

The all fall in the basalt

Earth, Planets and Space

FULL PAPER 

Open AccessContributions of poroelastic rebound and a weak volcanic arc to
the postseismic deformation of the 2011 Tohoku earthquake
Yan Hu*, Roland Bürgmann, Jeffrey T Freymueller, Paramesh Banerjee and Kelin Wang
Earth, Planets and Space 2014, 66:106 doi:10.1186/1880-5981-66-106
Received: 11 March 2014, Accepted: 18 August 2014, Published: 2 September 2014

Abstract
A better understanding of fluid-related processes such as poroelastic rebound of the upper crust and weakening of the lower
crust beneath the volcanic arc helps better understand and correctly interpret the heterogeneity of postseismic deformation
following great subduction zone earthquakes. The postseismic deformation following the 2011 Mw9.0 Tohoku earthquake,recorded with unprecedented high resolution in space and time, provides a unique opportunity to study these ‘second-order’
subduction zone processes. We use a three-dimensional viscoelastic finite element model to study the effects of fluid-related
processes on the postseismic deformation. A poroelastic rebound (PE) model alone with fluid flow in response to coseismicpressure changes down to 6 and 16 km in the continental and oceanic crusts, respectively, predicts 0 to 6 cm uplift on land, up
to approximately 20 cm uplift above the peak rupture area, and up to approximately 15 cm subsidence elsewhere offshore. PE
produces up to approximately 30 cm of horizontal motions in the rupture area but less than 2 cm horizontal displacements on
land. Effects of a weak zone beneath the arc depend on its plan-view width and vertical viscosity profile. Our preferred modelof the weak sub-arc zone indicates that in the first 2 years after the 2011 earthquake,the weak zone contributes to the surface deformation on land on the order of up to
20 cm in both horizontal and vertical directions. The weak-zone model helps
eliminate the remaining systematic misfit of the viscoelastic model of upper mantle
relaxation and afterslip of the megathrust.

Keywords: Poroelastic rebound; Weakened lower crust beneath the arc; Giantearthquake; Subduction zone; Viscoelastic postseismic deformation;
Finite element model; Numerical simulation
Figure 1*Corresponding author: Yan Hu, yhu@seismo.berkeley.edu

FULL PAPER 

Open Access

Seismic velocity structure in and around the Naruko volcano, NE
Japan, and its implications for volcanic and seismic activities
Tomomi Okada*, Toru Matsuzawa, Junichi Nakajima, Naoki Uchida, Mare Yamamoto, Shuichiro Hori, Toshio Kono,
Takashi Nakayama, Satoshi Hirahara and Akira Hasegawa
Earth, Planets and Space 2014, 66:114 doi:10.1186/1880-5981-66-114
Received: 14 December 2013, Accepted: 29 August 2014, Published: 10 September 2014

Abstract
Geofluids is important for understanding volcanic and earthquake generation processes. In this study, we obtained a detailed
seismic velocity structure in and around the Naruko volcano, northeastern Japan, using data from a dense seismic observation
network. We found a distinct seismic low-velocity zone (LVZ) beneath the Naruko volcano, with a diameter of nearly 10 to 20
km in the lower crust. This LVZ could correspond to a magma chamber. We also found a seismic low-velocity zone beneath theaftershock region of the 2008 Iwate-Miyagi Nairiku earthquake. This LVZ could correspond to an area with overpressurized
fluid, which promoted the occurrence of the 2008 Iwate-Miyagi Nairiku earthquake.

Keywords: Geofluids; Seismic velocity structure; Seismicity; Naruko volcano; 2008
Iwate-Miyagi Nairiku earthquake

Yakeishi

Kurikoma
OnikobeNarukoFigure 1*Corresponding author: Tomomi Okada, okada@aob.gp.tohoku.ac.jp
11Geofluid processes in subduction zones and mantle dynamics

FULL PAPER 

Open AccessArima hot spring waters as a deep-seated brine from subducting slab
Chiho Kusuda, Hikaru Iwamori*, Hitomi Nakamura, Kohei Kazahaya and Noritoshi Morikawa
Earth, Planets and Space 2014, 66:119 doi:10.1186/1880-5981-66-119
Received: 3 June 2014, Accepted: 19 August 2014, Published: 19 September 2014

Abstract
Non-volcanic hot springs are generally believed to originate through circulation of meteoric or buried sea water heated at
depth. In this study, we report the geochemical characteristics of the Arima and Takarazuka hot spring waters, known as
Arima-type deep brine, in a forearc region of southwestern Japan. We examine 14 water samples to determine the levels of 12
solute elements or components and the isotopic ratios of H, He, C, O, and Sr, and we perform correlation analysis of the data to
deduce the source materials and origin of the deep brine. Moreover, we perform numerical modeling of oxygen and hydrogenisotopic fractionation along subducting slabs to examine the composition of slab-derived fluid as a possible candidate of the
deep brine. The results suggest that the high salinity and solute concentrations with characteristic oxygen, hydrogen, carbon,
and strontium isotope compositions, as well as high 3He/4He ratios, can be explained by a dehydrated component of the
subducted Philippine Sea slab. Hence, this study may provide an invaluable understanding of geofluid processes over asignificant depth range.

Keywords: Subduction; Geofluid; Slab-fluid; Hot spring; Arima

Figure 1*Corresponding author: Hikaru Iwamori, hikaru@jamstec.go.jp

FULL PAPER 

Open Access

Groundwater, possibly originated from subducted sediments,
in Joban and Hamadori areas, southern Tohoku, Japan
Yoko S Togo*, Kohei Kazahaya, Yuki Tosaki, Noritoshi Morikawa, Hiroyuki Matsuzaki, Masaaki Takahashi and Tsutomu Sato
Earth, Planets and Space 2014, 66:131 doi:10.1186/1880-5981-66-131
Received: 19 November 2013, Accepted: 19 September 2014, Published: 20 October 2014

Abstract
We studied the origin of deep groundwater in the Joban and Hamadori areas in southern Tohoku, Japan, based on δD, δ18O, 129I/I, 36Cl/Cl, and3
H concentrations. Deep groundwater was collected from the basement rocks (Cretaceous granite) and from the margin of the Joban
sedimentary basin (latest Cretaceous to Quaternary sedimentary rocks deposited on the basement rocks). We sampled groundwater pumped
from depths ranging from 350 to 1,600 m in these areas. A hypothetical end-member of deep groundwater was estimated from therelationship between δ18O and Cl concentrations, and our data reveal a much higher iodine concentration and lower Br and Cl concentrations
than found in seawater. The iodine ages inferred from 129I/I are quite uniform and are about 40 Ma and36
Cl/Cl almost reached the secular equilibrium. The relationship between iodine and Cl can be explainedby mixing a hypothetical end-member with meteoric water or seawater. Moreover, the I/Cl ratio
increases linearly with increasing water temperature. The water temperature was high in Joban, with amaximum of 78°C at a depth of 1,100 m. The geothermal gradient in the Joban basin is 18°C km−1, andthe temperature even at a depth of 3 km in the basin was not high enough to supply thermal water tothe sampling sites. Thus, sedimentary rocks in the Joban basin are unlikely to be the source of iodine in
the deep groundwater. Several active faults such as the Futaba Fault are developed in and around thestudied areas. The Iwaki earthquake occurred 1 month after the 2011 Tohoku-oki earthquake, andnormal-fault type surface ruptures formed and discharged hot groundwater in Joban. The deep
groundwater we studied probably came up through the basement rocks from greater depths. There are
no sedimentary rocks younger than Tertiary age beneath the pre-Cretaceous basement rocks, and thesubducted sediments in the Japan Trench are a possible source of iodine in the groundwater. The Joban
and Hamadori areas may be an ideal window to look into the water circulation in the forearc of the
Tohoku subduction zone.

Keywords: Iodine age; 36Cl/Cl; Source of iodine; Subducted sediments; Halogen; Joban;
Hamadori; Tohoku

Figure 1*Corresponding author: Yoko S Togo, yoko-togo@aist.go.jp
12Earth, Planets and SpaceLETTER

Open AccessElectrical conductivity of brine-bearing quartzite at 1 GPa:
implications for fluid content and salinity of the crust
Akira Shimojuku*, Takashi Yoshino and Daisuke Yamazaki
Earth, Planets and Space 2014, 66:2 doi:10.1186/1880-5981-66-2
Received: 16 October 2013, Accepted: 26 February 2014, Published: 1 April 2014

Abstract
The electrical conductivity of brine-bearing quartzite with fluid fractions of 0.19 to 0.30 and salinity of 3 to 17 wt.% was
measured at 800 to 1,100 K and 1 GPa. The conductivity of the brine-bearing quartzite increases with salinity and fluid
fraction, but is almost independent of temperature. Our results suggest that regions of high conductivity (10−3 to 10−2 S/m) in
the crust could be explained by the presence of quartzite with fluids of salinity similar to that of seawater. To account for thoseregions with the highest conductivity of 10−1 S/m, quartzite with fluid of high salinity (>10 wt.%) is required.

Keywords: Electrical conductivity; Fluid; Brine; High-conductivity anomaly(b) Fluid fraction: 0.2(a) Fluid fraction:0.19; Salinity: 3 wt.% (Run A2354)
SiO2

SiO2

SiO

fluid
SiO2

SiO2
fluid

fluid

SiO2

SiO

Figure 1*Corresponding author: Akira Shimojuku, simojuku@eri.u-tokyo.ac.jp

LETTER

Open AccessMarkov random field modeling for mapping geofluid distributions
from seismic velocity structures
Tatsu Kuwatani*, Kenji Nagata, Masato Okada and Mitsuhiro Toriumi
Earth, Planets and Space 2014, 66:5 doi:10.1186/1880-5981-66-5
Received: 22 December 2013, Accepted: 25 March 2014, Published: 7 April 2014

Abstract
We applied the Markov random field model, which is a kind of a Bayesian probabilistic method, to the spatial inversion of theporosity and pore shape in rocks from an observed seismic structure. Gaussian Markov chains were used to incorporate thespatial continuity of the porosity and the aspect ratio of the pore shape. Synthetic inversion tests were able to show theeffectiveness and validity of the proposed model by appropriately reducing the statistical noise from the observations. The
proposed model was also applied to natural data sets of the seismic velocity structures in the mantle wedge beneath
northeastern Japan, under the assumptions that the fluid was melted and the temperature and petrologic structures were
uniformly distributed. The result shows a significant difference between the volcanic front and the forearc regions, at a depthof 40 km. Although the parameters and material properties will need to be determined more precisely, the Markov random
field model presented here can serve as a basic inversion framework for mapping geofluids.

Keywords: Bayesian estimation; Markov random field; Geofluid; Mantle
wedge; Data-driven science

(b)

(a)

5

1

4
3.5



0.2

0.3

Figure 1*Corresponding author: Tatsu Kuwatani, kuwatani@mail.kankyo.tohoku.ac.jp
13

3
0

.1

0.1

=

4.5

 =0 =0.01


6
0

.1

6.5

=1

7

(km/s)

7.5

 =0 .01 =0(km/s)

8

0.1



0.2

0.3

Geofluid processes in subduction zones and mantle dynamics

LETTER

Open AccessNumerical modeling of trace element transportation in subduction
zones: implications for geofluid processes
Akihiko Ikemoto* and Hikaru Iwamori
Earth, Planets and Space 2014, 66:26 doi:10.1186/1880-5981-66-26
Received: 29 November 2013, Accepted: 24 March 2014, Published: 30 April 2014

Abstract
This study presents the first numerical model for trace element transportation associated with dehydration and fluid
migration from the subducting slab and aims to incorporate both fluid dynamical processes (e.g., flow mode and mass fluxes)
in subduction zones and associated geochemical evidence (e.g., chemical compositions of arc lavas). The model includes
temperature and flow structures associated with slab subduction and mantle-fluid two-phase flow, as well as phase relationsof hydrous phases (e.g., dehydration-hydration reactions and melting) and trace element partitioning among the phases(solid, aqueous fluid, and melt). The model calculations show that if instantaneous chemical equilibrium is achieved
associated with porous flow of slab-derived fluid, the elements expelled with the ascending fluid (e.g., Pb) are absorbed into
the down-going hydrated mantle layer developed above the slab. As a result, these elements are considerably depleted in the
resultant magma generated by fluid-flux melting in the core part of the mantle wedge, and it therefore fails to reproduce thegeochemical characteristics of arc lavas. In contrast, if disequilibrium elementtransport (e.g., associated with channel flow) is assumed when the hydrated mantle
layer liberates the fluid, then the key elements are delivered to the melting region to
reproduce certain arc lava signatures. These results suggest that disequilibrium fluid
transport in the wedge mantle, such as through channels, plays an important role inelement cycling in subduction zones.

Keywords: Subduction; Slab-fluid; Arc magma; Numerical modeling; Trace element
Figure 1*Corresponding author: Akihiko Ikemoto, ikemoto.a.aa@m.titech.ac.jp

LETTER

Open AccessHydrous origin of the continental cratonic mantle
Kyoko N Matsukage* and Toshisuke Kawasaki
Earth, Planets and Space 2014, 66:29 doi:10.1186/1880-5981-66-29
Received: 7 October 2013, Accepted: 11 April 2014, Published: 1 May 2014

Abstract
We performed melting experiments of hydrous pyrolite at pressures from 3 to 8 GPa and temperatures from 1,100°C to
1,800°C to identify the origin of chemical variation in cratonic garnet peridotites with high contents of magnesianorthopyroxene. In hydrous conditions, the stability field of residual orthopyroxene expands relative to olivine above solidus,
and the harzburgitic residue contains large amounts of Mg-rich (Mg# > 0.92) orthopyroxene at 4.5 to 6 GPa. The residual
chemistry obtained from our experiments indicates that the chemical variation of the cratonic garnet peridotites possiblyreflects formation by melt depletion under various water contents from almost anhydrous to a maximum of approximately 1%
to 2% in the upper mantle at depths of about 100 to 200 km.

Keywords: Cratonic mantle; Peridotite; Hydrous pyrolite; Partial melting; Residue;
High-pressure experiment

Figure 1*Corresponding author: Kyoko N Matsukage, kmatsu@gaia.h.kyoto-u.ac.jp
14Earth, Planets and SpaceLETTER

Open AccessDistribution of CO2 fluids in the Shimanto belt on Muroto Peninsula, SW
Japan: possible injection of magmatic CO2 into the accretionary prism
Atsushi Okamoto*, Michimasa Musya, Yoshitaka Hashimoto and Noriyoshi Tsuchiya
Earth, Planets and Space 2014, 66:33 doi:10.1186/1880-5981-66-33
Received: 18 November 2013, Accepted: 14 April 2014, Published: 15 May 2014

Abstract
Carbon dioxide and methane are major components in geofluids; however, there is little evidence showing how C-H-O fluids
evolve in a subduction zone. We investigated fluid inclusions in quartz veins from the Eocene-Oligocene Shimanto belt
(Murotohanto subbelt) on Muroto Peninsula, SW Japan using microthermometry and laser Raman spectroscopy. Quartz veinsthat cut the cleavage of the host rocks in the Murotohanto subbelt contain one-phase carbonic inclusions (CH4) and twophase aqueous inclusions (CH4 ± CO2 vapor and H2O liquid). The vapor in the two-phase inclusions is essentially CH4 in thenorthern part of the belt and a CO2-CH4 mixture in the southern part; values of XCO2(=CO2 / (CO2 + CH4)) vary from 0 to 0.9.
Within a single CO2-bearing vein, XCO2 values decrease from the vein wall ( XCO2 = 0.5 to 0.9) to the vein center ( XCO2 = 0), and thehomogenization temperature increases from approximately 180°C to 240°C-250°C, indicating a transition of the carbonicspecies from CO2-CH4 to CH4 during vein formation. CO2-dominant fluids are rare in most accretionary prisms formed under
low-grade metamorphic conditions, and the generation of CO2 cannot be explained by diagenesis of organic matter insediments under the P-T conditions of formation of the CO2-bearing veins (235°C to 245°C, 165 to 200 MPa). The CO2 fluids are
distributed preferentially near an out-of-sequence thrust that brings the Murotohanto subbelt into contact with the late
Oligocene-early Miocene Nabae subbelt and its many volcanic and intrusive rocks. We therefore suggest that the CO2 fluids
were generated in association with near-trench magmatism during the middle
Miocene and that the fluids were injected and mixed with the CH4 pore fluids ofthe sediments in the accretionary prism.

Keywords: C-H-O fluid; Fluid inclusion; Shimanto belt; Magmatic CO2; Quartz
vein

Figure 1*Corresponding author: Atsushi Okamoto, okamoto@mail.kankyo.tohoku.ac.jp

LETTER

Open Access

Effect of fluid H2O on compressional wave velocities in quartz
aggregate up to 500°C at 0.5 GPa
Masahiro Ishikawa* and Yuki Matsumoto
Earth, Planets and Space 2014, 66:35 doi:10.1186/1880-5981-66-35
Received: 15 December 2013, Accepted: 23 April 2014, Published: 15 May 2014

Abstract
Compressional wave velocities (Vp) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on Vp at highpressure-temperature (P-T). Ultrasonic measurements were conducted on dry and wet quartz aggregate from room
temperature to 500°C at 0.5 GPa using a piston cylinder apparatus. The experiment showed a 4% decrease in measured Vp inquartz aggregate with increasing H2O content to 1 wt.%, whereas the temperature derivative of Vp (∂Vp/∂ T = −2.8 to−4.9 × 10−4 km s−1 °C−1) in wet quartz aggregate remained almost the same as for the dry quartz aggregate(∂ Vp/∂ T = −5.2 × 10−4 km s−1 °C−1). Our high-pressure, high-temperature experiments show that a small amount of pore fluid(0.4 to 1.0 wt.% H2O) can significantly reduce Vp under the P-T conditions of the middle crust.

Keywords: Vp; Fluid; Quartz

Figure 1*Corresponding author: Masahiro Ishikawa, ishikawa@ynu.ac.jp
15

Geofluid processes in subduction zones and mantle dynamics

LETTER

Open AccessThree-dimensional electromagnetic imaging of fluids and melts beneaththe NE Japan arc revisited by using geomagnetic transfer function data
Wataru Kanda* and Yasuo Ogawa
Earth, Planets and Space 2014, 66:39 doi:10.1186/1880-5981-66-39
Received: 15 January 2014, Accepted: 12 May 2014, Published: 27 May 2014

Abstract
The three-dimensional distribution of fluids and melts under the NE Japan arc was imaged using its resistivity structure,modeled with geomagnetic transfer functions. The data were collected at 37 stations located on a 20-km grid, at periods
ranging from 16 to 256 s. In spite of the narrow period band nature, these periods turn out to be sensitive to conductors in the
deep crust and upper mantle. The geomagnetic transfer functions represent lateral resistivity variations, which yield
inherently nonunique model results when using the geomagnetic transfer functions alone.
139˚
140˚
142˚
141˚
However, by fixing the resistivity structure of the surrounding seawater distribution, the
trait
ru S
a
g
intrinsic nonuniqueness is alleviated. In this study, we show an inversion result using a
u
Ts
41˚
41˚
100-Ωm uniform Earth with fixed resistivity of surrounding oceans. As a result, it was foundthat the features of the short period transfer function require shallow conductors in the
L0upper crust, which is suggested to represent the northern Tohoku conducting belt of a
L1
L2
previous study. The final model is characterized by a highly conductive zone along the
40˚
40˚
L3
L4
quaternary volcanic arc in the depth range of the lower crust to the upper mantle. The
L5
conductor, which is obtained mainly from the features of longer-period data, is particularly
clear beneath the Sengan geothermal area. The deep crustal conductor implies the
39˚
39˚
existence of partial melt and/or high-salinity fluids.
OSR

HKD

IWK

TWD

YKY HCM

CHK

Pacific Ocean

Ou Backbone

Japan Sea

Range

IWT
KMG

KKM

NRG

Keywords: NE Japan; Quaternary volcanoes; Arc magma; 3-D modeling; Electricalresistivity

HJO

139˚

140˚

−4000

−3000

142˚

141˚
−2000

bathymetry (m)

−1000

0

Figure 1*Corresponding author: Wataru Kanda, kanda@ksvo.titech.ac.jp

LETTER

Open Access

Fluid-metapelite interaction in an ultramafic mélange: implications
for mass transfer along the slab-mantle interface in subduction zones
Yasushi Mori*, Miki Shigeno and Tadao Nishiyama
Earth, Planets and Space 2014, 66:47 doi:10.1186/1880-5981-66-47
Received: 10 December 2013, Accepted: 16 April 2014, Published: 4 June 2014

Abstract
The slab-mantle interface in subduction zones is a site of tectonic mixing of crustal and mantle rocks. It is the interface for
fluid flow of slab-derived components into the mantle wedge. To assess the fluid-rock interaction along the slab-mantle
interface, we studied the bleaching of pelitic schist in an ultramafic mélange. The Nishisonogi metamorphic rocks in Kyushu,
Japan, comprise ultramafic mélanges intercalated with epidote-blueschist facies schists. The ultramafic mélange consists oftectonic blocks of various lithologies and a matrix of chlorite-actinolite schist and serpentinite. Along the contact with the
mélange matrix, pelitic schist blocks are bleached mainly due to the modal increase of albite and the consumption ofcarbonaceous material. The bleaching is probably attributed to infiltration of Na-rich external fluid from the mélange matrix.
Mass balance analysis indicates losses of C, Rb, K2O, Ba, Pb, and SiO2 from the bleached pelitic schist, although Al2O3, TiO2, Sc, Y,
Zr, Nb, La, Ce, and Nd remain immobile. This suggests fractionation of large-ion lithophile elements (LILE) and Pb from thehigh-field-strength elements and rare earth elements during the bleaching. If this ultramafic mélange is analogous to theslab-mantle interface, similar infiltration metasomatism will promote liberation of C,
Si, LILE, and Pb from subducting metapelites and enhance metasomatism of the
mantle wedge.

Keywords: Element fractionation; Fluid-rock interaction; Metapelite; Subduction
zone mélange; Nishisonogi metamorphic rocks

Figure 1*Corresponding author: Yasushi Mori, mori@kmnh.jp
16Earth, Planets and SpaceLETTER

Open Access

A 3-D electrical resistivity model beneath the focal zone of the 2008
Iwate-Miyagi Nairiku earthquake (M 7.2)
Hiroshi Ichihara*, Shin’ya Sakanaka, Masaaki Mishina, Makoto Uyeshima, Tadashi Nishitani, Yasuo Ogawa,
Yusuke Yamaya, Toru Mogi, Kazuhiro Amita and Takuya Miura
Earth, Planets and Space 2014, 66:50 doi:10.1186/1880-5981-66-50
Received: 11 December 2013, Accepted: 26 May 2014, Published: 10 June 2014

Abstract
The 2008 Iwate-Miyagi Nairiku earthquake (M 7.2) was a shallow inland earthquake that occurred in the volcanic front of thenortheastern Japan arc. To understand why the earthquake occurred beneath an active volcanic area, in which ductile crust
generally impedes fault rupture, we conducted magnetotelluric surveys at 14 stations around the epicentral area 2 months
after the earthquake. Based on 56 sets of magnetotelluric impedances measured by the present and previous surveys, weestimated the three-dimensional (3-D) electrical resistivity distribution. The inverted 3-D resistivity model showed a shallow
conductive zone beneath the Kitakami Lowland and a few conductive patches beneath active volcanic areas. The shallow
conductive zone is interpreted as Tertiary sedimentary rocks. The deeper conductive patches probably relate to volcanic
activities and possibly indicate high-temperature anomalies. Aftershocks were distributed mainly in the resistive zone,
interpreted as a brittle zone, and not in these conductive areas, interpreted as ductile
Altitude (m)(a)
zones. The size of the brittle zone seems large enough for a fault rupture area capableof generating an M 7-class earthquake, despite the areas distributed among theductile zones. This interpretation implies that 3-D elastic heterogeneity, due toregional geology and volcanic activities, controls the size of the fault rupture zone.
Additionally, the elastic heterogeneities could result in local stress concentration
around the earthquake area and cause faulting.
138˚

140˚

142˚

144˚

−8000

40˚

0

1
Y1

38˚

30

20

Y1

Y1

0
40 50 16
Y
Y1 Y1

−6000

I8

09

K

I8

10

I8

N1

Keywords: Magnetotelluric; Iwate-Miyagi earthquake; 3-D resistivity; Inland
earthquake

00 10
N1 N1

38˚40'(b)140˚20'N1
40N1

140˚30'

0
16

N
50

N1

65

N1

140˚40'

30

Y2

40
Y2

11

31

I8

Mukaimachi Caldera

30

Y2

Y

2000

A
ES

I8

38˚50'
20

0

20

Y2

1
0 2
30
32 2 I8 1 2 2
K2
I8 I8
4 2 4
0
20
I8 I8 I8 23 43
10 20 90
I8 I8
K2K2 K K1
30
I8
50
40
K1
0
8
30
K1
0
K1
K1
16
K
Mt. Kurikoma 0
Onikobe Caldera
7
20
K1
K1

39˚00'

−2000

0
21

00

Mt. Yakeishi

08

0
24

−4000

0
70 18 190
Y Y
Y1

10

K1

05

K1

0
70 5
N1 N17 180 N19
N

km

Narukovolcanoes
140˚50'0
141˚00'141˚10'10
141˚20'20
141˚30'Figure 1*Corresponding author: Hiroshi Ichihara, h-ichi@jamstec.go.jp

LETTER

Open AccessPore pressure distribution in the focal region of the 2008 M7.2
Iwate-Miyagi Nairiku earthquake
Keisuke Yoshida*, Akira Hasegawa, Tomomi Okada, Hiroaki Takahashi, Masahiro Kosuga, Takaya Iwasaki, Yoshiko Yamanaka,
Hiroshi Katao, Yoshihisa Iio, Atsuki Kubo, Takeshi Matsushima, Hiroki Miyamachi and Youichi Asano
Earth, Planets and Space 2014, 66:59 doi:10.1186/1880-5981-66-59
Received: 28 March 2014, Accepted: 9 June 2014, Published: 20 June 2014

Abstract
The pore fluid pressure distribution in the focal region of the 2008 Iwate-Miyagi Nairiku earthquake was investigated through ananalysis of the diversity of focal mechanisms. We inverted stress orientations and focal mechanisms directly from P-wave polarity dataobtained from a dense aftershock observation network and other temporarily and routinely operated stations. The estimated stressorientation is consistent with that typical of NE Japan. Specifically, the σ1 axis is oriented WNW-ESE nearly parallel to plateconvergence, and the σ3 axis is nearly vertical, consistent with a reverse-faulting stress regime, with some exceptions in the central
part of the aftershock area. We obtained 2,497 well-determined focal mechanisms whose average number of P-wave polarity data ismore than 70. The spatial distribution of pore fluid pressure was estimated by using the obtained orientations of the principal stresses
and earthquake faults. The pore pressure ratio for each earthquake fault was calculated
under the assumption that reduced frictional strength was caused by pore fluid pressure.
The results showed that the diversity of the focal mechanisms here obtained requires highpore fluid pressures at many of the earthquake faults in the focal region. The spatial
pattern of pore pressure ratio shows that areas of higher pore pressure ratio are
distributed around the large coseismic slip area near Kurikoma volcano. Immediately
beneath these high pore pressure areas, there exists a distinct seismic low-velocity zonethat continues down to the mantle wedge below. These observations suggest that crustal
fluids supplied from the mantle wedge have contributed to producing high pore pressuresand to lowering the frictional strengths of those faults. Crustal fluids may also havecontributed to generating the mainshock rupture.

Keywords: 2008 Iwate-Miyagi Nairiku earthquake; NE Japan; Focal mechanism; Pore
fluid pressure; Stress tensor inversion*Corresponding author: Keisuke Yoshida, k-yoshida@aob.gp.tohoku.ac.jp
17

Figure 1

Geofluid processes in subduction zones and mantle dynamics

LETTER

Open Access

FTIR and Raman spectroscopy characterization of fluorine-bearing
titanian clinohumite in antigorite serpentinite and chlorite harzburgite
Kenneth T Koga*, Carlos J Garrido, José A Padrón-Navarta, Vicente López Sánchez-Vizcaíno and María T Gómez-Pugnaire
Earth, Planets and Space 2014, 66:60 doi:10.1186/1880-5981-66-60
Received: 14 November 2013, Accepted: 26 May 2014, Published: 26 June 2014

Abstract
Titanian clinohumite is an accessory phase found in peridotites, and it can be a key repository of volatile and other traceelements in sub-arc mantle. To characterize spectroscopic variations due to volatile elements in the phase, we haveinvestigated the infrared spectroscopic characteristics of a suite of naturally occurring Ti clinohumite minerals with varying F
and Ti concentrations. Samples were ultramafic rocks from Cerro del Almirez, Spain and Cima di Gagnone, Switzerland. The
infrared spectra corresponding to OH vibrations showed systematic variation in regard to the abundance of F in Ti
clinohumite. In particular, the intensity ratios of infrared absorption spectra at 3,565 and 3,390 cm−1 correlated linearly withthe abundance of F independently of the crystal orientation. Raman spectra did not corroborate the Fourier transform infrared(FTIR) results. This intensity ratio provides an alternative analytical criterion for the
Atg-serp. (Al96-20)
0.45
characterization of Ti clinohumite.
Vein in Atg-serp. (Al96-15B)
Cpx in Atg-serp. (Al96-10)
Chl-harzb. (Al96-1c)
En vein in Chl-harzb. (Al01-7b)
Marble in Chl-harzb. (Al98-29a)
Marble in Chl-harzb. (Al98-32)
Recrystallized Grt-per. (MG-304B)

0.40
0.35

XF

0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.00

0.10

0.20

0.30

0.40

XTi

0.50

0.60

Figure 1*Corresponding author: Kenneth T Koga, k.koga@opgc.univ-bpclermont.fr

LETTER

Open Access

Guided wave observations and evidence for the low-velocity
subducting crust beneath Hokkaido, northern Japan
Takahiro Shiina*, Junichi Nakajima, Genti Toyokuni and Toru Matsuzawa
Earth, Planets and Space 2014, 66:69 doi:10.1186/1880-5981-66-69
Received: 14 December 2013, Accepted: 30 June 2014, Published: 11 July 2014

Abstract
At the western side of the Hidaka Mountain range in Hokkaido, we identify a clear later phase in seismograms for earthquakes
occurring at the uppermost part of the Pacific slab beneath the eastern Hokkaido. The later phase is observed after P-wave
arrivals and has a larger amplitude than the P wave. In this study, we investigate the origin of the later phase from seismic
wave observations and two-dimensional numerical modeling of wave fields and interpret it as a guided P wave propagatingin the low-velocity subducting crust of the Pacific plate. In addition, the results of our numerical modeling suggest that the
low-velocity subducting crust is in contact with a low-velocity material beneath the Hidaka Mountain range. Based on ourinterpretation for the later phase, we estimate P-wave velocity in the subducting crust beneath the eastern part of Hokkaido
by using the differences in the later phase travel times and obtain velocities of 6.8 to 7.5 km/s at depths of 50 to 80 km. The
obtained P-wave velocity is lower than the expected value based on fully hydrated mid-ocean ridge basalt (MORB) materials,
suggesting that hydrous minerals are hosted in the subducting crust and aqueous fluids may co-exist down to depths of atleast 80 km.
(a)

Keywords: Guided wave; Subducting crust; Pacific slab; Hokkaido; Finite difference

44˚

141˚

142˚

143˚

144˚

145˚

146˚

200

method; Dehydration; Intermediate-depth earthquake

160
46˚

43˚

44˚

120

Hokkaido
ril

Ku

40

80

?

?

?

HidakaMountain range

Tohoku140˚Figure 1*Corresponding author: Takahiro Shiina, shina@aob.gp.tohoku.ac.jp
18

142˚

Japan trenc
h

?

42˚

ch

tren

42˚

40˚
The Pacific plate~8.0 cm/y

144˚

146˚

38˚

Earth, Planets and SpaceLETTER

Open Access

Non-volcanic seismic swarm and fluid transportation driven by
subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan
Aitaro Kato*, Atsushi Saiga, Tetsuya Takeda, Takaya Iwasaki and Toru Matsuzawa
Earth, Planets and Space 2014, 66:86 doi:10.1186/1880-5981-66-86
Received: 14 November 2013, Accepted: 21 July 2014, Published: 4 August 2014

Abstract
To understand the mechanism of an intensive non-volcanic seismic swarm in the Kii Peninsula, Japan, we used a dense seismic
linear array to measure fine-scale variations of seismic velocities and converted teleseismic waves. A low-velocity anomaly
confined to just beneath the seismic swarm area is clearly imaged, which correlates spatially with an uplifted surface area anda highly conductive and strong attenuative body. These results suggest that fluids such as partial melt or water are present
beneath this non-volcanic seismic swarm area. It is notable that the island arc Moho below the seismic swarm area is at a
depth of approximately 32 km in the northern part of the seismic swarm area andshallows to approximately 20 km towards the south, due to the raised structure ofEP
the serpentinized mantle wedge. In addition, we show that the hydrated oceanic
Kii
34.4˚
Peninsulacrust of the subducting Philippine Sea slab is characterized by low velocities with a
PSP
km
0
-4
high Poisson’s ratio at depths of less than 40 km. In contrast, dehydration conversion
X=
34.2˚
from oceanic basalt to eclogite takes place at depths greater than 50 km. Water
released from the subducting oceanic crust could cause serpentinization of the
34˚
mantle wedge and infiltration into the forearc base of the overlying plate. The
0 km
X=interaction between dehydration of the subducting oceanic crust and hydration ofSeismic Stations
33.8˚
Temporary
the mantle wedge and overlying plate exerts an important role in driving the nonPermanent
volcanic seismic swarm activity in the Kii Peninsula.
M3
M2
M1 LFE
33.6˚
10

20

135˚

X=

m

50 k

135.2˚

0 km

Serpentinized mantle wedge

km
0

33.4˚
134.8˚Y=

Keywords: Non-volcanic seismic swarm; Fluid; Dehydration of oceanic crust;

135.4˚

135.6˚

0 10 20 30 40 50 60
Depth (km)135.8˚136˚Figure 1*Corresponding author: Aitaro Kato, aitaro@seis.nagoya-u.ac.jp

LETTER

Open Access

Water content in arc basaltic magma in the Northeast Japan and Izu arcs:
an estimate from Ca/Na partitioning between plagioclase and melt
Masashi Ushioda*, Eiichi Takahashi, Morihisa Hamada and Toshihiro Suzuki
Earth, Planets and Space 2014, 66:127 doi:10.1186/1880-5981-66-127
Received: 13 December 2013, Accepted: 15 September 2014, Published: 29 September 2014

Abstract
The variation in water content of arc basaltic magmas in the Northeast Japan arc and the Izu arc was estimated using a simple
plagioclase phenocryst hygrometer. In order to construct a plagioclase phenocryst hygrometer optimized for arc basalt
magmas, we have conducted high-pressure melting experiments of relatively primitive basalt from the Miyakejima volcano, afrontal-arc volcano in the Izu arc. As a result of the experiments, we found that the Ca/Na partition coefficient between
plagioclase and hydrous basaltic melt increases linearly with an increase in H2O content in the melts. We then selected fromliterature geochemical data sets of relatively primitive basaltic rocks with no evidence of magma mixing and the mostfrequent Ca-rich plagioclase phenocrysts from 15 basaltic arc volcanoes including both frontal-arc and rear-arc volcanoes. In
the 15 volcanoes studied, plagioclase phenocrysts of high anorthite content (An > 90) were commonly observed, whereas
plagioclase phenocrysts in rear arc volcanoes usually had a lower anorthite content(90 > An > 80). In all volcanoes studied, the estimated H2O content of basaltic magma
was at least 3 wt.% H2O or higher. The magmas of volcanoes located on the volcanic
front have about 5 wt.% H2O in magma whereas those from the rear-arc side areslightly lower in H2O content.

Keywords: Island arc basalt; Water content; Plagioclase; Hydrous melting
experiments; Across-arc geochemical variation

Figure 1*Corresponding author: Masashi Ushioda, ushioda.m.ab@m.titech.ac.jp
19

Geofluid processes in subduction zones and mantle dynamics

LETTER

Open AccessThree-dimensional magnetotelluric imaging of crustal fluids andseismicity around Naruko volcano, NE Japan
Yasuo Ogawa*, Masahiro Ichiki, Wataru Kanda, Masaaki Mishina and Koichi Asamori
Earth, Planets and Space 2014, 66:158 doi:10.1186/s40623-014-0158-y
Received: 4 April 2014, Accepted: 13 November 2014, Published: 4 December 2014

Abstract
We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the aim of imaging 3-D
distribution of fluids in the crust for its volcanic and seismogenic implications. The data were recorded at 77 sites in total: 30
sites are new and are arranged in an approximately 5 × 5 km grid whereas the remaining older sites constitute two separate
east-west profiles. We ran a 3-D inversion using full components of impedance tensors in the period range between 0.13 and400 s. The resulting model showed that a sub-vertical conductor exists a few kilometers below Naruko volcano. The conductor
extends from the surface of the volcano and dips towards the south, away from the volcano towards the backbone range.
High levels of seismicity are observed in the upper crust above and around the conductors. We suggest that the seismicity is
fluid driven and that a fluid trap is created by the precipitation of quartz owing to a reduction in solubility at shallow depth.
The Quaternary volcanic front is characterized by a sharp resistivity contrast and ahigh-resistivity zone and extends 10 to 15 km towards the east. A fore-arc conductor
OnikobeShinjowas observed at mid-crustal levels even farther towards the east. The sub-verticalBasin
Mukaimachi
L1
conductors along the arc and the fore-arc conductor have resistivities of 1 to 10 Ωm.
NarukoL2
Assuming a Hashin-Shtrikman model with saline fluids of 0.1-Ωm resistivity, aL3
Akakuraporosity of 1.5% to 15% is required to explain the observed conductive anomalies.
L4

Keywords: Magnetotellurics; 3-D modeling; Saline fluids; Northeastern Japan;
Quaternary volcanoes; Seismicity

SendaiPlain

Yamagata
Basin

Funagata-yama

Figure 1*Corresponding author: Yasuo Ogawa, oga@ksvo.titech.ac.jp20

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Contents
Special issue ‘Geofluid processes in subduction zones and mantle dynamics’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tatsuhiko Kawamoto, Junichi Nakajima, Bruno Reynard and Hiroaki Toh
Geophysical assessment of migration and storage conditions of fluids in subduction zones . . . . . . . . . . . . . . . . . . Anne Pommier
The roles of quartz and water in controlling unstable slip in phyllosilicate-rich megathrust fault gouges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sabine AM den Hartog, Demian M Saffer and Christopher J SpiersGeochemistry of continental subduction-zone fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yong-Fei Zheng and Joerg Hermann
Seismic attenuation beneath Kanto, Japan: evidence for high attenuation in the serpentinized subducting mantle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Junichi Nakajima
Polybaric crystallization differentiation of H2O-saturated island arc low-K tholeiite magmas: a case study of the Izu-Oshima
volcano in the Izu arc . . . . . . . . . . . . . . . . . . . . . Morihisa Hamada, Yuko Okayama, Takayuki Kaneko, Atsushi Yasuda and Toshitsugu Fujii
Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy andshear localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sejin Jung, Haemyeong Jung and Håkon Austrheim
A trial derivation of seismic plate coupling by focusing on the activity of shallow slow earthquakes. . . . . . . . . . . . . . . . . . Keisuke Ariyoshi, Toru Matsuzawa, Ryota Hino, Akira Hasegawa, Takane Hori, Ryoko Nakata and Yoshiyuki Kaneda
Large-ion lithophile elements delivered by saline fluids to the sub-arc mantle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tatsuhiko Kawamoto, Kenji Mibe, Hélène Bureau, Solenn Reguer, Cristian Mocuta, Stefan Kubsky,

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Dominique Thiaudière, Shigeaki Ono and Tetsu Kogiso

8

Toshio Kono, Takashi Nakayama, Satoshi Hirahara and Akira Hasegawa

11

Yusuke Yamaya, Toru Mogi, Kazuhiro Amita and Takuya Miura

17

Hiroshi Katao, Yoshihisa Iio, Atsuki Kubo, Takeshi Matsushima, Hiroki Miyamachi and Youichi Asano

17

Vicente López Sánchez-Vizcaíno and María T Gómez-Pugnaire18

A large mantle water source for the northern San Andreas fault system: a ghost of subduction past
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stephen H Kirby, Kelin Wang and Thomas M Brocher 9Rheological profile across the NE Japan interplate megathrust in the source region of the 2011 Mw9.0 Tohoku-oki
earthquake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ichiko Shimizu 9
Seismic activity near the Moriyoshi-zan volcano in Akita Prefecture, northeastern Japan: implications for geofluid
migration and a midcrustal geofluid reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Masahiro Kosuga 10
Volatile (F and Cl) concentrations in Iwate olivine-hosted melt inclusions indicating low-temperature subduction. . . . . . . . . . . . Estelle F Rose-Koga, Kenneth T Koga, Morihisa Hamada, Thomas Hélouis, Martin J Whitehouse and Nobumichi Shimizu 10
Contributions of poroelastic rebound and a weak volcanic arc to the postseismic deformation of the 2011 Tohoku
earthquake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yan Hu, Roland Bürgmann, Jeffrey T Freymueller, Paramesh Banerjee and Kelin Wang 11
Seismic velocity structure in and around the Naruko volcano, NE Japan, and its implications for volcanic and seismic
activities . . . . . . . . . . . . . . . . . . . . . . Tomomi Okada, Toru Matsuzawa, Junichi Nakajima, Naoki Uchida, Mare Yamamoto, Shuichiro Hori,
Arima hot spring waters as a deep-seated brine from subducting slab
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chiho Kusuda, Hikaru Iwamori, Hitomi Nakamura, Kohei Kazahaya and Noritoshi Morikawa 12
Groundwater, possibly originated from subducted sediments, in Joban and Hamadori areas, southern Tohoku, Japan. . . . . . . . . . . . . . . Yoko S Togo, Kohei Kazahaya, Yuki Tosaki, Noritoshi Morikawa, Hiroyuki Matsuzaki, Masaaki Takahashi and Tsutomu Sato 12
Electrical conductivity of brine-bearing quartzite at 1 GPa: implications for fluid content and salinity of the crust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Akira Shimojuku, Takashi Yoshino and Daisuke Yamazaki 13
Markov random field modeling for mapping geofluid distributions from seismic velocity structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tatsu Kuwatani, Kenji Nagata, Masato Okada and Mitsuhiro Toriumi 13
Numerical modeling of trace element transportation in subduction zones: implications for geofluid processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Akihiko Ikemoto and Hikaru Iwamori 14
Hydrous origin of the continental cratonic mantle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kyoko N Matsukage and Toshisuke Kawasaki 14
Distribution of CO2 fluids in the Shimanto belt on Muroto Peninsula, SW Japan: possible injection of magmatic CO2 into theaccretionary prism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atsushi Okamoto, Michimasa Musya, Yoshitaka Hashimoto and Noriyoshi Tsuchiya 15
Effect of fluid H2O on compressional wave velocities in quartz aggregate up to 500°C at 0.5 GPa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Masahiro Ishikawa and Yuki Matsumoto 15
Three-dimensional electromagnetic imaging of fluids and melts beneath the NE Japan arc revisited by using geomagnetictransfer function data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wataru Kanda and Yasuo Ogawa 16
Fluid-metapelite interaction in an ultramafic mélange: implications for mass transfer along the slab-mantle interface insubduction zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yasushi Mori, Miki Shigeno and Tadao Nishiyama 16
A 3-D electrical resistivity model beneath the focal zone of the 2008 Iwate-Miyagi Nairiku earthquake (M 7.2)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . Hiroshi Ichihara, Shin’ya Sakanaka, Masaaki Mishina, Makoto Uyeshima, Tadashi Nishitani, Yasuo Ogawa,Pore pressure distribution in the focal region of the 2008 M7.2 Iwate-Miyagi Nairiku earthquake. . . . . . . . Keisuke Yoshida, Akira Hasegawa, Tomomi Okada, Hiroaki Takahashi, Masahiro Kosuga, Takaya Iwasaki, Yoshiko Yamanaka,
FTIR and Raman spectroscopy characterization of fluorine-bearing titanian clinohumite in antigorite serpentinite andchlorite harzburgite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kenneth T Koga, Carlos J Garrido, José A Padrón-Navarta,
Guided wave observations and evidence for the low-velocity subducting crust beneath Hokkaido, northern Japan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Takahiro Shiina, Junichi Nakajima, Genti Toyokuni and Toru Matsuzawa
Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii
Peninsula, Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aitaro Kato, Atsushi Saiga, Tetsuya Takeda, Takaya Iwasaki and Toru Matsuzawa
Water content in arc basaltic magma in the Northeast Japan and Izu arcs: an estimate from Ca/Na partitioning between
plagioclase and melt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Masashi Ushioda, Eiichi Takahashi, Morihisa Hamada and Toshihiro Suzuki
Three-dimensional magnetotelluric imaging of crustal fluids and seismicity around Naruko volcano, NE Japan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yasuo Ogawa, Masahiro Ichiki, Wataru Kanda, Masaaki Mishina and Koichi Asamori

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Cover image: Pommier, A., Earth, Planets and Space 2014, 66:38 doi:10.1186/1880-5981-66-38