SMP43-01

Room:A03

Time:May 24 14:15-14:30

Analysis of metamorphic history recorded in garnet: A combined EBSD and EPMA
study
ENAMI, Masaki1∗ ; NAGAYA, Takayoshi2
1

Center for Chronological Research, Nagoya University, 2 Graduate School of Environmental Studies, Nagoya University

Pressure-temperature and deformation histories recorded in garnet grains in metapelites were analyzed with an effective combination of EBSD (Electron Backscatter Diffraction) and EPMA (electron-probe microanalyzer) data.
Sanbagawa metapelite (UKE04N07b):
This sample was collected from the eclogite-unit in the Besshi region, central Shikoku, which experienced the following successive metamorphic pressure-temperature path: prograde eclogite facies stage (1.7-1.9GPa/470-530 ℃) → decompression andhydration reaction stage → prograde epidote-amphibolite facies stage (up to 1.0-1.1GPa/600-630 ℃) (e.g., Kouketsu et al., 2014,
IAR, 263-280). The main matrix phases are garnet, biotite, phengite, epidote, albite, quartz, and graphite. The analyzed garnet grain is composed of inner and outer segments formed in the eclogite and epidote-amphibolite facies stages, respectively.
The inner segment (Alm67−73 Sps3−10 Prp4−10 Grs16−21 ) contains paragonite and quartz with high residual pressure (up to 0.80.9GPa). The outer segment, which has Mn-poorer and Ca-richer composition (Alm56−66 Sps0−10 Prp4−9 Grs26−36 ), mantles theinner segment in a compositional discontinuous change. The analyzed garnet grain seems to have grown as a single crystal,although it records a break in the growth period between the inner and outer segments. The EBSD data, however, implies thatthe garnet grain is composed of four domains with different crystallographic orientations, respectively, and misfits between these
domains are 40-59 degrees. Sets of quartz grains included in garnet on both sides of the domain boundaries sometimes sharethe same crystallographic orientation (misfits are less than1-6 degrees). The four domains are all composed of inner and outer
segments. Thus, the EPMA and EBSD data suggest that the garnet grain studied was formed through the following process:prograde formation of polycrystalline garnet during the eclogite facies stage → resorption around the garnet grain and along
the domain boundaries during exhumation → recrystallization of the outer segment and domain boundaries during the prograde
epidote-amphibolite facies stage.
Mogok metapelite (S22b):
This sample was collected from an upper-amphibolite and granulite facies region in the Mogok metamorphic belt, northwestof Mandalay, Myanmar. The main matrix phases are garnet, biotite, plagioclase (An43+/−4 ), K-feldspar, quartz, ilmenite, andgraphite. Sillimanite occurs as inclusions in garnet. The peak metamorphic conditions are estimated at about 0.8GPa/800 ℃(Maw Maw Win, personal communication, 2014). The garnet grain is separated into sub-grains of various sizes by resorption
during the exhumation and cooling stages. Each sub-grain is mostly homogeneous, and shows a gradual increase of Mn and Fe
and a decrease of Mg in the outermost margin (Alm60−70 Sps1−3 Prp20−33 Grs5−7 ). Aggregates of biotite, plagioclase, and quartz
fill the sub-grain boundaries, suggesting that the resorption stage progressed under the relatively high-temperature conditionsof 0.2-0.4GPa/500-600 ℃. The EBSD analysis shows that the sub-grains share the same crystallographic orientation (misfits
are less than 1-4 degrees) and show no rotation or deformation. These data suggest that the sample has not experienced any
dynamic deformation causing revolution of garnet grains after the resorption stage, and may have been exhumed under stationary
conditions from at least 6-12 km of depths.
Keywords: EBSD, EPMA, garnet, metamorphic history

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SMP43-02

Room:A03

Time:May 24 14:30-14:45

Metamorphism of dolomite-bearing eclogite in the Seba eclogitic basic schists, Sambagawa belt, central Shikoku, Japan
KABIR, Md Fazle1∗ ; TAKASU, Akira1 ; KISHIRA, Naohito1
1

Shimane University

The Sebadani area is located in the Sambagawa metamorphic belt, Besshi district, central Shikoku. The Sebadani metagabbromass and surrounding Seba basic schists (Seba eclogitic basic schists), and pelitic and siliceous schists occur in the area (Takasu
and Makino, 1980; Takasu, 1984). Eclogitic mineral assemblages are sporadically preserved in both the Sebadani metagabbromass and the Seba eclogitic basic schists (e.g. Takasu, 1984; Naohara and Aoya, 1997; Aoya, 2001). The Onodani eclogites
are preserved within the Seba eclogitic basic schists, and they have a complex metamorphic history, with two different eclogitic
metamorphic episodes (first eclogitic episode 530-590 o C/19-21 kbar; second eclogitic episode 630-680 o C/20-22 kbar) (Kabirand Takasu, 2010). The second eclogitic episode is similar to that of the Seba eclogitic basic schist of Aoya (2001) (610-640 o C
and 12-24 kbar). The pelitic schists intercalated within the Seba eclogitic basic schists also underwent eclogite facies metamorphism of 520-550 o C and c . 18 kbar (Zaw Win Ko et al ., 2005; Kouketsu et al ., 2010).
The eclogites exposed in the northeastern part of the Seba eclogitic basic schists consist mainly of garnet, epidote, amphibole (glaucophane, barroisite, taramite, Mg-taramite, Mg-katophorite, edinite), omphacite (X Jd 0.27-0.43), phengite (Si 6.5-7.1
pfu). Minor amounts of albite, carbonates (mostly dolomite and few calcite), rutile, titanite, biotite, chlorite and quartz. The
schistosity is defined by preferred orientation of phengite, amphibole and epidote. Garnets are almandine-rich in composition,with a compositional zoning of increasing almandine (X Alm 0.54-0.60), pyrope (X P rp 0.07-0.13) and decreasing spessartine(X Sps 0.10-0.03) from core to rim. They contain inclusions of epidote, omphacite (X Jd 0.27-0.41), dolomite, titanite and quartz.
They also contain symplectite aggregates of barroisite/Mg-katophorite and albite. Omphacites in the matrix are zoned from palegreen cores to colorless rims (X Jd 0.27-0.43) and contain inclusions of epidote, and they are partly replaced by amphibole(barroisite/magnesiokatophorite) + albite symplectite. Amphibole in the matrix are zoned, barroisite/Mg-katophorite cores toedenite rims. Dolomites in the matrix are up to 0.5 mm across and they contain inclusions of omphacite, amphibole (winchite,barroisite, magnesiokatophorite), epidote, albite, calcite, rutile and quartz. A chemical zoning in dolomite is well defined bya continuous core-to-rim Mg increasing and Fe and Mn decreasing. Dolomites have mutual contact with eclogitic minerals ofgarnet, omphacite, barroisitic amphibole and phengite in the matrix.
Texturally abundant dolomites in the Seba eclogitic basic schists exposed in the northeastern part suggest X CO2 fluid mightstable in the eclogitic facies conditions. Supposing the peak metamorphic conditions are the same as the second eclogitic metamorphic episode of the Onodani eclogites (630-680 o C and 20-22 kbar), considerable amounts of CO2 (X CO2 0.02-0.05) were
included in metamorphic fluid during the peak metamorphism.
Carbonates are major constituents of the altered oceanic crust and of the sedimentary materials entering the orogenic cycle.
Extensive experimental work on phase relationships in carbon-bearing systems reveals that carbonates are extremely stable up
to mantle pressures and the transfer of carbon to the mantle wedge at subduction zones is linked to the extent of decarbonation
and/or dissolution in aqueous fluids, or to the attainment of a carbonatitic solidus if a thermal relaxation occurs, e.g., upon subduction stagnation. Dolomite is a very common rock-forming mineral still waiting for further exploration and for innovative
applications to the reconstruction of dynamic processes in the Earth’s interior.

Keywords: Sambagawa metamorphic belt, eclogite, omphacite, dolomite, Seba basic schists

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SMP43-03

Room:A03

Time:May 24 14:45-15:00

Unit division and metamorphic conditions of the Northern Chichibu belt in central Shikoku
ENDO, Shunsuke1∗
1

GSJ-AIST

There is a general consensus that part of the Northern Chichibu belt underwent the Sanbagawa metamorphism (i.e., Cretaceous high P/T metamorphism). However, the Sanbagawa belt proper represents metamorphosed Late Cretaceous accretionary
complex, and thus tectonic implications of the Sanbagawa metamorphism in the Mikabu and N. Chichibu belts (Jurassic to Early
Cretaceous accretionary complex) must be reconsidered. For this purpose, it is important to unravel metamorphic history of each
unit within the N. Chichibu belt. The present study focuses on the Motoyama district of central Shikoku whereby primary structural relationship among the Sanbagawa, Mikabu and N. Chichibu belts are well preserved. I will report the results of geologicalmapping and petrological observation on ˜200 metabasite samples from the Mikabu and N. Chichibu belts in the Motoyama
district.
The N. Chichibu belt in the Motoyama district is composed of three units: the Kashiwagi, Kamiyoshida and Sumaizuku units,
following to the unit terminology of Matsuoka et al. (1998). The Kashiwagi unit shows an interfinger relationship with the
Mikabu ophiolitic unit, and they can be treated as the Mikabu-Kashiwagi unit. The Kamiyoshida unit overlays the Kashiwagi
unit and is overlain by the Sumaizuku unit by south-dipping boundaries.
The Mikabu-Kashiwagi unit was unambiguously affected by the Sanbagawa metamorphism, and the occurrence of metamorphic aragonite (Suzuki & Ishizuka, 1998) suggests peak metamorphic pressures of >0.7 GPa at 300 ℃. However, relatively low
jadeite content in alkali pyroxene coexisting with quartz, and amphibole compositions (magnesioriebeckite to actinolite) in thepresence of epidote suggest that the main stage of metamorphic recrystallization took place at lower pressure conditions.
Although the general trend of southward decrease in metamorphic grade has been inferred from the degree of metamorphic
recrystallization and deformation structures, quantitative metamorphic conditions of the Kamiyoshida and Sumaizuku units havenot been constrained. The Kamiyoshida unit is characterized by the occurrence of alkaline basaltic volcanic breccia with metamorphic minerals of magnesioriebeckite, calcite and stilpnomelane. Recently, jadeite has been discovered from quartz- andriebeckite-free metaigneous rocks in the Kamiyoshida unit. Decompression P-T path from 0.6-0.7 GPa, 300 ℃ to 0.4 GPa,210-260 ℃ has been derived from zoned sodic pyroxene with a jadeite core and an aegirine rim (Endo, 2015).
The Sumaizuku unit is characterized by the occurrence of prehnite-pumpellyite-epidote-quartz veins in massive basalt anddolerite. No alkali pyroxene or Na amphibole is found. These observations appear to imply the lack of high-P/T metamorphismon this unit. However, lawsonite-pumpellyite-quartz veins were newly discovered from this unit. Lawsonite in the vein locallyforms fine-scale Lws-Qz intergrowths with a prismatic outline, interpreted as pseudomorphs after laumontite. This texture suggests compression to >0.3 GPa at 200-250 ℃. It is likely that prehnite-bearing veins formed during a decompression stage.
The N. Chichibu belt has long-term history in the accretionary wedge. Apparently gradual Sanbagawa metamorphism of the
N. Chichibu belt may be related to exhumation-related metamorphism caused by underplating of new accretionary units in the
Cretaceous subduction zone.

Keywords: Northern Chichibu belt, low-grade metamorphism, pressure-temperature history, jadeite, lawsonite

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SMP43-04

Room:A03

Time:May 24 15:00-15:15

Study of geological structure and Paleogene kinematic history of the Fault system along
the MTL, the west Shikoku.
KUBOTA, Yasu’uchi1∗ ; TAKESHITA, Toru1
1

Hokkaido University

For the long time span of the Paleogene period, the fault movement along the MTL (Median Tectonic Line) has not been fully
clarified. Kubota and Takeshita (2008) inferred that Paleogene kinematic history of the MTL is divided to 63-58 Ma (Ichinokawa
phase) and 45-25 Ma (Pre-Tobe phase), the pre-Tobe phase defined by N-S directed shortening, which is responsible for a largescale folding of the Izumi Group and thrusting. The Okamura Fault, Kawakami Fault, and Iyo Fault distribute parallel to thetrend of the MTL, and northern part of the MTL in the west Shikoku. We study the geological structure and the deformation
structure of fault fracture zone for these faults.
The Okamura Fault has been recognized as active fault, and as right-lateral strike-slip faults (Ehime Prefecture 2001). And,
Aoya et al.(2013) reported the development of left-hand en echelon folds along the Okamura Fault, and this study the folds withwavelength of ˜500m of map scale and ˜10m of outcrop scale. The fault fracture zone develops in alternating beds of sandstone
and mudstone in the Izumi Group, The whole fault with ˜25m width has been consisted of foliated cataclasite zone with ˜15m
width. Left lateral slip and top to the south movement sense by the observation of foliation structure. Furthermore, cataclasite
zone with breccia and develops. It has been weakly foliation and shear band, partially remained bedding plane. The fault gouge30-45cm thick develops at southern margin of fault fracture zone with foliation and shear band has shown movement sense ofright lateral slip predominantly. Furthermore, in this study the deformation conditions had been discussed by the microscopeobservation of fault rocks. Further, the Kawakami and Iyo Fault had been the development of left-hand en echelon folds of
map-scale along the Fault, and fault fracture with cataclasite zone with slip sense of left lateral slip and top to the south.
It indicates that the faults had been formed with movement sense of left lateral slip and top to the south. This movement period
has been inferred the Paleogene according to the result of K-Ar age dating of the other faults in north of the MTL (Shibata et al.
1989), accordingly the movement is important data for clarify of Pre-Tobe phase of MTL.
Aoya, M.,Noda, A.,Mizuno, K., Mizukami, T., Miyachi, Y., Natsuura, H., Endo, S., Toshimitsu, S. and Aoki, M., 2013,
Geology of the Niihama district. Quadrangle Series, 1:50,000, Geological Survey of Japan, AIST, 181p.( in Japanese withEnglish abstract, 3P.);EHIME PREFECTURE 2001. Report on active faults in Ehime Prefecture, a summary-Investigation on
the MTL fault systems in the northwestern part of Ehime Prefecture, the northern border of the Ishizuchi Mt. and the southernborder of the Sanuki mountain range. pp. 47, Ehime Prefecture. (in Japanese).;Kubota, Y., Takeshita, T., 2008. Island Arc, vol.
17, p. 129-151.;SHIBATA K., NAKAJIMA T., SANGAWA A., UCHIUMI S. & AOYAMA H. 1989. K-Ar ages of fault gouges
from the Median Tectonic Line in Shikoku. Bulletin of the Geological Survey of Japan 40, 661-71 (in Japanese with English
abstract).
Keywords: Median Tectonic Line, Paleogene, kinematic history

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SMP43-05

Room:A03

Time:May 24 15:15-15:30

Spatio-temporal fluctuation of garnet and cracks
TORIUMI, Mitsuhiro1∗ ; FUKUYAMA, Mayuko2
1

JAMSTEC, 2 Akita Univ.

In the previous papers of JpGU meeting (1), we studied the grain size distribution patterns of metamorphic garnet and albite
in the banded metamorphic rocks with grain size grading. The average grain size increases with increasing distance across thebanding but normalized distribution patterns of the grain sizes within the individual bands are very similar with each other. The
banding structure should be derived from the unidirectional flow of metamorphic fluid with ionic diffusion, therefore suggestingthat the growth conditions changed across the bands. It follows that the distribution patterns of grain size of garnet and albite
display the summation of multiple simple distribution function such as Ostwald type or simply Gaussian, forming the lognormal
to power law type.
In the plate boundary region, the metamorphic rocks also experienced frequent generation of small cracks with fluid and thenoccupied by minerals. However, the mechanical conditions controlling the crack formation and propagation must be fluctuatedin terms of stresses, fluid pressure, temperature, and other parameters. Then, the observed frequency distribution of cracks filledwith fluid and also minerals should show the summation of many simple distribution functions and it is approximately lognormal
or power law. The fluctuation of the distribution patterns can be simply represented by drifts of mean and variant values withtime and space.
In this paper, we would like to discuss the rapid growth of grains and cracks at the case of over - the critical fluctuations bydrifts by means of stochastic resonance.
(1) Toriumi M. and M. Fukuyama, 2014, Grain size grading in the Liesegang banding of the plate boundary rocks. Proceedingof JpGU meeting 2014.

Keywords: size distribution, average and variance, spatio-temporal fluctuation, garnet, crack

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SMP43-06

Room:A03

Time:May 24 15:30-15:45

Timescale of metamorphsim and U-Pb ages of the Sanbagawa Metamorphic Complex
MIYAZAKI, Kazuhiro1∗ ; WAKITA, Koji2 ; DANHARA, Tohru3 ; IWANO, Hideki3 ; HIRATA, Takafumi4
1

GSJ AIST, 2 Yamaguchi Univ., 3 Kyoto FT, 4 Kyoto Univ.

Timescale of high-pressure metamorphism is not well known, but is crucial for solid mass transport and fluid flux in the
subduction zone. Here, we report timescale of high-pressure metamorphism for the Sanbagawa Metamorphic Complex in thearea of 1:200,000 geological map of Matsuyama, western Shikoku, Japan.
We collected psammitic and pelitic rocks from the Iyo and Ozu units of the Sanbagawa Metamorphic Complex, weakly
metamorphosed and non-metamorphosed Togano units of the southern Chichibu belt and non-metamorphosed Hanyama unit of
the Shimanto belt. The samples are used for zircon U-Pb and phengite K-Ar dating. Histogram of detrital zircon U-Pb ages
(H(tzrn ) ) of non-metamorphosed Togano unit is similar to H(tzrn ) of weakly metamorphosed Togano unit, and ages of theyoungest cluster of detrital zircon U-Pb ages (tzrn−yc ) are 174.7±1.9 Ma and 181.6±1.4 Ma, respectively. The H(tzrn ) s ofthe Hanyama unit, Ozu unit and upper part of the Iyo unit are identical to each other. The tzrn−yc s of the Hanyama and Ozu
units, and the upper part of the Iyo unit are 111.3±2.4 Ma, 110.3±4 Ma, and 111.2±2.9 Ma, respectively. This implies that
protolith of the Ozu unit and the upper part of the Iyo unit, both units are a part of the Sanbagawa Metamorphic Complex, is the
Hanyama unit of the Shimanto belt. On the other hand, the H(tzrn ) of the lower part of Iyo unit is quite different from those of
the above-mentioned 3 samples, and the tzrn−yc is 89±1.0 Ma. The phengite K-Ar ages (tphn )of the upper and lower parts of
the Iyo unit are 83.8±2.1 Ma and 86.9±2.2 Ma, respectively.
Maximum value of the timescale of high-pressure metamorphism can be defined by the difference between the tzrn−yc andthe tphn . The maximum value of the timescale for the upper part of the Iyo unit is 27 Myr, although that for the lower part of
the Iyo unit is 2 Myr. Metamorphic zircon rims have grown around detrital zircon grains of the sample from the upper part of
the Iyo unit suffered garnet zone metamorphism. Average of U-Pb ages of the metamorphic rims is 94.4±1.2 Ma. It is inferredthat the metamorphic zircon rim have grown at the peak temperature of the Sanbagawa metamorphism. Therefore, difference
between the U-Pb age of the metamorphic rim and the tphn should give minimum value of the timescale of the high-pressure
metamorphism. The value is 11 Myr.
Results show that the timescale of high-pressure metamorphism ranges from <2Myr to 11-27 Myr in the same unit. The upper
part of the Iyo unit suffered higher-grade metamorphism than the lower part of the Iyo unit. Numerical simulation of viscous
fluids shows that lower viscosity part of metamorphic rocks, in which metamorphic dehydration reaction actively takes place,will be elongated by shear deformation, and intrude into lower-grade metamorphic rocks coming newly in the metamorphic field
at deeper part of the subduction zone.

Keywords: Sanbagwa, metamorphism, metamorphic rock, zircon, U-Pb age

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SMP43-07

Room:A03

Time:May 24 15:45-16:00

Heat transportation recorded in the southern part of the Hidaka metamorphic belt
SAKATA, Ryugen1∗ ; OZAWA, Kazuhito1
1School of Science, The University of Tokyo

The earth’s continental crust has granitic upper crust and gabbroic lower crust with andesitic average composition, which wasdeveloped by various magmatic processes driven by thermal and material transportation through the sub-continental crust-mantle
boundary. There are three ways of heat transportation from the mantle to the crust with respective time and spatial scales: heat
conduction, solid-state flow of the mantle and the crust, and magmatism. This study aims to evaluate the relative importance of
these elemental mechanisms in an exhumed ancient arc crustal section, Hidaka metamorphic belt, Hokkaido, Japan.
Seismic wave tomography has revealed that the lithospheric mantle shows continuity to the shallow crustal level near the
Hidaka Main Thrust, where the Horoman peridotite complex is exposed, suggesting shallow uplift of the upper mantle (Kita etal., 2012). The Horoman peridotite complex is shown to underwent isothermal ascent with local heating up to <1GPa followedby rapid cooling (Ozawa, 2004), which could have heated the lower crust. Previous studies pointed out that basaltic magma
frozen as gabbroic bodies caused crustal partial melting and melt transportation on the basis of geological and geochemical data
(Osanai et al., 1991; Owada et al., 2003; Tagiri et al., 1988; Shimura et al, 2006). However, the role of mantle-derived heat andits transportation mechanism are still unclear.
Field survey was conducted along the Nikanbetsu river in the southern end of the Hidaka metamorphic belt. In the study
area, a small peridotite body called Nikanbetsu mass is exposed on the west and a large tonalite body on the east. Metamorphic
rocks are distributed in between them. The dominant lithology is banded garnet biotite gneiss intercalating <100m thick zone ofmafic metamorphic rocks, which consists of amphibolite and mafic granulite with many leucocratic veins and layers. The banded
garnet biotite gneiss shows remarkable foliation except for the one located near the Nikanbetsu mass.
We applied biotite-garnet Mg-Fe exchange thermometer (Ferry and Spear, 1978) for average chemical compositions of biotite
and garnet in the banded garnet biotite gneiss and leucocratic veins including garnet and biotite in the zone of mafic metamorphic
rocks. The results show a temperature decrease by ˜100 ℃ within ˜1km from the east of the peridotite mass to the west of thetonalite body with an exceptionally high value of 750 ℃ around the mafic metamorphic rocks. An application of biotite-garnet
thermometer to the core and the rim of the largest garnet and the average value of biotite gives >900 and ˜750 ℃, respectively.
The garnet zoning, occurrence of euhedral plagioclase with normal Na-Ca growth zoning, and weak foliation suggests partial
melting of the rock followed by rapid cooling. We also applied two-pyroxene thermometer (Lindslay, 1983) for orthopyroxene
coexisting with clinopyroxene in mafic metamorphic rocks with leucocratic veins. The calculated temperature ranges 1000˜700℃, which is due to a decrease in Wo content from the core to the rim suggesting rapid cooling.
Veins with various structure, morphology, and chemical composition suggest diverse processes during melt transportation, suchas brittle failure of the host rock, permeable leakage to and reaction with the host rock, and differentiation and crystallizationin the veins. Less differentiated veins may have records of a melt directly migrated from the deep crust, whereas differentiatedveins may have records of partial melting of pelitic gneiss.
We detected a thermal gradient of ˜100 ℃/km from the Nikanbetsu mass, suggesting the mass acted as a heat source to affectthe adjacent metamorphic rocks through heat conduction. We also detected a thermal gradient of À100 ℃/km around the zoneof mafic metamorphic rocks generated by magma transportation overlapping the much gentler thermal gradient.
Keywords: Hidaka metamorphic belt, pelitic gneiss, peridotite, heat source, partial melting

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SMP43-08

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Time:May 24 16:15-16:30

Aqueous fluid activity in the MCT zone and its role in High Himalayan leucogranite formation, Dhankuta, Eastern Nepal
KAWAKAMI, Tetsuo1∗ ; SAKAI, Harutaka1 ; SATO, Katsushi1
1

Graduate School of Science, Kyoto University

Significant aqueous fluid activity during the prograde to retrograde metamorphism in the footwall side of the Main Central
Thrust (MCT) is observed in the MCT zone around Dhankuta, Eastern Nepal. A term ’MCT zone’ in this study is used to represent the garnet to the kyanite zones developed in the footwall side of the MCT, where inverted metamorphism is observed. In the
MCT zone, several evidences of continuous fluid activities during metamorphism and their movement cutting the schistosity canbe observed.
The first and most important is the abundant quartz veins. They are found as sheared lenses in the MCT zone, and asymmetrictextures show top-to-the-S sense of shear indicating the deformation during the MCT movement. In the kyanite zone, quartz
veins contain mm- to cm-sized crystals of kyanite and minor plagioclase. Garnet and kyanite are coarse-grained only at thevicinity of the quartz veins, and in the staurolite and garnet zones as well, garnet tends to be coarser-grained around the quartz
veins. These observations suggest that the aqueous fluid infiltration that formed the quartz veins took place at the prograde topeak stage of the metamorphism in the MCT zone.
Meta-dolostone in the kyanite zone is also a good indicator of H2 O movement. It is commonly almost completely metamorphosed to tremolite schist. In such rocks, radiated aggregates of tremolite form a flat, oval-shaped aggregate are arranged
parallel to define the schistosity. Locally, such a tremolite arrangement discordantly cut the schistosity like a vein. In somemeta-dolostones, dolomites are still preserved, and veins of tremolite discordantly cut the schistosity as well as stem out parallelto the schistosity. These observations indicate that SiO2 -bearing aqueous fluid infiltrated into the dolostone and reacted withdolomite to form tremolite, calcite and CO2 along the vein and schistosity.
Tourmaline (Tur) is an important sink mineral of incompatible element B, and thus is often abundant in the environment wherewater-rock interaction took place. Unusually abundant Tur is locally found in metapelites of the MCT zone. It is localized inaluminous, muscovite-rich layers and can be formed through the input of external B into the appropriate whole-rock composition
for Tur growth. Such a B-bearing fluid infiltration continued from the prograde stage because garnet with prograde chemicalzoning includes abundant Tur crystals. B-bearing aqueous fluid infiltration continued in the post-peak stage as suggested by thepresence of Tur-rich vein cross-cutting the schistosity. In the kyanite zone, Tur veins are found cutting the schistosity and/or stemout parallel to the schistosity. In such samples, although the B-rich fluid infiltration postdates schistosity formation, staurolite
includes or partly overgrows the Tur crystals formed simultaneously with the Tur-rich vein, suggesting that the Tur vein wasformed under relatively high-temperature condition slightly after the peak metamorphism.
These aqueous fluids are likely to have moved upwards through the veins to the MCT and to the Higher Himalayan Crystallines(HHC) where P-T conditions above water-saturated solidus of muscovite-bearing pelitic rocks are estimated. In the hanging wallside of the MCT in the Dhankuta area, patches of Tur-bearing leucogranites are found in the migmatitic Grt-Ms-Bt gneisses. Oneof these leucogranite samples gave the U-Pb zircon age of 25.9 +/- 2.3 Ma, and other gneiss sample from the same area gave
U-Pb zircon age of ca. 17 Ma (Sakai et al. 2014). These ages are well consistent with the ages of High Himalayan leucogranites(HHL, Searle et al. 2010), which is commonly tourmaline-bearing, so segregation and extraction of these B-bearing melts is alikely process of the HHL formation. Therefore, input of aqueous fluids released from or passed through the MCT zone into the
HHC can be an important process for the formation of HHL (e.g., Le Fort et al., 1981).

Keywords: aqueous fluid, quartz veins, tourmaline, partial melting, leucogranite, Himalayas

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SMP43-09

Room:A03

Time:May 24 16:30-16:45

Garnet-hornblende vein formation and mass transfer by brine infiltration during upper
amphibolite facies metamorphism
HIGASHINO, Fumiko1∗ ; KAWAKAMI, Tetsuo1 ; TSUCHIYA, Noriyoshi2 ; SATISH-KUMAR, Madhusoodhan3 ;ISHIKAWA, Masahiro4 ; GRANTHAM, Geoffrey5
1

Kyoto University, 2 Tohoku University, 3 Niigata University, 4 Yokohama National University, 5 Council for Geoscience, South
AfricaThe importance of chloride brines during metamorphism is being increasingly recognized among various metamorphic fluids.
This is because chloride brines can coexist with a CO2 -rich fluid under the granulite facies condition (Heinrich, 2007), has
low a H2O , and acts as a powerful solvent not only for metals but also for various oxide and silicate minerals (Newton andManning, 2010; Tropper et al., 2011). Therefore, chloride brines would play an important role in mass transfer especially when
the pressure-temperature (P-T ) conditions of metamorphism are around the wet solidus, because XH2O in the brine can control
the melting/non-melting behavior of the rock (Aranovich et al., 2013).
In the Sør Rondane Mountains (SRM), East Antarctica where Late Proterozoic to Cambrian granulites are widely exposed,
Cl-rich hornblende and biotite in mafic gneisses are locally but widely distributed for ca. 200 km (Higashino et al., under review).
Formation mechanisms of these Cl-rich minerals can be different if the modes of occurrence of them are different. Therefore,
this study deals with the Cl-rich hornblende-bearing garnet-hornblende (Grt-Hbl) vein which discordantly cuts the gneissose
structure of a mafic gneiss in the Brattnipene area, and discuss the formation mechanism and mass transfer that accompanied thevein formation.
In the Grt-Hbl vein, Cl contents of hornblende and biotite, K content of hornblende, as well as the development of a Na-richer
rim of plagioclase decrease with a distance from the vein center. Whole-rock composition analyses as a function of distancefrom the vein show mass imbalances around the vein, suggesting that the Grt-Hbl vein was formed through an open systemprocess. Taking into account the possibility of partial melting, distribution of Cl between melt, aqueous fluid and minerals, andmicrostructural evidences of minerals, the Grt-Hbl vein was shown to have formed by the Cl-rich aqueous fluid infiltration. The
Cl-rich aqueous fluid was possibly NaCl brine because whole-rock analyses showed that Na was added to the vein comparedto the wall rock. We estimated that the Grt-Hbl vein was formed at ca. 700 ℃ and 0.70 GPa. This means that the NaCl brine
infiltrated into the wall rock at the early stage of retrograde metamorphism in this area. The whole-rock analyses and fractional
mass change values calculated according to Ague (2001) also revealed that the NaCl brine infiltration caused additions of Si, Ti,
Al, Fe, Mn, Mg, Ca, Na, Li, Sc, V, Cu, Zn, Ge, Sr, Y, Ba, Pb, Bi, Th and U to the wall rock. These added elements are similar
to those contained in previously reported brines which were present in mineral assemblages implying subduction metamorphism
and implying metal segregation in hydrothermal systems (e.g., Heinrich et al., 1992; Philippot and Selverstone, 1991). The
Grt-Hbl vein formed by the NaCl brine infiltration as shown in this study is a clear example that brine could move at least a few
meters, and was playing a role in mass transfer at ca. 700 ℃ and 0.70 GPa in the lower crust of the continental collision setting.
Keywords: NaCl brine, trace elements, metasomatism, continental collision, Sor Rondane Mountains, Antarctica

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SMP43-10

Room:A03

Time:May 24 16:45-17:00

Fluid activity during corona formation in ultramafic gneisses of Lutzow-Holm Complex,
East Antarctica
IKEDA, Takeshi1∗ ; SHIMADA, Asami1
1

Kyushu University

In Lutzow-Holm Complex, East Antarctica, it is common that symplectic intergrowth of spinel, orthopyroxene and plagioclase
occurs between garnet and hornblende in mafic to ultramafic gneisses. This reaction microstructure has suggested that the complex experienced decompression after peak of metamorphism. In contrast, this study found a corona that is composed of biotite
and plagioclase around garnet in ultramafic gneisses. This study describes the mode of occurrence and discusses its significance.
Garnet in the centre of the corona shows convavo-convex shape. Some isolated grains of garnet also occur that have colloded form. Biotite and plagioclase constituent of the corona are euhedral, in contrast to the common occurrence of symplectic
intergrowth of spinel, orthopyroxene and plagioclase. Chemical composition of these minerals show almost constant range irrespective of distance from the garnet. Grain size of biotite in the corona represents lognormal distribution. The corona has a bulk
composition equivalent to the sum of garnet and matrix plagioclase and biotite together with additional K2 O and H2 O.
These features suggest that K2 O-bearing H2 O fluid infiltrated during corona formation. Absence of the common symplectite
in spite of the presense of hornblende in the matrix implies the fluid infiltration preceded the reaction to form symplectite. The
shape and size distribution of corona minerals suggest that the corona minerals crystalized in a melt phase of which degree ofsupersaturation decreased with time. This study concludes that the complex experienced an infiltration of K2 O-bearing H2 O fluidat early stage after peak metamorphism, which caused partial melting and following crystallization with relative rapid coolingrate without significant annealing.

Keywords: corona, metamorphic fluid, Lutzow-Holm Complex

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SMP43-11

Room:A03

Time:May 24 17:00-17:15

Interplay of irreversible reactions and deformation: a case of hydrofracturing in the system rodingite - serpentinite
NISHIYAMA, Tadao1∗ ; YOSHIDA, Chisato1 ; MORI, Yasushi2 ; SHIGENO, Miki2
1

Graduate School of Science and Technology, Kumamoto University, 2 Kitakyushu Museum of Natural History and Human History
This paper examines hydrofracturing caused by reactions between rodingite and serpentinite during a regional metamorphism.
Hydrofracturing is driven by rapid increment of fluid pressure, and therefore will be likely to occur in the contact metamorphic
aureole due to rapid and irreversible reactions (Nishiyama, 1989). This paper aims to show the same type of hydrofracturing canoccur even in the regional metamorphic terrane.
Rodingites occurs ubiquitously in serpentinite from the Nomo metamorphic rocks, western Kyushu, which is a Cretaceous
accretionary complex of greenschist to epidote - amphibolite facies condition (Miyazaki and Nishiyama, 1989). Fukuyama et al.
(2014) made geochemical and geochronological studies on these rodingites, and gave U-Pb age of zircons from the rodingites as
108 - 105 Ma. This study classified the rodingites into two types depending on the occurrence and the rock texture: vein typeand dyke type. Mineralogy of both types of rodingites are almost the same, consisting of diopside, garnet (grandite), chlorite,
vesuvianite and titanite with rare occurrence of epidote and pumpellyite. Both vein-type and dyke-type rodingites are associatedwith reaction zones between serpentinite. Tremolite veins commonly develop from the reaction zone into serpentinite, representing hydrofracturing associated with the formation of the reaction zone. A conspicuous feature is that perovskite occurs in somereaction zones consisting mainly of diopside and chlorite, whereas titanite is common in rodingites. The reaction perovskite+ SiO2 = titanite indicates the condition poorer in SiO2 in the reaction zone. We investigated the reaction relation between
rodingites and serpentinites using the singular value decomposition (SVD) technique (Fisher, 1989). Constant solid volume isassumed during the formation of the reaction zone because of lack of ductile deformation in the reaction zone. The condition of
constant solid volume is incorporated into the SVD analysis as was firstly done by Yuguchi et al. (2015).
The seven component system CaO - SiO2 - Al2O3 -Fe2O3 - FeO - MgO - H2O is considered. Antigorite (serpentinite),diopside, garnet and chlorite (rodingite), and diopsideR and chloriteR (reaction zone) are considered. The superscript R denotes
minerals from the reaction zone, because they also occur in the rodingite but have different compositions. We took the following
strategy to find the reaction relation. First we tried to find reaction relations which hold the conservation of pseudoquarternarycomponents CaO - SiO2 - AF (Al2O3 + Fe2O3) - FM (FeO + MgO) among the mineral assemblage, but we got no reaction
relation. Next we omitted CaO as an inert component from the system, and consider reaction relations that hold conservationof pseudoternary SiO2 - AF - FM components, then we got three reactions cosuming CaO and evolving H2O. This strongly
suggests increment of fluid pressure associated with the progress of the reactions. We have further examined the system AF FM, having the following reactions:
1Serp + 22.71Di + 6.79Chl + 4.11CaO + 0.40SiO2 = 26.01DiR + 10.49ChlR + 1.43H2O
1Serp + 6.88Di + 3.39Grt + 3.74CaO + 3.32SiO2 = 19.46DiR + 3.24ChlR + 5.06H2O
1Serp + 3.24Grt + 0.26Chl + 3.61CaO + 2.74SiO2 = 12.25DiR + 3.51ChlR + 5.01H2O
1Serp + 0.34Di + 3.37Grt + 3.62CaO + 2.75SiO2 = 12.95DiR + 3.23ChlR + 5.14H2O
All of these reactions consumes SiO2 and CaO, and evolves H2O. This relation holds if we take any linear combination ofabove reactions. When we consider the perovskite formation from titanite in the reaction zone, reactions in the system AF-FM
are preferable, because SiO2 liberated by the titanite breakdown will be consumed by the above reactions in the system AF - FM.

Keywords: rodingite, serpentinite, hydrofracturing, irreversible reactions, singular value decomposition

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