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

1/1

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

1/1

SMP43-P01

Room:Convention Hall

Time:May 24 18:15-19:30

Construction of Raman geothermobarometer using aluminosilicate minerals in garnet porphyroblast
KOUKETSU, Yui1∗ ; TAGUCHI, Tomoki2
1

Geochemical research center, Graduate School of Science, The University of Tokyo, 2 Graduate School of Environmental Studies, Nagoya University
In recent years, the development of geothermobarometer applying Raman spectroscopy has been actively examined. Several
studies report the detection of new information of the metamorphic history that was difficult to obtain using conventional thermodynamic approaches. Especially, the “quartz Raman barometer” that can constrain the metamorphic condition using Raman peakshifts of quartz inclusions in garnet porphyroblasts show remarkable achievements in the Sambagawa belt. However, quartz transforms to coesite or β-quartz under the ultrahigh-pressure or high-temperature conditions, respectively, and applicable geologicalzone is limited. In the present study, we focused on aluminosilicate minerals, sillimanite and kyanite, in garnet porphyroblasts
and examined whether the metamorphic condition can constrain using these Raman spectra as with quartz Raman barometer.
First, we calculated the relation between the metamorphic P-T condition and residual pressure using the elastic moduli ofsillimanite, kyanite, and garnet. As a result, the residual pressure of sillimanite in garnet is independent of pressure condition,and depends on only temperature condition. On the other hand, the residual pressure of kyanite in garnet depends on pressure
condition rather than temperature condition. Next, we measured the natural samples of sillimanite and kyanite inclusions ingarnet porphyroblasts. Ultrahigh-temperature and high-pressure metamorphic rocks were measured; Garnet-Sillimanite gneisscollected from Rundvagshetta, Lutzow-Holm Complex in eastern Antarctica, and Kyanite-Quartz eclogite collected from Besshi
region, Sambagawa belt in central Shikoku. The Raman spectra of sillimanite inclusions in garnets of Garnet-Sillimanite gneissshow characteristic peaks at around 962 and 1182 cm−1 , and these peaks shift to high wavenumber side of around 4 to 5 cm−1 .
The Raman spectra of kyanite inclusions in garnets of Kyanite-Quartz eclogite show characteristic peaks at around 325 and 486
cm−1 , and these peaks shift to high wavenumber side of around 1 cm−1 .
The residual pressures were estimated to be 0.8 GPa for sillimanite and 0.3 GPa for kyanite using previously reported experimental data of aluminosilicate minerals. The residual pressure value of sillimanite inclusions in ultrahigh-temperature metamorphic rocks is converted to the metamorphic temperature of around 1000 ℃, and this result is consistent with previous studies. On
the other hand, the residual pressure of kyanite inclusions is calculated as negative value with increasing metamorphic pressure,but measured values in high-pressure metamorphic rocks of the Sambagawa belt are positive. The elastic modulus of kyanite
selected in the present study seems to have some problems, but it’s expected to be solved by improving the equation of state ofkyanite. These results indicate that Raman spectra of aluminosilicate minerals are useful to estimate metamorphic condition for
high- to ultrahigh-pressure and -temperature metamorphic rocks.
Keywords: Raman geothermobarometer, sillimanite, kyanite, garnet, high-temperature metamorphic rock, ultrahigh-pressure
metamorphic rock

1/1

SMP43-P02

Room:Convention Hall

Time:May 24 18:15-19:30

Metamorphic evolution of ultrahigh-pressure rock revealed by residual pressure of SiO2
inclusion in garnet
TAGUCHI, Tomoki1∗ ; ENAMI, Masaki2 ; KOUKETSU, Yui3
1

Graduate School of Environmental studies, Nagoya Univ., 2 Center for Chronological Research, Nagoya Univ., 3 Graduate Schoolof Science, The Univ. of Tokyo
Residual pressures are generated in metamorphic host minerals and sealed inclusions due to the difference of their physicalproperties. If the residual pressure recorded in a host mineral or inclusion could be quantitatively analyzed, it would provide
useful data for the estimating the crystallization conditions of the host phase and the metamorphic pressure-temperature (P-T)
history. Enami et al . (2007, AM, 1303-1315) proposed a method to estimate the residual pressure recorded in quartz inclusions
in garnet using a frequency shift in the Raman spectrum of quartz (quartz-Raman barometry). Kouketsu et al . (2014, AM, 433442) calculated the relationship between the residual pressure of quartz inclusions in garnet and the P-T conditions of the garnet
crystallization stage under α-quartz stable conditions and proposed a novel method to constrain the metamorphic P-T conditions.
As quartz-Raman barometry is independent of the thermodynamic model, this technique could be a powerful tool to determine theevolution of progressive metamorphism. However, the quartz-Raman barometry cannot be applied to ultrahigh-pressure (UHP)
metamorphic rocks formed under coesite-stable conditions, at least in principal. That said, quartz inclusions trapped by garnet
under quartz-stable conditions may preserve the information preserve the effects produced during the early stages of prograde
metamorphism. In this study, we examine the metamorphic evolution of a UHP metamorphic rock can deduced from the residualpressure of quartz inclusions in garnet.
The samples studied were collected from the Yangzhuang region of the Sulu UHP metamorphic belt, eastern China. Althoughcoesite has not been reported from in Yangzhuang samples, quartz-pseudomorph after coesite has been reported, and coesite
stability conditions of 2.7-3.5 GPa/660-830 ℃ are estimated for the peak metamorphic stage (Enami and Nagasaki, 1999, IAR,
459-474). These results suggest that the Yangzhuang samples might record the prograde P-T path from quartz to coesite stability.
Garnet grains in the Yangzhuang samples were divided into inner (Alm49−54 Prp16−28 Grs21−29 Sps1 , XM g = 0.22-0.36) andouter (Alm45−52 Prp18−31 Grs23−29 Sps1 , XM g = 0.29-0.41) segments, the boundary between the two defined by discontinuouschanges in grossular content. In the inner segment, the SiO2 phases are all α-quartz, and quartz-pseudomorphs after coesite andany radial cracks around the quartz inclusion are not observed. Residual pressures retained by the quartz inclusions systematicallyincreased with decreasing grossular content from the crystal center to the margin in the inner segment and indicated a value of
0.9 GPa. Metamorphic pressure, estimated by an inverse calculation based on the measured residual pressure, implies that thequartz inclusions were trapped at pressure conditions just below the quartz/coesite transition. In the outer segment, quartzpseudomorphs after coesite with radial cracks in the surrounding host garnet were observed. Coesite was identified for the firsttime in this region as an inclusion in a kyanite grain from the outer segment. The occurrence of coesite in the Yangzhuang
sample supports the P-T conditions previously estimated by conventional geothermobarometry. These results suggest that (1)quartz inclusions in the inner segment were trapped by garnet under quartz-stable conditions, avoided phase transition to coesite
at the peak metamorphic stage, and still preserved P-T information gained during the early stage of prograde metamorphism and(2) SiO2 inclusions in the outer segment were included as coesite; and most of these translated into quartz and released theirresidual pressure during exhumation. These results suggest that the quartz-Raman barometry is a useful tool for determining P-T
conditions at an early prograde stage even in the case of UHP metamorphism.
Keywords: quartz, residual pressure, quartz-Raman barometry, ultrahigh-pressure rock, Sulu belt

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SMP43-P03

Room:Convention Hall

Time:May 24 18:15-19:30

Examination of extrusion model of Himalayan metamorphic belt by study of exhumation
process of metamorphic nappe
SAKAI, Harutaka1∗ ; IWANO, Hideki2 ; DANHARA, Tohru2
1

Department of Geology, Kyoto University, 2 Kyoto Fission-Track Co. Ltd.

A ductile extrusion model explains that metamorphic core of the Himalaya, called the Higher Himalayan Crystallines (HHC),was originated by ductile channel flow of partially melted mid-crust from beneath the Tibetan plateau. No definite evidence ofthe model has yet been documented that shows the melted mid-crust extruded to form the HHC though many numerical models
were proposed and their simulation was performed.
We performed thermochronological study of the HHC nappe by means of zircon and apatite fission-track dating in order toexamine the extrusion model on the basis of emplacement and cooling history of the HHC nappe, which extensively covers theLesser Himalayan autochthon ranging in width of 80 to 120 km. As the results, we could have revealed the emplacement historyof the nappe, which has strong constraints on the extrusion model: the HHC of more than 10 km thick extruded on the groundat 15-14 Ma, and advanced to the SSW with the rate of 3-4 cm/yr retaining hot condition more than 300 ℃ . The nappe finallyterminated its movement at 11 Ma. Early Miocene foreland basin sediments on the top of the Lesser Himalayan autochthon haveundergone weak metamorphism after covering of hot nappe at 11-10 Ma. Both metamorphic nappe and the underlying forelandbasin sediments cooled down below 240 ℃ by 10 Ma and below 110 ℃ by 8 Ma. The metamorphic nappe laterally cooled
down toward the NNE from its front at the rate of ca. 1cm/yr, and root zone area of the nappe reached 240 ℃ by 4 Ma and 110℃ by 1 Ma.One more constraint is that estimated P-T condition is consistent from the nappe front to the root zone: maximum
temperature is around 750 ℃ and maximum pressure is 11-12kb.
Under these constraints, we examined the disposition of the HHC nappe before its extrusion, considering width of nappe as
80 km and inclination angle of metamorphic belt as 20 degree. After simple calculation of position of root zone of nappe under
12kb, it is concluded that root zone was located at 53 km to the north of the front of partially melted mid-crust of Tibet and seated
39 km in depth. It indicates that the HHC nappe must have been originated from partially melted mid-crust of Tibet.

Keywords: extrusion, nappe, fission-track dating, zircon, Himalayan metamorphic belt, Lesser Himalaya

1/1

SMP43-P04

Room:Convention Hall

Time:May 24 18:15-19:30

Late Cretaceous detrital zircon from the Eclogite unit of the Sanbagawa belt: implications
for exhumation tectonics
ENDO, Shunsuke1∗
1

GSJ-AIST

Eclogite facies rocks in the Sanbagawa belt can be classified into two types: 1) coarse-grained mafic-ultramafic complex
such as the Iratsu body, and 2) surrounding fine-grained mafic, pelitic and siliceous schists. The former type has poly-phasemetamorphic history with an early metamorphic stage in Early Cretaceous (c. 116 Ma), whereas the latter type has short-term
history of a Late Cretaceous (c. 90 Ma) subduction-exhumation cycle (Wallis et al. 2009 JMG; Endo et al. 2012 Lithos;
Aoya et al. 2013 Geology). However, there is another proposal that entire the high-grade Sanbagawa belt underwent peakmetamorphism at Early Cretaceous (120-110 Ma) followed by pervasive retrograde recrystallization during Late Cretaceous (9080 Ma)(Okamoto et al. 2004 Terra Nova; Aoki et al. 2009 Lithos; Itaya et al. 2011 JAES). To solve the controversial viewsin geochronology of the high-grade Sanbagawa belt, this study use detrital zircon geochronology to place constraints on thedepositional ages of eclogitic pelitic schists at the trench. Zircon grains were separated from two pelitic schist samples fromthe oligoclase-biotite and albite-biotite zones in the Besshi area of central Shikoku. The sample localities belong to the Eclogite
unit (Mouri & Enami 2008 Geology; Kouketsu & Enami 2010 IAR). Separated zircon grains exhibit oscillatory-zoned detritalcores and very thin metamorphic rims on CL images. LA-ICP-MS U-Pb dating of detrital zircon from the oligoclase-biotite andalbite-biotite zone samples yields weighted mean ages of the youngest group as 101.7±1.6 Ma (n=12, youngest grain: 94.4±4.8Ma) and 94.2±2.5 Ma (n=9, youngest grain: 87.6±4.6 Ma), respectively. Zircon rims from the two samples yield metamorphic
ages of 90.0±4.1 Ma (n=4) and 86.9±5.7 Ma (n=1), respectively. These results reconfirm Late Cretaceous accretionary complex
origin of the eclogite-facies region except for the coarse-grained mafic-ultramafic bodies. Late Cretaceous (c. 90 Ma) subductionof voluminous metasedimentary rocks to great depth (˜70 km) resulted in formation and subsequent buoyancy-driven rapid
exhumation of the Eclogite unit (consisting of the coarse- and fine-grained types) in the Sanbagawa belt.
Keywords: Sanbagawa belt, eclogite, pelitic schist, zircon, U-Pb age

1/1

SMP43-P05

Room:Convention Hall

Time:May 24 18:15-19:30

Metamorphic formation of arrested charnockite in Sri Lanka: significance of bulk composition and mass transformation
YAMASAKI, Yukiko1∗ ; IKEDA, Takeshi1 ; MOTOYOSHI, Yoichi2 ; HIROI, Yoshikuni3 ; PRAME, Bernard4 ;TSUNOGAE, Toshiaki5
1

Kyushu University, 2 National Institute of Polar Research, 3 Chiba University, 4 Geological Survey of Sri Lanka, 5 Tsukuba University

Arrested charnockite, that represents granulite facies mineral assemblage, occurs in several decimeters scale within amphibolite facies gneisses. The gneissosity in the gneiss becomes, in general, obscure toward center of charnockite. This suggeststhat the gneiss was metamorphosed into charnockite in local scale. The local charnockitization may be caused by fluid influx
and/or partial melting or difference of local bulk composition (e.g. Newton et al., 1980; Hiroi et al., 1990; Burton and O’Nions,
1990; Ravindra Kumar, 2004; Endo et al., 2012, 2013). This study described mode of occurrence of arrested charnockite in Sri
Lanka, and reveals cause of metamorphic formation of arrested charnockite. Mass transformation during charnockitization was
also discussed.
Arrested charnockite in Sri Lanka occurs as a number of patches in Hbl-Bt gneiss. The modal abundance of minerals in bothrocks indicates that the elements transformed between melanocratic and leucocratic parts. The elements constituent of Bt in
leucocratic part moves to melanocratic part, and those of Pl, Ksp and Qtz of melanocratic part, instead, move to leucocratic part.
The modal abundance of Bt of leucocratic part in Hbl-Bt gneiss decreases into the charnockite near the boundary. This suggeststhat mass transformation also be caused across the boundary.
The formation of Opx can be described by the following two reactions,Ti-rich Bt + Qtz = Ti-poor Bt + opx + Ilm + Ksp + H2 O andTi-rich Hbl + Qtzz = Ti-poor Hbl + Opx + Ilm + An + Ab + Ksp + H2 O.
These reactions suggest the possibility that the fluid influx and/or the partial melting produced arrested charnockite. However,similar chemical composition of apatite in both rocks implies that there is no positive evidence to support the above possibility.
The pseudosection modeling of mineral assemblage in NCKFMASHTO system shows that the local difference of bulk composition is responsible for the local charnockitization.

Keywords: Sri Lanka, Arrested charnockite, Hornblende-biotite gneiss, Mass transformation, Pseudosection

1/1

SMP43-P06

Room:Convention Hall

Time:May 24 18:15-19:30

Metamorphism of garnet amphibolite from the Neldy Formation, Makbal area in the Kyrgyz Northern Tien-Shan, Kyrgyzstan
KASYMBEKOV, Adil1∗ ; TAKASU, Akira1 ; KABIR, Md fazle1 ; BAKIROV, Apas2 ; SAKIEV, Kadyrbek2
1

Shimane University, Japan, 2 Institute of Geology, Academy of Science, Kyrgyz Republic

The Makbal Complex in the Kyrgyz Northern Tien-Shan is one of several HP/UHP metamorphic complexes in the Tianshan
orogenic belt located in the western segment of the CAOB. The metamorphic rocks exposed in the Makbal district are divided
into the Akdzhon and the Scharkyrak Groups based on their metamorphic conditions (Tagiri and Bakirov, 1990). The metamorphic sequence of the Akdzhon Group in the Northern Tien-Shan is devided into two contrasting metamorphic formation the
structurally lower Makbal Formation and the upper Neldy Formation. The Neldy Formation is mainly composed of pelitic schists(garnet chlorotoid-bearing schist, garnet-phengite schist) and chlorite-carbonate rocks along with minor metaquartzites, marbles
and amphibolites. Garnet amphibolites occur in the pelitic schists as lenses or blocks up to 50m across. Eclogites are preservedin the core of the garnet amphibolite bodies (Togonbaeva et al ., 2010).
The garnet amphibolites are crops out in the Neldy Formation is composed mainly of amphibole (Brs, Mhb, Act, Fprg, Fts,Ts), garnet and chlorite with small amounts of quartz, epidote and albite. Accessory minerals are biotite, paragonite, muscovite,
oligioclase, titanite, ilmenite and calcite. A schistosity is defined by preferred orientation of amphibole (Brs, Mhb), chlorite andbiotite. The garnets occur as porphyroblasts up to 1.4 mm in diameter, which show distinct compositional zoning, in which X Sps(0.22-0.04) decreases, X Alm (0.34-0.63) and X Grs (0.30-0.64) increase, and slightly increases X P rp (0.01-0.03) from the coreto the rim. The core of garnet contains inclusions of epidote, titanite, ilmenite, calcite and quartz. The rim of the garnet contains
inclusions of amphibole (Act, Mhb), chlorite (X M g 0.37-0.42), epidote (X P s 0.13-0.25), quartz and also contain polyphaseinclusions of muscovite + chlorite + epidote and chlorite + paragonite + epidote + olgioclase (An <18), although some of them
are connected outside with cracks. Box-shaped polyphase inclusions of paragonite+epidote±chlorite±muscovite±oligoclasesuggest a possibility of pseudomorphs after lawsonite. Porphyroblastic garnets are sometimes replaced by amphibole (Fprg, Ts),chlorite (X M g 0.46-0.52) and epidote (X P s 0.13-0.23) along rim and cracks. Amphiboles in the matrix show a zoning with
Mg-hornblende and actinolite (NaB 0.15-0.48 pfu) core, barroisite (NaB 0.50-0.63 pfu) mantle, and Mg-hornblende and tschermakite (NaB 0.18-0.46 pfu) rim. Amphiboles replacing the garnets have a zoning with barroisite (NaB 0.62-0.65 pfu) core andferrotschermakite, ferropargasite and Mg-hornblende (NaB 0.11-0.48 pfu) rim.
Based on the texture and mineral composition, two metamorphic events have been distinguished from the garnet amphibolites.
The prograde to peak stage of the first metamorphic event is characterized by core to rim of the porphyroblastic garnets andinclusion minerals therein (i.e. amphibole, epidote, chlorite, biotite, paragonite, titanite, ilmenite, calcite and quartz). The peakmetamorphic conditions are probably stable in the epidote-amphibolite facies. The retrograde stage is characterized by chlorite,
which replaces the porphyroblastic garnets. The prograde stage of the second metamorphic event is characterized by barroisite
core of the amphiboles and epidote replacing the garnets. The peak stage is characterized by fracture connected inclusions of
muscovite and oligoclase and tschermakite and ferropargasitic amphibole developed at the rim of the amphiboles replacing thegarnets, probably suffered amphibolite facies metamorphic conditions. The retrograde stage is characterized by albite and quartz
in the matrix.
The petrological study suggests that the garnet amphibolites probably suffered metamorphism events of (i) high-pressure epidote amphibolite facies and (ii) amphibolite facies. These metamorphic events are related to the tectonics of the oceanic platesubduction and subsequent continental collision.

Keywords: Garnet amphibolite, Makbal Complex, Neldy Formation, amphibolite facies, Kyrgyz Northern Tien-Shan

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SMP43-P07

Room:Convention Hall

Time:May 24 18:15-19:30

Geothermobarometry of the Mogok pelitic gneisses from the Sagaing area, Central Myanmar
Maw Maw Win1∗ ; ENAMI, Masaki2 ; KATO, Takenori2
1

Graduate School of Environmental Studies, 2 Center for Chronological Research

The amalgamation of continental blocks that drifted from the northeastern margin of Gondwanaland from Late Paleozoic
to Cenozoic formed the present landmass of eastern and southeastern Asia (e.g., Metcalfe, 2011). Myanmar is tectonicallydivided into eastern and western provinces by the Sagaing Fault, which is a 1200-km-long right-lateral strike-slip fault. The
eastern province consists of the Sibumasu (Shan-Thai) Block and the western province consists of the West Burma Block andthe Indo-Burma ranges. Both the Sibumasu and West Burma Blocks belong to the Sundaland. For the present study, samples
were collected from the Mogok metamorphic belt (MMB), which borders the eastern province along the western edge forming asigmoidal structure. It is 50 km wide and extends southwards from the eastern Himalayan syntaxis in the north to over 1500 km,
where it joins the high-grade metamorphic belts of northern Thailand.
Our study area is situated at the central part of the MMB, north of Sagaing, and is bound by two parallel N-S trending ridges
̶ Sagaing Ridge in the east and Minwun Ridge in the west. These two-parallel ridges are separated by the Sagaing fault valley,
which varies in width from 0.5 to 1 km. Metamorphic rocks exposed in this area include gneisses, marbles, calc-silicates, schists,
and amphibolites. Detailed mineralogical and petrological studies were conducted on garnet-biotite gneisses taken from theSagaing Ridge (S30a, S26, S22a & b, and S39 from north to south). CHIME monazite ages indicate three possible crystallization
events during the Paleogene period: 48.0 ± 2.4, 37.1 ± 0.8 and 27.6 ± 0.6 Ma (2-sigma level). The common mineral assemblages are garnet, biotite, plagioclase, and quartz with minor amounts of rutile, ilmenite, graphite, apatite, monazite, and zircon.
Additionally, the sample S30a contains prismatic sillimanite in the matrix. In sample S26, garnets contain fibrolite inclusions
and the matrix consists of prismatic sillimanite. The samples S22a and b contain fibrolite inclusions in garnet and K-feldspar
matrix. In the sample S39, spinel occurs as inclusions in garnet. Garnet grains are mostly homogeneous and exhibited high Mncontent and low Mg content locally at the grain boundaries: Alm63−67 Prp28−30 Sps3 Grs4−5 , Alm55−72 Prp20−38 Sps1−5 Grs4−5 ,Alm59−65 Prp30−35 Sps1−2 Grs5−7 , Alm58−63 Prp30−33 Sps1Grs4−6 , Alm62−72 Prp17−28 Sps1−3 Grs6−10 in samples S30a, S26,
S22a & b, and S39, respectively. Biotites were texturally categorized as (i) inclusions in garnet, (ii) isolated grains in matrix(iii) symplectitic aggregate with plagioclase around the garnet grains, and (iv) in veins through the garnet grains. Biotite inclusions and biotite content in matrix contain 5.6 wt% and 2.0 wt% of TiO2 and F, respectively. Spinel contains 4.9 wt% ZnO and
its XM g [=Mg/(Mg+Fe2+ )] and YAl [=Al/(Al+Fe3+ +Cr)] values are about 0.35 - 0.40 and 0.95, respectively.
The garnet-biotite geothermometer and two geobarometers characterized by garnet-biotite-plagioclase-quartz and garnetplagioclase-sillimanite-quartz equilibria were employed for the pressure/temperature (P/T) estimations of the samples collectedfrom Sagaing. Three groups of datasets were used for the calculations: (1) biotite and plagioclase inclusions and their garnet
host, (2) garnet core along with biotite and plagioclase matrix, and (3) symplectite and garnet rim. The estimated equilibrium
P/T conditions were 0.3 - 0.7GPa/580 - 700 ℃ and 0.6 - 0.9GPa/780 - 880 ℃ for the inclusion and matrix assemblages,
respectively. Symplectitic assemblages around the garnets exhibit equilibrium conditions at 0.2 - 0.3GPa/580 - 610 ℃. The
high TiO2 content of the biotite grains coexisting with rutile and/or ilmenite indicate a temperature of crystallization of 800 ℃,
when the Ti content of biotite is used as the geothermometer as proposed by Henry et al. (2005).

Keywords: CHIME monazite ages, P-T conditions, pelitic gneisses, Mogok metamorphic belt, Myanmar

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Petrological studies of spinel and quartz-bearing paragneiss from Zayetkwin-Onzon area,
central Myanmar
Ye Kyaw Thu1∗ ; ENAMI, Masaki2
1

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

The Mogok Metamorphic Belt (MMB) extends for over 1450 km, from the Andaman Sea to the eastern Himalayan syntaxis
along the western margin of the Shan-Thai block. This belt is mainly composed of high-grade metamorphic rocks, from upperamphibolite facies to granulite facies, and younger intrusions. Previous studies concluded that an assemblage of the high-grade
metamorphic rocks formed during a Paleogene regional metamorphic event that was caused by collision or underthrusting of
the Indian microcontinent with the Eurasian continent. The study area is situated in the middle part of the MMB, 100 km
north of Mandalay, and is mainly composed of paragneisses overlain by marbles and calc-silicate rocks. These lithologies are
intruded by quartz syenite, biotite-granite, and pegmatite. The marbles and calc-silicate rocks are mainly composed of diopside,
forsterite, phlogopite, spinel, graphite, and chondrodite, which record upper amphibolite facies equilibria. Paragneisses aremainly garnet-biotite gneisses with intercalations of biotite gneisses and leucogneisses, and show general NE - SW foliation.
Paragneiss samples studied are medium- to coarse-grained, well-banded, and show porphyroblastic and gneissose texture. Mostof them contain garnet, biotite, plagioclase, quartz, sillimanite, and K-feldspar with a minor amount of graphite, ilmenite andmonazite. Porphyroblastic garnet grains are 2 - 5 mm in diameter, and contain numerous inclusions of biotite, plagioclase, quartz,
and sillimanite. Biotite grains occur as four-generation phases, an inclusion phase in garnet, an isolated phase in the matrix, a
symplectitic aggregate around garnet, and a vein phase replacing cracks in the garnet.
Coexisting spinel and quartz are newly found in a garnet-biotite gneiss collected from the Zayetkwin-Onzon area. This sample
contains porphyroblastic garnet and cordierite, and biotite, plagioclase, quartz, and graphite in the matrix. Spinel and sillimanite
coexisting with quartz, plagioclase, biotite, and ilmenite occur only as inclusions in cordierite. Spinel is a Zn-poor spinelhercynite solid solution with XM g [= Mg/(Mg + Fe2+ )] = 0.34 - 0.35, YAl [=Al/(Al + Fe3+ )] = 0.97 - 0.99, TiO2 = 0.0 - 0.2
wt%, and ZnO = 1.8 - 2.3 wt%. The matrix assemblage gives pressure/temperature estimates of 0.7 - 0.8 GPa/780 - 840 ℃ using
a garnet-biotite geothermometer and garnet-biotite-plagioclase-quartz geobarometer. Biotite grains in the spinel-bearing sample
and associated paragneisses contain a distinctly high TiO2 content of up to 6.9 wt% (0.39 per formula unit for O = 11), which
probably progressed mainly because of the Ti♦R−2 substitution (R is the sum of divalent cations and ♦ represents vacancy inthe octahedral sites). The fluorine content is up to 2.0 wt%, and the chlorine content is less than 0.1 wt%. The Ti-rich biotite
suggests temperatures of 800 ℃ or higher if Ti is employed in the biotite geothermometer, as proposed by Henry et al. (2005).
The occurrence of a spinel-quartz-cordierite-sillimanite assemblage in the Zayetkwin-Onzon sample and the high-temperature
estimates of around 800 ℃ suggest granulite facies equilibrium of the Mogok metamorphic rocks. Orthopyroxene-bearing garnetgneisses were reported from the Mogok area, about 80 km NE of the Zayetkwin-Onzon area (Yonemura et al., 2013). These datasuggest wide distributions of granulite facies metamorphic rocks in the northern part of the MMB.

Keywords: spinel, paragneiss, P-T conditions, Mogok Metamorphic Belt, Myanmar

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Olivine megacrysts in the Horoman Peridotite Complex, Hokkaido, northern JapanMINAMIYAMA, Akari1∗ ; SODA, Yusuke1 ; HAMADA, Morihisa2 ; MORISHITA, Tomoaki1
1

Kanazawa University, 2 Japan Agency for Marine-Earth Science and Technology

Mineral grain size in the upper mantle affects many geological processes, such as mantle flow, fluid/melt migration and so on.
Olivine grain size in the upper mantle conditions is generally less than 1 cm (Ave Lallemant et al, 1980; Karato, 2011). However,olivine, which is larger than 1 cm in grain size (olivine megacryst hereafter), often occurs in peridotites. Therefore, understandingof the characteristic of olivine megacrysts is crucial to investigate a possibility of the formation of megacrysts in the upper mantle
conditions. In this study, peridotite samples with olivine magacrysts from the Horoman peridotite complex, Japan, are studied
by crystallographic orientation analysis, FT-IR analysis, EPMA. Especially, we focused on the change of crystal and subgrainboundary orientation by deformation
Peridotite samples are from MHL (Main Harzburgite-Lherzolite) suite of Takahashi (1991) in the Lower Zone of the Horomanperidotite complex (Niida, 1984). Olivine magacryst, which is often darker in color than fine-grained olivines, occurs subparallels to the foliation. Fine-grained layer shows porphyroclastic texture. Olivine megacryst and porphyroclast olivine in thefine-grained layer develop subgrain boundaries and include lamellae of chromian spinel, clinopyroxene and amphibole.
Slip systems of olivine [001](100) and [100](001) are estimated observed in the central part and the edge of olivine megacryst,
respectively, based on the U-stage measurements of subgrain boundaries and crystal orientations. Olivines in fine-grained layers
show A-type fabric resulting from the dominance of [100](010) slip system (Jung et al., 2006). Crystal orientation of fine-grained
olivines near megacryst show transitional characteristics in olivine fabric between the megacryst and the fine grains.
Structural hydroxyl species are not observed by FTIR in both olivine megacryst and olivine grains in fine-grained layer. There
are no differences in the Fo content and NiO wt% between olivine megacryst and fine grains by EPMA.
Presence of amphibole lamellae in olivine megacryst suggest that olivine megacryst had existed under wet condition. Finegrained olivine fabrics near megacryst and slip system of olivine megacryst edge suggest that olivine megacryst had existed whenA-type fabric of olivines forms in fine-grained layer. A-type fabric peridotite was reported in the Horoman peridotite complex
and interpreted that the A-type fabric formed during uplifting of the Horoman peridotite complex from the upper mantle to thecrust (Sawaguchi, 2004).
Consequently, olivine megacryst had existed under water-rich condition in the upper mantle followed by A-type fabric formation in the fine-grained layers during uplifting of the Horoman peridotite complex from the upper mantle.

Keywords: olivine megacrysts, Horoman peridotite, CPO

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SMP43-P10

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Elastic wave velocity and microstructures of Hida gneisses
KOIKE, Kanta1∗ ; WATANABE, Tohru1
1Department of Earth Sciences, University of Toyama

Seismic velocity is one of the most important sources of information about the Earth’s interior. For its proper interpretation,
we must have a thorough understanding of the dependence of seismic velocity on microstructural elements, including the modal
composition, the crystal preferred orientation (CPO), the grain shape, the spatial distribution of mineral phases, etc. For its
complexity, the influence of the spatial distribution of mineral phases has been poorly understood. In this study, we focus on alayered structure seen in gneisses. We are studying elastic wave velocities and microstructures in Hida gneisses.
Rock samples of Hida gneisses were collected at Kubusu River (Yatsuo, Toyama Pref.). A rectangular parallelpiped (the edge
length∼40 mm) was made from rock samples. Two faces are parallel to the foliation plane, and two faces perpendicular to theelongation direction. Preliminary velocity measurements were made at room conditions by the pulse transmission techniqueusing Pb(Zr, Ti)O3 transducers with the resonant frequency of 2 MHz. One compressional wave velocity and two shear wave
velocities were measured in each of three orthogonal directions. Two shear waves propagating in one direction oscillate inmutually orthogonal directions. The fastest compressional wave velocity (5.91 km/s) was observed in the direction parallel to theelongation, while the slowest (5.51 km/s) perpendicular to the foliation. When a shear wave propagated along the foliation plane,
it showed slightly higher velocity for oscillating along the foliation than for oscillating perpendicular to the foliation plane.
However, these velocity values cannot be compared with microstructures, because they must be affected by pores in rocksamples. We are now conducting velocity measurements under confining pressures of up to 180 MPa to remove the influence ofpores. The relationship between velocity under confining pressures and microstructures will be presented in our poster.

Keywords: gneiss, seismic velocity, anisotropy, microstructure, CPO

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SMP43-P11

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Relation of the Tsukiyoshi Fault and orientation distribution of microcracks in the borehole MIU-3 core in Mizunami CityOHTANI, Tomoyuki1∗ ; YOKOI, Kosuke1 ; OKAZAKI, Kazunari1 ; NISHIMURA, Yuki1 ; KOJIMA, Satoru1 ;KUBOSHIMA, Koji2 ; SASAO, Eiji2
1

Gifu Univ., 2 JAEAThe orientation measurement of microcracks was performed using the borehole core penetrating a fault to clarify the relation of
the microcrack distribution pattern near a fault. The studied borehole is MIU-3 drilled by Japan Atomic Energy Agency (JAEA).
The MIU-3 borehole is 1014 m length and penetrates the Tsukiyoshi fault at the depth of 707 m. The host rock of the Tsukiyoshi
Fault is the Late-Cretaceous Toki Granite. The Tsukiyoshi Fault trends E-W and dips about 70 degree to the south. The senseof shear is mainly reverse after the deposition of the Miocene Mizunami Group, although the evidence of normal and strike-slip
was also reported based on the texture analysis of the fault rocks (Niizato, 2003).
Seven granite samples from the MIU-3 borehole were used for this study. Sampling depths are 496 m, 623 m, 662 m, 698 m,
755 m, 851 m and 996 m. Four samples from the hanging wall are course-grained granite, and three samples from the footwall
are medium-grained granite. Attitude of microcracks developed in quartz grains in the granite are measured by the method of
Vollbrecht et al. (1991), which is performed under the optical microscope with the universal stage using three perpendicularthin sections. The target of measurement is healed and sealed microcracks. Open microcracks are excluded from measurement
because of the possibility of artificial formation during drilling.
From the occurrence of the microcracks, the formation of healed microcracks is probably prior to that of sealed microcracks.
From the orientation measurement, the preferred orientations of the healed microcracks are subhorizontal to gentle dip and N-S
strike with steep dip in all depths, and moderate dip except 496 m depth. As healed microcracks with moderate dip strikes E-W
in 623 m depth and N-S in 662 m depth, their preferred strikes are different among the samples. The preferred orientations of
the sealed microcracks are subhorizontal to gentle dip, N-S strike with steep dip and E-W to WNW-ESE strike with steep dip in
most depths. The concentration of N-S and E-W strikes with moderate dip is also recognized in the samples of 698 m and 755m,
which are located near the fault.
As described above, both healed and sealed microcracks with moderate dip appears near the fault. Moore and Lockner (1995)
revealed the microcrack pattern from an experimental study to generate shear fracture in laboratory. The microcracks that wereformed during the experiment are principally tensile cracks of which orientations reflect the local stress field: those formed prior
to the nucleation of the fault are roughly parallel to the cylinder axis, whereas those generated in the process zone make angles
averaging 30 degree to the overall fault strike (and 20 degree to the cylinder axis). The appearance of microcracks with moderate
dip near the Tsukiyoshi Fault shows that the preferred orientation of microcracks near the natural fault is also different from thatfar from the fault. The zone of the sealed microcracks with moderate dip is thinner than that of the healed microcracks. The
microscopic features show that the formation of the healed microcracks is prior to that of the sealed microcracks, so that the
thicker zone of the healed microcracks with moderate dip was developed in the intact granite at the earlier stage of the faulting
history, and thinner of the sealed microcracks was in the weak fault zone which has repeated rupturing and healing at the later.
Moore, D. E. and Lockner, D. A. (1995), Journal of Structural Geology, 17, 95-114.
Niizato, T. (2003), Abst. Japan Geosciences Union Meeting 2003, G018-P004.
Vollbrecht, A., Rust, A. and Weber, K. (1991), Journal of Structural Geology, 13, 787-799.
Keywords: microcracks, orientation distribution, Tsukiyoshi Fault, borehole MIU-3 core

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SMP43-P12

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Numerical model for subduction zone dynamics
ISHII, Kazuhiko1∗
1

Graduate School of Sceiences, Osaka Prefecture University

I present a numerical model for subduction zone dynamics. This model is composed of upper and lower continental crust, upper and lower oceanic crust, mantle lithosphere and asthenosphere, seawater and air. The model includes various processes suchas the subduction and deformation of oceanic plate, the deformation of mantle wedge and continental crust, the metamorphic
processes in the subducting oceanic crust (eclogitization and dehydration) and the mantle wedge (serpentinization), the reductionof effective frictional coefficient due to increase in fluid pressure, melting of peridotites, permeable flow of melt and aqueous
fluids, and temperature-dependent solid flow of mantle peridotites with water- and melt-induced weakening. The final goal ofthis modeling is to understand (1) the coupling depth and strength of the plate interfaces, (2) the mechanism for exhumation ofmetamorphic rocks, (3) the processes and conditions for the accretion and tectonic erosion, and (4) the deformation and stress
distribution in the arc crust.
Keywords: subduction zones, numerical model, strength of plate interfaces, exhumation of metamorphic rocks, crustal deformation and stress, accretion and tectonic erosion

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SMP43-P13

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Kondo theory for spherical shells tectonics
KIKUCHI, Kazuhei1∗ ; NAGAHAMA, Hiroyuki1
1

Department of earth science, Tohoku University

Buckling phenomenon in spherical shells of the lithosphere in subduction zone is studied by spherical shell tectonics. We
show a similar relationship between Batdorf parameter for length of the slab and normalized hydrostatic pressure (Kikuchi andNagahama, 2015). Length of the slab is approximately proportional to the length of the arc and thickness of the lithosphere.
However, spherical shells tectonics cannot give us the curvature with high order strain of buckling equation for the lithosphere.
On the other hand, Kondo (1955) used the concept of Riemannian geometry in yield and buckling of the curved material. So, by
Kondo theory, we derive a buckling equation of spherical shells for the curvature in the lithosphere.
Kikuchi, K. and H. Nagahama (2015) Batdorf parameter for the spherical shells tectonics, EGU General Assembly Conference
Geophysical Research Abstracts Vol. 17.
Kondo, K. (1955) Theory of Metaphorical Plates and Shells, RAAG Memoirs, Vol. I, (ed). K. Kondo, pp. 47- 60.
Keywords: Spherical shells tectonics, Kondo theory

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SMP43-P14

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Radiolarian fossils and crystal growth of metamorphic minerals in low-grade metamorphic rocks
ONO, Akira1∗
1

None

Radiolarian fossils are commonly found in weakly metamorphosed slates and siliceous rocks of the Atogura Nappe andChichibu Complex on the basis of the observation by using a loupe. Pelitic schists and Kashio mylonites from the Ryoke
belt of the Takato-Hase region were also examined to elucidate the existence of radiolarian fossils. The results were reported
before [1]. In the present article, radiolarian fossils in thin sections are described in relation to metamorphic grade and crystal
growth of minerals.
Radiolarian fossils of a siliceous slate of the Atogura Nappe
A siliceous slate in a chert block exposed in the Yatsu, Yorii town was studied. Figure A shows radiolarian fossils observed
under an optical microscope. Many white ring structures are filled with fine colored minerals. Ring structures become indistinct
when concentrations of internal colored minerals are low. The concentrations of colored minerals, chlorite and opaque minerals
are often low in the central parts of the ring structures. In this case a broad dark ring structure of fine-grained colored minerals
is formed. White and dark ring structures are considered as traces of radiolarians fossils. Similar textures are recognized inmetamorphic rocks formed under fairly high temperatures. An example is shown in Figure B which is a muscovite-biotite schist
exposed in Takato town, Ina city, Nagano Prefecture.
Metamorphic grade and radiolarian fossil
The Ryoke metamorphic belt of the Takato-Shiojiri area is divided into three zones; chlorite-biotite zone, biotite zone andsillimanite zone. Metamorphic temperature increases in this order. Radiolarian fossils were confirmed under an optical microscope in the chlorite-biotite zone, but it was unable to recognize radiolarian fossils in the biotite and sillimanite zones. Recently,
however, many small white rings (Figure B) were recognized by using a loupe and usb microscope for biotite schists near the sillimanite isograd. The ring structures are traces of radiolarian fossils which are preserved in spite of the existence of large biotite,muscovite, plagioclase and quartz. The preservation of the ring structures is mainly due to the existence of very small carbonaceous materials within the ring structures (Figure C). The small grain sizes of the carbonaceous materials suggest the slow ratesof crystal growth and transportation of carbonaceous materials under relatively low metamorphic temperatures. Carbonaceous
materials of pelitic Ryoke gneisses, however, considerably grow up in the sillimanite zone of the Takato area. Therefore it isalmost impossible to recognize relics of radiolarian fossils in the sillimanite zone.
Mineral growth and radiolarian fossil
A large metamorphic tectonic block is distributed in the northern part of the Kiroko greenstone melange of the Atogura Nappe.
Psammitic metamorphic rocks are common in the tectonic block. Many small ring structures of approximately 40-100µm in
diameter are recognized by using a loupe for a siliceous psammitic rock. The siliceous rock is mainly composed of quartz andsmall amounts of fine brown minerals which are not identified yet. Quartz crystals larger than 100µm are common. The finebrown minerals are distributed forming circular structures and broad dark ring structures within quartz crystals according to theobservation by using an optical microscope. Fine brown minerals were included in quartz crystals during the crystal growth ofquartz crystals. Shapes of radiolarian fossils were partly preserved in spite of high-temperature metamorphism.
[1] A. Ono, 2012, Abs. Geol. Soc. Japan, Meeting, R4-P-24, p.228.

Keywords: Radiolarian fossil, Metamorphic temperature, Recrystallization

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Metamorphic P-T evolution of the eclogitic pelitic schists in the Sambagawa belt, central
Shikoku, Japan
TAKASU, Akira1∗ ; KABIR, M.f.1
1

Shimane University

The Seba area in the Sambagawa metamorphic belt is located in the central part of the Besshi district, central Shikoku, and it iscomposed of the Sebadani metagabbro mass and surrounding Seba basic schists. Eclogitic mineral assemblages are sporadicallypreserved in both the Sebadani metagabbro and the Seba basic schists (Takasu, 1984; Aoya, 2001). Pelitic schists are intercalated
within the Seba eclogitic basic schists, and they consist mainly of quartz, phengite, chlorite and garnet minor amounts of epidote, amphiboles (sodic, sodic-calcic and calcic-amphibole), omphacite, albite, biotite and carbonaceous matter. Rutile, titanite,
calcite, chloritoid, K-feldspar, tourmaline, apatite and zircon are occasionally present as accessories. Amphiboles in the matrix
sporadically grow oblique to the main schistosity. These amphiboles are strongly zoned, with glaucophane core, barroisite/Mgkatophorite mantle and edenite/actinolite rim.
Three distinct metamorphic events are identified from the pelitic schists. These are (i) precursor metamorphic event, (ii) firsthigh-pressure metamorphic event, and (iii) second high-pressure metamorphic event. The precursor metamorphic event (i) is
defined by calcic amphibole (pargasite, Mg-hornblende and taramite) and muscovite (Si 6.05-6.13 pfu) inclusions in the core of
the garnets. These minerals suggest relatively high-temperature metamorphic conditions such as high-temperature portions of
the epidote amphibolite or the amphibolite facies. The prograde path of the first high-pressure metamorphic event (ii) is from theepidote?blueschist facies, passing through the epidote?amphibolite facies, to reach peak metamorphic conditions in the eclogite
facies. P?T pseudosection (MnNCKFMASHO model system) was calculated and compositional isopleths suggested the peakmetamorphic conditions of 640?660 ℃ and 21?23 kbar. The prograde metamorphic conditions were also obtained as 460 ℃ and
8 kbar.
Aoya (2001) suggested a prograde path of the Seba eclogitic basic schists that garnet and omphacite growth mainly occurred
during the decompression stage after the pressure peak. During garnet cores growing pressure and temperature increased, andduring garnet rim and omphacite growing temperature continuously increased whereas pressure decreased. According to thepresent study both omphacite and garnet grew under the conditions of temperature and pressure increasing. During decompression amphibole+albite±less-jadeite omphacite symplectites developed after omphacite, suggesting both pressure and temperature
decreased into epidote amphibolite facies conditions after the peak metamorphism. The second high-pressure metamorphic event(iii) is defined by distinctly zoned amphiboles suggesting a prograde crystallization of the amphiboles from blueschist facies to
epidote amphibolite facies conditions, and it is probably correlated with the metamorphism of non-eclogitic schists surrounding
the eclogite bodies (Aoya, 2001; Kabir and Takasu, 2010).
References
Aoya M. (2001) P?T?D path of eclogite from the Sambagawa belt deduced from combination of petrological and microstructural analyses. Journal of Petrology 42, 1225-1248.
Kabir M.F. and Takasu A. (2010) Evidence for multiple burial-partial exhumation cycles from the Onodani eclogites in the
Sambagawa metamorphic belt, central Shikoku, Japan. Journal of Metamorphic Geology 28, 873-893.
Takasu A. (1984) Prograde and retrograde eclogites in the Sambagawa Metamorphic Belt, Besshi district, Japan. Journal of
Petrology 25, 619?643.

Keywords: Sambagawa, eclogite, P-T pseudosection, garnet, Besshi, Seba

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SMP43-P16

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Electron Probe Microanalyser and Laser Raman analyses of reaction textures in breccia
veins, Tokunoshima, SW JapanSADAKANE, Takeyoshi1∗ ; YAMAMOTO, Hiroshi1 ; UEDA, Shuro2 ; TERABAYASHI, Masaru3
1

Graduate School of Science and Engineering Kagoshima University, 2 Dia Consultants CO.,Ltd, 3 Department of Safety Systems
Construction Engineering, Kagawa University
Dark colored veins have been recognized in metamorphic body of Akirigami river in the western Tokunoshima, the Amami
Islands (Ueda et al ., 2012). This Dark colored veins are filled with breccia, microbreccia and fine-grained matrix derived fromfault activity. Those matrices include circular opaque minerals which show bright rims and very dark cores under reflection
microscope. The element concentration mapping by Electron Probe Microanalyser shows that bright rims consist mostly of Ti
and dark cores are Ca-rich. Laser Raman Spectroscopic mapping differentiates that the small anatase grains (Ti rim) enclosing
calcite (Ca ‐ rich core). The circular opaque minerals are not found from host rocks (peltic ‐ psammitc schists) and titaniteis the only Ca ‐ Ti bearing mineral phase in the host rocks. These observations indicate that the titanite-breakdown reaction
operated during or shortly after injection of ultracataclastic veins under temperatures around 200 ℃ (e.g., Chakhmouradian,2004) or higher.
Chakhmouradian, Anton R., 2004, American Mineralogist, 89, 1752-1762.
Ueda, S, Yamamoto, H, Terabayashi, M, 2012, the 119th Annual Meeting of theGeological Society of Japan.

Keywords: Laser Raman Spectroscopy, Ryukyu arc, Tokunoshima, Kagoshima Prefecture

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