SMP43-P01

Japan Geoscience Union Meeting 2016

Phase equilibrium modeling and P-T evolution of high-P/T Sambagawa Metamorphic rocks in
Kanto Mountains, Central Japan*Yusuke Kuribara1, Toshiaki Tsunogae2
1.Graduate School of Life and Environmental Sciences, University of Tsukuba , 2.Faculty of Life andEnvironmental Sciences, University of Tsukuba
Sambagawa metamorphic belt, which extends about 800 km from east (Kanto Mountains) to west (East
Kyushu Island), is regarded as an excellent example of high-P/T type metamorphic belt located at
the northernmost edge of the Outer Zone of southwest Japan. The high-pressure rocks were probably
formed by complex subduction-accretion processes in western Pacific region during Cretaceous(Isozaki and Itaya, 1990). Numerous petrological, geochronological and structural studies have been
done on the belt particularly focusing on P-T evolution and tectonics, but they are mainly on thewestern part of the belt in Shikoku Island which metamorphic grade is higher than the eastern part.
In contrast, only very few studies have been done on the Sambagawa metamorphic rocks in Kanto
Mountains which corresponds to the eastern end of the belt. This study reports new petrological and
P-T data of the Sambagawa pelitic schists from Kanto Mountains and compare the results with thoseof Shikoku Island. This is the first report of quantitative P-T path estimated for Sambagawa schistfrom this region based on phase equilibria modeling approach.
The studied pelitic schist is dark grayish, very fine- to fine-grained, well foliated, and contains
phengite, hematite, chlorite, biotite, epidote, garnet, quartz, and plagioclase. Plagioclase isporphyroblastic and occurs as spots. Phengite defines major foliation of the rock. Garnet is finegrained (less than 30 microns) and almandine-rich in composition. It’s spessartine component
decreased from core to rim, showing normal zoning. Although biotite could be a stable assemblage,
it was probably completely replaced by chlorite due to later hydration event. Metamorphic P-T
evolution of the rocks was evaluated using THERIAK-DOMINO ver.16.10.2012 software based on thechemical system Na2O-CaO-K2O-FeO- MgO-Al2O3-SiO2-H2O-TiO2 (NCKFMASHT). The peak P-T condition of therock was inferred from the stability field of the inferred peak assemblage (plagioclase + ilmenite+ garnet + phengite + biotite + zoisite + quartz) as 580-630oC and 9-13 kbar, which is nearlyconsistent with the results of garnet-phengite geothermometry applied to the same sample. The event
was followed by decompressional cooling toward a retrograde stage of 370-440oC and 1.4-5.5 kbar as
inferred from a retrograde assemblage of plagioclase + ilmenite + chlorite + garnet + phengite +biotite + quartz. The peak condition is, however, about 100oC higher than the available P-T data of
Fe-Mn rich nodule from the studied region (7-12 kbar and 460-540oC; Hirajima, 1995), but nearlyconsistent with the condition of Oligoclase-Biotite zone of the Sambagawa schists from Central
Shikoku Island. The results of this study therefore suggest that the Sambagawa metamorphic belt in
Kanto Mountains might have experienced a similar metamorphism with the belt in Shikoku. The
Sambagawa metamorphic rocks in the two areas probably subducted to a similar depth and underwent
similar high-pressure metamorphism.
Keywords: Sambagawa metamorphic belt, Phase Equilibria Modering, Pelitic schist, Peak P-T
conditions, Kanto mountains©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P01 -SMP43-P02

Japan Geoscience Union Meeting 2016

Geology of the Atogura Nappe of the Yorii-Ogawa district in the northeastern Kanto
Mountains*Akira Ono

Geology of the Atogura Nappe was studied in the Yorii-Ogawa district. The surveyed area is situatedin the northeastern part of the Sanbagawa belt and is characterized by the wide distribution of
Atogura (Atokura) Nappe. The results are shown in the attached figure. The geological map is partly
based on the maps published before by the present writer [1, 2].
1) The Atogura thrusts were reported or supposed at locations a –e. In other localities the Atogura
Nappe is in contact with pre-Miocene geological units by high-angle faults. Miocene deposits
unconformably overlie the Atogura Nappe. Clasts of Ryoke metamorphic and granitic rocks are common
in the Miocene deposits. The provenance of the clasts is the Ryoke Nappe tectonically superposed on
the Atogura Nappe. The W-E geological section is figured on the basis of the assumption that the
Ogawa Miocene sedimentary basin is a small half-graben.
2) The Atogura Nappe consists of various geological units. Large geological units are elongated in
E-W directions. The large geological units are in contact with each other by high-angle faults.
Many small tectonic blocks are distributed along the high-angle faults. Fault gouges andmetasomatic rocks are accompanied by the high-angle faults. Prehnite is not found near thehigh-angle faults although prehnite is common in the Atogura Nappe.
3) Tectonic blocks of mid-Cretaceous Higo-Abukuma granitic and metamorphic rocks were found at many
locations. Common rock-types are psammitic, calcareous and mafic metamorphic rocks. The metamorphic
rocks exhibit variable metamorphic grades of amphibolite facies. Fusulinacean fossils are observedin some outcrops, but sillimanite- K-feldspar gneisses are exposed in a few outcrops.
4) Metamorphic rocks near the Kinshozan quartz diorite are usually described as Permian hornfels.
It is however uncertain that all the metamorphic rocks are hornfels and were metamorphosed at
Permian. Hence, the name of Shimonita metamorphic rocks is used here instead of Permian hornfels.
5) Acidic tuff and Higo-Abukuma granitic and metamorphic rocks are shown in the southernmost partof the Atogura Nappe. These rocks are members of the Kiroko greenstone mélange which mainly
consists of Kiroko metamorphic rocks, serpentinite and various kinds of tectonic blocks.
6) Deformation and alteration are not observed at the boundary zone between tectonic blocks andKiroko metamorphic rocks although prehnite veins and quartz-albite veins were formed in some
tectonic blocks. The tectonic blocks did not suffer the Kiroko metamorphism.
7) K-Ar whole-rock dating for the Kiroko metamorphic rock was carried out on a greenstone
containing many small pelitic lenses. Secondary recrystallization of constituent minerals cannot be
detected for the studied sample. The dating result is 57.4Ma. The result suggests that the Kiroko
high-pressure type regional metamorphism occurred in early Paleogene.
8) Highly altered massive tonalites are exposed in the Tochimoto, Kibe district. They are tectonic
blocks of the Kiroko greenstone mélange. As fine epidote and felsic minerals are recrystallized
abundantly in the altered tonalites, it is often difficult to detect initial plutonic textures.
K-feldspar is very small in amount. Hence, the tonalites appear to be plagiogranites.
9) Yorii acidic rocks mainly consist of early Paleogene pyroclastic rocks and porphylitic granites.
These acidic rocks are believed to be formed very far from the subduction zone where serpentinites
and the high-pressure-type Kiroko metamorphic rocks were exhumed. Hence, a considerable Nappetectonics is supposed to take place before the formation of the Atogura Nappe.
[1] A. Ono, 2008, Abs. Japan Geosci. Union Meeting, G119-P002.
[2] A. Ono, 2013, Abs. Japan Geosci. Union Meeting, SGL41-P04.

©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P02 -SMP43-P02

Japan Geoscience Union Meeting 2016

Keywords: Atogura Nappe, Greenstone melange, Tectonic block, K-Ar dating, Nappe tectonics©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P02 -SMP43-P03

Japan Geoscience Union Meeting 2016

Petrological and geochronological study of orthogneiss from the Tromsø Nappe in
Scandinavian Caledonides*Yasuhiro Monta1, Takao Hirajima1, Hideyuki Obayashi1, Takafumi Hirata1
1.Department of Geology and Mineralogy, Graduate School of Science, Kyoto University
Orthogneiss is the predominant lithotype in ultra-high pressure (UHP) terranes in the world but it
generally consists of low pressure metamorphic minerals of mainly amphibolite facies. However,extensive petrological studies succeeded to find several signs of UHP minerals from the county
gneiss, and hence, most of the country gneiss shared the UHP metamorphism. The Scandinavian
Caledonides were formed by collision between Baltica and Laurentia Cratons during Ordovician to
Devonian, and are composed of several allochthons which have juxtaposed onto Precambrian cover.
Evidences of UHP metamorphism are found from the Western Gneiss Region (WGR) in Lower Allochthon(Hacker et al., 2001), the Seve Nappe in Middle Allochthon (Majka et al., 2014), and the Tromsø
Nappe in Uppermost Allochthon (Janák et al., 2013). In the WGR, UHP evidences occur widely in the
NW part, however in the Seve and Tromsø Nappes UHP evidences are sporadic, so the areal extent of
UHP metamorphism remains unclear. The Tromsø Nappe is mainly composed of eclogites, gneisses,
schists and marbles. Krogh et al. (1990) estimated the peak P-T conditions of country gneisses andpelitic schists as 670-700 C and 1.5-1.7GPa during D1 stage. After that, Janák et al. (2012)
estimated the UHP metamorphic conditions of 720-800 C and 3.2-3.5 GPa using pseudosection analysis
and conventional geothermobarometry for eclogite in Tromsdalstind. Janák et al. (2013) finallyfound microdiamond from garnet-rich carbonate-bearing gneiss in Tønsvika. However, UHP evidence has
not been reported from the country gneiss and schists. In this study, we report mineral paragenesis
and zircon U-Pb age of orthogneiss hosting UHP eclogites in the Tromsø Nappe. Studied sample wascollected from large blocks of orthogneiss distributing on the ridge around N69°26’0”, E19°9’33”(garnet-muscovite schist unit: Zwaan et al., 1998). Main constituent minerals are garnet,
muscovite, plagioclase, alkali-feldspar, and quartz with minor amounts of kyanite, rutile, biotite,
hornblende, epidote, chlorite, ilmenite, and zircon. The alignments of mica and plagioclase
porphyroclast characterize the gneissose structure. The LA-ICP-MS U-Pb dating of zircon inorthogneiss gives the majority of the concordant ages between 470 and 420 Ma, and minor inherited
ages of about 1500-1300 Ma and 800 Ma. The weighted mean 206Pb/238U age (± 2σ) of rim of zircon is454.2 ±5.2 Ma (n=21). This age is consistent with metamorphic age of Tønsvika eclogites (452.1 ±1.7
Ma; Corfu et al., 2003) within error. Most of garnets with a few 10 to 100 μm diameter have Fe-richcompositions (Alm0.68-0.74Prp0.11-0.18Grs0.10-0.18Sps0.01). They include quartz, rutile, zircon, and rarekyanite as primary inclusions. Some of them have Ca-rich rim (Alm0.63-0.68Prp0.09-0.11Grs0.20-0.26Sps0.01)
with a distinct chemical gap to the core. In some plagioclase, Ca-content decreases from the core
(An=0.26-0.33) to the rim (An=0.17-0.28). Biotite commonly replaces rim of muscovite or occur as
fine laths of a few 10 μm diameter, suggesting the secondary origin, while muscovite is relatively
coarse grained {100-500μm diameter; Si=6.13-6.38 (O=22), TiO2=0.17-1.34, XFe=0.28-0.50}. GASP
geobarometer and Grt-Ms Fe/Mg exchange geothermometer give 450-500 °C and 1.1-1.2 GPa for the
core-core pairs of garnet and plagioclase and 530-570 °C and 1.6-1.7 GPa for the rim-rim pairs ofgarnet and plagioclase, indicating the pressure increase is necessary for the rim formation. P
condition estimated from the rim-rim pairs is consistent with D1 stage (1.5-1.7 GPa) of the country
gneiss in the same nappe (Krogh et al., 1990), but T condition obtained by the same pair issignificantly lower than that of D1, which may be caused by the modification of muscovitecomposition.

©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P03 -SMP43-P03

Japan Geoscience Union Meeting 2016

Keywords: UHP terrane, Caledonides, orthogneiss, Ziricn U-Pb dating©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P03 -SMP43-P04

Japan Geoscience Union Meeting 2016

Deformation microstructures of metamorphic mafic rocks close to the boundary to the
Tanzawa plutonic complex*Tomoki Mizuno1, Katsuyoshi Michibayashi2
1.Graduate School of Science, Shizuoka University, 2.Institute of Geosciences, Shizuoka University
The purpose of this study is to understand microstructural development of metamorphosed mafic rocks
close to Tanzawa plutonic complex. Samples are collected from the southern region within 1 km fromthe boundary with Tanzawa plutonic complex. The mafic rocks consist mainly of amphibole andplagioclase with secondary minerals such as quartz and clinopyroxene. For microstructural analyses,
we used well polished thin sections cutting perpendicular to the foliation and parallel to thelineation (i.e. XZ plane). Under a microscope, amphibole grains are well elongated. Plagioclase
grains are polygonal and partly dynamically recrystallized.
Crystal-preferred orientations (CPOs) of both amphibole and plagioclase were measured. Amphibole
CPOs commonly showed intense (100) [001] patterns. Plagioclase CPOs showed strong (001) [100]patterns in relativity monomineralic domains. In polymineralic domains where plagioclase andamphibole were coexisted, plagioclase CPOs showed remarkably weak (010)[001], (100)[001] patterns,
or random patterns. Crystal orientations maps in amphibole dominant domains show that subgrains
occur in amphibole grains. Some grain boundaries between amphibole grains are oriented
perpendicular to the foliation. Cao et al. (2010 , JSG) showed that these grain boundaries wereformed by dislocation wall resulting from dislocation creep. Therefore, we suggest that dislocation
creep was dominant in deformation mechanism for amphibole. In polymineralic domains of amphibole
and plagioclase, amphibole CPOs showed (100)[001] pattern, whereas plagioclase CPOs showed random
patterns, where grain sizes are smaller than those with intense CPOs patterns in both amphibole andplagioclase. It suggests that grain-size sensitive creep may become dominant, as decreasing grain
sizes of plagioclase due to the mixing with amphibole during deformation. As a consequence, thedeformation mechanism could be switched from dislocation creep to grain-size sensitive creep during
deformation in the metamorphic mafic rocks.
Keywords: dislocation creep, Tanzawa , CPO©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P04 -SMP43-P05

Japan Geoscience Union Meeting 2016

Inconsistency between SEM image and Crystal orientation data obtained by SEM-EBSD systems*Akira Miyake1, Aki Takigawa1,3, Yohei Igami1, Shugo Ohi2, Ryuta Nakamura1, Akira Tsuchiyama1
1.Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, 2.Faculty ofeducation, Shiga university, 3.The Hakubi Center for Advanced Research, Kyoto University
Recently, a scanning electron microscope (SEM) equipped with electron back-scattering diffraction(EBSD) have become a strong and common tool to obtain the crystallographic information fromminerals and various materials. SEM-EBSD can evaluate not only crystal orientations of individual
crystals but also alignment property of crystal orientations in a wide area. For obtaining the
crystallographic information by an SEM-EBSD system, we need a software program to detect andanalyze EBSP (electron back-scattering diffraction pattern), which is generally developed by
EBSD-detector venders or some laboratories.
El-Dasher et al. (2009) reported the possible inconsistencies between SEM images and crystal
orientations obtained by SEM-EBSD systems. However, this crucial problem has not been widely known.
In this presentation, we will report the result of experimental tests about this problem performedin our laboratory.
We carried out a series of experiments using our SEM-EBSD system consisting of JEM-7001F (JEOL) andHKL channel 5 (Oxford instruments). Single crystals of Si, corundum, and quartz with known crystal
planes were used in the experiments. The crystal plane was set with its typical axis slightly
tilted for easier analysis and discussion. Trigonal or orthorhombic crystals are more suitable forthis test than that with the cubic crystals in order to avoid the confusion by equivalentorientations.
We confirmed the systematic inconsistency between SEM images and crystal orientations obtained by
HKL channel 5. The orientation shown by HKL channel 5 was just consistent with the SEM image
rotated by 180 degrees around the sample normal direction. The same inconsistency may occur in many
SEM-EBSD systems in other laboratories. We will also report the cases for other combinations of
SEMs and EBSD-detectors.
Keywords: SEM-EBSD, crystal orientation©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P05 -SMP43-P06

Japan Geoscience Union Meeting 2016

Elastic wave velocity and microstructures of amphibolite gneisses
Kanta Koike2, Hiroto Endo4, Katsuyoshi Michibayashi3, *Tohru Watanabe1
1.Gradudate School of Science and Engineering, University of Toyama, 2.Faculty of Science,
University of Toyama, 3.Institute of Geosciences, Shizuoka University, 4.Graduate School of
Science, Shizuoka University
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 preferredorientation (CPO), the grain shape, the spatial distribution of mineral phases, etc. We havestudied seismic velocities and microstructures of amphibole gneisses. Rock samples of amphibole
gneisses were collected at Momose River (Yatsuo, Toyama Pref.). They are mainly composed of quartz(34-36vol.%), plagioclase (18-27vol.%) and hornblende (34-46vol.%). Quartz and plagioclase crystals
are almost randomly oriented, while c-axes of hornblende crystals are strongly aligned parallel tothe lineation and a-axes perpendicular to the foliation. A rectangular parallelpiped (the edge
length ~ 40 mm) was made from rock samples for ultrasonic velocity measurements. Two faces areparallel to the foliation plane, and two faces perpendicular to the elongation direction. Velocity
measurements were made under confining pressures of up to 180 MPa at room temperature. The pulse
transmission technique was employed by using Pb(Zr, Ti)O3 transducers with the central frequency of
2 MHz. Under the confining pressure of 180 MPa, the fastest compressional wave velocity wasobserved in the direction parallel to the lineation, and the slowest one in the direction
perpendicular to the foliation. Velocities calculated with the VRH averaging scheme reasonably
reproduce the measured velocities. The anisotropy in velocity is caused by the CPO of hornblende
crystals, though the anisotropy due to aligned hornblende crystals is largely weakened by almost
randomly oriented quartz and plagioclase crystals. The influence of the grain shape of hornblendeon the anisotropy in velocity will also be discussed in our poster.
Keywords: amphibolite, gneiss, anisotropy, elastic wave velocity, crystal preferred orientation©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P06 -SMP43-P07

Japan Geoscience Union Meeting 2016

Olivine megacrysts in mantle peridotites*Akari Minamiyama1, Yusuke Soda1, Akihiro Tamura1, Shoji Arai1, Tomoaki Morishita1
1.Earth and Environmental Sciences Coarse, School of Natural System,Kanazawa University
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 lessthan 1 cm (Ave Lallemant et al, 1980; Karato, 2011). However, olivines, which are larger than 1 cm
in grain size (olivine megacryst hereafter), often occur in peridotites. Therefore, understandingof the conditions of olivine megacrysts is critical to understand the upper mantle processes. In
this study, peridotite samples with olivine magacrysts from the Horoman peridotite complex, Japan,
and the Western Gneiss Region of Norway (WGR) are studied by crystallographic orientation analysis,
ICP-MS and EPMA.
One peridotite sample is from MHL (Main Harzburgite-Lherzolite) suite in the Lower Zone of the
Horoman peridotite complex. Olivine magacryst occurs subparallels to the foliation and looks darker
than fine-grained olivines. Fine-giraned layer show porphyroclastic texture. Olivine megacryst andporphyroclast olivine in fine-grained layer developed subgrain boundaries and include lamellae ofchromian spinel, clinopyroxene and amphibole.
Slip systems of olivine [001](100) and [100](001) are observed in the central part and the edge ofolivine megacryst respectively, based on the U-stage measurements of subgrain boundaries andcrystal orientations. Olivines in fine-grained layers show A-type fabric resulting from thedominance of [100](010) slip system (Jung et al., 2006). A-type fabric peridotite was reported in
the Horoman peridotite complex and interpreted as the A-type fabric formed during uplifting of the
Horoman peridotite complex from the upper mantle to the crust (Sawaguchi, 2004). Fine-grained
olivine fabric near megacryst and slip system of olivine megacryst edge suggest that olivine
megacryst would exist before the formation of A-type fabric in fine-grained layer.
Original olivine megacryst compositions before exsolution might relatively higher in Al, Cr, Na, Ti
and Ca contents than fine-grained olivine. Adittion to this, presence of amphibole lamellae inolivine megacryst suggest that olivine megacryst was either originally hydrous olivine or hydrated
after exsolution of unhydrous silicate minerals such as clinopyroxne. In the presentation, we will
present results of chemical and structural observations of olivine megacrysts from the Horoman and
WGR.

©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P07 -SMP43-P08

Japan Geoscience Union Meeting 2016

Metasomatic reactions at crust-mantle boundary in subduction zone: an example fromTomisato ultramafic body in the Tomisato area, central shikoku, Japan*Ryosuke Oyanagi1, Atsushi Okamoto1, Masaoki Uno1, Noriyoshi Tsuchiya1
1.graduate school of environmental studies, tohoku university
A large amont of element transfer could occur during the metamorphism along the subduction zone.
Serpentinite, which was formed via hydration and/or metasomatic reaction of mantle peridotite,
controls slab slip behavior (e.g., Peacock and Hyndman, 1999; Mizukami et al., 2014).
Si-metasomatism of mantle peridotite is discussed in MgO-SiO2-H2O system (Manning, 1995, 1997).
However, detailed analytical studies of on-land exposures of peridotites metasomatized by
subduction-zone fluids are limited (e.g., Peacock, 1987; King et al., 2003). Therefore, thepossible relationships between devolatilization reactions and related fluid and mass transfer are
not clear.
In this study, we studied metasomatic reaction around a ultramafic body in the high pressure
Sanbagwa metamorphic belt in Tomisato area, central Shikoku, Japan. Hereafter, we call thisTomisato ultramafic body. This ultramafic body is ~20m in size, and it is located at the garnetzone. The Tomisato ultramafic body is almost fully serpentinized (i.e., no olivine relict) andbrucite is not observed. A lack of pyroxene relicts suggests the protolith of the Tomisato
ultramafic body is dunite. Within the body, serpentinite has block-in-matrix or brecciated texture
with fragments of fine-grained antigorite in coarse-grained matrix antigorite.
At north of the Tomisato ultramafic body, ultramafic rocks contact with basic rocks and veins of
tremolite and talc was observed. On the other hand, at south of the Tomisato ultramafic body,
ultramafic rocks contact with pelitic schist and vein of talc was observed. At the north boundary,reaction zone of Tremoite + Talc + Chlorite / Antigorite + Talc / Antigorite was observed.
Tremolite and Talc zones were localized at ~80 cm and ~110cm from the contact, respectively. In
contrast, at the south boundary, reaction zone of Antigorite + Talc / Antigorite was observed. Talc
zone was observed ~80 cm from the boundary. Both boundaries are composed mainly of antigorite
clasts embedded in a talc and/or tremolite veins, and matrix antigorite is not associated withthese veins. These observations suggest that Si-metasomatic reaction occurred after block
antigorite formation, and the mineralogy depends on the contact crustal rocks. We will discuss thetimings of the Tomisato ultramafic body was taken in Sanbagawa metamorphic belt, metasomatic
reaction, mass transport between crustal and mantle material, and possibility of hydrofracturing.
Keywords: crust-mantle boundary, metasomatism, serpentinite, Sanbagawa metamorphic belt, pelitic
schist, basic schist©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P08 -SMP43-P09

Japan Geoscience Union Meeting 2016

Estimation of Minimum Fe-Mg content for Plagioclase-Cordierite replacement*Noboru Furukawa1, Yoshikuni Hiroi1, Yoichi Motoyoshi2
1.Graduate School of Science Chiba University, 2.National Institute of Polar Research
Conventional studies suggested that chemical compositions of metamorphic fluid consist of C-H-O-S
system, and other elements such as Na, Ca, and Si are not transported with the fluid. Theseelements, however, do dissolve in the fluid in some instances, as exemplified by quartz-filled vein
and as demonstrated by various studies of fluid inclusions. For example, in tonalitic granulite in
Sri Lanka, plagioclase was substituted locally by cordierite.
We attempt to obtain the essential data about the element transport within the metamorphic fluid,by experimentally reproducing the chemical reactions that are responsible for element inflow andoutflow. They include the solubility of mineral to the fluid, the chemical composition andconcentration of the fluid, and their change in the pressure and temperature conditions. Byutilizing this information, we should be able to limit the range of the chemical composition andconcentration, and the P-T values.
This study has determined the minimum ratio of Mg/(Fe+Mg) and the minimum concentration of (Mg,
Fe)Cl2 for the plagioclase-cordierite replacement, by utilizing hydrothermal experiments. Because
the ample amount of tonalitic-granulite specimen in Sri Lanka for this experiment is not available,
we have used powdered specimens of anorthosite from the Natal region, South Africa, and chloride
solution of Mg and Fe. These materials were sealed into gold capsule with or without CO2 and were
held at a pressure of 100 MPa and a temperature of 600 ℃ in autoclave for 130-400 hours. We haveobtained the following results:
The minimum concentration of MgCl2 for the plagioclase-cordierite replacement is approximately 0.08
mol/kg.
The minimum ratio of Mg/(Fe+Mg) for the plagioclase-cordierite replacement is approximately 0.2.
These minimum values derived above are not influenced by the presence of CO2.
It is estimated that the Mg/(Fe+Mg) ratio of the fluid responsible for the plagioclase-cordierite
replacement in the tornalitic granulite in Sri Lanka is approximately 0.2.

©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P09 -SMP43-P10

Japan Geoscience Union Meeting 2016

Formation of Corona around Corundum in the Lützow-Holm Complex, East Antarctica*Yuki Mori1, Takeshi Ikeda2
1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University,
2.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University
Corona structures preserve both reactant and product minerals, which gives us information of its
formation process including mass transformation. We investigated a corona structure incorundum-bearing ultramafic rocks in Akarui Point of the Lützow-Holm Complex, East Antarctica. The
studied samples are composed mainly of calcium amphibole, plagioclase and corundum with minor
biotite, spinel and sapphirine. The corundum grains are surrounded by the corona composed ofspinel, sapphirine and plagioclase. These minerals are regularly arranged from corundum to thematrix. In the corona, cracks in spinel usually continue to sapphirine, but never extend further
into plagioclase nor continue to corundum. We consider that the corona was produced by reaction
between corundum and matrix calcium amphibole. Mass-balance in the CaO-MgO-Al2O3-SiO2-H2O systemprovides the following equation: corundum + spinel + calcium amphibole = sapphirine + plagioclase +H2O-fluid. This equation shows spinel as reactant, which is inconsistent with the microstructure.
This suggests that the corona was formed in an open system. We employed following additional
assumption based on the microstructure. Continuity of cracks in spinel and sapphirine is indicativeof former single phase. Provided that sapphirine was formerly spinel, corundum changed to spinel by
supply of MgO from calcium amphibole. The remaining components in calcium amphibole may produce
plagioclase, and excess SiO2 would be released. After this reaction, significant amount of spinel
was transformed to sapphirine due to supply of SiO2. Alternatively provided that spinel wasformerly sapphirine, corundum and calcium amphibole produced sapphirine and plagioclase. Similar to
the former case, this reaction also released SiO2. After that, sapphirine was partially transformed
to spinel and released SiO2. The net reaction based on both two cases is corundum + calcium
amphibole = spinel + sapphirine + plagioclase + H2O-fluid + SiO2. This open-system reaction
suggests that decrease of SiO2-activity triggered the corona-forming reaction.
Keywords: corona, reaction microstructure, corundum, Lützow-Holm Complex©2016. Japan Geoscience Union. All Right Reserved.

- SMP43-P10 -SMP43-P11

Japan Geoscience Union Meeting 2016

Petrological studies of high-grade paragneisses from Onzon and Thabeikkyin areas, central
Myanmar*Thu YE Kyaw1, Masaki Enami2
1.Graduate School of Environmental Studies, Nagoya University, 2.Institute for Space-EarthEnvironmental Research, Nagoya University
The sigmoidal and elongated Mogok metamorphic belt extends for 1500 km from the Andaman Sea in thesouth to the eastern Himalayan syntaxis in the north and has variable metamorphic conditions
throughout the belt. It lies at the western margin of Shan-Thai block and comprises high-grade
metasedimentary rocks and metaigneous rocks with subduction-related granitoid intrusions. Previous
radiometric studies, based on U-Th-Pb and Ar-Ar dating, concluded that an assembly of thesehigh-grade metamorphic rocks was formed during Paleogene to early Neogene event that was caused by
the collision of remnants of Gondwanaland with the Eurasian continent and subsequent underthrusting
and collision of Indian plate with Eurasian plate. The metamorphic grade of the Mogok metamorphic
rocks reaches upper amphibolite facies and granulite facies in some places.
Samples were collected from the middle segment of the Mogok belt, ~100 km north of the Mandalay
region, where the geology is dominated by high-grade paragneisses overlain by various types ofmarbles and calc-silicate rocks trending toward the NE-SW and ENE-WSW directions. The marbles occur
in massive or scattered blocks and are medium- to coarse-grained, showing polycrystalline texture.
Their common mineral assemblage contains diopside, forsterite, chondrodite, garnet, phlogopite, andgraphite, suggesting metamorphic grade up to upper amphibolite facies. In places, the marbles are
intruded by biotite micro-granite, syenite, and pegmatite.
The paragneisses are medium- to coarse-grained and show well-banded gneissose texture defined byelongated layers of biotite, feldspar, and quartz. The matrix of the paragneisses is mainlycomposed of garnet, cordierite, biotite, plagioclase, K-feldspar, quartz, ilmenite, and rutile.
Graphite and monazite are common accessory minerals. Sillimanite mainly occurs as inclusions withingarnet. Most porphyroblastic garnet grains (> 3 mm) show retrograde zoning with increasing
almandine {Xalm = Fe / (Ca + Mg + Fe + Mn) = 0.53 –0.58} and decreasing pyrope contents {Xpyr = Mg /(Ca + Mg + Fe + Mn) = 0.37 –0.43} towards the rim. Grossular (Xgros = 0.03) and spessartine (Xsps =0.02) contents are low and fairly constant. Cordierite grains {XMg = Mg / (Mg + Fe) = 0.68–0.83}
occur as the matrix phase, inclusions in garnet, and as pseudomorphs after garnet. Using
garnet–biotite geothermometer and garnet–biotite–plagioclase–quartz (GBPQ) geobarometer, the matrix
assemblage estimates pressures (P) and temperature (T) conditions of 0.5–0.8 GPa and 750–870°C.
Biotite grains occur as an isolated phase in the matrix, inclusions in garnet, and a symplectic
phase around garnet. Fluorine and chlorine contents are up to 0.6 wt. % and less than 0.1 wt. %,respectively. The Ti-in biotite geothermometer suggests 800° C or higher-temperature for theTi-rich isolated biotite grains. Zr-in-rutile geothermometer gives temperature estimates of 750–935°C (at P = 0.8 GPa), which are consistent with those estimated using a conventional
geothermometer.
The samples analyzed in this study demonstrate that metamorphic conditions in the Mogok Belt
reached 800°C or higher, implying wide distribution of granulite facies metamorphic rocks in the
middle segment of the Mogok metamorphic belt.
Keywords: paragneiss, granulite, metamorphic conditions, Mogok metamorphic rocks, Myanmar©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Deformation environment of the mylonite zone to the west of Shirakami Mountains, Northeast
Japan*Shunsuke Watanuki1, Hidenori Saka2, Takuto Kanai1, Hideo Takagi1
1.Waseda University, 2.New Energy and Industrial Technology Development Organization
The N-S striking ductile shear zone (Takahashi, 2001; Fujimoto and Yamamoto, 2010; Sakai et al.,2012) along the western coastline of southernmost Aomori Prefecture is developed in the Cretaceous
Shirakamidake granitic body (Katada and Osawa, 1964). This mylonite zone is called Shirakamidake
mylonite zone (Fujimoto and Yamamoto, 2010). In this presentation, (1) detailed occurrence andmicrostructures are described, and (2) deformation environment is estimated on the basis of
crystallographic preferred orientation (CPO) pattern of recrystallized quartz grains in the
mylonitic rocks.
(1) The mylonite zone extends N-S for ~2 km with a width of ~600 m. The center of the mylonite zone
with a width of ~200 m consists of ultramylonite and locally cataclasite overprinting
ultramylonite. The foliation of the mylonites strikes mainly N-S and dips 40-80° to the east. The
lineation plunges at 30-70° to the northeast. Asymmetric deformation microstructures (e.g.
asymmetric pressure shadow) indicate sinistral normal shear as Takahashi (2001) already described.
(2) We measured CPO and grain size of recrystallized quartz in two transects across the mylonite
zone using SEM-EBSD method. As a result, most fine-grained ultramylonite in the central part of the
mylonite zone in both transects show a random CPO pattern and mean grain size of recrystallized
quartz is about 8.5 μm. Other samples apart from central part of the mylonite zone show a type I
crossed girdles and Y-maximum CPO pattern and mean grain size of recrystallized quartz is 13.1-198
μm. The former suggests that the diffusion creep was the dominant deformation mechanism from mean
grain size of recrystallized quartz and CPO pattern (Passchier and Trouw, 2005), whereas the lattersuggests that the dislocation creep took place at 350-450 °C which is switching temperature fromtype I crossed girdles to Y-maximum (Takeshita, 1996). From mean grain size of the mostfine-grained sample with clear CPO pattern and estimated deformation temperature (about 400 °C),the differential stress is about 87 MPa using paleo-piezometer (Stipp and Tullis, 2003), and thestrain rate is about 10-10 s-1 using flow law for dislocation creep (Hirth et al, 2001). On theother hand, the diffusion creep took place locally about 70 m thick ultramylonite zone after theformation of entire mylonite zone deformed by dislocation creep, because differential stress (<10MPa) is estimated during diffusion creep using flow laws for dislocation creep and diffusion creep(Coble, 1963). The mylonite zone was therefore deformed by dislocation creep at about 400 °C, andsubsequently diffusion creep took place locally in a center of the shear zone. At shallower depth,
brittle deformation took place to form cataclasite locally.
References
Coble, R. L., 1963, Jour. Appl. Phys., 34, 1679-1682.
Fujimoto, Y. and Yamamoto, M., 2010, Earth Sci. (Chikyu Kagaku), 64, 127-144.
Hirth, G., Teyssier, C. and Dunlap, W. J., 2001, Int. J. Earth Sci., 90, 77-78.
Katada, M. and Osawa, M., 1964, Bull. Geol. Surv. Japan, 15, 87-94.
Passchier, C. W. and Trouw, R. A. J., 2005, Springer, Berlin, p44.
Sakai, T. Nishikawa, O. and Fujimoto, Y., 2012, Abst. 119th Ann. Meet. Geol. Soc. Japan, R14-O13,
144.
Stipp, M. and Tullis, J., 2003, Geophys. Res. Lett., 30, 2088.
Takahashi, H., 2001, Abst. 108th Ann. Meet. Geol. Soc. Japan, P-25, 210.
Takeshita, T., 1996, Jour. Geol. Soc. Japan, 102, 211-222.

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Keywords: Shirakami Mountains, Cretaceous granitic rocks, Mylonite, quartz CPO©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Coexisting Omphacite-Diopside in Ab-CaCO3phases vein developed in Epidote-amphibolite
olistolith in kamuikotan Metamorohic belt.
*Shusuke Kinoshita1, Takao Hirajima1
1.Department of Geology and Mineralogy, Graduate School of Science, Kyoto University
Ca-Na pyroxene is a common mineral in eclogite and blueschist facies metamorphic rocks. Omphacitewith an intermediate composition between jadeite and augite is considered to be a clinopyroxenegroup with ordered P2/n symmetry, because the cation partitioning and ordering in NaAl-CaMg
substitution took place below the critical temperature. At further lower temperatures, two
miscibility gaps were proposed between omphacite and C2/c sodium-rich augite, and omphacite andC2/c impure jadeite in the jadeite-augite binary system based on a thermodynamic theory andpetrographic evidences (Carpenter, 1980). As natural Ca-Na pyroxenes generally incorporates Fe3+ as
an aegirine component at various degrees, several phase diagrams of Ca-Na pyroxenes concerning withstability fields of C2/c and P2/n symmetries have been proposed in the jadeite-aegirine-augite
ternary system based on a number of thermodynamic models (e.g. Carpenter, 1980; Holland, 1990;
Green et al., 2007). As the low-temperature stability conditions of Ca-Na pyroxenes harm theirsynthetic study, thus it is necessary to justify the validity of proposed phase diagrams using
natural samples. In this study, we report the petrology of omphacite and sodium-rich augite pairwhich was newly found from high-pressure mineral veins developed in an epidote amphibolite blockcollected from the Horokanai area in the Kamuikotan metamorphic belt, central Hokkaido. Shibakusa(1989) divided the metamorphic rocks in the Horokanai area into three zones, Zone I {lawsonite
blueschist (BS) facies} to Zone III (epidote BS facies), based on the mineral assemblages of mafic
rocks. Imaizumi (1984) reported the occurrence of epidote amphibolite blocks from the Horokanai
pass area, which is located in Zone III of Shibakusa (1989), and he concluded that these blocks
represent olistoliths within the Kamuikotan metamorphic rocks prior to the BS-facies metamorphism.
We identified three kinds of metamorphic veins; 1) Pale green, 2) yellowish green and 3) whiteveins. The pale green vein is about 1 cm thick and its central part is mainly composed of Ca-Na
pyroxenes, carbonate (aragonite and calcite) and albite, while apatite is partly developed in theouter part of the vein. Yellowish green veins and white veins are less than 1 mm thick and mainlycomposed of pumpellyite and albite, respectively. The composition of pumpellyite is identical tothose of Zones II and III of Shibakusa (1989). Calcite is considered to have developed after theformation of aragonite, as aragonite is always surrounded by calcite. These observations suggestthat the vein-forming conditions are about 250-350 °C and less than 7-10 kbar (P-T estimation forZone II/III of Shibakusa, 1989). Most of Ca-Na pyroxenes occur as anhedral grains, ca. 1mm inlength, in the central part of the pale green vein. They are composed of two domains, 20-100 μm in
width, separated by straight boundary which can be easily identified by their different
birefringence. The chemical composition of the two domains is omphacite (Jd30-40Acm15-25Di38-55) andsodium-rich augite (Jd4-8Acm9-15Di77-95), respectively, showing an obvious gap, probably between P
lattice omphacite and C lattice sodium-rich augite. Tsujimori (1997) reported the coexistence ofomphacite and sodium-rich augite in an omphacitite collected at the Osayama serpentinite mélange,
Sangun-Renge belt. They are less Fe3+ contents compared with our data and are associated withpumpellyite. The results of our study and Tsujimori (1997) propose a miscibility gap between
omphacite and sodium-rich augite at 250-350 °C, which is slightly wider than that proposed by
Carpenter (1980) at 350 °C and there is a tendency that omphacite slightly prefers Fe3+ content
rather than the coexisting sodium-rich augite.

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Keywords: kamuikotan metamorphic belt, omphacite-diopside gao, aragonite©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Metamorphic conditions of Gotsu blueschists in the Suo metamorphic belt, SW Japan*Akira Takasu1, Weimin Li2, Kabir Md Fazle1
1.Department of Geoscience, Faculty of Science and Technology, Shimane University, 2.College ofEarth Science, Jilin University, China
The Suo metamorphic belt in SW Japan is a representative of Jurassic accretionary terranes
characterized by blueschist facies metamorphism of 160-230 Ma in metamorphic age (Nishimura, 1998).
The metamorphic facies series of the Suo schists from pumpellyite-actinolite facies throughglaucophane schist facies to epidote amphibolite facies (e.g. Nishimura, 1998). The Gotsu area in
the Suo metamorphic belt is composed mainly of glaucophanic metamorphic rocks of blueschists andpelitic schists.
The metamorphism of the Gotsu blueschists is divided into three stages, i.e. pre-peak, peak andretrograde stages. The peak metamorphism of Gotsu blueschists is defined by porphyroblastic
epidote, glaucophane, phengite, chlorite, hematite and titanite, suggesting epidote-blueschist
facies conditions of 430-530 °C and 12-15.5 kbar.
The blueschists from the the Gotsu area and the Heilongjiang Complex, NE China suggest that both
blueschists were formed within the same subduction system, which is related to the Paleo-Pacificplate subduction. This subduction event produced voluminous Jurassic accretionary complexes along
the eastern margin of the Asian Continent.
Keywords: blueschist, Heilongjiang Complex, NE China, Suo metamorphic belt

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

The source rock age of Renge metamorphic rock in the Omi-area, Itoigawa city.
*Takumi Yoshida1, Madhusoodhan Satish-Kumar1, Hayato Ueda1
1.Niigata university
The Omi area located in the westernmost Niigata prefecture, is known for its LT/HP metamorphic
rocks of Paleozoic age. Previous studies conducted in the Omi area reported that this area consistof serpentinite-melange, including LT/HP type metamorphic rocks and serpentinite. The highest
metamorphic grade reported in this area is eclogite facies, which led to the demarcation of
eclogite unit (EC-unit) and non-eclogite unit (N-EC unit) in the Omi area (Matsumoto et al., 2011).
However, the tectonic evolution of metamorphic rocks in this area is not clear, especially, therelation between EC unit and N-EC unit is not clear. In this study, we present new result on the
U-Pb zircon ages of high-pressure metamorphic rocks in EC unit and consider the tectonics ofPaleozoic Japan.
The sample used for analysis is a Grt glaucophanite, occurring as a layer or lenticular form
surrounded by politic schists (Grt-Ms schist). It comprises of euhedral~subhedral garnet
porphyroblast (1-4mm) and large amount of euhedral glaucophane. Chlorite occurs in the altereddomain. This sample contains a lot of zircon, which has bright rim and dark core under the CL
image. About 200 zircon grains were hand picked and U-Pb analysis was carried out using an Agilent
7500a LA-ICPMS at Niigata University.
Off the 115 zircons analyzed, 34 spot gave concordant ages. Zircon core age is about 420-690Ma andthe most prominent peak is seen in the range of about 450-460Ma. In contrast, some of the zircon
core show about 1200-1460Ma.
The U-Pb results in this study (450-460Ma) are older than 280-340Ma of K-Ar age (Kunugiza et al.,2004) and 380Ma of eclogite metamorphism (Tsujimori, 2010). However, the sample has basaltic
chemical composition. But it is hard to conclude that the protolith of this sample is basalt,because it contain large amount of zircon and those zircon shows a large spread of ages. Therefore
it is necessary to examine the sedimentation history and tetonic evolution of the Omi area in moredetail, which is ongoing.
Keywords: Renge metamorphic rock, U-Pb age©2016. Japan Geoscience Union. All Right Reserved.

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