Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The Dai Loc Complex, located in the southern Truong Son Belt, is separated from the northern Kontum Massif by the early Paleozoic Tam Ky–Phuoc Son suture zone. This study presents new zircon U–Pb ages and petrographic observations of the migmatitic pelitic gneisses and mylonitized granite intrusions from the Dai Loc Complex in order to constrain the Early Paleozoic thermal history of the eastern Indochina Block. The identification of metamorphic zircon with sillimanite inclusions, euhedral cordierite, and garnet in the migmatitic pelitic gneisses indicates high temperature metamorphic conditions at ca. 430–440 Ma. The metamorphism was followed by an isobaric cooling stage defined by the replacing of cordierite by kyanite–staurolite–quartz symplectite. The Dai Loc granite likely intruded the metapelites at ca. 430 Ma and was subsequently mylonitized. The thermal event in the Dai Loc Complex may be correlated with Ordovician–Silurian low pressure/high temperature metamorphism caused by subduction related arc magmatism in the Kannack and Ngoc Linh Complexes of the Kontum Massif. However, the frequency distribution of detrital zircon ages suggests the metasedimentary rocks from Dai Loc Complex have a unique provenance that was distinct from those of the neighboring A Vuong Formation and South China Block.

DOI： 10.1016/j.jseaes.2021.105070

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DOI： 10.2465/jmps.210830

Language：Others   Publishing type：Research paper (scientific journal)  

To further constrain the tectonic evolution of the convergent margin of the West Mongolian segment in the Paleo–Asian Ocean, we have investigated coarse-grained kyanite metapelites associated with quartz veins in the Gobi Altai Mountains, Mongolia, where the metamorphic belt is in a thrust contact with a Paleozoic accretionary complex. The metapelites contain coarse-grained granoblastic kyanite grains that are surrounded by sillimanite (Sil-II) with moat-like andalusite (And-II). The garnet grains in the garnet-bearing kyanite metapelites contain inclusions of andalusite (And-I) in their cores and sillimanite (–Sil-I) in their mantles. Detailed textural characterization of the aluminosilicate phases indicates five distinct generations in the sequence andalusite (And-I), sillimanite (–Sil-I), kyanite (Ky), sillimanite (Sil-II), and andalusite (And-II). Thermobarometric calculations and thermodynamic modeling suggest a hairpin-shaped P–T evolution with prograde conditions starting from ~530 °C at 3.5 kbar, reaching a peak of 600 °C at 6 kbar, and then a retrogression to ~550 °C at 4 kbar. U-Pb zircon and U–Th–Pb monazite ages indicate that the multistage aluminosilicate formation has occurred during c. 260–245 Ma. The detrital zircon age distribution is essentially similar to those in the accretionary sedimentary rocks from the entire Altai Range (a sharp peak at 550–490 Ma and a broad peak at 900–700 Ma), but is characterized by more abundant Proterozoic zircon grains and an older maximum deposition age (Early Ordovician) compared with Devonian pelitic gneisses in the Mongolian Altai. These petrological and geochronological results indicate the following development of the orogen: (1) Subduction of an oceanic plate beneath a microcontinental block as early as 550 Ma, evidenced by the youngest peak of detrital zircon ages. (2) Development of the accretionary wedge and volcanic front due to maturation of the arc until c. 360 Ma. The development of the volcanic front due to the magmatism has provided abundant Paleozoic detritus to the accretionary wedge and has stemmed supply of Proterozoic detritus from the inland at the same time. (3) Burial of the youngest accretionary wedge at c. 360–350 Ma, which is not observed in the current samples. Ridge subduction has also been suggested to have occurred in this period. (4) Arc magmatism in the upper (older) part of the accretionary wedge during the late Permian that resulted in prograde high-T and low-P metamorphism (formation of And-I). (5) Burial of the heated accretionary wedge to a depth of ~20 km due to subsequent collision (formation of Sil-I and Ky) at c. 260 Ma. (6) Rapid exhumation of the buried accretionary wedge to a shallow depth by thrusting (formation of Sil-II and And-II) at c. 245 Ma. In summary, the metapelites in the Altai Range clearly preserve the evolution of both the accretion and collision events as well as their transformation processes, which are likely to be a good natural example of the Wilson cycle for a period of ~300 Myr.

DOI： 10.1016/j.lithos.2021.106362

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DOI： 10.1016/j.jas.2021.105377

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.5575/geosoc.2020.0044

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DOI： 10.1016/j.chemosphere.2020.127912

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jseaes.2019.104077

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jseaes.2019.104084

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DOI： 10.1111/iar.12374

Language：English   Publishing type：Research paper (scientific journal)  

Metamorphic P-T conditions and variation of REE between two garnet generations from granulites in the Sør-Rondane mountains, East Antarctica

DOI： 10.1007/s00710-019-00680-0

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2465/jmps.181115

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

The first investigation of arsenic (As) contamination in soil cores in the biggest estuarine ecosystem in northern Vietnam was conducted using FE-EPMA, ICP-MS and XRD techniques. Concentrations of arsenic and five heavy metals were measured and mineralogical characteristic of soils and sediments in different land uses were analyzed. Most of the soils contained high proportions of As and heavy metals in the potential mobility fractions and silicate minerals. High concentrations of As and heavy metals were observed in river sediments and top-layers of mangrove forest soil cores. Qualitative analyses using WDS technique on FE-EPMA found As on the iron (hydro)oxides and framboidal pyrite surfaces in the samples. The principal component analysis indicated the enrichment of As and heavy metals in the upper soil layers, suggesting that intensive human activities in upstream of the Red river in recent decades could be the cause of elevated levels of these toxic elements in the estuarine ecosystem.

DOI： 10.1016/j.microc.2018.03.005

Language：English   Publishing type：Research paper (scientific journal)  

The high-grade metamorphic rocks of Sri Lanka place valuable constraints on the assembly of central parts of the Gondwana supercontinent. They are subdivided into the Wanni Complex (WC), Highland Complex (HC) and Vijayan Complex (VC), but their correlation with neighbouring Gondwana terranes is hindered by a poor understanding of the contact between the HC and WC. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb dating of remnant zircon cores from 45 high-grade metamorphic rocks in Sri Lanka reveals two domains with different age characteristics that correlate with the HC and WC and which help constrain the location of the boundary between them. The HC is dominated by detrital zircon ages of ca. 3500–1500 Ma from garnet–biotite gneiss, garnet–cordierite–biotite gneiss, some samples of garnet–orthopyroxene–biotite gneiss and siliceous gneiss (interpreted as paragneisses) and igneous protolith ages of ca. 2000–1800 Ma from garnet–hornblende–biotite gneiss, other samples of garnet–orthopyroxene–biotite gneiss, garnet–two-pyroxene granulite, two-pyroxene granulite and charnockite (interpreted as orthogneisses). In contrast, the WC is dominated by detrital zircon ages of ca. 1100–700 Ma from paragneisses and igneous protolith ages of ca. 1100–800 Ma from orthogneisses. This clearly suggests the HC and WC have different origins, but some of our results and previous data indicate their spatial distribution does not correspond exactly to the unit boundary proposed in earlier studies using Nd model ages. Detrital zircon and igneous protolith ages in the HC suggest that sedimentary protoliths were eroded from local 2000–1800 Ma igneous rocks and an older Paleoproterozoic to Archean craton. In contrast, the WC sedimentary protoliths were mainly eroded from local late Mesoproterozoic to Neoproterozoic igneous rocks with very minor components from an older 2500–1500 Ma craton, and in the case of the WC precursor sediments there was possibly additional detritus derived from early to middle Neoproterozoic metamorphic rocks. The relic zircon core ages in the HC are comparable with those of the Trivandrum Block and Nagercoil Block of southern India. In contrast, those ages in the WC match the Achankovil Shear Zone and Southern Madurai Block of southern India. These comparisons are also supported by Th/U ratios of detrital zircon cores from paragneisses (Th/U ratios of &gt
0.10 for the former and not only &gt
0.10 but also ≤0.10 for the latter). Comparisons with the Lützow-Holm Complex of East Antarctica indicate that the geochronological characteristics of the HC and WC broadly match those of the Skallen Group, and the Ongul and Okuiwa Groups, respectively.

DOI： 10.1016/j.jseaes.2018.01.017

Language：English   Publishing type：Research paper (scientific journal)  

The oxidation states of Fe within olivine, orthopyroxene, clinopyroxene, and spinel in a spinel lherzolite xenolith from the Tariat Depression, Mongolia were investigated using57Fe Mössbauer spectroscopy to evaluate the redox condition of the upper mantle from which the Tariat spinel lherzolite xenolith was derived. The purity of separated minerals for the Mössbauer spectroscopic analysis was examined using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. Average Fo and Fe contents of olivine at the core part of the xenolith are 89.9(4) mol % and 0.195(3) atoms per formula unit, respectively. The Fe3+/ΣFe values of the olivine, orthopyroxene, clinopyroxene, and spinel, determined by Mössbauer spectroscopic analysis, are 0.027(2), 0.15(1), 0.26(3), and 0.34(5), respectively. TheMössbauer spectrum of olivine consists of two doublets assigned to Fe2+ at the octahedral sites and one doublet, with I.S. of 0.40(2) mm/s and Q.S. of 0.69(3) mm/s assigned to Fe3+ at the octahedral site. Since the Tariat spinel lherzolite xenolith in this study shows no evidence of metasomatism or thermal alteration, the existence of a small amount of Fe3+ in olivine and the fairly high Fe3+ contents of clinopyroxene, orthopyroxene, and spinel imply that the upper mantle under the Tariat area was in a rather oxidized condition.

DOI： 10.3390/min8050204

Language：Japanese  

Recent progress in lower crustal process : precise analyses on ultrahigh-temperature metamorphism

DOI： 10.5575/geosoc.2017.0059

Language：Others  

Excavations at Daram and Tevsh Sites: A Report on Joint Mongolian-Japanese Excavations in Outer Mongolia

Language：Japanese  

Revised stratigraphy and zircon U-Pb age data of the Hitachi metamorphic formations in the southern Abukuma Mountains, and reconstruction of the basement of the Northeast Japan Arc before the opening of the Japan Sea
We revised the stratigraphy of the Hitachi metamorphic district, based on supplementary U-Pb SHRIMP zircon ages and a review of the geochronological data available for this district. Early to late Cambrian formations and intrusives are grouped into the Cambrian Hitachi volcano-plutonic complex, which consists of the Akazawa Formation, the Tamadare Formation, meta-granites and meta-porphyry. Post-Silurian mica gneiss that occurs near the Tamadare Formation is newly defined as the Takizawa Formation, distinct from the Tamadare Formation. The Daioin and Ayukawa formations are early Carboniferous and early Permian in age, respectively. The contact between the Hitachi volcano-plutonic complex and the Daioin Formation is marked by a prolonged hiatus. There are no geochronological data available for the Omika Formation. Zircon U-Pb age data of the Nishidohira Formation indicate deposition during the Early Cretaceous. The Nishidohira Formation was intruded by 119 Ma granitoids and was metamorphosed during 118-96 Ma under conditions of the amphibolite facies, kyanite-sillimanite zone. Sedimentation, metamorphism and exhumation, and intrusion of granitic magma in the terrain of the Nishidohira Formation occurred over a short period of time during the Cretaceous. A similar rapid metamorphism and exhumation is also recorded in the Takanuki metamorphic rocks of the Abukuma Belt. We reconstructed the basement of the Northeast Japan Arc for the period before the opening of the Japan Sea, assuming that the Median Tectonic Line had a linear trend from the Southwest Japan Arc to the Northeast Japan Arc during the Paleogene. After the reconstruction, the Paleozoic Hitachi Formations and the Abukuma Belt move closer to the Jiamusi and Khanka blocks of Northeast China. This result indicates that the Cambrian Hitachi volcano-plutonic complex was originally marginal part of the North China Block.

DOI： 10.5575/geosoc.2016.0012

Language：English   Publishing type：Research paper (scientific journal)  

The ultrahigh-temperature (UHT) regional metamorphism of Sri Lanka has a significant role in understanding the tectonics and formation of the Gondwana supercontinent. Sri Lanka is specifically important because of its central position in Gondwana, located between southern India, Madagascar and eastern Antarctica. In particular, the Highland Complex has been the focus of several previous studies because of the prominence of metasedimentary rocks that experienced UHT metamorphism. The central Highland Complex of Sri Lanka consists of Spr-bearing Mg-Al rich granulites intercalated with other pelitic, mafic granulites and calc-silicates, which preserve several textural evidences for UHT metamorphism. The calculated peak metamorphic conditions for the Mg-Al rich granulite yielded a temperature range from 910 to 1005 degrees C at 1.0 GPa, and the pressure varies between 0.9 to 1.2 GPa. The estimated metamorphic P-T conditions and evolution path is in good agreement with previous studies and also to that of similar rock-types from southern Madagascar, southern India and East Antarctica.

DOI： 10.2465/jmps.151227

Language：English   Publishing type：Research paper (scientific journal)  

The regional ultrahigh-temperature (UHT) metamorphism of the Highland Complex, Sri Lanka is well established and has an important role in our understanding of the tectonic history of the Gondwana supercontinent. U-Pb zircon dating of sapphirine-bearing Mg-Al granulites yielded two major metamorphic age populations at approximately 620-590 and 563-525 Ma with no evidence of older zircon cores. Pelitic granulite samples with a Grt-Sil-Spl-Crd assemblage have similar metamorphic ages with concordant data clusters at similar to 602, 563, and 526 Ma and inherited zircon cores aged from 2040 to 1600 Ma. The pelitic granulites also underwent two stages of metamorphism (565-520 and 622-580 Ma). Some of these pelitic granulite samples have inherited zircon cores ranging from 3060 to 760 Ma. Zircons in mafic granulite samples have age ranges of 566-533 and 620578 Ma. A calc-silicate granulite sample also has similar age populations at 591, 541, and 524 Ma. Combining these new results with previously published ages from Sri Lanka and formerly adjacent continental fragments of Gondwana, we propose that the terranes in southern Madagascar (south of Ranotsara Shear Zone), Northern and Southern Madurai and the Trivandrum Blocks of southern India, the Highland Complex of Sri Lanka, and the Skallen Group in the Lutzow-Holm Complex of East Antarctica represent a unique metamorphic belt that regionally experienced the Ediacaran-Cambrian UHT event during the amalgamation of the Gondwana super-continent.

DOI： 10.2465/jmps.151230

Language：English   Publishing type：Research paper (scientific journal)  

This contribution reports the metamorphic evolution of the high-pressure metamorphic rocks from the Bantimala Complex, South Sulawesi, Indonesia. Barroisite-bearing and barroisite-free eclogites were examined to assess their metamorphic evolutions, which have implications regarding the tectonic conditions in this region. The eclogites mainly consist of garnet, omphacite, phengite, rutile, and epidote, with or without barroisite. The variations in mineral assemblages are interpreted to depend upon local changes in the bulk chemical composition. The barroisite-bearing eclogites contain two types of euhedral garnet: coarse- (1-1.5 mm) and fine-grained (< 0.5 mm). Mineral inclusions in the coarse-grained garnet core and mantle show epidote + titanite and glaucophane + epidote assemblages, that stabilized at 0.9-1.5 GPa and 350-550 degrees C within epidote blueschist- facies conditions. Mineral chemistry and chemical-mapping analyses indicate that both fine-grained garnet and the rim of coarse-grained garnet formed at peak P-T conditions, which were estimated as 2.3-2.7 GPa at 615-680 degrees C based on the garnet-omphacite-phengite-quartz equilibrium. Peak P-T conditions for barroisite-free eclogite were similar (2.5-2.7 GPa at 650-690 degrees C) to those for barroisite-bearing eclogite. Actinolite rims overgrowing matrix sodic-calcic amphiboles attest to retrogression at P < 0.5 GPa and T < 350 degrees C in a clockwise P-T path. The very low geothermal gradient experienced during the prograde path (similar to 5 degrees C/km) likely suggests the subduction of an old and cold oceanic crust. The low geothermal gradient on the retrograde path suggests decompressional cooling during exhumation, possibly favored by a serpentinite-dominated matrix within a subduction channel environment.

DOI： 10.2465/jmps.150907

Language：English   Publishing type：Research paper (scientific journal)  

The Kontum Massif is situated in the southern part of Trans Vietnam Orogenic Belt (TVOB), central Vietnam, and contains various types of magmatic and metamorphic rocks, the latter including both ultrahigh-pressure and ultrahigh-temperature units. While geochronological data indicate the existence of two main tectonothermal events at 480-420 Ma and 270-240 Ma, the most intense metamorphic and magmatic activity occurred between the Late Permian and Early Triassic due to continental collision between the South China and Indochina cratons. In this study, U-Pb LA-ICP-MS geochronological analyses of zircon obtained from two samples of metagabbro and one sample of charnockite from the massif yielded a magmatic age range of 260-250 Ma for all three samples and an inherited age of similar to 1400 Ma for the charnockite. These magmatic ages overlap with those documented for peak metamorphism in the Kontum Massif. When combined with Nd isotopic data for granitic rocks and pelitic gneisses from the region, these data suggest that the massif may have been derived from reworked continental crust. Geochemical characteristics of metagabbros from the massif reveal that the parental basaltic magma can be correlated with the Song Da igneous suite situated in the northern part of the TVOB, and was assimilated by crustal materials. The Song Da igneous suite is a member of the Emeishan large igneous province and resulted from Late Permian mantle plume activity. We conclude that the plume-related magma intruded into the deeper part of Kontum Massif and induced ultrahigh-temperature metamorphism of the lower crust by acting as a heat source.

DOI： 10.2465/jmps.151019b

Language：English   Publishing type：Research paper (scientific journal)  

Detrital zircon provenances for metamorphic rocks from southern Sor Rondane Mountains, East Antarctica: A new report of Archean to Mesoproterozoic zircons
The Sor Rondane Mountains in East Antarctica consist of the various metamorphic rocks and several plutonic rocks, which are related to formation of Gondwana supercontinent. In order to understand the detrital provenances, LA-ICP-MS zircon U-Pb dating were conducted from metamorphosed sedimentary rocks in southern Sor Rondane Mountains. Detrital cores with similar to 990-730 Ma ages were recognized from zircons in the pelitic gneisses and calc-silicate rocks from Menipa, Imingfjella, Mefjell and Arden, while the pelitic gneiss from Tvihogda exhibited the Archean to Mesoproterozoic ages of similar to 2630-1060 Ma. The Neoproterozoic zircon ages are recognized not only from metamorphosed sedimentary rocks but also from metamorphosed igneous rocks distributed in the central and southern parts of the mountains. However, the Archean to Mesoproterozoic zircon ages are rare in these areas. The results imply the detrital zircons with the Neoproterozoic ages were probably derived from neighbouring igneous rocks (present metamorphosed igneous rocks), while those with Archean to Mesoproterozoic ages have clearly different provenances because of the lack in the Neoproterozoic components. This study suggests the possibility that southern Sor Rondane Mountains can be considered to be juvenile late Mesoproterozoic to Neoproterozoic terrane partly mixed with the Archean to Mesoproterozoic components.

DOI： 10.2465/jmps.151001

Language：English   Publishing type：Research paper (scientific journal)  

This paper presents metamorphic evolution of metamorphic rocks from the Meratus Complex in South Kalimantan, Indonesia. Eight varieties of metamorphic rocks samples from this location, which are garnet-bearing epidote-barroisite schist, epidote-barroisite schist, glaucophane-quartz schist, garnet-muscovite schist, actinolite-talc schist, epidote schist, muscovite schist, and serpentinite, were investigated in detail its petrological and mineralogical characteristics by using polarization microscope and electron probe micro analyzer (EPMA). Furthermore, the pressure-temperature path of garnet-bearing epidote-barroisite schist was estimated by using mineral parageneses, reaction textures, and mineral chemistries to assess the metamorphic history. The primary stage of this rock might be represented by the assemblage of glaucophane + epidote + titanite ± paragonite. The assemblage yields 1.7 - 1.0 GPa in assumed temperature of 300 - 550 °C, which is interpreted as maximum pressure limit of prograde stage. The peak P-T condition estimated on the basis of the equilibrium of garnet rim, barroisite, phengite, epidote, and quartz, yields 547 - 690 °C and 1.1 - 1.5 GPa on the albite epidote amphibolite-facies that correspond to the depth of 38 - 50 km. The retrograde stage was presented by changing mineral compositions of amphiboles from the Si-rich barroisite to the actinolite, which lies near 0.5 GPa at 350 °C. It could be concluded that metamorphic rocks from the Meratus Complex experienced low-temperature and high-pressure conditions (blueschist-facies) prior to the peak metamorphism of the epidote amphibolite-facies. The subduction environments in Meratus Complex during Cretaceous should be responsible for this metamorphic condition.

DOI： 10.17014/ijog.2.3.139-156

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

Four amphibolite facies pelitic gneisses from the western Mongolian Altai Range exhibit multistage aluminosilicate formation and various chemical-zoning patterns in garnet. Two of them contain kyanite in the matrix and sillimanite inclusions in garnet, and the others have kyanite inclusions in garnet with sillimanite or kyanite in the matrix. The Ca-zoning patterns of the garnet are different in each rock type. U-Th-Pb monazite geochronology revealed that all rock units experienced a c. 360Ma event, and three of them were also affected by a c. 260Ma event. The variations in the microstructures and garnet-zoning profiles are caused by the differences in the (i) whole-rock chemistry, (ii) pressure conditions during garnet growth at c. 360Ma and (iii) equilibrium temperatures at c.260Ma. The garnet with sillimanite inclusions records an increase in pressure at low-P (5.2-7.2kbar) and moderate temperature conditions (620-660 degrees C) at c. 360Ma. The garnet with kyanite inclusions in the other rock types was also formed during an increase in pressure but at higher pressure conditions (7.0-8.9kbar at 600-640 degrees C). The detrital zircon provenance of all the rock types is similar and is consistent with that from the sedimentary rocks in the Altai Range, suggesting that the provenance of all the rock types was a surrounding accretionary wedge. One possible scenario for the different thermal gradient is Devonian ridge subduction beneath the Altai Range, as proposed by several researchers. The subducting ridge could have supplied heat to the accretionary wedge and elevated the geotherm at c. 360Ma. The differences in the thermal gradients that resulted in varying prograde P-T paths might be due to variations in the thermal regimes in the upper plate that were generated by the subducting ridge. The c. 260Ma event is characterized by a relatively high-T/P gradient (25 degrees Ckm(-1)) and may be due to collision-related granitic activity and re-equilibrium at middle crustal depths, which caused the variations in the aluminosilicates in the matrix between the rock units.

DOI： 10.1111/jmg.12154

Language：Japanese   Publishing type：Research paper (scientific journal)  

Early Cretaceous adakitic magmatism and tectonics in the Kitakami Mountains, Japan
Early Cretaceous igneous rocks in the Kitakami Mountains consist of volcanic rocks, dike rocks, and plutonic rocks, from older to younger. Plutonic rocks are composed mainly of adakitic granites in central part of zoned plutonic bodies surrounded by adakitic to non- adakitic granites in marginal part. These adakitic plutons is divided into E andWzones based on the ages and geochemistry. Zircon U-Pb ages were determined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for 22 samples from 13 rock bodies including the Early Cretaceous adakitic granites in the KitakamiMountains. Zircons from the adakitic granites of E zone give older ages (127-117 Ma) compared with those of W zone (119-113 Ma). Zircon ages of the calc-alkaline to shoshonitic rocks and dike rocks range from 128-124 Ma, which are similar to the oldest rocks of the E zone (127-125 Ma). Zircon ages become younger from the northern Hashikami pluton and marginal facies of the Tanohata pluton (127-125 Ma) to southern Takase granites (118-117 Ma), in the E zone adakitic granites. Petrochemical diŠerences between the E zone and W zone rocks indicate that the adakitic melt of E zone rocks are considered to be derived from vapor-absent melting condition, while those of W zone rocks are from higher pressure and vapor-present condition. Taking all these data into consideration, the Early Cretaceous magmatisms in Kitakami can be explained by the diŠerential subduction model of the Farallon-Izanagi plates or slab rollback model accompanied with asthenospheric upwelling.

DOI： 10.2465/gkk.131228

Language：English   Publishing type：Research paper (scientific journal)  

Multiple Collisions in the East African-Antarctica Orogen: Constraints from Timing of Metamorphism in the Filchnerfjella and Hochlinfjellet Terranes in Central Dronning Maud Land
Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age dating was applied to several types of cordierite-bearing gneisses and orthopyroxene-bearing gneiss from the basement rocks in central Dronning Maud Land, East Antarctica, to clarify the timing of tectonothermal events during the amalgamation of East and West Gondwana. The zircon ages of ca. 522-525 and 598-599 Ma were obtained in Filchnerfjella and Hochlinfjellet, respectively, and the cathodoluminescence images of analyzed zircons suggest that these were formed during high-temperature metamorphism. These two sets of ages are interpreted to represent periods that immediately followed the peak metamorphism. The dating results reveal an age gap of 80 Myr between the two areas, indicating different collisional events. In the cordierite-bearing samples in Filchnerfjella, zircon cores with oscillatory zoning have concordia ages that range from 1800 to 650 Ma. These are considered to represent the ages of detrital zircons derived over a long time from different source materials. In Hochlinfjellet, the inherited detrital zircons with oscillatory zoning have concordia ages of ca. 930, 780, and 730 Ma, indicating sedimentary protoliths derived from differently aged igneous source rocks, possibly formed in a subduction zone as an accretionary prism before the collision. According to previous age results, previously documented shear zones are now interpreted as representing a major tectonic boundary. The obtained age results imply that different allochthonous metamorphic terranes were assembled along the collisional zone of the East African-Antarctica Orogen during the period from 650 to 500 Ma.

DOI： 10.1086/679468

Language：English   Publishing type：Research paper (scientific journal)  

High-Mg, high-Al metasedimentary gneisses from the Altai Mountains, Mongolia, belonging to a subduction-accretion complex within the Central Asian Orogenic Belt can be divided into five rock types on the basis of mineral assemblages. Most rock types have high MgO and Al2O3 content and low CaO, Na2O, Rb, and Sr content. All rock types experienced a similar medium-pressure metamorphism characterized by a "hairpin"-shaped counterclockwise pressure-temperature path. U-Pb zircon and U-Th-Pb monazite ages indicated metamorphism at ca. 356 Ma and 277 Ma and inherited ages of 510-379 Ma, suggesting possible provenance to granitoids comparable to those in the Altai Mountains, China. The zircons that newly nucleated at ca. 356 Ma are characterized by high concentrations of light rare earth elements without a Ce anomaly-features common in zircons from hydrothermally altered rocks and a reducing environment. Petrological and geochronological results in this study suggest the following tectonic evolution: (1) continuous subduction and accretion of paleo-Asian oceanic crust during the Early Paleozoic, resulting in periodic granitoid magmatism in the period 510-380 Ma and a continuous supply of granite-derived sediments providing detrital zircon and monazite grains to the accretionary prism; (2) ridge subduction during the Late Devonian-Early Carboniferous (ca. 356 Ma), resulting in hydrothermal metamorphism of the accretionary prism and interaction with seawater that produced rocks with unusual whole-rock chemistry; and (3) closure of the ocean leading to continental collision in the Early Permian (ca. 277 Ma), with part of the accretionary prism squeezed into lower crustal levels to form medium-pressure metamorphic rocks.

DOI： 10.1086/675665

Language：Japanese   Publishing type：Research paper (scientific journal)  

LA-ICP-MS zircon U-Pb geochronology of Paleozoic granitic rocks and related igneous rocks from the Kurosegawa tectonic belt in Kyushu, Southwest Japan
&nbsp;&nbsp;The Yatsushiro area in Kyushu Island, southwest Japan, forms the western tip of the Kurosegawa tectonic belt. This area is underlain by a serpentinite melange with complicated tectonic block assemblage of granitic rocks, high-temperature (HT)-type metagabbro (Grt-Cpx granulite, Grt-amphibolite and Cpx-bearing amphibolite), and high-pressure (HP)-type metagabbro (Jd-Gln rock and Gln-bearing metagabbro). The granitic rocks and the gabbros are the protoliths of the HT-type metagabbro (HT-gabbro), and supposed to be derived from volcanic arc at an active continental margin based on their major, trace, and rare earth element (REE) chemistry, while geochemistry of the gabbro protoliths of the HP-type metagabbro (HP-gabbro) indicates mid oceanic ridge basalt (MORB)-like precursors. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the granitic rocks and the HT-gabbro gave the Ordovician magmatic ages (&sim; 450 Ma). On the other hand, the HP-gabbro showed the igneous age of the Late Cambrian (&sim; 490 Ma). Similar rock suites collected from the Kurosegawa tectonic belt in Shikoku and in the Kii-peninsula have the same chemical and age affinities according to their rock types. These results indicate the strong geological and tectonic similarities within the Kurosegawa tectonic belt. The similar assemblage is present in the South-Kitakami belt suggesting similarities in their origin.

DOI： 10.2465/gkk.131126

Language：English  

Zircon U–Pb age and its geological significance of late Carboniferous and Early Cretaceous adakitic granites from eastern margin of the Abukuma Mountains, Japan
The &#039;Wariyama Sheared Granodiorite&#039; occurs along the east side of the Futaba Fault with the Wariyama uplift zone, Miyagi, Japan. Rocks from the &#039;Wariyama Sheared Granodiorite&#039; can be geochemically classified as typical adakite, and further subdivided into medium-grained and K₂O- and Sr-poorer rocks, and coarse-grained and K₂O- and Sr-richer rocks. Zircons from the former yield U–Pb ages of 308 ± 3 and 302 ± 4 Ma, whereas zircons from the latter have ages of 118 ± 2 and 117 ± 1 Ma. On the basis of these results, the &#039;Wariyama Sheared Granodiorite&#039; can be redefined. The late Carboniferous granite is renamed the Wariyama Granite as in the past, but we use the term &#039;granite&#039; in a broad sense as describing the rock type. The Early Cretaceous granite is newly defined as the Takase Granite. The Takase Granite crops out on the eastern side of the central region of the Wariyama Granite with faulted contact. The Takase Granite is divided into the SiO₂-poor Takase Granite A and the SiO₂-rich Takase Granite B. The U–Pb zircon age of 300 Ma obtained here corresponds to an interval of five major granitic events, and the timing of the onset of Permian granitic magmatism (280 Ma) may actually be ca. 300 Ma. Typical adakites are considered to be the product of slab melting, which occurred in response to unusual tectonic conditions, such as subduction of young lithosphere and/or an active ridge at ca. 300 Ma.

DOI： 10.5575/geosoc.2014.0003

Language：English   Publishing type：Research paper (scientific journal)  

Here we report on the unexpected occurrence of felsic (granitic) inclusions with quench textures such as spherulite and dendrite (hereafter referred to as "felsite inclusions"), similar to some volcanic rocks, within garnet in presumably "slowly cooled" lower-crustal granulites of various geologic ages ranging from Early Proterozoic to Middle Paleozoic and wide global distribution (the Limpopo Belt, the Grenville Province, the Liltzow-Holm Complex of East Antarctica, the Highland Complex of Sri Lanka, and the southern Bohemian Massif). The well-preserved textures of felsite inclusions are indicative of melts formed by anatexis during high-pressure and high-temperature metamorphism, crystallization under far-from-equilibrium conditions (at >50 degrees C undercooling) and subsequent rapid cooling. The occurrence of felsite inclusions in granulites in restricted tectonostratigraphic zones in Sri Lanka, among other examples, may be the first geologic evidence for fast exhumation of lower-crustal rocks to andalusite-stable upper-crustal conditions by channel flow in a continental collision orogen. We hypothesize that granulites ascend episodically along discrete high-strain zones and cool as fast as some felsic magmas. This conclusion sheds new light on the debate regarding the deep crustal processes and necessitates changes to fundamental beliefs about exhumation rates based on rates of plate convergence (1-10 cm/year). (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2013.04.001

Language：English   Publishing type：Research paper (scientific journal)  

Contrasting metamorphic records and their implications for tectonic process in the central Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica
Metamorphic rocks in the central part of Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, are classified into three types based on petrological characteristics. (i) The Austkampane area preserves c. 800oC and 0.5-0.6 GPa peak metamorphic conditions followed by decompression and subsequent isobaric cooling and later hydration (A-type). (ii) The Brattnipene and eastern Menipa area preserve peak P-T conditions of c. 800oC and 0.7- 0.8 GPa with subsequent isobaric cooling and later hydration (B-type). (iii) The area including Lunckeryggen, southern Walnumfjella and western Menipa preserves an amphibolite-facies peak metamorphic condition with signatures of prograde metamorphism (L-type), which are typically unaffected by the retrograde hydration event. Peak granulite-facies metamorphism of A- and B-type rocks are contemporaneous at c. 640-600 Ma, but a difference in the P-T paths between these rocks can be explained by thrusting of the A-type rock unit onto the B-type rock unit. By contrast, the timing of the metamorphism of the L-type rocks is significantly younger at c. 550 Ma, possibly related to the intrusion of pegmatites and granitoids. These metamorphic records in the central part of the Sør Rondane Mountains can be a test ground for the regional tectonic processes proposed for the orogeny related to Gondwana formation. © The Geological Society of London 2013.

DOI： 10.1144/SP383.4

Language：English   Publishing type：Research paper (scientific journal)  

Possible armalcolite pseudomorph-bearing garnet-sillimanite gneiss from Skallevikshalsen, Lützow-Holm Complex, East Antarctica: Implications for ultrahigh-temperature metamorphism
A possible armalcolite pseudomorph has been identified in garnet-sillimanite gneiss from Skallevikshalsen, located c. 30 km NE of Rundvågshetta, in a terrane with the highest metamorphic grade in the Lützow-Holm Complex, East Antarctica. It occurs as an Fe-Mg-Ti compositional domain consisting of ilmenite, rutile and pseudorutile, partially mantled by rutile within ilmenite. The domain yields an average XMg of 0.171±0.036 exceeding by 3 wt% TiO2 from armalcolite stoichiometry, while the analysis closest to armalcolite stoichiometry has an XMg value close to 0.202. Host ilmenite with 0.4 mol% hematite is in contact with prismatic sillimanite, quartz, plagioclase and K-feldspar. In run products of annealing experiments performed to investigate the origin of the pseudomorph, armalcolite-ilmenite reaction coronae were developed around relict rutile in rock fragments of quartz eclogite from the Higashi-Akaishi mass of the Sanbagawa belt, central Shikoku, Japan. The experiments were carried out at 1 atm and 960-1050°C with wü stite-magnetite buffer and imply a minimum temperature of 1290°C for armalcolite stability when extrapolated to Skallevikshalsen pressures of 1.0 GPa. Mineral chemistry thermobarometry for Skallevikshalsen yields a metamorphic path with P-T peak conditions of 0.88-1.1 GPa and 970-1050°C, followed by retrograde metamorphism at 0.6 GPa and 780°C, and finally metasomatic alteration at c. 630°C. This P-T path matches that for similar ultrahigh-temperature metamorphic rocks from Rundvågshetta and Sri Lanka, and is markedly lower in temperature than the unreasonable estimates based on armalcolite stability. This discrepancy is inferred to reflect chemical impurities in armalcolite that lower its minimum temperature stability by more than 200°C. © The Geological Society of London 2013.

DOI： 10.1144/SP383.2

Language：English   Publishing type：Research paper (scientific journal)  

Geologic evolution of the Sor Rondane Mountains, East Antarctica: Collision tectonics proposed based on metamorphic processes and magnetic anomalies
The Sor Rondane Mountains of eastern Dronning Maud Land, East Antarctica can be subdivided into two different crustal terranes: the NE-terrane and the SW-terrane. The former is underlain by basement rocks of amphibolite-facies (unit A) and granulite-facies (unit B), and the latter by granulite-facies (unit C) to greenschist-facies (units D and D') rocks. The metamorphic evolution of the NE-terrane exhibits a clockwise pressure-temperature-time (P-T-t) path and the SW-terrane exhibits a counter-clockwise P-T-t path, and detrital zircon U-Pb ages are also different between the two terranes. The differences in the metamorphic evolution processes and detrital zircon provenance in these two regions can be explained by the collision of the NE-terrane and the SW-terrane which is constrained to have occurred at 600-650 Ma. The collision is interpreted to reflect convergence between the East Maud-East African orogen terrane and the Maud-Nampula terrane of the Kalahari Craton, which are bounded by the Main Tectonic Boundary and passes through the Sor Rondane Mountains. The RTP magnetic anomalies suggest this suture is cut by the subsequent collision boundary between the Kalahari Craton and the Rayner Belt, which is exposed in the Lutzow-Holm region. This collisional belt is considered to have formed at approximately 520-580 Ma. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.precamres.2013.05.017

Language：English   Publishing type：Research paper (scientific journal)  

Unraveling the metamorphic history at the crossing of Neoproterozoic orogens, Sor Rondane Mountains, East Antarctica: Constraints from U-Th-Pb geochronology, petrography, and REE geochemistry
The Sor Rondane Mountains in East Antarctica preserve two stages of tectonothermal events, at c. 650-600 Ma and c. 560-550 Ma, each of which is also widely preserved elsewhere in Gondwana within tectonic suture zones/orogens, although both ages of tectonothermal events are only rarely documented together in these other parts of Gondwana. A geochronological and petrogenetic study of highly retrogressed garnet-sillimanite-biotite-bearing pelitic gneiss, along with three generations of associated sub-concordant to discordant leucocratic felsic veins, which together are exposed in the southern Austkampane area in the central part of the Sor Rondane Mountains, provides important new constraints on the geological and age relationships between these two regional tectonothermal events. U-Pb SHRIMP dating of zircon grains isolated from the host garnet-sillimanite-biotite gneiss yields at least four distinct zircon age populations of c. 2800-720 Ma, c. 700 Ma, 640-630 Ma, and similar to 500 Ma. Chondrite-normalized REE patterns indicate that a pooled age of 637 +/- 6 Ma represents the timing of recrystallization of metamorphic HREE-depleted zircon, during which the zircon was in equilibrium with garnet. The earliest emplaced leucocratic vein (LV-1), which is partly intermingled with the host garnet-sillimanite-biotite gneiss (and enclosing garnet-bearing pelitic enclaves), contains a population of zircon grains that yielded a crystallization age of 635 +/- 4 Ma, which is almost identical to the age of zircons found within the host pelitic gneiss. The second-generation leucocratic vein (LV-2) occurs as a part of a set of sub-concordant veins/leucosomes comprising mostly biotite and muscovite. Although these particular leucosomes do not contain any zircon, they were found to contain abundant monazite, which yielded U-Pb ages of 640-630 Ma along with some older (relict) similar to 700 Ma ages. The third-generation leucocratic vein (LV-3) was sampled from a suite of pegmatitic veins that discordantly crosscut both the host pelitic gneisses and the older two sets of leucocratic veins. These third-generation veins contain magmatic zircons that exhibit HREE-enriched patterns typical of magmatic zircon crystallization, and which yielded a crystallization age of 550 +/- 3 Ma. The data imply that a major high-grade metamorphic event (possibly at granulite facies) took place in this region along with a subsequent late-stage re-hydration event, all within a relatively narrow time interval of <10 my. at similar to 635 Ma. A subsequent hydration event that took place much later on is recorded by the intrusion of a suite of discordant pegmatitic veins at similar to 550 Ma that are observed to crosscut and alter both the pre-existing pelitic gneiss and the other two older sets of felsic veins. These two ages of tectonothermal events in East Antarctica are coeval with the two major stages of Gondwana assembly. Hence, these results provide new insights into the development of metamorphic-fluid regimes within these major continent-transecting Neoproterozoic orogens. (C) 2012 Elsevier BM. All rights reserved.

DOI： 10.1016/j.precamres.2012.12.002

Language：English   Publishing type：Research paper (scientific journal)  

Timing of metamorphism in the central Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica: Constrains from SHRIMP zircon and EPMA monazite dating
In order to understand the tectonic evolution of the Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon dating and electron probe micro analyzer (EPMA) U-Th-Pb monazite dating were carried out on igneous rocks and metamorphic rocks whose P. T conditions have been well-constrained. Metamorphic rocks from northern part of Austkampane area recording a clockwise P. T path yield 600-640. Ma as the timing of peak granulite-facies metamorphism and 550-570. Ma for subsequent retrograde metamorphism. The same age relations were obtained from the metamorphic rocks from Brattnipene and eastern Menipa areas recording an anti-clockwise P. T path. Contemporaneous peak metamorphism with contrasting P. T paths can be explained by thrusting up (obduction) of the unit showing a clockwise P. T path onto the unit showing an anti-clockwise P-T path at ca. 660-640. Ma, which is considered to be the main metamorphic event. Metamorphic rocks from Lunckeryggen, southern Walnumfjella and western Menipa areas that preserve amphibolite-facies peak metamorphic conditions and are unaffected by the retrograde hydration, yield ca. 550. Ma. Ages of 500-550. Ma were also obtained on igneous rocks distributed throughout the whole area. Based on the close age relation between metamorphism of amphibolite-facies rocks and igneous activity, it is likely that metamorphism at ca. 550. Ma was caused by emplacement of voluminous igneous bodies. These precise correlation of metamorphic evolution and age would provide strong constraints on the construction of a tectonic model for Gondwana amalgamation. © 2012 Elsevier B.V.

DOI： 10.1016/j.precamres.2012.11.011

Language：English   Publishing type：Research paper (scientific journal)  

Sinistral transpressional and extensional tectonics in Dronning Maud Land, East Antarctica, including the Sor Rondane Mountains
In this paper we clarify the history of deformation in the Sor Rondane Mountains (SRMs), eastern Dronning Maud Land (DML), East Antarctica, and construct a form-line contour map of the metamorphic and plutonic rocks in order to comprehend their structural features and provide constraints on the collisional tectonics of East and West Gondwana. We divide the deformational history in the SRMs into 13 stages (D1-D13). The tectonic regime varied frequently from extension (D3-D4) to layer-normal compression and layer-parallel extension (D5), to compression (D6), extension (D7), sinistral transtension and sinistral strike-slip (D8), compression (D9-D11), and finally extension related to dextral shearing (D12-D13). D7 and D8 indicate major extensional tectonic activity in the southern part of the East African and Antarctic Orogen (EAAO) before the Pan-African compressional event, and after the c. 600 Ma peak of metamorphism. The Pan-African compressional event resulted in the formation of upright folds with horizontal axes that curve along the coastline in central to eastern DML during the D9 deformation that took place between 600 and 560 Ma. The coastline-parallel fold axes and subvertical axial-planes correspond to the X-axes and the XY-planes, respectively, of strain ellipsoids that were progressively rotated counterclockwise toward the central parts of a sinistral shear zone. Therefore, the curved fold axes and axial-planes suggest the EAAO acted as a zone of sinistral transpression during the collision of parts of East and West Gondwana. Around 560-550 Ma, during D12, parallel dyke swarms of granitic pegmatite were intruded along normal faults under a regime of NNE-SSW horizontal extensional stress. The extensional paleo-stress and its related structures suggest dextral rather than sinistral shearing took place along the north-trending EAAO during this late Pan-African event. There is the possibility of a reversal of trans-orogen asymmetry from sinistral to dextral in the southern part of the EAAO. The dyke swarms are considered to have been the heralds of the voluminous 530-500 Ma A-type granite intrusions in DML. At the same time, the Lutzow-Holm Complex was under a non-extensional tectonic regime, and may have been situated in a different orogen from the EAAO. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.precamres.2013.05.010

Language：English   Publishing type：Research paper (scientific journal)  

Multiple thermal events recorded in metamorphosed carbonate and associated rocks from the southern Austkampane region in the Sor Rondane Mountains, East Antarctica: A protracted Neoproterozoic history at the Gondwana suture zone
This paper provides a detailed analysis of the geological evolution of the southern Austkampane region in the Sor Rondane Mountains, Antarctica, using geological and petrographical observations, geochemical, geochronological, radiogenic, and stable isotopic data, and metamorphic petrological techniques. The study area is dominated by felsic gneisses intercalated with mafic and carbonate rocks. Carbonate rocks include several calc-silicate and mafic to ultramafic blocks with carbonatite-like characteristics. The new data presented here indicate the presence of five important thermal events in the geological history of the region, at c. 1060, 770-750, 655-635, 560-545, and <545 Ma. The c. 1060 Ma event is characterized by granitic volcanic arc magmatism, possibly in an active continental margin setting, involving magmas that may have been sourced from enriched mantle formed by subduction of older crustal material during the formation of Rodinia. The oldest T-(DM) age for this suite is 3.4 Ga. The 770-750 Ma event is characterized by both mafic and felsic magmatism in an active continental margin setting, with magmas being similar to bulk earth composition. The 655-635 Ma thermal event is represented by granulite-facies metamorphism along an anticlockwise pressure-temperature path, involving heating of the lower crust at a continental margin, and subsequent obduction of a cratonic counterpart during collision. Granitic and basaltic magmatism at 560-545 Ma is also associated with retrograde metamorphism and hydration-related partial melting of marble. The carbonate melt, and granitic and basaltic magmas during this event coexisted with each other and formed metasomatic calc-silicates and hornblendites, respectively. The final event at <545 Ma is characterized by the intrusion of an undeformed quartz syenite dyke, which may be related to either (1) collision and melting of preexisting lower crustal material, or (2) melting of slightly enriched mantle material in an extensional tectonic setting following the earlier collisional event. The five thermal events between c. 1100 and 500 Ma recognized in this study from a narrow region of the Sew Rondane Mountains, suggest that a combination of geochronological, whole-rock, and isotope geochemical analyses of metamorphic rocks and the pressure-temperature evolution could constrain the processes that operated during the amalgamation and break-up of Rodinia and the formation of Gondwana. A similar approach is essential in neighboring Gondwana terranes for modeling the protracted events of Neoproterozoic orogenesis. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.precamres.2012.10.009

Language：English   Publishing type：Research paper (scientific journal)  

The Ediacaran sediments in the Yangtze Block preserve valuable records of biological evolution and drastic climate changes. However, most of the Ediacaran fossil occurrences have been reported from the shallow platformal facies, and few fossils have been described from the deep basinal facies in the Yangtze Block. Here, we report mineralized microfossils from the basinal facies of the Ediacaran Doushantuo Formation at Fengtan in northwestern Hunan Province, China. The submillimeter-sized microfossils with oval-discoidal shapes have apatite walls of variable thickness. The lack of morphological regularity, ornamentation, and distinct apertures indicates that they are not protozoan shells or tests. The apatite walls have more likely replaced the recalcitrant organic walls of prasinophyte phycomata and/or algal resting cysts. These fell from shallow water and were quickly preserved in a deeper setting, associated with a local decline in pH caused by bacterial decomposition and elevated concentration of phosphate in seawater. This discovery provides new insight into the stratigraphic correlation between the shallow and basinal facies of the Chinese Ediacaran. © by the Palaeontological Society of Japan.

DOI： 10.2517/1342-8144-17.3.241

Language：English  

The Mogok Metamorphic Belt (MMB), situated in central Myanmar, contains an assemblage of high-grade metamorphic rocks believed to have been formed during a regional Early Eocene-Oligocene metamorphic event. We newly found Grt-Opx granulite in the Mogok area, which was formed under pressure-temperature (P-T ) conditions estimated as being 6.5-8.7 kbar and 800-950 °C. Based on the results of EPMA U-Th-Pb Mnz dating, the central MMB, which runs through the Mogok, Mandalay, and Meikthila areas, is characterized by an Eocene to Oligocene deformation and fluid infiltration event. In addition, several Mnz grains from the Meikthila and Mandalay areas record ages of the Late Triassic (~ 200 Ma) and Cretaceous (~ 80 Ma and 110 Ma) geologic events.

DOI： 10.2465/jmps.121019a

Language：English  

The Kurosegawa Tectonic Zone, which is one of the least geochronologically understood areas of the Japanese Islands, contains several rock types of contrasting ages in a serpentinite mélange. This paper presents the U-Pb ages of detrital zircons in pelitic schists and quartzite from the Kurosegawa Tectonic Zone, where high-pressure/ low-temperature metamorphic rock (e.g., blueschist) is one of the main constituents. We analyzed a variety of samples including glaucophane-bearing pelitic schist from the Itsuki area in Kyushu and the Toba area on the Kii Peninsula, and quartzite from the Anan area in eastern Shikoku. The U-Pb age distributions reflect similar characteristics for all three areas, indicating significant peaks at 450-500 Ma and ̃ 600 Ma, with additional scattered ages of 800-1800 Ma, and ages older than 2000 Ma. These results suggest that the provenance of the protolith of these high-pressure/low-temperature metamorphic rocks from the Kurosegawa Tectonic Zone would be the same between Kyushu and the Kii Peninsula through the Shikoku area. The distributions of detrital zircon ages in the Kurosegawa Tectonic Zone are similar to those from Permian-Triassic collision-related metamorphic rocks of the Ogcheon Metamorphic Belt and Gyeonggi Massif in South Korea, and from Devonian sedimentary rocks in the South China Craton.

DOI： 10.2465/jmps.121022a

Language：English  

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

The Central Asian Orogenic Belt consists of various terranes amalgamated in several periods from the Late Pre-cambrian/Early Paleozoic to the Late Mesozoic. Mongolia is situated in the center of this belt. Foliated garnet granite (Grt metagranite) and andalusite-bearing massive leucogranite (Leucogranite) are exposed in the Hanhohiyn region of northwest Mongolia. The results of monazite Th-U-Pb dating of the Grt metagranite and Leucogranite give ages of 508 +/- 10 Ma and 496 +/- 4 Ma, respectively. Cambrian granite with an age of similar to 500 Ma is also reported from the south-central part of Mongolia. Combined with previously published age data of metamorphic and intrusive rocks, these results show that the Cambrian orogenic belt spans over 800 km, from the northwest to the south-central part of Mongolia.

DOI： 10.2465/jmps.121021a

Language：English   Publishing type：Research paper (scientific journal)  

Lasail plutonic complex (4.7x3.8 km), as a typical example of late stage intrusive rocks, is located to the south of Wadi Jizi, and intrudes into the base of V1 volcanic rocks and sheeted dike complex. The Lasail plutonic complex consists of various rock types ranging from ultramafic cumulates to tonalite, and is associated with minor amounts of axis stage gabbro to quartz diorite. These rocks are classified into the following eleven rock types: massive gabbro 1, quartz diorite 1 (axis stage intrusive rocks), olivine websterite, olivine gabbronorite, gabbronorite, hornblende gabbronorite, leucogabbronorite (layered gabbros), massive gabbro 2, diorite, quartz diorite 2, and tonalite (late stage intrusive rocks). The layered gabbros are intruded by the massive gabbro 2, and often occur as large irregular blocks in the massive gabbro 2. The massive gabbro 2 intrudes into the layered gabbros, and sometimes grades into hornblende gabbronorite layer of the layered gabbros. In some places, anastomosing veins of the hornblende quartz gabbronorite injected into the gabbronorite, which continue to the layer of leucogabbronorite. These gabbroic rocks are intruded by small intrusions of diorite, quartz diorite 2, and tonalite. The quartz diorite 2 forms rather larger intrusive bodies that intrude into the gabbroic rocks in the higher level. The tonalite occurs as thin dike and sheet mainly in the layered gabbros. N-MORE normalized trace element patterns for the massive gabbro 2 are characterized by enrichment of LILEs relative to REEs, and resemble to 'subduction component' from the island arc tholeiite except a weak enrichment for middle to light REE and P. In contrast, the massive gabbro 1 (axis stage gabbro) shows rather flat pattern similar to MORE with no remarkable 'subduction component'. From the examination of Sr and Nd isotopic signature, the Lasail plutonic rocks are characterized by higher epsilon-Sr values than those of MORE. This suggests that the primitive magma of Lasail complex was influenced by the rocks with higher epsilon-Sr values than those of MORE, e.g., the axis stage rocks interacted with seawater. These lines of evidence suggests that the massive gabbro 2 was formed by the partial melting of residual MORE mantle which is contaminated with slab melt derived from the axis stage rocks interacted with seawater. In addition, petrogenesis of felsic rocks in the Lasail complex can be explained by the partial melting model of pre-existing layered gabbro. U Pb zircon ages analyzed by LA-ICPMS are 100 +/- 2 and 99 +/- 2 Ma for late stage tonalite and 100 +/- 1 Ma for axis stage quartz diorite. These ages are slightly older than the ages reported for felsic rocks in the Oman ophiolite (ca., 95 Ma), and suggest that the conversion from ridge stage to detachment stage took place rapidly. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2012.10.013

Language：English   Publishing type：Research paper (scientific journal)  

Counterclockwise P-T path and isobaric cooling of metapelites from Brattnipene, Sør Rondane Mountains, East Antarctica: Implications for a tectonothermal event at the proto-Gondwana margin
In this paper we provide evidence for a counterclockwise P-T path and isobaric cooling for metapelitic rocks from the Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica. The counterclockwise path was determined using the following mineral textures and relationships: (1) garnet coronae on sillimanite where the sillimanite is associated with spinel in orthopyroxene-bearing granulite
(2) garnets that contain inclusions of spinel, sillimanite, and corundum, and where the sillimanite and corundum have sparse tiny spinel inclusions
(3) the garnet-orthopyroxene-plagioclase-quartz equilibria relationships using the contrasting compositions of high-Mg garnet - plagioclase inclusions and high-Ca garnet coronae - matrix plagioclase point to an increase in pressure. The peak metamorphic conditions were determined by thermobarometry and pseudosection analyses, and are consistently within the ranges 850-900°C and 8-9kbar. Orthopyroxene porphyroblasts close to garnet coronae have relatively high Al2O3 contents (~6.1wt.%), consistent with the highest temperature conditions reported so far from the Sør Rondane Mountains. Prismatic subidioblastic staurolite formed as a secondary mineral along the margins of the garnets, and this retrograde staurolite indicates a back-reaction during isobaric cooling. The conditions for staurolite formation are taken to be 680-700°C and 8.5kbar using isopleths, and this is consistent with the appearance of secondary kyanite in the matrix. On the basis of the metamorphic P-T path and the tectonic setting of the precursor rocks, the following tentative scenarios can be inferred: (1) the heat source for the early sequence of metamorphism was derived from advective heat flow at an active continental margin, and (2) the subsequent increase in pressure was caused by overthrusting or obduction of either oceanic crust or oceanic island arc onto the Brattnipene region. These tectonothermal events took place along a possible proto-Gondwana margin at ca. 650-600Ma. © 2012 Elsevier B.V.

DOI： 10.1016/j.precamres.2012.10.002

Language：English   Publishing type：Research paper (scientific journal)  

Late Proterozoic juvenile arc metatonalite and adakitic intrusions in the Sør Rondane Mountains, eastern Dronning Maud Land, Antarctica
This study is a detailed investigation of the petrology and geochronology of the Late Proterozoic metatonalite in the Sør Rondane Mountains, eastern Dronning Maud Land, Antarctica. Metatonalite is dominant over roughly 100×20km2 area in the southwestern end of the mountain range and is classified into five lithologies: gneissose Bt-Hbl metatonalite, weak gneissose Hbl-Bt metatonalite, Hbl metagabbro, Hbl-Bt tonalitic gneiss, and Bt metatonalite. The gneissose Bt-Hbl metatonalite is the main lithotype widely distributed over this area, which is geochemically categorized as low-K tholeiitic granitoid. Petrological studies suggest that the tholeiitic magma was derived from low-K basalt melting at the crustal depth, and the most plausible tectonic setting is a juvenile oceanic arc. The other four metaplutonic rocks are scattered as stocks or small intrusions in this area. They are geochemically regarded as calc-alkaline adakites related to oceanic slab melting. U-Pb SHRIMP zircon ages of the tholeiitic metatonalite are concentrated at 998-995Ma, whereas the calc-alkaline adakitic rocks are younger and divided between ages 945-920Ma and 772Ma. We believe that the tholeiitic metatonalite was formed first as a juvenile arc component between 998 and 995Ma, followed by adakitic magmatism and oceanic slab melting at 945-920Ma and 772Ma. Magmatism during this stage is not recorded in the western to central Dronning Maud Land. Moreover, the exposure of an adakitic equivalent continues at the farther eastern side of the Sør Rondane Mountains. This suggests that the tectonic framework of the Sør Rondane Mountains, eastern Dronning Maud Land, is different from the western to central Dronning Maud Land. © 2012 Elsevier B.V..

DOI： 10.1016/j.precamres.2012.09.026

Language：Japanese  

Identification of the Origin for Mold Stones, Processing of Mold Material and Distribution in Northern Kyushu in the Yayoi Period

Language：English  

LA-ICP-MS U&ndash;Pb zircon and FE-EPMA U&ndash;Th&ndash;Pb monazite dating of pelitic granulites from the Mt. Ukidake area, Sefuri Mountains, northern Kyushu
This paper reports on the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U&ndash;Pb dating of zircon and on the field emission electron probe microanalyzer (FE-EPMA) U&ndash;Th&ndash;Pb dating of monazite from pelitic granulites and the surrounding Itoshima granodiorite from the Mt. Ukidake area, Sefuri Mountains, northern Kyushu. Zircons from the Itoshima granodiorite give an age of 102 ± 2 Ma. Metamorphic domains within zircons from pelitic granulites yield a slightly older age of 105 ± 2 Ma, which is consistent with ages of 100&ndash;120 Ma obtained from analysis of monazite by U&ndash;Th&ndash;Pb dating using FE-EPMA. Analysis of inherited domains within zircons from the pelitic granulite gives a narrow range of ages from 400 to 510 Ma, with a youngest age of 360 Ma. These ages are comparable with those of the Renge metamorphic rocks in north Kyushu, although the age and conditions of metamorphism at Renge are significantly different from the granulites analyzed here. Metamorphic ages for the granulites are nearly identical to the reheating age of the Higo metamorphic rocks in central Kyushu, as well as the main meta-morphic age of the Ryoke metamorphic rocks in southwest Japan. However, the age distributions of detrital zircons from the Mt. Ukidake area are different from those of the Higo and Ryoke metamorphic rocks, implying a different provenance for each metamorphic rock unit.

DOI： 10.5575/geosoc.2011.0022

Language：English   Publishing type：Research paper (scientific journal)  

Inferred ultrahigh-temperature metamorphism of amphibolitized olivine granulite from the Sor Rondane Mountains, East Antarctica
This paper reports the first evidence of ultrahigh-temperature (UHT) metamorphism from the Sor Rondane Mountains, eastern Dronning Maud Land, East Antarctica, which is evident as orthopyroxene + spinel symplectite in an amphibolitized mafic granulite. The granulite consists of olivine, orthopyroxene, clinopyroxene, pargasitic amphibole, plagioclase, and ilmenite, and it possesses a within-plate alkali basalt signature. The local bulk chemical composition of symplectite, major and trace element compositions, and thermodynamic calculations for the symplectite, suggest the presence of garnet at the high-pressure stage and that the symplectite formed from garnet, olivine, and primary orthopyroxene by decompression from more than 12 kbar at 1000 degrees C. The granulite records a subsequent amphibolite-facies overprint (<700 degrees C at <6 kbar) that involved the chemical re-equilibration of several phases. The obtained pressure-temperature (P-T) conditions and P-T path are different from the UHT metamorphism from the Schirmacher Hills, central Dronning Maud Land, which is considered to have occurred in a back-arc tectonic setting. The relatively high-P conditions and the decompression path reconstructed in the present study are similar to those reported for southern India, Sri Lanka, and part of northeastern Mozambique, possibly reflecting continental thickening and exhumation during the main collision event between East and West Gondwana. (C) 2011 Elsevier B. V. and NIPR. All rights reserved.

DOI： 10.1016/j.polar.2011.03.005

Language：Japanese  

The oldest formations in Japan
茨城県多賀山地の日立変成古生層は，産出化石により前期石炭紀以降の地層とされてきた．しかし最近広範にSHRIMP年代が測定され，多賀山地に日本最古のカンブリア系が60 km²以上にわたって広く分布することが明らかになった．A班では，原岩構造のわかるカンブリア系のうち，枕状構造や発泡構造，急冷組織などがみられる火山岩を原岩とする赤沢層と，堆積構造を残す砂泥質堆積岩や礫岩を原岩とする西堂平層，さらに赤沢層に貫入するカンブリア紀花崗岩類を見学する．また，赤沢層を不整合で覆う石炭系大雄院層基底部の礫岩などを見学する．今後，これらの露頭は日本におけるカンブリア系の模式地となることが予想される．今回は当初の研究成果に基づくものであり，今後さらに多くの研究者によってより深く研究され，日本列島形成の初期の様子が明らかになるであろう．

DOI： 10.5575/geosoc.117.S1

Language：English   Publishing type：Research paper (scientific journal)  

Ion microprobe dating of zircon from meta-igneous samples of the Hitachi metamorphic terrane of eastern Japan yields Cambrian magmatic ages. Tuffaceous schist from the Nishidohira Formation contains ca 510 Ma zircon, overlapping in age with hornblende gneiss from the Tamadare Formation (ca 507 Ma), and meta-andesite (ca 507 Ma) and metaporphyry (ca 505 Ma) from the Akazawa Formation. The latter is unconformably overlain by the Carboniferous Daioin Formation, in which a granite boulder from metaconglomerate yields a magmatic age of ca 500 Ma. This date overlaps a previous estimate for granite that intrudes the Akazawa Formation. Intrusive, volcanic, and volcaniclastic lithologies are products of a Cambrian volcanic arc associated with a continental shelf, as demonstrated by the presence of arkose and conglomerate in the lowermost Nishidohira Formation. Granitic magmatism of Cambrian age is unknown elsewhere in Japan, except for a single locality in far western Japan with a similar geological context. Such magmatism is also unknown on the adjacent Asian continental margin, with the exception of the Khanka block in far northeastern China. A 'great hiatus' in the Paleozoic stratigraphy of the Sino-Korean block also exists in the Hitachi terrane between Cambrian volcanic arc rocks and Early Carboniferous conglomerate, and may indicate a common paleogeographic provenance.

DOI： 10.1111/j.1440-1738.2011.00764.x

Language：English   Publishing type：Research paper (scientific journal)  

Major and trace element zoning of euhedral garnet in high-grade (> 900 degrees C) mafic granulite from the Song Ma Suture zone, northern Vietnam
In this study, mafic granulite and related leucosomes from the Song Ma Suture zone in northern Vietnam were investigated. Euhedral garnet appears in both granulites and leucosomes, whereas the former is partly to mostly replaced by orthopyroxene + plagioclase symplectite. Most garnets occurring both in granulite and leucosome contain an Mg-rich and Ca-poor core as well as an Mg-poor and Ca-rich mantle. Garnets in leucosomes have an Mg-rich and Ca-poor thin rim. Amphibole + quartz association is observed only in the core and mantle and not in the rim and matrix. Garnet core is characterized by flat middle to heavy rare earth element (REE) patterns and depletion of light REEs. The rim also contains high concentrations of middle REEs, whereas light and heavy REEs are further depleted in comparison with the core. The REE patterns of the mantle are completely different from core and rim, which show considerable depletion in light to middle REEs and extreme enrichment in heavy REEs. The petrographical features and REE patterns of the associated mineral phases suggest that the complex chemical zonation of garnet might be formed by dehydration melting of amphibole and multiple recrystallization of garnet.

DOI： 10.2465/jmps.100620a

Language：Japanese  

Hitachi Metamorphic Rocks : Occurrence and Geology of Meta-granitic Rocks with Cambrian SHRIMP Zircon Age
&emsp;Hitachi metamorphic rocks located in the southern part of the Abukuma Mountains, Northeast Japan, distinctively contain meta-volcanic rocks and meta/sheared granitoids. The igneous ages of meta-granite and meta-porphyry from the Hitachi metamorphic rocks were determined by the SHRIMP zircon method. In this paper, we describe occurrence, petrography, and petrochemical characteristics of these studied rocks. Meta-porphyry, with an igneous age of 506 Ma, intrudes into the meta-volcanic rocks of the Akazawa Formation of the Hitachi metamorphic rocks and has a micrographic texture and a spherulitic texture of an igneous origin. Previous studies have already reported an igneous age of 491 Ma for meta/sheared granitoids using the SHRIMP zircon method. Cambrian meta/sheared granitoid samples occur widely as a granitic body in the northeastern part of the Hitachi metamorphic rocks. (A) Meta-granite of the same age (498 Ma) as the sample used for the above dating is found as boulders in meta-conglomerates. The meta-conglomerate, which is found in the Daioin Formation of the Hitachi metamorphic rocks, lies unconformably on a Cambrian meta-granite body. Both meta-volcanic rocks and meta/sheared granitoids have chemical characteristics commonly associated with island arc volcanism. As such, the Akazawa Formation is likely to have originated in the Cambrian era, although we have no SHRIMP age for meta-volcanic rocks of the Akazawa Formation.

DOI： 10.5026/jgeography.119.245

Language：English   Publishing type：Research paper (scientific journal)  

Titanium behavior in quartz during retrograde hydration: Occurrence of rutile exsolution and implications for metamorphic processes in the Sor Rondane Mountains, East Antarctica
In the central Sor Rondane Mountains, East Antarctica, orthopyroxene felsic gneiss (OPG) was converted to hornblende-biotite felsic gneiss (HBG) by hydration that accompanied the intrusion of pegmatite. The retrograde HBG contains exsolved rutile in quartz. The composition of orthopyroxene and clinopyroxene in OPG suggests a temperature of 840 degrees C (interpreted as the near-peak temperature), and the composition of hornblende and plagioclase in HBG suggests a temperature of 670-700 degrees C (interpreted as the temperature during hydration). Ti concentrations in quartz were measured using an electron probe micro-analyzer, and Ti-in-quartz thermometers were applied. Measured Ti concentrations were 110 ppm (equivalent to 760-820 degrees C) for homogeneous quartz from OPG and 35 ppm (650-700 degrees C) for an exsolution-free area of a quartz grain from HBG. The pre-exsolution Ti concentration in quartz from HBG was reconstructed with 100 mm beam diameter and 25 kV of accelerating voltage, giving 103 ppm, similar to the value obtained for homogeneous quartz in OPG. The temperatures obtained using a Ti-in-quartz thermometer are consistent with those estimated using other thermometers. Although analysis of the main constitute minerals in HBG yields the conditions of hydration, the reconstructed pre-exsolution Ti content in quartz within HBG yields the pre-hydration conditions. Thus, the Ti-in-quartz thermometer is a potentially powerful tool with which to identify the peak or near-peak temperature conditions, even for retrogressed metamorphic rocks. (C) 2009 Elsevier B.V. and NIPR All rights reserved.

DOI： 10.1016/j.polar.2009.08.005

Language：Japanese  

第49次日本南極地域観測隊(JARE-49)夏隊・セール・ロンダーネ山地地学調査隊は,ドロンイングモードランド航空ネットワークを利用して航空機で日本から直接南極内陸山地に赴き,2007年11月23日～2008年2月5日の75日間,キャンプ生活を送りながらスノーモービルと徒歩によりセール・ロンダーネ山地中央部地域の地質学的野外調査を実施した.また,ベルギー基地,インド基地等を訪問し,国際交流を実施した.今回の野外調査は,航空機を利用した南極内陸地域野外調査の初の試みであり,2007年度にスタートした国際極年(IPY)とも連動した国立極地研究所の一般プロジェクト研究(課題番号P-5-1:代表・本吉洋一)の初年度調査でもある.本報告では,設営面での計画の立案・準備から実施経過に至る過程について詳しく述べる.The Sør Rondane Mountains field research party, part of the summer party of the 49th Japanese Antarctic Research Expedition (JARE-49), carried out geological field work in the central part of the Sør Rondane Mountains and improved international goodwill with Belgian, Indian and other national expeditions for 75 days from November 23, 2007 to February 5, 2008. The field party tried to access the Sør Rondane Mountains directly from Japan by using the Dronning Maud Land Air Network (DROMLAN), which is the first attempt at an Antarctic inland field survey just using an airplane through the 50 years of JARE history. This research expedition was linked together with the International Polar Year and also the first operation program of a research project of National Institute of Polar Research (No. P-5-1: leader, Y. Motoyoshi). This report gives the details on the operation planning and a summary of the fieldwork including logistics and weather report.

DOI： 10.15094/00009458

Publisher：Geological Magazine  

This paper reports geochemical characteristics of mafic gneisses and granulites collected from four localities in central Dronning Maud Land to evaluate the tectonic setting of their precursor rocks. Precursor rocks for the mafic gneisses and granulites in central Dronning Maud Land were formed in different geological backgrounds and tectonic settings. The mafic gneisses and granulites in the Schirmacher Hills were derived from basaltic rocks in a back-arc setting. Published U-Pb zircon ages and the geochemical variation of the basement rocks indicate their emplacement between 800 and 650 Ma, close to peak metamorphism. While similar protoliths were recognized in the inland nunataks of Hochlinfjellet, in Filchnerfjella the mafic gneisses/granulites were derived from basaltic rocks formed in marginal continental arcs or island arcs. Highly disturbed trace-element patterns indicate that the metamorphic process influenced the geochemical composition during the prograde metamorphic stage. Our results imply that the outcrops in central Dronning Maud Land with different metamorphic ages contain mafic gneisses/granulites from precursor rocks formed under different tectonic settings.

DOI： 10.1017/S0016756823000092

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Event date： 2022.9

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Venue：早稲田大学（新宿区）   Country：Japan  

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Paleostress inversion in hydro-fractured metamorphic complex using 3D aerophotography images (Sør Rondane Mountains, East Antarctica)

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Venue：国立極地研究所，立川市およびオンライン   Country：Japan  

Event date： 2020.11 - 2020.12

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Venue：国立極地研究所，立川市およびオンライン   Country：Japan  

Event date： 2020.11 - 2020.12

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Venue：国立極地研究所，立川市およびオンライン   Country：Japan  

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Metamorphic process of the Tromso Nappe in the Scandinavian Caledonides based on P-T-t history of felsic gneiss

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Andalusite and sillimanite in coarse-grained kyanite-bearing pelitic rocks from the Altai Range, Mongolia

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Geology of the Cambrian Horei felsic rocks in southern Kitakami Mountains, Japan

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Formation of biotite-quartz symplectite in Fe-Al rich granulites, north Sør Rondane Mountains, East Antarctica

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Paleogeographic consideration to the basement of the Northeast Japan Arc before the opening of the Japan Sea from the viewpoint of the belonging of the Hitachi Cambrian.

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Contrasting pressure-temperature records from the Altai Range, Mongolia; constraints from multiple growth of garnet, aluminosilicates and monazite

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LA-ICP-MS Zircon U-Pb ages for metamorphic rocks from the Highland and Wanni Complexes, Sri Lanka

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Deep crustal processs in continental collision orogens inferred from felsite inclusions in granulites

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Sr-Nd isotopes compositions of the Hikami granitic Rocks and Paleozoic granitic rocks

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Amphibolite-facies metamorphism in the Sor Rondane Mountains, East Antarctica

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Decompressional metamorphic texture of mafic granulite in Brattnipene, Sør Rondane Mountains, East Antarctica

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Partial melting of mafic metamorphic rock in the Main Zone of the Hidaka metamorphic belt in Hokkaido

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U-Pb zircon age and petrochemistry of the granitic rocks from the core of MITI-Kesennuma Oki Well, Japan

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Venue：東京学芸大学   Country：Japan  

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Venue：福岡大学   Country：Japan  

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LA-ICP-MS Zircon U-Pb ages of metamorphic rocks from the central parts of Highland Complex, Sri Lanka

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Geochronological characteristics of granitic and metagabbroic rocks from the Kurosegawa Tectonic Belt

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Source mantle of the Cretaceous magmatism in the North Kyushu and western Ryoke belt

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Metamorphic texture of Fe-rich granulites in Vesthaugen, north Sør Rondane Mountains, East Antarctica

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Petrochemical study of the Hikami Granitic rocks in the south Kitakami Mountains

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Petrology and geochronology of late Cambrian granitic rocks from southern Kitakami Mountains, Japan

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Clockwise and anti-clockwise metamorphic evolutions from the Altai Mountains in Mongolia

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High P-T experiments for h&ouml;gbomite-group minerals

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Metamorphic evolution of South Sulawesi, Central Java, and South Kalimantan in Indonesia

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Metamorphic evolution and tectonics of the Altai Mountains, Mongolia

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Geochronology of the metamorphic rocks from east-central Madagascar : constraints on crustal evolution process

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Petrology and geochronology of pelitic gneisses in the Hanhohiyn Mountains, the northwestern part of Mongolia
Hanhohiyn Mountains is located in the northwestern part of Mongolia. The mountains are mainly composed of marble, meta-quartzite and pelitic gneisses intercalating with lenticular garnet-amphibolite, garnet-orthopyroxene gneiss and so on. Pelitic gneisses are classified into garnet-sillimanite-biotite gneiss, garnet-cordierite-biotite gneiss and garnet-biotite gneiss. These gneisses indicate the peak metamorphic condition of 600-700 degree and 5.5-6 kbar accompanied by decompression. The EPMA U-Th-Pb Monazite ages concentrate between 480-510 Ma which is interpreted as the timing of the peak metamorphism.

Event date： 2011.9

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Consideration of tectonics setting to bulk chemical compositions of blueschist from the Kurosegawa tectonic zone in Japan.
We report petrography and bulk chemical compositions of Kurosegawa blueschists from Kyushu, Shikoku and Kii peninsula, and discuss their origin. Blueschists from Yaeyama metamorphic complex will also be discussed.

Event date： 2011.9

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Paleozoic subduction and collision magmatism in west Mongolia: Evidence from geochronology and geochemistry of the intrusive rocks
The Central Asian Orogenic Belt (CAOB) resulted from amalgamation of voluminous subduction – accretionary complexes of Late Neoproterozic to Mesozoic time. Mongolia is the heartland of the CAOB and geologically divided into four complexes; continental blocks, subduction complexes, sedimentary basins and Cenozoic cover sequences. The magma activity in the southern part of Lake zone would, therefore, be related to the continental collision event. Considering geochronology and geochemical features of the intrusive rocks, the subduction and collision events occurred in the Lake zone during Cambrian time. Finally, the North China craton collided to the Siberia craton, giving rise to collision-type metamorphism and S-type granite magmatism during Permian time in the Mongolian Altay region.

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High-Al-Mg gneisses and related rocks from the Mongolian Altay Mountains
We report results on geochemistry, geochronology, and P-T analyses of high-Al-Mg gneisses from the Mongolian Altay Mountains.

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Garnet, Clinopyroxene megacrysts and Garnet-bearing mantle xenoliths from the Tariat Depression, Mongolia

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Stable isotope study of metacarbonate rocks from western Mongolia : Implications for fluid-rock interaction processes in the Central Asian Orogenic Belt

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Paleozoic subduction and collision magmatism in west Mongolia : Evidence from geochronology and geochemistry of the intrusive rocks

Event date： 2011.9

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Event date： 2010.9

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Understanding metamorphic and igneous histories of the Inthanon Belt, western Thailand
Several metamorphic and igneous ages were obtained from the Inthanon Belt, western Thailand.

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Inclusions of sector zoned garnet in pelitic gneiss from the Nujiang river area, SW China

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Consideration of tectonics setting to bulk chemical compositions of blueschist from the Kurosegawa tectonic zone in Japan

Event date： 2010.9

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Zircon chemistry in UHT metamorphic rocks : examples from Napier Complex, East Antarctica

Event date： 2010.9

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Collision boundary between E- and W-Gondwana in Dronning Maud Land, East Antarctica

Event date： 2010.9

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EPMA dating of monazite in pelitic granulite from Mt. Ukidake, Kyushu

Event date： 2010.9

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Geochemical signature and P-T conditions of layered gneiss complex in the Mongolian Altai Mountains: A preliminary report

Event date： 2010.9

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Collision boundary between E- and W-Gondwana in Dronning Maud Land, East Antarctica
Recently the Dronning Maud Land region including the Sør Rondane (SR) Mountains attracts attentions for their tectonic and metamorphic evolutions through the Gondwana Super continent evolution and construction. The region is considered as the main portion of the East-West Gondwana collision during the East Africa-Antarctica Orogen (EAAO: e.g. Jacobs and Thomas, 2004). We suggest that the western and the eastern blocks would be belonging to the EAAO and E-Gondwana, respectively. The final collision boundary between them would have formed during the Pa-African time of 530-550 Ma.

Event date： 2010.9

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Whole rock geochemistry and mineral assemblage of mafic gneisses in Central Dronning Maud Land, East Antarctica

Event date： 2010.9

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Corundum and quartz in Sør Rondane Mountains, East Antarctica

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A preliminary report of EPMA dating of metamorphic rocks in the western part of Mongolia.

Event date： 2010.4

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Graphite with growth spirals in Mg-Al-rich granulite from the area to the south of Syowa Station, Antarctica

Event date： 2010.4

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Orthopyroxene- and/or spinel-bearing symplectites in mafic granulite from the Sor Rondane Mountains, East Antarctica

Event date： 2010.4

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Pan-African collision metamorphism in the Sor Rondane Mountains, Eastern Dronning Maud Land, East Antarctica

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Compositional variation of monazite in leucocratic vein from Sor Rondane Mountains, East Antarctica

Event date： 2007.9

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Metamorphic evolution of Sor Rondane Mountains, Doronning Maud Land, East ANtarctica: reconsideration
東南極セールロンダーネ山地に広域的に分布する苦鉄質変成岩類の化学組成により原岩構成に基づき帯区分され，NW-SE方向に帯状配列するA～D帯とENE-WSW方向のE～G帯である． A～D帯の最高変成条件は，約８kbar，900℃が見積もられ，メソパーサイト，転移ピジョン輝石などの超高温変成作用の痕跡もみとめられる．これらの中で，昇温期変成作用の痕跡を残すザクロ石中の残留藍晶石・十字石はA～C帯のみに見出され，後退変成過程では珪線石安定領域から紅柱石の安定な条件に至る．D帯では後退変成作用時に２次的生成された藍晶石−黒雲母−石英共生がみとめられる．一方E～G帯では緑色片岩相から珪線石や十字石−石英共生が安定な角閃岩相の変成条件しか見出されず，後退変成過程で紅柱石が生成されている．これらの３つの異なる変成過程は， SRS形成時の大陸衝突にともなう衝突型変成作用の進行過程で形成されたことが考えられる．

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Venue：国立極地研究所   Country：Japan  

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Venue：幕張   Country：Japan  

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Venue：幕張   Country：Japan  

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Venue：北海道大学   Country：Japan  

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Venue：Fukuoka   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：秋田大学   Country：Japan  

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Venue：Dali   Country：China  

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Venue：国立極地研究所   Country：Japan  

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Venue：国立極地研究所   Country：Japan  

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Venue：国立極地研究所   Country：Japan  

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Event date： 2010.9

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Understanding metamorphic and igneous histories of the Inthanon Belt, western Thailand

Language：Japanese  

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Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

Language：English  

Metamorphic texture in mafic granulites collected from talus in the Brattnipene, Sør Rondane Mountains, East Antarctica
Retrograde metamorphic P－T paths of garnet—pyroxene—bearing mafic gneisses from the Brattnipene nunataks in Sør Rondane Mountains, East Antarctica, were examined. The majority of samples preserve irregular—shaped garnet coexisting with clinopyroxene, quartz and plagioclase that developed around magnetite, ilmenite and orthopyroxene. The garnet contains fine—grained worm—like quartz inclusions. The occurrences are common in other mafic gneisses in northern Brattnipene and are interpreted as isobaric cooling textures. In another sample, garnet porphyroblasts have been replaced by symplectites of fine orthopyroxene and plagioclase. The mineral textures indicate near isothermal decompression. Retrograde P－T conditions estimated from rock containing orthopyroxene—plagioclase symplectite are within the range of 6.5 ~ 7.2 kbar, 700 ~ 780℃. Previous reports have revealed that metamorphism around Brattnipene is characterized by counterclockwise P－T path involving near—isobaric cooling. Our new finding suggests that metamorphic rocks formed by isothermal decompression should be present at higher altitude in the Brattnipene or relevant nunataks.

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Rapid techniques for zircon separation and the application for U-Pb dating
本稿では、ジルコンの迅速分離手法とLA-ICP-MSを用いたU-Pb年代測定の実例を報告する。ジルコンは岩石中には副成分鉱物として産するため、その量的な問題から多くの場合、試料からの分離が必要となる。ジルコンの分離には、現在においても重液を用いた分離法が一般的である。しかしながら、重液の使用に対する非効率性や人体に及ぼす危険性、高コストが指摘されてきた。そこで、小論ではこれらの問題を解決するために、重液を用いないジルコンの迅速分離手法を考案した。本手法では、粉末試料をビーカーや時計皿による水簸および椀掛けをすることでジルコンを30分以内に抽出することが可能であり、重液分離と比べると極めて迅速で効率よく、低コストで安全な手法といえる。ジルコンはU-Pb年代測定のほかに、包有物解析や化学組成から様々な地質事変を制約できる鉱物である。本手法は膨大なジルコン分析に対応した地質学的研究に非常に有用な手法であるとともに考古学などの他分野への応用も期待される。This report provides the rapid separation techniques of zircons and an example of U-Pb dating of the zircons using LA-ICP-MS. Zircons have been commonly separated from a sample using heavy liquid. However, previous reports have pointed out the inefficiency, harmful effect and high cost of the heavy liquid method. In this report, we provide the rapid techniques for zircon separation without using heavy liquid, and procedures just before zircon analysis, including separation, hand picking, mounting, and observation under cathodoluminescence image. In the method introduced here, the zircons can be separated only for 30 minutes per one sample just by panning with a beaker and watch glass. Therefore, this method is more efficient, quicker, lower cost and safer compared with heavy liquid separation.

DOI： 10.15017/1456056

Language：Japanese  

Geochronology of the metamorphic rocks from east-central Madagascar : constraints on crustal evolution process

Language：English  

Metamorphic evolution and tectonics of the Altai Mountains, Mongolia

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Multi-depth analysis of inclusions in metamorphic minerals
変成鉱物中の細粒包有物は, 多くの場合包有する変成鉱物の成長時に取り込まれることによって形成される. したがって, 細粒包有物の同定・解析は, 変成作用の過程を明らかにする上で有用である. しかし, これまで鏡下観察や電子プローブマイクロアナライザーによる表面分析では, 細粒包有物は充分に同定できない場合があった. 本稿では, この問題を克服するために, 九州大学大学院比較社会文化研究院地球変動講座に設置されているデジタルマイクロスコープと顕微ラマン分光分析装置を用い, 多数の微細包有物を解析する多深度解析手法を確立した. この手法では, 1μm間隔で撮影した鏡下写真とそれらの合成画像から, 包有物の三次元位置, 形状, 粒径, 色を迅速に明らかにすることができる. また, 形態による分類と包有された位置を元に, 顕微レーザーラマン分光分析装置を用いてすべての種類の包有物が同定可能である. 本手法は, 岩石学的研究はもとより, 透明物質中の内部包有物や不純物を扱う他分野にも応用できるものである.Fine-grained inclusions in metamorphic minerals are generally regarded to be trapped during the growth of the host metamorphic minerals. It suggests that identification and analyses of the each fine-grained inclusion are quite important in understanding each metamorphic evolution. However, identification and confirmation of the each inclusion phase are often difficult using conventional methods such as optical microscope observation and surface analysis by an electron microprobe analyzer. In this paper, we introduce a new analytical technique, named multi-depth analyses, to rapidly identify very fine-grained inclusions in metamorphic minerals using digital microscope and laser Raman microspectroscopy installed at Department of Environmental Changes, Faculty of Social and Cultural Studies, Kyushu University. Using this technique, three-dimensional position, shape, grain size and colors of fine-grained inclusions are distinguished easily by the multi-depth composite image in 1μm depth interval. The minerals or fluid inclusions are identified by the obtained Raman spectra even if the inclusions are quite fine-grained (≃1μm) or are situated in deeper position in thin section. This technique should be useful not only for petrological studies, but also for the other studies, e.g., archaeology, using inclusions or impurities in non-opaque matrix.

DOI： 10.15017/26212

Language：English  

Late Proterozoic juvenile arc metatonalite and adakitic intrusions in the Sor Rondane Mountains, East Antarctica

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U-Pb zircon ages of metamorphic rocks associated with blueschists from Kurosegawa Tectonic Belt

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Zircon U-Pb geochoronology and petrochemistry of Early Cretaceous adakitic granites in the Kitakmai Mountains, Japan

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Evolution of high-Al gneisses from the Mongolian Altay Mountains

DOI： 10.14824/jakoka.2011.0.99.0

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Continental collision boundary between Shanthai/Sibumasu blocks

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Paleozoic igneous activities in south-central Mongolia

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Metamorphic Evolution of High-Pressure Metamorphic Rocks from Bantimala and Barru Complex in South Sulawesi, Indonesia

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Rapid techniques for quantitative determination of major, trace and rare earth elements in low dilution glass bead using XRF and LA-ICP-MS
This report provides analytical techniques for major, trace and rare earth elements by X-ray fluorescence spectrometry (XRF) and laser ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) at Department of Environmental Changes, Faculty of Social and Cultural Studies, Kyushu University. Totally 42 elements can be measured from low dilution glass bead (sample:flux ratio of 1:2). 23 elements (SiO_2, TiO_2, Al_2O_3, total Fe_2O_3, MnO, MgO, CaO, Na_2O, K_2O, P_2O_5, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb and Ba) of each sample were measured in 80 minutes by XRF. The other 19 elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th and U) were later measured in 5 minutes by LA-ICP-MS. Synthetic samples prepared from pure chemical reagents as well as standard samples provided by Geological Society of Japan (GSJ) (20 samples) were used to define individual calibration lines for XRF analysis, and SRM612 glass standard issued by the National Institute of Standard and Technology (NIST) was used as the calibration standard for LA-ICP-MS analysis. Analytical results of the GSJ standard samples appear an agreement with their recommended values mostly within 15% differences. The system can provide abundances of the most elements in rocks, and requires only 1.8g of sample powder, hence it should be very useful not only for geological but also for archeological samples.

Language：English  

Garnet, Clinopyroxene megacrysts and Garnet-bearing mantle xenoliths from the Tariat Depression, Mongolia

DOI： 10.14824/jakoka.2011.0.100.0

Language：English  

Petrology and geochronology of pelitic gneisses in the Hanhohiyn Mountains, the northwestern part of Mongolia
Garnet and clinopyroxene megacrysts and spinel-garnet-bearing websterite from Quarternary alkali basalt erupted in the Tariat Depression of central Mongolia will be presented.

DOI： 10.14824/jakoka.2011.0.100.0

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Stable isotope study of metacarbonate rocks from western Mongolia : Implications for fluid-rock interaction processes in the Central Asian Orogenic Belt

DOI： 10.14824/jakoka.2011.0.101.0

Language：English  

High-Al-Mg gneisses and related rocks from the Mongolian Altay Mountains

DOI： 10.14824/jakoka.2011.0.99.0

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Understanding metamorphic and igneous histories of the Inthanon Belt, western Thailand

DOI： 10.14824/jakoka.2010.0.202.0

Language：Japanese  

Consideration of tectonics setting to bulk chemical compositions of blueschist from the Kurosegawa tectonic zone in Japan

DOI： 10.14824/jakoka.2010.0.173.0

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Zircon chemistry in UHT metamorphic rocks : examples from Napier Complex, East Antarctica

DOI： 10.14824/jakoka.2010.0.207.0

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Collision boundary between E- and W-Gondwana in Dronning Maud Land, East Antarctica

DOI： 10.14824/jakoka.2010.0.181.0

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EPMA dating of monazite in pelitic granulite from Mt. Ukidake, Kyushu

DOI： 10.14824/jakoka.2010.0.221.0

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Inclusions of sector zoned garnet in pelitic gneiss from the Nujiang river area, SW China

DOI： 10.14824/jakoka.2010.0.203.0

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Graphite with growth spirals in Mg-Al-rich granulite from the area to the south of Syowa Station, Antarctica

DOI： 10.14824/jakoka.2009.0.15.0

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Orthopyroxene- and/or spinel-bearing symplectites in mafic granulite from the Sor Rondane Mountains, East Antarctica

DOI： 10.14824/jakoka.2009.0.89.0

Language：English  

Pan-African collision metamorphism in the Sor Rondane Mountains, Eastern Dronning Maud Land, East Antarctica

DOI： 10.14824/jakoka.2009.0.43.0

Language：Japanese  

Compositional variation of monazite in leucocratic vein from Sor Rondane Mountains, East Antarctica

DOI： 10.14824/jakoka.2009.0.57.0

Language：Japanese  

O-203 Metamorphic evolution of Ultramafic Complex from the Sor Rondane Mountains, Dronning Maud Land, East Antarctica

DOI： 10.14863/geosocabst.2008.0.260.0

Language：Japanese  

O-204 Macroscopic geological structures and deformation in the central part of the Sor Rondane Mountains, eastern Dronning Maud Land, East Antarctica

DOI： 10.14863/geosocabst.2008.0.261.0

Language：Japanese  

O-205 Unraveling poly-metamorphic records in the high-grade metamorphic rocks from central Sor Rondane Mountains, East Antarctica

DOI： 10.14863/geosocabst.2008.0.262.0

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O-208 Relationship between orthopyroxene felsic gneiss and hornblende-biotite felsic gneiss in the Brattnipene area, Sor Rondane Mountains, East Antarctica

DOI： 10.14863/geosocabst.2008.0.265.0

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O-207 Metamorphism of the Brattnipene region, Sor Rondane Mountains, East Antarctica

DOI： 10.14863/geosocabst.2008.0.264.0

Language：Japanese  

O-206 Origin of carbonates from the southern Austkampane in the Sor Rondane Mountains, East Antarctica

DOI： 10.14863/geosocabst.2008.0.263.0

Language：Japanese  

P-15 Metamorphic history of the Yoshimi Metamorphic Rocks

DOI： 10.14863/geosocabst.2007.0.81.0

Language：Japanese  

Metamorphic evolution of Sor Rondane Mountains, Doronning Maud Land, East Antarctica : reconsideration

DOI： 10.14824/jakoka.2007.0.225.0

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture