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The study of microstructures and crystallographic fabrics in a granulite-facies shear zone of the Hidaka Metamorphic Belt showed that the strong shearing localized within the mylonite resulted in the asymmetrical elongation of the inherited orthopyroxene porphyroclasts and the generation of fine-grained plagioclase and orthopyroxene layers as asymmetric tails of orthopyroxene porphyroclasts. The orthopyroxene porphyroclasts and the coarse plagioclase matrix surrounding them have a strong crystallographic preferred orientation acquired through deformation by dislocation creep. In contrast, the small orthopyroxene and plagioclase grains located in the tails have equant shapes and random fabric that are interpreted as the result of deformation by grain-boundary sliding. The small orthopyroxene grains are generated on the sheared rims of the orthopyroxene porphyroclasts by subgrain rotation, inheriting the orientation of the porphyroclasts before deforming by grain-boundary sliding (GBS) and losing this fabric. Additional mechanism of grain-size reduction is the disruption of orthopyroxene porphyroclasts by synthetic shear zones localized on clinopyroxene exsolutions. The switch in deformation mechanism from dislocation creep to GBS, associated with the grain-size reduction, yielded estimates of deviatoric stress one order smaller than lithostatic pressure. Besides, such theological evolution attests of the mechanical softening during deformation, which contributed to the localization of the strain within the mylonite. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.12.012

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We report the first quantitative compositional data on fluid inclusions in ultrahigh-temperature (UHT) granulites from the Napier Complex of Enderby Land, East Antarctica. Fluid inclusions in various high-grade minerals such as garnet, orthopyroxene and sapphirine from three UHT localities in the Amundsen Bay area were studied in terms of petrography and microthermometry as well as laser Raman spectroscopy. Measured melting temperatures of inclusions from all the three localities indicate that the trapped fluid phase is dominantly carbonic. Raman analyses confirmed a near pure CO2 composition with only minor dilutants such as N2 (&lt
6.0 mol%), CH4 (&lt
0.3 mol%), and H2O(&lt
0.1 mol%). CH4-bearing fluid associated with sapphirine granulites suggests low oxygen fugacity (f O2) conditions for the rocks, whereas CH4 was not detected from fluid inclusions in magnetite-bearing high-f O2 garnet granulite. The range of CO2 isochores computed from density measurements in fluid inclusions from the granulites pass through the peak P-T conditions of the Napier metamorphism (T = 1050-1150 °C, P = 9-11kbar) indicating synmetamorphic nature of the fluids. Inclusions in garnet from Bunt Island coexist with carbonate minerals (magnesite) and graphite along with dense CO2-rich fluid, indicating probable derivation from deep-seated primary magmatic sources. The ubiquitous association of carbonic fluids in the UHT mineral assemblages suggests CO2 influx during extreme crustal metamorphism of the Napier Complex. The carbonic fluid probably played an important role in transporting heat from mantle or mantle-derived magmas and in stabilizing the dry mineral assemblages. © The Geological Society of London 2008.

DOI： 10.1144/SP308.15

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This paper presents a form-line map of the Napier and Rayner Complexes, East Antarctica, constructed from attitude data for foliations shown on published geological maps, and discusses the macroscopic geological structures. The form-line map shows that the two complexes consist of several, structurally distinct, units or blocks bounded by east-west-,NE-SW- and NW-SE-striking faults. The major boundary between the two complexes, as indicated on the published geological maps, is a structural discontinuity shown as a large fault on the form-line map. On the form-line map, east-west- and NE-SW-trending folds are abundant and NW-SE-trending ones occur locally in both complexes. North-south-trending folds are also abundant in the Napier Complex. Dome-and-basin fold patterns on a regional scale occur in some regions. The regional strikes, macroscopic structures, and the major boundary between the two complexes are considered to have resulted from the same later deformation episode. The form-line map and distribution map of key mineral assemblages show that the Napier Complex is not uniform and includes at least two types of metamorphic units or fragments of the Archaean crust that were formed through distinct P-T-t evolutionary processes and divided by several faults. © The Geological Society of London 2008.

DOI： 10.1144/SP308.6

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The Geological Survey of Japan, AIST, has been monitoring groundwater in and around the Kinki and Tokai districts for earthquake prediction research. The Niigata Prefectural Office has also been observing groundwater for monitoring land subsidence in Niigata Prefecture. The 2004 Niigata-Chuetsu (M(JMA) 6.8) and 2007 Chuetsuoki (M(JMA) 6.8) earthquakes occurred in Niigata Prefecture, Japan, on October 23, 2004 and July 16, 2007, respectively. The two earthquakes have a similar magnitude, epicenter, and mechanism. At many of the observation wells, we detected changes in groundwater level or pressure related to the two earthquakes, but no clear precursory changes. At all of our observation wells in Niigata Prefecture, trend changes were observed after coseismic step-like changes for both of the earthquakes. At some of the Stations in and around the Kinki and Tokai districts, coseismic trend changes and/or step-like changes were observed. The pattern of the changes were almost similar for the two earthquakes. Those changes were considered to be caused not by the static crustal deformation but by the ground shaking.

DOI： 10.1186/BF03352873

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Asia grew in the Late Permian by the collision of a number of micro-continents. Syn- to post-collisional magmatism occurred along the continental collision zones. In this study, we report two types of granitic rocks, garnet granite (Grt granite) and orthopyroxene granite (Opx granite), from the Kontum massif, central Vietnam, which is situated on the continental collision zone between the South China and Indochina cratons. These granitic rocks were formed at ca. 250 Ma when high-temperature (HT) and ultrahigh-temperature (UHT) metamorphism took place in the same zone. Based on the petrological and geochemical features compared with previously reported experimental results, garnet-bearing granite is derived from pelitic gneisses by partial melting, whereas orthopyroxene-bearing granite is produced by the partial melting of garnet-bearing mafic granulites. We inferred that a significantly high-geothermal gradient is required to produce Vietnamese granitic magmatism and related HT to UHT metamorphism. This geotherm may be attributed to upwelling mantle plume beneath the Kontum massif during the Late Permian. (c) 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2006.11.001

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This paper presents a regional scale observation of metamorphic geology and mineral assemblage variations of Kontum Massif, central Vietnam, supplemented by pressure-temperature estimates and reconnaissance geochronological results. The mineral assemblage variations and thermobarometric results classify the massif into a low- to medium-temperature and relatively high-pressure northern part characterised by kyanite-bearing rocks (570-700 degrees C at 0.79-0.86 GPa) and a more complex southern part. The southern part can be subdivided into western and eastern regions. The western region shows very high-temperature (> 900 degrees C) and -pressure conditions characterised by the presence of garnet and orthopyroxene in both mafic and pelitic granulites (900-980 degrees C at 1.0-1.5 GPa). The eastern region contains widespread medium- to high-temperature and low-pressure rocks, with metamorphic grade increasing from north to south; epidote- or muscovite-bearing gneisses in the north (< 700-740 degrees C at < 0.50 GPa) to garnet-free mafic and orthopyroxene-free pelitic granulites in the south (790-920 degrees C at 0.63-0.84 GPa). The Permo-Triassic Sm-Nd ages (247-240 Ma) from high-temperature and -pressure granulites and recent geochronological studies suggest that the south-eastern part of Kontum Massif is composed of a Siluro-Ordovician continental fragment probably showing a low-pressure/temperature continental geothermal gradient derived from the Gondwana era with subsequent Permo-Triassic collision-related high-pressure reactivation zones. (c) 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2007.01.003

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DOI： 10.5575/geosoc.112.654

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Nd model ages using depleted mantle (TDM) values for the sedimentary rocks in the Inner Zone of the SW Japan and western area of Tanakura Tectonic Line in the NE Japan allow classification into five categories: 2.6-2.45, 2.3-2.05, 1.9-1.55, 1.45-1.25, and 1.2-0.85 Ga. The provenance of each terrane/belt/district is interpreted on the basis of the TDMs, Sm-147/Nd-144 vs. Nd-143/Nd-144 relation, Nd isotopic evolution of the source rocks in East China and U-Pb zircon ages. The provenance of 2.6-1.8 Ga rocks, which are reported from Hida-Oki and Renge belts and Kamiaso conglomerates, is inferred to be the Sino-Korean Craton (SKC). The 2.3-1.55 Ga rocks, mostly from Ryoke, Mino and Ashio belts, are originally related with the SKC and/or Yangtze Craton (YC). The provenances of the sedimentary rocks with 1.45-0.85 Ga, from the Suo belt, Higo and some districts in the Mino and Ashio belts, are different from the SKC and YC. Especially, the Higo with 1.2-0.85 Ga is considered as a fragment of collision zone in East China. Akiyosbi belt probably belongs to the youngest age category of 1.2-0.85 Ga.
Some metasedimentary rocks from the Ryoke belt have extremely high Sm-147/Nd-144 and Nd-143/Nd-144 ratios, whose main components are probably derived from mafic igneous rocks within the Ryoke belt itself and from the adjacent Tamba belt. (c) 2005 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2005.11.001

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The Higo terrane in west-central Kyushu Island, southwest Japan consists from north to south of the Manotani, Higo and Ryuhozan metamorphic complexes, which are intruded by the Higo plutonic complex (Miyanohara tonalite and Shiraishino granodiorite). The Higo and Manotani metamorphic complexes indicate an imbricate crustal section in which a sequence of metamorphic rocks with increasing metamorphic grade from high (northern part) to low (southern part) structural levels is exposed. The metamorphic rocks in these complexes can be divided into five metamorphic zones (zone A to zone E) from top to base (i.e., from north to south) on the basis of mineral parageneses of pelitic rocks. Greenschist-facies mineral assemblages in zone A (the Manotani metamorphic complex) give way to amphibolite-facies assemblages in zones B, C and D, which in turn are replaced by granulite-facies assemblages in zone E of the Higo metamorphic complex. The highest-grade part of the complex (zone E) indicates peak P-T conditions of ca. 720 MPa and ca. 870 degrees C. In addition highly aluminous Spr-bearing granulites and related high-temperature metamorphic rocks occur as blocks in peridotite intrusions and show UBT-metamorphic conditions of ca. 900 MPa and ca. 950 degrees C. The prograde and retrograde P-T evolution paths of the Higo and Manotani metamorphic complexes are estimated using reaction textures, mineral inclusion analyses and mineral chemistries, especially in zones A and D, which show a clockwise P-T path from Lws-including Pmp-Act field to Act-Chl-Epi field in zone A and St-Ky field to And field through Sil field in zone D. The Higo metamorphic complex has been traditionally considered to be the western-end of the Ryoke metamorphic belt in the Japanese Islands or part of the Kurosegawa-Paleo Ryoke terrane in south-west Japan. However, recent detailed studies including Permo-Triassic age (ca. 250 Ma) determinations from this complex indicate a close relationship with the high-grade metamorphic terranes in eastern-most Asia (e.g., north Dabie terrane) with similar metamorphic and igneous characteristics, protolith assembly, and metamorphic and igneous ages. The north Dabie high-grade terrane as a collisional metamorphic zone between the North China and the South China cratons could be extended to the N-NE along the transcurrent fault (Tan-Lu Fault) as the Sulu belt in Shandong Peninsula and the lmjingang belt in Korean Peninsula. The Higo and Manotani metamorphic complexes as well as the Hida-Oki terrane in Japan would also have belonged to this type of collisional terrane and then experienced a top-to-the-south displacement with forming a regional nappe structure before the intrusion of younger Shiraishino granodiorite (ca. 120 Ma). 0 2005 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2005.06.008

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The Mid-Niigata Prefecture earthquake in 2004 (M-JMA 6.8) generated surface ruptures along the eastern rim of the Uonuma Hills. To elucidate the structural linkage between the surface ruptures and the source fault at depth, the high-resolution seismic reflection profile across the surface ruptures and nearby active faults, and the data of aftershock distribution are examined. The 5.2-km-long, high-resolution, depth-converted seismic section reveals an emergent thrust beneath the surface ruptures. A two-dimensional model of the fault geometry has been constructed based on the aftershock distribution and the shallow reflection profile. The development of the main geologic structure are well explained by forward modeling using a balanced cross-section method. In detail, the fault system generated the main shock dips at a steep angle (60 degrees) below 5 km depth and more shallowly (30 degrees) near the surface.

DOI： 10.1186/BF03351832

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DOI： 10.1186/BF03353343

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DOI： 10.1186/BF03353344

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The Nd-isotopic data on sedimentary and metamorphic rocks of SW Japan Arc allow their discrimination into five different depleted mantle (TDM) model age clusters, 2.6-2.45 Ga, 2.3-2.05 Ga, 1.9-1.55 Ga, 1.45-1.25 Ga, 1.2-0.85 Ga. The 2.6-2.45 Ga and 1.9-1.55 Ga model ages are also coincident with U-Pb inherited zircon ages of the above two epochs as well as the major magmatic activity in the Sino-Korean Craton (SKC). The 2.3-2.05 Ga model ages can be considered as the initial formation ages for the precursors of sedimentary rocks. The Nd-isotopic data suggest that the Hida Belt was most likely formed as a part of the SKC. The mantle underlying the Ryoke Belt had continental lithospheric signature during Triassic-Jurassic period. The 1.9-1.55 Ga model ages, especially 1.8 Ga∼, can be associated with the formation of this belt. The source material for the sedimentary rocks occurring in the accretionary terrane of northeastern areas in the SW Japan Arc was probably in and around the SKC of the Ryoke Belt itself. The sedimentary rocks occurring in southwestern areas of the Arc were mainly composed of materials derived from a relatively younger source (1.45-0.85 Ga).

DOI： 10.2183/pjab.80.1

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Garnet-bearing mafic granulites from the Ngoc Linh Complex of the Kontum massif in central Vietnam occur as lenses or blocks within felsic gneisses. Some of these granulite blocks show some evidences for ultrahigh-temperature and high-pressure metamorphism. Samples studied here consist mainly of garnet (Alm34-48, Prp27-34, Grs18-24, Sps0-3), clinopyroxene (Mg# = 0.73-0.87) and quartz, which are relatively large grains. The garnet and clinopyroxene are surrounded by symplectites composed of orthopyroxene, plagioclase, magnetite and sometimes spinel. Therefore, the presumed equilibrium peak-pressure assemblage could be of garnet, clinopyroxene and quartz, which was stable at eclogite-facies conditions. Dual-stage generated symplectites involving orthopyroxene and plagioclase were identified among garnet, clinopyroxene and quartz. The first-generated symplectite is composed of Al- and Mg-poor orthopyroxene (Mg# = 0.61-0.68, Al 2O 3 = 1.5-2.6 wt%) and Na-rich plagioclase (An45-53). The second symplectite is composed of Al- and Mg-rich orthopyroxene (Mg# = 0.69-0.72, Al 2O 3 = 4.1-5.3 wt%), Na-poor plagioclase (An86-93), spinel (Mg# = 0.42-0.48) and magnetite. The compositional differences between the two symplectites can be interpreted to be due to the difference in metamorphic reaction stages. The first symplectite had been formed by the reaction between garnet, clinopyroxene and quartz, which occurred during the decompression process just after peak-pressure conditions. The second symplectite could be produced during the late breakdown of garnet. Temperature and pressure conditions around peak-pressure conditions are estimated from the garnet-clinopyroxene thermometries and from the reaction of jadeite + quartz = albite, respectively. The results indicated peak-pressure conditions as ca. 950°C and 1.6 GPa. The pressure-temperature conditions for the formations of first- and second-symplectites were 1000°C at 1.3 GPa and 850°C at 0.8 GPa, respectively. Whole mineral assemblages of the mafic granulites show that the metamorphic evolution took place under completely dry conditions. The textual observations as well as the pressure-temperature estimations indicate a near isothermal decompression process for this granulite. This evolution path is consistent with that of ultrahigh-temperature pelitic granulites from the Kannak Complex. Thus, the possibility of simultaneous ultrahigh-temperature metamorphic event in the Kontum massif can be argued.

DOI： 10.2465/jmps.99.242

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Many pseudotachylytes and their related fault rocks are found in the Hidaka metamorphic belt representing an ancient crustal section. On the basis of field observations of the pseudotachylytes and related fault rocks, nature of seismogenic faulting in the Hidaka crust is examined. The field observations suggest the following conclusions. (1) Two structural types of pseudotachylytes are distinguished: layer-parallel and layer-oblique. The latter are scattered in the metamorphic belt, but the former occur only in the southern part of the metarnorphic belt. (2) An abundance of the layer-parallel pseudotachylytes suggests that earthquakes occurred repeatedly and frequently in the southern part, where complicated and duplicated crustal structures occur with many low-temperature thin mylonite zones. The southern part with such crustal structures was an ancient seismogenic area containing asperities and having a radius of a few tens of kilometers in the Hidaka crust. In the seismogenic area, the layer-parallel pseudotachylytes resulted from seismic slip on the mylonitic foliation within the low-temperature mylonite zones with strong preferred orientation of micas. (3) The layer-parallel pseudotachylytes and the subsequent layer-oblique pseudotachylytes post-date the latest and very-low-temperature mylonitization in the metarnorphic belt. The former pseudotachylytes formed just above the upper side of the brittle-plastic transition zone.

DOI： 10.1186/BF03353342

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The Kontum massif in central Vietnam consists of low-grade schists and amphibolite- to granulite-facies metamorphic rocks, that have been intruded by S-type and I-type granites. This terrane was formerly considered to be composed mainly of Archean granulites (the Kannak Complex), Proterozoic amphibolite-facies metamorphic rocks (the Ngoc Linh Complex) and low-grade schists (the Kham Duc Complex). They were thought to be the basement of the Indochina Craton in south-east Asia. The Kannak Complex is dominated by pelitic-semipelitic gneisses metamorphosed under high- to ultrahigh-temperature (UHT) conditions into granulite-facies. A minor amount of mafic and calc-silicate rocks are also intercalated within the gneisses. The major types of ultrahigh-temperature pelitic metamorphic rocks in this complex are garnet-orthopyroxene-sillimanite-cordierite gneiss, orthopyroxene-bearing garnet-cordierite-silliamnite-biotite gneiss and garnet-orthopyroxene charnockitic gneiss. The highest-grade metamorphic condition is determined from garnet-orthopyroxene-sillimanite-cordierite gneiss, which indicates that multi-stage symplectite formation during retrograde stage started from isothermal decompression in UHT condition (1000°C&lt
). Because of the high amount of pyrope (up to 59 mole%) in garnet and high-Al 2O 3 in orthopyroxene (up to 10 wt%), these minerals were unstable in the P-T conditions during the retrograde stage. On the other hand, the newly found garnet-clinopyroxene-orthopyroxene granulites (eclogitic ultrahigh-temperature mafic granulite) from the Ngoc Linh Complex shows a series of changes in divariant assemblages from garnet-clinopyroxene-quartz to hornblende-quartz through clinopyroxene-orthopyroxene-plagioclase-(garnet). It was identified that these rocks were formed as a result of their metamorphic evolution of isothermal decompression followed by nearly isobaric cooling. The ultrahigh-temperature metamorphic rocks in the Kontum massif, which are exposed along the Dac To Kan shear zone, show a clockwise pressure-temperature path with the peak metamorphic condition of ca. 12 kbar and ca. 1050°C (M1 metamorphism). High-pressure M0 metamorphism (ca. 17 kbar&lt
, ca. 1000°C) as part of the prograde metamorphism and low-pressure (but still ultrahigh-temperature) M2 metamorphism (9-10 kbar, ca. 1000°C) as part of the retrograde metamorphism during the clockwise pressure-temperature evolution are also recognized. The widely reported Permo-Triassic metamorphic event (ca. 240-260 Ma) from the ultrahigh-temperature metamorphic rocks would indicate a rapid metamorphic evolution from M0 stage to low-pressure and low-temperature retrograde stage (later M2 stage). The recently determined Sm-Nd internal isochron age of 670 Ma for the garnet amphibolite and monazite-CHIME age of ca. 480-500 Ma for the pelitic granulites from the Kannak Complex would also indicate that the Kontum massif had also undergone the Pan-African metamorphic event. The present results indicate that ultrahigh-temperature metamorphic rocks from the Kontum massif are remnants of previously metamorphosed rocks that might be derived from the Gondwana super continent and then re-metamorphosed by the Permo-Triassic metamorphism during the continents collision in eastern Asia.

DOI： 10.2465/jmps.99.225

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Pargasites (F/(F + Cl + OH) ratio (X-F) of up to 0.48) from Tonagh Island in Enderby Land, East Antarctica are closely associated with typical high-grade minerals such as orthopyroxene in quartzo-feldspathic, mafic, and ultramafic granulites, and is regarded as a stable mineral at the peak metamorphic conditions (>1100 degreesC) calculated for the ultrahigh-temperature Archean Napier Complex. Although experimental investigations have suggested that the upper thermal stability limit of F-free pargasite is below 1050 degreesC, thermodynamic calculations for the present pargasite +quartz assemblage indicate that the thermal stability limit of pargasite with X-F = 0.5 is about 150 degreesC higher than that of the hydroxyl end member. Fluorine substitution in the pargasite therefore allowed the mineral to survive the ultrahigh-temperature metamorphism at Tonagh Island.
A positive correlation between the F content of pargasite and coexisting biotite indicates that the minerals approach chemical equilibrium in terms of F-OH distribution. Although the fluorine composition of pargasites (X-F=0.12-0.48) and bulk rock (300-2500 ppm) varies widely, the log(f(H2O)/F-HF) values calculated for these rocks are relatively constant (3.2-3.7), which is consistent with infiltration of an F-bearing fluid during prograde metamorphism. The infiltration of such a fluid is also supported by the higher bulk F content of most of the analyzed samples compared to those of continental and oceanic basaltic rocks, that is, F had been added from an external source. A positive correlation between bulk MgO and F content suggests that F may have been selectively trapped in high-X-Mg pargasite in MgO-rich rocks. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0024-4937(03)00087-2

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Sm-Nd internal isochron ages involving retrograde garnet determined from three ultrahigh-temperature (UHT) gneisses taken from Tonagh Island, the western part of the Napier Complex, East Antarctica gave 1870±82 Ma, 1897±50 Ma and 1557±35 Ma. These ages are younger than the late Archaean timing of UHT metamorphism in the Napier Complex. The ca. 1900 Ma age is considered to reflect an important tectonothermal event in the Napier Complex including a tholeiite dyke intrusion. On the other hand, the ca. 1600 Ma age represents a thermal modification lacking signs of deformational events, and separates from the ca. 1900 Ma event. The related East Gondwana fragments such as the Rayner Complex in Antarctica and the Eastern Ghats Belt in India record extensive tectonothermal event of ca. 1400-1600 Ma, and rare indications of ca. 1900-2000 Ma. It is stressed that the assembly of East Gondwana including the Napier Complex, the Rayner Complex, and the Eastern Ghats Belt, if it existed, should be before ca. 1600 Ma, and may be traced back to ca. 2000 Ma of the supercontinent 'Columbia' era.

DOI： 10.1016/S1342-937X(05)70972-2

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The ultrahigh-temperature “UHT” metamorphism of the Napier Complex is characterized by the presence of dry mineral assemblages, the stability of which requires anhydrous conditions. Typically, the presence of the index mineral orthopyroxene in more than one lithology indicates that H2O activities were substantially low. In this study, we investigate a suite of UHT rocks comprising quartzo-feldspathic garnet gneiss, sapphirine granulite, garnet-orthopyroxene gneiss, and magnetite-quartz gneiss from Tonagh Island. High Al contents in orthopyroxene from sapphirine granulite, the presence of an equilibrium sapphirine-quartz assemblage, mesoperthite in quartzo-feldspathic garnet gneiss, and an inverted pigeonite-augite assemblage in magnetite-quartz gneiss indicate that the peak temperature conditions were higher than 1,000 °C. Petrology, mineral phase equilibria, and pressure-temperature computations presented in this study indicate that the Tonagh Island granulites experienced maximum P-T conditions of up to 9 kbar and 1,100 °C, which are comparable with previous P-T estimates for Tonagh and East Tonagh Islands. The textures and mineral reactions preserved by these UHT rocks are consistent with an isobaric cooling “IBC” history probably following an counterclockwise P-T path. We document the occurrence of very high-density CO2-rich fluid inclusions in the UHT rocks from Tonagh Island and characterize their nature, composition, and density from systematic petrographic and microthermometric studies. Our study shows the common presence of carbonic fluid inclusions entrapped within sapphirine, quartz, garnet and orthopyroxene. Analysed fluid inclusions in sapphirine, and some in garnet and quartz, were trapped during mineral growth at UHT conditions as 'primary' inclusions. The melting temperatures of fluids in most cases lie in the range of -56.3 to -57.2 °C, close to the triple point for pure CO2 “-56.6 °C”. The only exceptions are fluid inclusions in magnetite-quartz gneiss, which show slight depression in their melting temperatures “-56.7 to -57.8 °C” suggesting traces of additional fluid species such as N2 in the dominantly CO2-rich fluid. Homogenization of pure CO2 inclusions in the quartzo-feldspathic garnet gneiss, sapphirine granulite, and garnet-orthopyroxene gneiss occurs into the liquid phase at temperatures in the range of -34.9 to + 4.2 °C. This translates into very high CO2 densities in the range of 0.95-1.07 g/cm3. In the garnet-orthopyroxene gneiss, the composition and density of inclusions in the different minerals show systematic variation, with highest homogenization temperatures “lowest density” yielded by inclusions in garnet, as against inclusions with lowest homogenization “high density” in quartz. This could be a reflection of continued recrystallization of quartz with entrapment of late fluids along the IBC path. Very high-density CO2 inclusions in sapphirine associated with quartz in the Tonagh Island rocks provide potential evidence for the involvement of CO2-rich fluids during extreme crustal temperatures associated with UHT metamorphism. The estimated CO2 isochores for sapphirine granulite intersect the counterclockwise P-T trajectory of Tonagh Island rocks at around 6-9 kbar at 1,100 °C, which corresponds to the peak metamorphic conditions of this terrane derived from mineral phase equilibria, and the stability field of sapphirine + quartz. Therefore, we infer that CO2 was the dominant fluid species present during the peak metamorphism in Tonagh Island, and interpret that the fluid inclusions preserve traces of the synmetamorphic fluid from the UHT event. The stability of anhydrous minerals, such as orthopyroxene, in the study area might have been achieved by the lowering of H2O activity through the influx of CO2 at peak metamorphic conditions “&gt
1,100 °C”. Our microthermometric data support a counterclockwise P-T path for the Napier Complex.

DOI： 10.1007/s00410-001-0343-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Inc.  

DOI： 10.1016/S1342-937X(05)70518-9

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DOI： 10.5575/geosoc.105.729

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)  

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