Electron microprobe technique for U-Th-Pb and REE chemistry of monazite, and its implications for pre-, peak- and post- metamorphic events of the Lutzow-Holm Complex and the Napier Complex, East Antarctica

Monazites in high-grade metapelites from the Lutzow-Holm Complex and Napier Complex have been examined in terms of U, Th, Pb and rare earth element (REE) chemistry using an electron microprobe. The studied samples include four granulite-facies garnet-biotite-bearing metapelites from Skallen within the Lutzow-Holm Complex, and a re-hydrated garnet-sillimanite gneiss from the Mt. Riiser-Larsen area within the UHT zone of the Napier Complex. Two out of four garnet-bearing metapelitic samples from Skallen gave simple 560-500Ma monazite U-Th-Pb ages, whereas the other two samples yielded two age populations, i.e., 560-500Ma and 650-580Ma. The younger age group is consistent with the 550-520Ma metamorphic ages reported by SHRIMP. The older>580Ma monazites are relatively enriched in Nd, Sm, Gd, Dy (MREE) and depleted in Si (Ca and Th) compared with the younger (560-500Ma) ones. These older monazites possibly formed through M-HREE-enriched conditions such as garnet-free conditions, suggesting that the growth of these monazites pre-dated the peak metamorphism. Garnet-sillimanite gneiss from the Mt. Riiser-Larsen area shows various post-UHT re-hydration textures such as biotite-sillimanite aggregates, and fine-grained biotite flakes around or intracrystalline fractures within garnet porphyroblasts. Monazites enclosed within garnet cores have 2480-2440Ma U-Th-Pb ages consistent with the reported zircon and monazite SHRIMP dates. On the other hand, those associated with re-hydrated zones gave fluctuating 2200-700Ma ages. These younger ages are thought to reflect the incomplete chemical disturbance during the post-UHT crustal processes

TiO2 solubility in garnet coexisting with orthopyroxene, quartz and rutile: Ti-in-garnet thermometer for ultrahigh-temperature granulites

第6回極域科学シンポジウム[OG] 地圏11月16日（月）　国立極地研究所１階交流アトリウ

ダイ42ジ ナンキョク チイキ カンソクタイ エットウ ケイカ ホウコク 2001-2002

第42次南極地域観測隊越冬隊(第42次越冬隊)は,越冬隊長本吉洋一ほか39名が昭和基地で越冬し,第V期5カ年計画の最終年次ならびに昭和基地整備10カ年計画の最終年次にあたる観測・設営活動を行った. 昭和基地の運営は,2001年2月1日から開始し2002年1月31日に終了した.この間,昭和基地の施設の維持を行うとともに,定常観測,モニタリング研究観測を継承し,さらに宙空系,気水圏系,地学系,生物・医学系のプロジェクト研究観測を実施した. 越冬中の主な研究観測としては,宙空系のファブリーペローイメージャー,ナトリウム温度ライダー,MF/HFレーダーを用いた観測,気水圏系のエアロゾル・大気微量成分観測,内陸での浅層ボーリング,地学系の超伝導重力計,VLBI,微動アレイ観測,生物・医学系の定着氷下での光合成,光学CTD観測,ペンギンコロニー調査,ヒトの生理学的研究などが実施された.また,共通項目として多目的アンテナによるERS-2,NOAA衛星受信が行われた. 基地周辺の野外観測としては,航空機を用いた大気成分サンプリング,生物・医学および地学沿岸調査,将来の大型機導入に向けた氷上滑走路の調査などが実施された.さらに合計3回の内陸旅行が行われ,ドームふじ観測拠点再開に向けた燃料ドラムの輸送,観測拠点の保守に加え,各種雪氷学的調査が行われた. 設営関係では,機械,通信,調理,医療,航空,環境保全,設営一般(建築,フィールド・装備,映像記録,多目的アンテナ,庶務)各部門とも,昭和基地設備の運用とその維持・管理に加え,野外行動へのサポートにも力を注いだ.年々大型化・複雑化・多様化する設備の維持・管理は,とくに越冬隊設営部門に大きな負担となりつつある.特筆すべき事項として,第42次隊では新焼却炉棟が建てられ,焼却炉,生ゴミ処理機が稼働を始めた.航空部門では,越冬開始直後に発生したピラタス機の事故により,セスナ機のみの運用となった.映像記録は,年間を通じ南極の自然と隊員の姿を映像に収めた.The 42nd Japanese Antarctic Research Expedition (JARE-42) wintering team has conducted the Vth five-year JARE program during the period of February 1st 2001 to January 31st 2002, in which 40 members were engaged in the various scientific activities and maintenance of Syowa Station. The major observation programs of JARE-42 were as follows : Upper Atmo-spheric Physics-observations using Fabry-Perot imager, sodium Lidar and HFMF radar; Atmospheric Sciences and Glaciology-aerosols and air sampling, and shallow ice core drilling; Geophysics-superconducting gravity measurement, geodetic VLBI observations, and natural earthquake monitoring; Biology and Medicine-photosynthesis under sea water, populations census of penguins, and physiological and psychological adaptation to Antarctic environment, etc. In addition, satellite data receiving from ERS-2 and NOAA were also performed by using multi-purpose antenna at Syowa Station. Field activities included air sampling by using an aircraft, biological and geophysical observations, and reconnaissance survey for a possible aircraft runway around Syowa Station. Three inland traverse parties were organized, in which fuel transportation, maintenance of Dome Fuji Station, and various glaciological and geophysical observations were performed. A great efforts were made to maintain the facilities at Syowa Station by logistic personnel including mechanical engineers, radio operators, chefs, medical doctors, aircraft pilots and an engineer, an environmental engineer, a carpenter, a field assistant, a cinematographer, a satellite engineer, and an administrative officer. They were also involved in the support of field activities

Basement geological research of East Antarctica

The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

Timing of thermal events in eastern Dronning Maud Land, East Antarctica

Using cathodoluminescence (CL)images,the zircons analyzed by K. Shiraishi et al.(J.Geol.,102,47,1994) for SHRIMP U-Pb dating (prior to the use of CL images) have been re-examined in order to unravel the periods of multiple zircon growth in eastern Dronning Maud Land.In addition four new SHRIMP U-Pb zircon age determinations are presented:two from the Yamato Mountains and two from the Lutzow-Holm Complex (LHC).The major conclusion from this study is that the Grenvillian basement is not ubiquitous in the LHC.Some outcrops are of late Archean-Paleoproterozoic crustal fragments reworked during the Pan-African event. In such cases,there is no indication of a Grenvillian event.Other protoliths are derived from Meso-Neoproterozoic juvenile crust and recycled continental sediments from the margin of the craton.Thus the pre-history of the Pan-African LHC is not uniform.In the Yamato Mountains,two stages of the Pan-African event are suggested,at ~620 Ma and ~535 Ma. These two stages are similar to those recorded in the Sφr Rondane Mountains and central Dronning Maud Land further to the west.These new and revised,updated results provide important constraints on tectonic models for the formation of Gondwana

Geology of the eastern Dronning Maud Land, East Antarctica: Missing link to Sri Lanka

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Geology of Byobu Rock and Gobanme Rock, Prince Olav Coast, East Antarctica

We report here the geology of Byobu Rock and Gobanme Rock outcrops hitherto unmapped in the Prince Olav Coast, East Antarctica. Both these outcrops expose high-grade metamorphic and igneous rocks. The metamorphic rock units comprise mainly of gneisses migmatized to variable extent and amphibolites, whereas igneous rocks comprise of granites and pegmatites. Preliminary structural data obtained from the outcrops identified the regional, steep to moderately dipping foliation trend in the WNW-ESE at Byobu Rock, whereas they trend in the NW-SE direction at Gobanme Rock. Two generations of folding were identified, an earlier tight isoclinal intrafolial folds and a late regional open fold. The three deformational events identified are comparable and consistent with those reported in the neighboring outcrops in the Prince Olav Coast. Metamorphic P-T conditions estimated based on various geothermobarometries indicate that the rocks have experienced granulite grade conditions during peak metamorphism (770-880°C and 6-9kbar). The finding of orthopyroxene at Byobu Rock in this study extends the orthopyroxene-in isograd in the progressive metamorphic zone in the Lutzow-Holm Complex further eastward beyond Tenmondai Rock. Inclusions of kyanite within garnet in metapelitic rocks suggest a clockwise P-T path, consistent with the P-T paths suggested for the Lutzow-Holm Complex. Preliminary bulk rock geochemical investigations indicate that granitic rocks and quartzo-feldspathic gneiss mostly belong to volcanic arc granite suite, though their origin remains indistinct. Electron microprobe dating of monazites from representative rocks gave Pan-African ages (557±33Ma), consistent with the regional metamorphic ages reported earlier. Thus, based on the similarities on structural, petrological, geochemical and geochronological data, the Byobu Rock and Gobanme Rock are considered to be integral part of the Pan-African Lutzow-Holm Complex with analogous geological history

Rare Earth Element analysis of mafic metamorphic rocks in the Lutzow-Holm Complex, East Antarctica, using X-ray Fluorence Spectrometer

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日（木） 国立極地研究所　2階大会議室前フロ

Mineral ages for multi isotope system in phlogopite-bearing pyroxene granulite and felsic gneiss, the Howard Hills, Enderby Land, East Antarctica: Possible Proterozoic tectonothermal events in the Napier Complex

Large mafic to ultramafic blocks in felsic gneisses on the northern part of the Howard Hills, Napier Complex, East Antarctica are accompanied by phlogopite-bearing pyroxene granulite occurring in the margins of the block. In order to understand the crustal evolution of the Napier Complex, especially regarding the thermal history after peak metamorphism, Rb-Sr, Sm-Nd and U-Pb isotopic analyses have been carried out on different minerals from the phlogopite-bearing pyroxene granulite and adjacent orthopyroxene felsic gneiss. Zircon grains from the orthopyroxene felsic gneiss yielded near concordant U-Pb isotopic ages of about 2.5Ga by conventional isotope dilution methods and defined a discordia with 2.44±0.02Ga lower intercept age. This age shows the waning stage of UHT granulite facies metamorphism in the Howard Hills. Rutile fractions from pyroxene granulite yielded a near concordant U-Pb isotopic age of about 1.5Ga. This age is interpreted as the final thermal episode, excepting local igneous intrusions, in the Howard Hills region. Fluorophlogopite fractions from pyroxene granulite yielded Rb-Sr model ages of about 1.85Ga, although evidence of retrograde metamorphism with fluid activity or deformation were poor in the pyroxene granulite. An internal Sm-Nd isochron of whole rock and orthopyroxene and feldspar separated from the same sample shows 1.85±0.15Ga. The Rb-Sr phlogopite model age, along with the Sm-Nd internal isochron age, records the time when the rocks of the Howard Hills underwent medium to high grade metamorphism at temperatures well above the currently accepted closure temperature of biotite (about 300-350°C )

Calc-silicate rocks and marbles from Lutzow-Holm Complex,East Antarctica, with special reference to the mineralogy and geochemical characteristics of calc-silicate mega-boudins from Rundvagshetta

We report here the mode of occurrence of calc-silicate rocks and marbles from the Lutzow-Holm Complex, East Antarctica, and a worked example from Rundvagshetta. Calc-silicate boudins were observed in Cape Hinode, Akarui Point, Byobu Rock, Skarvsnes, Skallevikshalsen and Rundvagshetta, whereas they were reported earlier from Sinnan Rock, Cape Ryugu, Akebono Rock, Cape Hinode, Niban Rock, Kasumi Rock, Daruma Rock, Cape Omega, Langhovde, Ytrehovdeholmen and Skarvsnes. They vary in size from decimeters to few meters and are commonly enclosed within pelitic or psammitic gneisses. In addition, extensive layers of marbles and calc-silicate rocks are distributed in Skallevikshalsen. The calc-silicate mega-boudins within the layered pyroxene-gneiss from Rundvagshetta, up to 5m long and 2m thick, comprises of coarse to medium grained assemblage of scapolite+anorthite+garnet+clinopyroxene+calcite+quartz+titanite±wollastonite. Co-existing scapolite and plagioclase suggest a "minimum" estimate of peak metamorphic temperature of ～830°C . Peak metamorphic mineral assemblages equilibrated at moderate to high X_(CO2) conditions (0.3-0.7) and temperatures between 850 and 1000°C , consistent with the ultrahigh temperature metamorphic conditions reported in the region. Multistage garnet corona formation preserved in the calc-silicate assemblage suggests a local increase in hydrous fluid activity during retrogression. Preliminary bulk rock geochemistry of different mineralogical zones in the boudin shows chemical potential gradients in some major elements, especially SiO_2, Al_2O_3 and CaO, possibly controlled by the compositional variations in the protolith. Altogether, these results suggest that calc-silicate rocks preserve information on the metamorphic evolution and help us in deducing the geodynamic evolution of high-grade terrains