Pan-African adakitic rocks from the Sør Rondane Mountains, East Antarctica

The Sør Rondane Mountains (22°E -28°E ) are located in eastern Dronning Maud Land, East Antarctica, and consist of amphibolite to granulite facies metamorphic rocks and various intrusive rocks. Peak metamorphism took place during the Pan-African event. Considering the mode of occurrence and previously reported age data, felsic magma activity started at the waning stage of the metamorphism. In this study, we report on the petrogenesis of discordantly intruding post-tectonic pyroxene tonalite (Px tonalite) with adakitic composition. In addition, the petrogenesis of posttectonic biotite granite (Bt granite), of which the geochemical features are similar to high-K adakite in the collision zone, are reevaluated with reference to the Px granite. The initial Sr isotopic ratios (SrI) corrected to 525Ma of Px tonalite and Bt granite represent limited values (0.7037-0.7052) that are included within the SrI of the Proterozoic metatonalite corrected to the same age (525Ma). These Sr isotopic signatures combined with geochemical modeling suggest that chemical variation of Px tonalite and Bt granite can be explained by partial melting of the Proterozoic metatonalite with various degrees of melting, leaving garnet as a residual phase, subsequent to fractional crystallization and/or accumulation of specific phases. Taking the tectonic situation and geochemical signature into account, Px tonalite and Bt granite from the Sør Rondane Mountains are correlated to the collision zone adakite and represent the post-collision magmatism in the suture zone during the Gondwana formation of the Pan-African event

Resetting and closing codition of Rb-Sr whole-rock isochron system: some samples of metamorphic and granitic rocks from the Gondwana super-continent and Japan Arc

The closure temperature of the Rb-Sr whole-rock system for felsic rocks has been generally considered to be ca. 700゜C, but it falls to ca. 400゜C, as a result of efficient action of fluids,especially H_2O. Thus,the Rb-Sr whole-rock ages obtained by rocks collected from a single outcropto specimen-size are not always coincident with those of emplacement of granitic magma or partial melting under high grade metamorphism.Although the Rb-Sr whole-rock isochron ages of metamorphic rocks collected from a wide area have been sometimes interpreted as those of metamorphism,careful consideration for these ages is needed

Geology of eastern Muhlig -Hofmannfjella and Filchnerfjella in Dronning Maud Land, East Antarctica; A preliminary report of a Japan-Norway-Germany joint geological investigation

The geological history of Filchnerfjella and surrounding areas (2゜E to 8゜E) in central Dronning Maud Land,East Antarctica,is constructed from metamorphic and igneous petrology,and structural investigations.The geology of Filchner-fjella consists mainly of metamorphic rocks accompanied by intrusive rocks.Two stages of metamorphism can be recognized in this area.The earlier stage metamorphism is defined as a porphyroblast stage (garnet,hornblende,and sillimanite stable), and the later one is recognized as a symplectic stage (orthopyroxene and cordieritestable).Taking metamorphic textures and geothermobarometries into account,the rocks experienced an early high-P/medium-T followed by a low-P and high-T stage. Partial melting took place during the low-P/high-T stage,because probable melt of leucocratic gneiss contains cordierite.The field relationships and petrography of the syenite at Filchnerfjella are similar to those of post-tectonic plutons from central Dronning Maud Land,and most of the post-tectonic intrusive rocks have within-plate geochemical features.The structural history in Filchnerfjella and surrounding areas can be divided into the Pan-African stage and the Meso to Cenozoic stage that relates to the break-up of Gondwana

Fluid inclusions in an osumilite-bearing granulite from Bunt Island in the Archean Napier Complex, East Antarctica: implications for a decompressional P-T path?

We report high-density CO_2-rich fluid inclusions in garnet,orthopyroxene,and quartz from an osumilite-bearing aluminous granulite from Bunt Island of the Archean Napier Complex,East Antarctica.The melting temperatures of fluids lie in the range of -56.8 to -57.8゜C being close to the triple point for pure CO_2 (-56.6゜C ). Homogenization of the CO_2,-rich fluids into the liquid phase occurs at temperatures in the range of -35.4 to 24.7゜C. This translates into CO_2 densities in the range of 0.788-1.084g/cm^3 .The estimated CO_2 ,isochore for high-density inclusions in garnet intersects the P-T trajectory of Bunt Island at around 10 kbar at 1050゜C, which corresponds to the peak metamorphic conditions of the region derived from mineral phase equilibria.We therefore infer that CO_2 ,was the dominant fluid species present during the ultrahigh-temperature metamorphism in Bunt Island.CO_2 inclusions with lower density occurring in quartz and garnet provide isochores that intersect the P-T path at <7 kbar and <950゜C indicating density reversal of originally high-density inclusions along a decompressional exhumation path of the ultrahigh-temperature rocks in the Bunt Island

Effect of bond valence sum on the structural modeling of lead borate glass

The structural model of 66.7PbO-33.3B2O3 glass was constructed using a reverse Monte Carlo (RMC) method, in which bond valence sum (BVS) was added as a constraint condition to suppress formation of unrealistic local structures. Based on the crystal structures, the optimal BVS calculating conditions were determined. As a result, BVS distributions with small deviation were successfully achieved without lowering the reproducibility of other experimental constraints. The geometric asymmetry of PbOn polyhedra was evaluated from the eccentric distance between Pb and gravity center of oxygen atoms. The average eccentric distance was shorter than that in the lead borate crystals, indicating less asymmetry of PbOn units in the RMC glass model. The connectivity between BOn and PbOn units was investigated. It was consequently concluded that the glass had a different network structure from the crystal with the same composition, which might be due to the different chemical bonding character between the lead borate glasses and crystals

Mineral paragenesis and its implications in the högbomite-bearing skarn, Sør Rondane Mountains, East Antarctica

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

ナンキョク ヤガイ チョウサ ニ オケル タイヨウコウ ハツデン システム ノ カツヨウ ダイ50ジ ニホン ナンキョク チイキ カンソクタイ セール・ロンダーネサンチ チガク チョウサタイ ノ レイ

第50次日本南極地域観測隊(第50次隊)夏隊のセール・ロンダーネ山地地学調査隊は67日間におよぶ野外調査を行い,その間に必要な電力を太陽光発電で賄った.今回使用した太陽光発電システム(出力電圧約12 V)の1日あたりの発電量は6724 Ahであった.そして,この調査によって以下の3つの重要なことが明らかとなった.1)南極での野外調査生活に必要な電力は太陽光発電システムにより得ることが可能である.2)最大出力電流2.3 Aの太陽パネルは1日あたり910 Ahを発電する.3)夏季の南極は白夜のために日照が途絶える事はないが,当山地では0000 LTから0500 LT (昭和基地時刻) の間に太陽光発電ができない.The field party in the Sør Rondane Mountains, a part of the summer party of the 50th Japanese Antarctic Research Expedition (JARE-50), performed as outdoor survey using a solar-electric system for field camping over a period of 67 days. The total amount of power generation (output: ca 12V) varied from 67 to 24 Ah/day. We obtained three important conclusions: 1) Electric power is sufficiently supplied from the solar-electric system in the field camp. 2) The solar panel (maximum output 2.3 A) used by JARE-50 generates 9-10Ah/day. 3) The solar panel did not produce electric power during the midnight sun (0000-0500 LT; the time for Showa Station area) in the Antarctic summer season

ヒガシ ドロンイングモードランド, セール・ロンダーネ サンチ チガク チョウサタイ ホウコク 2008-2009 (JARE-50)

第50次日本南極地域観測隊(JARE-50)夏隊・セール・ロンダーネ山地地学調査隊は,山地西部地域の地質調査を実施した(国立極地研究所一般研究プロジェクト,P-5-1:代表・本吉洋一).調査地へは,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空路ケープタウンから山地に入った.メンバーの構成は,地質調査担当5名とフィールドアシスタント1名である.調査地では三つのキャンプ(ベースキャンプ,前進キャンプ1および前進キャンプ2)を設営し,75日間すべてテントで生活した.本報告では,セール・ロンダーネ山地地学調査隊の設営,西部の気象条件および野外調査結果を含め,調査計画から実施に至る過程について記述する.The Sør Rondane Mountains field party, part of the summer party of the 50th Japanese Antarctic Research Expedition (JARE-50), consisted of five geologists and one field assistant, and conducted geological fieldwork in the western Sr Rondane Mountains, Eastern Dronning Maud Land, as part of a research project of the National Institute of Polar Research (#P-5-1). The field party accessed the mountains using the Dronning Maud Land Air Network (DROMLAN) from Cape Town to a runway close to the Belgian base, via the Novolazarevskaya runway. The field party made three campsites (Base Camp, Camp 1, and Camp 3) and stayed on the snowfield for 75 days. Here, we report the detailed operation plans and present a summary of the fieldwork, including information on logistics and weather reports for the western Sør Rondane Mountains

Isobaric cooling retrograde metamorphism in Dronning Maud Land, East Antarctica.

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