著者

Yoshikuni Hiroi Tomokazu Hokada Tatsuro Adachi Kazuyuki Shiraishi Yoichi Motoyoshi Edward S. Grew

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.221209, (Released:2023-03-28)

被引用文献数

3

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Grandidierite, (Mg,Fe)Al3O2(BO3)SiO4, was found in a garnet-clinopyroxene-ilmenite-rich mafic granulite from Austhovde in the Late Neoproterozoic to Early Cambrian Lützow-Holm Complex (LHC), East Antarctica, the first reported occurrence of this borosilicate in a mafic granulite. It occurs in one of the many nanogranitoid inclusions (NIs) in garnet. Quartz, sodic plagioclase, myrmekite, K-feldspar, epidote and biotite are also found only as inclusions in garnet. Garnet porphyroblasts show marked compositional zoning: Ca increases and Mg decreases from the core to rim with little change in Fe and Mn contents except for the outermost rim. Anorthite content of inclusion plagioclase increases from core to rim of host garnet in parallel with increase in garnet Ca towards the rim. This together with the distinctly different mineral assemblages within and exterior to garnet porphyroblasts suggests that partial melting took place and produced melts were extracted leaving a mafic and calcic restite. Partial melting also occurred locally in garnet porphyroblasts consuming different hydrous mineral inclusions to produce various NIs ranging from K-feldspar-rich to K-feldspar-free. Subsequent decompression at high temperatures resulted breakdown of garnet to orthopyroxene + calcic plagioclase with further consumption of quartz, such that none remained in the matrix of the granulite. Grandidierite may have formed by a reaction between a trapped boron-bearing aluminous granitic melt and host garnet upon cooling.

著者

シライシ カズユキ カガミ ヒロオ Kazuyuki SHIRAISHI Hiroo KAGAMI

雑誌

Proceedings of the NIPR Symposium on Antarctic Geosciences

巻号頁・発行日

no.3, 1989-09

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We report the preliminary results of whole-rock Rb-Sr and Sm-Nd isochrons dating on granulite-facies metamorphic rocks from Brattnipene, central Sør Rondane Mountains, East Antarctica. Samples : Isotopic ratios of eight samples were measured with a MAT 261 mass spectrometer at the Institute for Study of the Earth's Interior, Okayama University. Four samples are enderbites consisting of Opx, Cpx, Hbl, Bt, Pl and Qtz with or without Grt and Kfs (mineral abbreviations after R. KRETZ : Am. Mineral., 68,277,1983). These rocks were collected within a hundred meters of each other. The other four samples are hornblende gneisses as follows : Bt-Hbl-Pl, Bt-Hbl-Kfs-Pl-Qtz, Cpx-Hbl-Pl-Qtz and Bt-Hbl-Pl-Qtz. Two of them have been slightly altered to form secondary epidote and/or bluish green hornblende. All samples crop out within 500m. The peak metamorphic conditions of the enderbites were estimated from geothermobarometry to be 800℃ and 7-8.5kb (K. SHIRAISHI and S. KOJIMA : Proc. NIPR Symp. Antarct. Geosci., 1,129,1987). The hornblende gneisses were presumably metamorphosed under the same conditions. Rb-Sr data : The ^<87>Rb/^<86>Sr ratios for eight samples are low (0.02-0.15) and no meaningful isochron can be drawn due to the considerable scattering of the data. Four enderbites, however, define an isochron of 1167±127 Ma with initial ratio 0.7040. Sm-Nd data : The ^<143>Nd/^<144>Nd vs. ^<147>Sm/^<144>Nd ratios for all eight samples defined an isochron of 999±164 Ma with an initial ratio of 0.51158. The calculated uncertainty is high because the spread of the ^<147>Sm/^<144>Nd ratios is limited. T_<(DM)> model ages (ε_<ND(0)>=+10) range between 1150 and 1300 Ma.Previous work has shown that the region was affected by a thermal event associated with plutonism about 500Ma ago. This event may be the cause of the scatter in the Rb-Sr data. Nonetheless, four enderbites, which seem to be fresh under the microscope, yield a Rb-Sr isochron whose age is consistent with the Sm-Nd age within the uncertainties. There are two possible explanations for the 1000Ma ages : crust formation or metamorphism. We tentatively interpret the 1000Ma could date granulite-facies regional metamorphism although the Sm-Nd isochron age has been thought to date a crust formation because of the immobility of rare earth elements during metamorphism. Resetting of Sm-Nd whole-rock isochrons may have been possible under the estimated conditions of granulite-facies metamorphism as discussed for the Napier Complex of Enderby Land (M. T. McCULLOCH and L. P. BLACK : Earth Planet. Sci. Lett., 71,46,1984).

著者

Kenji HORIE Tomokazu HOKADA Yoichi MOTOYOSHI Kazuyuki SHIRAISHI Yoshikuni HIROI Mami TAKEHARA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.111, no.2, pp.104-117, 2016 (Released:2016-05-05)

参考文献数

50

被引用文献数

2 10

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U–Pb zircon geochronology was applied to nine metasedimentary samples collected from Mt. Yuzhnaya, Condon Hills, and Mt. Lira in the inland region of the Rayner Complex of western Enderby Land, East Antarctica, in order to define the eastern limits of the western Rayner Complex that underwent the Pan–African metamorphism and to evaluate potential source areas of metasedimentary rocks. Condon Hills and Mt. Lira revealed metamorphic ages of ~ 894 and ~ 934 Ma, respectively, which are consistent with previously reported metamorphism in association with Rayner Structural Episode (RSE). Mt. Yuzhnaya samples affected by the RSE contain zircon grains rejuvenated during 590–570 Ma, which indicates that the Pan–African reworking can be extended up to Mt. Yuzhnaya. On the other hand, the Condon Hills samples include Archean detritus, and the age peaks from 3850 to 2491 Ma are the oldest components in the Rayner Complex of western Enderby Land. There is no evidence of reworked Napier Complex rocks in the studied Rayner samples.

著者

岩田 修二 白石 和行 海老名 頼利 松岡 憲知 豊島 剛志 大和田 正明 長谷川 裕彦 Decleir Hugo Pattyn Shuji Iwata Kazuyuki Shiraishi Yoritoshi Ebina Norikazu Matsuoka Tsuyoshi Toyoshima Masaaki Owada Hirohiko Hasegawa Hugo Decleir Frank Pattyn

雑誌

南極資料 = Antarctic Record (ISSN:00857289)

巻号頁・発行日

vol.35, no.3, pp.355-401, 1991-11

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第32次南極地域観測隊(JARE-32)夏隊のセールロンダーネ山地地学調査隊は, 1990年12月24日あすか観測拠点を出発し, 1991年2月7日に再び「あすか」に帰り着くまでセールロンダーネ山地中央部で, 地形・地質・雪氷調査を行い測地作業も実施した。雪上車とスノーモービルを利用してキャンプを移動しながら調査するという従来と同じ行動様式をとったため, 設営面でもおおかたはこれまでの方式と同じである。地学調査は, 地形では, 野外実験地の撤収, 岩石の風化の調査, モレーン・ティルのマッピング, 地質では, 構成岩石の形成順序の解明, 構造地質学的・構造岩石学的そして地球化学的研究のためのサンプリング, 測地では, 重力測量, 地磁気測量, GPSによる基準点測量が行われた。ベルギーからの交換科学者は氷河流動・氷厚などを測定した。The Sor Rondane field party as part of the summer party of the 32nd Japanese Antarctic Research Expedition (JARE-32) carried out geomorphological, geological, geodetic, and glaciological fieldworks in the central area of the Sor Rondane Mountains for 45 days from December 24,1990 to February 7,1991. The field trip was conducted by two parties, consisting of 9 persons, traveling from mountains to mountains to shift tented camps using 4 snow vehicles towing their equipments on sledges behind. Nine snowmobiles (motor toboggans) were used for their field researches on glaciers. Geomorphologists carried out measurements in the periglacial field experimental sites, observations of rock weathering, and mapping of chronological sequence of tills and moraines. Geologists studied chronological sequence of rock formation and collected rock specimens for structural, petrological, and chemical analyses. A surveyor set up geodetic control stations using GPS satellite positioning system and made gravity surveys on glaciers as well as at some control stations. Two Belgian glaciologists took part in the fieldwork as exchange scientists and studied dynamics of glacier movement and ice thickness.