著者

MAMI TAKEHARA KENJI HORIE TOMOKAZU HOKADA SOTARO BABA ATSUSHI KAMEI IPPEI KITANO

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.230331, (Released:2023-09-07)

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The Napier Complex in East Antarctica has a complex thermal history, including ultra-high-temperature (UHT) metamorphism. Geochronology, trace element, and isotope geochemistry of zircon, apatite, and monazite in three felsic gneisses collected from Harvey Nunatak were studied using a sensitive high-resolution ion microprobe (SHRIMP) for the first time. Most zircons showed nebulous to fir-tree zoning, which is a common feature of zircons in granulite facies rocks, regardless of the core or rim. The U-Pb dating and rare earth element abundance of zircon indicated that zircon crystallization by regional metamorphism continued from 2567–2460 Ma, consistent with the previously proposed timing of UHT metamorphism. The zircon grains contained a large amount of Li (59–668 ppm). Li was incorporated with Cl at the interstitial sites of the zircon structure, and the zircons crystallized in melts with an abundant supply of Li and Cl. Monazite crystallized from apatite after the UHT metamorphism events of 2071 Ma and 1799 Ma. The U-Pb system of apatite was completely disturbed by the crystallization of monazite at 1785 Ma. In addition, the U-Pb systems of apatite and monazite were disturbed at approximately 500 Ma.

著者

Yuki MORI Tomokazu HOKADA Tomoharu MIYAMOTO Takeshi IKEDA

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.221124, (Released:2023-05-15)

被引用文献数

2

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We determined the metamorphic age and pressure–temperature conditions recorded in a sillimanite-garnet-bearing pelitic gneiss from Niban-nishi Rock, which is part of Niban Rock, on the Prince Olav Coast, eastern Dronning Maud Land, East Antarctica. Niban-nishi Rock is recognized as a component of the Lützow-Holm Complex (LHC), which is characterized by metamorphic age of 600–520 Ma and metamorphic grade of amphibolite to granulite facies. Electron microprobe U–Th–Pb monazite dating of the examined gneiss revealed that, unlike the typical exposures of the LHC, Niban-nishi Rock experienced Tonian metamorphism at 940.1 ± 9.8 Ma (2σ level), and is thus more similar to the neighboring exposures of Cape Hinode and Akebono Rock. Small numbers of younger monazite ages of 827–531 Ma were also detected, and some of which might relate to the metamorphism of the LHC. Phase equilibrium modeling and geothermobarometry indicate metamorphic conditions of 690–730 °C/0.38–0.68 GPa and 620–670 °C/0.42–0.60 GPa for peak and retrograde stages, respectively. The obtained peak temperature is lower than that of typical exposures in transitional- and granulite-facies zones of the LHC, such as Akarui Point and Skallen. Metamorphic features of Niban-nishi Rock, such as the upper amphibolite-facies condition and occurrences of garnet with retrograde zoning and sillimanite in the matrix, differ from those of Cape Hinode and Akebono Rock, with the former belonging to granulite facies and the latter showing kyanite in the matrix and garnet with growth zoning. Investigating Niban-nishi Rock is key in revealing the tectonic relation between the LHC and Cape Hinode (the Hinode Block). Further field surveys are required to reveal the metamorphic variations and the relations among exposures on the Prince Olav Coast.

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

1

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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

Tomokazu HOKADA Tatsuro ADACHI Yasuhito OSANAI Nobuhiko NAKANO Sotaro BABA Tsuyoshi TOYOSHIMA

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.117, no.1, pp.220317, 2022 (Released:2022-08-20)

参考文献数

38

被引用文献数

3

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We have found corundum in direct contact with quartz and biotite and as inclusions in garnet in the pelitic gneisses of northern Austkampane in the Northeastern (NE) Terrane of the Sør Rondane Mountains (SRM), East Antarctica. Our samples, which include corundum–bearing gneisses, show petrographic features such as staurolite inclusions in garnet, compositional zoning of orthoamphibole with Al decreasing toward the rims, and late–stage cordierite formation, and these features are characteristic of a clockwise P–T trajectory. The observations are consistent with the proposed regional clockwise P–T evolution of the NE Terrane in the SRM. The corundum and other inclusions observed in the garnet porphyroblasts are interpreted to have formed owing to either staurolite breakdown or metastable crystallization relative to kyanite prior to the peak metamorphism. The close association of biotite and quartz surrounding corundum inclusions suggests fluid– or melt–related processes. These petrographic features imply that the corundum and quartz (rarely observed in high–grade metamorphic rocks) formed as a result of metastable crystallization during the prograde stage of the clockwise P–T evolution of a continental collision zone.

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.