1995 Fiscal Year Final Research Report Summary
Pan-African event in the East Antarctica : significance in the formation of the Gondwana
| Project/Area Number |
06640591
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Geology
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| Research Institution | National Institute of Polar Research |
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Principal Investigator |
SHIRAISHI Kazuyuki National Institute of Polar Research, Department of Crustal Studies, Professor, 研究系, 教授 (90132711)
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| Co-Investigator(Kenkyū-buntansha) |
KAGAMI Hiroo Okayama University, Institute of Earth Interior Studies, Associate Professor, 地球科学研究センター, 助教授 (20108179)
MOTOYOSHI Yoichi National Institute of Polar Research, Department of Crustal Studies, Associate P, 研究系, 助教授 (90211606)
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| Project Period (FY) |
1994 – 1995
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| Keywords | East Antarctica / Geochronology / Metamorphism / Ion Microprobe / SHRIMP / Gondwana / Pan-African / Proterozoic |
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| Research Abstract |
1. The metamorphic and protolith ages of the Rayner Complex(RC) have been examined using SHRIMP U-Pb zircon ages in combination with Sm-Nd and Rb-Sr mineral and whole rock isochron ages. Within the RC we have determined distinct Proterozoic to Cambrian events ; -520-540 Ma at the coastal outcrops, -900-1000 Ma in more inland outcrops. These ages are considered to represent two high-grade metamorphic events. Another grouping of U-Pb zircon ages at -780-800 Ma is consistent with previously reported 770 Ma igneous activity. we intend to further examine the extent and nature of this event. The new U-Pb zircon data show that part of the area formerly considered to represent the western margin of the Proterozoic Rayner Complex underwent high grade metamorphism during the Cambrian (Pan-African) and we propose that it is an eastward continuation of the Lutzow-Holm Complex (LHC).
2. A Rb-Sr and Sm-Nd isotope study of meta-trondhjemites and a pelitic gneiss from Cape Hinode, LHC,has been performe
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d. Taking into account the initial ratios and the previous zircon U-Pb study, we concluded that the -1000 Ma age indicates the time of igneous crystallization of the trondhjemite. The pelitic gneiss, which probably originated from middle Proterozoic supracrustal material, is the host rock of the trondhjemite intrusion. However, the -500 Ma high grade metamorphic age, which is ubiquitous in the LHC,is not documented in these rocks, because of either the extent sample collection area or allochtonous origin of the terrane.
3. Data calibration for a X-ray fluorescence analyzer which was newly intstalled at NIPR was performed and geochemical studies at the Sor Rondane Mountains, Yamato Mountains and RC were carried out using the XRF.The results are compiled in the database at NIPR.
In conclusion, the Pan-African event extensively affected these terranes much more than previously considered and we presume the collisional tectonics playd an important role. Further geochemical and isotopic examination of the metamorphic and plutonic rocks from these area is ongoing. Less
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[Publications] Shiraishi, K., Ellis, D.J., Fanning, C.M., Hiroi, Y., Kagami, H.and Motoyoshi, Y.: "Re-examination of the Metamorphic and Protolith Ages of the Rayner Complex, Antarctica : Evidence for the Cambrian (Pan-African) regional metamorphic event." Proc.7th Intl Symp.Antarct.Earth Sci., Siena, Italy. (in submitting.).
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「研究成果報告書概要(欧文)」より
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