| Project/Area Number |
06640628
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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 |
地球化学
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| Research Institution | University of Tsukuba |
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Principal Investigator |
MIYANO Takashi Inst.of Geoscience, Univ.of Tsukuba Associate Professor, 地球科学系, 助教授 (60133039)
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| Co-Investigator(Kenkyū-buntansha) |
TSUNOGAE Toshiaki Fac.of Ed., Shimane Univ.Lecturer, 教育学部, 講師 (50252888)
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| Project Period (FY) |
1994 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1995: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | mass spectrometry / SIMS / zircon / U-Pb age / secondary ion / Archean / 二次イオン質量分析計 / SIMS / U-Pb年代 / ジンバブエ / 変成帯 |
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| Research Abstract |
Single zircon U-Pb geochronology by secondary ion mass spectrometry (SIMS) is now considered to be the most reliable dating technique for Precambrain/Paleozoic rocks. The advantage of SIMS compared to the conventional U-Pb method is its in situ analysis of small areas within a single crystal. This research project aimed to obtain new U-Pb dating technique for Precambrian metamorphic rocks by analyzing with a commercial SIMS instrument (CAMECA IMS-3F ion microprobe). High mass resolution (M/DM=ca.6000) obtained by 3F was sufficient to datermine Pb/KU rations of zircon crystals without any significant mass interferences.
The analytical technique was applied to Precambrian metamorphic rocks from the Northern Marginal Zone of the Limpopo Belt in southern Africa. U-Pb ages of euhedral zircons from the NMZ cluster at around 2.8 Ga for core and 2 to 1.7 Ga for rim. Although the Limpopo Belt is considered to have suffered granulite facies metamorphism during "Limpopo Orogeny" at about 2.65 to 2.70 Ga, 1.7 to 2 Ga zircon overgrowth from the Northern Marginal Zone implies younger metamorphic events. Our data suggests that the Northern Marginal Zone suffered at least two stages of metamorphism ; 2.7 and 1.7 to 2Ga.
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