New U-Pb dating technique by a scecondary ion mass spectrometry

新的二次离子质谱 U-Pb 定年技术

• 批准号: 06640628
• 负责人: MIYANO Takashi
• 金额: $ 1.41万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1995
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06640628/
• 关键词: 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

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.

二次离子质谱法（西姆斯）单颗粒锆石U-Pb年代学是目前公认的前寒武纪/古生代岩石最可靠的定年方法。与传统的U-Pb方法相比，西姆斯的优点是它可以在单晶内的小区域进行原位分析。本研究旨在利用商用西姆斯仪器（CAMECA IMS-3F离子探针）获得前寒武纪变质岩U-Pb测年新技术。3F获得的高质量分辨率（M/DM=约6000）足以测定锆石晶体的Pb/KU比值，而没有任何明显的质量干扰.该分析技术应用于南非林波波带北方边缘带前寒武纪变质岩. NMZ群自形锆石U-Pb年龄为核部2.8Ga左右，边缘2Ga ~ 1.7Ga。尽管林波波带被认为在大约2.65至2.70 Ga的“林波波造山运动”期间遭受了麻粒岩相变质作用，但来自北方边缘带的1.7至2 Ga锆石过度生长意味着更年轻的变质事件。我们的数据表明，北方边缘带至少经历了两个阶段的变质作用：2.7和1.7 - 2Ga。

项目成果

Tsunogae, T.: "Preliminary SIMS zircon ages of pelitic gneiss, Oki-Dogo Island" Mem.Fac.Ed., Shimane Univ.29. 61-68 (1995)

Tsunogae, T.：“Oki-Dogo 岛泥质片麻岩的初步 SIMS 锆石年龄”Mem.Fac.Ed.，Shimane Univ.29。

Mizuno, K. and Miyano, T.: "Phase analysis of meta carbonate rocks around Mt. Hiiragi, Kasama,Ibaraki Prefecture." Ann. Rept. , Inst. Geosci. , Univ. Tsukuba.21(in press). (1995)

Mizuno, K. 和 Miyano, T.：“茨城县笠间柊山周围偏碳酸盐岩的相分析。”

Tsunogae, T. and Yurimoto, H.: "Single zircon geochronology of the Limpopo Belt by secondary ion mass spectrometry." Geochemical Journal. 29. 197-206 (1995)

Tsunogae, T. 和 Yurimoto, H.：“通过二次离子质谱法对林波波带的单锆石地质年代学。”

Hisada,K.: "Petrographic feature of metamorphic nocks from Topisi in the western margin of the Limpopo belt" Ann.Rept.,Univ.of Tsukuba. 20. 51-57 (1994)

Hisada,K.：“林波波带西缘 Topisi 变质诺克的岩相特征”Ann.Rept.，筑波大学。

Tsunogae,T.and Yurimoto,H.: "Single zircon geochronology of the Limpopo Belt by secondary ion mass spectrometry." Geochemical Journal. 29. 197-206 (1995)

Tsunogae,T. 和 Yurimoto,H.：“通过二次离子质谱法对林波波带的单锆石地质年代学”。