| 江南古陆南缘四堡群同位素地质年代学研究 |
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| 引用本文：韩发,沈建忠,聂凤军,丁孝石,李世朝,杨开泰,杨淳.1994.江南古陆南缘四堡群同位素地质年代学研究[J].地球学报,15(z1):43-50. |
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| 中文摘要:四堡群浅变质火山-沉积岩系主要出露于桂九万大山地区，是华南最古老的地层单元之一。对坛地区罗布山枕状玄武岩中细粒原生锆石进行单颗粒锆石蒸节-沉积法年龄测定，两组锆石样品获得207Pb/206Pb年龄分别为1374±20（2σ）Ma和1863±7（2σ）Ma。对宝坛地区基性和超基性火山岩进行了Sm-Nd同位素研究，获等时线年龄为1782±820（2σ）Ma，与锆石单颗粒207Pb/206Pb年龄一致，充分说明四堡群形成于中元古代早期。火山岩的εNd（t）为0.6，表明基性-超基性岩浆源自于亏损地幔。这套岩石的 |
| 中文关键词:锆石207Pb/206Pb年龄 全岩Sm-Nd年龄 同位素地质年代学 四堡群 |
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| the geochronical studies of sibao group in the southern margin of jiangnan massif |
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| Abstract:The 207Pb/206Pb-ages on single zircons by using kobers method ,and Sm-Nd and Rb-Sr isotopic systems have been studid for the mafic-ultramafic volcanic rocks from Sibao Group in Baotan district along the southem margin of Jiangnan massif.The 207Pb-206Pb determinations on single zircons separated from pillowed basalt lave in the upper part of Wentong Formaition show that two groups of finegrained primary zircons give the 207b/206Pb ages of 1734±20Ma and 1863±7Ma,respectively.Eight samples of mafic and ultramafic volcanic rocks collected from Wentong,Yangjia,Shaping,and Jiepai gives a Sm-Nd isochron age of 1782±82Ma,with the initial Nd value of 0.51035,which is very consistent with the 207Pb/206Pb ages of fine-grained primary zircons,which indicate the formation of Sibao Group from the late Early Proterozoic to early Middle Proterozoic time.The εNd(t)of 0.6 for the analyzed samples implies the derivation of mafic-ultramafic magma from a depleted mantle source.The Rb-Sr isotopic system has been strongly disturbed probably by the late tectonic movement,magmatic intruions,and metamorphism,and reveals the lack of correlation between 87Sr/86Sr and 87Rb/86Sr,which can not give any meaning of rock-forming age .The delineation of the forming age for Sibao Group causes our reconsidering the forming ages of the corresponding metavolcano-sedimentary sequences in Jiangnan massif ,and excludes the possibility of the relict ophiolite suites for those metavolcano-sedimentary sequences. |
| keywords:207Pb/206Pb-ages on single zircons Sm-Nd isochron age on the mafic-ultramafic volcanic rocks geochronical studies Sibao Group |
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