| 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(1,2):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北九万大山地区，是华南最古老的地层单元之一。对宝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发－沉积法年龄测定，两组锆石样品获得￣(207)Pb-￣(206)Pb年龄分别为1734±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±82（2σ）Ma，与锆石单颗粒￣(207)Pb-￣(206)Pb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 |
| 中文关键词:锆石￣（207）Pb／￣（206）Pb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 ￣(207)Pb/￣(206)Pb-ages on single zircons by using kober's method,and Sm-Nd and Rb-Sr isotopicsystems have been studied for the mafic-ultramafic volcanic rocks from Sibao Group in Baotan districtalong the southem margin of Jiangnan massif.The￣(207)Pb-￣(206)Pb determinations on single zirconse separat-ed from pillowed basalt lava in the upper part of Wentong Formation show that two groupe of fine-grained primary zircons give the ￣(207)Pb/￣(206)Pb ages of 1734±20 Ma and 1863±7 Ma,respectively.Eight samples of mafic and ultramafic volcanic rocks collected from Wentong,Yangjia,Shaping,andJiepei gives a Sm-Nd isochron age of 1782±82 Ma,with the initial Nd value of 0.51035,which isvery consistent with the ￣(207)Pb/￣(206)Pb ages of fine-grained primary zircons,which indicate the formationof Sibao Group from the late Ealy Proterozoic to early Middle Proterozoic time.The εNd(t) of 0.6 forthe analyzed samples implies the derivation of mafic-ultramafic magma from a depleted mantle source.The Rb-Sr isotopic systein has been strongly disturbed probably by the late tectonic movement,mag-matic intrusions, and metamorphism,and reveals the lack of correlation between ￣(87)Sr/￣(86)Sr and￣(87)Rb/￣(86)Sr,which can not give any meaning of rock-forming age.The delineation of the forming agefor Sibao Group causes our reconsidering the forming age of the corresponding metavolcano-sedimen-tary sequences in Jiangnan massif,and excludes the possibility of the relict ophiolite suites for thosemetavolcano-Sedimentary sequences. |
| keywords:(207)Pb/￣(206)Pb-ages on single zircons Sm-Nd isochron age on the mafic-ultramaficvolcanic rocks geochronical studies Sibao Group |
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