| 江南古陆南缘四堡群同位素地质年代学研究 |
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| 关键词:(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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| THE GEOCHRONICAL STUDIES OF SIBAO GROUP IN THE SOUTHERN MARGIN OF JIANGNAN MASSIF |
| 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. |
| HAN Fa,SHEN Jian-zhong,NIE Feng-jun,DING Xiao-shi,LI Shi-chao,YANG Kai-tai,YANG Chun.1994.THE GEOCHRONICAL STUDIES OF SIBAO GROUP IN THE SOUTHERN MARGIN OF JIANGNAN MASSIF[J].Acta Geoscientica Sinica,15(1,2):43-50. |
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