庐山前震旦纪岩石中锆石U—Pb法定年与其地质意义

U-Pb ZIRCON DATING OF PRESINIAN ROCKS AT LUSHAN MT.AND ITS GEOLOGICAL IMPLICATION

庐山前震旦系由星子群、双桥山群和筲箕洼一汉阳峰组地层构成。通过对庐山前震旦系中锆石U-Pb法定年测定,星子群的斜长角闪岩中锆石的U-Pb法定年结果是1 869±40Ma,由此表明星子群是晚元古代江南造山带的最古老结晶基底;筲箕洼-汉阳峰组中细碧岩和流纹岩的锆石U-Pb法定年结果,分别是917±36Ma和878±51Ma。它们在时代上与邻区登山群、井潭组、松木坞组和上墅组中细碧岩/玄武岩和流纹岩相当,是江南晚元古造山带的重要组成;侵入于星子群和双桥山群的辉绿岩岩墙群中的锆石U-Pb法定年结果是793±156Ma,它是上述造山带的最后岩浆活动的产物。此外,还讨论了"庐山飞来峰"问题。

In this paper the dating results of Presinian system of Lushan Mt. by means of the U-Pb zircon method are reported. The Presinian system in Lushan Mt. is composed of Xingzi group, Shuangqiaoshan group and Shaojiwa-Hanyangfeng formation. The U-Pb zircon age of plagioclase amphibolite of Xingzi group is 1869±40Ma, implying that it is the oldest crystallization basement of late-Proterozoic Jiangnan Orogenic Belt. The age values of spilite and rhyolite of Shaojiwa-Hanyangfeng formation are 917±36Ma and 878±51Ma, respectively, which correspond to those of spilites /basalts and rhyolites of Dengshan group, Jingtan formation, Songmuwu formation and Shangshu formation in the neighboring region. These volcanic series are the important members of this oroganic belt. the U-Pb zircon age value of diabase swarm that intruded into Xingzi group and Shuangqiaoshan group is 793±156Ma, suggesting that they are the last products of magmatism. Also, the problem of 'Lushan klipple' is discussed.