北京地区太古宙岩石同位素年龄及其意义

ISOTOPIC AGE OF THE ARCHEAN ROCKS IN BEIJING AREA AND THEIR GEOLOGICAL IMPLICATIONS

北京地区太古亩大漕．沙厂表壳岩系的麻粒岩相区域变质作用年龄，苇子峪TTG(A)－MMe杂岩中表壳岩系的高角门岩相区域变质作用年龄，以及两个单元中的早期TTG质岩成岩年龄均为2650Ma左右，推测表壳岩成岩时代为中太古代晚期；四合堂表壳岩系的低角闪岩相区域变质作用年龄和该单元内太古宙TTG质岩的成岩时代约为2539Ma至2580．7Ma，推测表壳岩系成岩时代为新太古代早期（2650～2800Ma）；阳坡地TTG-M-Me杂岩中的太古宙晚期ITG质岩成岩时代为2522~2563Ma，推测其中表壳岩系的角闪岩相区域变质作用及早期TTG质岩的成岩时代稍大于2563Ma；马圈子TTG-M-Me杂岩中TTG质岩成岩时代为新太古代晚期（2500～2650Ma）。结论为本区太古宙表壳岩系峰期区域变质作用和太古宙TTG质岩形成时代均发生于新太古代。

About 20 samples of U-Pb single zircon and Sm-Nd isotope age were selected fromMiyun-Huairou,Beijin area. They suggest that 2 650 Ma is the age of the regional metamorphism(granulite facies) of the Archean Dacacr-Shachang supracrustal rock series, and of the regionalmetamorphism (high-amphibolite facies) of the supracrustal rock series distributing in theWeiziyu TTG(A)-M-Me complex, and of the lithognesis of the early 'TTG' within the abovementioned two unites. So the later stage of the Mesoarchean is supposed to be the lithognetic ageof those supracrustal rocks. It is about 2 539 ~2 580. 7 Ma that might be the age of the regionalmetamorphism (lower-amphibolite facies) of the Sihetang supracrustal rock series, and thelithogenetic age of the Archean 'TTG', which means the early stage (2 650~2 800 Ma) of theNeoarchean is supposed to be the lithogenetic age of the Sihetang supracrustal rock series; It isabout 2 522 Ma^2 563 Ma that might be the lithogenetic age of the later 'TTG' of the Archeanin the Yangpedi TTG-M-Me complex. Slightly>2 563 Ma is supposed to be the lithogenetic ageof the early Archean 'TTG', and of the regional metamorphism (amphibolite facies) of thesupracrustal rocks in it; The later stage (2 500~2 650 Ma) of the Neoarchean is the lithogeneticage of the 'TTG' in the Majuanzi TTG-M-Me complex. Summary, it is during Neoarchean thatArchean 'TTG'took place and the regional metamorphism of the Archean supracrustal rock seriesoccured.