山东沂水太古宙麻粒岩区年代学研究成果简介

STUDY ON THE ISOCHRON AGE IN THE ARCHEAN GRANULITE TERRAINS OF YISHUI,SHANDONG PROVINCE

本文以详细研究本区麻粒岩－斜长角闪岩等表壳岩的岩石学、地球化学和Ｓｍ－Ｎｄ同位素定年为重点。所取得的成果，对华北陆台古老地层的分布和古构造格局的探索提供了实际资料。

The metabasites in the Archean Yishui complex of Shandong province were dated for the first time by the Sm-Nd whole rock isochron method at 2997 Ma,which confirms the existence of Middle Archean granulite facies supercrust rock in the Tancheng-Lujiang fault of Central Shandong.The Yishui complex consists mainly of two-pyroxene plagioclase granulite, two-pyroxene plagioclase gneiss,two-pyroxene itabirite（small amounts）,two-pyroxene amphibolite and charnockite. They make up the oldest massif in Shandong──the Gongdanshan massif,which corresponds approximately to the Jiaodong Group in age but might be somewhat lower in horizon.The Yishui complex has been subjected to high amphibolite facies to granulite facies metamorphism, and the protolith of metabasites is some-thing like K- depleted tholeiite whose REE patterns are of flat type and LREE-enriched type with εNd（t）being +3.8±0.3.The materials came from the depleted（upper）mantle,which is lithologically very similar to some granulite facies rocks in the northern margin of the North China platform,suggesting the similarityof their provenances in chemical characteristics.Nevertheless,their major REE patterns are somewhat different from each other,indicating the geochemical inhomogeneity of Archean rocks in different areas.