THE STRATIGRAPHIC DIVISION OF THE TAISHAN GROUP IN WESTERN SHANDONG AND THE CHARACTERISTICS OF ITS PROTOLITHS

According to the latest data of research,the author has re-established the stratigraphical sequence of the Taishan Group in the western Shandong area. From below upwards the group is divided into the Yanlingguan,Shaneaoyu and Liuhang Formations.The Yanlingguan Formation consists mainly of plagioclase amphibolite,whose protolith is basic-ultrabasic lavas,with Sm-Nd isochron age of 2684.9+278.1 Ma.The Shancaoyu Formation is dominated by biotite- oligoclase granulitite,whose protolith is argillo-arenaceous sedimentary rocks containing small amounts of intermediate-acid volcanic rocks,with a zircon U-Pb concordia upper intercept age of 2498 Ma.The Lower Subformatiou of the Liuhang Formation is made up of plagioclase amphibolite （intermediate- basic volcanic rocks） and its Upper Subformation consists of metaconglomerate （intermediate-acid volcanic rocks）.The zircon in its cements gave a U-Pb concordia upper intercept age of 2599 Ma.Besides,the granodiorite intruding the Taishan Group has a whole-rock Rb-Sr isochron age of 2586 Ma and tonalite has a zircon U-Pb age of 2628 Ma.Through synthesizing the above- mentioned data,it may be inferred that the Taishan Group was formed roughly at 2700 Ma ago.