Genesis And Geological Significance Of Amphibolites From South Liaohe Group At Sanjiazi Area,Eastern Liaoning Province

There is a set of amphibolite facies metamorphic basic rocks in Paleoproterozoic at Sanjiazi Area in Eastern Liaoning Province.Due to the lack of studies about systematic petrography,mineralogy,metamorphism,geochemistry and geochronology,etc,its discussion on genesis and tectonic significance is severely restricted.Aiming at these problems to be solved,this paper takes amphibolite of South Liaohe Group in Sanjiazi Area as the study object and carries studies of systematic petrography,mineralogy,metamorphism,geochemistry.Combining with the limited chronological and geochemical test and analysis data of predecessors,the purpose of this study is to investigate the origin of amphibolite of South Liaohe Group in Sanjiazi Area,providing valuable information for the sedimentary environment and crustal evolution then of South Liaohe Group.Amphibolite in Sanjiazi Area occur in the north part of South Liaohe Group,they primarily occur as stratiform,stratoid or lenticular shapes in granulite,leptite and paleoproterozoic granite.The kinds of rocks includ amphibolite and diopside amphibolite.Detailed petrography and metamorphism reveal that they are mainly composed of amphibole and plagioclase,with minor diopside in some very local areas.According to the geochemistry,amphibolites of South Liaohe Group in Sanjiazi Area have features of tholeiitic series with delpletion of high field strength elements such as Nb,Ta,Zr and Hf;they derived from continental lithospheric mantle with crustal contamimation.These show that the formation of protolith relate to island arc or active continental margin.The study of mineral chemistry indicates that amphibolite of South Liaohe Group in Sanjiazi Area has experienced regional metamorphism of high amphibolite facies overall.Its range of temperature and pressure is T=646-755 ?,P=0.47-0.71 Gpa.The study on sotope chronology shows that the age of amphibolite of the Lieryu formation of South Liaohe Group is 2150 Ma and its metamorphic age is 1850 Ma.It indicates that stratigraphic sedimentation of South Liaohe Group begin in about 2150 Ma combining wtih the data of detrital zircons`s age of granulite in this group and the Jiao-Liao-Ji orogenic belt is formed in this region which had a metamorphism in about 1850 Ma.