| The studied area is located on the west side of northern Great Hinggan orogen,an area amalgamated by several blocks.In this paper,the writer compared different samples of Precambrian strata to restore the metamorphic protolith and stratigraphic sequence,analysis its material source and to discuss the tectonic setting.Precambrian strata in this area consist of Xinghuadukou formation,Jia Gedan formation and the Erguna River formation,with anorthosite-amphibolite,gneisses,leptites,schists,quartzites,hornfelses,and marbles as main rocks.Sm-Nd dating result gave a pattern age of 1077Ma,In Naiji region,constraining the age of Xinghuadukou formation to the Middle Proterozoic.Main elements,rare earth elements and trace elements analysis,together with the protolith restoration diagrams,shows that the original rock is a volcanic-sedimentary formation composed of metamorphic basic-intermediate volcanic rocks and metamorphic sedimentary rocks.The Erguna River formation is conformably overlapped by Jia Gedan formation.The Xinghuadukou formation is exposed fragmentally.The research area has undergone regional metamorphism and contact metamorphism,but dominated by regional metamorphism.Based on the analysis of mineral assemblage of metamorphic,we found the Precambrian strata metamorphic facies belongs to the greenschist facies to low amphibolite facies.The result of sedimentary rocks provenance analysis suggests that the rocks originated from continental island-arc and active continental margin,belonging to transitional sedimentary clastic rocks.The characteristics of main elements,trace elements and rare earth elements suggest that metamorphic rocks formed under the continental island arc or active continental-margin environment.The Metamorphic basic volcanic rocks belong to island-arc tholeiite.All the evidences show that the tectonic setting is complex,the trend from the activity of a strong continental island arc environment evolved to weaker activity in active continental-margin environment. |
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