The Study In Metamorphism Of Amphibolite In Guanghua Group In Tonghua,Jilin Province

Jilin Guanghua area north of Guanghua town area,exposed in the area of ancient Paleoproterozoic Guanghua rock group.The lithology of the Shuangmiaoyan Formation in the lower part of the rock group is mainly plagioclase amphibolite,which is one of the major metamorphic rocks constituting the Precambrian basement.As one of the three rock groups including Guanghua Group,Ji'an Group,and Laoling Group in the Paleoproterozoic strata in Tonghua area,Guanghua rock group plays an important role in understanding the tectonic evolution process of Paleoproterozoic in this area.However,due to the lack of study in this rock group,especially the lack of metamorphism of the study,and metamorphism of the rock group has important significance on the study of its tectonic evolution and metamorphism of the tectonic background.Based on the study of field geological survey,this paper studies the petrology,geochemistry and metamorphism of the amphibolite systematically,and combines with the chronology and geochemical characteristics from other experts,aiming to confirm the metamorphic effect of amphibolite in Guanghua rock group and obtain the P-T path of metamorphism,and then provide a new basis for studying the tectonic evolution of Paleoproterozoic in Tonghua area.Guanghua rock group is mainly discovered at the boundary between the Longgang block and Liaoji orogenic belt,and was striped east-west distribution,mainly by the Archean granite gneiss wrapped,and the surrounding rock Between the structure for the contact relationship.It is known that the amphibolites underwent a total of three stages of metamorphism,prograde stage,peak stage and retrograde stage.Minerals assemblage at prograde stage is Gt₁+Hbl₁+Pl₁?An=13¹6?+Q,temperature and pressure range P=4.7-5.2kbar,T=544-555?;minerals assemblage at peak stage is Gt₂+Hbl₂+Pl₂?An=28³1?+Ilm₂+Bt₂+Q,temperature and pressure range P=8.1kbar-8.8kbar,T=655-673?;minerals assemblage at retrograde stage is Gt₃+Chl+Ath+Hbl₃+Bt₃+Ilm₃+Pl₃?An=16¹8?+Q,the temperature and pressure range P=7.9kbar-8.3kbar,T=546-557?.The metamorphic evolution process of the amphibolite shows the counterclockwise P-T path,which is characterized by near-isobar cooling?IBC?processes.The original rock of the amphibolite mainly belongs to subalkaline basalt,which is formated in the island-arc setting.Above all,Guanghua rock group plagioclase amphibolite formed in the island arc tectonic environment,and then experienced with the magma invasion of the role of metamorphism.It suggests that the amphibolite may reflect that there is a tectonic evolution from the Archean-Paleoproterozoic proto-ocean to collision of orogeny,and then orogenic taper and the last magmatic undergrowth at Tonghua area.According to the similarities between Guanghua Group and Ji'an Group,and the tectonic relationships between Guanghua Group and the Archean granite gneiss,it would be suggested that Guanghua Group may be the klippes from Ji'an Group.