Geochronology,Geochemical Characteristics And Geological Significance Of "Liaohe Group" In Kaiyuan Area,Northern Liaoning

The Kaiyuan area in northern Liaoning,located in the eastern part of the northern margin of the North China Craton,bounded by the Yitong-Yilan fault in the west,and adjacent to the Solonker-Xar Moron-Changchun-Yanji suture zone in the north.A set of medium-low metamorphic rock series is exposed along the Qinghe fault in the region,mainly composed of amphibolite plagioclase gneiss,metamorphic tuff,metamorphic andesite and marble.In the 1970 s,this set of metamorphic rock series was first classified into the Paleoproterozoic Liaohe Group.Later,more and more research found that this set of metamorphic rock series was significantly different from Liaohe Group in Liaodong in terms of material composition,formation age and occurrence of minerals.So it was successively named "Qinghezhen Group","Kaiyuan Group" and "Qinghe tectonic melange" and so on.However,there was no relatively complete and unified understanding of this set of metamorphic rock series.This paper takes this set of medium-low metamorphic rock series in Kaiyuan area as the research object,through field geological investigation,geochemistry,and zircon U-Pb chronology systematic research,to determine the material composition,formation age and tectonic environment of the "Liaohe Group" in Kaiyuan area.Combined with previous research results,this paper attempts to find out the geological origin and geological significance of the "Liaohe Group" in Kaiyuan area.The protolith of amphibolite plagioclase gneisses in Kaiyuan area is andesite.Zircon U-Pb age shows that the protolith age is 2497±10 Ma and metamorphic age is 2433±11 Ma.It is enriched in LREE and LILE,and depleted in HFSE such as Nb,Ta and Ti.The primary magma originated from the partial melting of the mantle wedge metasomatized by subduction fluids,and was formed in subduction environment.It may be the product of the Jilin-Liaoning-Hebei orogenic event in the Neoarchean North China Craton.The protolith of metamorphic tuff is andesitic tuff,with a protolith age of 1881 ± 15 Ma and a metamorphic age of 1803 ± 13 Ma.It is enriched in LREE and LILE,and depleted in Ta,Nb,and Ti.The primary magma originated from the partial melting of the mantle wedge metasomatized by subduction fluids,and also was formed in a subduction environment,which may be the product of the Jiao-Liao-Ji orogenic event in Paleoproterozoic.Zircon U-Pb age of metamorphic andesite indicates that it was formed at 248±5.5 Ma,enriched in LREE and LILE,and depleted in Ta,Nb and Ti.The primary magma originated from the partial melting of the mantle wedge metasomatized by subduction fluids,and was formed in a subduction environment.It may be the active continental margin volcanic rocks formed during the subduction of the Paleo-Asian ocean southward into the North China Plate in the Early Triassic.The protolith of amphibolite diopside plagioclase granulite is a calcareous argillaceous sedimentary rock,which was formed between 251 and 248 Ma,with a metamorphic age of 245 Ma,representing the time of collision orogenic events and the final closure time of the ancient Asian Ocean.According to the above research,the "Liaohe Group" in Kaiyuan area was disintegrated into metamorphic supracrustal rock of Neoarchean North China Craton,metamorphic tuff of Paleproterozoic North China Craton,active continental margin volcanic rocks and carbonate rocks intercalated with metamorphotes of Late Permian-Early Triassic.The Neoarchean was the accretive orogenic setting of the Jilin-Liaoning-Hebei arc-land collision,the Paleoproterozoic was the Jiao-Liao-Ji orogenic setting,and the Late Permian-Middle Triassic was the subduction and closing setting of the Paleo-Asian Ocean.The complex accumulation of the North China Craton destroyed by the subduction and closure of the Paleo-Asian Ocean.