Tectonic Setting Of Early Deposit For The South Liaohe Group

Lieryu Formation of the South Liaohe Group,located in the Huanghuadian area of the Liaodong peninsula,is predominated by intermediate-acid volcanic rocks and meta-mafic rocks subjected to amphibolite facies metamorphism.Its depositional environment that is of great significance for the tectonic setting and evolution of the crust in this area,remains unkown up to now.In this papar,we selected the amphibolites and felsic gneisses of the Lieryu formation as the main study subjects and studied their geochronology,geochemistry and chronology,to discuss the provenance of these massive meta-sedimentary rocks.Combined with previous geochronological and geochemical data,we further defined the relation between the Lieryu Formaiton and Liaoji granite,and deduced the depositional and structural environment,protolith and metamorphic ages of the South Liaohe Group.The amphibolites occur as layers,or lenses in the bedded felsic;gneiss which is thrusted by the Paleoproterozoic granites.The amphibolites mainly are dominated by hornblende and plagioclase with magnetite,while felsic the gneisses mainly consist of biotite tourmaline,plagioclase and quartz.The amphibolites depleted in high field strength elements such as Th,Nb,Hf,indicates they were formed in an arc-related or active continental margin-related setting and underwent crustal contamimation.The protoliths of felsic gneiss with a weak negative Eu anomaly,have the affinity to sandstone.Which were deposited in a short source reflected by the CIA,CIW indexs.Based on zircon LA-ICP-MS U-Pb dating,the protolith ages of the amphibolites are 1995±13Ma and 2150±21Ma and the metamorphic age is 1879 Ma,while the peak ages of the detrital magmatic zircons from the felsic gneiss are 1936 Ma,2082Ma,2178 Ma and 2574 Ma.And the third-peak of 2178 Ma is very similar to the protolith age of Liaoji Paleoproterozoic granite,which is a major provenance for the Lieryu Formation.The other protoliths of the Lieryu Formation might be derived from the Archean basement of the craton,and affected by ~1.88 Ga metamorphism.Combined with regional geological data,the study area which contains the Liaohe Group might be rifted from a continental margin as a back-arc basin at the age of 2.2 Ga,underwent a subduction setting in 2.15~2.0Ga and orogenetic event in~1.88 Ga forming the Jiao-Liao-Ji orogenic belt at last.