Geochronology And Hf Isotope Geochemistry Of The Permian Acid Volcanic Rocks In Southern Mongolia-erenhot Area: Tectonic Implications

Tectonic environment and regional tectonic evolution of Permian in Southern Mongolia-Erenhot area?SMEA?exist controversial.The Permian volcanics lithology combination,spatial-temporal distribution,material composition in genetic area and tectonic environment of magma formation studies provide significant information for this issue.SMEA,located in the southeastern Central Asian orogenic belt,is characterized by extensive development of mass Neopaleozoic volcanic rocks.Previous studies basically focus on volcanic rocks in the SMEA.However,the researches of volcanic rock on border and even the territory of Mongolia are weak and tectonic environment of Neopaleozoic volcanic rocks are still limited.This paper conduct particular petrography,zircon U-Pb chronology,rock geochemistry and zircon Hf isotopic study of representative volcanics in the Hatanbulag and Erenhot.Addtionally,we mapped the spatial-temporal distribution figure and discussed the volcanic rocks formation.It's a important information to limit Permian tectonic setting in south Mongolia to-Erenhot region.The SMEA volcanic rocks can divide into mylonitization and un-mylonitization rhyolites,which zircon U-Pb chronology vary 278Ma-292Ma?292-285Ma and282-278Ma,respectively?.The results show volcanic rock formed in the early Permian.Furthermore,un-mylonitization rhyolites were unconformable overlying the mylonitization rhyolites based on the field,which suggests that there are two period of volcanic activity and a strong deformation event during the volcanic activities.These volcanic rocks have similar geochemical characteristics,belonging to the calc-alkaline series.Rhyolites'main elements have high SiO₂ and K₂O and low TiO₂and MgO,with high rare earth contents.Geochemical characteristics of majory element and trace elements suggest that depletion of HFSEs,such as Nb and Ta,can not be explained by simple residue of minerals,which are enriched in HFSEs in magmatic source,or by contamination of crustal materials.These results indicate that the rhyolite has experienced a certain degree of separation and crystallization,which may beimplyingjuvenilesourceatdepthandcrustalgrowth.Zircon Hf isotopic characteristics of Hatanbulag?292Ma-274Ma?,(T_DM22.2Ga-1.1Ga),?_Hf?t?=+3.62--0.63,Other Sample?280Ma?T_DM2=1181-565Ma,?_Hf?t?between+7.58⁺1.06.Hf isotopic characteristics of InnerMongoliavolcanic rocks T_DM2=1.6Ga-1.0Ga,?_Hf?t?=3.89-11.8?Shows the early?²90Ma??_Hf?t?lower than285²80Ma,than became lower again.It indicates a large magmatic activity between295-270Ma.Border area in the early Permian strong volcanic activities,volcanic rocks are widely distributed and has the characteristics of marginal magma arc,south Mongolia-Inner Mongolia region from north to south by the active continental margin into a passive continental margin environment.Combined with this paper obtained the Permian age?²80 Ma?and the geographic location,north of volcanic rocks in solon sutures after may tend to be formed in the subduction collision transition under the background of the construction of the back.