Zircon U-Pb ages and O-Hf isotopes of Quaternary trachytes from the East Sea:Implications for the genesis of low-δ^(18)O magmas  

作　　者：Hyun-Ok Choi Jihye Oh Chang Hwan Kim Soon Young Choi Won Hyuck Kim Chan Hong Park 

机构地区：[1]Dokdo Research Center,East Sea Research Institute,Korea Institute of Ocean Science and Technology,Uljin 36315,Republic of Korea [2]Deep-Sea and Seabed Mineral Resources Research Center,Korea Institute of Ocean Science and Technology,Busan 49111,Republic of Korea [3]Division of Science Education,Kangwon National University,1 Gangwondaehak-gil,Chuncheon-si,Gangwon-do 24341,Republic of Korea

出　　处：《Geoscience Frontiers》2024年第2期41-54,共14页地学前缘（英文版）

基　　金：This research was supported by a project on the sustainable research and development of Dokdo(Grant No.PG52911);which is funded by the Ministry of Oceans and Fisheries,South Korea.

摘　　要：Quaternary intraplate magmatism formed several volcanic islands and seamounts,including Dokdo(DD),Ulleungdo(UD),Simheungtack(ST),Anyongbok,and Isabu in the southwest of the East Sea back-arc basin.In this study,we present whole-rock geochemical,zircon U–Pb age,and in situ O–Hf isotope data for the submerged volcanic rocks from DD,UD,and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes.All samples used in this study were trachytes and exhibited ferroan,alkalic,and metaluminous to weakly peraluminous characteristics.They showed light rare earth element(REE)-enriched patterns with(La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot.In addition,they were enriched in large-ion lithophile elements and high field strength elements;they exhibited positive Pb anomalies and strongly negative Ba,Sr,P,and Ti anomalies.The zircons yielded a weighted-mean 206Pb/238U age of 2.61,0.348–0.704,and 2.76–2.94 Ma for the DD,UD,and ST trachytes,respectively.All zircons exhibited lowerδ^(18)O values than normal depleted mantle values,regardless of the crystallization age and spatial distribution of volcanoes.Theδ^(18)O values showed no correlation with U contents or Th/U ratios,indicating that the lowδ^(18)O signatures were of primary magmatic origin.The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive eHf values.Binary O–Hf mixing modeling revealed that low-δ^(18)O rocks with positive eHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ^(18)O and positive eHf signatures and an enriched mantle source with normalδ^(18)O and negative eHf values.The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting.In contrast,the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks(Triassic–Jur

关 键 词：Quaternary intraplate volcanism East Sea Zircon O-Hf isotopes Low-δ^(18)O magma Recycled juvenile oceanic crust 

分 类 号：P588.11[天文地球—岩石学] P597[天文地球—地质学]