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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

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Geoscience Frontiers 2024年第2期15卷 41-54页

作者： Hyun-Ok Choi Jihye Oh Chang Hwan Kim Soon Young Choi Won Hyuck Kim Chan Hong Park Dokdo Research Center East Sea Research InstituteKorea Institute of Ocean Science and TechnologyUljin 36315Republic of Korea Deep-sea and seabed Mineral Resources Research Center Korea Institute of Ocean Science and TechnologyBusan 49111Republic of Korea Division of Science Education Kangwon National University1 Gangwondaehak-gilChuncheon-siGangwon-do 24341Republic of Korea

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 *** 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 *** samples used in this study were trachytes and exhibited ferroan,alkalic,and metaluminous to weakly peraluminous *** 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 *** 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 *** 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,*** zircons exhibited lowerδ^(18)O values than normal depleted mantle values,regardless of the crystallization age and spatial distribution of ***δ^(18)O values showed no correlation with U contents or Th/U ratios,indicating that the lowδ^(18)O signatures were of primary magmatic *** Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive eHf *** 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 *** juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to *** contrast,the felsic magma that formed the DD volcanoes may have assimilated with regional

关键词： Quaternary intraplate volcanism east sea Zircon O-Hf isotopes Low-δ^(18)O magma Recycled juvenile oceanic crust

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Depositional environment in the southern Ulleung Basin,east sea(sea of Japan),during the last 48000 years

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Acta Oceanologica Sinica 2010年第5期29卷 52-64页

作者： LIU Yanguang SHA Longbin SHI Xuefa SUK Bong-Chool LI Chaoxin WANG Kunshan LI Xiaoyan Key Laboratory of Marine Sedimentology and Environmental Geology First Institute of Oceanography State Oceanic Administration Qingdao 266061 China Department of Geography East China Normal University Shanghai 200062 China South sea Research Institute Korea Ocean Research and Development Institute （KORDI） Geoje 656-830 Korea

The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin,the east sea（sea of Japan）.The data include sediment color（L^＊）,X-ray radiographs,grain size distribution and AMS^14C *** kinds of sediments（homogeneous,laminated,crudely laminated and hybrid sediments） are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water *** of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the east Asian monsoon（EAM）.The relative contributions of the east China sea Coastal Water（ECSCW） and the Tsushima Warm Current（TWC） were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the east sea since the last 48 ka *** the interstadial,the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia,and then more strongly low-salinity,nutrient-enriched water was introduced into the east *** ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water *** the lowest stand of sea level in the last glacial maximum（LGM）,the isolated east sea dominated by stratified water masses and the euxinic depositional environment *** homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the east sea gradually with the stepwise rise of sea level and the bottom water oxygen level was *** the late Younger Dryas（YD） period,the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer *** TWC strengthened and the bottom water became oxic again from 10.5 ka BP.

关键词： east sea depositional environment east Asian monsoon Tsushima Warm Current

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