首页|Transition from oceanic subduction to continental collision:Insights from volcanogenic-sedimentary rocks of the Tannuola terrane(northern Central Asian Orogenic Belt)
Transition from oceanic subduction to continental collision:Insights from volcanogenic-sedimentary rocks of the Tannuola terrane(northern Central Asian Orogenic Belt)
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Magmatism associated with oceanic subduction plays a dominant role in crustal growth during the Earth's evolution.The Tannuola terrane,situated in the northern Central Asian Orogenic Belt(CAOB),is a key area to understanding oceanic subduction and initial collision processes in the northern CAOB.In order to investigate the switch from subduction to collision settings,detailed field mapping,zircon SHRIMP U-Pb geochronological and whole-rock geochemical studies of volcanogenic-sedimentary rocks from the Tannuola terrane were carried out.Zircon U-Pb ages indicate multi-stage volcanism lasted at least 30 Ma from～540 to～510 Ma,that can be divided into three events:the late Ediacaran(before～540 Ma),the early Cambrian(～520 Ma)and the middle Cambrian(～510 Ma).These ages are inter-preted to the initial,main and final stages of oceanic subduction during the late Proterozoic-early Paleozoic.During the late Ediacaran,tholeiitic basalts with high εNd(t)values(from+7.4 to+8.5)were emplaced.Likely forming by the 10％-30％partial melting of spinel-garnet mantle source during slab subduction.During the early Cambrian,transitional from tholeiitic to calc-alkaline basaltic rocks withεNd(t)value(+5.6)and coeval intermediate-felsic volcanic rocks with similar εNd(t)values(+5.9 and+6.5)formed.The early Cambrian basaltic rocks are interpreted to be derived by 10％-30％partial melt-ing of a depleted mantle source metasomatized by slab-derived fluids released from the subducting ocea-nic slab.The middle Cambrian calc-alkaline basaltic rocks with εNd(t)value of+6.2 might be emplaced as a result of low(5％-10％)degree partial melting of a metasomatized mantle followed by fractional crys-tallization of clinopyroxene and plagioclase.Associated intermediate-felsic volcanic rocks with εNd(t)values from+6.0 to+6.8 were formed through fractionation of the juvenile Neoproterozoic sources.The middle Cambrian volcanism is interpreted to be triggered by the slab break-off during the transition to a collisional setting.
Island-arc magmatismEdiacaranCambrianzircon U-Pb datingNd isotopesCentral asian orogenic belt
E.V.Vetrov、N.I.Vetrova
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V.S.Sobolev Institute of Geology and Mineralogy SB RAS,Koptyuga ave.3,Novosibirsk,Russia
Russian Science Foundationstate assignment of IGM SB RAS,fieldwork
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