ConstraintsofU-PbzircondatingontheevolutionoftheNan-UttaraditsuturezoneinnorthernThailand

Nan-UttaraditsuturezoneinnorthernThailandisanarrowN-StrendinganddiscontinuousophiolitebeltalongtheNanRiver(BarrandMacDonald,1987).ItwasinterpretedasthePaleo-TethysoceanicremnantsthatseparateShan-Thai(Sibumasu)terraneandIndo-chinaterrane(Bunopas,1981;Hada,1999),andrein-terpretedastheboundaryofSukhothai(orSimao)terraneandtheIndochinaterranethatrepresentingasegmentoftheback-arcbasin(BarrandMacDonald,1991;UenoandHisada,2001;Metcalfe,2006;Ferrarietal.,2008;SoneandMetcalfe,2008).ThiszoneisdominatedbyCarboniferoustoPermianPhaSomMetamorphicComplex(HessandKoch,1975).ThePhaSomMetamorphicComplexconsistsofseveraltectonostratigraphicslicesofvolcanicrocks,schists,meta-greywacke,serpentiniteandbeddedchert.AnditisinfaultcontactwithPakPatvolcanicrocks.BothofPhaSomMetamorphicComplexandPakPatvolcanicrocksarecoveredbytheUpperTriassicandtheJuras-sicredsandstoneswithangularunconformity.Previ-ousstudiesmainlyfocusedontheamalgamationepi-sodesoftheSukhothaiterraneandIndochinaterrane.TheLateCarboniferoustoEarlyPermianageoftheopeningofthebasinwasproposedbysomeauthors(SingharajwarapanandBerry,2000;Metcalfe,2006;Ferrarietal.,2008)onthebasisoftheregionalstrati-graphy,differentdatingofcherts,andschistsfromthePhaSomMetamorphicComplex.