This study presents a re-examination of historical specimens(DG136 and DG167)from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element(REE)distribution between garnet and monazite(and other accessory minerals)during metamorphism.Nine-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed(re)crystallization histories.Trace element data collected from the same ablated volume,interpreted in the context of new phase equilibria modelling that includes monazite,xenotime and apatite,link ages to specific portions of the pressure-temperature(P-T)paths followed by the specimens.These linkages are further informed by garnet Lu-Hf geochronology and xeno-time petrochronology.The clockwise P-T paths indicate prograde metamorphism was ongoing by ca.80 Ma in both specimens.The structurally deeper specimen,DG136,records peak P-T conditions of～755-770℃and 8.8-10.4 kbar,interpreted to coincide with(re-)crystallization of low Y monazite at～75-70 Ma.Near-rim garnet isopleths from DG167 cross in the observed peak assemblage field at～680℃and 9.3 kbar.These conditions are interpreted to correspond with low Y monazite(re-)crystallisation at～65 Ma.Both specimens record decompression along their retrograde path coincident with high Y 70-55 Ma and 65-55 Ma monazite populations in DG136 and DG167,respectively.These findings broadly agree with those initially reported～20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic reactions.Modern phase equi-libria modelling and in situ petrochronological analysis,however,provide additional insight into mon-azite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite.

Kyle P.Larson;Sudip Shrestha;John M.Cottle;Carl Guilmette;T.Alex Johnson;H.Daniel Gibson;Félix Gervais

Department of Earth,Environmental and Geographic Sciences,University of British Columbia Okanagan,3247 University Way,Kelowna,BC V1V 1V7,Canada;Fipke Laboratory for Trace Element Research,University of British Columbia Okanagan,3247 University Way,Kelowna,BC V1V 1V7,Canada;Department of Earth Science,University of California,Santa Barbara,Santa Barbara,CA 93106-9630,USA;Géologie et Génie Géologique,Université Laval,Québec City,Quebec,Canada;Department of Earth Sciences,Simon Fraser University,8888 University Drive,Burnaby,BC V5A 1S6,Canada;Départment des Génies Civil,Géologique et des Mines,Polytechnique Montréal,Montréal,QC H3T 1J4,Canada

地学前缘（英文版）

[1]Kyle P.Larson;Sudip Shrestha;John M.Cottle;Carl Guilmette;T.Alex Johnson;H.Daniel Gibson;Félix Gervais-.Re-evaluating monazite as a record of metamorphic reactions)[J].地学前缘（英文版）,2022(02):237-254

DG136,DG167,Monashee,Cordillera,petrochronology,xenotime,isopleths,crystallisation,libria,petrochronological,azite

Re,evaluating,monazite,metamorphic,reactions,This,study,presents,examination,historical,specimens,from,complex,southeastern,Canadian,that,critical,current,understanding,rare,earth,REE,distribution,between,garnet,other,accessory,minerals,during,metamorphism,Nine,hundred,fifty,one,new,spot,analyses,different,grains,across,two,outline,detailed,crystallization,histories,Trace,data,collected,same,ablated,volume,interpreted,context,equilibria,modelling,includes,apatite,specific,portions,pressure,temperature,paths,followed,by,These,linkages,further,informed,Lu,Hf,geochronology,clockwise,indicate,prograde,was,ongoing,Ma,both,structurally,deeper,records,peak,conditions,kbar,Near,rim,observed,assemblage,field,correspond,Both,decompression,along,their,retrograde,coincident,high,populations,respectively,findings,broadly,agree,those,initially,reported,years,ago,confirm,early,interpretations,using,trace,elements,generally,reliable,markers,Modern,situ,analysis,however,provide,additional,insight,into,behaviour,anatexis,effects,potential,buffering,bearing,phases,such

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