SpatialandtemporalevolutionofkimberlitemagmaatA154N,Diavik,Northwest Territories,Canada !

a b s t r a c t a r t i c l ein f o TheA154NkimberlitepipeispartoftheDiavikkimberliteclusterintheNorthwestTerritories,Canada.The pipeis!lledbydepositsthatrecordasequenceoferuptiveandintrusiveeventsforwhichwehave establishedrelativetimesandmodesofemplacement.Assuch,thissequenceofkimberlitedepositsprovides auniqueopportunitytoexploretheconnectionsbetweenmagmaproperties,pipeorconduitgeometryand eruptionstyle. DepositswithintheA154Npiperepresentfourdiscretevolcaniceventsincluding:(1)anarrayofpre-cursor dykesofcoherentkimberlitethatintrudetheadjoiningcountryrock(CK 1 );(2)pyroclasticdeposits recordingtheexplosiveeruptionofA154N(PK 1 );(3)latedykesofcoherentkimberliteintrudingthemain in!llofthepipe(CK 2 );and(4)asequenceofwater-laidpyroclasticdepositsthatsourcedfromanother kimberlitevolcano(PK 2 ).Weuseobservationsonpolishedslabsandthinsectionstocharacterizethemagma thateruptedtoproduceeachdeposit.Imageanalysistechniquesareusedtoquantifyolivinecontent (abundanceandsizedistributions)andabundancesofvesicleswithindepositsandwithinindividual juvenilepyroclasts.Ouranalysisshowsthatduringtheeruptioncycle(CK 1 toPK 1 toCK 2 ),olivinecontent increasedandvolatilecontentdecreased. Lastly,weestimatephysicalpropertiesforthemagmasthatproducedeachdeposit.Themagmaproperties arecombinedwith3-Dmodelsforthegeometryoftheconduitatthetimeoferuptiontoconstrainthemass "uxanddurationofeacheruptiveevent.Steady-stateassumptionsforvelocityandmagma"uxyieldtotal eruptiondurationsofminutestohours.Thediversityoftexturesandcompositionsrecordedinpyroclastic