ReportontheNSF-GeoPRISMSRiftInitiationandEvolutionTheoreticalandExperimentalInstitute

TheGeoPRISMSRiftInitiationandEvolution(RIE)TheoreticalandExperimentInstitute(TEI)washeldinAlbuquerque,NMfromFebruary7-10.TheobjectivesofthemeetingweretosummarizeprogressandrecentscientificadvancesrelatedtotheRIEinitiative,identifyhigh-priorityscienceforfutureGeoPRISMSRIEeffortsandpromotecommunitybuildingandformationofnewcollaborations.Tomeetthoseobjectives,adiversegroupofscientistswasenlistedtoserveontheconveningteam,giveinvitedandcontributedtalksandtocontributetothemeetingasattendees.Theexpertiseofconveners,speakersandattendeesspannedabroadrangeofinterestsconnectedwiththeRIEinitiative,fromdeepgeodynamicalprocessesunderlyingriftingtosurfaceprocessescontrollingsyn-andpost-riftevolution.ScientistsundertakingstudiesintheRIEprimarysites(theEastAfricaRiftandtheEasternNorthAmericanMargin)andworkingatotherriftsandriftedmarginswereencouragedtocontributetoallaspectsoftheworkshoptoensurediverseperspectives.Themeetingwasattendedby133participants,59ofwhichwerestudentsandpostdoctoralresearchers.Besidesattractingalargegroupofearlycareerscientists,attendeesincludedmid-careerinvestigatorswhowererelativelynewtoRIEscience.ScientistsfromabroadwereinvitedtoattendtoprovideinsightsregardingtheRIEprimarysitesandonriftsingeneral.

Grouppicture,outsideHotelAlbuquerque

ThemeetingstructurewasdesignedtocoverthebroadspectrumofscienceincludedintheGeoPRISMSRIEscienceplan,toencourageinterdisciplinarityandtobringindiverseperspectives.Themainmeetinghadsevenmainoralsessions:1)Riftevolutionfrominitiationtopostriftarchitecture,2)GeodynamicsofRiftandPost-riftProcesses,3)MagmatismandVolatileExchanges,4)FaultingandStrain,5)Surfaceprocessesandfeedbacksbetweendeep/surfaceprocesses,6)Hazardsassociatedwithriftingenvironments.Therewassubstantialtimeallocatedfordiscussionandinteraction;themeetingincludedseveralpostersessionsatvarioustimesofday,twobreakoutsessions,onesmall-groupdiscussionandplenary

discussionaftereachoralsessionandthroughoutthemeeting.Asdescribedinmoredetailbelow,thespeakerssuccessfullysynthesizedthestateofknowledgeonvariousaspectsofrift

evolutionandofhighlightingimportantoutstandingquestions.Thebreakoutsanddiscussionweredynamic,generatingexcellentideasandinsights.Themainmeetingwasprecededbyahalf-daystudentandpostdocsymposiumorganizedandledbythreepostdocs.

Mapshowinghomeinstitutionsofparticipantsatthemeeting.Overviewofsciencepresentedatmeeting:Student-PostdocSymposiumThestudent-postdocsymposiumwasheldtheafternoonbeforethemainmeetingandwasledbyYelebeBirhanu(Bristol),JamesMuirhead(Syracuse),andJean-ArthurOlive(LDEO).TheorganizersbeganthesymposiumwithapresentationthatprovidedanoverviewoftheoutstandingsciencequestionsrelatedtoRIE.Thesequestionsfocusedonthetopicsofriftinitiation,the4-Driftarchitecture,long-andshort-termriftdeformationmechanisms,riftvolcanism,magmatismandvolatilefluxesaswellasprocessesrelevanttothesurfaceprocessesatriftsandriftedmargins.Thesetopicswerethefocusofsmallgroupdiscussionslaterintheafternoon,andthediscussionleaderssummarizedthesediscussionsduringthefirstdayofthemainmeetingtoallattendees.Thesymposiumalsoincludedpop-upsbyallparticipantsontheirRIErelatedresearch.Over60peopleattendedthestudent-postdocsymposium,includingnearlyallstudentsandpostdocsatthemeetingandafewrepresentativesfromtheGeoPRISMSOfficeandGSOC,NSFandtheconveningteamofthemainmeeting.Thescientificdiscussionswerefollowedbyacareerdevelopmentpaneldiscussionwherestudentsandpostdocshadtheopportunitytoengagedirectlywithscientistsatavarietyofstagesintheircareers.MainmeetingThemainpartofthemeetingbeganwithasessiononriftevolutionfrominitiationtopostriftarchitecture.RogerBuck(LDEO)emphasizedtheroleofmagmathroughoutthelifeofrifts,fromdikingduringriftinitiationtotheassociationofriftedmarginswithlargemagmaticoutpouringsandseawarddippingreflectors.HarmvanAvendonk(UTIG)reviewedinsightsonriftingprocessesfromstudiesofbothmagma-poorandmagmaticriftedmargins,whererecentstudiesshowinterestingvariationsindistributionandtimingofmagmatisminrelationwithrifting,includingprovocativecluesfromENAMondistributionofmagmatismandhighlythinnedcontinentalcrust.DannyBrothers(USGS)focusedonpostriftevolutionofriftedmargins,includinghowsedimentdeliveryandpre-failureconfigurationcontrolevolutionandevidenceforactivefluidventing,slopefailureandsedimentcompaction.

Session2focusedongeodynamics,andJolanteVanWijk(NMTech)providedanoverviewofnumericalmodelingapproachesandtheimportanceoftestingandcomparingmodelstobothobservationsandothernumericalsolutions.ZachEilon(Brown)synthesizedgeophysicalobservationsfromtheWoodlarkRiftinPapuaNewGuineaandshowedevidenceoflimitedmelt,lithosphericremovalandopeningdirectionparallelanisotropy.AndrewSmythe(PennState)showedhowhigh-temperaturethermochronologyanddiffusionspeedometerscanbeusedtoassessmantleupwellingratesandhowstrainisverticallydistributedduringrifting.RobertHarris(OregonState)showedhighresolutionheatflowresultsfromtheGulfofCaliforniaandemphasizedtheroleoffluidflowaswellasconductiveheattransfer.ColtonLynner(Arizona)showednewshear-wavesplittingresultsfromtheENAMcommunityseismicexperimentandsuggeststhat3-Dedgedrivenflowattheedgeofthemargincanexplaintheirobservations.Session3followedwithtalksonmagmatism,volcanismandvolatileexchanges.CorneliaClass(LDEO)gaveanoverviewofthegeochemicalandpetrologicaltoolstoidentifymagmaandvolatilesourcesinriftsettings,highlightingtheimportanceofusingmultiplegeochemicalsystemstoidentifymantlecomponents.SaraMana(SalemState)showedchronologicalandgeochemicaldatafromtheNorthTanzaniaConvergencezoneandhighlightedtheevidenceforpulsedmagmatismandametasomatizedmantlesource.JulianeHubert(Bristol)providednewinsightsonmagmastorageandpathwaysusingmagnetotelluricdataintheMainEthiopianRift.MadisonMeyers(Oregon)emphasizedtheoccurrenceoflargesilicicvolcaniccentersinriftsettingsandshowedhowdetailedworkonvolatilesrecordedbymeltinclusionsallowforthequantificationofmagmaascentrates.PhilipKyle(NMTech)endedthesessionwithanoverviewofthemagmatichistoryoftheWestAntarcticRift.Day2startedoffwiththesessiononfaultingandstrain,whereCindyEbinger(Tulane)provideda‘recipeforrifting’forcratonicandorogenicriftswherethedifferenceinbothcrustandmantlerheologyareofcriticalimportanceforriftarchitectureandextension,includingthepossiblyimportantbutpoorlyknownhydrationstateanddistributionofvolatilesatdepth.PaulUmhoefer(NorthernArizonaUniv.)showedhowvariationsininheritedstructures,strainpartitioning,angleofobliquityandsedimentinputcontrolextensionintheGulfofCalifornia–Saltontroughplateboundary.JamesMuirhead(Syracuse)showedtheresultsfromaninterdisciplinarystudyintheEastAfricanRiftthatbetterconstraintheroleandsourcesoffluidsandmantlemeltingintheearlystagesofriftingandtheirconnectiontofaulting.HannahMark(WHOI)providednewinsightsfrommodelingofobservedseismiccouplingcoefficientsthatshowhowthethermalregimescaleswithseismiccouplinginMORandcontinentalrifts.ElifuranaSaria(Ardhi)endedthesessionbyprovidinganoverviewofgeodeticconstraintsoncrustaldeformationinAfricaemphasizingthefactthatlargepartsofthecontinentarenotadequatelymonitoredgeodetically.Session5focusedonsurfaceprocessesandfeedbacksinrifts,whereKyleStraub(Tulane)showedhowgeomorphologysignalsarestoredinthestratigraphicandlandscaperecord.HistalkwasfollowedbyJean-ArthurOlive(LDEO)whodiscussedtheroleofsurfaceprocessesin

thestabilizationofhalf-grabenstructures.ErinDiMaggio(PennState)talkedabouttheconnectionbetweenriftdevelopmentaspreservedinthestratigraphicrecordandthedevelopmentoftheLedi-Gerarupaleontologicalsite.LiangHan(VirginiaTech)showedhowrapidsedimentationintheSaltonToughresultedintheformationofnewcrust,delayedcontinentalbreakupandseafloorspreading,andhowmetamorphismofsedimentcanfurtherdelayfinalcrustalbreakup.RobGawthorpe(ColoradoSchoolofMines)endedthesessionwithinsightsfromtheonshore-offshoreexperimentsattheCorinthRift,Greece.Thefinalsciencesessionhighlightedhazardsinriftsandriftedmargins.KarenFontijn(Oxford)focusedmainlyonvolcanichazardsintheEastAfricanRift,emphasizingthelowviscosityofriftmagmas,thehighpotentialforphreaticeruptions,andtheabundanceoflargecalderasystemsaswellastheroleofhazardousCO2degassing.AtalayAyele(AddisAbabaU.)highlightedthechallengesindisasterriskmanagementinAfricathatareduetolimitedcapacityinequipmentandhumanresourcesandthegenerallevelofunderstandingofpotentialrisk.Healsopointedtorecentsuccessessuchascapacitybuildingefforts,advancesinreal-timedataflows,andnationalworkshops.MauriceLamontagne(GSC)showedhowearthquakesandtsunamisrelatedtoriftingarethemainhazardsinEasternCanadaandhowdetailedmappingofancientfaultstructuresprovideskeyinsightsonearthquakemechanismsanddistributionsintheregion.SangMookLee(SNU)highlightedthegeohazardsoftheEastSeaandtheSeaofJapanandtheirpotentialtoaffectnuclearpowerplantsafety.CollaborativeopportunitieswerediscussedwithpresentationsontheRiftVolcinitiative,connectionsbetweenriftingandhydrology,EarthScopeandAfricaArrayupdates.Sciencethemeswithopportunitiesfornear-termfuturestudiesTheTEIwasdesignedtoprovideampleopportunitiesforparticipantstoaskquestionsanddiscussscientificissuesrelatedtothepresentations.Thiswasachievedthroughapaneldiscussionfollowingeachsessionincludingallspeakers.Additionalfocuseddiscussionsoccurredduringtwobreakoutsessionsandsmallgroupdiscussions,whichfocusedontheidentificationofhighprioritysciencequestionsandworkneededtotacklethesequestions.ThefollowingmajorsciencethemesemergedfromdiscussionsattheTEI.Foreachofthesethemes,discussionsfocusedonexcitingrecentfindingsandopportunitiesfornear-termresearchprogressthroughtheGeoPRISMSRIETEIinitiative.1. Trackingfluids(volatilesandmagmas)throughthelithosphereandwithtime

Theimportanceoffluidsforaspectrumofinterconnectedprocessesthroughoutthelifeofriftsandriftedmarginswasatopicofsignificantinterestatthemeeting.Meetingpresentationscoveredrecentresultsthathaverevealedstrong,nonlinearinteractionsbetweenvolatilesandfaults(e.g.,talkbyMuirhead),theimportantinfluenceofpreriftandsynriftmetasomaticeventsonmagmatism(e.g.,talkbySana),andthecapacityoffluidstoadvectheatandstronglymodulatethethermalstructureofrifts(e.g.,talkbyHarris).Geochemicaltracerscanbeusedto

constrainthemodificationofthelithospherebymagmaticevents(e.g.,talkbyClasstalk).Newstudiesofriftedmarginsalsorevealunexpectedmantlestructureandmagmatism,hintingatactiveprocesseslongafterrifting(e.g.,talkbyLynner).Thesenewscienceresultspointtoseveralexcitingnear-termfuturesciencedirections:

• Understandingtheconnectionsbetweendeepvolatilesandshallowobservations,includingconstrainingmagmaandvolatilesresidencetimesandpathways

• Developingaquantitativeunderstandingoftheimpactofvolatiles/magmatismonstrainlocalizationandrheology(connectstotheme2)

• Connectinggeneralrheologicalmodelstomorphologicalandprocess-baseddifferencesbetweenmagma-poorandmagma-richregions

• Investigatingtheoriginandsignificanceofpost-riftmagmatismonriftedmargins

2. ControlsondeformationandlocalizationatdifferenttemporalscalesElucidatingcontrolsondeformationandlocalizationarecentraltounderstandingriftprocesses,andwereanothermajorfocusofmeetingpresentationsanddiscussions.Magmaisclearlygreatlocalizerofstrain(e.g.,talkbyBuck,Ebinger),butmagmaisnotpresenteverywhere,atleastnotinabundance.Inmagma-poorlocations,fluids,pre-existingstructuresand/orchemicalheterogeneitymaybeimportantfactors(e.g.,talksbyVanAvendonk,Eilon).Volatilesappeartoinfluencecrustalrheologyandfaultbehavior(e.g.,talksbyMuirhead,Ebinger),butarestillpoorlyunderstood.Theroleofpre-existinglithosphericstructureinstrainlocalizationappearstovaryamongriftsystemsandatdifferentscalelengths(e.g.,Lynner&Eilontalks).Theslipbehaviorofriftfaults(creeping,locked,etc.)ispoorlyknown(Marktalk),andtherearefewconstraintsonhowitmightchangeovertimeorwithriftevolution(VanAvendonk).Thesenewscienceresultspointtoseveralexcitingnear-termfuturesciencedirections:

• Integrationofriftingprocessesacrossarangeoftimescalesfromtheearthquakecycletogeologictime

• Understandingvariationsintemporal/spatialpatternsofdeformationbetweenmagmaticandmagma-poorsystems

• Comparingtransientbehaviorinrifts(creep,slowslip)tosubductionandtransformzones

• Observinghowvolatilesaredistributedthroughlithosphere(connectstotheme1)withanemphasisonhowtheyimpactrheology,faulting,andtransientdeformation

• Constrainingmantlerheologyonavarietyoftimescalesandasafunctionofvolatileabundance,metasomatismandmeltextractionprocesses(connectstotheme1).

3. Surfacemasssedimentaryfluxesandfeedbackswithrifting

Recentstudieshavedemonstratedstrongconnectionsbetweensurfaceprocessesandallstagesofriftevolution.Theseincludetheformationofnewcrustthroughrapidsedimentation(e.g.,talkbyHan),theimpactoferosiononfaultevolution(e.g.,talkbyOlive),thestructuralcontrolofsedimentpathwayslongafterrifting(e.g.,talkbyGawthorpe),andthestructuralcontrolofslopefailure(e.g.,talksbyBrothersandLamontagne).Theverticaldisplacementsandcrustalarchitectureassociatedwithextensionaltectonicsstronglyinfluencethespatialandtemporaldistributionofdepositionaldomains(e.g.,talksbyStraub,Brothers).TheseresultspointtowardsseveralImportantnear-termfuturesciencedirections:

• Developingmorecomprehensivesedimentaryhistoriesofriftstoimproveunderstandingofrift-relatedmasstransport

• Improvingconceptualandnumericalmodelsofsedimentinfluenceonextensionalprocesses,includingthermalandmechanicalfeedbacks

EffortsneededtomakeprogressonthemeswithinGeoPRISMSToaddressoutstandingquestionsrelatedtothethemesabove,thefollowingfutureeffortswerehighlightedasparticularlyimportant.Synthesis:ComparingamongandwithinriftsisimportanttoaddressmanyoftheoverarchingRIEsciencequestionsandthespecificquestionswithinthethemesabove.Agrowingvolumeofdataisnowavailableinbothprimarysitesandinotherriftsystemsoneverythingfromsurfaceprocessestomagmatismanddeepgeodynamics.TheseobservationsincludeexistinggeophysicaldatasetsonbothEARandENAMfromGeoPRISMSandotherefforts,growinggeochemicaldataanddrillingdatainvariousrifts.Particularthemesdiscussedforsyntheseswere:

• Geochemicalvariationsalong/acrossENAM/EAR• Sedimentmassfluxesfromexisting(limited)drillingdata• Geochronologicaldataonmagmatic/volcaniceventsandsurfaceprocesses• Crustal/lithosphericstructureofriftsfromexistinggeophysicalimaging,withfocus

oncomparisonsbetweenandwithinsystemswithvariablemagmatism• Geochemicaldatafromgeothermalexplorationprojects(drilling)involcanicand

non-volcanicsettings.Newdatacollectionandexperimental/numericalwork:Fromdiscussionatthemeeting,itisclearthatnewdataandexperimentsarerequiredtotacklemanyimportantsciencethemes,andseveralkeygapsemergedfromdiscussionsatthemeeting.Belowareexamples:

• Studiesofvolatilesystemstounderstandtheirdistribution/abundance/residencetimeatvariouslevelsinthelithosphere.ThiswouldinvolveintegratedgeophysicalimagingincludingbutnotlimitedtoMT,seismicanddetailedgeochemicalstudiessuchasmeltinclusions,samplingvolatilesatthesurface,highdensityfluxmeasurementsandotherapproaches.

• Experimentalandnumericalmodelingdirectedattheimpactofvolatilesandlowercrust/mantlelithospherehydrationstate/compositionsondeformationthroughoutthelithosphere,

• Observationstoconstrainthetimescalesofprocessesareneeded.Theseincludebutarenotlimitedtomoregeodeticobservationstounderstandaverageratesandobservetransienteventsaswellasinvestigationsofpaleoseismologytounderstandlongertermaccommodationofstrainbyevents.Onalongertimescale,betterandimprovedgeologictiminginformationisneeded.

• Newconstraintsonsedimentaryfluxesinriftsincludingbutnotlimitedtocosmogenicdatingtechniquesandriverincisionrates.