WHY I DISLIKE RIEDEL SHEARS - LinkedIn

For me, Riedel shears are a well-documented phenomena associated with strike-slip faults developed in relatively homogeneous rock-types and ... Riedelshears.Alotofgeologistslovethem.Me,Ihavegrown,possiblyunfairly,todislikethem–butwe’llgettothat.BackgroundMostgeologistshaveheardofRiedelstructures,eveniftheyaren’tfamiliarwiththeworkerswhodefinedthem.TheyarenamedforWRiedel,basedonhis1929paperandfirstreportedbyCloos(1928).Theyappearinmostofthewidelydistributedstructuralgeologytextbookswithanoft-repeateddiagramshowingthevariouslyorientedstructures,similartotheoneIhavedraftedbelow. IhaveheardsomepeoplecallthesediagramsTchalenkodiagrams,butIdisagreewiththisbecause,althoughTchalenko(1968)usedtheterminology,henevercitedRiedel(1929).Forme,Riedelshearsareawell-documentedphenomenaassociatedwithstrike-slipfaultsdevelopedinrelativelyhomogeneousrock-typesandtypically(butnotalways)inacoversequenceoveratranscurrentbasementstructure.Thereareexceptionsandmodificationstothisgeneralview,mainlyasafunctionoftheorientationoftheprincipalstressaxesrelativetotheprincipaldisplacementzonethathasdevelopedinthesamedeformationregime.However,thegeneraldescriptionisadequateforthethesisofthispost.Thisgeneralviewisconsistentwiththegoodcorrelationofstructuresdevelopedintheoriginalmodelingoffeaturesdevelopedinclaylayersoverashearedsubstratewiththoseseeninnature.Therearecharacteristicangularrelationshipsandkinematicsassociatedwiththestructuresthatdevelopovertimeandunderafairlyconsistentlyorientedstressregime(diagramabove).ThebasicgeometryoftheRiedelstructureconsistsofconjugateshearbandsarrangedinen-echelonarraysanddenotedbyRandR’.TheotherimportantstructureisthePsurface.ThesequentialdevelopmentofshearsurfacesinnaturalRiedelsystemsispoorlyunderstood,butthegeneralconsensusisthatRandPshearsdevelopbeforetheR’shears,whichformatamuchhigherangletotheprincipaldisplacementzone.Justasimportantly,individualshearsgenerallyremainactiveaftertheothersheartypesdevelop.Thismeansthat,astheshearzoneevolves,thestrainwithintheRiedelsystemisaccommodatedbysynchronousmovementonallfracturescomprisingthezone. ThereisrecognitionthattheRiedelshearsystemsevolvefromProto-RiedelZones(terminologyfromAhlgren,2001),andarecentLinkedInpostbyAppliedStratigraphixshowedagoodexampleofthese.ThediagrambelowisfromAhlgren(2001)andshowsthesequentialdevelopmentofaRiedelsystemdevelopinginasinistralstrike-slipregime.Where’stheproblem?Nowhere’stherub.Perhapswrongly,IhavegrowntodislikeRiedelshears.Morecorrectly,IhavegrowntodislikethementionofRiedelshears.Althoughtheyarepartofagreatmodelofhigh-crustalleveldeformationprocesses,theyaremisused.InmyworkIgettoreviewalotofcompanyreportsanddocuments.Verycommonly,inzonesofrockinwhichfaultsaremappedorinferred,amodelofRiedelsheardevelopmentisinvokedbycompanygeologistsandconsultants.So,whereistheproblem?Inmostcases,themodelsofRiedelshearsystemshavebeeninvokedbecausesomeonehasthoughtthefaultgeometriesareconsistentwiththeRiedelmodel.However,thethinkingprocessseemstostopthere.ManyofthefaultedvolumesIsee‘described’havebeenaffectedbymorethanonedeformationevent,commonlywithdevelopmentoffoliationsathighanglestoeachother.So,thestressaxisorientationsrelativetotheoldestfaultpopulationscanhavechangedmarkedly.This,inturn,meansthatthekinematichistoryonanyonestructurecanbecomplex.TheoldchestnutoffaultreactivationthrowstheuseofRiedelshearmodelstoexplainfaultgeometriesintodoubt.Why?BecauseIveryrarelyseeageologicalhistoryprovidedfortheareadescribedinreports.Thatis,overprintinghistoriesthatdefinewhetherprogressive,sequentialorcoevalstructuredevelopmentoccurredareabsent.Andthemovementsensesonthestructureshavenotbeenresolvedsuchthatthekinematichistoriescanbeintegratedwithgeologicalhistory.Ivisitminingandexplorationprojectsinrocksofallvintages,fromArchaeantoProterozoictoPalaeozoictorelativelyrecent.Theserockshavehadalotoftimetoenjoyalotofdeformation,commonlywithmarkedlyvaryingorientationsoffar-fieldstressesovertime.However,theRiedeltemplateiscommonlyemployedwithnoregardtostructuralhistory.Thishasmajorimplicationsforunderstandingthestructuralcontrolstovolumesoffault-controlledhydrothermalmineralisation,especiallyifpeopleareinterpretingfaultmosaicsasRiedelsystems.Faultpopulationshavetobeinterrogatedandcharacterised,withtheiroverprintinghistoriesandkinematicscommonlybeingmoreimportantthantheirorientationswithrespecttoeachother.Furthermore,manyofthese‘models’areappliedirrespectiveofthelithologiesinwhichtheyaredeveloped.Thedistributionoflithologiesplaysahugeroleinthewaystrainisdistributed,withzonesofshorteningstrain,shearingstrainandstrainaccumulationallbeingstronglyinfluencedbyrock-typeandvariationsinrock-type.So,toblithelyinterpretlinearfaultgeometriesacrossmarkedlydifferentlithologicalpackagesandthenascribeittoaRiedelsystemshowsalackofunderstandingand/orinterest.Eitherway,itisdoingtherocksadisservice.Ifpeoplearehonestwiththemselves,IsuspecttherearemanydepositsouttherethataretoutedasforminginaRiedelsystemthathavebeentotallymisinterpreted.Worsestill,thereisoneconsultant(whowillremainnameless)whothinkseverysysteminterpretedfromgeophysicaldataisaRiedelsystem,whichcompelsthisconsultanttoinvokeformationofeverystructureduringthesameorogeniceventwiththesamestressaxes,regardlessofestablishedgeologicalhistory.Isuspecttheconsultantinquestionisnotalone.ThefewbreathsoffreshairIgetarewhenIseereportsbycolleaguessuchasDavidRhys,GerardTripp,MollyTurko,JamesLally,JamesSiddornetc,becauseIknowtheywillhavedonethestructuralhistoryjusticeandresolvedthekinematics,insteadofsimplythrowingastructuralgeologicalfrisbeewithsetangularorientationsoveramapandinstantlyproclaimingitisaRiedelsystem.Beingtruetotherocks–concludingcommentsAsgeologistsworkingonhydrothermalmineraldeposits,weshouldbedealingwithunderstandingprocessesovertime.Weshouldberesolvingchangesinkinematics,identifyingstructurereactivation,understandingthecontrolsonpermeability,documentingoverprintingandgeometricrelationships,undertakingveinsystemanalysis,integratingalterationandfluidfloweventsetcinacoherenthistory.Allofthesearefundamentaltothetenetsofmineralsystemanalysis.SimplyascribingageometrytoaRiedelsystembasedonorientationsandangularrelationsandmovingonisnot.Anyway,thisismysoapboxbasedonthefrustrationofseeingthepoororincorrectapplicationofaverygoodstructuralgeologicalconcept.Unfortunately,ithasmademedislikethem,or,morecorrectly,thementionofthem,andthatshouldnotbethecase.Enoughsaid!ReferencesAhlgren,S.G.,2001.ThenucleationandevolutionofRiedelshearzonesasdeformationbandsinporoussandstone.JournalofStructuralGeology,23,1203-1214.Cloos,H.,1928.ExperimentenzurinnerenTektonic.CentralblattfürMineralogieundPaleontologieB,609.Riedel,W.,1929.Zurmechanicgeologischerbrucherscheinungen.Zentral-blattfürMineralogie,GeologieundPaleontologieB,354-368.Tchalenko,J.S.,1968.Theevolutionofkink-bandsandthedevelopmentofcompressiontexturesinshearedclays.Tectonophysics,6,159–174. 300 83Comments Like Comment Share WinifredOppeBejarano Excelente  Like Signintolikethiscomment Reply Signintoreplytothiscomment 1Like 2mo Reportthiscomment BobKrantz Hi,Brett.Ijustranacrossthiswhilewritingthestrike-slipfaultssectionofthefaultschapterforthecoming4theditionoftheDavisetal.structuretextbook.Idislike"Riedel"evenmorethanyou!Myprincipalrantcentersonthedependencyoftheorientationofstructureswithinastrike-slipfaultzone,including"R"and"R'"faults,andtheinstantaneousorfinitestrainellipse,onthedegreeofconvergentordivergentstrainacrossthezone(i.e.transpressionortranstension).IpublishedapaperinJSG,alongwithpubsbyothers,toshowthevariationinhorizontalstrainratiosandorientations.ThereisNOsingletemplateforstrike-slipdeformation. Mybiggerrantaboutstrike-slipsystemsishowoftenthesehavebeenmis-diagnosed.Peopleseeconfusingorfuzzystructures,orcherrypickafewspecificfeatures("Look,it'senechelon!")andcallitstrike-slip.Ortheyfindsomethingcomplexandnoteasilyinterpreted,andblameinonstrike-slip.Thus,strike-slipcanbetheinterpretationoflastresort.Ispentmuchofmycareerde-bunkingthosesortsofinterpretations. Like Signintolikethiscomment Reply Signintoreplytothiscomment 1Like 2mo Reportthiscomment BrettDavis ThanksforthefeedbackBob.It'sausefultemplatetounderstandtheidealorientationsandtypesofstructures,but99timesoutofa100(probablymore)itsimplygetsmisused.Thecherrypickingisatypicalexampleofthis. Like Signintolikethiscomment Reply Signintoreplytothiscomment 2mo Reportthiscomment KalidouTraoré likeittomuch Like Signintolikethiscomment Reply Signintoreplytothiscomment 7mo Reportthiscomment SigitArdiansyah "Asgeologistsworkingonhydrothermalmineraldeposits,weshouldbedealingwithunderstandingprocessesovertime.Weshouldberesolvingchangesinkinematics,identifyingstructurereactivation,understandingthecontrolsonpermeability,documentingoverprintingandgeometricrelationships,undertakingveinsystemanalysis,integratingalterationandfluidfloweventsetcinacoherenthistory.Allofthesearefundamentaltothetenetsofmineralsystemanalysis."Ididandiagree.Thanksforsharing. Like Signintolikethiscomment Reply Signintoreplytothiscomment 1Like 8mo Reportthiscomment CampbellMackey IalwayswantedtogotoRiedelHigh. Like Signintolikethiscomment Reply Signintoreplytothiscomment 8mo Reportthiscomment EdwinMalliquinga Agree.WhenImapandinterpretephitermaleventsinundergroundminefromoneblasttoanother,onerealizesthere'smuchhistoryinvolvedbecauseofitsabruptstructuralchangeswherethosemoveschangedtheinfluxfluidwhichinjectedthecommodity. Like Signintolikethiscomment Reply Signintoreplytothiscomment 1Like 8mo Reportthiscomment AntonioHuizi KelseyCrook Like Signintolikethiscomment Reply Signintoreplytothiscomment 8mo Reportthiscomment TimElliott Iseeanindustryobsessedwithdeformationphasesthatthinksadrillfencelineisacrosssectiontobe"interpreted"in2D. Therearebiggerproblems. I'veyettoseeanyonerecognizeafault,whentheyarestandingonone.Notonepersonoutofhundreds.Includingstructuralconsultants. SoIdrawablankonthis.Faultsappeartobemythicalintheresourcesector. Like Signintolikethiscomment Reply Signintoreplytothiscomment 2Likes 8mo Reportthiscomment TimElliott JeremyBurtonthere'sanelementtothisstorythathelpsexplainhowthisallhappens. TherewasabeautifulstructuralmapofastyleIlike.Oneoffourcontradictorymaps.Alldoneinblackpen,showingcomplexfolding.WhenIgroundcheckedit,thefoldswerefrommegaclastswithinabreccia.Soitwasgibberish. Itoldtheseniorgeothisandsheblewupatme."Thatmapwasdonebyoneofthemostrespectedstructuralgeologists,whodareyouquestionit"etcetc Twoweekslatershesawhimataconferenceandmentionedthemap. Hisreplywas"throwthatmapaway,IdiditinfourdayswhenIwaspostdocandItookmynewgirlfriendinthefield". Like Signintolikethiscomment Reply Signintoreplytothiscomment 8mo Reportthiscomment TimElliott JeremyBurton100%outcrop. I'mcompletelyopentosomeoneexplainingthistome. Like Signintolikethiscomment Reply Signintoreplytothiscomment 8mo Reportthiscomment KeenanJennings Sadly,structuralgeologistsaregettingmoreandmorerare.ThenumberoftimesthatIhavetoaskforevenabasicstructuralarchitectureofanareaofinterest....Idreamofthedaythatnotonlyisthereastructuralarchitecturemap,butthereisalsoakinematichistory.Appearsthatifwedonotstartvaluingmorethisfundamentalelementofmineralsystems,weruntheriskoflosingtheskill.ThanksBrettforhighlightingtheneedforsoundsciencethroughourreporting. Like Signintolikethiscomment Reply Signintoreplytothiscomment 4Likes 9mo Reportthiscomment BrettDavis ThanksKeenan.Thereisacommonthemetomyposts,fromhowtoestablishaveinoverprintinghistorytocautionondocumentingfaultkinematicstothispostonRiedels.Allofthemshowafundamentalgradualerosionofbasicskills,thecausesofwhicharemany. Like Signintolikethiscomment Reply Signintoreplytothiscomment 9mo Reportthiscomment DrKyliePrendergast Agree-abasicarchitecturetostartwithgetseveryoneinto3D.Kinematicselevateitto4D Like Signintolikethiscomment Reply Signintoreplytothiscomment 1Like 9mo Reportthiscomment CornéKoegelenberg Brett,thanksforthearticle.Icannotagreemore.You'vehighlightedacommonassumption(thisisaRiedelShearSystem)thattooeasilypassesfortheoryinreports(andpublications!),withoutprovidinganysubstance. Like Signintolikethiscomment Reply Signintoreplytothiscomment 9mo Reportthiscomment Seemorecomments Tovieworaddacomment,signin Tovieworaddacomment,signin ESTABLISHINGAVEINOVERPRINTINGHISTORY Dec29,2021 Compositeveins Dec26,2021 Anoteonfaults,movementsenseandimplicationsofterminology Jun26,2021 Structuralgeology-BusuaBeach2005 Jun16,2021 Therolesofveinsinadeformedrockvolume–Part6 Jun12,2020 Therolesofveinsinadeformedrockvolume–Part5 Jun1,2020 Therolesofveinsinadeformedrockvolume–Part4 May29,2020 Therolesofveinsinadeformedrockvolume–Part3 May26,2020 Therolesofveinsinadeformedrockvolume–Part2 May25,2020 Therolesofveinsinadeformedrockvolume-Part1 May22,2020 Othersalsoviewed Veinsystemanalysis–somecommentsonveinmorphology BrettDavis 2y HostrockstructuralpatternsoftheKurokovolcanogenicmassivesulfidedeposits:PART2 JunCowan 8mo Whymakinginterpretationerrorsaspartofyourgeologicalroutineisimportant JunCowan 1mo FracturedBasementReservoirs:Big,bashful,belligerent,butultimatelybeautiful DaveWaters 4y Climatechange.Whatactuallyisthepre-requisiteforactionandwhydelay? DaveWaters 3mo StructuralGeology—aforgottendisciplineinmineralexploration JunCowan 4y WhatHappensAfterThat? PeterLawlor 4mo LearnconceptsofEarthquakeResistantDesign BhavinShah 7mo Exploretopics Workplace JobSearch Careers Interviewing SalaryandCompensation Internships EmployeeBenefits SeeAll