Paleomagnetic evidence for Neoarchean plate mobilism

Domain: earth_science
Published: 2024-12-30
Editorial outcome: major_revision

Abstract
PlatetectonicsisauniquefeatureofEarth,butitsproposedtimeofinitiationisstillcontroversial,withpublishedestimatesrangingfromca.4.2to0.7Ga.Paleomagneticdatacanprovidearobustargumentforoneessentialaspectofplatetectonics:large-scalerelativelateralmotionsofdistinct,rigidcrustalblocks.Previously,theoldestrelativehorizontalmotionbetweentwoormoreblockswasconstrainedtoabroadageintervalofca.2.7–2.17Gausingpaleomagneticdata.Inthisstudy,weobtainarobustca.2.48GapaleomagneticpolefromWyomingcraton.Combiningthisresultwiththeca.2.7–2.17GaapparentpolarwanderpathsfromWyomingandSuperiorcratons,wesuggestthattheyassembledduringca.2.7–2.5Gaandremaineddirectlyjuxtaposeduntilca.2.17Ga.TectonostratigraphicdataandgeologicalproxiesalsosuggestWyomingandSuperiorcollidedatca.2.6Ga.TheresultsprovidestrongevidenceforrelativehorizontalmotionbetweencrustalblocksduringtheNeoarchean.Togetherwithothertectonicproxies,thedatasuggestplate mobilisminoperationpriorto2.5Ga.

Introduction
PlatetectonicsispresentlythemajormechanismforheatdissipationandmaterialcirculationbetweenEarth’sinteriorandsurface.Howfarbackintimeplatetectonicshasoperated,andhowitmayhaveinitiated,aremajorquestionsintheEarthsciences1–5.ExistingestimatesfortheonsetofplatetectonicsrangefromtheHadeantoNeoproterozoic(Supplementary Fig. S1), based on diverse constraints from geology1,4,6,7,geochemistry8–11,paleomagnetism4,12–14,andgeodynamicmodels15,16, many of which are complicated by terminological ambiguitiesandimprecisionofempiricalconstraints3.

Inprinciple,oneofthemostrobustargumentsforArcheanplatetectonicscan comefrom paleomagnetism. However,the paleomagneticargumentforplatetectonicsisweakenedifrelativemotionisnotdemonstrated.Forexample,3.45–3.18GapaleomagneticdirectionsofvolcanicrocksfromPilbaracratonhavebeeninterpretedtorepresentlateralmotionsbyplate-tectonicprocess13,14,17;however,datafroma single craton can also be explained by true polar wander (TPW)18. Documenting significant relative motion between two or more cratons,whichisnecessarytoresolvesuchambiguities,requiresdifferingpaleomagneticapparentpolarwanderpathsbetweentheblocksoverthesametimeinterval12.RobustpathsareestablishedforPilbaraandKaapvaalcratonsfrom2.8to2.7Ga,butthedatapermittheircommonmotionasasingleArcheanblock19.Untilnow,theoldestrobustdocumentationofsignificantdifferentialmotionsbetweentwoormorecratonsisconstrainedtoabroadagerangebetween2.71and2.17Gabasedontheirtwopairsofpaleomagneticpoleages20,21.Inthisstudy,wereportanewU-Pbageandpaleomagneticpolefromthe2.48GaElbowCreekmaficdikesintheWyomingcraton.Aidedbytheca.2.48GapolesfromSuperiorcratonand2.71Gapolesfrombothblocks,thedata provide quantitative kinematic constraints for the assembly ofWyomingandSuperiorcratonsbetween2.71and2.48Ga,withintheNeoarchean portion of the previously broadly constrained time interval.Ourresultsdocumenttheoldestsubstantialrelativemotionbetween crustal blocks, providing a potential minimum age for the initiationofplatetectonicmobilism.

WyomingCratonhasarichArcheanhistoryextendingbackto3.5 Ga,anditsnorthernandcentralregionswerestabilizedby2.71Ga22–24. Thesouthernaccretedterrane,whichconsistsofvariousfragmentsof arcsandmicro-continents,wassuturedtothecratonalongtheOregon Trailstructuralbeltatca.2.65–2.63Ga23,25,26.Afterstabilizationofthe Wyomingcraton,multiplegenerationsofNeoarchean-Paleoproterozoic maficintrusionswereemplacedintothebasement,includingtheca.2.71 GaStillwaterComplexandnumerousswarmsofmaficdikes21,27–29.The Wyoming craton arrived at its current position relative to Superior during the amalgamation of Laurentia at ca. 1.8–1.7 Ga28,30. Laramide orogenicupliftduringlateCretaceoustoCenozoictimedenudedand exposedthebasementrocks23.

Theca.2.71GaStillwaterComplexisexposedwithintheBeartooth MountainsinsouthernMontana29.AftertheemplacementoftheStillwaterComplex,maficdikesintrudedintotheComplexanditsbasement footwall(Fig.1).ThedikesareNW-trendingorNE-trendingdiabaseor gabbroandareusually5–10mwide;theirpetrographyandgeochemistry atthetypelocalityofElbowCreek,neartheStillwaterMine,isdescribed byRogersetal.31.ThecomplexandthedikesareoverlainbyPaleozoic andMesozoicsedimentaryrocks,andtheentiresuccessionwasstructurallyimbricatedwithnortherlyvergenceduringtheCretaceousLaramideorogeny32.DespitesteepdipsoftheStillwaterlayeredseries,the cross-cuttingdikesaregenerallyverticalormoderatelysouth-dipping, and shallow dips of the nonconformably overlying Paleozoic strata indicateonlyminorLaramidetiltingofthecentralzoneofupliftwhere themajorityofpaleomagneticsitesarelocated33.Inthisstudy,samples werecollectedfrom26dikes.Conductingbaked-contactteststoconstraintheageofthemagnetization,wealsocollectedsamplesfromtheir hostrocksincludinganorthositesfromtheca.2.71GaStillwaterComplex anditsca.2.8GafootwallMouatquartzmonzonite(Fig.1).Blocksamples ofthedikeswerecollectedforzirconandbaddeleyitegeochronology.

Results
Isotopedilutionthermalionizationmassspectrometry(ID-TIMS)on fourbaddeleyitefractionsofoneElbowCreekdikeneartheStillwater Mine (J20S24, Fig. 1) produced U-Pb data that are 1–2% discordant. Linear regression yields upper and lower intercept dates of 2480±4Maand717±500Ma.The2480±4Madateisinterpretedas thecrystallizationageofthedike(Fig.2).

RockmagneticresultsincludingtheK-Tcurves,hysteresisloops, isothermalremanentmagnetization(IRM)andback-fielddemagnetizationofIRMshowthatthemainmagneticcarriersaresingle-domain orpseudo-singledomainmagnetite(SupplementaryFigs.S2andS3).

Stepwisethermaldemagnetizationwasconductedonallpaleomagneticsamples.Alow-temperaturecomponent(LTC)wasremoved before500°C.LTCsareeithersimilartothepresent-daymagneticfield directionorscattered(SupplementaryFig.S4).Amiddle-temperature component(MTC)wasisolatedbetween500and560°Cfromthree dikesandtheiradjacenthostrocks(SupplementaryFig.S4).Afterthe removalofLTCandMTC,thehigh-temperaturecomponents(HTCs) wereisolated.ThirteendikesyieldedanHTC(hereafterreferredtoas component A), which is directed south-southeast and down with a moderate inclination (Fig. 2; Supplementary Fig. S5).Lessabundant dikesiteswithotherstableHTCdirectionsarelistedinSupplementary TableS1anddescribedintheSupplementarySectionA3.2.Theyare interpreted as intrusions of various Proterozoic ages, including five dikeswithnorthorsouthshallowremanence(componentB),onedike withsoutheastandmoderateupwarddirection(componentC),and onedikewithashalloweastremanence(componentD).

ComponentAisclearlydistinctfromtheHTCsofhostrocksinthe StillwaterComplex,whicharedirectedsouth-southeastandupward34; and a suite of baked-contact tests, with one particularly definitive result,demonstratethatcomponentAcanbeinterpretedasprimaryin origin (Supplementary Section A2.3; Supplementary Figs. S7–S9). Additionally, one positive regional stratigraphic consistency test demonstratesthatcomponentCcouldalsobeprimaryinorigin,which wouldfurtherruleoutwidespreadregionalremagnetizationacrossthe studyarea(SupplementarySectionA2.3;SupplementaryFig.S9).After applying a uniform Laramide tilt correction using Paleozoic strata, which are locally preserved atop the central outcrop region of the StillwaterComplexwithvariablebutlownortherlydips32,33,themean direction of the thirteen dikes with Component A is: D=145.8°, I=59.6°,k=31.5,α95=7.5°,andthemeanpoleforthesethirteendikes is:2.0°N,275.3°E(A95=10.2°).Apaleosecularvariationtestshowsthat ourpaleomagneticresultslikelyprovideasufficienttimeaverageof geomagnetic variations, therefore the pole can be used for robust paleogeographiccomparisons(SupplementarySectionA2.5).Ournew pole fulfills six of seven quality criteria for paleomagnetic poles35, lackingonlydualpolarityofremanence,andcanbetreatedasakey paleomagneticpolefortheWyomingcratonat2480Ma.

AssemblyofWyomingandSuperiorduringca.2.7–2.5Ga
Striking stratigraphic and sedimentological similarities between the Huronian and theSnowyPass Supergroupsled Roscoe and Card36 to proposethatWyomingandSuperiorcratonswereaconjugateriftpair, connectedalongtheirpresentsouthernmarginsbetweenca.2.4and2.1 Ga. The matching of large igneous province temporal “barcodes” between the two cratons also suggests their proximal relationship throughouttheearlyPaleoproterozoic(SupplementaryFig.S17)37.The connectionfindsadditionalsupportfromthetwocratons’ca.2.17Ga paleomagneticpoles21,38,aswellastwoca.2.22Gavirtualgeomagnetic poles (VGPs) from Wyoming and the ca. 2.22 Ga poles from Superior20,39,40.Thepresentstudyextendstheconnectionbacktoca.2.5 Gabasedonournewca.2.48GaElbowCreekpolefromWyomingcraton andthepolesfromtheca.2.50GaPtarmigan-Mistassinidikesandthe 2.47–2.45GaMatachewandikesfromSuperior(Fig.3B)38.Inthecommon referenceframeoftheconjoinedassembly,however,theca.2.71Gapoles fromtheStillwaterComplexoftheWyomingcratonandtherocksfrom theAbitibisubprovinceofSuperioraresubstantiallyseparatedfromeach other(Fig.3B);thisrequirescratonicassemblywithrelativemotionson theorderofthousandsofkm(minimum~30°ofarcdistance;Fig.3C,D, Supplementary Fig. S16A) during ca. 2.71–2.48 Ga. Within that time interval,theca.2.65–2.63GaOregonTrailstructuralbeltisthemostlikely manifestation of their assembly23,25,26,36. Using the Oregon Trail age estimate for the amalgamation, the apparent polar wander path convergenceof~3000kmin70millionyearsindicatesanaveragerateof about4–5cm/yr.Thesecalculationsareintentionallyapproximatedueto the inherent paleolongitudinal uncertainties of paleomagnetic reconstructions,buttheyareconsistentwithpresent-dayplatemotionrates14.

Paleomagnetismconstrainstheoldestrecognizedrelative cratonicmotion
Ourpresentstudyisthefirsttodocumentapaleomagneticallyrobust Archean record of assembly between cratons in a geologically compellingreconstruction.Theca.2.71–2.17Gaapparentpolarwander paths for Wyoming and Superior previously suggested they experiencedrelativemotionpriortoca.2.17Ga,butwithoutaprecisetemporalconstraint20.Beforethisstudy,theminimumageofindisputable relativemotionbetweenanytwocratonswasconstrainedtoRhyacian time:Buchanetal.41andMitchelletal.42documentedrelativemotion betweenSlaveandSuperiorcratonsatca.2.2–2.0Ga.AlthoughCondie et al43. suggested changes of relative positions between Superior, Kaapvaal and southern Indian cratons through ca. 2.4–2.1 Ga, the method they used is not definitive (Supplementary Fig. S18); such methodologicalambiguityalsocompromisesanearliersuggestionof Neoarcheanrelativecratonicmotions4.

Various models of global-scale Neoarchean-Paleoproterozoic paleogeographic reconstruction aresimilarlyambiguous. Liuetal.44 presentedtwopaleogeographicoptionsfortheinterval2.62–2.41Ga: onewithsubstantialrelativemotionbetweentwocratongroups,and theotherwithrelativerigidityyetasizablegapbetweenthegroups. Salminenetal.45concludedthatseparatelydriftingcratonsweremore likely than a supercontinent through this time interval, but relative motionscouldnotbeconclusivelydemonstrated.

LateArcheanplatemobilism
Modern-style plate tectonics has at least three important features: large lateral mobility, rigid lithosphere, and temporally continuous seafloor spreading balanced by subduction1,5. The present study documentsNeoarcheanrelativelateralmotionbetweencratonsonthe orderofthousandsofkm,demonstrablybetween2.71and2.48Ga,and likelyoccurringpriorto2.63Ga.Basedonthepreservedglobalrock record(Fig.3A),rigidityoflithosphericplatesdevelopedbetween3.2 and2.5Ga5,orperhapsevenearlier3.Inparticular,changesinthebulk compositionofcontinentalcrust10,theemplacementofdikeswarms5, and replacement of dome and keel structures by linear thrust- imbricated belts46 all suggest that many lithospheric plates were rigidsinceatleastlateArchean.

Whethermodern-styleseafloorspreadingandsubductionexisted inArcheantimeismoredifficulttodemonstrate.Oceaniclithosphere ofsuchantiquityisnotpreservedinsitu,thusproxyrecordsmustbe soughtwithincontinentallithospherethatwouldhavebeenoverriding oradvancingtowardtheconvergencezones.Large-scalelithospheric mobility canbe accommodated either continuously or episodically, depending on the planetary mode of convection3. Episodic mantle overturning has been proposed for Neoarchean time11,15, but such models predictglobal-scale tectonic quiescence onthe order ofca. 100millionyearsbetweentheputativeoverturneventsthatarecontradicted by a continuity of aggregate records for convergence throughthe2.8–2.5Gainterval(Fig.3A).

Geodynamic modeling, isotopic data from mantle xenoliths, kimberliticdiamonds,andinheritedordetritalzirconsindicatethat materialsthatformednearorclosetoEarth’ssurfacewererecycled intothesub-lithosphericmantlepriorto2.5Ga(SupplementarysectionA1)47–50.Robustpetrologicandmetamorphiclinesofevidencefor subduction(Fig.3E)arehigh-P/low-Tmetamorphicrockslikeblueschists, jadeitites, eclogites, and lawsonite-bearing rocks6, but those proxiesgenerallyappearinthegeologicrecordonlyduringvarious stagesofProterozoictime51,52,withrareanddebatedinstancesinthe Neoarchean7,53. Archean lithospheric recycling may have differed in style from modern subduction11,54,55. But in the context of these broaderdatasets,the2.7–2.5GapaleomagneticdatafromWyoming and Superiorcratons now provide a quantitative kinematic demonstrationofArcheanplatemobilism.

Methods
U-PbID-TIMSgeochronology
Approximately200gofeachsamplewasprocessedatthedepartmentofGeology,LundUniversity,followingtheproceduredescribed by Söderlund and Johansson56. Approximately 40 brown baddeleyite grains of excellent quality were recovered from one sample from dike J20S24 near the Stillwater Mine (45°23'36.91“N, 109°52'58.26“W).

Thebest-qualitybaddeleyitegrainsweretransferredtoTeflon© dissolutioncapsulesandrinsedrepeatedlyinultrapure7MHNO3 and H2OinordertodilutethePbblank.AnultrapureHF-HNO3 mixturewas addedtothedissolutioncapsulestogetherwitha205Pb-233-236Utracer solution.Capsuleswerethenplacedinanovenat190°Cfor3days until the grains were fully dissolved. After dissolution, the samples weredrieddownonahotplateandre-dissolvedinultrapure6.2MHCl withtheadditionofultrapure0.25MH3PO4 beforebeingdrieddown againonahotplate.Thesamplesweredissolvedin2μlofsilicageland loadedonoutgassedRefilaments.TheUandPbisotopiccompositions were measured at the Department of Geosciences at the Swedish Museum of Natural History in Stockholm using a Thermo Finnigan Triton Mass Spectrometer equipped with Faraday cups and a SecondaryElectronMultiplier(SEM).Theintensitiesof208Pb,207Pb,206Pb and205PbweremeasuredinstaticmodeusingtheFaradaydetectors. An ETP SEM equipped with a RPQ filter was used to measure the intensityof204Pb.TheSEM-Faradaygainwascontrolledbymeasuring a~5–10mV signal alternating between Faraday and SEM detectors priortoeachPbanalysis.The233U,236Uand238Uisotopicmeasurements were made in dynamic (peak-switching) mode at filament temperaturesgreaterthan1350°C.Proceduralblanksaretypically0.3pgPb and0.03pgUattheSwedishMuseumofNaturalHistory.Massfractionationis0.1%permassunitforPb,determinedbyreplicateanalyses ofNBSstandardsSRM981andSRM983.Ufractionationwasdetermineddirectlyfromthemeasured233U/236U isotopic ratio. Initial PbcompositionsweretakenfromthemodelcommonPbevolution curve57. The decay constants used were 1.55125×10−11 for 238U and 9.8485×10−10 for 235U58, with the isotopic composition of U being 238U/235U=137.8859.ThelisteduncertaintiesinPb/Uratioswerecalculatedbypropagatingthewithin-runerrorformeasuredisotopicratios, withtheuncertaintiesinfractionation(±0.04forPb,absoluteuncertainties),PbandUblankconcentration(±50%),andPbblankcomposition(2.0%for206Pb/204Pband0.2%for207Pb/204Pb).Analyticalresults werecalculatedandplottedusingtheMicrosoftExcelMacro,Isoplot60.

Rockmagneticandpaleomagneticanalyses
Inthisstudy,aportabledrillwasusedinsamplecollectionformost sites; oriented block samples were collected when drilling was not feasible.Orientationforthecoresampleswasachievedusingamagnetic compass with clinometer, usually supplemented by a solar compass.Nosignificantdifferencewasobservedbetweentheresults usingthetwoorientationdevices.Allthesampleswerecutinto1–3 cylindrical paleomagnetic specimens (2.5cm in diameter, and approximately1–1.5cminheight)inthelaboratory.

Allsamplesweresubjectedtostepwisethermaldemagnetization in15–25stepsupto580or590°Cinanitrogen-gasenvironmentusing an ASC-Scientific TD-48 furnace in which internal residual fields is ~10nT. Sister samples for sites J20S24-26 were also selected for alternating-field demagnetization using a Molspin tumbler AF demagnetizer.Measurementsofthenaturalremanentmagnetization (NRM)andallsubsequentdemagnetizationstepswereconductedon anautomated2G-EnterprisesDCSQuIDmagnetometer.Thedemagnetizationsandremanencemeasurementswereconductedinashieldedchamber,whichhasanambientfieldtypicallylessthan300nT.To characterizethepropertiesofmagneticcarriersinthesamples,rock magnetic studies were conducted on representative samples. Thermomagnetic curves of bulk susceptibility versus temperature were achieved by measuring the bulk susceptibility from –192 to 700°C followedbycoolingbacktoroomtemperatureinargonatmosphere. The measurements wereconducted using an AGICOKLY-4S Kappabridgeequippedwithahigh-temperatureapparatusandacryostat.All theseexperimentswereconductedinthePaleomagneticLaboratoryat YaleUniversity.Inaddition,hysteresisloopsandbackfieldcurveswere obtainedbetween–500mTand500mTusingaPrincetonMeasurement Corporation MicroMag 2900 Series alternating gradient magnetometer(AGM)attheYaleArchaeomagnetismLaboratory.

The paleomagnetic data were analyzed using the computer packagesdevelopedbyEnkin61andCogné62.Directionaldatawerefit usingprincipalcomponentanalysis63,andthemeandirectionswere calculatedusingFisherstatistics64.Thepaleogeographic reconstructionsweremadeusingtheGPlatesfreewarepackage65.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Manuscript by Ding et al.\nTitle: Paleomagnetic evidence for Neoarchean plate mobilism\nThis manuscript presents a new 2.48 Ga paleomagnetic pole from the Elbow Creek mafic dykes of the\nWyoming carton. The paleomagnetic data presented here is of high-quality (key pole), with a positive\nfield stability test (positive baked contact test). The new 2.48 Ga pole is used here to explore the relative\nhorizontal plate motions between crustal blocks (Wyoming and Superior cratons) and the data is used to\nstudy the operation of plate tectonics. (i.e., plate mobilism). Based on differing paleomagnetic apparent\npolar wander paths of Wyoming and Superior in during 2.7-2.5 Ga authors make a well justified\nsuggestion that the plate tectonics was in operation prior to 2.5 Ga.\nPlate tectonics have had major impact on Earth’s geologic, climatic and biologic record, but onset time\nof plate tectonics is debated. Time estimates range from the Hadean to the Neoproterozoic depending\non the used proxy (e.g., geology, geochemistry, paleomagnetism, geodynamic models). The results from\nthis study will interest many people in several geoscience disciplines as the onset of plate tectonics is\none of the major questions in the Earth sciences. As geological record of the operation of plate tectonic\nmay have been lost, the paleomagnetic method remains one of the most robust methods to explore the\nrelative horizontal motion of tectonic plates (i.e. plate tectonics) at Archean.\nThe manuscript is well written and it is an excellent and clear compilation of data. By combining\npaleomagnetic data with proxies for lithospheric rigidity and petrological and metamorphic evidence for\nsubduction the manuscript presents a very nice study of the onset of plate tectonics. Illustration of the\nmanuscript is of very high quality, especially Figure 3, which combines proxies for plate tectonics.\nThe chosen selection between main body text and supplementary information is adequate.\nI have one major concern and few minor comments on the manuscript.\nBaked contact test.\nBaked contact tests are the key for this study in providing proofs of the primary magnetization. Authors\nclaim that there are positive baked contact tests for the dykes J20S24 (cutting anorthosite, ca. 2710 Ma\nStillwater Complex) and J20S28 (cutting granite, ca 2800 Ma Mouat quartz monzonite in Fig. 1).\nDyke J20S24. Authors write that the samples from the site J21S12 (baked anorthosite) yielded an HTC\nthat is directed SE and down with moderate inclination, broadly similar to that of the dyke. However,\nthe mean directions from the dyke and from the baked host rock seem to be 40 apart (Fig. S6) and their\nalpha95 confidence cones are not overlapping. Therefore, the directions are not the same and this does\nnot support a positive baked contact test.\nDyke J20S28. This dyke site shows more convincing positive baked contact test than the dyke J20S24.\nHowever, the unbaked direction is obtained only from three samples. Please discuss this.\nHow reliable are the unbaked directions from these sites? There are only three unbaked samples for the\ndyke J20S28, more for the dyke J20S24. Directions obtained from unbaked samples for these dykes are\nvery different. Please address this.\nMinor comments:\nBoth AF and TH methods were used for cleaning the magnetization and authors choose to use only TH\nresults because there is difference between these. The manuscript is lacking a discussing of possible\nreasons for this, and it should be added. Moreover, if only TH method is used to define the pole, the\ncriteria #2 of Meert et al (2021) is not fulfilled and the pole scores 0 from this criterion  fulfils 5 of the 7\nseven criteria. Not 6 as indicated in the manuscript.\nLine 226 (supplementary). Dyke JLQ15? Should it be the dyke J20S24?\nLines 231-232. There is some words missing from the sentence starting: ”The HTCs of the baked samples\nfrom sites J20S12, J20S15…”\nLines 243-259: Confusion with component B and component C. Text reads as: “…with dike J20S14,\nthe results suggest that its HTC (component B) should be primary…” “…high-temperature component C from\ndike J20S14 should be primary…”", "reviewer_2": "Overview:\nThe study presented by Ding et al., on ‘Paleomagnetic evidence for Neoarchean plate mobilism’\npresents new paleomagnetic data from a suite of dykes that intrude the Stillwater Complex on the\nWyoming craton. The authors identify 4 distinct high-temperature components in the dyke\ndemagnetization at different sites, which they refer to as Component A, Component B, Component\nC and Component D. They use a baked contact test and fold test to argue that Component A is\nprimary and has not experienced subsequent remagnetization after emplacement ca. 2480 Ma.\nComponents B, C and D are attributed to various events by comparing the recovered directions with\nthose of other well-dated events: Component B is also thought to be a similar age to the Stillwater\ncomplex, Component C is associated with the 2210 Ma Claye Butte dykes and Component D is\nassociated with the ca. 780 Ma Gunbarrel dykes.\nThe authors argue that their new paleopole at 2.48 Ga provides evidence for the joining together of the\nWyoming and Superior cratons, requiring at least 30° of lateral motion since 2.71 Ga. While the\napproach presented here is a good one for addressing relative plate motions in the Archean, many lines\nof argument are hard to follow, figures are mis-cited, and I have some significant concerns about the\ninterpretation of paleomagnetic results. I outline major comments below, which should be addressed\nbefore this can be considered for publication, followed by minor line-by-line comments. If the authors\ncan address these comments then I believe this manuscript may still be suitable for publication at\nNature Communications, since evidence for early plate tectonics is sufficiently controversial and of wide\ninterest to the scientific community.\nMajor Comments:\nThe timing and evidence for previous locations of the Wyoming and Superior cratons needs to be\nexplained in substantially more detail. For example, it is really not clear to me when reading the\nmanuscript where the constraint on the location of the two cratons comes from for 2.71 Ga? The data\nshown in Figure 3B and 3C in the main text needs to be explained in more detail to explain which\nconstraints are from this study versus those from existing literature. It is also not clear how a palepole\nconstraint for 2.48 Ga makes the argument for the lateral movement of these cratons relative to one\nanother stronger than it was from existing paleopoles. Please clarify.\nThe new paleomagnetic data presented here is generally nice – I agree with the interpretation of\nstable magnetic carriers, and recovery of a unidirectional component ‘Component A’. However, there are many\nsweeping statements that are not supported by the data as it stands. In particular, these include\ncomparing directions e.g., the 2.48 Ga direction to that recovered from the 2.71 Ga Stillwater complex.\nBoth directions need to be stated, and shown to be different with statistical significance (e.g., by\ncalculating Watson’s VW statistic). Similarly, it is stated that the baked contact tests pass, even though\nthey appear ambiguous and no statistical tests are carried out. In almost all cases, the baked directions\ndo not agree with the dyke direction – an explanation needs to be given for this. Similarly, the expected\nwidth of the baked regions, and the width of the dykes are not stated. While the baked contact tests do\nnot clearly ‘pass’, neither do they clearly fail. This somewhat weakens the results presented here, but\ndoesn’t nullify them. I recommend the authors re-phrase their interpretation of the results to make it\nclear they’re not without uncertainty.\nThe origin of Components B is difficult to follow. This direction does not appear to be unidirectional,\nand I am also unclear on the discussion of which age this component corresponds to. Is it thought to\nbe older than Component A? In addition, can you include fold tests for components B, C and D in order to\ncomment on their timing of remanence acquisition relative to tilting? This will strengthen your\narguments regarding their interpreted ages.\nThe paleopole presented here was calculated from 100% untilted directions, even though the maximum\ndegree of clustering was found at 20% untilting. I disagree with the authors’ interpretation that this is\nevidence for dyke emplacement after tilting – it looks much more like dyke emplacement syn-tilting to\nme. I would like to see a paleopole reconstruction for this maximum clustering at 20% untilting. How\nmuch does this change things?\nThe authors are a little vague on their definition of tectonics in terms of a large degree of lateral\nmotion. It would be nice to see upper/lower limits on plate motion calculated from the extent of\nlateral motion inferred here, and a discussion of how that fits in with present day tectonic motions.\nI think this would add real significance to the results presented here.\nMain Text Comments:\nLine 61-62 – can you clarify how this is a comparison between two separate blocks? Since you are\nonly providing new measurements here for one locality, it needs to be made clearer how this will be\ncompared to go above and beyond the studies of Brenner et al.,\nLine 95-96 – which lithology was sampled in the Stillwater Complex? By ‘host rocks’ do you mean the\ncountry rock that the dykes are intruded into? The phrasing could be clearer here.\nLines 120-121when you say Component A is ‘clearly distinct’ from that of the Stillwater Complex,\nplease state both dec, inc and alpha95s of recovered directions, I would recommend calculating\nWatson’s Vw statistic to demonstrate that they are distinct with statistical significance. I’m assuming\nthe fact that Component A is distinct is highlighting that it is younger than the magnetization in the\nhost rocks? If so please clarify this in the main text.\nLine 140 – Figure S15 referenced before S13 and S14, I am also not sure you mean S15 here, since it\nprovides no evidence for LIPs\nLine 151-152 – given the timeframe and 30 degrees of separation, can you comment on the minimum\nrate of plate motion required and how this compares to modern tectonics?\nLine 166 – I think you mean to refer to Figure S14 here, not S13.\nLine 164-168 and Figure S14 – I find this quite difficult to follow. I can see that the reconstructions\nbased on this method are non-unique, and this is nicely illustrated. However, even within the\nambiguity, these studies still appear to conclusively demonstrate relative motion between plates (i.e., there does not\nseem to be any possible solution between 2775 Ma and 2440 Ma that does not involve differential\nmotion between the plates?). Also, why are ages out of order in Figure S14? This makes it very difficult\nto follow!\nLine 178-179 – how large is ‘large lateral mobility’? Is there a minimum rate of lateral motion that is\nrequired to meet the definition of tectonics? How do your constraints on plate motion compare to this?\nLine 203 – I don’t think you mean A2.3 here, since that’s the section on baked contact tests.\nSupplementary Material Comments:\nFigures S2D – for IRM acquisition, please plot dIRM/dB vs field. I would recommend using MAX UnMix to\nidentify the different coercivity populations in your samples (DOI: 10.1016/j.cageo.2016.07.009)\nPlease add more details in the figure caption for Figure S4 – there’s a lot going on here, and it’s difficult\nto interpret the different components at the moment. Also please clarify what kind of projection is used,\nand whether negative inclinations are projected in the top or bottom hemisphere.\nSection A2.2.1 states that 12 dykes had a stable, SE trending HTC. However, only 6 of these are\nshown in Figure S3. Please clarify. It would help significantly to show the identified components as\narrows on the zijdervelds, with zoom-ins of HTCs, and please plot all diagrams with same axes so they can be readily\ncompared.\nSection A2.3 - why is the baked direction different to the dyke direction for dyke J20S24? Can you show\nthe LTC, MTC and HTC directions for the baked units as a function of distance from the dyke? How wide\ndo you expect the baked region to be – what is the width of the dyke, and what assumptions do you\nmake about heating of surrounding country rock? And why no samples between 1 and 100m?? Also\nplease calculate Watson’s Vw statistic for each site to show whether the dyke and baked direction are\nthe same and the unbaked direction distinct, and with what statistical significance.\nSection A2.4 - when the tilt correction is applied, you find maximum clustering of directions 19.4%\nand claim this suggests that the dykes post-date folding. This doesn’t make sense to me, surely this\nimplies that the dykes were emplaced in the early stages of tilting/folding, since after applying a\n100% tilt correction your directions are significantly more dispersed than when they are not tilt\ncorrected at all? How does it impact your interpretation if the dykes are emplaced syn-tilting? How\ndoes the pole calculated from the direction recovered from 20% untilting compare to that presented?\nDoes it change the implications of your results?\nSection A2.5 – presumably taking into account the best clustered direction above will also strengthen\nthe results presented here?\nSection A2.3 – I disagree that Figure S7 provides evidence that component A is not the result of\npervasive remagnetization. These are not passed baked contact tests – they are ambiguous at best,\nsince in almost all cases the baked and unbaked directions overlap and are distinct from the dyke,\nwhen we would expect the baked and dyke directions to be the same, and then unbaked directions to be\ndistinct. This requires further clarification, but certainly cannot be sold as a cut and dry ‘pass’.\nFigure S15 – for the location of Superior/Wyoming at 2170 Ma, how sure are you about the polarity?\nThis seems like a big jump compared to if both were still in the southern hemisphere? I suspect this\nis well-constrained by previous studies, but please provide details/clarification for how you know both are\nin the northern hemisphere at this time."}, "author_response": "REVIEWER COMMENTS\nReviewer #1 (Remarks to the Author):\nManuscript by Ding et al.\nTitle: Paleomagnetic evidence for Neoarchean plate mobilism\nThis manuscript presents a new 2.48 Ga paleomagnetic pole from the Elbow Creek mafic dykes of the\nWyoming carton. The paleomagnetic data presented here is of high-quality (key pole), with a positive\nfield stability test (positive baked contact test). The new 2.48 Ga pole is used here to explore the relative\nhorizontal plate motions between crustal blocks (Wyoming and Superior cratons) and the data is used\nto study the operation of plate tectonics. (i.e., plate mobilism). Based on differing paleomagnetic\napparent polar wander paths of Wyoming and Superior in during 2.7-2.5 Ga authors make a well\njustified suggestion that the plate tectonics was in operation prior to 2.5 Ga.\nPlate tectonics have had major impact on Earth’s geologic, climatic and biologic record, but onset\ntime of plate tectonics is debated. Time estimates range from the Hadean to the Neoproterozoic\ndepending on the used proxy (e.g., geology, geochemistry, paleomagnetism, geodynamic models).\nThe results from this study will interest many people in several geoscience disciplines as the onset\nof plate tectonics is one of the major questions in the Earth sciences. As geological record of the\noperation of plate tectonic may have been lost, the paleomagnetic method remains one of the most\nrobust methods to explore the relative horizontal motion of tectonic plates (i.e. plate tectonics) at\nArchean.\nThe manuscript is well written and it is an excellent and clear compilation of data. By combining\npaleomagnetic data with proxies for lithospheric rigidity and petrological and metamorphic evidence\nfor subduction the manuscript presents a very nice study of the onset of plate tectonics. Illustration\nof the manuscript is of very high quality, especially Figure 3, which combines proxies for plate\ntectonics.\nThe chosen selection between main body text and supplementary information is\nadequate. Many thanks for the positive comments.\nI have one major concern and few minor comments on the manuscript.\nBaked contact test.\nBaked contact tests are the key for this study in providing proofs of the primary magnetization. Authors\nclaim that there are positive baked contact tests for the dykes J20S24 (cutting anorthosite, ca. 2710 Ma\nStillwater Complex) and J20S28 (cutting granite, ca 2800 Ma Mouat quartz monzonite in Fig. 1). Dyke\nJ20S24. Authors write that the samples from the site J21S12 (baked anorthosite) yielded an HTC that\nis directed SE and down with moderate inclination, broadly similar to that of the dyke. However,\nthe mean directions from the dyke and from the baked host rock seem to be 40 apart (Fig. S6) and their\nalpha95 confidence cones are not overlapping. Therefore, the directions are not the same and this does\nnot support a positive baked contact test.\nThanks for the comments and suggestion. [First a note about site numbering: in our initial manuscript\nsubmission, we had combined two (field notes) site numbers from same locality and had renumbered\nsome “downstream” sites in order. In retrospect we consider that decision unwise, and we now have\nreverted to all the original field numbering. Thus, what we had initially submitted as a baked-contact\ntest of dike J20S24 with exocontact J21S12, we have now reverted to the original field numbers of\ndike J20S25 with exocontact J21S13. We apologize for any confusion this might cause, but our current\nrevised manuscript, figures, and this response are all internally consistent with the original field\nnumbering.] We collected eight samples (J21S13A-H) from the anorthosites which are 0.1 to 1.0 m far\nfrom the margin of the dike J20S25 as shown in the modified fig. S7. J21S13A and J21S13B are close\nto the margin, J21S13G and J21S13H are around 1.0 m from the margin. The paleomagnetic results\nshow that the mean direction of the HTCs from J21S13A-D are (n=4): Dg = 134.7°, Ig = 29.9°, α95 =\n17.8°, which has errors overlapping the overall mean of the Elbow Creek swarm (Dg = 157.8°, Ig =\n44.6°, α95 = 8.2°). The HTCs from J21S13E and J21S13F are: Dg = 141.3°, Ig = 14.8° and Dg = 140.4°,\nIg = 13.7° respectively. The HTCs from J21S13G and J21S13H are Dg = 151.3°, Ig = -7.1° and Dg =\n138.6°, Ig = 4.3° respectively (Fig. S7). These results show the samples close to the dike yielded\nintermediate inclinations, and the farther ones yielded shallow inclination. The HTCs from J21S13E\nand J21S13F were located between the HTCs of the baked zone and the host rock site J20S27. In total,\nthe results indicate a classical baked-contact test with a hybrid zone (Meert et al., 2020). The offset\nbetween the HTC mean of the dike itself from this array is interpreted as being due to paleosecular\nvariation, because the dike was sampled at its chill margin, which acquired magnetization when the\nlocal field was\ndirected modestly away from the time-averaged dipole (Fig. S5). We have added the above\ndescription to our supplementary file.\nDyke J20S28. This dyke site shows more convincing positive baked contact test than the dyke J20S24.\nHowever, the unbaked direction is obtained only from three samples. Please discuss this. Thanks for\nthe comments and suggestion. We actually have six samples from the unbaked monzonite from site\nJ20S30 (Fig. S7I): three samples with northwesterly declination and positive inclination (filled blue\nrectangle) and three samples with easterly declination and negative inclination (open blue rectangle).\nThe unbaked samples record dual polarities, they are quite distinct from the HTC directions of the\ndikes and baked samples, and their direction is entirely consistent with that of the Stillwater Complex\nregionally (Selkin et al., 2008). We have modified the figures to show these results much clearer.\nHow reliable are the unbaked directions from these sites? There are only three unbaked samples for\nthe dyke J20S28, more for the dyke J20S24. Directions obtained from unbaked samples for these\ndykes are very different. Please address this.\nThanks for the comments and suggestion. As mentioned above, for dike J20S28, we obtained the\nHTCs from six samples. Due to the age differences between the host rocks, the results from the\nunbaked anorthosites are different from the unbaked Mouat quartz monzonite. The Mouat quartz\nmonzonite was emplaced at ca. 2800 Ma, while the anorthosites were emplaced at ca. 2710 Ma.\nTaken together, these results further suggest that the region has not undergone remagnetization.\nMinor comments:\nBoth AF and TH methods were used for cleaning the magnetization and authors choose to use only\nTH results because there is difference between these. The manuscript is lacking a discussing of\npossible reasons for this, and it should be added. Moreover, if only TH method is used to define the\npole, the criteria #2 of Meert et al (2020) is not fulfilled and the pole scores 0 from this criterion\nfulfils 5 of the 7 seven criteria. Not 6 as indicated in the manuscript.\nIn Meert et al (2020), it is advised to “Attempt at least two methods of stepwise demagnetization (e.g.\nalternating field and thermal, Meert et al., 1995; or thermal/chemical, Billardello and Kodama, 2010)\non at least pilot suite of samples to demonstrate that individual vector components are being separated\neffectively”. The R2 criterion technically does not require statistical comparison between the methods;\nwe think (note that D.Evans is a coauthor on that paper and was extensively involved in discussions of\nthese points) that its intention is to use multiple methods to understand the magnetic mineralogy as a\nbasis for an ultimate choice of which technique works best to isolate the components. After conducting\nadditional alternating-field (AF) demagnetization analysis, three components of consistently variable\ncoercivity were identified (Fig. S6). A soft component (SC) was isolated below 11 mT, a medium-\ncoercivity component was isolated at 11-70 mT, and a high-coercivity component was identified at steps\ngreater than 70 mT. The MCC is directed south-southeast and down with intermediate inclinations (Fig.\nS6), which is similar to the Component A of the thermal demagnetization results, and consistent with\nthe rock magnetic data indicating near-stoichiometric magnetite as the carrier of Component A.\nTrajectories of AF demagnetization also tend toward a shallower HCC direction at the highest steps\n>70mT, which is similar to the MTC of thermal\ndemagnetization. Because the MCC’s direction is slightly biased toward the shallower\ninclinations of HCC, thermal demagnetization is likely a better indicator of the pure magnetite-borne\ncharacteristic remanence. There is a sufficient number of samples from thermal demagnetization\nsuch that only those data are used for the final directional calculation. We therefore consider our\ndataset to have satisfied the R2 criterion and score 6 out of 7 for the R-rating; and we have included\nthe above descriptions in our revised supplementary file.\nLine 226 (supplementary). Dyke JLQ15? Should it be the dyke J20S24?\nThanks for the suggestion. Yes, the new figure now shows results from both J20S24 and J20S25\ndikes (original field site numbering), along with a cartoon depiction of the outcrop for clarity.\nLines 231-232. There is some words missing from the sentence starting: ”The HTCs of the baked\nsamples from sites J20S12, J20S15...”\nThanks for the comment. We have modified the text to read: “The HTCs which were isolated from\nthe baked samples (sites J20S12, J20S15 and J20S17) are located amid the HTCs of the dikes and\nthe unbaked host rocks”.\nLines 243-259: Confusion with component B and component C. Text reads as: “...with dike J20S14,\nthe results suggest that its HTC (component B) should be primary...” “...high-temperature component\nC from dike J20S14 should be primary...”\nThanks for finding our error. We have modified the text to read: “the results suggest that its HTC\n(component C) should be primary.” The HTC of dike J20S14 does in fact correspond to “component\nC” but not “component B”.\nReviewer #2 (Remarks to the Author):\nOverview:\nThe study presented by Ding et al., on ‘Paleomagnetic evidence for Neoarchean plate mobilism’\npresents new paleomagnetic data from a suite of dykes that intrude the Stillwater Complex on the\nWyoming craton. The authors identify 4 distinct high-temperature components in the dyke\ndemagnetization at different sites, which they refer to as Component A, Component B, Component\nC and Component D. They use a baked contact test and fold test to argue that Component A is\nprimary and has not experienced subsequent remagnetization after emplacement ca. 2480 Ma.\nComponents B, C and D are attributed to various events by comparing the recovered directions with\nthose of other well-dated events: Component B is also thought to be a similar age to the Stillwater\ncomplex, Component C is associated with the 2210 Ma Claye Butte dykes and Component D is\nassociated with the ca. 780 Ma Gunbarrel dykes.\nThe authors argue that their new paleopole at 2.48 Ga provides evidence for the joining together of the\nWyoming and Superior cratons, requiring at least 30° of lateral motion since 2.71 Ga. While the\napproach presented here is a good one for addressing relative plate motions in the Archean, many lines\nof argument are hard to follow, figures are mis-cited, and I have some significant concerns about the\ninterpretation of paleomagnetic results. I outline major comments below, which should be addressed\nbefore this can be considered for publication, followed by minor line-by-line comments.\nIf the authors can address these comments then I believe this manuscript may still be suitable for\npublication at Nature Communications, since evidence for early plate tectonics is sufficiently\ncontroversial and of wide interest to the scientific community.\nThanks for the comments and suggestions. We have carefully revised the manuscript according to\nall the comments and suggestions. And following are the responses to the reviewer’s comments and\nquestions one by one.\nMajor Comments:\nThe timing and evidence for previous locations of the Wyoming and Superior cratons needs to be\nexplained in substantially more detail. For example, it is really not clear to me when reading the\nmanuscript where the constraint on the location of the two cratons comes from for 2.71 Ga? The data\nshown in Figure 3B and 3C in the main text needs to be explained in more detail to explain which\nconstraints are from this study versus those from existing literature. It is also not clear how a\npaleopole constraint for 2.48 Ga makes the argument for the lateral movement of these cratons\nrelative to one another stronger than it was from existing paleopoles. Please clarify.\nThanks for the comments and suggestions. We modified Figure 3. We also modified the introduction\nand to illustrate what we discovered and how important our result is: “Until now, the oldest robust\ndocumentation of significant differential motions between two or more cratons is constrained to a\nbroad age between 2.71 and 2.17 Ga based on their two pairs of paleomagnetic pole ages (Kilian,\n2015, 2016a; supplementary information). In this study, we report a new paleomagnetic pole from the\n2.48 Ga Elbow Creek mafic dikes in the Wyoming craton. Aided by the ca. 2.48 Ga poles from\nSuperior craton and 2.71 Ga poles from both blocks, the data provide quantitative kinematic\nconstraints for the assembly of Wyoming and Superior cratons between 2.71 and 2.48 Ga, within the\nNeoarchean portion of the previously broadly constrained time interval. Our results document the\noldest substantial relative motion between crustal blocks, providing a potential minimum age for the\ninitiation of plate tectonic mobilism.”\nThe new paleomagnetic data presented here is generally nice – I agree with the interpretation of\nstable magnetic carriers, and recovery of a unidirectional component ‘Component A’. However,\nthere are many sweeping statements that are not supported by the data as it stands. In particular, these\ninclude comparing directions e.g., the 2.48 Ga direction to that recovered from the 2.71 Ga Stillwater\ncomplex. Both directions need to be stated, and shown to be different with statistical significance\n(e.g., by calculating Watson’s VW statistic). Similarly, it is stated that the baked contact tests pass,\neven though they appear ambiguous and no statistical tests are carried out. In almost all cases, the\nbaked directions do not agree with the dyke direction – an explanation needs to be given for this.\nSimilarly, the expected width of the baked regions, and the width of the dykes are not stated. While\nthe baked contact tests do not clearly ‘pass’, neither do they clearly fail. This somewhat weakens the\nresults presented here, but doesn’t nullify them. I recommend the authors re-phrase their\ninterpretation of the results to make it clear they’re not without uncertainty.\nThanks for the comments and suggestions. First, we have added this analysis, and the Watson’s V\nstatistic results for the HTCs (component A) from the dikes and the Stillwater Complex show they\nare distinct (Figure R1). We obtained the Watson’s V statistic results for the dike J20S14, J20S25\nand J20S28, and we have added them to the supplementary as Fig. S9.\nFigure R1. the Watson’s V statistic for the component A and the HTCs from the Stillwater. The\nresults show the two HTC’s are distinct.\nThe following text is taken from our reply to the other reviewer about the baked contact tests: We\ncollected eight samples (J21S13A-H) from the anorthosites which are 0.1 to 1.0 m from the margin of\nthe dike J20S25 as shown in the modified fig. S7. J21S13A and J21S13B are close to the margin,\nJ21S13G and J21S13H are around 1.0 m from the margin. The paleomagnetic results show that the\nmean direction of the HTCs from J21S13A-D are (n=4): Dg = 134.7°, Ig = 29.9°, α95 = 17.8°, which\nhas errors overlapping the overall mean of the Elbow Creek swarm (Dg = 157.8°, Ig = 44.6°, α95 =\n8.2°). The HTCs from J21S13E and J21S13F are: Dg = 141.3°, Ig = 14.8° and Dg = 140.4°, Ig = 13.7°\nrespectively. The HTCs from J21S13G and J21S13H are Dg = 151.3°, Ig = -7.1° and Dg = 138.6°,\nIg = 4.3° respectively (Fig. S7). These results show the samples close to the dike yielded\nintermediate inclinations, and the farther ones yielded shallow inclination. The HTCs from J21S13E\nand J21S13F were located between the HTCs of the baked zone and the host rock site J20S27. In\ntotal, the results indicate a classical baked-contact test with a hybrid zone (Meert et al., 2020). The\noffset between the HTC mean of the dike itself from this array is interpreted as being due to\npaleosecular variation, because the dike was sampled at its chill margin, which likely acquired\nmagnetization when the local field was directed modestly away from the time-averaged dipole (Fig.\nS5).\n“Dyke J20S28. This dyke site shows more convincing positive baked contact test than the dyke J20S24.\nHowever, the unbaked direction is obtained only from three samples. Please discuss this.”\nThanks for the comments and suggestion. We have six samples from the unbaked monzonite from\nsite J20S30 (Fig. S7G): three samples with northwesterly declination and positive inclination (filled\nblue rectangle) and three samples with easterly declination and negative inclination (open blue\nrectangle). The unbaked samples record dual polarities, they are distinct from the HTC directions of\nthe dikes and baked samples, and their direction is entirely consistent with that of the Stillwater\nComplex regionally (Selkin et al., 2008). We have modified the figures to show these results much\nclearer.\nThe origin of Components B is difficult to follow. This direction does not appear to be unidirectional,\nand I am also unclear on the discussion of which age this component corresponds to. Is it thought to\nbe older than Component A? In addition, can you include fold tests for components B, C and D in\norder to comment on their timing of remanence acquisition relative to tilting? This will strengthen\nyour arguments regarding their interpreted ages.\nThanks for the comments and suggestions. According to the paleomagnetic data, after applying the\nstepwise tectonic correction using the Stillwater complex layers to component B, the HTCs clustered\noptimally in geographic coordinates and suggest that component B was acquired after the Stillwater\ncomplex tilted. After applying the regional tilt correction using the Cambrian strata, the B direction\nis similar to the component C1 of Stillwater Complex reported by Selkin et al. (2008) as shown in\nfigure S15. Based on the 2710-2480 Ma APWP, if we follow the trend, the component B looks like\nyounger than Stillwater complex, and older than Component A, but we don’t know how exactly old\nthe component B was. Because the component C came from two dikes and component D came from\nonly one dike, we did not apply fold tests to them.\nFigure R2. Results of stepwise unfolding of the mean HTC direction (component B) based on the\nmagmatic layering from the Stillwater Complex.\nThe paleopole presented here was calculated from 100% untilted directions, even though the\nmaximum degree of clustering was found at 20% untilting. I disagree with the authors’ interpretation\nthat this is evidence for dyke emplacement after tilting – it looks much more like dyke emplacement\nsyn-tilting to me. I would like to see a paleopole reconstruction for this maximum clustering at 20%\nuntilting. How much does this change things?\nThanks for the comments and suggestions. There is some confusion regarding which layers are\nbeing untilted. In fact there are two sets of structural corrections that we can test: Laramide folding\nand Stillwater magmatic layering. Our 18.3% maximum clustering (but really indistinguishable from\n0%) refers to untilting of the magmatic layering in the Stillwater complex host rocks. When we report\n100% untilting results, we are referring to the Laramide deformation of Paleozoic (Cambrian) strata\nexposed near our sampling sites. The mean direction for 18.3% untilting of Stillwater layering is D\n= 147.5°, I = 53.0°, α95 = 7.3°, which is similar to the mean direction after applying the Laramide\ntilt-correction using the Cambrian strata: D = 145.8°, I = 59.6°, α95 = 7..5°. However, a syn-Stillwater\nremanence (as suggested by the reviewer) for the A component is not possible because it is so distinct\nfrom the published Stillwater C1 direction, supported by the Watson tests above. We show both the\nin-situ (pole W2480 in figure 3) and the Laramide-corrected (pole W2480t in figure 3) results.\nWhichever the pole W2480 or W2480t was used, the results both show Wyoming and Superior\nexperienced relative motion from 2.71 Ga to 2.48 Ga. Importantly, the reviewer’s comment has\nprompted us to clarify the distinction between Stillwater layering versus Laramide deformation\nthroughout the discussion.\nThe authors are a little vague on their definition of tectonics in terms of a large degree of lateral\nmotion. It would be nice to see upper/lower limits on plate motion calculated from the extent of\nlateral motion inferred here, and a discussion of how that fits in with present day tectonic motions.\nI think this would add real significance to the results presented here.\nThanks for the comments and suggestion. We now add these sentences to the main text of the paper:\n“Using the Oregon Trail age estimate for the amalgamation, the apparent polar wander path\nconvergence of ~3000 km in 70 million years indicates an average rate of about 4-5 cm/yr. These\ncalculations are intentionally approximate due to the inherent paleolongitudinal uncertainties of\npaleomagnetic reconstructions, but they are consistent with present-day plate motion rates (Brenner\net al, 2022).”\nMain Text Comments:\nLine 61-62 – can you clarify how this is a comparison between two separate blocks? Since you are\nonly providing new measurements here for one locality, it needs to be made clearer how this will be\ncompared to go above and beyond the studies of Brenner et al.,\nThanks for the comments and suggestions. We have modified some sentences and make our conclusion\nmuch clearer. In Brenner et al. (2020, 2022), they reported two paleomagnetic poles (3.25 Ga and 3.18\nGa) from Pilbara. They suggested Pilbara experienced latitudinal motion during 3.34-3.25 Ga. Because\nthe results come from one continent, the motion could also be the result of true polar wander which is\nalso mentioned in their papers. And we also mentioned in line 50-53 “3.45-3.18 Ga paleomagnetic\ndirections of volcanic rocks from Pilbara craton have been interpreted to represent lateral motions by\nplate-tectonic process (Brenner et al., 2020, 2022, 2023); however, data from a single craton can also\nbe explained by true polar wander (TPW; Mitchell and Jing, 2023).” We identified the oldest relative\nmotion between Wyoming and Superior from 2.71 to 2.48 Ga by comparing their 2.71-2.16 Ga\napparent polar wander paths (APWPs). Before this study, Wyoming and Superior had two pairs of\ncoeval poles (2.71 and 2.17 Ga), and their relative motion could only be constrained to between 2.71\nand 2.17 Ga. We got a new 2.48 Ga pole from Wyoming craton. With the aid of ca. 2.5 Ga Ptarmigan-\nMistassini pole from Superior, we added a new pair of poles (ca. 2.5 Ga) to constrain that their relative\nmotion occurred between 2.71 and 2.5 Ga, which is the oldest relative motion constrained by\npaleomagnetic data.\nLine 95-96 – which lithology was sampled in the Stillwater Complex? By ‘host rocks’ do you mean\nthe country rock that the dykes are intruded into? The phrasing could be clearer here.\nThanks for the comments and suggestions. The host rocks that we collected from the Stillwater\ncomplex for baked-contact tests are anorthosites. We have added it to the main text and modified\naccordingly.\nLines 120-121when you say Component A is ‘clearly distinct’ from that of the Stillwater Complex,\nplease state both dec, inc and alpha95s of recovered directions, I would recommend calculating\nWatson’s Vw statistic to demonstrate that they are distinct with statistical significance. I’m assuming\nthe fact that Component A is distinct is highlighting that it is younger than the magnetization in the\nhost rocks? If so please clarify this in the main text.\nThanks for the comments and suggestions. We have added more details to the text and make it\nclearer. The component A directed south-southeast and down with moderate inclinations (D = 158.2° I\n= 44.6°, α95 = 7.5°), while the HTCs from Stillwater directed south-southeast and up with steep\ninclinations (D = 167°, I = -60°, α95 = 2.9°). The Watson’s V statistic shows that they are distinct as show\nin the figure R1 and Fig S8. Component A is distinct from the HTCs of the Stillwater, and the baked-\ncontact test demonstrate the Component A should be primary instead of a remagnetization. Based on the\nfact that the dikes intruded into the Stillwater complex, we know the dikes are younger than the Stillwater\ncomplex. According to the dating results, we know the dikes are 200 million years younger than the\nStillwater complex, which also readily explains their distinct HTCs.\nFigure R3. the Watson’s V statistic for the component A and the component C2 from the Stillwater\ncomplex suggest they are distinct.\nLine 140 – Figure S15 referenced before S13 and S14, I am also not sure you mean S15 here, since\nit provides no evidence for LIPs\nThanks for the comments and suggestions. We have modified it accordingly.\nLine 151-152 – given the timeframe and 30 degrees of separation, can you comment on the minimum\nrate of plate motion required and how this compares to modern tectonics?\nThanks for the comments and suggestions. Our main conclusion is the relative motion of 30° between\nWyoming and Superior from 2.71 to 2.48 Ga (and 2.71 to 2.64 Ga, if the Orgon Trail structural belt\nage is used as the likely time of suturing between Wyoming and Superior). We added two clarifying\nsentences of text in the main manuscript, as noted above.\nLine 166 – I think you mean to refer to Figure S14 here, not S13.\nThanks for the comments and suggestions. We have modified it accordingly.\nLine 164-168 and Figure S14 – I find this quite difficult to follow. I can see that the reconstructions\nbased on this method are non-unique, and this is nicely illustrated. However, even within the\nambiguity, these studies still appear to conclusively demonstrate relative motion between plates (i.e.,\nthere does not seem to be any possible solution between 2775 Ma and 2440 Ma that does not involve\ndifferential motion between the plates?). Also, why are ages out of order in Figure S14? This makes\nit very difficult to follow!\nThanks for the comments and suggestions. We have modified the figure (now Fig. S18 after the\ninsertion of new figures earlier in the supplement) accordingly and show them now in the same\nlayout as presented by Cawood et al. (2018). The 2775 to 2720 Ma paleomagnetic results come from\nPilbara and Kaapvaal, whereas the 2440 Ma comparison involves Superia, Kaapvaal, and Karelia.\nThe original Cawood et al. (2018) figure might be confusing because Karelia and Pilbara are shown\nin nearly the same colors – but the 2775 and 2440 comparison suggested by the reviewer is an\napples/oranges situation (no equivalency of the two tests). We mostly retained the color scheme from\nthe original Cawood et al. (2018) figures, but now added a distinct yellow color for Pilbara for the\nsake of further clarity.\nLine 178-179 – how large is ‘large lateral mobility’? Is there a minimum rate of lateral motion that\nis required to meet the definition of tectonics? How do your constraints on plate motion compare to\nthis?\nThanks for the comments and suggestions. We used the relative motion between the cratons to\ndemonstrate the “large lateral mobility”. The relative motion between Wyoming and Superior could\nbe around 30°. As noted above, we have added a possible estimate of 4-5cm/yr average convergence\nrate between Wyoming and Superior, noting that this is merely an approximation.\nLine 203 – I don’t think you mean A2.3 here, since that’s the section on baked contact tests.\nThanks for the comments and suggestions. It should be A2.1 now. We have modified it accordingly.\nSupplementary Material Comments:\nFigures S2D – for IRM acquisition, please plot dIRM/dB vs field. I would recommend using MAX\nUnMix to identify the different coercivity populations in your samples (DOI:\n10.1016/j.cageo.2016.07.009)\nThanks for the comments and suggestions. We have modified it accordingly as shown in the\nsupplementary Fig. S3.\nPlease add more details in the figure caption for Figure S4 – there’s a lot going on here, and it’s difficult\nto interpret the different components at the moment. Also please clarify what kind of projection is used,\nand whether negative inclinations are projected in the top or bottom hemisphere. Thanks for the\ncomments and suggestions. The results were shown in the equal-area plots. Negative inclinations are\nprojected in the upper hemispheres. We have modified it accordingly.\nSection A2.2.1 states that 12 dykes had a stable, SE trending HTC. However, only 6 of these are\nshown in Figure S3. Please clarify. It would help significantly to show the identified components as\narrows on the zijdervelds, with zoom-ins of HTCs, and please plot all diagrams with same axes so they can be readily\ncompared.\nThanks for the comments and suggestions. We presented the representative thermal demagnetization\nresults for all the 13 dikes that hold component A, and we also showed the identified components as\narrows on the zijderveld diagrams: green, light blue and red arrows indicate the low temperature\ncomponent (LTC), middle temperature component (MTC) and high temperature component (HTC)\nrespectively (Fig. S4).\nSection A2.3 - why is the baked direction different to the dyke direction for dyke J20S24? Can you\nshow the LTC, MTC and HTC directions for the baked units as a function of distance from the dyke?\nHow wide do you expect the baked region to be – what is the width of the dyke, and what assumptions\ndo you make about heating of surrounding country rock? And why no samples between 1 and\n100m?? Also please calculate Watson’s Vw statistic for each site to show whether the dyke and\nbaked direction are the same and the unbaked direction distinct, and with what statistical\nsignificance.\nThanks for the comments and suggestions. We provided a detailed discussion of the J20S25 baked\ncontact test in our general response to this reviewer, above, so will not repeat that discussion here.\nThe dike J20S25 is around seven meters in width (we have added this information to our data\ntable), and we expected the baked region could be on the order of one meter. Based on the\npaleomagnetic results, the region baked above 580°C was only about a half meter, potentially\nindicating very shallow levels of present exposure. There are numerous dikes in the area of J20S24-\n26, and due to incomplete exposure with widespread colluvial cover on the steep mountain slopes,\nwe wanted to be sure that our unbaked Stillwater anorthosites are far removed from any possible\nyounger intrusions. Additionally, the 150m-distant unbaked Stillwater site J20S27 was desirable\nbecause it contains measurable magmatic layering, which is not particularly common in this specific\narea of the complex.\nThe Watson’s Vw statistic results are shown in the Figure R2 and Fig. S8. The results suggest the\ncomponent A and the HTC from host rocks of sites J20S27 and J21S14 are distinct (Fig. R2B). The\ncomponent A is different from the mean direction of the four baked samples. Because the HTC\ndirections of the samples gradually changed with the distance, the results thus suggest it is a classical\npositive baked-contact tests with the hybrid zone (Meert et al., 2020), and it demonstrates the HTCs\nfrom the dike should be primary. For dike J20S28, the Watson’s Vw statistic results support that the\nHTC (component A) of the dike and the HTC of the baked samples of site J20S29 are similar (Fig.\nR2), while they are different from the unbaked host rocks of site J20S30 (Fig. R2). Also for dike\nJ20S14, the HTC of the dike (component C) are similar with the MTC of the host rocks of site J20S13\n(Fig. R2), they are different from the HTC of the host rocks of site J20S13. These results demonstrate\nboth the component A and C could be primary in origin.\nFigure R4. the Watson’s V statistic results for the component A of dike J20S25 versus the baked\nsamples (A), the component A of dike J20S25 versus the Stillwater host rocks from sites J20S27 and\nJ21S14 (B), the baked samples versus the host rocks from Stillwater sites J20S27 and J21S14 (C). The\nWatson’s V statistic results for the component A of dike J20S28 versus the baked samples of host rocks\nJ20S29 (D), the component A of dike J20S28 versus the unbaked host rocks of J20S30 (E), and the\nbaked J20S29 versus unbaked host rocks J20S30 (F). The Watson’s V statistic results for the\ncomponent C of dike J20S14 versus the MTC of host rocks J20S13 (G), the component C of dike\nJ20S14 versus the HTC of J20S13 (H), and the MTC versus HTC of host rocks J20S13 (I).\nSection A2.4 - when the tilt correction is applied, you find maximum clustering of directions 19.4%\nand claim this suggests that the dykes post-date folding. This doesn’t make sense to me, surely this\nimplies that the dykes were emplaced in the early stages of tilting/folding, since after applying a\n100% tilt correction your directions are significantly more dispersed than when they are not tilt\ncorrected at all? How does it impact your interpretation if the dykes are emplaced syn-tilting? How\ndoes the pole calculated from the direction recovered from 20% untilting compare to that presented?\nDoes it change the implications of your results?\nThanks for the comments and suggestions. We have responded to this point above, clarifying now\nin the main text and supplement, that the 100% applied tilt corrections are for Laramide deformation\nusing Paleozoic (mainly Cambrian) stratification as a datum. In contrast, the test that produced the\napparent 19% partial unfolding maximum was obtained according to magmatic layering in the\nStillwater Complex, which is only slightly better clustered than the 0% unfolded result of that test.\nThis test was merely a confirmation of the expected result, that initial Stillwater deformation\noccurred prior to emplacement of the Elbow Creek dikes at 2480 Ma.\nSection A2.5 – presumably taking into account the best clustered direction above will also strengthen\nthe results presented here?\nThanks for the comments and suggestions. If the Elbow Creek dikes were emplaced during the last\n20% of folding of the Stillwater Complex as the reviewer hypothesizes, then we would expect the\ndikes themselves to show variable orientations as a result of that final 20% deformation. The\nStillwater layering is typically very steep, so 20% tilting would be noticeable in the dikes – but that’s\nnot the case.\nSection A2.3 – I disagree that Figure S7 provides evidence that component A is not the result of\npervasive remagnetization. These are not passed baked contact tests – they are ambiguous at best, since\nin almost all cases the baked and unbaked directions overlap and are distinct from the dyke, when\nwe would expect the baked and dyke directions to be the same, and then unbaked directions to be\ndistinct. This requires further clarification, but certainly cannot be sold as a cut and dry ‘pass’. Thanks for the comments and suggestions. Based on only figure S10 (which is our new numbering of the earlier S7\nreferred to by the reviewer because of inserted additional figures), we indeed cannot be sure the\ncomponent A is primary. We have clarified in the text and figure caption that we don’t interpret these\nresults as positive tests, but merely are doing our diligence in reporting the results of\nour attempts. However, considering the difference between component A and the HTCs from the\nStillwater complex, which have similar unblocking temperatures, the results from these tests do\nsuggest there is no pervasive resetting of magnetite in the region. Three possible reasons lead to the\nobservation that the baked and unbaked samples hold similar HTCs in these inconclusive tests. First,\nthe anorthosites usually have very fine grained magnetite indicating by their unblocking temperature\naround 580°C. Second, the reheating (and possible hydrothermal activity) caused by dike J20S14\nduring its intrusion imparted a locally widespread MTC (Fig. S11). Third, the samples that we\ncollected for some baked samples (J20S09, J20S20) were a little far from the margin, thus they were\napparently not baked as high as 580°C. In any case, inconclusive baked-contact tests are common\nin paleomagnetic studies, and we take most of our confidence from the two tests illustrated in Fig.\nS7 (by our new numbering – the tests on dikes J20S25 and J20S28).\nFigure S15 – for the location of Superior/Wyoming at 2170 Ma, how sure are you about the polarity?\nThis seems like a big jump compared to if both were still in the southern hemisphere? I suspect this\nis well-constrained by previous studies, but please provide details/clarification for how you know\nboth are in the northern hemisphere at this time.\nThanks for the comments and suggestions. The 2510-2170 Ma apparent polar wander path (APWP)\nof Superior was established using ca. 2505 Ma Ptarmigan-Mistassini dikes, ca. 2466-2446 Ma\nMatachewan dikes, ca. 2217 Ma Nipissing sills and ca. 2218 Ma Senneterre dikes, and 2170 Ma\nBiscotasing dikes. Following the APWP trend, we therefore put them in the northern hemisphere at\ndemonstrate a more continuous sense of motion, but the equivalent-aged Clay Butte VGPs from\nWyoming aren’t compelling enough (yet) to highlight in this figure.\nREVIEWER COMMENTS\nReviewer #2 (Remarks to the Author):\nThe authors have provided a detailed rebuttal to the points raised by both reviewers. While they have\nnow included the statistical analyses I suggested, and clarified several of my queries, there are still\nseveral outstanding points that are still not clear and need further clarification. I have outlined\nthese below.\nThe point regarding dyke J20S28 and why the unbaked directions are only contained by very few\nsamples (raised by Reviewer #1) is still not really adequately addressed. The authors rebut that they in\nfact measured 6 samples, but these have dual polarities. This makes the interpretation rather complex,\nand it’s unclear why so few samples were measured. This needs to be discussed in more detail as I am\nstill unconvinced the baked contact tests are not unambiguous.\nFigure S8 – thank you for including a statistical analysis of whether your directions are the same or\ndifference. In each case, please clarify whether this is a ‘pass’ or ‘fail’ so it’s clear to a reader not familiar\nwith these statistics. However, this hasn’t really alleviated my concerns – what is the difference between\n‘host rocks’ and ‘samples close to the dyke’? In addition, it seems that almost all of the directions pass as\nbeing distinct, when for baked samples you would expect them to fail. There still doesn’t appear to be\nan explanation for why samples taken near the dyke do not show the same direction as the baked\nregion?\nI still don’t find the directions for the Stillwater Complex vs the Wyoming Craton stated clearly in the\ntext, and neither is it included in the rebuttal. Can you please include the directional values used\nto produce Figure R1?\nDiscussion of the ‘hybrid zone’ that is captured by the baked zone is not discussed in the main text. It\nneeds to be highlighted in more detail that these are not straightforward baked contact tests. As I\nsaid before, I still buy the results – but they are more ambiguous than the authors are trying to state.\nPlease don’t hide this in the supplementary!! I also disagree with the statement that this is a ‘classical\npositive baked-contact test’ since you don’t have any baked samples that directly overlap with the\ndyke. Those would be needed as well.\nThank you for clarifying the difference between Stillwater layering vs Laramide deformation – that\nsubstantially helps to clarify things, although you still only appear to show the fold test for the\nmagmatic layering rather than Laramide deformation, even though both are considered/discussed.\nCan you show results for both?\nAuthors’ response to the comments and suggestions from the editor and\nreviewers\nBlack: Comments, questions and suggestions from the editor and reviewers\nBlue: Responses and answers from authors\nReviewer #2 (Remarks to the Author):\nThe authors have provided a detailed rebuttal to the points raised by both reviewers. While they\nhave now included the statistical analyses I suggested, and clarified several of my queries, there are\nstill several outstanding points that are still not clear and need further clarification. I have outlined\nthese below.\nThanks for the comments and suggestions. We have carefully revised the manuscript according to\nall the comments and suggestions. And following are the responses to the reviewer’s comments and\nquestions one by one.\nThe point regarding dyke J20S28 and why the unbaked directions are only contained by very few\nsamples (raised by Reviewer #1) is still not really adequately addressed. The authors rebut that they\nin fact measured 6 samples, but these have dual polarities. This makes the interpretation rather\ncomplex, and it’s unclear why so few samples were measured. This needs to be discussed in more\ndetail as I am still unconvinced the baked contact tests are not unambiguous.\nThanks for the comments. The reviewer is here referring specifically to the 6 samples collected from\nthe distant host rock site J20S30, which is one of three sites constituting the overall baked contact\ntest of J20S28, S29, and S30. In total, the baked contact test comprises 32 collected samples, with\nacceptable results from 23 (including all 6 from the distant host rock site J20S30). We note that a\ncommunity standard “minimum of 3 samples per site” for (bare minimum) acceptable statistics was\nrecommended by Meert et al. (2020), and our 6 samples from site J20S30 well exceed that threshold.\nWhen we collected six samples from that site, of course we did not have the benefit of knowing that\nit would contain two polarities of remanence, but as we have added to our supplementary text, the\nresults are entirely explicable for a coarse-grained granitic rock:\n“In principle, the dual polarity of this unbaked granitic host rock could result from (1) remanence\nacquired during protracted cooling of the granite, (2) self-reversal in some specimens due to\ndifferent magnetic carriers, or (3) protracted secondary remagnetization. The data favor the first\noption. According to the orthogonal plots of stepwise thermal demagnetization results, all the\nsamples have similar unblocking temperature around 580℃, so the possibility is low that the dual\npolarities result from self-reversal of different magnetic carriers. Based on the demagnetization\nresults of the dikes, the samples from the baked granite, unbaked granite and the Stillwater complex\nall hold the HTC with unblocking temperature around 580℃,which suggests the HTCs could not\nresult from a single thermal event heating this region to 580 ℃ after the dike intruded. Based on\nthe Watson’s V statistic results, the HTC direction from the baked granite samples and the\ncomponent A of the dikes are similar (Figs. S8D), but both of them are markedly different from the\nHTC of the unbaked samples (Figs. S8E and G; note the difference in hemispheres for the southeast-\ndirected groups). As the unbaked host rock samples share similar petrologic and rock-magnetic\nattributes to the baked samples, with the latter only differing in their remanence direction parallel\nto the adjacent younger dike, this result is a positive baked contact test.”\nFigure S8 – thank you for including a statistical analysis of whether your directions are the same or\ndifference. In each case, please clarify whether this is a ‘pass’ or ‘fail’ so it’s clear to a reader not familiar\nwith these statistics. However, this hasn’t really alleviated my concerns – what is the difference between\n‘host rocks’ and ‘samples close to the dyke’? In addition, it seems that almost all of the directions\npass as being distinct, when for baked samples you would expect them to fail. There still doesn’t appear to be\nan explanation for why samples taken near the dyke do not show the same direction as the baked\nregion?\nThanks for the comments. We think that this concern is mainly due to lack of clarity of our earlier\npresentation. To address this, we added more information in both the supplementary text and Fig.\nS8 to clearly label “dike” versus “baked host rocks” versus “distant host rocks” in both figure panels\nand captions. We also specify explicitly whether the directions from the dike, the baked samples\nand the unbaked samples have a common mean or not. For dike J20S28 and baked site J20S29,\nthe Watson’s V value (0.6) for the directions from the dike and the baked samples is smaller than\nthe critical value (6.9), suggesting they have a common mean. In contrast, both the Watson’s V\nvalues (133.9, 119.3) for the directions from the dike versus the unbaked host samples, and the\nbaked samples versus the unbaked host samples, are much larger than the critical values (7.5, 6.8),\nimplying that the HTC from the unbaked host samples don’t have a common mean with either the\ndike or the baked samples (Fig. S8). Therefore, the baked contact test is definitively positive for\ndike J20S28. For dike J20S14’s HTC and the baked exocontact J20S13’s MTC, the calculated\nWatson’s V value (1.9) is smaller than the critical value (7.1), suggesting they have a common mean.\nThe calculated Watson’s V values (25.2, 29.4) are bigger than the critical values (10.4, 9.0) for the\nHTC directions from the HTCs of the unbaked host samples and the dike samples, the HTC and\nMTC of the site J20S13 (Fig. S8). For dike J20S25, the Watson’s V value (17.3) is larger than the\ncritical value (9.3) for the HTCs from the baked samples and the dike suggesting they are different.\nThe Watson’s V values (275.2, 33.7) are much larger than the critical values (6.7, 8.9) for the HTCs\nfrom the unbaked host rocks versus the dike and the baked samples. For dike J20S25, we did not\nget a similar mean direction from the baked samples with the dike, while the direction of the baked\nsamples changed gradually with the distance increasing from 0.2 m to around 1.0 m far from the\nmargin of the dike, and the unbaked host samples are distinctly different from the direction of the\ndike. This show it should be a positive but not perfect baked contact test.\nI still don’t find the directions for the Stillwater Complex vs the Wyoming Craton stated clearly in\nthe text, and neither is it included in the rebuttal. Can you please include the directional values used\nto produce Figure R1?\nThanks for the comments. The C2 direction from the Stillwater Complex in Selkin et al. (2008) were\nused for calculation. A new group of data was obtained by using the resampling method based on\nthe mean C2 direction (D = 171°, I = -63°, α = 2.9°, κ = 32, N = 74). The calculated Watson’s V\n95\nvalue (1172.2) is much, much larger than the critical value (6.5), strongly suggesting they do not\nhave a common mean and the two HTC’s are distinct. The resampling directions are listed in the\ntable R1, appended below.\nFigure R1. Watson’s V statistic for the Elbow Creek dikes component A and the HTCs from the\nStillwater Complex.\nDiscussion of the ‘hybrid zone’ that is captured by the baked zone is not discussed in the main text.\nIt needs to be highlighted in more detail that these are not straightforward baked contact tests. As I\nsaid before, I still buy the results – but they are more ambiguous than the authors are trying to state.\nPlease don’t hide this in the supplementary!! I also disagree with the statement that this is a ‘classical\npositive baked-contact test’ since you don’t have any baked samples that directly overlap with the\ndyke. Those would be needed as well.\nThanks for the comments. We added the “hybrid zone” part to the supplementary text. Yes, the\nbaked-contact test for the dike J20S25 is not perfect because the HTCs from the baked samples are\nnot exactly same with the directions of the dike according to the Watson’s V statistic results. We\nhave noted in the supplementary text that in this particular instance the baked rocks’ remanences are\ncloser to the overall dike swarm mean direction (Fig. S7E), and we hypothesized that the baked\nrocks are affected thermally or hydrothermally by more than one dike in this area. Existence of a\nhybrid zone supports the notion that the test is positive, but the reviewer is correct that in this case\nthe test is non-ideal. We have modified our text with additional caution in the case of test J20S25.\nWe maintain that the test on J20S28 is very strong in its fundamental distinction between baked\nversus unbaked samples (and identical overlap of baked rocks against the dike). Our main text\nnow also clarifies that the suite of attempted baked contact tests yield mixed results, but together\nthey argue strongly against the likelihood of component A being a younger overprint.\nThank you for clarifying the difference between Stillwater layering vs Laramide deformation – that\nsubstantially helps to clarify things, although you still only appear to show the fold test for the\nmagmatic layering rather than Laramide deformation, even though both are considered/discussed.\nCan you show results for both?\nThanks for the comments. Because the Stillwater layering could be measured in the neighborhood\nof almost every sampled dike site, we were able to perform a partial unfolding calculation (Fig.\nS13). In contrast, the Cambrian strata are only locally preserved atop the central outcrop region,\nand they are far from some dikes. Therefore, we averaged the Cambrian bedding directions and\ntreated the whole area as gently tilted to the NNE (Fig. S14) with a uniform regional correction. In\nthis case of uniform Laramide correction, a partial unfolding diagram such as what we illustrated in\nFig. S13 (for the Stillwater layering) would only show a flat line, thus not very illustrative. We\nadded a few words of clarification on this point in the supplementary text.\nTable R1. The resampling directions for the C2 from the Stillwater complex\nD (°) I (°) \n172.4 -57.4 \n191.9 -60.8 \n130.8 -66.2 \n154.8 -38.4 \n186.0 -57.9 \n153.8 -47.7 \n121.4 -58.6 \n119.9 -69.9 \n184.9 -42.0 \n143.0 -57.2 \n132.3 -74.0 \n154.0 -71.9 \n172.2 -44.7 \n145.8 -58.8 \n180.8 -59.9 \n179.7 -53.9 \n186.5 -55.6 \n172.6 -71.9 \n159.6 -72.3 \n168.2 -49.0 \n213.9 -81.4 \n221.8 -58.0 \n152.8 -63.3 \n149.5 -56.0 \n167.8 -71.5 \n191.9 -51.4 \n166.6 -67.6 \n178.5 -46.2 \n171.8 -64.7 \n181.0 -78.7 \n169.6 -45.5 \n153.9 -63.8 \n149.9 -58.9 \n182.4 -53.9 \n161.9 -74.0 \n205.2 -62.2 \n143.4 -60.2 \n185.7 -44.9 \n162.7 -65.6 \n205.3 -57.7 \n173.9 -53.7 \n173.7 -68.7 \n183.4 -55.2 \n127.3 -64.1 \n151.6 -53.2 \n172.0 -49.8 \n193.5 -55.6 \n218.2 -80.3 \n160.2 -63.9 \n196.2 -60.4 \n165.1 -52.0 \n179.9 -55.0 \n147.0 -58.8 \n169.5 -66.4 \n169.4 -71.2 \n180.6 -64.2 \n161.6 -61.8 \n144.5 -67.6 \n166.8 -70.5 \n182.4 -49.6 \n185.1 -65.2 \n162.7 -72.7 \n165.2 -47.6 \n157.1 -45.1 \n153.4 -78.8 \n181.2 -67.2 \n170.9 -57.1 \n160.4 -56.8 \n162.6 -54.2 \n176.4 -55.1 \n156.6 -65.4 \n155.0 -43.2 \n193.8 -55.1 \n149.7 -53.9"}]

Decision letter
REVIEWERS' COMMENTS
Reviewer #2 (Remarks to the Author):
The revised manuscript is substantially clearer, and now makes a compelling case for relative plate
motions while also acknowledging some non-ideality in the presented data. The figures in the
supplementary now make the main text much easier to interpret. I don't have any further comments,
and recommend publication. I would also like to apologise for the delayed review due to extensive
fieldwork and field teaching in the previous two months.