Hacker, B.R., Andersen, T.B. Johnston, S., Kylander-Clark, A.R.C., Peterman, E. Walsh, E.O., and

21 Pages·2009·2.93 MB·English

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TECTO-124697;NoofPages23
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ContentslistsavailableatScienceDirect
Tectonophysics
journal homepage: www.elsevier.com/locate/tecto
High-temperature deformation during continental-margin subduction &
exhumation: The ultrahigh-pressure Western Gneiss Region of Norway
Bradley R. Hackera, Torgeir B. Andersenb, Scott Johnstona,1, Andrew R.C. Kylander-Clarka,
Emily M. Petermana,2, Emily O. Walsha,3, David Younga,⁎,4
aDepartmentofEarthScience,UniversityofCalifornia,SantaBarbara,CA93106,USA
bUniversitetetiOslo,DepartmentofGeosciences,P.O.Box1047Blindern,0316Oslo,Norway
a r t i c l e i n f o a b s t r a c t
Articlehistory: Anewdatasetforthehigh-pressuretoultrahigh-pressureWesternGneissRegionallowsthedefinitionof
Received27January2009 distinctstructuralandpetrologicaldomains.MuchofthestudyareaisanE-dippinghomoclinewithE-plunging
Receivedinrevisedform30July2009 lineationsthatexposesprogressivelydeeper,morestronglydeformed,moreeclogite-richstructurallevels
Accepted10August2009
westward.AlthougheclogitescropoutacrosstheWGR,Scandiandeformationisweakandearlierstructures
Availableonlinexxxx
arewellpreservedinthesoutheasternhalfofthestudyarea.TheScandianreworkingincreaseswestward,
culminatinginstrongScandianfabricswithonlyisolatedpocketsofolderstructures;thedominantScandian
Keywords:
Norway deformation was coaxial E–W stretching. The sinistrally sheared Møre–Trøndelag Fault Complex and
Eclogite Nordfjord Mylonitic Shear Zone bound these rocks to the north and south. There was moderate top-E,
Exhumation amphibolite-faciesdeformationassociatedwithtranslationoftheallochthonsoverthebasementalongits
Ultrahigh-pressuremetamorphism eastern edge, and the Nordfjord–Sogn Detachment Zone underwent strong lower amphibolite-facies to
Symplectite greenschist-faciestop-Wshearing.A northwestward increaseinexhumation-relatedmelting isindicated
byleucosomeswithhornblende,plagioclase,andScandiansphene.Inthewestern2/3ofthestudy area,
exhumation-related, amphibolite-facies symplectite formation in quartzofeldspathic gneiss postdated
most Scandian deformation; further deformation was restricted to slip along biotite-rich foliation planes
andminorlocalfolding.ThattheWesternGneissRegionquartzofeldspathicgneissexhibitsastronggradientin
degreeofdeformation,impliesthatcontinentalcrustingeneralneednotundergopervasivedeformation
duringsubduction.
©2009ElsevierB.V.Allrightsreserved.
1.Introduction Assessing the scale of (U)HP metamorphism assists in defining the
tectonicsettinginwhich(U)HPtectonismoccursandthemagnitudeof
Howcontinentalcrustisexhumedfromultrahigh-pressuredepths its impact on Earth evolution. ii) How was deformation partitioned
remainsoneofthemostintriguingtectonicproblems.Anexcellentplace throughoutthe(U)HPterraneduringsubductionandexhumation—i.e.,
tostudyultrahigh-pressure(UHP)rocksandtheirexhumationisthe werethe(U)HProckssubductedandexhumedasacoherentandintact
Western Gneiss Region (WGR) of Norway, where the ~5000 km2 sheet or did they disaggregate/delaminate during subduction and/
CaledonianUHPterraneissurroundedtothenorth,eastandsouthby or exhumation? iii) How did deformation vary temporally, from the
associatedhigh-pressurerockscovering30,000km2(Fig.1).Thispaper beginning of subduction to the end of exhumation—e.g., did intense
integratesstructuralgeologyandstructuralpetrologyfromageologic deformation mark the entire subduction and exhumation cycle? iv)
transectacrosstheWGRtoaddressfourlarge-scalequestions:i)What Whatwastherelationshipbetweendeformationandmetamorphism
was the volume of rock that was exhumed from (U)HP conditions? duringsubduction and exhumation—e.g., did deformation and meta-
morphismoccurinstagesorweretheycontinuousandcoevalduring
exhumation?
⁎ Correspondingauthor.
To addressthesequestions,this paperpresents outcropto thin-
E-mailaddress:[email protected](B.R.Hacker).
1 NowattheDepartmentofPhysics,CaliforniaPolytechnicStateUniversity,SanLuis section observations of structures and metamorphic minerals. It
Obispo,CA,93407,USA. begins with an overview of the study area; explains how various
2 NowattheDepartmentofEarthandPlanetarySciences,UniversityofCalifornia, deformation and metamorphic events can be distinguished; char-
SantaCruz,CA95064,USA.
acterizestheeclogite-,granulite-,andamphibolite-faciesstructures;
3 NowattheDepartmentofGeology,CornellCollege,MountVernon,IA,52314,USA.
4 NowattheDepartmentofGeology,UniversityofTexas,SanAntonio,TX,78249, describesvariousstructuraldomains;andendswithadiscussionof
USA. theimplicationsforthequestionsposedabove.
0040-1951/$–seefrontmatter©2009ElsevierB.V.Allrightsreserved.
doi:10.1016/j.tecto.2009.08.012
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
ARTICLE IN PRESS
2 B.R.Hackeretal./Tectonophysicsxxx(2009)xxx–xxx
Fig.1.TheWesternGneissRegionconsistsofWesternGneisscomplexbasementoverlainbyallochthons(gray,afterLutroandTveten(1998)andTvetenetal.(1998)).Multiple
featuresshowageneralnorthwestwardincrease:i)theintensityofScandiandeformation(greenshading)(notdeterminedintheallochthonseastoftheWesternGneissRegionor
intheDevonianbasin);ii)eclogitepressures(locationsofisobarsarepoorlyconstrained);iii)peakmetamorphictemperatures(Kylander-Clarketal.,2008);iv)theabundanceof
hornblende-bearingleucosomes;andv)thepresenceofsymplectite-bearinggneiss.SphenehaveScandianagesinthenorthwestandPrecambrianagesinthesoutheast(Tucker
etal.,1990;Kylander-Clarketal.,2008).NEboundaryofNordøyaneUHPdomainafterVrijmoedetal.(2006).Allcontactsshownarefaults,excepttheNWedgeoftheDevonian
basin.(Forinterpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.)
1.1.TheWesternGneissRegion locallyimbricatedwithCaledoniannappeunits—assuggestedbythe
presence of a structurally lower gneiss–quartzite unit (Gee, 1980;
The Western Gneiss Region (Fig. 1) is composed of Proterozoic Krill,1980)inthenortheasternpartofthestudyarea(Storlithrustof
Fennoscandiangneisses(chieflyorthogneissesfromc.1650Maand Tucker et al., 2004) (Fig. 1)—but the main parts of the WGR is
950Ma)(cf.Austrheimetal.,2003;SkårandPedersen,2003),often autochthonous as shown by the continuous exposures below the
referred to as the Western Gneiss Complex (WGC), overlain by nappesacrossfromtheforelandtothehinterlandregion.
continentalandoceanicallochthons(seebelow).TheearlyPaleozoic ThemostcommonrocktypeoftheWGCinthestudyareaisbiotite±
orogenyduringwhichtheseunitsweredeformed,metamorphosed, hornblende ± garnet tonalitic and granodioritic gneiss with 5–80%
andjuxtaposedistheCaledonianOrogeny(Fig.2).Thefinalstageof (typically 20–40%) cm-scale granitic leucosomes (Gjelsvik, 1951;
this orogeny–called the Scandian Orogeny–included the following: Bryhni, 1966; Dransfield, 1994). This tonalitic gneiss grades with
i)closureoftheIapetusoceanandemplacementofallochthonsonto increasing K-feldspar abundance into biotite granitic gneiss that
Balticafrom~430to410Ma(Tuckeretal.,2004;HackerandGans, underlies ~10% of the study area, and with increasing muscovite
2005); ii) Baltica–Laurentia collision and westward subduction of intoatwo-micatonaliticgneissthatcomprises~5%.Alltheserocktypes
the Baltica basement and portions of the allochthons to ultrahigh- are cut by pegmatitic biotite-bearing granite dikes and all contain
pressure depths from ~425 to 400 Ma (Andersen et al., 1991; meter-tomillimeter-scaleblocksandlayersofmaficrock:biotitegneiss,
Andersen, 1998; Bingen et al., 2004; Root et al., 2004; Terry and amphiboliteand/oreclogite(Eskola,1921)(themineralogydependson
Robinson, 2004; Root et al., 2005; Kylander-Clark et al., 2007; bulk composition, block/layer size, and degree of retrogression).
Kylander-Clarketal.,2008);and iii)exhumation toshallowcrustal Subordinate rock types include quartzite, carbonate, anorthosite,
levels from ~400 to ~385 Ma (Andersen, 1998; Terry et al., 2000a; gabbro, garnet–mica gneiss, and peridotite (Gjelsvik, 1951; Bryhni,
Tucker et al., 2004; Hacker, 2007; Walsh et al., 2007). The WGC is 1966;Dransfield,1994;Robinson,1995).
Fig.2.WesternGneissRegionexperiencedasequenceofgranulite-faciesPrecambrian,earlyCaledonianamphibolite-facies,ScandianUHP,andScandianamphibolite-facies
metamorphic–deformationevents.
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
ARTICLE IN PRESS
B.R.Hackeretal./Tectonophysicsxxx(2009)xxx–xxx 3
TheWGCisstructurallyoverlainbydiscontinuousremnantsofthe Oneormoreepisodesofgreenschist-toamphibolite-faciesmeta-
Caledonian allochthons thrust southeastward over the autochthon morphism,peakingat~725°Cand1.2GPa,occurredduringthepre-
during the early part of the Scandian orogeny (Gee, 1975). These ScandianphasesoftheCaledonianOrogenybetween480and430Ma
allochthonsarebestexposedeastoftheWGRandincludequartzites, in the allochthons east of the WGR (Gee, 1975; Hacker and Gans,
muscovite-bearinggneisses,megacrysticaugengneisses,anorthositic– 2005);thiseventhasnotbeenrecognizedintheWGC.TheCaledonian
gabbroicgneisses,garnetamphibolites,andgarnet–micaschists(Fig.1). UHP metamorphism (Smith, 1984) that makes the WGR such an
TheseallochthonscanbetracedwestwardacrosstheWGRalongthe exciting scientific subject reached peak metamorphic conditions of
northern part of Fig. 1 (Surnadalsøra to Løvsøya, Robinson, 1995); 800°Cand3.6GPa(LappinandSmith,1978;seesummaryinHacker,
similarrockscropoutdiscontinuouslyacrosstheWGRfarthersouthin 2006) between 420 and 400 Ma (see summary in Kylander-Clark
theareaofFig.1(WalshandHacker,2004;Rootetal.,2005;Johnston et al., 2007). Mafic bulk compositions suitable for forming eclogite
etal.,2007b). make up ~2% of the WGR; northwest of the ‘eclogite-in’ isograd
(Fig. 1), perhaps 70–90%(?) of such mafic rocks did transform to
1.1.1.MetamorphicoverviewoftheWesternGneissRegion eclogite,withtherestremainingunreacted(StraumeandAustrheim,
TheWGRisapolymetamorphicterraneinwhichthesequenceof 1999;Krabbendametal.,2000;WalshandHacker,2004).ABarrovian
metamorphic events is relatively well understood (Bryhni and to Buchan amphibolite-facies overprint–with local partial melting–
Andréasson, 1985) (Figs. 2 and 3) due to incomplete overprinting occurredat650–800°Cduringpost-UHPdecompressionfrom>1.5GPa
reactions. An amphibolite- to granulite-facies metamorphism at to~0.5GPa,almostcompletelyobliteratingtherecordof(U)HPmeta-
c. 950 Ma was associated with extensive plutonism and reached morphism(Krogh,1980;Chauvetetal.,1992;Dransfield,1994;Straume
peakconditionsof~800–900°Cand1.0GPa(e.g.,Cohenetal.,1988; andAustrheim,1999;Hackeretal.,2003b;TerryandRobinson,2003;
Tuckeretal.,1990;Krabbendametal.,2000;Kühnetal.,2000;Bingen Labrousseetal.,2004;WalshandHacker,2004;Rootetal.,2005;Engvik
et al., 2001; Wain et al., 2001; Corfu and Andersen, 2002; Skår etal.,2007).Importantly,thismetamorphichistorydocumentsthatthe
and Pedersen, 2003; Røhr et al., 2004; Root et al., 2005; Glodny UHProckswereexhumednearlyisothermallytodepthsof15–20km.
et al., 2008). Decameter- to kilometer-scale relicts of this event U–Pbspheneagesshow thatmeltingassociatedwiththis metamor-
(Krabbendam et al., 2000) comprise ~1% of the WGC, but are more phism occurred around 398 Ma in the center of the study area and
commonincontinentalallochthonsthatwerethrustovertheBaltica around 389 Ma along the northwestern edge (Tucker et al., 2004;
basementatanearlystageofthecollision(Jolivetetal.,2005).Thelocal Kylander-Clark et al., 2008). Muscovite 40Ar/39Ar ages show cooling
survival of these granulite-facies assemblages through subsequent through~400°CalongtheeasternedgeoftheWGRat400Maandalong
overprintingepisodesisattributedtolowHOactivity,coarsegrainsize, thenorthwesternedgeby385Ma;thecoresoftheUHPdomainshave
2
andlackofdeformation(Austrheim,1987;Krabbendametal.,2000). younger muscovite ages down to 375 Ma (see summary in Hacker,
2007).Notably,thedifferenceinspheneandmuscoviteagesis4–5Myr,
implying300–400°Ccoolingatarateof>50°C/Myr.
1.1.2.StructuraloverviewoftheWGR
The WGR has a complex deformation history to match the
metamorphic record. The Precambrian (c. 950 Ma) amphibolite- to
granulite-facies rocks and associated plutons vary from undeformed
to strongly deformed (Austrheim and Griffin, 1985). In general,
Precambrianfabricsarebestpreservedinthesoutheasternpartofthe
study area (Fig. 1; see below), but there are enclaves of preserved
Precambrian structures and igneous protoliths throughout the study
area—even in the far west where Scandian deformation was most
intense(Krabbendametal.,2000).Scandianeclogite-faciesstructures
arepreservedinscatteredbodiesofeclogiteacrosstheWGRinthestudy
areaandfarthersouth(Andersenetal.,1994;KrabbendamandWain,
1997;LundandAustrheim,2003;TerryandRobinson,2004;Foremanet
al.,2005;Engviketal.,2007).Earlybrittleeclogite-faciesstructuressuch
as eclogite-facies pseudotachylites are preserved locally (Lund
andAustrheim,2003;Johnetal.,2009),buttheeclogitetectonitesare
dominated by foliations, lineations and folds formed during ductile
deformation. Scandian amphibolite-facies structures are, however,
predominant throughout the WGR (Fig. 4). They consist mostly of
gentlyplungingENE–WSWtoESE–WNWlineations,isoclinallineation-
parallelfolds,andgenerallysymmetricalfabricsimplyingcoaxialstrain
histories with a constrictional component (Andersen et al., 1994;
Dransfield, 1994; Krabbendam and Wain, 1997; Krabbendam and
Dewey,1998;Labrousseetal.,2002; Hackeretal.,2003a;Terry and
Robinson, 2003; Engvik et al., 2007; Barth et al., 2010). Along the
westernedgeoftheWGR,thesefabricsareoverprintedbyormergeinto
the Nordfjord–Sogn Detachment Zone (NSDZ), an amphibolite- to
Fig.3.Ultrahigh-pressuremetamorphismintheWesternGneissRegionwaslikely
greenschist-facies,W-dipping,top-Wshearzonethatformedtoward
precededbytheBarrovian~1GPametamorphismseenintheallochthons(Hackerand
Gans,2005),andwasfollowedbyBarrovianmetamorphismbeginningat~1.2GPaand theendoftheScandianorogeny(Norton,1987;AndersenandJamtveit,
then by Buchan metamorphism at ~0.5 GPa (ellipses show PT conditions for 1990;seesummaryinJohnstonetal.,2007a).
metamorphismsummarizedinHacker,2007);the950Magranulite-faciesmetamor-
phism is not shown. Breakdown of K-white mica + garnet + Na-plagioclase to
1.1.3.Decipheringthepolyphasehistory
plagioclase+biotitesymplectitewaswidespreadinthewesternWGRduringthepost-
These multiple metamorphic and deformational events make it
UHP Barrovian metamorphism (Peterman et al., in press). The PT path shown is
schematicandpertainsmostcloselytotheUHPdomains. difficulttoascertainthehistoryofanygivenkilometer-tomillimeter-
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
4
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physics(2009),doi:10.1016/j.tectoredeformationduringcontinenta Tectonophysicsxxx(2009)xxxxxx– EINPRESS
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xh Fig.4.Theamphibolite-faciesstructuresoftheWesternGneissRegiondefinedistinctdomains.Equal-area,lowerhemispherestereonetsoffoliation(left),lineation,foldaxis,and‘tension’gash(right).Numberofdataofeachtypeindicatedby
um “n=…,…,…,…”Best-fitlineation,“L=”,calculatedbyField2k(Mainprice,2005).Alldataarefromthisstudy.
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B.R.Hackeretal./Tectonophysicsxxx(2009)xxx–xxx 5
scalestructure,butsuchdeterminationsarenecessarytounravelthe partofthestudyarea(“UHPdomains”inFig.1).TheUHPeclogites
questions posed in the introduction. There are numerous ways to recordpressuresof3.6–2.7GPa(LappinandSmith,1978);pressures
assess the sequence of events and to place structures at individual generallydiminishsoutheastwardfromthesedomains(Fig.5),until,
outcropsinaregionalcontext.1)Outcrop-scaleoverprintingrelation- atmetamorphicpressuresof~1.8–2.0GPa,theeclogitesgivewayto
shipsarethemostdirectmeansofestablishingtherelativetimingof amphibolite-faciesparagenesesalongthedashedlineinFig.1(Krogh,
events.ThemosttypicaloverprintingrelationshipintheWGRisthat 1977;WalshandHacker,2004;Youngetal.,2007).Themainrocks
amphibolite-faciesstructures–suchasboudinnecks,strainshadows, in the WGR are quartzofeldspathic gneisses that in general do not
recrystallized tails, and hydrated, deformed zones–fringe eclogite contain eclogite-facies minerals. Such rocks are not expected to
blocks (Terry and Robinson, 2003; Engvik et al., 2007). Also well preserveeclogite-facies minerals(Heinrich,1982), but whetherthe
knownareeclogite-faciesoverprintsongranulite-faciesassemblages bulk of the WGR transformed to eclogite-facies minerals (and then
(Austrheim,1987;Jolivetetal.,2005).2)Geochronologycanprovide backreacted to low-pressure phases) or not has been difficult to
absolute ages. Some eclogite-facies minerals have been dated as assess.High-pressuremineralsinWGRquartzofeldspathicrocksare
Scandian (Kylander-Clark et al., 2007; Kylander-Clark et al., 2009), rareandtypicallyconfinedtothemarginsofeclogiteblocks(Engvik
and structures in a rock cut by undeformed in situ melt with, for andAndersen,2000;Wainetal.,2000).
example, 395 Ma igneous sphene, must be older than 395 Ma Byfarthemostcommonmetamorphicfaciesinthestudyareais
(Kylander-Clark et al., 2008). 3) Structures in igneous bodies with amphibolite-facies (Bryhni, 1966;Mysen and Heier, 1971; Labrousse
Scandian crystallization ages are clearly Scandian or younger (e.g., etal.,2002;TerryandRobinson,2003;Tuckeretal.,2004;Walshand
Hackeretal.,2003a;LundmarkandCorfu,2008). Hacker,2004;Rootetal.,2005).Themainquartzofeldspathicgneissesin
thestudyareacontainquartz+plagioclase+biotite±hornblende±
2.Metamorphismofthestudyarea garnet ± K-feldspar. Pelites, whichcomprisea minor fraction of the
WGR,havequartz+plagioclase+muscovite+biotite+garnet±
AlloftheWGRhasundergoneregionalmetamorphism,however, kyanite and/or sillimanite; mafic rocks contain plagioclase + horn-
relictigneousandmetamorphicmineralshavebeenpreservedover blende±garnet±sphene.Thesemineralassemblagesformedchiefly
largeareasbecauseofcoarsegrainsize,lackoffluids,and/orlackof attemperaturesof600–800°Candpressuresof1.5–0.5GPa—conditions
deformation(Gjelsvik,1951;Mørk,1985;Krabbendametal.,2000). characteristic of Barrovian and then Buchan metamorphism (Fig. 3).
Granulite-faciesrocksarefoundthroughoutthestudyareabut,except A general northwestward increase in metamorphic temperature is
intheNordfjordarea(Bryhni,1966;Krabbendametal.,2000;Wain indicatedbycalculatedtemperatures,U–Pbspheneages,thedistribu-
et al., 2001), are too few to warrant discussion in this paper. The tionofsillimanite,andtexturalevidenceofinsitupartialmelting(Fig.1)
eclogite-faciesmetamorphism(Krogh,1977;LappinandSmith,1978) (Labrousseetal.,2002;TerryandRobinson,2003;Tuckeretal.,2004;
(Fig.3)ismosteasilyrecognizedinthesmallfractionofmaficrocks WalshandHacker,2004;Rootetal.,2005).
scatteredthroughouttheWGR,butisalsolocallypreservedinmore- Much of the quartzofeldspathic gneiss in the western half of the
felsiclithologies(EngvikandAndersen,2000;Wainetal.,2000).The study area (‘symplectite in’ line in Fig. 1) contains fine-grained
domainsoftheWGRthatcontainUHPeclogitesarein thewestern amphibolite-facies symplectite of biotite + plagioclase (Fig. 6a)
Fig.5.Three-dimensionalrenderingofeclogitepressures.BasedondataofMedaris(1984),Wain(1997),Cuthbertetal.(2000),Terryetal.(2000b),CarswellandCuthbert(2003),
Hackeretal.(2003a),Labrousseetal.(2004),andRavnaandTerry(2004).
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
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6 B.R.Hackeretal./Tectonophysicsxxx(2009)xxx–xxx
Fig.6.Outcrop-scalestructures;locationgiveninupperleftandmarkedinFig.8.a)Earlydeformationfabricpseudomorphedbysymplectite;nosubsequentdeformation.b)Garnet
andplagioclasestableduringearlyamphibolite-faciesdeformation.c)Minorfoldswithaxialplanarbiotitecleavage.d)Amphibolite-faciesshearbands(lookingtoward184°).
e)Biotite+chloritestableshearbands(lookingtoward003°).f)Amphibolite-faciesasymmetricboudin(lookingtoward050°).g)DeltaclastwithinmegacrysticK-feldsparaugen
gneiss(lookingtoward245°).h)WeaklydeformedPrecambrianmetamorphicfabricscutbyPrecambrianintrusions.i)Undeformedgraniticsegregationsformedfrominsitu
meltingspatiallyassociatedwithstatichornblendegrowth.j)Stronglydeformedgraniticsegregations.k)MyloniticrocksinStadlandetUHPdomain.l)High-strainfoldsinSørøyane
UHPdomain.m)myloniticrocksinSørøyaneUHPdomain.n)AsymmetricboudinsandmyloniticgneissinNordfjord–SognDetachmentZone(lookingtoward005°).o)Mylonitic
K-feldsparaugengneissinVågsøydomain.p)MyloniticfoliationinÅmotsdalendomain.
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
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B.R.Hackeretal./Tectonophysicsxxx(2009)xxx–xxx 7
Fig.6(continued).
(Dransfield,1994),whereasthegneisssoutheastofthe‘symplectitein’ nowherecontainsymplectite.Texturesinafewoutcropsandinmany
lineinFig.1hascoarsegranoblastictexturesandnosymplectite(Fig.1). thin sections reveal that the symplectite minerals formed from the
Rocks such as quartzite, biotite schist, and K-feldspar augen gneiss decomposition of high-pressure amphibolite-facies K-white mica +
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
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physics(2009),doi:10.1016/j.tectoredeformationduringcontinenta Tectonophysicsxxx(2009)xxxxxx– EINPRESS
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h Fig.7.Eclogite-faciesstructuresarerelativelysteepwithinNordøyaneandNordfjord,butmoregentlyinclinedelsewhere.BoxesshowtheNordfjordandNordøyaneareasstudiedbyDransfield(1994),KrabbendamandWain(1997)andTerry
u
m andRobinson(2004).(Onlyeclogitestructuresareshown,noteclogite-faciescountryrockstructures.)
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Fig.8.Amphibolite-faciesfoliationsinthestudyareaarefoldedaboutlineation-parallelE–Wfolds.SomedatafromDransfield(1994),KrabbendamandWain(1997),LutroandTveten(1998),Tvetenetal.(1998),andTerryandRobinson(2003).FilledcirclescorrespondtolocationsinFig.8.
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012
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Fig.9.Amphibolite-faciesfoldaxesparallelthedominantamphibolite-faciesE–Wstretchinglineation.SomedatafromRobinson(1995),KrabbendamandWain(1997)andTerryandRobinson(2003).Stereonetsshowfoliations(left)andlineations,foldaxesandpolesto‘tension’gashes(right).Numberofdataofeachtypeindicatedby“n=”.
Please cite this article as: Hacker, B.R., et al., High-temperature deformation during continental-margin subduction & exhumation: The
ultrahigh-pressureWesternGneissRegionofNorway,Tectonophysics(2009),doi:10.1016/j.tecto.2009.08.012