Metasedimentary rocks, associated intrusions and tec- tonic features of the Precambrian in eastern Bamble, South Norway: an interpretative study

PETER PADGET ^{NGU-BU L L442 , 20 0 4 -PAGE} 39

Metasedimentary rocks, associated intrusions and tec- tonic features of the Precambrian in eastern Bamble, South Norway: an interpretative study

PETERPADGET

Padget,P. 2004:Metasedim entaryrocks, associated int rusions and tectonic feat ures of thePrecambrianineaste rn Bamb le, Sout h Nor way:an interpretative st udy.Norgesgeologiskeundersekelse Bulletin442,39-51.

Based on the resultsofmappingprogammesand map com pilat ionworkcarriedout bythe authorinrecentyears,a subdivisionof thebed rock geology ofthe easte rnmostpartof theBam ble Sectorintotw odom ainsisproposed - theKrageroandPorterdomains,separatedby a majorfaultzone.Thesedomains showcont rast ingsedimentary and magmatichistories,part icularly in their earlier phases.InthePorter domain,a large,elongatebody of dioritetogra- nodiori teis ident ifie dbutnotyetdate d isotopi caliy. lthasno equiva lentintheKragero domain where the levang GraniteGneissDom e(l GGD)isadominating feature.Thelatteris assessed intermsofsynpluto nismanditsrelati- onship to adja centmetasedim ent aryrocks and their fold patt erns.Thesig nificanceof existingisot opicagedatain relati ontofielddata isalsoconsidere d.Theexistence ofanearlydevelopedtroughorhalf-grabeninto which clastic sedi ments of theKragero domainweredepo sited is envisaged.

PeterPadget,Norgesgeologiskeundersekelse,7491Trondheim,Norway.

PresentAddress:Jonsvannsveien36,705 1Trondheim,Norway.

E-mail:[email protected]

Introduction

The area of study extend sfrom Riser northeastwards in the direction of Krageroand beyond as far as the border with theOsloRift(Figs.1Aand1B).Therocks wit hin thisrhomb- shaped areaform part of the Bamb le Sector and are of Precambrian age, except for a few, non-metamorphosed dolerite dykesbelieved to be of Permian age,and have clearly a longand complex evolutionary history.

Geological field data, publishedand unpublished,have recentlybeenassembl edby the author in map compilations at scales of 1:250,000 (Arendal bedrock map)and 1:50,000 (Tvedest rand 1612.1,Riser 1712.3,Gjerstad 1612.1,Kragero 1712.4 and Langesund 1712.1).The relati on of the1:50,000 sheets to the areaofst udyis show n in Fig.1B.

The purpose of the present paper is to identify and describe variou s metasedim entary sequences and focus attentiononsomeof the st ruct ural,metamorphic and intru- siveeventswhich have affected them.Someof themajor intrusion spresent in thearea areshow n inFig.2.Theconclu- sionsreached areprimarilybasedon fieldobservat ion sbut alsoincor porate the resultsof thefew isotopicage st udies so farcarried out on the rocksof thearea.It isclear,however, that furtherisotopicage st udiesare necessaryto determine not only thedepositional age and if possiblethe source of the sediments,but also subsequent tectonic and metamor- phic events.Hopefully,thispaper will serveto focus atten- tiononrelat ionshipsandevents in needof further geologi- caland geochron ologi cal st udy.

For purposes of description itisconvenienttodivide the area into two part s,known hereafter as the Kragero and Porter domains(Fig.3).These differ in both theirsedimen-

tary record and thetype of intrusions which have affected them.The two domainsare separated byamajor faultcom- plex,referredto hereafter asthe Haslumki len-Langholm en FaultZone(HLFZ), nowpart iallyintrud edby maficrocks.

Regarding mafic rocks, the term diabaseisused in thi s articlefor those having an intrusiveorigin (dykes andsills) and which have undergone thermal metamorphismor tec- tonic deformation,or both.The term dolerite isreservedfor mafic dykesor sills,themineralog yand textureofwhichare little affected by laterthermal and tectonic event s.

The Krager0 domain

The metasedimentaryrocks:general features Theexistence of rocks of undoubted sedi mentary origin in the BambleSector haslong been recognized (Breqqer 1934, Bugge 1965, Morton 1970, 1971,Starmer 1976,1978).They are invariably intruded by magm aticrocksandaffected by tectonicmovement s ref lect ing post-depo sitional events in the evolution of theSector.Theynormally represent thefirst recognizable event(e.g.,Starmer1991,P 119)thoughlittle is said, or known,about thebasementonwhich they accumu- lated.

In thepresent area of study,metasedimentaryrocksare well represented(Fig.4), particularly in theKragerodom ain.

They are normally recrystallizedwit h the development of met amorphic minerals and textures(Fig.5)but therecan be no doubt as to their sedimenta ry origin.The common est types present are quartzites, micaceous quartzites and pelitic (argillaceous) gneisses. Here, as elsewhere in the Bamble Sector, carbonate rocksare hardly present atall.So

NGU-BUL L442,2004 - PAGE40 PETER PADGET

Fig1.Maps showinglocationof the areaofstudy insouthernNorway;

(A) its locationin the Bamble Sector.B- Bamble Sector, PKF- Porsgrunn-KristiansandFault Zone; (B) relationto the1:50,000bedrock map-sheets.

far,no attempt hasbeen made to estab lish astratigra phic successionforthedomain,thus openingthe wayfor paleo- geographic,provenance and other st udies. Onereason for thisis a lack ofreliable struct ural data,anot her thepaucityof dataconcerningprimary depositionalfeat ures.

One exception to this is on Aroy (Fig.2) and on the

nearby Jesperislands in the easternmost part of Kraqeros skjeerqard, Here, quartziticoutcrops show abundant signsof cross-bedding (Morton 1971).Thoughsomewhatdefo rmed the'wayup'ofthe beds,bot h hereandin the near vicini ty (present author' s observations), can be determined. Collect ively, these observat ions indicate overfo lding and somethrustin g of thebedstotheSSE.There is anabruptline of contact betw een the metasedi men tary rocks here and diversegneissic rocks possiblybelonging to an older base- ment (See alsothe secti onon the Skatoy triang le,p.00)At Rosholmen (Fig. 4), the line of contact is also partially marked by a remarkable conglomerate.This is markedly polymict ic andwas described by Morton(1971,plate2)as a metapyroclastic breccia.It may form part,possiblythe low- erm ost part, of the local stratigraphic succession . After unravellingthe local fold st ructure Morton concluded that the quartziti c sedime ntaryrockson Aroyweredeposit ed by currentsflowingfromthenorthwest.

Perhapsthe greatest thicknesses ofquartzitic rocks are to be fou nd sout hwestofKragero.Here,severalthickunits makeupthe NW flank of a major antiformalstructure (the MorjeheiaDome)andhave been commercially exploited for manyyears atLitangenand Snekkevik(Fig.2).A sim ilar large quarrying operatio nwas located in athickquartziteuniton Beerey(Figs. 2 and4),1.5km eastof Kragero. In both areas, recrystallization is extreme and no sedimentarystructures haveyet beenreport ed.

Alarge areaoccupiedby metasedimentaryrocks includ- ingquartzites,micaceousquartzites and mica schist soccurs in thewestern partofthe study area,more specificallyon and aroundthemountain Heiberg (Figs. 2 and 4).Field data andmap compilations byStarmer(1976, 1978)givea fairly good pictur e of the geology and have been used in the compilat ion of the 1:50,000 map-sheet Gjerstad 1612.1 (Padget1993c).There are,unfortunately,fewdatawhich can beusedto establi shan order of succession,possibly due to the present highly metamorphosed nature of the rocks.

Field relations involving certain conglomeratic and quartziticrocks1.5km sout heastofthe summit of Heiberg (Starmer 1978,pp. 52-53) can be inte rpreted to indicate youngingofthebedstothe nort heast.This,inconju nction wit hast udyof the regionalfolding inthe area,meansthat the local stratigraphical sequence is one where the main quartzit eoverlies a sequence of sillimanite-bearing parag- neisses.Nobasement can be identifiedto thelatter but the quartzit esseemtobe equivalent to those of the Morjehe ia Dome(Fig.4)mentionedabove.

Metasedi mentary rocks encircle most of the Levang peninsula(Fig.4)andseemto dipoutwardstowardsthe sur- rounding sea areas.An important lithologicalunit exposed on the sout hside of thepenin sula is a well banded,some- what micaceou s quartzite with a minimum thickness of about 15metres. Itisheretermedthe RapenQuartzit e(Fig.

6) and at one place displays cross-bedding indicating youngerbeds southwards tow ardsStolefjorden(Fig.2).It is probablyoverlainhere by sillimanite-bearingmetasedimen- tary rockswhichoccupy a major synform (Fig.4) offshore.

59°

N

o_t

/

V

171 2.1 LANGESUND

1712.3 RIS0R KRAGER0

~ ~ ,? AREA

~ ^{: / OF STUDY}

~

9°

~-=",RI SOR

1712.3 e{l,

-r

TVEDESTRAND

J

A

B

PETER PADGET ^{NGU-BULL 442,20 0 4 -PAGE 41}

. ^,

t::::3

c=J

~ Levang granitegneissdome(L G GD).Morjeheia

E3

5845'

c==J

H LFZ Haslumkilen-Langholmen FaultZone

ST Skatoy triangle

s-ao

Fig2.Map of the area of studyshowingth emain int rusion s and place nam esreferred to inthe text.

Fig 3. Lo cation of the Kragera and Porter doma in s and the faul t zon e (HLFl j sepa rat ing them.

NGU- BULL 442 ,200 4 - PAGE 42

-.r •

, r"

"~h' ^{10km <:b}

========'" . '--..<>-- r,

Fig 4.Distribut ion ofthe main metasedime ntary rock format ions in the Kragero and Porte r domains. The major mafic int rusions are omitted.

The quartzite hereis steeplydip ping and terminates a short distance from the coastline, against a thick, variegat ed amphibolite whi ch has partly intr uded it. No further metasedimentary rockshavebeendetectedon the oppo-

PETERPADGET

/ /

/ 1

- - -LevangGrarute Gnerss Dome (LGGDj D,onte - oranocorne(0 -gl

I

domain ••••••• Rapen Quartzite

Anthophyll coness [volcanoctasc?j leuco M,gmatrte

Porter {c==JParaqnetss.teisrcgneiss.gr.eygnel~s domain c==JMelanocratJc mlgmatrte,bo c gneiss

_ _~_Pillow lava(?)asxenontnsIn granodlonte

---- Fauh - -' - Thrust

HlFZ .Haslum len.langholmen Fau Zone

">t Ma/or QuarryInQUartz e

site, i.e.northern side of the amphibolite.The quartzite, whichis conglomeratic in a few places,can be tracedon Hofseths map(1942) along the whole lengt h of the north coast ofthe Levang peninsula as far as Hansjo(Fig.4).Onthe

Fig S. Pelitic gneiss showing quartz-sillimanite nodules arranged ina fold wit h asubhorizontal/- gentlydippingfold axis.The long axes of the nodu- les tendto be parallelwiththe fold axis.Location:

700 metres nort h of Stavseng fyr, Skatoy(Kragero domain).Lensgives scale.

PETER PADGET

Fig 6. The Rapen Quartzite. Steeply dippi ng, well banded layersof quart z(light)and biotitic gneiss(dark).CoastalexposureontheLevang peninsula,900 met resnort heastofBekkevika (Kragerodom ain).

NGU-BULL 442,20 0 4 - PAGE43

south coast, however, 350 metres west-so ut hwest of Bekkevika (Fig.2),a dark,micaceous gneissunit inter venes betweenthequart zite andthe amphiboliteand is probably stratigraphicallylower than the former.

Clearly,additional observations of primary sediment a- tion featuressuchas cross-bedding are needed to confirm (or refute) the conclusions reached so far regarding the order of strati gra phic succession,both here and elsewhere in thearea of study.

Meanw hile,one may conclude from the map compila- tions(Fig.4,this article),(Padget1993a,2000a, 2001)thatthe greatest thicknesses of quartzi te are locate d towardsthe north west and exte nd along st rike northeas twards from Songe vat netasfar asValle and the boundarywit h Cam bro- Siluriansediment ary rocks of theOslo Rift(Fig.4), adistance of nearly 50 km.They termin ate to the north west rath er abrupt lyagainsta seriesoffaults(t heValleFault ,for exam- ple). Sout heastwards they are less pro mi nent and are tho ug htto thi n outorare replaced by more pelitic,silliman- ite-bearinggneisses(facieschange).From thisit isthoug ht that deposition tookplace inanelongate troug htrending NE-SWand possib ly fault-boundedonit s northwe stmargin

Fig 7.Cross-section(schemat ic)overtheLevangGranite GneissDom e andassociated rocksof the Kragero and Porterdomain s showi ngsome ofthemainst ructural features.Notethefoldi ngofthe foliationplanes in thegranitegneissandsteeply inclin edmarginalfaults.Thelatter may be anindicat ion of some upward,diapiricriseof the granite gneiss body.

Porter

I-NNW- - - Kragem domain- - - -+->+--(domain- - SSE-

Porter domain Kraqere

domain

1 ~

^{·+ ·· ·· ··}

. . .

m

{ ~

Granite-graniticgneiss Quartzite

RapenQuartzite Pelitic Gneiss Migmatite

Paragneiss

Metad iorite- granod iorite Metadiorite

LG GD LevangGraniteGneissDome Faultwithsenseof movement

HLFZ Haslumkilen-Langholmen - - - FaultZone

--- Foliation

I

I

NGU-BULL442,2004 - PAGE 44 PETERPADGET

CD

•. . . . .. I

e

!~~ ~

'0'0-

f

Input:'\.I I

(Fig.7).The presentfaulted margin of the metasedime nta ry unitis younger in age but thisis probablyarejuvenative effect.

The lack of continuit y between the main outc rop sof metasedimentaryrock demonstratesthe magnitudeof sub- sequent events, particularly the emplacement of large igneousbodies.

Fig 8.Schematic drawingstodemonst ratethe early evolutionofthe LevangGranit eGneiss Dome.1)depositionalphase,2)intrusion of mafic magma,3)maingraniteint rusion.The configurationof thegra- nite at depth is uncertain,4)a more pear-shaped form,narrowing downwards,is alsopossible.

Fig.8.Thischannelcouldbe fault -defined. inviting compari- sonwit h the Main DonegalGranit e,Ireland (Hutton 1982), for which an elaborate model was developed relati ng emplacement to fault tectonics.However,the configuration ofthe graniticgneiss of the LGGD at dept h is thought to be pear-shaped to accord better with the steeply dipping natureof thecon tact s observable in surface outcrops.

!...1Peli ic Gneiss ... uartzue

c=J Granite

c=J Mafic rocks.

diabase - .- Fault(f)

It Conduu or

f

Mal ic magma

f

- ! -:.?pemng

f

- _ -

\~ " ~; ~ r~

'0

a.

®

®

Intrusions

TheLevangGraniteGneiss Dome

The general features of the Levang Granite GneissDome (LGGD) were first outlinedby Hofseth(1942)whowent on to conclude that the granitic gneissrepresented a syn kine- matic intrusion in an antiformal struc ture .The concordant and sharply defined contact between the granitic gneiss and the enclosing rocks, recrystallization of the mineral compone nts and widespread development of foliation seemed to support this view.Burrell(1964) andElder(1964) carried out moredetailed studiesof the Dome,the latter concentr ating parti cularly on the chemical composition and structure of the granit icgneiss.He made good use of aerial photo coverage to iden tify apparent fold structu res and went on to confirm their existe nce by detailed field studies involving measurement of foli ation surfaces,fold axesand lineati ons. He concluded that the granitic rocks were formed"synkinematicallythroug hthetransformat io n of a pre-existingseriesof supr a-crustaIrocksby processesof metasomaticqranitizat ion'Th isconclusio n was almost cer- tainlyinfluenced bycurrentthink ingat the tim eofwriti ng."

Thepresent aut horhas carriedout reconnaissance stud- iesof the area andcan confirm the existenceoffolded folia- tion planes,but there is no sign of supracrustal rocks of undoubted sedimentary origin wit hin the area of granitic gneiss.Ot herw ise, the gneiss is recrystallized to various degrees, a feature marked byincreased grain size and dif- fuse grain boundaries.This makesany primary magmatic features difficult to discern. However,xenolithsoccur at two places,one being a metre-long block of metad ior ite at 0degaard,a now derelict farm 800 metres northwest of Rapen,the other a blockof granite,now somewh atgneissic, in granitic gneiss atRapenitself.Veinsof microgranite,par- tially invaded bythe surroundinggranite,are also presentat Rapen.Leucocraticveining is common towardsthe south- ern margin of the granitic gneiss and is also foliated . However,Elder(1964) recordsthe existenceof apatch of quartz-rich granite gneissnearSolli(Fig. 2)and, close by,a sizeable body of amphibo lit ic greenston e. The latt eris still inadequately mapped but isveined bygranite and clearly incorporated in the granitegneissandmust pre-datethelat- ter.Theseobservations indicate to thepresent authorthat the graniticgneiss ofthe LGGDwas origina llyanintr usion.

The present elongate,ellipsoidal shape of the granitic gneiss may reflect the former existe nce of an ENE-W5W- trendi ng 'crack' or mega-fract ure in basement rocks up whichgranite magma could ascend.Apossible config ura- tionof the granitic bod y atdepth,withanassociatedaccess channelthroughbasement rocks,is shown schematically in

PETER PAOGET

A calibrat io n of this intrusive event and later distu r- bances is clearly desirable.A U-Pbzircon date of 1587±6 Ma was obtainedby Raheim (unpub lished datain Lam b et al. 1986)forthe granite(now ort hogneiss)and is considere d tobe aminimum age for itsem p lacement. Earli er st udies by O'Nion set al.(1971)gave aRb-Sr who le-roc k isochron of 1616 ±38 Mafor amet amorphic event affecti nggranit ic rocks of theLGGD.Analte rnativeageof 1582±37Mabythe Rb-Srmeth od is cite d by Sta rmer(1991, p.122),presumably for the same event. More preciseage dete rm inat io nsare needed here,focusing on the age ofem p laceme nt of the granite. This is im por tan tsincefieldst udiesindicate clearly that the granite hasintruded the metasedim ent ary rocks (and associated mafic intrusion s) and therefore must be younger thanthese.Themetased iment aryrocksthem selves mustbe significa nt ly olde r thanrecent U-Pbzircon dating st udies on ot her met asedim ent ary rocks in the Bambl e Sect orindicate.Oneof theseisfor aquartzitefrom thevicin- ity of Kraqere (Ahall 1998) which gave adeposition al age not olde r than 1499 Ma. Other ages from the Secto r (Knudsenetal. 1997) indicate depo sition in the inte rval 1500 to1370Ma.This appa rent differencein thedepo siti on al age of the sedime nta ry rocks of theLGGDand those elsewhere in the Bambl eSect orneedsfurther investig ati on.Oneexpl a- nat ion may bethatthe age of thegraniteis as oldasindi- cated butits intrusivecontacts are theresult of remob iliza- tion,thusopen ingthewayforabasem ent / coverinterpr et a- tionof thefieldrelation ship s.Thereis,however,noevidence tosupport this at thepresenttime.

Basic intrusions

Theseinclud edykes,mega-dykes,small- to medium-sized gabbros and lop olith s as on Gumey-Lanq ey,They intrude the metased im ent ary rocks and are charact eri stic for the who le dom ain.A few (meta)perido ti tesin associatio nwit h metagabbro areknow n from exposureson the coastsout h of Rapen (Fig.4).Theyprobably intruded atvarioussta ges and help edtomaintainhigh heatlevelsin thispart of the crust over lon gperiod s of time. Someideaofthe com p lexity andabundanceof these intr usions maybe gained frommap compilati on sby Sta rme r(1969) in theRiser areaand in later papers (1985,1991,see reference list).Morto net al.(1970, pp.21-28)wereimpressed bythenumber ofseparate intru- sionsand their generalconcorda ncewit h the st rikeof the rocks ineaste rn most Bamb le.Thereislittlepublished geo- chemical data on these rocks.

Inthe absence of geochro no logical datathe intrusive agesof theserockscan only be viewed in arelative way,that is, in relati onto eachot herand totheirhost rocks. Fact ors such asdegr ee of metamorp hism and defor mat io n must also betakeninto account.

In the presentst udy,at te nt io n is confi ned tomaficdykes in theLGGD.lnthe granit icgneiss,forexam p le,they occur in swarms (Fig.9), are com mo nly conco rdant with the oute r contact zon e andwit h the inte rnalst ruct ureof the gneiss.

Intrusion may have been facilit ated by the presence of (?

cooling)jointsin thegranit e.Thedykes are now metamor-

NGU-BUL L 442,2004 - PAG E45

Fig 9.Steeply dipping diabasicdykes (synpluton ic)intrud edint o grani- tic gneiss.Rapen,Levang peninsula(Kragerodomain).Camerabag gives scale.

phosedbut only rarely st ret ched tothe pointofbeing seg- mented.Theseintrusion s areconsid eredtobe synp luto nic andint rudedatsomestage during the consolida tion of the graniti cbody.

Arat hersim ilar patt ern of mafic int rusionsseems to be presentin theMorj eheiaDom e, sout hwestofKraqere,judg- ing from map com pilatio ns on the Kragero map-sheet (Pad get,2000a). Here, a seriesof stee ply dipp ing, diabase intrusion s occurs.These are con cordant or near-con cordant wit h thehostquartzites, and therefore sill-like inthei rmode of occurrence. Intrusion seem sto have followed bedding and/or foliation planes in the quartzites.

One part icular intrusion lies betwee n quartzi tic rocks and the granit ecore.It isnorm ally5 to15 m thick,somewhat variegate das regard s inte rnalst ruct ureandcan befoll owed around most of the Levang peninsula. It intr udes the quart zitic rocks(Rapen Quartzite)ina sill-like manner and hencehas analmost st rat igrap hic mod e ofoccurrence.Itis conside red to havebeen intruded into the metasedimen- tary rocks befor e intru sion of the granit e (See also p.OO regardin g itssig nif icance inanevo lutio narysense).

Anumber of maficdykes,aroundametr e or so inthick- ness,intrudethe above-menti oned mafic int rusio nas well themet asedim ent aryrocks surro undi ng the granitegneiss.

NGU-BUL L442 , 2004 - PAGE 46

These showvariousdegrees of metamo rphism,somebeing rich in porphyroblastic garnet, ot hers merely fine- to medium -grained metamorphosed diabases(metadolerit es).

Cross-cutting relation ships are commonly observed betweenthesedykesindicati ng repeated int rusion ofmafic magma,possibly over along time interval. Themetamor- phismmayberelatedtotheimpact oftheSveconorwegian orogeny.

Structural features in the Kraqere domain The domain is containedwit hintwo majorfault zones,rep- resented by the Valleand 0yfj elldalen Faultstothe nort h- west and the Haslumkilen-LangholmenFault Zone(HLFZ) to the sout heast (Fig. 10).The for mer is responsi ble for abruptterminat ionsof metased iment aryformations tothe northwest(Fig. 4)andismarkedbyst ro ngmylon it izationin theValle area, and nort heastw ardsasfar asthe boundary wit h rocksof the Oslofield.TheHLFZisa comp lexzone,up to 500 mwideinwhich quart zit icrocksarehighlydefor med wit h thedevelopmentofsillima nite and micaceou sminer- als.This zonewas int ruded atalater datebydiabase (met a- dolerit e),nowamphibolitized.Betweenthesetwozonesthe LGGD is a major domal feat ure which,ina way,seemsto deflect foldaxes in the surrounding metasediment ary suc- cession(Fig. 10).Theseaxeshavethenorm alNE-SWBamble trend andaretermedFl in thisst udy.Mineral lineationsand minor fold axesarenearhorizont alin thenort heast (Aroy area)but plungesout hwesterlyaroundtheLGGD.

Interpret ationof air photos and fieldst udiesshow that foliation surfaces in the granitic gneissof the LGGD are folded,themostconvincing expr essionofwhichis the Myra dome (Fig.10).Thisant ifo rmalstruct ure, andot herless well definedfolds,haveaxesroughlyparallelwit h thelong axis of the graniticgneiss,and foli ationsurfaces concordantwit hits contacts.Despit e having the same general Fl trendofother foldaxesin the areaofst udy,itisnot certaintheybelong to the Fl phaseintime,but could havebeen formed later in connection,forexample, wit hthedom alupri seof theLGGD.

Southwestof the LGGD,the two fault zones converge and theFl fold sin between areaffected by a later set of foldsheretermedF2.Theresult is asuperimposedfold pat- tern.Thispattern is furt hercomplicated,ifnotaccent uated, by folds(ant iforms) thoug ht to be duetothe riseof mafic magma, e.g., Barmen(Figs.2and 10),thoughthis intrusion maybe,to some extent,fault -controlled.The LGGDis sur- roundedby synforms(rimsynfo rms).Thesemaybe aconse- quence of the upward int rusionof thegranitic magma,fur- ther accent uated by diaparism ofthe solidified magma ata laterstage.The schematic cross-secti on(Fig. 7)through the Kragero and Porte r domainsdemo nstrates some of these st ruct ural features.

Finally, certa in larger intrusions such as the mafic Gumoy-Langoy and possiblytheValberg bodies (Fig.2)now occupy synfor malorbasin-likestructures andcanbetermed lopolith ic.These could be due to theloading effect of the bodiesthemselves causingapassive downwarpofthecrust andareprob ablyindep endent of any specific foldphase.

PETER PADGET

Th e Skat0Y Tr iangle

Anareaofspecial interestliestothe east ofthe LGGD.Here, a triangular area of ground, largely coinciden t wit h the island Skatey,is limitedon threesides by faults (Fig. 3)and consistsof various formationsof a gneissic character(Figs. 2 and 4).The ENE-WSW- trending boundary can be traced throu gh the islands Straholmen and Straholrnstein (Fig.4) and is interpretedas a basalthrust to a package of metased- imentary rocks overfolded to the southeast.The southerly boundary of the triangle is part of the HLFZfault zone, locally markedby an intrusion of amphiboliticdiabase.The thirdsidetrends NW-SEandoccupies the channel between Skatey and the Levang peninsula. It is considered to be a high -angle fault of some magnitude judging from the strong ly deformed nature of the rocks observable on the Skatey sideofthe channel.

The rocks present in the triangle include migmatites, graniticgneissand anthophyllitegneiss.There is also an area wherelarge blocksof amphibolitic diabase are embedded in a younger potassicgranite (Fig. 2),the whole having an agmatiticappearance.Tangentialto this is a vertical 'wall' of granite,20m thick, and exte ndingeast-westfor a distance of nearly 2 km.It is thoug ht to have been intruded along a crustalfracture,possibly a fault.These intrusive features are thought to be the result of extensional stresses set up in connection withfault ing between Skatoy and the eastern part oftheLevang peninsula. Thewhole triangleis consid- ered tobe a fragment of an older basement sequence,pre- datin g the metasedi mentary succession described earlier.

Therocks seem to beakin to thoseof the Porter domain.

Evolution oftheKraqe re dom ain

On thebasis of field studies it is now possible to envisage some of the main events in the evolution of the Kragero domain.These are depictedschematicallyin Fig.8.

1)Init ialsedimenta tionon a basement of unknownchar- acter but probably containing a high percentage of crys- talline, felsic rocks. Inputofwaterlain, clasticsediments from thenort hwest into a sinking trough or semi-graben .More argillaceoussedimentstothe southeast.

2) Mega-fracture in basement arising from tensional forces allow ing upward rise and lateral intrusion of mafic mag ma into a thicksequence of sediments.

3)Forcefulintrus ionofgranit ic magma from a deep level inthebasement causing updoming of the metasediments (LGGDandMorjeheiaDome).Upward and outward limitto the intr usionmarked by athick diabasic intrusion

C

4)Theimmediate post-intrusional phase is marked by cooling,crystallizationandthe developmentof joints. In this phase,diabase(metadoleritic) dykes were intrudedinto the granitic coreofthe LGGD.These are considered to be syn- plut on ic andnotxenoliths from a pre-graniticterrane.

(5) The final major episode in the evolution of the domain wasundoubtedly one of deformation and regional metamorp hism.The development of foliation surfaces in

PETERPADGET

Fig10.Map showingthemainst ruct u ralelements presentinthe areaofst udy.

NGU-B ULL 442,2004 - PAGE 47

"

':~;:.~^{-: Formlines,trace of}foliation planesIn LGGD

==---

-+----

-+----

-+----

-+----

- - - - Fault

----1:>..-Reversedfault/thrust

t!LE~.:::_~ Haslumkilen -Langholmen FaultZonewith senseof movement

§L£~__ Sandnes-Lillesand Fault Zone

the granite probably belongs to this episode but their apparentfoldingcould bea reflectionof F1foldingalready imprintedonthe metasedimentaryrockswhichformed the roof of the intr usion. The st eep, marginal,contact zonesto the granitic gneissof the LGGD(Fig.7),together wit h a more pear-shapedconfiguration of thegranitic gneiss at depth (Fig. 8),may reflect a diapiricmovementrelated to compres- sional forces.Thisfinalepisode can possiblybe relatedto the Sveconorwegianorogeny which was most active during the 1100-1200 Ma interval.

(6) Stabilization.The long period ext ending from the Early Neoproterozoic into the Phanerozoic is marked by cooling,brittlefaulting andthe intrusionofpegmati tesand dolerite dykes. The latter are markedly discordant to pre- existing bedrock structuresand one representative,trace- able for 500 min theRapen area (Fig.4), penetratesgranitic gneiss.It isvertica l,non-met amorph ic andinsharpcontact wit h the host gneiss.A Permian age for this and ot her

dolerite dykes seems most likely thoughaVendian age can- not be excluded.

Joints in themetasedimentarysuccession are commonly at high anglesto most st ruct uralsurfaces and sometimes havequartz-carbonateveining.In a fewcases,brittle faulting can be seen.

Pegmatites are alsocommon in the Kraqero domain as elsewhere in the BambleSector.Good examplesaretobe found in the Rapen area where they aretypicallynon -meta- morphic and general lyconcordantwit h the structureofthe rocks into which they are emplaced,though cross-cutting relations hipsare also observed.They show littleor no differ- entiation except for poorly defined quartz cores. A Neoproterzoicageforthe pegmatitesispossible.

In a few places,foldedpegmatitesarepresent but these are thoug ht to belong to an earlier,possibly Svecofennian, episode. Thenottoo dista nt Fenint rusive complexisrepre- sente d by alampr ophyr ic (damtjernite)dyke onSkatey,This

NGU-BULL442,2004 - PA GE 48

hasbeen dated by the40Ar/³⁹Ar method to 588 ± 10 Ma (Meertetal. 1998).

The Porter domain

This lies seaward of the Kragerodomain and morespecifi- cally between two major fault zones, the Haslum kilen- LangholmenFault Zone(HLFZ) and the5andnes-Lillesand Fault Zone(SLFZ,Fig. 10).

Metasedimentary and other layered rocks These include:(i)paragneisseswit h associated orthogneis- ses on Jomfr uland (Decca station area,Fig.4). (ii) biotite gneissesand migmati tic rocksinthe Riser and Straholmen - Straholm stein areas(Kragero's skjeerqard),(iii)a possiblepil- low lava format ion preserved as xenolithsin granod ioritein coastalexposuressouthofPorter(Fig.4).

(i)Therocksexposedon Jomfrul and arelargelyintrusive but some interlayered gneissesprob ably have a sedimen- tary origin.Outcropsofthelatt er intheDecca station area

Fig 11.Paragneisses(?metased iments)of uncerta in origin,invadedby diabasic dykes(darkinphot o). The parallelismachieved is broken by minor transverse fault s. Coastal exposures on the SE sho re of Jomfruland,close totheDeccastation.(Porter domain).

PETERPADGET

Fig 12.Coastal exposure at Grytodd en,1.1km sout hw estof Porter sho- wing possiblepillowlavas(dark)in axenolithin granodi orite.Ayounger

(Precambrian)diabasic dykecut s both gneiss andxenolith.Compass

gives scale. (Po rte r domain}

are interlayere d wit h mafic and felsic rocks (Fig. 11).The mafic rocksare consider edto represent deformed sillsand dykes int rusive into a pre-existing terrane consisting of quartzit ic and arkosic sedi men tary rocks which in a few places showprim ary clast icfeaturesand traces of cross-bed- ding. There are also a number of rather indeterminate gneissescharacterised by a significant conte nt of biot it e.

They seem to be more akin to gneisses exposed in an enclave in larvikitesat l.evallto thenorth-no rth east(seethe Langesundmap-sheet,Padg et2000b).The wholesequence is onerepresent at ive of high strain,marked by strongshear- ing, pronounced ductil e deformation and rotation which transposedall rocksintoparallelism.

(ii)Inthe islandchain (Straholmen,Straholmstein,etc.) nort heastof Jomfrulan d(FigA). outcrops of dark,biotite-rich gneiss,in places epidote-bearing,are clearly of a different nature.They are also penetrated by mafic (amphibolitic) dykes and sills as well asbeing foldedin a complicatedman- ner.Out crop s arerelativelysmalland do not allowfar-reach- ingconclusionsto be drawn.The relationsh ipof the biotite- richgneisses to the rockson Jomfrulandis unknowndue to lack ofexposure(sea covered).

In the extreme southwestof the Porterdomain,around

PETER PADGET

Riser,dark mica schists and gneissesarecomm on and gen- erally exist asxenolit hs in late rintrusi ons (St armer 1969).

Migmati tic rocks arealso widespreadin the same area and havebeendescribed asmelanomigm at ic by Starmer (1969), presumably onaccount ofthe abundance of dark mineral comp onent s such as biotite and hornblende.Theyare folded intoan anti for m of regionaldimension s east of Riser (Padget 1993b) and are in faulted contact wit h metasedimentary rocks ofthe Kragero domainto the north(Fig.4) andwit ha majorlineament, the SLFZ(Fig.10),to thesouthand south- east (cf.Padget 2000a,Fig.2).A possibl econnection wit h paragneissesas far to the nort heast as Jomfruland is sug- gested.Though the inte rmediate area is sea-covered, a northeasterlytrend,concordant wit h thePortergranit e-gra- nodiorit ebody on thenearby land area, seems reasonable.

Elsewhere in the domain,certain gneissesare particularly quartz-richand may havesedimentary origins.One example is a quartz-rich gneiss on Fengesholmen(Stelefjorden), 2 km northeastof Porter.Itsstratigraphic and structural relation- ships cannot be ascertained.

(iii) Finally,mention canbemade of certain amphibolit ic rockswhich occur wit hinwell exposed granod ioriteon the coast at Stangnes and at Grytodden (600 met reseast of Ko lstangen, Fig.2) ),sou th and southeastofLevang(Fig.4).

They aretyp ically angular,xenoli t hic blocksof varyingshape andsize and areusually insharp contactwit h the enclosing granodior it e (Fig. 12). They exhibit foliat ion,shearing and veining,features which clearly pre-date their enclosure in the granodiorite. Thereis also a considerable re-distribution of thedark and light mineralcomponents giving the rock a semi -bandedappearance.The author is of the opinion that these rocks could be somewhat deformed and metamor- phosedpillow lavas and hence belong to a supracrustal for- mation asyet unrecognized elsew here in the domain.The lightercolouredamphiboliteis consideredto represent the pillowsand the darker,melanocraticamphibolite the matrix.

So far,thecharacteristicpillo wshapeseenin undeformed, non-metamorphic pillow lavashas not been seen.Rather simila r rocks are reported from the Fiskencesset region, SouthwestGreenland(Myers 1984,p.101), where a transition to lessdeformed,indisputable pillow lavas can be followed in outcrop .

Intrusive rocks

Rocks ofint rusiveorigin make upa large partof the Port er domain.A mega-unitin thisrespectisa foliated dio rite -g ra- nodiorite body (Fig. 2), well exposed in the region of the Porter communitywhere it is intrudedbygranit icveins(Fig.

13).ltcontinuesinto the sea areawest of Jomfrulandwhere thesamerocks and relationship scan beobserved on sev- eral small islands.On Jomfruland it self, at the west coast landing -pi er,metadioritic and amphibolitic rocks probably belong to thesame intrusion.

On themainl and,quartzdioritic to granodioritic rocks arein contact wit h the metad ior it eand occupy largeareas to the sout hwest in the direction of Riser.Thecontact relationships betweenthese varioustypes of dioriteare not yet knownin

NGU-B U LL 442, 2004- PAG E49

Fig 13.Gran it ic veinsinvadingmetadioritealonga pre-exi stingfault sys- tem.600met resWSW of Porter,Por t orenga.Compass mirror gives scale.

(Porte r domain)

detail though some seem to be transition al. Mafic dykes, now amphibolitic, and lessregul ar bodiesof amphiboli te intrude the dioritic rocks and are both folded and sheared on a regional scale.

In good exposures,ason Blabcersholmen (Bersund hol men), a small,elongate island 1.6 kmeast-sout heast of Levang(Fig.

4), severalphases of dyke intrusion can beseen, theyounger mafic ones being both narrower and lessdeformedthanthe older ones (Wegmann& Schaer 1962).A fragment of the inferred pillowlava mentioned aboveis also present at this locality, representinganearlier,pre-dykephase.A latergen- erati on of granitic orfelsicdykeint rusion is also evidentin manyof theseand other outcropsin thedomain,a feature which seems to increasein importance to the northeast.

Near 0ysang(Fig. 2)at theextremesouthwes tern end of the int rusion, the metadioritic -granod io rit ic rocks are folded and can best be described as melanocraticorthogneiss.

All in all, there is strong evidencefor the intrusion of diorit ic and granodioritic magmas into a rather mixedassemblage of layered rocks,the true natur eof which isst ill not sat isfac- torily resolved.Subsequently, diversemagmas of mafic,felsic and granitic composition invaded these rocks in several episodes.All the rocks show evidenceof regional metamor- phism and ductile deformation.

NGU-BULL 442,20 0 4 - PA GE 50

Structural features of the Porter domain

The wholedom ain is characterized by a marked st ructural trend varying between 060°and 065°.This is particularlyevi- dent on air photos and is theresult of theintersectio n of foli- ation and bedrock surfaces (B-tectonites).lt is,how ever,pos- sible to identify2 folds of region al ext entsout h of Levang,a synfo rmanda complementaryantiform(Fig.10).Linear fea- tures suchasmineral orientationsand fold axesshowa con- sistent plunge towards 245°.A complicated pattern of joint- ing is superimpos edon thefolds.

Geochronology in the domain

Isot op ic dati ngofcertaingranitic rocksinthePort er domain using the Rb-Srwhole-rock method (O'Nions et al. 1971) gave a poorly constrained age of 1167±50Ma.Thisageis difficult to interpret but may indicate anint rusion age for certain granit ic rocks related to the Sveconorweg ian orogeny.The age of emplacementof the metadioritein the domain has not yet been satisfactorily dete rmined in the author'sopinion.It seems to beadistinctintrusionwit hout any obvious connection with, for examp le, the granit ic gneiss of the LGGD.Dating of the metasedime nt aryrocks has not yet beenunderta ken.

Dolerite dykes and fault breccias transect the Precambri an rocks at many placesand though minor fea- tures they representlater episodesin the geologicalevolu- tion of the domain, probably extend ing into the Phanerozoic.Many of the mafic dykes aremost prob ably relatedto the developmentof theOsloRiftin thePermian.

The inter-domain contact zone

The contact between thetwo domains(Fig. 3) isreadil ydis- cernibleon map compilat ionsat all scalesandcan betraced for nearly40km. Itis part icularlyclearoverthe cent ral sec- tion (map-sheet 1712.4 Kraqero,and in Fig. 1B)where it is marked by migmat itic rocks, together wit h strongly deformed quartzites. Here,there is a steep northwesterly dip.To the southwestthe contact isless clear due to the presenceoflarge, cross-cutting int rusions of(meta)gabbro, now largely amphibolit ic,such astheBarm en and Avreid bodies.The line of contact is really a zone,up to0.5 km in widt h, of duct ile fault ing,here termed the Haslum kilen- Langho lmen Fault Zone (HLFZ) and has been invaded by both maficand felsic rocks.Thesense of movement is not clear but the F2 folds west of theLGGD (Kraqeredomain) may berelatedto a sinistral movementalon g this fault zone.

Conclusions

Thearea of st udy isan impor tan t part of theBamble Sector in the southern partof Norw ay. Recentl y completed mapcompilationshavebroug ht to light anumber of geo- logicalfeat uresof aregional natur eprovidingthe basisfor interpretationstudies.These includetherecogn ition oftwo fault-defineddomains,referredto as theKrageroand Porter domains. These are separated by the Haslumkilen- Langholmen Fault Zone(HLFZ).Gneissic rocks intheSkatey

PETER PADGET

area are of Porte r-domaintypebut make up atriangu lar, fault-bounded enclave inthe Kragero domain.Maj or faults and fault zones delim it the area of st udy to the north (0 yfjelldalen and Valle Faults) and to the south (Sand nes- Lillesand Fault Zone).

Metasedimentaryrocks are presentin both terranes but differ intype as well as in degree of deformation and meta- morph ism.No satisfacto ryorderof stratigraphicsuccession hasbeen worked out forthese sedimentary sequences but most of the clasticand associatedsediments in theKraqere domain are thought to have been deposited in an elongate trough or half-gr aben. Certain mafic rocks in the Porter domain are interpretedaspossiblepillowlavas.

Intrusions,bothmafic andfelsic,penet ratethe metasedi- mentaryrocks of both domains.In the Kragero domain,the LevangGraniteGneiss Dome(LGGD)is thought to havean int rusivegranite corewhich post-datesthe hostmetasedi- ment aryrocks andmost of their associatedmafic intrusions.

This precludesasimp le basement/corerelation ship.At the sametim ethe relativehigh intrusion age forthis graniteof 1616± 38 Ma(fi rstreported byO'Nionset al. 1971)means that the immediate host rocksmust beeven older.Thelatter are then significantlyolder than sim ilar rocks elsewhe re in the Bamb le Sector (Knudsen et al. 1997 and Ahall 1998) depositedinthe1500to 1370Ma interval.Italso meansthat the Kragero domain,as defined above,containstwo sedi- mentarysequencesof differentages.

Some ideaofthe episodicdevelopmentof thisterrane is depicted schematically inFig 8.

The major, post-sediment ary intrusions in the Porter domain arediorit icto granodioritic and these are,inturn, invadedby granitic rocks of probableSvecono rweg ianage.

The int rusionofmafic rocks(diabases,gabbros)traditionally dated to the 1200-1 100 Ma interv al(Starmer 1985),affects both domains but took placein severalphases over along periodof time.Dolerit ic dykes and pegmati tesare common inlate Precambrian(Neoproterozoic) time.

From the above,it is clearthatthereis a greatneed for additionalisotopic datesto clarifytheevoluti on of thispart ofthe Bamble Sector.

Finally,these rocks and part icularly those of the Porter domain areofsome inte restsincea recently published com- pilation(Sigmond2002)showsthemto bepart of an ext en- sive areaof supposed Precambriangneissesin theinnerpart of theSkagerrak,a conclusion basedon int erpretati on s of geop hysicaldata (e.g., Hoden 1973).The nearestoutcrops which can be inspected are, in fact,those in the Porter domainand in the enclave ofPrecamb rian rocksin Permian vulcanit e at l.ovall, 1.2 km east of Nevlungha vn (Padget 2000b).

Ackno wledgements

Thispaperis written partlytoacknowledgefieldwo rkcarriedoutover theyears intheBambleSector byst udent and post-graduategroups basedinBritainand theNetherlands.Manyhave kindlysupplied copies oftheirmapcompilationsonacost-freebasis.Theseare nowlodgedin the archivesof theGeologicalSurvey ofNorway,Trondheim,providing a morepermanentrecord oftheir activit ies.They havealso been much

PETERPADGET

used bythepresentauthor in themap-sheetcompilat ionsonwhich the present st udy ispartially based .

Theco mme nt s andconstructivecriticism ofthetworeferees, Mogens Marker and Geert -Jan L.M.de Haas, are greatly ap pre ciated.Irene Lundqu ist(NGU) isthank ed for skilfullyimprov ing thequality ofthe textfigu res.

References

Brogger,w.e. 1934:Onseveral Archeanrocksfro m thesout h coastof Norway .Nodula rgranitesfrom the environ sof Kragero.Det norske vide nskaps-akademi iOslo 1933, 1. Matematisk-Naturvidenskapelig klasse,2.97 pp.

Bugge,A.1965 :lakttag elserfrarektangelbladetKragero og denst ore grunnfje llsb reksj e. Norges geologiske undersekeise229,115pp.

Burrell,D.e.1964:Thegeolog yof thecountry westof Levangpeninsula, south Nor way.Unp ub lishedPhD.thesis,Univ.ofNot tingham.

Elder,T.G.1964:A petro logicalandstru cturalstudyoftheLevangGneiss Dome, southern No rway.Unpu blishedPhD .thesisUniv.of Durham.

240 pp.

Flod en,T.1973:Not es on thebed rockof easternSkagerrakwithrem arks on Pleistocene dep osit s. StockholmCon tribu tionsin Geology24,79- 102.

Hofset h,B.1942:Geologiskeundersokelser ved Kragero,i Holl eia og Trams.Norge sgeologiskeundersekel se157,11-46.

Hut t o n,D.HW.1982: A tectonic model forthe emplacementof the Main Donegal Granite,NW Ireland.Journalof theGeologicalSocietyof London 139,615-631.

Kn udsen,T-L.,Ande rsen,T.,Whitehouse,M.J.&Westin,J.1997: Det rit al zir- con agesfro msouthernNorway- implicati onsfortheProt erozoi c evolut io n of the sout hwes te rn Baltic Shield. Contributio ns to Mineralogyand Petr ology 130,47- 58.

Lam b, R.e., Smalley,P.e. &Field,D.1986:P,Tcondit io ns for the Arendal granu lites, sout hernNorw ay:implicatio nsforthe roles of P,T and CO,in deep crust aI L1LEdepl eti on.Journalof metamorphic geology 4,143-160.

Meert, J.G.,Torsvik,T.H.,Eid e,EA &Dahl gr en, S. 1998: Tectonicsigni fi- canceof theFen provi nce,S. Norway:constraints from geochrono- logy and paleomag net ism.Journalof Geology 106,553-564.

Morton, RD.,Batey,R.&0'Nions,R.K. 1970: Geological investigatio ns in the BambleSectoroftheFennoscandian Shield,southNorway. 1.The geo- logyofeastern Bamble.Norgesgeologiske undersekelse263,72pp.

Morton,RD.1971:Geologicalinvestigationsin the BambleSectorofthe Fenn oscandi an Shield,S.No rw ay. 2. NorskGeologisk Tidsskrift51,63- 83.

Myer s,J.5.1984:Archa eantect oni cs in theFisken aessetregionofsouth- west Greenland.In:Kroner,A&Greiling,R.(eds)1984:Precambrian TectonicsIllustrated. E.5chw eitzerb art' scheVerlag sbuch hand lung.

St ut tga rt,95-112.

NGU-BU LL44 2,2004 - PAG E51

O'Nions,R.K. &Baadsgaard,H. 1971:Arad io m et ricst udyof polym eta- morp hism in the Bambleregion, Norway.Beitraqe zu r Mineralogie und Petrologie34,21pp.

Pad ge t, P. 1990:Tect o nic and lit hostratig raph ic relat io nshi psin the Bam blesector,southNorway:aninterpreta t iveview.In:Gower,e.F.

River s,T.&Ryan,A.S. (eds.).Mid-Proterozoic Laur entia-Balti ca.Geo l.

Assoc. Canada,Spe cialPaper 38, 307-316.

Padg et,P.1993a:Tvedestr and.Berggrunnskart 1612.1-1:50 000,forelo- pigutg ave.Norges geologiskeunderso kelse.

Padg et, P.1993b :Risor Berg g ru nnskart 17 12.3- 1:50 000, forelopig utgave.Norgesgeologiskeundersekeise.

Padget,P. 1993c:Gjerstad Berggrun nskart 1612.1-1:50000for elop ig utgave.Norg esgeologiskeund erse kelse.

Padget,P.2000a: Notes to accompanyprelim in arymap sheetKragero 1712.4. Bedrock 1:50 000.Norgesgeologiskeundersekelse.Report 2000.009,3 8pp.

Padget,P.2000b:Notesto accompan ymap sheets Lang esund 1712.1 and Stavern 1812.4. Bedrock 1:50000.Norgesgeol ogiskeunderse- kelse.Report2000.008,24 pp.

Padge t, P.2001:Arendal1611 .4. Notesto accompa nythemapco m pila- tion (p relim ina ry)of1997 with rev isio ns year 2000.Norgesqeoio- giske undersekelse.Repo r t2000.010,56pp.

Sig mo nd,E.M.O.2002:Geolog ical map,Land andSea Areasof Northern Euro pe1:1 million.Geological Surveyof Norway.

Starme r, Le. 1969:Themigmatitecomplexof the Riserarea,Aust-Agd er, Nor w ay. NorskGeologiskTidsskrift49,33-56.

Sta rme r,Le.1969:Basicplutonicintrusion sof theRiso r-Sonde ledarea, south Norway:the original lithologi esand their meta m o rp hism.

NorgesGeol og iskTidsskrift49,403-43 1.

Starrner. l.C,1976:Theearlymajorst ruct ureand pet rol og y ofrocksinthe Bam bl e Series, Sondeled-Sandnesfj ord,Aust-Agder.Norges qeolo- giskundersekelse327,77-9 7.

Starme r,Le. 1978:The majortect o ni csof the BambleSeriesbet w een Sondeledfjo rdandKilsfj ord(Aust-Ag derandTelernark).Norg esqeo- logi skeundersekelse338,37-58.

Starmer,Le.1985:The evolut io nof thesout hNorwegianProterozo icas revealed by major and mega-t ect on ics of the Kongsberg and Bamblesectors. 259-290.In:Tobi,A.e.&To urer. Lt.Rfed s.):Thedeep ProterozoicCrustin the North AtlanticProvin ces,Nato ASI Series,Ser.

e.158. D.Reide l259-290..

Starme r,Le. 1991:TheProterozoic evo lutionoftheBamble sector shear belt,southe rn Norway:correlations across sout he rn Scandinavia andthe Grenvillian controver sy.Precam br ianResearch49,107-139. Wegman n,e. E.&Schaer,J.P.196 2:Chronologie et defo rma tions des

filon s basiquesdan slesform at ionsprecambriennesdu sud dela Norveqe,NorskGeolog iskTidsskrift42,371-3 87.

Ahall,K.1.1998:Ionprob e zirco ndatingofmetasedimenta ryunitsacro ss the Skage rrak:new const raintsfor earlyMesoprot erozoi c growthof theBalticShield.Precambrian Research87,117-134.