New data on net-veined complexes in the Oslo Rift, southeastern Norway

TOMANDERSEN,VIORICAMOROGAN&HENNINGS0RENSEN NG U- BULL 442,20 0 4 - PAGE 29

New data on net-veined complexes in the Oslo Rift, southeastern Norway

TOM ANDERSEN,VIORICAMOROG AN&HENNING S0RENSEN

Ande rsen,T., Morogan, V.&Sor ensen,H.2004:Newdata on net- vein ed comp lexesinthe Oslo Rift,sout heasternNorway.NorgesgeologiskeundersekelseBulletin442, 29-38.

Bodiesofbasaltic trachyand esit eoccu rinthe endocontac tzoneoftheMykl egraniteagainstthe largeSkrimlarvi - kite massifinthe sout hern part of the Osloigneo usprovince.

NewSrand Nd isotope dat aind icatethatthe8'Sr/86Sr(0.704023-0.70544)andENd(0.7-2.8)at272 Ma ofthebasalt ic trachyandesite arewith in thecorrespondingrang esoflarvikite and theVestfoldbasalts, butdifferentfro mtheSkien basalts.The isot opi cdata sup po rtamod elfor the originof thetrachyandesitebymixin g of basic and graniticorsye- niticmelts,whichis alsoin accordance wit h trace eleme nt dataand petr o gr aphi cobser vati on s.Blackandem ulsified trachyande siteshaveuniformENd(+2.2±0.5),butvariable8'Sr/ 86Sr, which indicate thatthemelts were heterogene- ous inSrisoto pesat thetime of em placem ent, mostprob ablybecause ofselect iveintro duct ionof radio genic Sr fro molder rock sby afluidphasebefore or duringem placeme nt. Globu larbodi es ofgranite inthe basalt ic trachyan- desite aresurroun ded bybiot it ehaloes in thetrachyand esite andare thou ghtto belu mpsofpartially consolid ated graniteor of thealready conso lida tedgranitepickedupbythehottrachyand esiticmagma.

Tom Andersen,tnstitutt forgeofag, UnivetsitetetiOslo,Postboks1047BJindern,N-0316Oslo,Norge.VioricaMorogan, Rorstrandsqatan 19,4tr;5-11340Stockholm,Sverige.HenningSerensen,Geologisktnstitut,0sterVoldgade 10,DK-1350 KobenhavnK,Danmark.

Introduction

Net-veinedcomplexes composedofglob ular masses of fine- grained basic igneous rocks and vein sof coarser grained syenitic and granitic rocks were described from the Late PalaeozoicOslo Riftby Morogan & Serensen(1994).The net- veined complexesoccur inthe area around Lake Mykle in thesouthwesternpart of theRift,wherethey are located in the complicated contact zone of a body of granite which intr udesinto pluto nicmasses oflarvik ite(Boni n&Serensen 2003).

Theresult s of Morogan & Serensen(1994) indicatethat magma of basaltic trachyand esit e (for simplicity hereaft er called trachyandesite) were em placed into a granitic- syenitic magma chamber and rose along the walls ofthe chamberin a zone of weakness between a marginal shell of already consolidated granite and the main mass of still at least partially fluid granitic magma. The trachyandesite formedsheetsalong the walls which wereinvaded by sev- eralgenerati onsofveins ofsyeniteandgranite(Morogan &

Serensen 1994,fig. 19).

Inthepresentpaper,newinform at ion onthe net-veined complexesofthe Myklearea arereported:(1) Sr- andNd-iso- tope data on most of the trachyandesites analysed by Morogan & Serensen(1994) and on some associated gran- ites;(2) description of an emulsified type of basic enclavesin acidic rocks; and(3)ellipsoi dal bodiesof graniteenclosedin the main mass of trachyandesite .

Field relationships and petrography

Mor ogan & Serensen (1994) disti ng uished threetyp es of basaltictrachyandesite:grey,blackandhybrid.The grey type

is slig ht ly more coarse-grained thanthe black type. Three stagesof crysta llizationwere observed intheblack type:1.

Macrocrysts of plagioclase and c1inopyroxene;2.Granula r amphibole, biotite, c1inopyroxene, feld spar, iron-titanium oxides,apatite and titanite;somequartzwas also formedin the grey rock at this stage.3.A densematrix of feldspar, c1inopyroxene,amphibole,biotite,titaniteand a multitud e of apati te needl esand skeletalcrystalsofiron-t itanium oxides.

Onlystages1 and2 arepresentinthegreytype.Xenocr ysts of c1inopy roxene and plagioc lase indicate that the basaltic trachyand esiti cmagm aswere form ed bymixin g of basalt ic and trachyti cmagm as.Trachyand esit escontaini nggrainsof quartzand potassium feldspar represent the hybrid typ e distinguished by Morogan& Sorensen(1994).(We usethe term'macrocryst' asa general,non-genetic term for phe- nocrysts and xenocrysts.Xenocrysts are distingu ished by theirmorphology,reaction rims and chemi calcomposition.)

Emulsified type of basic enclaves in granite AtSerrnyrtothenorth w est of Lake Mykle(Fig.1).the con- tact betw een theMykle granite body and the large Skrim massif oflarvikit eto the northis sharpandwellexposed.The medium -g rainedredd ish graniteof the contactzone is30 m wideand withoutanytraces of basic enclaves.Tothe sout hit borders on a sheet of trachyandesite whichisa massive,fine- grained to aphanitic,grey and black rockintersected bysev- eral generations of veins of syenite and granite. The youngest of these is coarse-grained and identical to the ekerite (peralkalinegranite)which forms the maj or part of the Myklegrani tebody (Bonin& Serensen2003,fig. 4).The hom ogeneou s trachyand esite passes, afte r a few metres, into a mott led rock composed of grey to black rounded

NGU-BULL 442,2004 -PAGE 30 TOMANDERSEN, V/OR/CAMOROGAN

s

^HENN/NGS0RENSEN

Fig.2.Emu lsifie dtrachyandesit e withinterst itial granite.Note the blackdotsof denser blackcolour in the upper and lowerparts of the photograph.Sormyrto the northwestoflake Mykl e. (Hammer head17 cm long).

Fig.1.Simp lifiedgeolog icalmap of the Mykle region.

3km 2 I

!

K

Krokvan n

S

Sormyr

o

!

~ Net-veined

~ complex

I ':" :"

;I#'\"'_':~

',1

~. ^Granites,inc!.ekerite

1>::::::::::1

Syenite

t:"Y~':3...:......\'.: Porphyri ticsyenite

f:::::::::::::J

^{Larvikit e}

~ Diarite -gabbra

Ellipsoidal bodies of granite in trachyandesite

The massive trachyandesite at Sormyrconta insscattered ellip soidal 'globules'of coarse-grained granite measuring up to about 20 cm along theirlong axes(Figs. 3,4).Two granite globulesappearto coalesce and par- tially overlap (Fig. 4).There is acon- cent ration of biot ite in the contact zonebetweengraniteand trachyan- desite which is difficult to see on fresh surfaces(Fig. 3) but very dis- tinct on weathered surfaces(Fig.4).

globules enclosed in a matrixwhich appearsto be a mixtureof trachyan- desite and granite(Fig. 2).The glob- ulesvary in sizefrom afew millime- tres to several centimetr es. The largest are of a more dense, black colourthanthe smaller ones(Fig.2).

Thismelange of basic globu lesand more felsicmat rixrecalls the emulsi- fied typ e of basic enclaves in acid rocksdescribe dbyGourgaud(1991).

The transiti on from the emulsified rockto the main mass of granit eto thesout h is unexposed.

The massive trachyand esite (101252) isof the black type distin- guished by Morogan & Sorensen (1994).It is composed of amphibole, biotite, plagioclase, tit anite, apatit e needl es andcrysta lsas well as skele- tal crystalof Fe-Tioxide s.Theamphi- bole ispartly overgrown by biotite.

Patches of chlorite most probabl y represent alt ered c1ino pyroxene.

Quartz wasnot observed.

The emulsified rock(101253) is a melang e of trachyandesite and a net wor k ofveins andnestsofquartz and turbid pert hit ic pot assium feld spar.The grainsizeofquart z and K-feldsparis similar to or largerthan thatofthetrachyandesit e. It should benoted that there is noconcentr a- tion of biot ite in the felsic parts of the emulsifie d rockand thatthetra- chyand esit edoesnot appear to have been modifiedduring the ming lin g of basicand acid material.Itis,how- ever, distinguished from the tra- chyandesite to the north of the emulsified rock by the presence of scattered grains of quartz.

TOMANDERSEN,V/OR/CA MOROGAN&HENN/NGS0RENSEN NGU-BU LL 442, 2004 - PA GE 31

Fig 3.Graniteglobulein trachyandesite; Serrnyr, Theglobuleis15cm in lengt h.The light-colou- red surface above the hammer head is disco- louration of a fract ure surface.

The region algranite (101268) iscoarsegrainedand com- posed of quart z and turbid perthite.It contai ns scat t ered grainsof plagiocl ase.There aresmall grain s of blotit e,zircon and opaque minerals and aggregates of rusty material which,from other exposures, are known to be alteration product sof pyroxeneand/oramphibole.Thisrock belong s to the fine- to medium-grain ed reddish granites distin - guishedby Bonin&Ser ensen(2003).

Thegraniteof theglobules (92064,101254,101269)is coarsegrained and domin ated by quart z and perth it e,in part in micrographic intergrowth s,and contain s scat te red sma llgrains of brown biotite but also,in places, small grain s of green to bluish am phibole. There are aggregates of am phibole, biotite,tit anite, opaque minerals and apat ite which are interpreted to beenclaves of trachyande site.In thecontact agai nst the enclosing trachyand esitethereisa concentrati on of biotitewhich, togetherwith some quart z, impregnatesthe trachyande sit e.It sho uld be noted that thereappearsto beno K-feld sparpresent in thetrachyan- desite.

Mineral chemistry

The chemi cal com posit ion of the main minerals was analysed wit h aJEOL 733 electron microprobe equi p ped withaTRACOR energy-d ispersivesyste mat theGeological Institute, University of Copenh agen.The pyro xenes were classified after Morim oto et al.(1988)and the amp hiboles after Leake etal.(1997).

Homogeneous trachyandesite and emulsified basic enclaves

The main mafic phase in the hom og eneou s basalti c tra- chyande sit e (101252)isbiotite wit h a highTi conte ntanda

lowSi content (Table 1,no.2).The am phi bo lesbelong tothe calcicgroup(CaB>1.5) and display a commo n magm ati cto sub- mag mati c trend of crystalli zat ionfrommagn esio-h orn- blend eto act ino lit eand alsoeden ite (Tab le 2,nos. 1,2,3), simi lar to theamphib ol e analysesof Morog an & Serensen (1994).

The emulsified basalti ctrachyand esite (101253c) con- tain s small grainsofagreeni shpyroxene classifiedas analu- minian (AI>0.1) andsodian(Na>0.1) augi te(Tab le3,nos.1, 2).This augite containsonly 26%Wo,very closeto asubcal- cicaugit e composit ion which involvesAc(Na-Fe3+),Jd(Na- Alvi)and AI-Ts (Alvi-Aliv) subst it ut io ns.It sho uld be not ed thatsim ilar pyroxenesoccur in thegroundmassofthetra-

Fig.4. Coalescinggraniteglobulesintrachyandesite which is enrichedin bioti teadjacenttothegranite.Theweat heredtrachyandesiteiswhite.

Serrny r,

NGU-BULL 442,2004 - PAGE32 TOMANDERSEN,VIORICA MOROGAN

s

HENNING S0RENSEN

*see Table3for abbreviations

Tab le 1.Representativecompositionsof biotite.

Table2.Repr esentat iveamp hibol e compos itions.

1 Sample 101252 Rock type* h.b.tra

chyandesite hosting graniti cellipsoidalbodies (Table 3,nos.

3,7).

Ellipsoidal graniticbodies in trachyandesite Themin eralchemist ry ofthebasalti c trachyand esite(92064, 101254,10269)hosting the granite globules(92064,101269) was found to be very similar to that of therocksdescribed by Morogan &Sorensen(1994).Three pyroxenetypeswere identified:aluminian diopside macrocrysts (Table 3,nos. 5, 6),diopside phenocrysts(Table 3, no.4)and small ground- mass grainsofalumi nian andsodian augite(Table 3,nos.3, 7).Thebiotite ofthetrachyandesiteshows fairly high Ti and low Si contents (Table 1,nos.5,6),relativeto the biotite of the contactzone betweentrachyandesit e and graniteellip - soids(Table 1,nos. 3 and 4) which exhibit scomposit ions moresimilar to those of the granite.

At the contact with the graniteellipsoid s,the trachyan- desite contai nsvery few augi te grain s(Table 3,no.7)sur- rounded by biot ite. Calcic amphiboles, magnesio- hornblende(Table 2,no.7)andedenite (Table 2,no.6)are the main mafic mineralsin the trachyandesiteenclosingthe granit e ellipsoids. The granite ellipso ids contain sodic amphiboles (NaB> 1.5)such as magnesio-arfvedson ite and magnesio-r iebeck ite (Table 2,nos. 4, 5).TheFe-Tioxidesof trachyandesite and granite ellipsoids(Table 4)show extensivere-equilibration.

0.47 96.46 39.10 2.8 1 10.98 22.22 0.32 11.05 0.08 0.09 9.81

5.99 1 0.324 1.983 2.84 7 0.042 2.523 0.013 0.027 1.917 6 92064 gt/b.tra

0.51 96.05 39.14 2.79 11.38 20.55 0.42 11.82 0.00 0.10 9.85

5.974 0.320 2.047 2.623 0.054 2.689 0.000 0.030 1.918 5 101269 b.tra/gt 4

36.97 3.58 12.42 21.75 0.13 11.14 0.16 0.09 9.99 96.23 37.89

3.66 12.18 19.26 0.18 12.07 0.09 0.06 9.97 95.36

2 3

101254 b.tra 36.29

3.90 11.80 25.76 0.19 8.02 0.00 0.00 9.66

0.36 0.53 0.48

95.62

Cations(0=22) 5.739 5.806 5.695 0.464 0.422 0.415 2.199 2.200 2.255 3.407 2.468 2.802 0.025 0.023 0.017 1.890 2.757 2.558 0.000 0.015 0.026 0.000 0.018 0.027 1.949 1.949 1.963 37.12

2.84 11.83 25.64 0.41 9.01 0.23 0.15 8.80

0.39 96.03

5.806 0.334 2.181 3.354 0.054 2.101 0.039 0.045 1.756 Tota l

SiO, TiO, AI,O ) FeO MnO MgO CaO Na,O K,O

XMg Si Ti AI Fe"

Mn Mg Ca Na K

"h.b.t ra =ho m og eneous basaltic trachyande site;b.tra= basalt ictrachyand esite;gt=granit e

**ed=edenite;act=act inolite;Mhb=mag nesio-h ornbl ende;Marf= magesino-arvedsonite; Mrieb

=

magn esio-riebeckit e

3 4 5

101269 gt/b.tra Mhb Marv f Mri eb

Cations(0 = 23) 8.210 8.305 0.000 0.000 0.166 0.077 0.076 0.090 0.866 1.699 0.018 0.037 2.233 1.814 0.089 0.157 2.430 2.171 0.212 0.177

7 8

92064 gt/b.t ra

Mhb Mhb

Whole-rock major and trace element chem- istry

Four samples were selected for chemical analyses:101252represent s the homogeneous sheet of trachyan- desite;101253cis a sing leblackglob - ular body about 5 cm in diameter from the emulsified type of rock;

101253a is a collect ion of dark glob- ules from the emulsifi edrock hand- picked from the mixed rock; and 101253bis the wholeemulsifiedrock composed of basic and acid parts.

The results are presented in Table 5 together wit h the rangesin chemical composition of the varioustypesof trachyandesitefrom net-veinedcom- plexes examined by Morogan &

Sorensen(1994).

The chemicalcompositionof the homogeneous massive trachyan- desite from Serrnyr falls within the range in composition indicated for the grey type of trachyandesite.The singleblack globule of basic rock and the collect ion of dark globules fall 49.02

0.9 1 4.06 14.98 0.65 13.27 10.66 2.04 0.52 96.11

7.361 0.639 0.103 0.080 1.651 0.083 2.970 1.715 0.594 0.100

1.715 0.309 0.409 0.230 0.64 49.26

1.13 4.63 16.04 0.47 12.97 11.02 2.35 0.64

ed Mhb

98.5 1

9 10

1.740 0.487 0.607 0.000 0.59 7.26 1 0.739 0.125 0.065 1.977 0.059 2.849 1.740 0.672 0.01 20 51.03

0.59 3.23 15.49 0.46 14 .07 10.84 1.80 0.41 97.92

7.495 0.505 0.065 0.054 1.90 3 0.057 3.080 1.706 0.513 0.077

1.706 0.138 0.452 0.000 0.62 50.7 8

0.70 3.81 14.51 0.54 14.26 10.81 1.70 0.39 97.50

7.455 0.545 0.077 0.114 1.781 0.067 3.120 1.700 0.484 0.073

1.700 0.14 1 0.416 0.000 0.64 98.10

ed

49.10 0.80 4.69 16.76 0.37 12.65 10.82 2.33 0.58 6

7.281 0.719 0.089 0.101 2.078 0.046 2.796 1.719 0.670 0.110

1.719 0.071 0.70 0.000 0.57 54.52

0.67 0.50 22.91 0.29 7.99 0.96 7.35 0.91 96.10

0.094 1.906 0.442 1.220 0.52 53.32

1.43 0.42 19.21 0.14 9.73 0.54 8.14 1.08 94.01

0.056 1.944 0.698 1.608 0.72 50.31

0.77 3.38 16.45 0.27 12.89 11.19 1.71 0.36 97.33

7.474 0.526 0.086 0.066 2.044 0.034 2.584 1.781 0.493 0.068

1.781 0.136 0.425 0.000 0.58 97.25 51.66 0.58 2.77 15.70 0.53 13.39 10.64 1.77 0.21 2

act

7.623 0.377 0.064 0.105 1.937 0.066 2.945 1.682 0.506 0.04 0

1.682 0.202 0.344 0.000 0.60 49.66

1.00 4.67 15.46 0.30 13.91 10.77 2.24 0.45 98.46

7.275 0.725 0.110 0.081 1.894 0.037 3.037 1.691 0.363 0.084

1.691 0.149 0.571 0.000 0.61 1 101252 h.b.tra ed

Tot al SiO, TiO, AI,O ) FeO MnO MgO CaO Nap K,O Sample Rocktype*

Name**

Si AI/V Ti AIVI Fe"

Mn Mg Ca Na K

CaB NaB (Na+K)A Fe)' Mg/Mg +Fe

TOMANDERSEN,V/OR/CAMOROGAN&HENN/NGS0RENSEN NGU-BULL442, 2004 - PAGE33

Tab le 3.Rep resentative com pos itionsof pyroxenefromSerrnyr, a

1 Sa m ple 101252 Rocktype* h.b.tra

2 3

101254 b.tra

4 5 6 7

101269 b.t ra/gt

Granites,Myklearea 1.5

Si0₂ Ti0₂ AI203

FeO MnO MgO CaO Na₂₀ K20

50.61 1.11 4.32 16.92 0.52 13.12 11.08 1.77 0.46

50.90 1.10 4.51 16.07 0.52 13.53 11.00 1.76 0.53

54.99 0.16 1.81 12.82 0.44 16.87 11.81 0.79 0.19

51.23 0.53 1.92 9.26 0.47 12.67 23.40 0.40 0.08

50.62 1.03 3.02 7.71 0.56 13.42 23.04 0.54 0.05

48.79 2.11 4.13 9.61 0.24 13.70 20.83 0.57 0.00

53.71 0.27 1.8 7 14.60 0.75 15.42 11.53 1.49 0.00

en

l -

<0

co"'i::

t-

en

_1.0

co

Age

=

²⁷² +1/-6Ma Initial87Srfl6Sr=0.70 33±0.0032

Robustregression

*e.b.t ra=em ulsified basaltictrach yand esite;b.tr a=basaltictrachyan - desit e; gt=grani te

Q 1.6

J 0.3

End mem ber s

Wo 26

En 42

Fs 32 2.0

200

1.5 100

0.5 0.705

0.703 0.0 0.711

0.5

o

0.713 b

en

l - ^0.709

<0

co"'i::

t-

en

0.707 co

Fig.6.Rb-Srisoch rondiagr am a:Gran it es.b:Basaltic trachyan d esit es, com pa redtothegraniterefer enceline (solidline)andits errorenve lope (broken lines).

26 47 27 1.9 0.2 2.004 0.000 0.008 0.082 0.002 0.454 0.024 0.858 0.461 0.108 0.000 99.64

44 40 16 99.98

1.818 0.182 0.059 0.000 0.105 0.195 0.00 8 0.761 0.832 0.041 0.000 1.9 0.1

48 39 13 1.880 0.120 0.029 0.012 0.091 0.149 0.018 0.743 0.917 0.039 0.002 1.9 0.1 99.99

48 36 16 1.9 0.1 99.96

26 48 16 1.8 0.2 99.88 Cations(0=6)

2.038 1.91 8 0.000 0.082 0.004 0.015 0.079 0.003 0.000 0.083 0.498 0.207 0.014 0.01 5 0.93 2 0.707 0.469 0.938 0.057 0.029 0.009 0.004

26 44 30 1.6 0.3 1.90 3 0.097 0.031 0.102 0.085 0.417 0.016 0.754 0.441 0.128 0.025 99.92

1.90 0 0.100 0.031 0.091 0.098 0.433 0.01 7 0.734 0.446 0.129 0.022 99.91

Si AIIV Ti AiVI Fe³+

Fe2+

Mn Mg Ca Na K Total

chemically between thehomog eneoustrachyand esite and the composition of thehybridtypesanalysedby Morogan&

Sorensen (1994), whereas the mixture of basic and acid rocks (10 1253b) falls beyond the rang e indicated for the hybrid,but still homogeneou stypeofMoroga n&Sorensen (1994).Thesingleblackglobule(101253c)and thecollect ion of dark globules (101253a) diffe r from the hom og eneous trachyandesite (10 1252) in their distinctlyhigherNa₂0 and low erKp,Rb and Ba which indicatesthatthey havea lower contentof potassium feldspar.Thesingle blackglobulealso has low ercontents of REE.lnthechondrite-normalisedREE diagr am (Fig. 5), the homogeneou s basic rock (101252) show sa st rongenrichment in LREErelati ve to HREE and no Eu anomaly,as describ edby Morogan &Ser ensen,1994,fig.

13)for the grey and black trachyand esite.The em ulsified rocks(101253 aand b) display weak Eu anomaliesand an enri chment in the HREE, as also found by Morogan &

Sor ensen (1994)for the hybrid trachyand esit e.

---cr101252homogeneou strachyande site

-+-101253c black globule - 0 -101253a composite.black - 0 -102253b black emulsified

Fig. 5 Chondrit e nor m alized REE diag ram s.Cho nd ritic values from Boynton(1984).

Ranges:

~ ^Hybrid

I1III11111 Black Grey 10

La Ce Nd Srn Eu Tb Yb Lu

100

:g2 co s:o

1000

NGU-B U L L 44 2 , 2004 -PAGE 34 TOM ANDERSEN,V/OR/CAMOROGAN&HENN/NGS0RENSEN

Table4.Compo sition s ofiron-tita niumoxides.

2003).The ageind icated by the regres-

lA) IImenite (B) Magnetite sion line is indi stinguishable from

1 2 3 1 1 3 whole-rock Rb-Srisochron ages of 270

Sam ple 101 254 1012 69 92064 Sam p le 101253 101269 92064

± 4 Ma for syenitefrom the Siljanarea Rock type b.t ra b.t ra/gt gt/b.tra Rocktype e.b.tra b.tra/gt gt/b.tra

(Sundvoll & Larsen 1990)and 271 ± 2

sio ,

0.23 0.42 0.26

sio ,

0.16 0.16 0.35 Ma for ekerite from the Eikern pluton

TiO, 50.01 50.01 50.30 TiO, 0.28 0.51 0.00

(Rasmussen et al. 1988). The initi al

AI,03 0.00 0.17 0.00 A/,03 0.00 0.19 0.00

Cr,03 0.00 0.01 0.00 Cr,03 0.02 0.08 0.06 87Sr/⁸⁶Sr ratios of those isochrons

FeO 47.17 45.91 42.57 FeO 92.62 91.14 91.84 (0.7042±0.0003 and 0.7053 ± 0.0006,

MnO 2.59 3.06 3.67 MnO 0.21 0.14 0.00 respectivel y)are also indistinguishable

NiO 0.03 0.00 0.12 NiO 0.00 0.00 0.00 from the initial ratio of the present

MgO 0.00 0.20 0.00 MgO 0.35 0.15 0.00

regression line,with in it slarge uncer- Tot al 100.03 99.78 96.92 Total 93.64 92.37 92.25 tainty.The poor fit may be due to a het-

Cati on s(0=2) _Cations

°

^{=3) erogeneousinitial S}r isoto piccomposi-

Si 0.006 0.011 0.007 Si 0.006 0.006 0.014 tion on the scale sampled here,or to a

Ti 0.946 0.946 0.984 Ti 0.008 0.0 15 0.000

minordisturbance of some of the sarn-

AI 0.000 0.005 0.000 AI 0.000 0.000 0.082

pies wit h very high Rb/Sr;the elevated

Cr 0.000 0.000 0.000 Cr 0.001 0.002 0.002

Fe 0.992 0.966 0.926 Fe 2.959 2.955 2.985 Rb/Srand low Sr concentration make

Mn 0.055 0.065 0.081 Mn 0.007 0.005 0.000 these rocks suscept ib leto lossof radi-

Ni 0.001 0.000 0.003 Ni 0.000 0.000 0.000 ogenic Sr during late-stagehydrother-

Mg 0.000 0.007 0.000 Mg 0.020 0.009 0.000

mal alterationand recent weathering.

Fe3• 0.096 0.082 0.019 ^Fe3• 1.971 1.947 1.971 The samples of grey, black and

Fe'· 0.896 0.884 0.907 Fe'· 0.987 1.008 1.014 emulsifie d trachyandesite have higher

Sr concent rations (133-78 1 ppm) and

End members% End members% correspondingly low 87Rb/86Sr(= 1.82).

iI 95 96 99 ulv 2 5 0 All points plot above the regressionline

hm 5 4 1 mt 98 95 100

0.7100 0.7080

Skienbasalts VestfoldandJel0Ybasalts Larvikite.Larvik pluton Syenite and granite Porphyritic syenite.lae Mykle Preferredmantlesource, Vestfoldbasalts (Neumann etal.2002)

*

86Sr^{/ 86S}r_t 0.7060

0.7055

°

Grey trachyandesite - -~ • Blacktrachyandesite

, 0 Dyke

2

o

Emulsified trachyandesite

± a 0 Granite 0.7040

. '

•• •

, ~

' .

c <):>

!

!

\

\\.

t=272

M V

3 -

2 0.7040 5

0-+---;;-+- + -- --'--- - - - -'>-- - 1

-5 0.7020

10+-~-'-~--l.-~-+~--'-~--'-~---'~---''--'---l

-cZ

W

Fig.7.Sr andNdisot opic composi tionsat272Ma.Theexpan d eddet ail in thelower left part ofthe diagram showsthe com posi tionsof black and emulsifi ed trach yand esit es at272Ma,with±2crerror bars, where these exceedthe sym bo lsize(sy m bo lsasin themainpart of thefigure).

Blackarro w s:Mixin gtrend s illust ratin ghydrotherma l(ho rizont al arrow) and bulk (sloping arrow) contamination trends of mant le-derived magma with old,crustal mat erial.Sourcesof reference data:Skien basalt s:Dunworth etal.(2001),Vest foldand Jel0Ybasalts:Neu ma n net al.(2002),Larvikite,syen iteand granite:Neum ann etal.1988 ,Tro nnes&

Brandon(1992),Porphyrit icsyenite:Andersen etal.(2004).Thedyke is a disruptedbasicdykedescribed by Morogan&Sorensen(1994).

Rb-Sr and Sm-Nd isotope systematics

Rb,Sr,Sm and Nd concentrations in 10 samplesofbasalti c trachyand esit e,and6samples of granite were determi ned byisot op edilut ion analysis,andSrandNd isoto peratios by thermal ionization mass spect romet ry, using Finn igan MAT262 and VG 354 mass spectrometersin the Laboratory of Isotope Geology at the Mineralogical-Geolog ical Museum,Universit y of Oslo (Table6).Chemicalseparatio n, spikingand analytica lprocedureswere thesame as used in Andersenet al.(2001). Duringtheperiodof analysis,theNBS SRM 987 Sr isotope standard gave 87Sr/86Sr = 0.710190 ± 0.000050 (Zo, and the John son and Matthey batch No.

S819093A NdP3gave143Nd/144Nd = 0.511101±0.000013 (Zo). Samples 101252,101253a,b,c, were analysed at the Geological Institute,University of Copenhagen,bymethods described inAndersen etal.(2004). The mean value for the inte rnal JM Ndsta ndard(referenced against La Jolla)during the period of measurement was0.511115for143Nd/144Nd, with a 2a externalreproducibilityof±0.000013(fivemea- surements ).The mean87Sr/86Sr value of the NBS987 Srstan- dard was 0.710248 with a 2a external reproduci bility of 0.000011 (four measurements).Geochron ologic al calcula- tionsweremadeusing IsoplotlE x3.0(Ludw ig 2003).

The sixsamplesof granitehavelowSr concent rations(3- 37 pprn),and high 87Rb/86Sr ratios (9.8-208),and define a poor (MSWD=43) correlati on line with an ageof272+1/-6 Ma andan init ial87Sr/86Sr rati o of0.7033±0.0032(Fig. 6a), using the robust regressionalgorithminIsoplotlEx(Ludwig

TOMANDERSEN,V/OR/CA MOROGAN

s

HENN/NGS0RENSEN NGU-BU L L442, 2004 - PA G E35

Table5. Chemicalanalysesof trachyandesiteshee tandemulsified typeof enclavesfromSormyr,NWoflake Mykle,theOslo igne ousprovince together withanalysesquoted from Morogan& Serensen(1994).

101 252 101253c 101253a 102253b rangein range^In range in

homogeneous singleblack hand-picked totalanalysisof composi tionof compos itio nof comp osition of sheetof globule in conce ntrateof emulsified grey typeof blacktypeof hybridtype of trachyandesite emulsified darkpart of trachya ndes ite trachyand esitc1) trach yande sitc') trachyandesi te' )

trachyandesite emulsified comprising trachyandesitc basieandacid

components Weight percent oxides

Si02 51.29 54.33 54.95 58.13 50.6-52.1 51.9-52.1 55.0-56.3

Ti02 2.89 2.53 2.47 2.08 2.6-3.1 2.6-2.7 2.1-2.2

AI20 3 14.19 14.19 14.32 13.86 14.2-14.6 14.5-14 .8 14.7-15.0

Fe20 3 3.23 3.13 3.38 3.45 0.8-3.2 1.1-2.2 1.8-2.6

FeO 7.30 6.43 5.82 4.46 7.3-9.2 7.3-8. 5 5.7-5.9

MnO 0.23 0.22 0.22 0.24 0.2 0.2 0.2

MgO 3.51 3.23 3.01 2.47 3.3-4.2 3.3-3.4 2.5-2.7

CaO 5.48 4.89 4.85 4.12 5.4-6.5 5.6-5.9 4.2-4.5

Na20 5.01 7.18 6.55 4.94 4.2-5.3 5.2-5.4 5.3-5.5

K20 3.07 0.63 1.39 3.75 2.3-3.4 3.1-3.2 3.5-3.9

P20^j 1.73 1.47 1.43 l.21 1.0-1.8 1.6 I.1-3.1

loi 1.25 0.8l 0.86 0.70 1.6-2.3 1.3-1.5 1.5

total 99. 18 99.04 99.25 99.42

CIPW norm

q 0 0 0.77 6.68 0 0 0-0.06

/le 0 0 0 0 0-0.65 2.08-2.89 0

hy 1.53 5.44 8.22 5.44 0.28-7.10 0 2.01- 8.92

Partsper million

Sc 19.2 17 16.5 14.6 18.0- 19.7 17.9- 19.0 14.8-16.6

Cr 3 4 3 <3 3.0-3.6 3.0-3.4 4.0-4.1

Rb 141 66 109 202 106-124 81-132 119-135

Sr 494 328 355 322 503-739 515-528 382-412

Pb 10 II 9 14

Ba 1020 127 270 683 727-1090 1030-1060 913-9 16

Zr 475 547 565 605 304-506 475-536 717-771

Hf 13.6 n.d 15.4 17.2 8.1- 11.2 10.9-11.9 16.5-18.1

b 163 133 128 132

Ta 6.0 n.d 7.1 7.6 3.7-5.2 5.1-5.4 6.8-8.0

Y 79 87 86 87 48-68 61-86 67-76

Th 9 10 13 19 5.3-7.9 6.9-16.8 13.7-2 1.8

U n.d. n.d n.d n.d n.d 2.8 4.9-5.2

Cs 6.1 n.d. 6.2 4.0 3.9-5.2 1.8-4.5 2.2-6.4

La 100 54 68 74 61- 100 94- 102 101-111

Ce 232 150 186 174 137-21 5 203-22 4 226-235

Nd 115 92 102 91 78- 116 109-117 112- 116

Sm 20 n.d. 20 19 12.5-1 7.8 18.2-19.8 18-18.1

Eu 5.8 n.d. 5. 1 4 3.7-5.9 5.9-6.0 5.1-5.5

Tb 3.0 n.d. 3.2 3 1.92-2.63 2.58-2.94 2.58-2.70

Yb 8.1 n.d. 5.5 8.1 4.33-5.76 4.97-7.12 6.34-7.55

Lu 1.0 n.d. 1.2 1.2 0.61-0.73 0.71-0.87 0.83-0.94

Zn 17 99 94 91

Ni 13 4 4 3

V 193 135 141 112

Cr 3 4 3 <3

Ga 25 27 28 27

Th/L a 0.09 0.19 0.19 0.26 0.07-0.08 0.07-0 .16 0.14-0.20

Th/Ta 1.50 1.83 2.50 1.35- 1.54 1.36-3.11 2.01-2.72

Analysedatthe Geological SurveyofDenmark andGreenlandandtheGeologicalInstitute, Universityof Copenhagen (J.c.Baily)and TracechemA/S,Copenhagen(R.Gwozdz).

I)from Morogan andSorensen(1994). n.d.

=

not analysed

NGU-BULL442, 2004 - PAGE 36 TOMANDERSEN,V/OR/CA MOROGAN

s

HENN/NG S0RENSEN

Ta ble 6.5rand Nd isotopedata

Sample Rb Sr 87Rb/8'Sr 87Sr/8'Sr +-2cr Sm Nd'47Sm/'44Nd 143Nd/'44Nd +-2cr 87Sr/8'Sr

pa rtspermillion pa rt spe r million 272 Ma

Basalt ictracbyandesites

92061 dyke(dark) 125 781 0.4637 0.70610 0.000011 20.1 108 0.1138 0.512598 0.000007 0.704310

23279 black 25 133 0.5345 0.70751 0.000043 5.69 30.8 0.1124 0.512630 0.000009 0.705440

23289 black 118 412 0.8305 0.70786 0.000042 22.2 123 0.1098 0.512604 0.00000 6 0.704643

77219 black 136 536 0.7337 0.70716 0.000009 21.0 112 0.1144 0.512609 0.000010 0.704 318

77192 black 80 527 0.44 10 0.70629 0.000013 22.3 122 0.1117 0.512621 0.000010 0.704 585

78312 black 138 384 1.0422 0.70839 0.000010 22.8 125 0.1111 0.512620 0.000005 0.704352

77232 grey 112 488 0.6616 0.70679 0.000056 22.3 121 0.1124 0.5126 18 0.000008 0.704 225

77238 grey 124 507 0.7076 0.70702 0.000012 23.5 125 0.1145 0.512625 0.000007 0.704 285

77241 grey 109 734 0.4283 0.70636 0.000087 15.4 82.0 0.1144 0.512526 0.000007 0.704 701

77191 grey 124 505 0.7111 0.70708 0.000024 22.4 121.9 0.1118 0.512601 0.000006 0.704 330

Emulsified enclaves

H5101252* black,homog 141 494 0.8260 0.70744 0.000023 20.0 104 0.1159 1 0.512604 0.000005 0.704240 H5101253a* black emulsified 109 355 0.8886 0.70784 0.000017 19.3 95.1 0.12274 0.51261 5 0.000005 0.704401

H5 101253b* totalmixture 202 322 1.8155 0.71146 0.000023 17.7 89.3 0.11982 0.512611 0.000004 0.704435

H5101253c* sing leblackglobule 66 328 0.5823 0.7067 51 0.000020 17.9 91.4 0.11864 0.512621 0.000006 0.7044 97

Granites

86044 Medium-gra ined gra nite 82 24 9.817 0.74226 0.000009 7.78 44.4 0.1068 0.512622 0.0000 10 0.704271 86069 Fine -gra ined gra nite 236 18 38.6 1 0.85290 0.000022 16.6 72.0 0.1408 0.512676 0.000010 0.703461

86045 Eke rite 261 4 208.1 1.51013 0.000029 18.1 70.8 0.1559 0.512673 0.000007 0.704688

86057 Ekerite 272 37 21.32 0.7836 6 0.000027 10.9 45.3 0.1466 0.512688 0.000009 0.70 116 1

86035 Fine-g rained gran ite 265 17 46.33 0.88289 0.000012 19.1 102 0.1137 0.512608 0.000009 0.7035 90 86018 Fine-g raine d granite 88 3 97.89 1.07818 0.000029 1.30 6.29 0.1264 0.512638 0.000014 0.6993 42

*:Analysedat theGeological Instit ute,Cop enhage n Unive rsity,Denm ar k(Robe rt Fre i,analyst).

for thegranites,but arewit hin itslarge error envelope (Fig.

6b).Time-corr ected 87Sr/86Sr and ENdat 272 Ma are com- paredto the rangesofextrusiveandint rusive rocksfromthe OsloRegion inFig.7(forsourcesof referencedata,seefigure caption ).The black and emulsified trachyandesit es show uniform initialNd isotopecompos it ion(ENd= +2.2±0.5),but show variations in87Sr/86SrmMainexcessof analyt icalerror (Fig.7,expanded detail),defini ng asub-ho rizont altrend in the diagram towardsincreasing 87Sr/86Srm Ma'Adisrupted basic dyke, and three ofthefour samples of greytrachyan- desite,have Sr and Nd isotopic compositions at 272 Ma indistingu ishablefrom the low-87Sr/86Srend of thetrend of the black and emulsified trachyande sit es, whereas the four th sam ple of grey trachyand esit e (77241) falls off toward s significantlylowe repsilonNd and slightlyincreased 87Sr/86Sr270Ma,suggestinga separatemixingtrend.

The graniticsamples show ENdat 272 Ma in the range +2.1 to+ 2.8,overlapp ing with the main group of basaltic trachyandesite.The time -corrected87Sr/86Sr ratioshave such large uncerta int ies(above),that onlytwo of the six granite samplesanalysed(Table6)plot withi n the scale ofFig.7.

Discussion

Based on petrogr aphy,mineral chemi stry and major and trace element chemistry,Morogan& Sorensen(1994)pro- posedthat the trachyand esit icmemb ersof the net-veined

compl exes arehybrid rocksformed by mixing of basaltic and trachyt ic magmas inthe deep crust. Thesehybridmag- mas were inj ected into a partly consolidated granit ic/

syeniticmagma chamberwhich led to addit ion al hybridiza- tion.

The occurre nce of edenite in the homogeneous tra- chyandesite and in the trachyandesi te hosting the granite globules indicates that the trachyandesit ic magma was underinfl uence ofagraniticcomponentduring crystalliza- tion.This inference comes from the fact that edenit iccom- posit ion s are similar to the amphiboles formed close to granit edescrib ed by Moroga n & Sorensen (1994),and are consideredto reflect P-T-Xcondit ionsof crystallizationcon- trolled by the graniticmagma.

The low-Ca augite of the trachyand esit e could be explained by rapid cooling conditions;in thiscase,possibly due to smalldropsof a hotter basic magma quicklyemulsi- fied wit hina coolergranitic magma.Theemulsified type of enclavesmay be explainedbythe fragmentationof pillows of basic magma into smaller globules which were mixed wit hthe host acidicmagma(cf.Gourgaud 1991).Thechemi- cal dataofTable 5 show,however,that the basicglobul esof the emu lsified rock(101253a,c)are chemically distinctfrom the screen of homogeneou s trachyandesite (10 1252) and also from themixedrocks(101253b).When compared wit h the homogeneous trachyandesite, the emulsified bodies have highercontents of Si0₂,Nap,Zr andY,and lower con-

TOMANDERSEN,V/OR/CAMOROGAN&HENNING S0RENSEN NGU-BULL 44 2 , 2004 - PAGE 37

Conclusions

The new field and petrograph ical observati on s present ed here, and the major and trace eleme nt data, sup po rtapetr o- geneticmodelforthe generat ion of net- veined com plexes consisting of trachyand esiti c and granitic/syen itic com po- nents as proposed by Moro gan & Serensen (1994).The mod elinvolve sa first st ageof mixing of magm as at depth, follow ed by in-sit u mingling of mafic and felsic magm as when trachyande sit icmelt s wereinjecte d intoa solidifying granitic orsyenit ic magma chamber.Sr and Nd isotopedata add further support to thismodel,and indicat e thatthetra- chyandesit ic component in the net-veined com plexes is eit her geneticallyrelatedto larvikite or basaltic lavas of the Vestfold-Jeloya type, or derived from a sim ilar mantl e source.Variationsin initial st ront iumisot ope compositi on s in the trachyandesite, which are uncorrelated wit h neody mi um isot opes, aredueto select ive int roduct io n of more radiogenic st ro nt ium by a fluidphasebefore or during trend ,most likely at t ributa b le to bulk contamination wit h mate rial wit hCNd

=

0and87Sr/86Sr272Ma

=

0.7045.Precamb rian basement rocks (Ande rsen & Knudsen 2000) or crustally conta minate d, LatePaleozoicgraniti c orsyeniti c rocksmay be suita b leconta minants(Fig.7).

The elli psoidal bodies of granit e enclosed in massivetra- chyande sitepresent a special probl em.Thegranit eis coarse- grained andcannot be distingui shedfromthemainbod y of granite enclosing thenet-vein ed comp lexes.The enclosing trachy and esite is enric hed inbio ti te upto abo ut2 cm from the contac t wit h the granit e. The granite bodies have round edellipsoid al shapesand tw o such round bod iesmay coalesce. Thefollow ing explanatio ns maybe prop osed for the originof the granite bodie s.

(1) Thegranite glo b ules repre sent lumps of partl y con- solidate d granite eng ulfed bytheintruding basicmagma.

Crystallizati on of the granite was exte nded by inclu sion in thehotterbasicmagm a, whichexp lains thelarge grain size of the graniteand the coalescenceof tw o such partl yliquid globules.Fluids expelled from the crystallizing granit ic melt may exp lain theformation of biotite at the expenseof the am p hibole of theenclosing trachyande site.A variatio n of this exp lanat ionisthat fragm ents of already con sol idated granite werecaught bytheinvad in ghot basicmagm a and weresofte ned and perh aps part ly melt ed in theirmargin al part s, which expl ain sthe round ed shapes. Reaction s wit h volatil esreleasedfrom thepartlymoltengranitefragm ent s werethe cause of the formation of biotit e in thehostbasic rock.

(2)The elli psoidal bodies of granite arecross sect io nsof pipesof granite invadingthetrachyande sit e.

The lack of lon gitudin al sect io nsofsuch pipe s sugges ts that explanatio n(2) isunlikely, and exp lanat io n(1)isthere- fore preferred.Thus, the em ulsified rocks show minglin g of dropl et sof basicmagm a wit hgranit ic magm a,whereas the granite ellipsoid s in trachyand esite indicate the opposi te relation ship.

0.1 0.2 0.2 0.3 0.2 0.2 0.1 0.1 0.1 0.1 0.2 0.1 0.2 0.2 0.1 0.2 0.1 0.1 0.1 0.1 +-2 0

2.10 2.71 2.30 2.43 2.81 2.67 2.14 2.12 2.13 2.38 2.10

2.77 2.35 2.28 2.63 2.61 2.53 2.60 0.66 2.23

CNd

272 Ma

tents of Ti0₂,MgO,CaO,Kp, PP s, I.o.i.,Rb,Sr, Ba and LREE,contents which fall outside therang e of the earlier analysed trachyand esitesof Tabl e 5. When compared with the mixed rocks, the black globule s have higherTi0₂, AIP 3' MgO,CaO, Nap ,pp s,l.o.i.,ScandSr,and lower Si0₂,FeO,Kp ,Rb,Ba,Zr,Hfand Th.

Thisindicatesthat acombination of mechani cal and chemi cal mixin g hasbeeninvolved in theformation of the em ulsified rockand thatthe trachyand esitic magma waschemi- cally inhomogeneou s at thetime of intrusion.

Morog an and Sor ensen (1994) used theTh/La and Th/Taratiosof the Mykle net-vein ed rocks togeth er wit hrat ios ofsome ot her rocksfrom the OsloRift,inorde r to depict mixing betw een mantle- derived magma s and material of lower and/or upper crustaIorigin.

TheTh/La and Th/Ta rati osof the hom ogen eous trachyand esite (Table 5) are similar tothoseof the grey trachyandesite from Mykle, which plotted on a mixing line between mantle and lower crustal materials (Morogan & Soren sen 1994, fig. 18).The much higher rat ios exhibited by the emulsified trachyandesite samp les (Tab le 5) indicate mixing wit h an upper crustal material ,i.e.,in a granite/ syen it emagma chamber.

All but two of the samp les of basaltic trachyand esite analysed by Morogan & Sorensen (1994) fall within the range sof87Sr/86SrandCNdat 272 Ma of basaltic lavasof the Vestfold and Jeleya regions,andof larvikitefrom theLarvik pluton (Fig.7).On the other hand,the com posit ion of the basaltictrachyande siteis distinctlydifferentfrom thatof the Skien basalt s.The trachyand esitic compon ent in the net- veined comp lexesat lake Myklemay thereforebe geneti- callyrelatedtothemod erately alkaline lavasof theVestfold- Jele y area,and/or tolarvikite,or it may havebeen deriv ed from a similar mantl e source. Themuch more alkalineand silica -undersaturatedmagm asof the Skienbasalt s,and their mantle source, cannothave contributedto the petr og ene sis of the trachyand esite in thenet-veinedcomplexes.

Thetend ency ofa sub- horizon ta l trendtoward sincreas- ing initial 87Sr/86Sr in the black and em ulsified trachyan- desites (Fig.7,expanded detail) indicates thattheblacktra- chyand esite (including theblackcomp onentsin the em ulsi- fiedrock) wasinitiallyheterog eneou sinst ro nt ium isotopes, mostlikelybecauseofselective introducti onof Srwith ele- vated 87Sr/86Sr by an aqueo us fluid prior to or during em placement. The one out lying sam p leof grey trachyan- desite,on the ot her hand,may suggest adifferent mixing +-20

0.000029 0.000027 0.000012 0.000029 0.000009 0.000022 0.000023 0.000017 0.000023 0.000020 0.000011

0.000043 0.000042 0.000009 0.000013 0.000010 0.000056 0.000012 0.000087 0.000024

NGU-BULL442,20 04 - PAGE 38

emplacementof the trachyandesiti cmelt.Ellipsoidalbodies of granit e containedin the trachyandesite represent blocks of granit e or pockets of partly solidified granit ic melt engulfed in the mafic component during the mingl ing process.

Ackno wledgements

The fieldand labor atoryinvestigat ions of HS and VMweresup ported by theGeologi calSu rveyofNorway,theDanish NaturalScienceResearch Councilandthe Carlsberg Foun dat ion.We are gratefu lforanalyses and analyticalassistance providedby TorilEnger(M ineralogical-Geolog ical Museum,University of Oslo),the Geological Survey ofDenmarkand Greenland, John e. Bailey and Robert Frei (Geological Insti tute, Cop enh agen University)andR.Gwozdz(TracechemNS,Copenhagen).

BrittaMunch and Ole BangBerthelsenassiste dwith the preparatio nof illustrations.Constr uct ivecriticismfrom the reviewers CalvinBarnes and TorePrest vik,is grate fullyacknowledged.

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