Consequences of magmatic intraplating:Crustal melting and magma contaminationin the Norwegian Caledonides

Calvin BarnesAaron YoshinobuTore PrestvikGreg DumondMelanie Barnes Øystein Nordgulen

Norw

ay Sw

eden

Finlan

d

Magmatic intraplating:

Emplacement of hot, mafic magmainto lower or middle crust.Consequent crustal melting, thought by some to be the principalsource of granitic magmas.

Possible mafic magma evolution due to:--Fractional crystallization (heat lost to

melt host rocks)--Magma mixing--Assimilation

mafic underplateor intraplate

pluton emplacement

zone of crustal meltingand hybridization

Kvaløy

SklinnaHortavær

Vikna

HNC

KNC

Leka

Bindalsf jord

Tosen Majavatn

Namsskogan

Har ran

RNC

MOSJØEN

RNC MO I RANA

Dønna

Ran afjorden

Korgen

V efs

nfjo

rd

Røssvatn

HattfjelldalVega

Eite

råda

len

BRØNNØY-SUND

Velf jo rd

Sjo na

0 25 km

Anatectic granitoidsTourmaline graniteGranite, g ranodi oriteQuartz monzonite, syenitePorphyrit ic granitePorphyrit ic granodioriteDiorite, tonalite, granodi orite, trondhjemiteGabbro, diorite, monzodioriteMeta-supracrustal rocks of the HNC Metasupr acrustal rocks of the RNCGreenstone, gabbro, ultramafic rocksLeka ophiolite complex Køli Nappe ComplexWestern Gneiss RegionThrust / inferred thrust

Helgeland NappeComplex

Laurentian affinity.

Taconian-styledeformation:east-dipping, west-vergent thrust faults.

Bindal Batholith:475 to 430 Ma

TIMING

1. 500 to 490 Ma. Arc-relatedOphiolites develop between large continental fragments. Locally-derived cover sequences.

2. 477 to 468 Ma. Medium-grade metamorphism of ophiolite fragments and cover sequences.High-grade metamorphism of the shelf sequences. Migmatization of appropriate lithologies.

3. 468 to 448 Ma. Imbrication of alternating thrust slices of medium- and high-grade rocks.

4. 448 to 435 Ma. Emplacement of dioritic to granitic plutons.

high SiOstage 2

2

high K Ostage 2

2

N

0 1km

Hillstadfjellet

1

1

1

Akset-Drevli

Sausfjellet

x

Sva

rtho

pen

tourmalin

e granit

e

x

monzonite

monzodioritedioritega bbro

quartz monzonite

quartz diorite

quartz monzodiorite

within plutons: dikes, xenoliths, hornfels, etc.outside plutons: contact granitemetasediments, etc.

pyroxenite

migmatitic metapeliteand meta-arenite, marblenon-migmatitic cover sequences unconformable over ultramafic rocksperidotite

contac t granite

Velfjord plutons

tourmaline granite

x

x

x

x

x

x

x

x

area of Fig. 2B

area of Fig. 2C

Aunetpluton

porphyritic granite

VELFJORD448 to 445 MaPluton emplacement at7 – 8 kbar; liquidus Tsnear 1240ºC-----intraplating.

Melting of pelitichost rocks within1 km of contact.

Local concentrationof “contact granite”.

SAUSFJELLET PLUTONTwo intrusive stages.In Stage 2, quartz, hornblende,incompatible elements, δ18Oall increase from central to west

Stage 1

Stage 1

Stage 2.central zone

Stage 2.western/annular zone

Nonsdalenpluton

7244

390

7250

384

384

7250

peliticmigmatite

marble & calcareousmetasedimentary rocks

monzonitemonzodiorite

dioritegabbro

quartz monzonite

quartz diorite

quartz monzodiorite

West side in contact withmetapelitic diatexites,which are partly meltedin the aureole.

East side in contact with marbleand related refractory metasedimentary rocks.

Stage 1

Stage 1

Stage 2.central zone

Stage 2.western/annular zone

Nonsdalenpluton

72447244

390

3907250

384

384

7250

hornblende +/- pyroxene

three pyroxenes +/- biotite +/- hornblendeaugite + opx +/- biotite +/- hornblende

pyroxene + hornblende

European Datum 50; Zone 33

late amphibole after pyroxene

B

a

a

a

a

a

a

a

a aa

a

a

a

a

a

a

a

a

aa

a

a

a

1 km

amphibole cpx monzodiorite amphibole cpx nepheline diorite

0

5

10

15 Fe total (as Fe O )2 3

0 5 10 15 MgO

0

2

4

6

8

10

12

14

16 CaO

5 10 15 MgO

40

50

60

70 SiO2

5 10 15 MgO

0

0.5

1.0

1.5

2.0

2.5 TiO2

0 5 10 15 MgO

N

N

N

melts?

late-stage granitic dikes

Stage 1

Stage 2central zone diorite

western/annular zone

western/annular zone dikes

central zone anorthosite

N

compositions of contact migmatite and related granites

0

5

10

15

10

15

20

25

30

0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 0

1

2

3

4

5

6

0 2 4 6 8

Fe total as Fe O2 3Al O2 3

TiO2

MgO

K O2

MgO

parental magmas?late-stage granitic dikes

Stage 2central zone diorite

western/annular zonewestern/annular zone dikes

central zone anorthosite

700 900600 800

4

6

8

10

T ( C)o

P (k

bar)

VI

kyanite

andalusite

sillimanite

Opx As

Grt Crd

Grt Sil

Spl Crd

Bt G

rtO

px C

rd L

Bt As

Grt Crd

L

Ms A

bAs Kf

s L

Ms Ab

As Kf

s V

Bt G

rt Opx As LNaKFMASH

0.9

0.8

0.7

0.6

0.6

0.7

0.9

0.8M

s Ab

VAs

L

Grt Kfs L

Bt As

Grt As LCrd Kfs

Grt Kfs L

Crd Bt

I

IIIII

IV

V?

?

B

Regional migmatites:muscovite + biotite ± garnet ± sillimanite ± staurolite

Contact diatexites:sillimanite + garnet + biotite

SAUSFJELLET PLUTONTwo intrusive stages.In Stage 2, quartz, hornblende,incompatible elements, δ18Oall increase from central to west

Stage 1

Stage 1

Stage 2.central zone

Stage 2.western/annular zone

Nonsdalenpluton

7244

390

7250

384

384

7250

peliticmigmatite

marble & calcareousmetasedimentary rocks

monzonitemonzodiorite

dioritegabbro

quartz monzonite

quartz diorite

quartz monzodiorite

West side in contact withmetapelitic diatexites,which are partly meltedin the aureole.

East side in contact with marbleand related refractory metasedimentary rocks.

6

8

10

12

14 18O

0 5 10 15 MgO

western/annularzone

central zone

host migmatitesand granite

Sausfjellet plutonStage 2.

6

7

8

9

10

18O

100 200 300 400 ppm Zr

. 8

.7

. 8

.7

. 9

. 7

. 5

.3

. 7

. 5

parent?cental zone diorite

western/annular zonelow-MgO dikes

central zone anorthosite

Stage 2

0.5 (0.95)

1.2 (1.32)

0.9(1.14)

0.7(1. 05)

1.62 (1.6 4)

0.4 (0.89)

0.3(0.85)

0.2 (0.81)

0.1(0 .79)

M2

E2

E3

E1M1

M3

M4

Energy-conserved AFC

Fractionalcrystallization

Crysta

l acc

umulat

ion

δ18O

ppm Zr

One tectonic scenario for theHelgeland Nappe Complex

Arc-related ophiolites develop between large continental fragments. Locally-derived cover sequences.

Medium-grade metamorphism of ophiolites and cover sequences.High-grade metamorphism of the shelf sequences. Migmatization of appropriate lithologies.

Imbrication of alternating thrust slices of medium- and high-grade rocks.

Emplacement of dioritic to granitic plutons. Meltingin some pluton aureoles.

stromatic migmatitediatexitediatexite dikes

contact granite

high K leucosomesin situ

Na+Ca

Fe+Mg+Ti

K

garnet

biotite

Ksp

plag ms schist metawacke

metawackewith excess H O2

High-K (granitic) leucosomes.

Migmatites are refractory.Diatexites are the most refractory.

Contact granites:1. A distinct compositional trend.2. Felsic part of trend overlaps high-K leucosomes.3. Mafic part of trend IS NOT co-linear with migmatite trend.

K

K

stromatic migmatite

diatexite

high K leucosomes

Fe+Mg+T i

garnet

biotite

biotite-dehydrationmelting of metawacke

Na+Ca

Fe+Mg+Ti

garnet

biotite

Ksp

plag

+restite

+Ksp+plag

magmamixing

A

B

22 to 24% melting%

70% felsic me lt 8% mafic melt17% feldspar

3% garnet<1% ac cesso ries

conta

ct g

ranite

contac t granite

B

hybrid dikefeed s contac tgranite

dike to anatectic granite pluton

Velfjordpluton

migmatite

mafic dike

zone of hybridization

“synplutonic”mafic dike incontact graniteA

C

contact granite

stromatic migmatitediatexitediatexite dikes

low K leucosomesin situ

dikes in wall rocksdikes in plutonscontact granite

high K leucosomesin situ

Na+Ca

Fe+Mg+Ti

K

garnet

biotite

Ksp

plag ms schist metawacke

metawackewith excess H O2

N17

restiteunmixing

+Ksp

+plag+bio

-12

-10

-8

-6

-4

-2

0

2

epsi

lon

Nd

(448

Ma)

40 50 60 70 80

field of Velfjordplutons

SiO2

stromatic migmatitediatexitediatexite dikesquartz-rich migmatite

low K leucosomesin situ

dikes in wall rocksdikes in plutonscontact granite

high K leucosomesin situ

High-K (granitic) leucosomes:isotopically similar to migmatites.

Contact granites: Nd and oxygen isotopes are intermediate between leucosomes and diorites.

GEOLOGIC SETTING

Caledonian fold belt—collision of Laurentia and Baltica beginning at about 430 Ma and ending at about 400 Ma.Emplacement of four allochthons on the Baltic craton.

Uppermost AllochthonExotic to Baltica.Geologic history distinct from allochthons formed near the Baltic craton.

Amalgamated during Ordovician time,probably close to Laurentia.

Consists of ophiolite-floored metasedimentary units and high-grade shelf sequences.