consequences of magmatic intraplating: crustal melting and magma contamination in the norwegian...
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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.
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