thesis defence-thesis only

CONUMA RIVER AND LEAGH CREEK INTRUSIVE COMPLEXES:

WINDOWS INTO MID-CRUSTAL LEVELS OF THE JURASSIC BONANZA ISLAND ARC

VANCOUVER ISLANDBRITISH COLUMBIA

Karin FecovaM. Sc. Defense

Fall 2009

Location and Regional Geology

Vancouver Island

Queen Charlotte Islands

WR = Wrangellia Terrane

PE = Peninsular Teranne

Conum a River Leagh Creek

Scale100 km

Vancouver Is land

Conuma River and Leagh Creek intrusive complexes

Conuma River intrusive complex

Leagh Creekintrusive complex

Field observations Conuma River and Leagh Creek intrusive complexes can be interpreted as:

1. Field 2. Petrography 5. Age 6. P-T estimate4. Magma 7. Models3. Geochemistry

contemporaneous multiple pulses of crystal-poor magmas and crystal mushes

with temporal, spatial, volume, geochemical and textural variationsemplaced into host solidifying intrusions: Conuma River - dilation crack exploitation Leagh Creek - magma conduit exploitation

Conuma River and Leagh Creek intrusive complexes display:hornblendites, hornblende gabbros, hornblende diorites, tonalites

Ultramafic intrusion: olivine hornblendite

Ultramafic intrusion: hornblendite

Mafic intrusion: Spotted hornblende gabbro

Intermediate intrusion: Hornblende diorite

Felsic intrusion: Tonalite

Felsic intrusion: Trondhjemite

Conuma River and Leagh Creek intrusive complexes can be interpreted as:




numerous, contemporaneous small volume intrusions

Numerous, small volume intrusions

Numerous, small volume intrusions






1. Host intrusions- felsic - intermediate, hybridized

- vein network

HHost intrusion: tonalite

Ultramafic intrusion: hornblenditehosted by tonalite

H

Host intrusion: hybridized dioriteIntermediate intrusion: hornblende dioritehosted by hybridized diorite

Mafic intrusion: basalthosted by hybridized diorite

2. Layered intrusions- Conuma River locality

- sheets of hornblendites alternating with sheets of hornblende gabbros







- vein network


Mafic intrusion: hornblende gabbro Layered intrusion: olivine hornblendite









- vein network

3. Stocks- ultramafic to felsic

- irregular

S

A stock of hornblende gabbro

A stock of leucocratic variety of hornblende diorite

A stock of melanocratic variety of hornblende diorite









- vein network


- irregular

4. Magmatic enclaves- ultramafic to intermediate- chilled or non-chilled textures - oblate, elongate, subparallel

Magmatic enclaves

Host tonalite

Host tonalite










- vein network


- irregular

Magmatic flow

Magmatic flow Stretched mafic enclaves

Stretched, subparallel mafic enclaves

Smeared, plastically deformed hornblende gabbro










- vein network


- irregular

Magmatic flow

Magma mingling textures

Magma mingling

Petrography

1 mm


Ultramafic intrusion:Olivine hornblendite

Ol

Brown hbl

Green hbl

1 mm

Opx

Plag

1 mm

Cpx

Hbl

Hbl

Hbl

1 mm


Hbl

Hbl

Hbl

Hbl

Hbl

1 mm

Mafic intrusion: hornbledne gabbro Plag

Hbl

1 mm

Intermediate intrusion: hornblende diorite

Hbl

Hbl

HblQtz

Alkfels

1 mm Intermediate intrusion:Spotted hornblende diorite

Hbl

Hbl

Plag-Qtz gm

Plag-Qtz gm

1 mm Intermediate intrusion:Acicular hornblende diorite

Hbl Plag

Qtz

Mt

1 mm

Felsic intrusion: trondhjemite Qtz-Alk fels intergrowths

Qtz

Alkfels

Geochemistry

Picro-basalt

Andesite

RhyoliteTrachydacite

Trachyte

Phonolite

40 45 50SiO wt%2

Na

O+K

O w

t%2

2

55 60 65 70 750

2

4

6

8

10

12

14

16

Tephri-phonolite

Phono-phonolite

TephriteBasanite

Basaltictrachy-andesite

Trachy-andesite

Foidite

2

BasaltBasalticandesite

Trachy-basalt Dacite


LEGEND

Karmutsen country rock

Felsic intrusions

Intermediate and mafic intrusions

Ultramafic intrusions

Composition of intrusions: Picritic basalt - Rhyolite

LEGEND


Felsic intrusions



Calk-alkaline and tholeiitic signature

400

5

10

15

50 60 70 80SiO2

Tholeiitic

Calc-alkaline

ALEGENDFelsic intrusions



Island arc affinity

30

20

10

2 4 6 8 10Nb (ppm)

La

(p

pm

)

Orogenic Andesite

B


MnO*10 P2O

OIB-thol

ARC-thol

M ORB

OIB-alk

ARC-calc-alk

TiO2

A

5

Orogenic Andesite

N-MORB

E-MORB

Geochemistry


Crystallization modeling


SiO2 TiO2 Al2O3 FeO* MgO CaO Na2O K2O P2O5Parental KF07-P 1 1 1 1 1 1 1 1 1Model 1.95 1.44 1.11 4.37 8.50 1.06 1.03 1.00 1.59DM05-212A 1.79 1.45 1.15 4.59 8.75 0.99 1.24 0.72 1.66

0.1

1

10

Con

stra

ined

Cur

ves:

N

orm

aliz

ed t

o po

ssib

le p

aren

tal g

abbr

o (K

F07

-P)

Mineral Accumulation for Conuma River gabbro and hornblendite

Constrained by Ce

Parental KF07-P

Model

DM05-212A

CONUMA RIVER - BONANZA ISLAND ARC

Genetical link between:

Evolved sample: Hornblendite

Parental sample:Hornblende gabbro

through

Accumulation of:

OlivineMagnetitePlagioclase

Pearce element ratio diagrams

y = 0.8068x + 0.1006R² = 0.865

0.3

0.5

0.7

0.9

1.1

1.3

0.3 0.4 0.5 0.6 0.7 0.8

Pearce element ratio plot for Conuma River intrusionsCaO vs Al2O3

clinopyroxene fractionation

Al 2O

3CaOA

y = 2.0445x - 3.9836R² = 0.9276

0

1

2

3

4

5

0 2 4 6 8 10

Pearce element ratio plot for Conuma River intrusionsFeO* + MgO vs SiO2

FeO

* + M

gO

SiO2B


Magma paragenesis


Talkeetna island arc

Bonanzaisland arc

Yakounisland arcKey phases:

OlivineOrthopyroxeneClinopyroxenePlagioclaseMagnetite

Ar-Ar dating


Early to Middle Jurassic age

179.7 +/- 3 Ma184.3 +/- 2 Ma

Conuma River locality Leagh Creek locality

Pressure-Temperature estimate


Sack (1980) olivine – orthopyroxene thermometer

opx

ol

850oC +/- 20oC

cl

hbl

brown hbl

green hblErnst and Liu (1998) Al2O3 and TiO2 in hornblende thermobarometer

570-860oC3-19 kbar

green hbl

brown hbl

Pressure-Temperature estimate


Tectono-magmatic model of Conuma River and Leagh Creek intrusive complexes


Bonanza island arc

Early to Middle Jurassic age

Conuma River

Leagh CreekL

LEGEND

Paleozoic (Sicker) island arc crust

Triassic Karmutsen shallow crust

Jurassic (Bonanza) island arc surface

Jurassic (Bonanza) island arc undifferentiated intrusions

Jurassic (Bonanza) island arc felsic intrusions

Jurassic (Bonanza) island arc mafic intrusions

Conuma RiverJurassic age

L

LEGEND



Jurassic (Bonanza) island arc surface



Jurassic (Bonanza) island arc mafic intrusions

Conuma River intrusive complexTectono-magmatic model


L

LEGEND





Jurassic (Bonanza) island arc mafic magmas

Jurassic (Bonanza) island arc fractionating basaltic magmas

Mobilized fractionated basaltic magma



Leagh Creek intrusive complexTectono-magmatic model


L

LEGEND





Jurassic (Bonanza) island arc mafic magmas

Jurassic (Bonanza) island arc hybridized magmas/intrusions

Jurassic (Bonanza) island arc intermediate intrusions

Interpretation

• solidified commingled contemporaneous multiple pulses of crystal-poor magmas and crystal mushes

• with temporal, spatial, volume, geochemical and textural variations

• emplaced into host solidifying intrusions: Conuma River - dilation crack & conduit exploitation Leagh Creek - magma conduit exploitation

Conclusions Conuma River and Leagh Creek intrusive complexes display:

• numerous, contemporaneous small volume intrusions

• hornblendites, hornblende gabbros, hornblende diorites, tonalites

• calc-alkaline and tholeiitic signature of island arc affinity

• Early to Middle Jurassic age

• island arc mid-crust emplacement environment

• most of the intrusions cannot be genetically linked through crystallization modeling

• intrusions subjected to magma mingling/ mixing and assimilation processes

• magmatic flow

Dan Marshall

Derek Thorkelson

Dan Gibson

Graham Nixon

Reid Staples

Kevin Cameron

Geoscience BCMati Raudsepp from UBCTom Ullrich from UBCEfrem SpecognaHard Creek Nickel Corporation

Acknowledgements

thesis defence-thesis only

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