Evidence for a Palaeoproterozoic arcrelated setting western

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Evidence for a Palaeoproterozoic arc-related
setting western Pine Creek Orogen
Linda Glass Project Geologist
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Litchfield Province western Pine Creek Orogen
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Wangi Basics western Pine Creek Orogen
Wangi Basics

• A suite of mafic/ultramafic rocks
• Dominantly medium to coarse-grained quartz
  hornblende meta-gabbros, gabbronorite and
  dolerites rare basalt
• Occur as scattered outcrop/subcrop west of Giants
  Reef Fault
• Greenschist facies metamorphism - uralitisation
• Historically regarded as a homogeneous intrusive
  suite

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Wangi Basics Litchfield Province
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Magnetic imagery Litchfield Province
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Wangi mafic rocks western Pine Creek Orogen
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Wangi mafic rocks western Pine Creek Orogen
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Geochemistry of Wangi mafic rocks
Six Main Geochemically Distinctive
Suites Heterogeneous!

• 1 High-alumina gabbros and dolerites (HAG)
• 2 Depleted low-Ti gabbros (LTG)
• 3 Low-Ti dolerites (LTD)
• 4 High-Ti rift tholeiites (HTT)
• 5 Metamorphosed noritic cumulates (MNC)
• 6 Metaferrogabbro (MFG)
• Potassic rocks to SE (?lamprophyres)
• Low-Ti suite with crustal-like signature

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Geochemistry of Wangi mafic rocks
Tectonic discrimination diagram
Diagrams courtesy of WR Taylor 1999
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Chondrite and MORB-normalised diagrams
Low-Ti gabbro (LTG)
1000
100
10
100
MORB-normalised
Chondrite normalised
1
10
.1
MORB normalised
1
Chondrite normalised
.01
MORB normalised
Chondrite normalised
L
C
P
S
E
T
E
T
L
N
G
D
H
Y
T
T
S
P
Z
S
T
R
B
K
N
C
H
Y
Y
MORB normalised
r
r
a
e
Chondrite normalised
MORB normalised
m
u
o
u
r
i
d
d
m
b
b
a
f
r
y
b
e
b
h
Chondrite normalised
b
a
m
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Chondrite and MORB-normalised diagrams
Low-Ti dolerite (LTD)
1000
100
100
10
MORB-normalised
Chondrite normalised
1
10
.1
Chondrite normalised
1
MORB normalised
.01
MORB normalised
T
S
P
Z
S
L
P
S
E
E
L
R
B
K
T
N
C
H
T
Y
Y
C
N
G
T
D
H
T
Y
r
i
r
r
f
e
b
a
e
r
b
h
a
m
u
o
b
u
m
d
b
a
b
d
y
m
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Chondrite and MORB-normalised diagrams
Plagioclase accumulative suite High Alumina
Gabbro (HAG)
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Chondrite and MORB-normalised diagrams
Potential parental liquids suite HAG
Eu/Eu 1
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Chondrite and MORB-normalised diagrams
High-Ti rift tholeiite suite (HTT)
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Chemical Evolution Plots
Chemical Evolution Plots High Alumina Gabbros
Dolerites suite
Combination crystal accumulation and
fractionation can be modelled. High alumina
because magma was hydrous and therefore plagioclas
e crystallisation suppressed until very late stage
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Geochemistry of Wangi mafic rocks
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Geochemistry of Wangi mafic rocks
Geochemistry

• Heterogeneous suites
• Unusual highly aluminous suites Al2O3 gt17wt
  coupled with high CaO
• Positive Eu anomalies (plag accumulative) coupled
  with positive Sr and negative Nb -Ta
  arc-signature
• Arc signature present in rocks with flat Eu
• LTG have negative sloping REE patterns depleted
  source Troodos type high-Ca boninites
• LTG and LTD have positive ?Nd values
• Low-Ti dolerites similar to primitive arc
  tholeiites

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Links to the Halls Creek Orogen
Excerpt from Carson et al., 2006
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Chondrite and MORB-normalised diagrams
Depleted Tickalara Metamorphics Kimberley Region
100
1000
10
100
1
10
.1
MORB normalised
1
.01
Chondrite normalised
T
T
S
P
Z
S
T
L
P
S
E
T
E
T
L
R
B
K
N
C
H
Y
Y
C
N
G
D
H
Y
r
i
r
r
a
f
r
a
e
u
u
b
e
b
h
m
o
b
a
m
b
d
d
m
b
y
Tickalara geochemical data from Sheppard et al.,
1999
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Conclusions
Implications Wangi mafic suites

• Heterogeneous
• Arc signature some suites from a very
  depleted source
• HAG Subvolcanic magma chamber metamorphosed
• Results link with GSWA model for Kimberley Region
  Tickalara and Wangi LTG suite similar to
  Troodos back-arc basin
• Juxtaposition of mid-level suites against
  high-level extrusive rocks
• VHMS potential? Cu Zn