SHRIMP U–Pb zircon ages from Kutjara 1
and Mulyawara 1, northwestern South
Australia
GEOSCIENCE AUSTRALIA
RECORD 2014/05
N.L. Neumann and R. J. Korsch
Department of Industry
Minister for Industry: The Hon Ian Macfarlane MP
Parliamentary Secretary: The Hon Bob Baldwin MP
Secretary: Ms Glenys Beauchamp PSM
Geoscience Australia
Chief Executive Officer: Dr Chris Pigram
This paper is published with the permission of the CEO, Geoscience Australia
© Commonwealth of Australia (Geoscience Australia) 2014
With the exception of the Commonwealth Coat of Arms and where otherwise noted, all material in this
publication is provided under a Creative Commons Attribution 3.0 Australia Licence.
(http://www.creativecommons.org/licenses/by/3.0/au/deed.en)
Geoscience Australia has tried to make the information in this product as accurate as possible.
However, it does not guarantee that the information is totally accurate or complete. Therefore, you
should not solely rely on this information when making a commercial decision.
Geoscience Australia is committed to providing web accessible content wherever possible. If you are
having difficulties with accessing this document please email clientservices@ga.gov.au.
ISSN 2201-702X (PDF)
ISBN 978-1-922201-94-2 (PDF)
GeoCat 78792
Bibliographic reference: Neumann, N.L. and Korsch, R.J., 2014. SHRIMP U–Pb zircon ages from
Kutjara 1 and Mulyawara 1, northwestern South Australia. Record 2014/05. Geoscience Australia,
Canberra. http://dx.doi.org/10.11636/Record.2014.005.
Version: 1310
Contents
Executive Summary..................................................................................................................................1
1 Introduction ............................................................................................................................................2
2 U-Pb SHRIMP Results ..........................................................................................................................4
2.1 Unnamed granitoid, Kutjara 1 ..........................................................................................................4
2.1.1 Location details and lithological characteristics .........................................................................4
2.1.2 Zircon description .......................................................................................................................4
2.1.3 U–Pb isotopic results ..................................................................................................................5
2.1.4 Geochronological interpretation .................................................................................................6
2.2 Unnamed adamellite, Mulyawara 1 ...............................................................................................10
2.2.1 Location details and lithological characteristics .......................................................................10
2.2.2 Zircon description .....................................................................................................................10
2.2.3 U–Pb isotopic results ................................................................................................................11
2.2.4 Geochronological interpretation ...............................................................................................13
Acknowledgements ................................................................................................................................15
References .............................................................................................................................................16
SHRIMP Analytical Procedures ..........................................................................................17
A.1 Mineral separation .........................................................................................................................17
A.2 Mount preparation and SHRIMP analysis .....................................................................................17
A.3 SHRIMP data reduction and presentation .....................................................................................18
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
iii
iv
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
Executive Summary
The petroleum exploration wells Kutjara 1 and Mulyawara 1, drilled by Rodinia Oil (Australia) Pty. Ltd
in the Officer Basin in northwestern South Australia, each intersected granitic basement at depths
exceeding 2400 m. Zircons from both granites were isolated for U-Pb dating via Sensitive HighResolution Ion Micro Probe (SHRIMP), with the aim of determining magmatic crystallisation ages, and
constraining the ages of any subsequent high-grade metamorphic events. The sample from the
Kutjara 1 well yielded a magmatic crystallisation age of 1591 ± 11 Ma (all uncertainties quoted at 95%
confidence), and the zircons feature low-Th/U rims recording subsequent high-grade metamorphism at
1167 ± 7 Ma. The adamellite from Mulyawara 1 records a magmatic crystallisation age of 1168 ± 6
Ma, and contains a small number of 1615–1530 Ma inherited grains.
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
1
1 Introduction
This report contains new zircon U–Pb geochronological data obtained via Sensitive High-Resolution
Ion Micro Probe (SHRIMP) for granitic rocks from two wells in northwestern South Australia. The
Kutjara 1 and Mulyawara 1 petroleum exploration wells (Figure 1.1) were drilled by Rodinia Oil
(Australia) Pty. Ltd between June and December 2011, through Cambrian and Neoproterozoic
sedimentary rocks of the Officer Basin into granitoid basement. Details of both wells can be found in
well completion reports (Baily et al., 2012a; 2012b). These wells are the only intersection of basement
rocks below the Officer Basin for hundreds of kilometres - the nearest well would be Lake Maurice
East 1, about 185 km southeast of Kutjara 1.
The primary objective of this study is to determine the age of the granitic basement rocks from both
wells, in order to understand the basement geology of this region. This report provides detailed results
for each sample, including sample location details, zircon descriptions, analysis of geochronological
data, and a brief geochronological interpretation. Throughout this report, the term ‘granitoid’ is used as
the rock type for the Kutjara 1 sample, and ‘adamellite’ for the sample from Mulyawara 1, even though
these terms have been superseded in classification schemes, to ensure consistency with rock
descriptions in the well completion reports. A description of sample processing procedures,
preparation and analysis of SHRIMP mounts, and data reduction and presentation methods are
included in the Appendix, along with analytical session-specific details of the calibration data collected
on the reference 238U/206Pb and 207Pb/206Pb zircons.
2
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
Figure 1.1 Map of northwestern South Australia, showing the location of the Kutjara 1 and Mulyawara 1 petroleum
exploration wells (from Baily et al., 2012a).
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
3
2 U-Pb SHRIMP Results
2.1 Unnamed granitoid, Kutjara 1
Table 2.1 Summary of results: Unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851).
GA Sample No
2152082
GSSA (Registration) No
R1964851
Lithology
Granitoid
Stratigraphic Unit
Undefined
Collector
R. Dutch, W. Preiss and W. Cowley
Province/Region
Northwestern South Australia
1:250 000 Sheet
WYOLA (SH5207)
1:100 000 Sheet
WARRANGA (4839)
Location (GDA94)
129.680856ºE; 29.117775ºS
Analytical Session
130026 (see Appendix Table A.1 for parameters derived from
concurrent measurements of 238U/206Pb and 207Pb/206Pb reference
zircons)
Interpreted Age
1591 ± 11 Ma (95% confidence; 30 analyses)
Geological Attribution
Magmatic crystallisation
Isotopic Ratio(s) Used
207Pb/206Pb (204Pb-corrected)
Interpreted Age
1167 ± 7 Ma (95% confidence; 24 analyses)
Geological Attribution
Metamorphism
Isotopic Ratio(s) Used
207Pb/206Pb (204Pb-corrected)
2.1.1 Location details and lithological characteristics
This sample was collected from the base of the Kutjara 1 petroleum exploration well, northwestern
South Australia (Figure 1.1), in the depth interval 2445–2453.7 m. The sample occurs ~55 m below
the interpreted base of the Officer Basin. The sample was collected from drill cuttings, and is
interpreted to be a granitoid.
A thin section description from the Kutjara 1 well completion report (Baily et al., 2012a) indicates that a
sample of minerals and rock chips from a depth of 2442 m contains quartz, K-feldspar, plagioclase
and biotite, while other chips are classified as low-grade metasedimentary rocks.
2.1.2 Zircon description
Zircons from this sample range in length from ~60 µm to ~170 µm, with a few elongate grains up to
~250 µm in length (Figure 2.1). Most grains have euhedral to subhedral morphologies, and are clear
4
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
and colourless to light brown in colour. Cathodoluminescence images reveal that most grains have
oscillatory zoning or dark, sometimes irregularly-shaped core regions, and are generally mantled by
darker cathodoluminescence rims. Analyses focused on the range of cathodoluminescence response,
and on both core and rim regions of single grains, where possible.
Figure 2.1 Representative zircons from the unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851).
Transmitted light image is shown in the upper half; cathodoluminescence image in the lower half. SHRIMP
analysis sites are labelled.
2.1.3 U–Pb isotopic results
Fifty-eight analyses were undertaken on 48 zircon grains from the sample, the results of which are
presented in Table 2.2 and Figures 2.2 to 2.4. One analysis greater than 10% discordant and one
analysis with a common 206Pb content higher than an arbitrary value of 0.5% are considered
unreliable, and were removed from further consideration.
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
5
GA 2152082, GSSA R1964851
Unnamed granitoid
Kutjara-1
All; n = 58
0.12
1800
0.10
207
Pb/
206
Pb
1.5
1400
Th/U
0.08
1000
0
0.06
data-point error ellipses are 2s
0.04
2.5
3.5
4.5
238
U/
5.5
6.5
206
Pb
Figure 2.2 Tera-Wasserburg concordia diagram showing results of zircon analyses from the unnamed granitoid,
Kutjara 1 (GA 2152082, GSSA R1964851), coloured according to Th/U values. Open ellipse represents an
analysis greater than 10% discordant, and the grey-coloured ellipse represents an analysis with a common 206Pb
content higher than an arbitrary value of 0.5%.
The remaining 56 analyses are characterised by a wide range of U contents (41–1092 ppm), Th
contents (0–186 ppm) and Th/U (0.00–1.42). The analyses record 207Pb/206Pb ages between ~1657
Ma and ~1066 Ma, and form two distinct age groups (Figure 2.2). The MSWD for all 31 analyses in the
older age group (MSWD = 1.7) indicates that it is not a single population. If the oldest individual
(082.34.1.1; age = 1657 ± 17 Ma (1σ)) is excluded, the remaining 30 analyses combine to provide a
weighted mean 207Pb/206Pb age of 1591 ± 11 Ma (95% confidence; MSWD = 1.3; Probability of fit =
0.14; Figure 2.3).
The younger group of 25 analyses represent rims on zircon grains, and have much lower Th/U values
(generally 0.10 to 0.00). Excluding one analysis (082.24.1.1) which has a younger age ( 207Pb/206Pb
age = 1066 ± 21 (1σ)), the remaining 24 analyses combine to provide a weighted mean 207Pb/206Pb
age of 1167 ± 7 Ma (95% confidence; MSWD = 0.99; Probability of fit = 0.47; Figure 2.4).
2.1.4 Geochronological interpretation
The weighted mean 207Pb/206Pb age of 1591 ± 11 Ma (95% confidence) for 30 analyses in the older
age group is interpreted as the magmatic crystallisation age of this granitoid. As the younger
207Pb/206Pb age of 1167 ± 7 Ma (95% confidence; n = 24) is from zircon rims with low Th/U values, this
younger age is interpreted to represent a metamorphic event affecting the granitoid.
6
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
1720
1680
GA 2152082, GSSA R1964851
Unnamed granitoid
Kutjara-1
Older group; n = 31
1640
Age (Ma)
1600
1560
1520
1480
1440
Age = 1591 ± 11 Ma (95% conf.)
n = 30 of 31; MSWD = 1.3; Prob. = 0.14
1400
box heights are 2s
1360
Figure 2.3 Weighted mean age diagram showing 207Pb/206Pb ages of zircons from the older age group of the
unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851). Open box represents an analysis not included in
the age calculation.
1450
GA 2152082, GSSA R1964851
Unnamed granitoid
Kutjara-1
Younger group; n = 25
1350
Age (Ma)
1250
1150
1050
950
Age = 1167 ± 7 Ma (95% conf.)
n = 24 of 25; MSWD = 0.99; Prob. = 0.47
850
box heights are 2s
Figure 2.4 Weighted mean age diagram showing 207Pb/206Pb ages of zircons from the younger age group of the
unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851). Open box represents an analysis not included in
the age calculation.
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
7
Table 2.2 SHRIMP U–Pb zircon data from the unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851).
Sample.grain
.area.replicate
206Pb
c
(%)
U
Th
(ppm) (ppm)
232Th/
238U/
238U
206Pb
± 1σ
(%)
207Pb/
206Pb
± 1σ
(%)
207Pb/206Pb
Age (Ma)
± 1σ
(Ma)
disc
(%)
Older individual (n = 1)
082.34.1.1
-0.07
188
181
1.00
3.517
1.2
0.1018
0.9
1657
17
3
Older age group: magmatic crystallisation (n = 30)
082.14.2.1
0.01
79
85
1.10
3.513
1.6
0.1011
1.3
1644
24
2
082.9.1.1
0.07
106
100
0.97
3.679
1.8
0.1007
1.2
1638
22
5
082.42.1.1
-0.05
104
96
0.96
3.579
1.4
0.1004
1.2
1632
22
3
082.32.1.1
0.40
77
72
0.97
3.478
2.3
0.1004
2.0
1631
36
0
082.29.1.1
0.12
119
149
1.30
3.664
1.4
0.0998
1.1
1621
21
4
082.39.1.1
0.11
69
70
1.05
3.756
1.7
0.0997
1.7
1619
31
6
082.21.1.1
0.13
62
55
0.92
3.612
1.7
0.0996
1.5
1616
28
3
082.5.1.1
0.24
75
59
0.82
3.538
1.6
0.0995
1.8
1614
34
1
082.2.1.1
0.05
96
89
0.96
3.625
1.4
0.0989
1.7
1603
32
2
082.3.1.1
0.12
153
174
1.17
3.563
1.2
0.0987
1.0
1600
19
0
082.10.1.1
0.01
78
76
1.00
3.533
1.5
0.0985
1.3
1595
25
-1
082.8.1.1
0.25
107
104
1.01
3.623
1.8
0.0984
1.3
1595
25
1
082.19.1.1
0.04
234
186
0.82
3.586
1.3
0.0983
1.3
1592
24
0
082.47.1.1
0.13
180
157
0.90
3.615
1.2
0.0983
1.1
1592
21
1
082.26.2.1
0.03
134
183
1.42
3.513
1.4
0.0982
1.1
1591
21
-2
082.45.1.1
0.20
72
69
1.00
3.588
1.7
0.0982
2.0
1589
38
0
082.33.1.1
0.11
83
78
0.96
3.625
2.1
0.0981
1.6
1589
30
1
082.41.1.1
0.03
121
134
1.15
3.610
1.4
0.0979
1.1
1584
21
0
082.25.2.1
0.04
106
113
1.10
3.564
1.4
0.0978
1.2
1583
23
-1
082.23.1.1
0.12
98
106
1.12
3.561
2.2
0.0977
1.4
1582
26
-1
082.7.1.1
0.33
69
64
0.96
3.531
1.6
0.0977
1.5
1581
28
-2
082.20.1.1
0.32
118
113
0.99
3.553
1.3
0.0975
1.4
1576
27
-1
082.13.1.1
0.16
125
122
1.01
3.540
1.3
0.0971
1.3
1569
24
-2
082.44.1.1
0.08
120
119
1.03
3.510
2.1
0.0969
1.2
1565
22
-3
082.43.1.1
0.12
107
96
0.93
3.635
1.4
0.0969
1.8
1564
33
0
082.1.2.1
0.35
99
105
1.10
3.565
2.3
0.0966
1.7
1559
32
-2
082.40.1.1
0.28
72
77
1.11
3.552
1.6
0.0962
1.5
1552
28
-3
082.48.1.1
0.11
137
130
0.98
3.634
1.4
0.0962
1.2
1552
23
-1
082.24.3.1
0.45
121
112
0.95
3.665
1.3
0.0951
1.5
1529
29
-2
082.11.1.1
0.50
63
56
0.91
3.616
1.6
0.0934
2.4
1495
45
-5
5.105
2.2
0.0837
3.4
1286
66
10
Younger age group: metamorphism (n = 24)
082.15.1.1
8
-0.21
41
0
0.01
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
Sample.grain
.area.replicate
206Pb
c
(%)
U
Th
(ppm) (ppm)
232Th/
238U/
238U
206Pb
± 1σ
(%)
207Pb/
206Pb
± 1σ
(%)
207Pb/206Pb
Age (Ma)
± 1σ
(Ma)
disc
(%)
082.18.1.1
0.05
114
0
0.00
5.115
1.4
0.0801
1.5
1199
29
4
082.36.1.1
-0.02
640
25
0.04
5.051
1.0
0.0801
0.6
1199
12
3
082.12.1.1
-0.22
79
0
0.00
5.141
1.6
0.0795
2.1
1184
41
3
082.25.1.1
0.02
830
80
0.10
5.052
0.9
0.0791
0.5
1175
11
1
082.29.2.1
-0.01
860
81
0.10
5.023
0.9
0.0791
0.5
1174
10
0
082.14.1.1
0.18
150
2
0.01
5.147
1.3
0.0790
1.8
1172
36
2
082.37.1.1
0.28
74
1
0.01
5.150
1.7
0.0789
2.0
1170
40
2
082.30.2.1
0.05
720
40
0.06
5.036
0.9
0.0789
0.6
1169
12
0
082.22.1.1
0.05
905
97
0.11
5.078
0.9
0.0788
0.6
1167
11
1
082.1.1.1
0.03
872
62
0.07
5.105
0.9
0.0788
0.6
1166
11
1
082.27.1.1
0.01
909
72
0.08
5.058
0.9
0.0788
0.5
1166
10
0
082.12.2.1
-0.03
878
85
0.10
5.041
1.0
0.0787
0.5
1164
11
0
082.26.1.1
0.07
917
36
0.04
5.050
0.9
0.0786
0.9
1161
19
0
082.4.1.1
-0.02
662
10
0.02
5.067
1.0
0.0785
0.6
1160
13
0
082.35.1.1
0.01
766
94
0.13
5.061
1.1
0.0785
0.6
1160
11
0
082.46.1.1
0.14
265
2
0.01
5.131
1.1
0.0783
1.2
1155
24
1
082.28.1.1
0.12
228
1
0.00
4.997
1.2
0.0782
1.3
1152
26
-2
082.16.1.1
0.13
246
3
0.01
5.004
1.5
0.0775
1.2
1134
24
-4
082.31.1.1
0.14
121
1
0.01
4.959
1.9
0.0773
2.0
1128
40
-5
082.17.1.1
0.20
133
85
0.67
5.178
1.3
0.0772
1.8
1127
37
-1
082.38.1.1
0.09
150
1
0.00
5.090
1.3
0.0772
1.6
1126
32
-3
082.30.1.1
0.26
214
4
0.02
5.289
1.2
0.0770
1.5
1122
30
1
082.6.1.1
0.50
68
0
0.00
5.077
1.7
0.0762
3.9
1099
77
-5
1092
93
0.09
5.995
0.9
0.0749
1.0
1066
21
7
0
0.01
5.069
2.5
0.0878
4.1
1378
79
16
4.874
2.5
0.0759
23.2
1091
464
-10
Younger individual (n = 1)
082.24.1.1
0.46
Analysis >10% discordant (n = 1)
082.24.2.1
-0.51
Analysis with common
082.19.2.1
206
11.48
33
Pb >0.5% (n = 1)
65
2
0.03
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
9
2.2 Unnamed adamellite, Mulyawara 1
Table 2.3 Summary of results: unnamed adamellite, Mulyawara 1 (GA 2152083, GSSA R1964856).
GA Sample No
2152083
GSSA (registration) No
R1964856
Lithology
Adamellite
Stratigraphic Unit
Undefined
Collector
R. Dutch, W. Preiss and W. Cowley
Province/Region
Northwestern South Australia
1:250 000 Sheet
NOORINA (SH5203)
1:100 000 Sheet
NOORINA (4840)
Location (MGA94)
129.534193ºE; 28.839856ºS
Analytical Session
130026 (see Appendix Table A.1 for parameters derived from
concurrent measurements of 238U/206Pb and 207Pb/206Pb reference
zircons)
Interpreted Age
1168 ± 6 Ma (95% confidence; 22 analyses)
Geological Attribution
Magmatic crystallisation
Isotopic Ratio(s) Used
207Pb/206Pb (204Pb-corrected)
2.2.1 Location details and lithological characteristics
This sample was collected from the base of the Mulyawara 1 petroleum exploration well, northwestern
South Australia (Figure 1.1), in the depth interval 2682–2691 m. The sample occurs ~42 m below the
base of the Officer Basin. The sample was collected from drill cuttings, and is interpreted to be an
adamellite.
A thin section description from the Mulyawara 1 well completion report (Baily et al., 2012b) indicates
that a sample of minerals and rock chips from a depth of 2685 m contains quartz, K-feldspar,
plagioclase and biotite, while other chips are classified as low-grade sedimentary rocks.
2.2.2 Zircon description
Zircons from this sample form two main groups. Smaller elongate grains range in length from ~100 µm
to 200 µm, whereas a larger population have grains from ~220 µm up to ~280 µm in length
(Figure 2.5). Most grains have euhedral to subhedral morphologies, and the smaller size group are
clear and colourless, while the larger size group are clear and colourless to light brown in colour, with
abundant cracks. Cathodoluminescence images reveal that most grains have oscillatory zoning or
dark zones, while some grains have lighter coloured core regions with very thin dark
cathodoluminescence rims. Analyses focused on the range of cathodoluminescence responses,
except for the very thin dark cathodoluminescence rims, which were too small to analyse.
10
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
Figure 2.5 Representative zircons from the unnamed adamellite, Mulyawara 1 (GA 2152083, GSSA R1964856).
Transmitted light image is shown in the upper half; cathodoluminescence image in the lower half. SHRIMP
analysis sites are labelled.
2.2.3 U–Pb isotopic results
Forty-one analyses were undertaken on 41 zircon grains from the sample, the results of which are
presented in Table 2.4 and Figures 2.6 and 2.7. Seven analyses greater than 10% discordant were
considered unreliable and removed from further consideration. Of the remaining 34 analyses, nine
yielded common 206Pb contents higher than an arbitrary value of 0.5%, and these too were discarded.
The remaining 25 analyses are characterised by a wide range of U contents (62–1039 ppm), Th
contents (52–1865 ppm) and Th/U (0.09–3.68). The analyses record 207Pb/206Pb ages between ~1615
Ma and ~1152 Ma. There are 3 individuals with ages older than the main cluster; at ~1615 Ma, 1605
Ma and 1532 Ma (Figure 2.6). The remaining 22 analyses have a median Th/U value of 1.19, and
combine to provide a weighted mean 207Pb/206Pb age of 1168 ± 6 Ma (95% confidence; MSWD = 0.62;
Probability of fit = 0.91; Figure 2.7).
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
11
0.12
GA 2152083, GSSA R1964856
Unnamed adamellite
Mulyawara-1
All; n = 41
1800
0.10
0.08
Th/U
207
Pb/
206
Pb
4
1400
0
1000
0.06
600
data-point error ellipses are 2s
0.04
1
3
5
7
238
U/
9
11
13
206
Pb
Figure 2.6 Tera-Wasserburg concordia diagram showing results of zircon analyses from the unnamed adamellite
Mulyawara 1 (GA 2152083, GSSA R1964856), coloured according to Th/U values. Open ellipses represent
analyses greater than 10% discordant, and grey-coloured ellipses represent analyses with a common 206Pb
content higher than an arbitrary value of 0.5%.
1240
GA 2152083, GSSA R1964856
Unnamed adamellite
Mulyawara-1
Main group; n = 22
1220
Age (Ma)
1200
1180
1160
1140
1120
1100
Age = 1168 ± 6 Ma (95% conf.)
n = 22 of 22; MSWD = 0.62; Prob. = 0.91
box heights are 2s
Figure 2.7 Weighted mean age diagram showing 207Pb/206Pb ages of zircons from the main age group of the
unnamed adamellite, Mulyawara 1 (GA 2152083, GSSA R1964856).
12
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
2.2.4 Geochronological interpretation
Twenty-two analyses from the main age cluster combine to provide a weighted mean 207Pb/206Pb age
of 1168 ± 6 Ma (95% confidence). Given that all but one of these analyses have Th/U values greater
than 0.45, this age is interpreted as the magmatic crystallisation age of this adamellite. The older 3
ages within the sample range from ~1615 Ma to ~1532 Ma and are interpreted to record either
inheritance, or another sedimentary component within the sample.
Table 2.4 SHRIMP U–Pb zircon data from the unnamed adamellite, Mulyawara 1 (GA 2152083, GSSA
R1964856).
Sample.grain
.area.replicate
206Pb
c
(%)
U
Th
(ppm) (ppm)
232Th/
238U/
238U
206Pb
± 1σ
(%)
207Pb/
206Pb
± 1σ
(%)
207Pb/206Pb
Age (Ma)
± 1σ
(Ma)
disc
(%)
Older individuals (n = 3)
083.35.1.1
0.00
119
113
0.98
3.575
1.3
0.0995
1.0
1615
19
2
083.33.1.1
0.01
62
52
0.86
3.574
1.7
0.0990
1.5
1605
28
1
083.39.1.1
-0.05
163
112
0.71
3.866
1.2
0.0952
1.0
1532
19
3
Main age group: magmatic crystallisation (n = 22)
083.11.1.1
0.00
473
559
1.22
5.000
1.0
0.0799
0.7
1194
13
2
083.41.1.1
0.01
541
536
1.02
5.022
1.0
0.0796
0.7
1187
13
1
083.32.1.1
0.06
371
395
1.10
5.015
1.0
0.0794
0.8
1182
16
1
083.20.1.1
0.02
437
427
1.01
4.957
1.0
0.0794
0.7
1181
14
0
083.25.1.1
-0.01
595
537
0.93
5.012
1.0
0.0791
0.6
1174
12
0
083.34.1.1
0.00
498
524
1.09
5.060
1.0
0.0790
0.7
1173
14
1
083.15.1.1
-0.03
637
57
0.09
5.008
0.9
0.0789
0.6
1169
12
0
083.42.1.1
0.06
532
687
1.33
5.106
1.0
0.0789
0.8
1169
17
1
083.22.1.1
0.03
345
348
1.04
5.004
1.2
0.0788
1.0
1168
19
-1
083.28.1.1
0.09
1039
1865
1.86
5.097
1.0
0.0788
0.6
1167
12
1
083.36.1.1
0.09
652
285
0.45
4.992
1.0
0.0788
0.7
1166
14
-1
083.7.1.1
0.08
662
992
1.55
5.153
1.3
0.0786
0.8
1162
16
2
083.3.2.1
0.07
576
848
1.52
5.074
1.0
0.0785
0.7
1160
14
0
083.12.1.1
0.09
501
594
1.22
5.186
1.0
0.0785
0.8
1159
15
2
083.37.1.1
0.19
451
557
1.28
5.038
1.0
0.0784
1.2
1158
23
-1
083.5.2.1
0.07
385
374
1.00
5.258
1.0
0.0784
0.9
1157
19
3
083.14.1.1
0.04
471
569
1.25
5.094
1.0
0.0784
0.8
1157
15
0
083.17.1.1
0.06
396
397
1.03
4.980
1.0
0.0784
0.9
1157
17
-2
083.40.1.1
0.07
588
895
1.57
5.023
1.0
0.0784
0.7
1156
14
-1
083.26.1.1
0.06
426
496
1.20
5.293
1.3
0.0783
0.9
1155
17
3
083.29.1.1
0.01
380
431
1.17
5.040
1.0
0.0783
0.8
1155
16
-1
083.16.1.1
0.01
243
865
3.68
5.039
1.1
0.0782
1.0
1152
20
-1
Analyses >10% discordant (n = 7)
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
13
Sample.grain
.area.replicate
206Pb
(%)
232Th/
238U/
238U
206Pb
± 1σ
(%)
207Pb/
206Pb
± 1σ
(%)
207Pb/206Pb
Age (Ma)
± 1σ
(Ma)
disc
(%)
083.13.1.1
0.81
128
135
1.09
10.415
2.0
0.0770
4.9
1121
98
47
083.27.1.1
0.78
174
189
1.12
9.372
1.3
0.0742
3.3
1046
66
37
083.9.1.1
0.51
947
703
0.77
7.708
1.0
0.0740
1.1
1042
23
25
083.38.1.1
0.14
422
436
1.07
6.803
1.3
0.0783
1.1
1156
23
23
083.6.2.1
0.28
295
233
0.82
6.534
1.4
0.0779
1.4
1143
28
20
083.23.1.1
0.13
681
470
0.71
6.277
0.9
0.0765
0.7
1107
15
14
083.18.1.1
1.39
1074
1302
1.25
6.181
0.9
0.0756
2.4
1084
47
11
Analyses with common
14
U
Th
(ppm) (ppm)
c
206
Pb >0.5% (n = 9)
083.31.1.1
8.93
1492
1154
0.80
6.058
1.1
0.0724
15.4
998
313
1
083.4.2.1
1.97
4132
317
0.08
7.627
0.9
0.0683
3.4
877
70
9
083.30.1.1
1.45
686
1281
1.93
6.459
1.0
0.0736
2.6
1030
53
10
083.8.1.1
1.42
1007
1092
1.12
5.527
0.9
0.0737
2.5
1032
50
-4
083.24.1.1
1.19
891
1526
1.77
5.843
0.9
0.0734
2.3
1024
46
1
083.21.1.1
1.11
1743
1720
1.02
5.007
0.9
0.0748
1.8
1062
37
-11
083.1.1.1
0.76
1093
1066
1.01
5.198
0.9
0.0765
1.4
1107
28
-2
083.10.1.1
0.66
1301
916
0.73
5.328
1.1
0.0763
1.5
1103
29
-1
083.19.1.1
0.64
980
948
1.00
5.485
0.9
0.0765
1.3
1107
25
2
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
Acknowledgements
Rodinia Oil (Australia) Pty. Ltd are thanked for permission to analyse the samples from Kutjara 1 and
Mulyawara 1, and Sandy Menpes, Rian Dutch, Wolfgang Preiss and Wayne Cowley (Department for
Manufacturing, Innovation, Trade, Resources and Energy, South Australia) are thanked for collecting
the samples.
The SHRIMP zircon U–Pb analytical program was conducted using high quality zircon separates,
mounts, photographs and cathodoluminescence images professionally and skilfully prepared by staff
from the Geoscience Australia (GA) Mineral Separation Laboratory. Patrick Burke (GA) provided
valuable technical support and assistance in optimising analytical conditions on the SHRIMP IIe during
data acquisition. Natalie Kositcin and Simon Bodorkos (GA) are thanked for providing formal reviews
of this report.
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
15
References
Baily, T., Clark, R., Rowland, B. and Nicolson J. 2012a. Kutjara 1, Well Completion Report, Rodinia
Oil, unpublished report, 50p.
Baily, T., Clark, R., Rowland, B. and Nicolson J. 2012b. Mulyawara 1, Well Completion Report,
Rodinia Oil, unpublished report, 58p.
Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R., Campbell,
I.H., Korsch, R.J., Williams, I.S. and Foudoulis, C. 2004. Improved 206Pb/238U microprobe
geochronology by the monitoring of a trace element related matrix effect; SHRIMP, ID-TIMS,
ELAICP-MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology
205, 115–140.
Claoué-Long, J.C., Compston, W., Roberts, J. and Fanning, C.M. 1995. Two Carboniferous ages: a
comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar analysis. In:
Berggren, W.A., Kent, D.V., Aubry, M-P. and Hardenbol, J. (editors) Geochronology, time scales
and global stratigraphic correlation. Society for Sedimentary Geology, Special Publication 54, 3–21.
Compston, W., Williams, I.S. and Meyer, C. 1984. U–Pb geochronology of zircons from lunar breccia
73217 using a sensitive high mass-resolution ion microprobe. Journal of Geophysical Research 89,
Supplement B, 525–534.
Ludwig, K.R. 2001. SQUID 1.02: a user’s manual, Berkeley Geochronology Centre Special Publication
2.
Ludwig, K.R. 2003. User’s manual for Isoplot 3.6: a geochronological toolkit for Microsoft Excel®.
Berkeley Geochronology Center, Special Publication 4.
Nasdala, L., Hofmeister, W., Norberg, N., Mattinson, J.M., Corfu, F., Dörr, W., Kamo, S.L., Kennedy,
A.K., Kronz, A., Reiners, P.W., Frei, D., Kosler, J., Wan, Y., Götze, J., Häger, T., Kröner, A. and
Valley, J.W. 2008. Zircon M257 – a homogeneous natural reference material for the ion microprobe
U–Pb analysis of zircon. Geostandards and Geoanalytical Research 32, 247–265.
Stacey, J.S. and Kramers, J.D. 1975. Approximation of terrestrial lead isotope evolution using a twostage model. Earth and Planetary Science Letters 26, 207–221.
Stern, R.A., Bodorkos, S., Kamo, S.L., Hickman, A.H. and Corfu, F. 2009. Measurement of SIMS
instrument mass fractionation of Pb isotopes during zircon dating. Geostandards and Geoanalytical
Research 33, 145–168.
16
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
SHRIMP Analytical Procedures
All U-Pb isotopic results reported here were collected on the SHRIMP IIe instrument housed in the
SHRIMP Laboratory at Geoscience Australia, Canberra. A summary of key parameters from the single
analytical session is shown in Appendix Table A.1. The zircon analytical procedures adopted here,
and outlined below, follow those published by Compston et al. (1984) and Claoué-Long et al. (1995).
A.1 Mineral separation
Samples were washed in water and dried, prior to being milled in the GA Mineral Separation
Laboratory. Mineral density separation was undertaken using a Wilfley table, with multiple iterations
employed in order to reduce the sample to about 1-2% of its post-milling weight. Highly magnetic
minerals were removed with a hand magnet, before magnetic separation using a Frantz isodynamic
separator. Given the samples are igneous rocks, a selection of the least metamict grains were then
hand picked from the least magnetic fraction for mounting.
A.2 Mount preparation and SHRIMP analysis
The separated zircons were placed in rows on adhesive tape, together with a uranium concentration
standard (the Sri Lankan gem zircon M257 of Nasdala et al., 2008), a Pb/U ratio reference standard
(Temora-2; Black et al., 2004) and a Pb-Pb standard (OG1; Stern et al., 2009). The grains were then
mounted in epoxy, and once cured the mount surface was polished using a series of diamond pastes
until zircons were sectioned approximately in half, exposing their internal structure. They were
photographed subsequently in both transmitted light and reflected light and coated with 20 Å of gold
for cathodoluminescence imaging using a JEOL JSM-6490LV scanning electron microscope located
at Geoscience Australia. After imaging, the gold coat was removed and the mount recleaned before
being recoated with about 150 Å of gold for SHRIMP analysis.
Isotopic data were collected using a ~15 µm-diameter primary beam consisting of ionised oxygen
molecules (O2-) molecules, purified by a Wien filter. Before each analysis, the surface of the analysis
site was pre-cleaned by rastering of the primary beam for 3 minutes, in order to reduce the amount of
common Pb on the mount surface. Secondary ions were collected on a single electron multiplier via
cycling of the magnet through 6 scans through a run table consisting of ten different mass stations
(196Zr2O, 204Pb, background 204.1, 206Pb, 207Pb, 208Pb, 238U, 248ThO, 254UO, and 270UO2). All analyses
were carried out with a mass resolution of approximately 5000. Analyses were collected in a sequence
consisting of one analysis of a Temora-2 reference zircon and one measurement of an OG1 reference
zircon after every third or fourth unknown sample analysis.
For all samples, reflected light, transmitted light and cathodoluminescence (CL) images were used to
ensure that analyses were made on discrete zircon growth phases. In all cases, the area selected for
analysis was in the clearest portion of each grain, free from cracks, inclusions and metamict regions.
Zircons with a range of morphologies and cathodoluminescence responses were analysed to
determine a magmatic crystallisation age and to identify any inherited and/or metamorphic ages
present.
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1
17
A.3 SHRIMP data reduction and presentation
Data processing used the SQUID-1 software of Ludwig (2001) and processed data were plotted via
Isoplot 3 (revision of Ludwig, 2003), with 206Pb/238U ratios calibrated using the Temora-2 reference
zircon (238U/206Pb age = 416.8 Ma; Black et al., 2004), and 207Pb/206Pb ratios calibrated using the OG1
reference zircon (207Pb/206Pb age = 3465.4 ± 0.6 Ma; Stern et al., 2009), and U concentrations
calibrated to M257 (840 ppm U; Nasdala et al., 2008). See Appendix Table A.1 for session details.
Appendix Table A.1 Summary of session 130026 metadata, parameters obtained from analyses of 238U/206Pb and
207Pb/206Pb reference zircons.
Session:
130026
MountID:
GA6225
Session dates:
22–25 March 2013
238U/206Pb
Temora-2 (416.8 Ma)
reference zircon and age:
Analyses used:
29 of 29
238U/206Pb
1.65%
spot-to-spot error (2σ):
Index isotope for common Pb correction:
204Pb
207Pb/206Pb
OG1 (3465.4 Ma)
reference zircon and age:
Analyses used:
26 of 28
Mean 207Pb/206Pb date (Ma, 95% confidence):
3468.5 ± 2.5
Mass fractionation correction applied:
No
Assuming that all surface Pb was removed from the mount surface during rastering, analyses of the UPb standard were corrected for common Pb using measured 204Pb and a default isotopic composition
calculated using the model of Stacey and Kramers (1975), corresponding to a date of 416.8 Ma.
Common-Pb corrections for unknown samples were based on measured 204Pb and an isotopic
composition calculated using the Pb isotopic evolution model of Stacey and Kramers (1975), and a
time corresponding to a preliminary 206Pb/238U age calculated using the default common-Pb
compositions. The result of this calculation is expressed in Tables throughout this report as common
206Pb (206Pb ) as a percentage of total measured 206Pb. Analyses with relatively high 206Pb (i.e. >0.5%)
c
c
are excluded from data interpretations.
Discordance is a measure of the internal agreement of the dates derived from the independent
207Pb/206Pb and 238U/206Pb isotopic systems within a single analysis. In zircons of Mesoproterozoic and
older age, discordance values for single analyses (and discordance patterns within a population of
analyses) can provide important information about the timing and extent of radiogenic Pb loss, and are
usually a valuable indication of geological data quality. Discordance was calculated by the method: [1(206Pb/238U age/207Pb/206Pb age)*100]. Analyses >10% discordant were excluded from age
interpretations for all samples.
All ages discussed in this report are 204Pb-corrected 207Pb/206Pb ages, and quoted at the 95%
confidence level (ca. 1.96σ) unless otherwise specified. All ages quoted in the data tables are at the
1σ level.
18
New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1