GA Record Template › 78792 › Rec2014… · Web viewUpdated January 2013

SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1, northwestern South AustraliaGEOSCIENCE AUSTRALIARECORD 2014/05

N.L. Neumann and R. J. Korsch

Department of IndustryMinister for Industry: The Hon Ian Macfarlane MPParliamentary Secretary: The Hon Bob Baldwin MPSecretary: Ms Glenys Beauchamp PSM

Geoscience AustraliaChief Executive Officer: Dr Chris PigramThis paper is published with the permission of the CEO, Geoscience Australia

© Commonwealth of Australia (Geoscience Australia) 2014

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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

http://dx.doi.org/10.11636/Record.2014.005

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Contents

Executive Summary................................................................................................................................ 1

1 Introduction.......................................................................................................................................... 2

2 U-Pb SHRIMP Results......................................................................................................................... 42.1 Unnamed granitoid, Kutjara 1.........................................................................................................4

2.1.1 Location details and lithological characteristics........................................................................42.1.2 Zircon description..................................................................................................................... 42.1.3 U–Pb isotopic results................................................................................................................52.1.4 Geochronological interpretation................................................................................................6

2.2 Unnamed adamellite, Mulyawara 1..............................................................................................102.2.1 Location details and lithological characteristics......................................................................102.2.2 Zircon description................................................................................................................... 102.2.3 U–Pb isotopic results..............................................................................................................112.2.4 Geochronological interpretation..............................................................................................13

Acknowledgements............................................................................................................................... 15

References........................................................................................................................................... 16

Appendix A SHRIMP Analytical Procedures.........................................................................................17A.1 Mineral separation.......................................................................................................................17A.2 Mount preparation and SHRIMP analysis....................................................................................17A.3 SHRIMP data reduction and presentation....................................................................................18

New SHRIMP U–Pb zircon ages from Kutjara 1 and Mulyawara 1

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 High-Resolution 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).


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)


Geological Attribution Metamorphism


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 2.2). Most grains have euhedral to subhedral morphologies, and are clear


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 2.2 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.


0.04

0.06

0.08

0.10

0.12

2.5 3.5 4.5 5.5 6.5238U/206Pb

207 Pb

/206 Pb

data-point error ellipses are 2s

Th/U

0

1.5

1000

1400

1800

GA 2152082, GSSA R1964851Unnamed granitoid

Kutjara-1All; n = 58

Figure 2.3 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 2.3). 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 2.4).

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 2.5).

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.


1360

1400

1440

1480

1520

1560

1600

1640

1680

1720

Age

(Ma)

Age = 1591 ± 11 Ma (95% conf.)n = 30 of 31; MSWD = 1.3; Prob. = 0.14

box heights are 2s


Kutjara-1Older group; n = 31

Figure 2.4 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.

850

950

1050

1150

1250

1350

1450

Age

(Ma)


box heights are 2s


Kutjara-1Younger group; n = 25

Figure 2.5 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.


Table 2.2 SHRIMP U–Pb zircon data from the unnamed granitoid, Kutjara 1 (GA 2152082, GSSA R1964851).

Sample.grain.area.replicat

e

206Pbc

(%)U

(ppm)

Th (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

Younger age group: metamorphism (n = 24)



e

206Pbc

(%)U

(ppm)

Th (ppm

)

232Th/238U

238U/206Pb

± 1σ (%)

207Pb/206Pb

± 1σ (%)


± 1σ (Ma)

disc(%)

082.15.1.1 -0.21 41 0 0.01 5.105 2.2 0.0837 3.4 1286 66 10

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

Younger individual (n = 1)

082.24.1.1 0.46 1092 93 0.09 5.995 0.9 0.0749 1.0 1066 21 7

Analysis >10% discordant (n = 1)

082.24.2.1 -0.51 33 0 0.01 5.069 2.5 0.0878 4.1 1378 79 16

Analysis with common 206 Pb >0.5% (n = 1)

082.19.2.1 11.48 65 2 0.03 4.874 2.5 0.0759 23.2 1091 464 -10


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)


Geological Attribution Magmatic crystallisation


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 2.6). 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.


Figure 2.6 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 2.7). 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 2.8).


0.04

0.06

0.08

0.10

0.12

1 3 5 7 9 11 13238U/206Pb

207 Pb

/206 Pb

data-point error ellipses are 2s

Th/U

0

4

600

1000

1400

1800

GA 2152083, GSSA R1964856Unnamed adamellite

Mulyawara-1All; n = 41

Figure 2.7 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%.

1100

1120

1140

1160

1180

1200

1220

1240

Age

(Ma)


box heights are 2s

GA 2152083, GSSA R1964856Unnamed adamellite

Mulyawara-1Main group; n = 22

Figure 2.8 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).


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).


e

206Pbc

(%)U

(ppm)Th

(ppm)

232Th/238U

238U/206Pb

± 1σ (%)

207Pb/206Pb

± 1σ (%)


± 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



e

206Pbc

(%)U

(ppm)Th

(ppm)

232Th/238U

238U/206Pb

± 1σ (%)

207Pb/206Pb

± 1σ (%)


± 1σ (Ma)

disc(%)

Analyses >10% discordant (n = 7)

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 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


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.


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 two-stage 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.


Appendix A SHRIMP Analytical ProceduresAll 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 separationSamples 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.


A.3 SHRIMP data reduction and presentationData 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 2013238U/206Pb reference zircon and age: Temora-2 (416.8 Ma)

Analyses used: 29 of 29238U/206Pb spot-to-spot error (2σ): 1.65%

Index isotope for common Pb correction: 204Pb207Pb/206Pb reference zircon and age: OG1 (3465.4 Ma)

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 U-Pb 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 (206Pbc) as a percentage of total measured 206Pb. Analyses with relatively high 206Pbc (i.e. >0.5%) 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.


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