SHRIMP U Pb zircon ages from

Transcription

1 FOR OFFICIAL Record 2014/05USE ONLY GeoCat Professional Opinion 2013/xx GeoCat xxxxx SHRIMP U Pb zircon ages from Title Subtitle Kutjara 1 and Mulyawara 1, northwestern South Australia Author/s N.L. Neumann and R. J. Korsch Prepared for xxxxxxxxxxxxxxxx Month 2013 APPLYING GEOSCIENCE TO AUSTRALIA S MOST IMPORTANT CHALLENGES

2

3 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

4 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. ( 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 clientservices@ga.gov.au. ISSN X (PDF) ISBN (PDF) GeoCat Bibliographic reference: Neumann, N.L. and Korsch, R.J., SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1, northwestern South Australia. Record 2014/05. Geoscience Australia, Canberra. Version: 1310

5 Contents Executive Summary Introduction U-Pb SHRIMP Results Unnamed granitoid, Kutjara Location details and lithological characteristics Zircon description U Pb isotopic results Geochronological interpretation Unnamed adamellite, Mulyawara Location details and lithological characteristics Zircon description U Pb isotopic results Geochronological interpretation...13 Acknowledgements...15 References...16 Appendix A 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

6 iv New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

7 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 Ma inherited grains. New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1 1

8 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 238 U/ 206 Pb and 207 Pb/ 206 Pb zircons. 2 New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

9 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

10 2 U-Pb SHRIMP Results 2.1 Unnamed granitoid, Kutjara 1 Table 2.1 Summary of results: Unnamed granitoid, Kutjara 1 (GA , GSSA R ). GA Sample No GSSA (Registration) No Lithology Stratigraphic Unit Collector Province/Region R Granitoid Undefined R. Dutch, W. Preiss and W. Cowley Northwestern South Australia 1: Sheet WYOLA (SH5207) 1: Sheet WARRANGA (4839) Location (GDA94) Analytical Session Interpreted Age Geological Attribution Isotopic Ratio(s) Used Interpreted Age Geological Attribution Isotopic Ratio(s) Used ºE; ºS (see Appendix Table A.1 for parameters derived from concurrent measurements of 238 U/ 206 Pb and 207 Pb/ 206 Pb reference zircons) 1591 ± 11 Ma (95% confidence; 30 analyses) Magmatic crystallisation 207 Pb/ 206 Pb ( 204 Pb-corrected) 1167 ± 7 Ma (95% confidence; 24 analyses) Metamorphism 207 Pb/ 206 Pb ( 204 Pb-corrected) 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 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 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

11 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 , GSSA R ). Transmitted light image is shown in the upper half; cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled 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 206 Pb 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

12 0.12 GA , GSSA R Unnamed granitoid Kutjara-1 All; n = Pb/ 206 Pb Th/U data-point error ellipses are 2σ U/ 206 Pb Figure 2.2 Tera-Wasserburg concordia diagram showing results of zircon analyses from the unnamed granitoid, Kutjara 1 (GA , GSSA R ), 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 206 Pb content higher than an arbitrary value of 0.5%. The remaining 56 analyses are characterised by a wide range of U contents ( ppm), Th contents (0 186 ppm) and Th/U ( ). The analyses record 207 Pb/ 206 Pb 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 ( ; age = 1657 ± 17 Ma (1σ)) is excluded, the remaining 30 analyses combine to provide a weighted mean 207 Pb/ 206 Pb 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 ( ) which has a younger age ( 207 Pb/ 206 Pb age = 1066 ± 21 (1σ)), the remaining 24 analyses combine to provide a weighted mean 207 Pb/ 206 Pb age of 1167 ± 7 Ma (95% confidence; MSWD = 0.99; Probability of fit = 0.47; Figure 2.4) Geochronological interpretation The weighted mean 207 Pb/ 206 Pb 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 207 Pb/ 206 Pb 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

13 GA , GSSA R Unnamed granitoid Kutjara-1 Older group; n = Age (Ma) Age = 1591 ± 11 Ma (95% conf.) n = 30 of 31; MSWD = 1.3; Prob. = box heights are 2σ Figure 2.3 Weighted mean age diagram showing 207 Pb/ 206 Pb ages of zircons from the older age group of the unnamed granitoid, Kutjara 1 (GA , GSSA R ). Open box represents an analysis not included in the age calculation GA , GSSA R Unnamed granitoid Kutjara-1 Younger group; n = Age (Ma) Age = 1167 ± 7 Ma (95% conf.) n = 24 of 25; MSWD = 0.99; Prob. = box heights are 2σ Figure 2.4 Weighted mean age diagram showing 207 Pb/ 206 Pb ages of zircons from the younger age group of the unnamed granitoid, Kutjara 1 (GA , GSSA R ). Open box represents an analysis not included in the age calculation. New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1 7

14 Table 2.2 SHRIMP U Pb zircon data from the unnamed granitoid, Kutjara 1 (GA , GSSA R ). Sample.grain.area.replicate 206 Pb c U (ppm) Th (ppm) 232 Th/ 238 U 238 U/ 206 Pb ± 1σ 207 Pb/ 206 Pb ± 1σ 207 Pb/ 206 Pb Age (Ma) ± 1σ (Ma) disc Older individual (n = 1) Older age group: magmatic crystallisation (n = 30) Younger age group: metamorphism (n = 24) New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

15 Sample.grain.area.replicate 206 Pb c U (ppm) Th (ppm) 232 Th/ 238 U 238 U/ 206 Pb ± 1σ 207 Pb/ 206 Pb ± 1σ 207 Pb/ 206 Pb Age (Ma) ± 1σ (Ma) disc Younger individual (n = 1) Analysis >10% discordant (n = 1) Analysis with common 206 Pb >0.5% (n = 1) New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1 9

16 2.2 Unnamed adamellite, Mulyawara 1 Table 2.3 Summary of results: unnamed adamellite, Mulyawara 1 (GA , GSSA R ). GA Sample No GSSA (registration) No Lithology Stratigraphic Unit Collector Province/Region R Adamellite Undefined R. Dutch, W. Preiss and W. Cowley Northwestern South Australia 1: Sheet NOORINA (SH5203) 1: Sheet NOORINA (4840) Location (MGA94) Analytical Session Interpreted Age Geological Attribution Isotopic Ratio(s) Used ºE; ºS (see Appendix Table A.1 for parameters derived from concurrent measurements of 238 U/ 206 Pb and 207 Pb/ 206 Pb reference zircons) 1168 ± 6 Ma (95% confidence; 22 analyses) Magmatic crystallisation 207 Pb/ 206 Pb ( 204 Pb-corrected) 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 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 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

17 Figure 2.5 Representative zircons from the unnamed adamellite, Mulyawara 1 (GA , GSSA R ). Transmitted light image is shown in the upper half; cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled 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 206 Pb 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 ( ppm), Th contents ( ppm) and Th/U ( ). The analyses record 207 Pb/ 206 Pb 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 207 Pb/ 206 Pb 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

18 GA , GSSA R Unnamed adamellite Mulyawara-1 All; n = Pb/ 206 Pb Th/U U/ 206 Pb data-point error ellipses are 2σ Figure 2.6 Tera-Wasserburg concordia diagram showing results of zircon analyses from the unnamed adamellite Mulyawara 1 (GA , GSSA R ), coloured according to Th/U values. Open ellipses represent analyses greater than 10% discordant, and grey-coloured ellipses represent analyses with a common 206 Pb content higher than an arbitrary value of 0.5% GA , GSSA R Unnamed adamellite Mulyawara-1 Main group; n = Age (Ma) Age = 1168 ± 6 Ma (95% conf.) n = 22 of 22; MSWD = 0.62; Prob. = box heights are 2σ Figure 2.7 Weighted mean age diagram showing 207 Pb/ 206 Pb ages of zircons from the main age group of the unnamed adamellite, Mulyawara 1 (GA , GSSA R ). 12 New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

19 2.2.4 Geochronological interpretation Twenty-two analyses from the main age cluster combine to provide a weighted mean 207 Pb/ 206 Pb 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 , GSSA R ). Sample.grain.area.replicate 206 Pb c U (ppm) Th (ppm) 232 Th/ 238 U 238 U/ 206 Pb ± 1σ 207 Pb/ 206 Pb ± 1σ 207 Pb/ 206 Pb Age (Ma) ± 1σ (Ma) disc Older individuals (n = 3) Main age group: magmatic crystallisation (n = 22) Analyses >10% discordant (n = 7) New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1 13

20 Sample.grain.area.replicate 206 Pb c U (ppm) Th (ppm) 232 Th/ 238 U 238 U/ 206 Pb ± 1σ 207 Pb/ 206 Pb ± 1σ 207 Pb/ 206 Pb Age (Ma) ± 1σ (Ma) disc Analyses with common 206 Pb >0.5% (n = 9) New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

21 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

22 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 Improved 206 Pb/ 238 U 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, Claoué-Long, J.C., Compston, W., Roberts, J. and Fanning, C.M Two Carboniferous ages: a comparison of SHRIMP zircon dating with conventional zircon ages and 40 Ar/ 39 Ar 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, Compston, W., Williams, I.S. and Meyer, C U Pb geochronology of zircons from lunar breccia using a sensitive high mass-resolution ion microprobe. Journal of Geophysical Research 89, Supplement B, Ludwig, K.R SQUID 1.02: a user s manual, Berkeley Geochronology Centre Special Publication 2. Ludwig, K.R 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 Zircon M257 a homogeneous natural reference material for the ion microprobe U Pb analysis of zircon. Geostandards and Geoanalytical Research 32, Stacey, J.S. and Kramers, J.D Approximation of terrestrial lead isotope evolution using a twostage model. Earth and Planetary Science Letters 26, Stern, R.A., Bodorkos, S., Kamo, S.L., Hickman, A.H. and Corfu, F Measurement of SIMS instrument mass fractionation of Pb isotopes during zircon dating. Geostandards and Geoanalytical Research 33, New SHRIMP U Pb zircon ages from Kutjara 1 and Mulyawara 1

23 Appendix A 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 (O - 2 ) 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 ( 196 Zr 2 O, 204 Pb, background 204.1, 206 Pb, 207 Pb, 208 Pb, 238 U, 248 ThO, 254 UO, and 270 UO 2 ). All analyses were carried out with a mass resolution of approximately 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

24 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 206 Pb/ 238 U ratios calibrated using the Temora-2 reference zircon ( 238 U/ 206 Pb age = Ma; Black et al., 2004), and 207 Pb/ 206 Pb ratios calibrated using the OG1 reference zircon ( 207 Pb/ 206 Pb age = ± 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 metadata, parameters obtained from analyses of 238 U/ 206 Pb and 207 Pb/ 206 Pb reference zircons. Session: MountID: GA6225 Session dates: March U/ 206 Pb reference zircon and age: Temora-2 (416.8 Ma) Analyses used: 29 of U/ 206 Pb spot-to-spot error (2σ): 1.65% Index isotope for common Pb correction: 204 Pb 207 Pb/ 206 Pb reference zircon and age: OG1 ( Ma) Analyses used: 26 of 28 Mean 207 Pb/ 206 Pb date (Ma, 95% confidence): ± 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 204 Pb and a default isotopic composition calculated using the model of Stacey and Kramers (1975), corresponding to a date of Ma. Common-Pb corrections for unknown samples were based on measured 204 Pb and an isotopic composition calculated using the Pb isotopic evolution model of Stacey and Kramers (1975), and a time corresponding to a preliminary 206 Pb/ 238 U age calculated using the default common-pb compositions. The result of this calculation is expressed in Tables throughout this report as common 206 Pb ( 206 Pb c ) as a percentage of total measured 206 Pb. Analyses with relatively high 206 Pb c (i.e. >0.5%) are excluded from data interpretations. Discordance is a measure of the internal agreement of the dates derived from the independent 207 Pb/ 206 Pb and 238 U/ 206 Pb 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- ( 206 Pb/ 238 U age/ 207 Pb/ 206 Pb age)*100]. Analyses >10% discordant were excluded from age interpretations for all samples. All ages discussed in this report are 204 Pb-corrected 207 Pb/ 206 Pb 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