1. High Precision Pb Isotope Ratio Measurements of Zircon Zenon Palacz, Simon Meffan-Main, Patrick Turner, & Fadi Abou-Shakra

2. Introduction Lead isotope ratios conventionally determined in Zircons by TIMS/SHRIMP MC-ICPMS compliments conventional methods and expands geochronological horizons.

3. Advantages of an ICP as an Ion Source 4The degree of elemental ionisation across the periodic table is relatively high and uniform 4Gives predominantly singly charged ions 4Samples are introduced at atmospheric pressure and can be readily interchanged 4Most elements are ionised >99% 4Fractionation (Mass bias) in an ICP is stable and easily corrected

4. Sensitivity Ion:Atom % Ionisation cps/ppm Sr 1:124 0.08% 2.74 x 10 9 Nd 1:310 0.32% 6.74 x 10 9 Hf 1:400 0.25% 4.18 x 10 9 Os 1:500 0.20% 3.05 x 10 9 Pb 1:110 0.92% 1.34 x 10 10 Th 1:345 0.29% 3.75 x 10 9 U 1:200 0.50% 6.31 x 10 9

5. Sensitivity

6. Transmission efficiency of IsoProbe with CETAC MCN6000 0.001 0.01 0.1 1 050100150200250 MASS ion/atom efficiency (%) Sr

7. Cetac LSX-200 Laser Ablation Nd-YAG UV 216nm ! In-Situ Analyses from Polished thin sections or loose grains ! Speed of Analyses ! Spatial Flexibility in 3 Dimensions

8. Zircon Geochronology High Precision Spatial Resolution isotope ratios essential for zircon age determinations in many situations. SHRIMP - SIMS spot size down to 10microns. LA-MC-ICPMS - Offers High Precision Isotope Ratios and simplified sample introduction. STATIC analysis.

9. 50  m pit in zircon during ablation

10. Zircon KC81-135 (TIMS data) Multigrain fraction 0.8% discordant data 207 Pb/ 206 Pb 0.18071+/-0.00018 208 Pb/ 206 Pb 0.0055 206 Pb/ 204 Pb 26240 Pb 514ppm U 993ppm Age 2659+/-2Ma (Fernando Corfu per.com. Nov. 1996)  Multigrain fraction 0.8% discordant data  207 Pb/ 206 Pb 0.18071 ± 0.00018  208 Pb/ 206 Pb 0.0055  206 Pb/ 204 Pb 26240  Pb 514ppm  U 993ppm  Age 2659 ± 2Ma  (Fernando Corfu per.com. Nov. 1996)

11. 206 Pb (volts) down hole. 206 Pb Intensity v Time 0 0.5 1 1.5 2 2.5 0204060 Seconds 206 Pb Intensity

12. Isotopic variation down hole 207 Pb/ 206 Pb v Time 0.17 0.18 0.19 0.2 0.21 0.22 0204060 seconds 207 Pb/ 206 Pb

13. 208 Pb/ 206 Pb down hole 208 Pb/ 206 Pb v Time 0 0.02 0.04 0.06 0.08 0.1 0.12 0204060 Seconds 208 Pb/ 206 Pb

14. Down hole isotope variation zircon KC81135 second 206 Pb volts 208 Pb/ 206 Pb 207 Pb/ 206 Pb 206 Pb/ 204 Pb 0-100.850.061740.20076671.6 10-20s0.480.016630.185961582.6 20-30s0.490.017540.182592537.8 30-40s0.650.004720.183093418.2 40-50s1.230.003240.182235454.8 50-60s1.740.004360.182796537.8

15. Uqz-1 Zircon, 48ppm Pb

16. Ion:Atom Laser Transport Efficiency

17. ZIRCON 91500  Age 1062+/-0.4Myr (TIMS)  12ppm Pb  207 Pb/ 206 Pb 0.07488+/-0.00001 TIMS

18. Laser Ablation ICP-MS vs TIMS Precision vs Sample Size Zircon 91500 8.58E-08 9.38E-07 0.0008 0.074 0.0745 0.0750 0.0755 0.0760 0.0765 0.000000010.00000010.0000010.000010.00010.0010.01 Log Sample size (grams) 207 Pb/ 206 Pb TIMS samples are circa. 1000 x larger and 50 x more precise than 50  m ablations TIMS 50  m 100  m Sample size in grams

19. 1.2 1.15 1.1 1.05 0.95 0.9 0.85 1 0.0680000 0.0700000 0.0720000 0.0740000 0.0760000 0.0780000 0.0800000 207 Pb/ 206 Pb 50  m Average = 0.072148 % St. Dev. = 3.72 100  m Average = 0.072291 200  m Average = 0.073638 300  m Average = 0.074703 St. Dev. = 0.87 Age (Ga) IsoProbe 207 Pb/ 206 Pb Age (St. Dev. of 43) = 1008 +/- 46Ma TIMS Age = 1062 +/-0.4Ma 0.07488 91500 with Laser Induced Fractionation

20. 25 & 50  m pits in 91500 zircon

21. 25  m Spots in 91500 <1pg Pb 0.0650000 0.0700000 0.0750000 0.0800000 0.0850000 0.0900000 051015 207 Pb/ 206 Pb Average = 0.75936 St. Dev. = 4.4% (n=15) Weighted Mean = 0.0751 +/-10 (1.4%) Age = 1070 +/-30Ma TIMS Analysis no.

22. 0.0650000 0.0700000 0.0750000 0.0800000 0.0850000 0.0900000 024681012141618 207 Pb/ 206 Pb Average = 0.07495 St. Dev. =.00082 (1.1%; n=15) Weighted Mean = 0.07494 +/- 45 (0.61%) TIMS = 0.07488 +/- 1 TIMS Age = 1067 +/-12Ma TIMS Age = 1062.4 +/-0.4Ma Analysis no. 50  m Spots in 91500

23. Zircon prior to ablation 100  m

24. 3-D mapping of isotopic ratios using 50  m pits in zircon

25. Summary LA-MC-ICPMS - Offers high precision Isotope Ratios and simplified sample introduction. MC-ICPMS offers alternatives to conventional geochronological methods and expands geochronological horizons. LA-MC-ICPMS - Offers high precision Isotope Ratios and simplified sample introduction. MC-ICPMS offers alternatives to conventional geochronological methods and expands geochronological horizons.

26. Summary 2 We have demonstrated that accurate and precise Pb isotopic ratios can be determined from less than 1pg total Pb in 25  m ablation pits within a 15ppm zircon with Faraday ion collection. With multiple ion counting LA-ICPMS provides a tool to obtain reliable and accurate geochronology data from zircons at 10  m resolution. We have demonstrated that accurate and precise Pb isotopic ratios can be determined from less than 1pg total Pb in 25  m ablation pits within a 15ppm zircon with Faraday ion collection. With multiple ion counting LA-ICPMS provides a tool to obtain reliable and accurate geochronology data from zircons at 10  m resolution.