Appendix B

Operational parameters of instruments used for La-ICP-MS dating

Table B1. Operational parameters for La-ICP-MS dating of samples Kul-21 and Kul-22

Laboratory & Sample Preparation / Sample Kul-21 and Kul-22
Laboratory name / Geological institute of the Bulgarian Academy of Sciences
Sample type/mineral / Detrital, magmatic and metamorphic zircons
Sample preparation / Conventional mineral separation, 1 inch resin mount, 1um polish to finish
Imaging / CL and BSE imaging with a JEOL JSM-6610LV at the University of Belgrade
Laser ablation system
Model & type / New Wave UP193FX laser ablation system
Perkin-Elmer Sciex ELAN DRC-e ICP-MS
Ablation cell & volume
Forward Power / 1450 W
Gas flow rate
Nebulizer / 0.80 - 0.82 L min-1
Auxiliary / 0.90 - 0.92 L min-1
Plasma / 15.0 L min-1
He carrier gas flow / 0.90 - 0.92 L min-1
Lens Voltage / 6-10.5 V
Auto Lens / ON (5.5-11.25V)
Oxides / ThO+/Th+ <0.5 %
Wavelength / 193 mm
Energy / 8.5-8.9 J cm-2
Laser frequency / 8 Hz
Spot size / 35 μm
Pulse duration / 4 ns
Data acquisition
Data acquisition protocol / Time resolved analysis
Scanning mode / Peak hopping, 1 point per peak
Dwell time per isotope / 20 ms 232Th, 208 Pb; 30 ms 206Pb, 207Pb, 238U
Background and signal acquisition / 30 s gas blank and ~ 50 s ablation
Sweeps / 1
Reading/Replicate / 850
Replicates / 1

Table B2. Operational parameters for La-ICP-MS dating of sample Kul-6

Laboratory & Sample Preparation / Sample Kul-6
Laboratory name / Geological Survey of Denmark and Greenland (GEUS)
Sample type / mineral / Detrital zircons
Sample preparation / Conventional mineral separation, 1 inch resin mount, 1 µm polish to finish
Imaging / BSE-imaging, Philips XL 40 VP, 10 nA, 15 mm working distance
Laser ablation system
Make, Model & type / ESI/New Wave Research, UP213, Nd:YAG
Ablation cell & volume / Custom build low volume cell, volume ca.3 cm3
Laser wavelength / 213 nm
Pulse width / 3 ns
Fluence / 2.5 J/cm-2
Repetition rate / 10 Hz
Spot size / 30 µm
Sampling mode / pattern / 30 µm single spot analyses
Carrier gas / 100% He, Ar make-up gas combined using a T-connector close to sample cell
Pre-ablation laser warm-up (background collection) / 40 seconds
Ablation duration / 20 seconds
Wash-out delay / 30 seconds
Cell carrier gas flow / 0.3 l/min He
ICP-MS Instrument
Make, Model & type / Thermo Finnigan Element2 single collector HR-SF-ICP-MS
Sample introduction / Via conventional tubing
RF power / 1100 W
Make-up gas flow / 1.0 l/min Ar
Detection system / Single collector secondary eletron multiplier
Masses measured / 202, 204, 206, 207, 208, 232, 233, 235, 238
Integration time per peak / 4 ms
Total integration time per reading / Approx. 1 sec
Sensitvity / 20000 cps/ppm Pb
Dead time / 16 ns
Data Processing
Gas blank / 40 second on-peak
Calibration strategy / GJ-1 used as primary reference material, Plešovice & M127 used as secondary reference material (Quality Control)
Reference Material info / M127 (Nasdala et al. 2008; Mattey 2010)
Plešovice (Slama et al. 2008)
GJ-1 (Jackson et al. 2004)
Data processing package used / Correction for LIEF / Excel-based In-house data processing using intercept method for LIEF correction
Mass discrimination / Standard-sample bracketing with 207Pb/206Pb and 206Pb/238U normalised to reference material GJ-1
Common-Pb correction, composition and uncertainty / 204-method, Stacey & Kramers (1975) composition at the projected age of the mineral, 5% uncertainty assigned
Uncertainty level & propagation / Ages are quoted at 2 sigma absolute, propagation is by quadratic addition. Reproducibility and age uncertainty of reference material and common-Pb composition uncertainty are propagated.
Quality control / Validation / Plešovice: Wtd ave 206Pb/238U age = 339 ± 5 (2SD, MSWD = 0.7)
M127: Wtd ave 206Pb/238U age = 527 ± 5 (2SD, MSWD = 0.9)
Other information / Detailed method description reported by Frei & Gerdes (2009)