Open Access
Annexe B
Operating conditions for the LA-ICP-MS equipment for zircon, apatite and columbo-tantalite analyses.
Protocole analytique LA-ICP-MS pour le zircon, l’apatite et la columbo-tantalite.
| Laboratory & Sample Preparation | |
|---|---|
| Laboratory name | Géosciences Rennes, UMR CNRS 6118, Rennes, France |
| Sample types/minerals | Zircon, Apatite, Coltan |
| Samples preparation | Zircon (Zrn), separated grains mounted in an epoxy puck. Apatite (Ap) in-context in thin-section, Coltan in an epoxy puck. |
| Imaging | CL: Relion CL instrument, Olympus Microscope and Leica Color Camera |
| Laser ablation system | |
| Make, Model & type | ESI NWR193UC, Excimer |
| Ablation cell | ESI NWR TwoVol2 |
| Laser wavelength | 193 nm |
| Pulse width | < 5 ns |
| Fluence | 5.5 J/cm2 (Zrn); 5.8 J/cm2 (Ap); 6.2 J/cm2 (coltan) |
| Repetition rate | 3 Hz (Zrn); 5 Hz (Ap); 4 Hz (coltan) |
| Spot size | 30 µm (Zrn); 50 µm (Ap); 40 µm (coltan) |
| Sampling mode/pattern | Single spot |
| Carrier gas | 100% He, Ar make-up gas and N2 (3 ml/mn) combined using in-house smoothing device |
| Background collection | 20 s |
| Ablation duration | 60 s |
| Wash-out delay | 15 s |
| Cell carrier gas flow (He) | 0.75 l/min |
| ICP-MS Instrument | |
| Make, Model & type | Agilent 7700x, Q-ICP-MS |
| Sample introduction | Via conventional tubing |
| RF power | 1350 W |
| Sampler, skimmer cones | Ni |
| Extraction lenses | X type |
| Make-up gas flow (Ar) | 0.85 l/min |
| Detection system | Single collector secondary electron multiplier |
| Data acquisition protocol | Time-resolved analysis |
| Scanning mode | Peak hopping, one point per peak |
| Detector mode | Pulse counting, dead time correction applied, and analog mode when signal intensity > ∼ 106 cps |
| Masses measured | 204(Hg + Pb), 206Pb, 207Pb, 208Pb, 232Th, 238U + 43Ca (Ap) |
| Integration time per peak | 10–30 ms |
| Sensitivity/Efficiency | 23 000 cps/ppm Pb (50 μm, 10 Hz) |
| Data Processing | |
| Gas blank | 20 s on-peak |
| Calibration strategy | GJ-1 zircon, Madagascar apatite used as primary reference materials, Plešovice zircon and McClure and Durango apatite standards used as secondary reference material (quality control) |
| Common-Pb correction, composition and uncertainty | No common-Pb correction. |
| Reference Material info | GJ-1 (Jackson et al., 2004) Madagascar (Cochrane et al., 2014) Plešovice (Sláma et al., 2008) McClure (Schoene and Bowring, 2006) Durango (McDowell et al., 2005) |
| Data processing package used | Iolite 4 (Paton et al., 2011), U-Pb Geochronology (Zrn, Coltan, Paton et al., 2010); VizualAge_UcomPbine (Ap; Chew et al., 2014) |
| Uncertainty level and propagation | Ages are quoted at 2 sigma absolute, propagation is by quadratic addition according to Horstwood et al. (2016). Reproducibility and age uncertainty of reference material are propagated. |
| Quality control/Validation | Plešovice: 341 ± 6 Ma (n = 8, MSWD = 2.4) McClure: 528 ± 4.2 Ma (N = 19, MSWD = 2.4) Durango: 32.4 ± 1.4 Ma (N = 20, MSWD = 0.68) |
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