Zircon standard

The especially homogeneous zircon standard 91500 [13], dated by several reference techniques (mainly ID-TIMS) in highly reputable laboratories, was selected because the standard shows concordant ages. In addition, the standard is characterized by constant U and Th concentrations, and subsequently, constant radiogenic Pb concentrations. Furthermore, no common-Pb is observed in this reference zircon standard (no ° Pb). 

The laser was connected to the MC-ICP-MS, and the output energy at 213 nm was about 0.3 mJ/pulse. The laser was operated at a frequency of 10 Hz. The sample gas flow (Ar) was optimized by ablating the zircon standard 91500 (see Table 31.3). No He gas was used as aerosol carrier to increase sensitivity for Pb, because the MIC system is very sensitive at such a level that a real risk of counter saturation would occur for numerous U-enriched zircons and/or zircons of Precambrian age. 

Normalization Standard bracketing procedure Zircon standard 91500... 

Zircon standard Q1500 is free of common-Pb therefore, radiogenic Pb (Pb ) is identical to measured total Pb. 

H3). In addition, this ratio must be accurate. Thus, the Th/U is normalized using our zircon standard 91500. Considering that this standard does not contain any common-Pb, a correction coefficient is calculated to achieve a mean f m value equal to zero for all the standards analyzed during the session. 

TABLE 31.8 Summary of LA-MC-ICP-MS U-Pb Results for Zircon Standard 61.308B... 

The selection of a zircon standard is required for instrumental bias of the MC-ICP-MS and to adjust the parameters of the laser. A careful tuning of the MC-ICP-MS... 

Baddeleyite (Zr02) occurs in silica-poor rocks in which zircon may be absent. It generally has low common Pb and high U contents and is therefore very well suited to dating. It may be the one mineral for which external standardization with zircon could work, considering that zircon itself breaks down to baddeleyite with most commonly used lasers [40]. It has been analyzed by LA-Q-ICP-MS with zircon standardization [83], giving an Pb/ Pb age indistinguishable from that for zircons from the same mafic dyke sample (1353 + 14 versus 1345 + 12 Ma). 

TEMORA 1 a new zircon standard for Phanerozoic U-Pb geochronology. Chem. Geol, 200 (1-2), 155-170. 

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 206p /238u microprobe geochronology by the monitoring of a trace-element-related matrix effect SHRIMP, ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for a series of zircon standards. Chem. Geol, 205, 115-140. 

---