SIMS ANALYSIS OF U-PB ISOTOPES IN MONAZITE - MATRIX EFFECTS

The calibration of U-Pb and Th-Pb ratios in Tb-U-rich minerals measure d by SIMS usually assumes that there are no matrix effects arising fro m the compositional difference between standard and sample. Matrix eff ects have been observed during attempts to calibrate U-Pb ratios of mo nazite using a SIMS energy-filtering technique on the ISOLAB-120 ion p robe. Thus matrix effects cannot be assumed to be insignificant a prio ri for SIMS U-Pb or Th-Pb chronometry, and need to be investigated mor e thoroughly. A general approach to the investigation of matrix effect s for SIMS U-Pb and Th-Pb analysis is proposed. (C) 1998 Elsevier Scie nce B.V.