Nondestructive chemical dating of young monazite using XRF. 1. Design of a mini-probe, age data for samples from the Central Alps, and comparison to U-Pb (TIMS) data
Engi, M; Cheburkin, AK; Koppel, V
| HERO ID | 3576142 |
|---|---|
| In Press | No |
| Year | 2002 |
| Title | Nondestructive chemical dating of young monazite using XRF. 1. Design of a mini-probe, age data for samples from the Central Alps, and comparison to U-Pb (TIMS) data |
| Authors | Engi, M; Cheburkin, AK; Koppel, V |
| Journal | Chemical Geology |
| Volume | 191 |
| Issue | 1-3 |
| Page Numbers | 225-241 |
| Abstract | The analytical capabilities of an improved mini-XRF instrument for trace element analysis are explored to obtain U-Th-Pb ages. For single monazite grains as small as 50 gm, the detection limits for U, Th and Pb, with counting times of 10 min, are similar to10 ppm; counts collected for 40 min are sufficient to date single monazite grains as young as 15 Ma. The precision of the age data depends essentially on the counting statistics of the main X-ray peak (N-Pb (Lalpha) (1/2)) used to analyze for lead; the age uncertainty is proportional to the age of the grain, the total contents of Th and U, and the (squared) integration time. The reliability of the chemical dating method is tested using monazite separates from amphibolite facies metamorphic monazite samples from the central Alps, for which the chemical ages are compared to mass spectrometric (U-Pb TIMS) ages. We show that populations of analyses obtained using the new instrument on single grains as young as 25-30 Ma agree within error with the TIMS data. For monazite separates with complex age patterns, such as polymetamorphic samples yielding discordant isotopic ages, the statistical analysis of chemical age data, obtained from populations of 26-50 grains, is advantageous in that it may provide additional insight into the reasons for the discordancy. Chemical Th-U-Pb dating of monazite by the XRF method offers considerably improved accuracy and precision, compared with chemical dating by electron microprobe, which typically becomes impractical for samples less than 100-200 Ma in age. Conversely, the minimum grain size required for the new instrument (Phi similar to 50 mum) is well above the spatial ;resolution of the electron microprobe (Phi similar to 2 mum). A companion paper [Scherrer et al., this volume] describes further developments towards microanalysis by XRF, with improved spatial resolution. (C) 2002 Elsevier Science B.V All rights reserved. |
| Doi | 10.1016/S0009-2541(02)00158-4 |
| Wosid | WOS:000179511500014 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |
| Keyword | monazite; Th-U-Pb dating; XRF; chemical dating; Central Alps |