In:
Geostandards and Geoanalytical Research, Wiley, Vol. 42, No. 1 ( 2018-03), p. 25-47
Abstract:
Most monazite reference materials ( RM s) for in situ U‐Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix‐matched RM s, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low‐U and low‐Th Diamantina monazite from the Espinhaço Range, SE Brazil. It has a U‐Pb ID ‐ TIMS weighted mean 207 Pb * / 235 U ratio of 0.62913 ± 0.00079, 206 Pb * / 238 U of 0.079861 ± 0.000088 and 207 Pb * / 206 Pb * of 0.057130 ± 0.000031, yielding a weighted mean 206 Pb * / 238 U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods ( LA ‐(Q, SF , MC )‐ ICP ‐ MS and SIMS ) are within uncertainty of the ID ‐ TIMS data. U‐Pb LA ‐(Q, MC )‐ ICP ‐ MS runs, using Diamantina as a primary RM , reproduced the ages of other established RM s within 〈 1% deviation. The LA ‐ MC ‐ ICP ‐ MS analyses yielded homogeneous Sm‐Nd isotopic compositions ( 143 Nd/ 144 Nd = 0.511427 ± 23, 2 s ; 147 Sm/ 144 Nd = 0.1177 ± 13, 2 s ) and εNd (495 Ma) of −18.7 ± 0.5 (2 s ). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2 s ), confirming Diamantina's relative homogeneity at test portion masses below 1 ng.
Type of Medium:
Online Resource
ISSN:
1639-4488
,
1751-908X
DOI:
10.1111/ggr.2018.42.issue-1
Language:
English
Publisher:
Wiley
Publication Date:
2018
detail.hit.zdb_id:
2276474-4
detail.hit.zdb_id:
2595219-5
detail.hit.zdb_id:
2134777-3
Permalink