U-Pb dating of U-series disequilibrium zircons by secondary ion mass spectrometry
Determining the timescales of magma accumulation and storage prior to large eruptions is fundamental to understand the pre-eruptive history of magma reservoirs. Zircon 238 U- 230 Th dating has been widely used to recover the timescales of magma reservoirs younger than 400 ka. However, theoretically...
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Published in | Journal of analytical atomic spectrometry Vol. 36; no. 5; pp. 999 - 16 |
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Main Authors | , , , , , |
Format | Journal Article |
Published |
12.05.2021
|
Online Access | Get full text |
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Summary: | Determining the timescales of magma accumulation and storage prior to large eruptions is fundamental to understand the pre-eruptive history of magma reservoirs. Zircon
238
U-
230
Th dating has been widely used to recover the timescales of magma reservoirs younger than 400 ka. However, theoretically and practically, the uncertainties for zircons older than
ca.
150 ka,
i.e.
, two half-lives of
230
Th, are large because (
238
U)/(
230
Th) activities start to stabilize. On the other hand, the accumulation of radiogenic
206
Pb begins to increase significantly after two half-lives of
230
Th. Herein we theoretically demonstrate a calibration method for SIMS (Secondary Ion Mass Spectrometry)
238
U-
206
Pb dating within the timescales of U-series disequilibrium and apply it to zircons of the 75 ka Youngest Toba Tuff (YTT) in northern Sumatra, Indonesia. The
238
U-
206
Pb dates vary from
ca.
665 to 75 ka after common Pb and initial
230
Th disequilibrium corrections. This age range agrees with that obtained by previous studies using the
238
U-
230
Th method, but the precision of each age is improved by a factor of three or more.
238
U-
206
Pb and
238
U-
230
Th dating methods have advantages and disadvantages for zircons in U-series disequilibrium. The
238
U-
230
Th method is more suited to samples younger than 150 ka, but requires a large Th/U fractionation between the zircon and magma, and a high U content. The
238
U-
206
Pb method is more appropriate for samples older than 150 ka, but requires high U and low common Pb contents. Our approach improves the precision of
in situ
dating of zircon in U-series disequilibrium, which will contribute to investigations of the magmatic evolution beneath young volcanoes.
Theoretical and analytical methods for
238
U-
206
Pb dating of U-series disequilibrium zircons by secondary ion mass spectrometry are developed. U-Pb dates improve age precision 3 times better than U-Th dating for zircon >150 ka. |
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Bibliography: | 10.1039/d0ja00510j Electronic supplementary information (ESI) available. See DOI |
ISSN: | 0267-9477 1364-5544 |
DOI: | 10.1039/d0ja00510j |