10.6084/m9.figshare.3453920.v1
Georg F. Zellmer
Georg F.
Zellmer
Kenneth H. Rubin
Kenneth H.
Rubin
Christian A. Miller
Christian A.
Miller
J. Gregory Shellnutt
J.
Gregory Shellnutt
Alexander Belousov
Alexander
Belousov
Marina Belousova
Marina
Belousova
Resolving discordant U–Th–Ra ages: constraints on petrogenetic processes of recent effusive eruptions at Tatun Volcano Group,
northern Taiwan
Geological Society of London
2016
Tatun Volcano Group
Mt Cising
equilibrium
Ra
Huangzuei volcano
Shamao dome
eruption
isochron
disequilibrium
crystal
Th
lava
Mt Cising sample
Holocene
mineral
Geology
2016-06-21 11:46:09
Journal contribution
https://geolsoc.figshare.com/articles/journal_contribution/Resolving_discordant_U_Th_Ra_ages_constraints_on_petrogenetic_processes_of_recent_effusive_eruptions_at_Tatun_Volcano_Group___northern_Taiwan/3453920
<p>U–Th–Ra isotope analyses of whole rocks and mineral separates were conducted in order to perform isochron dating of three
morphologically young lavas from Tatun volcano, northern Taiwan (from Mt Cising, the Shamao dome and the Huangzuei volcano).
The data do not yield tight U–Th isochrons, indicating open-system magmatic processes. However, crystallization ages of two
samples can be constrained: namely, less than about 1370 years for the Shamao dome, based on <sup>226</sup>Ra–<sup>230</sup>Th disequilibrium in magnetite, and less than approximately 70 ka (but potentially Holocene) for a Huangzuei flow, based on
<sup>238</sup>U–<sup>230</sup>Th disequilibrium in plagioclase. Discordant Ar–Ar, <sup>238</sup>U–<sup>230</sup>Th and <sup>226</sup>Ra–<sup>230</sup>Th ages are best explained by young lavas having inherited some crystals from older lithologies (crystal mushes or rocks),
and indicate that the above ages represent maxima. Our study provides the first evidence of effusive volcanism at the Tatun
Volcano Group in Late Holocene times. All separates from the Shamao dome and Huangzuei volcano are in <sup>234</sup>U–<sup>238</sup>U equilibrium. Minerals in the Mt Cising sample are in <sup>234</sup>U–<sup>238</sup>U disequilibrium, despite the <sup>234</sup>U–<sup>238</sup>U equilibrium of the whole rock. We interpret this as uptake of a hydrothermally altered, old crystal cargo into fresh melt
prior to eruption. A different dating approach will thus be required to constrain the eruption age of Mt Cising.
</p>