Resolving discordant U-Th-Ra ages: Constraints on petrogenetic processes of recent effusive eruptions at Tatun Volcano Group, northern Taiwan

Georg F. Zellmer, Kenneth H. Rubin, Christian A. Miller, J. Gregory Shellnutt, Alexander Belousov, Marina Belousova

Research output: Chapter in Book/Report/Conference proceedingChapter

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Abstract

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 226Ra-230Th disequilibrium in magnetite, and less than approximately 70 ka (but potentially Holocene) for a Huangzuei flow, based on 238U-230Th disequilibrium in plagioclase. Discordant Ar-Ar, 238U-230Th and 226Ra-230Th 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 234U-238U equilibrium. Minerals in the Mt Cising sample are in 234U-238U disequilibrium, despite the 234U-238U 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.

Original languageEnglish
Title of host publicationGeological Society Special Publication
PublisherGeological Society of London
Pages175-188
Number of pages14
Edition1
DOIs
Publication statusPublished - 2015 Jan 1

Publication series

NameGeological Society Special Publication
Number1
Volume422
ISSN (Print)0305-8719

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ASJC Scopus subject areas

  • Water Science and Technology
  • Ocean Engineering
  • Geology

Cite this

Zellmer, G. F., Rubin, K. H., Miller, C. A., Shellnutt, J. G., Belousov, A., & Belousova, M. (2015). Resolving discordant U-Th-Ra ages: Constraints on petrogenetic processes of recent effusive eruptions at Tatun Volcano Group, northern Taiwan. In Geological Society Special Publication (1 ed., pp. 175-188). (Geological Society Special Publication; Vol. 422, No. 1). Geological Society of London. https://doi.org/10.1144/SP422.3