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Depositional age of the H imenoura G roup on the A makusa‐ K amishima area, K yushu, southwest J apan: U sing zircon U – P b dating of the acidic tuffs
Author(s) -
Tsutsumi Yukiyasu,
Miyake Yuka,
Komatsu Toshifumi
Publication year - 2017
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12194
Subject(s) - sedimentary depositional environment , zircon , geology , geochemistry , age groups , mineralogy , paleontology , demography , structural basin , sociology
The U pper C retaceous H imenoura G roup in the A makusa‐ K amishima I sland area, southwest Japan is subdivided into the H inoshima and A mura Formations. In order to determine the numerical depositional age of the formations, zircon U – P b ages were investigated using laser ablation inductively coupled plasma mass spectrometry ( LA – ICP – MS ) for acidic tuff samples from the lower part of the H inoshima F ormation and the upper part of the A mura F ormation. Although the two samples contain some accidental zircons, the samples have a definite youngest age cluster and their weighted mean ages are 85.4 ± 1.3 and 81.5 ± 1.1 M a, respectively (errors are 95 % confidence interval). These age data indicate that the H imenoura G roup in the A makusa‐ K amishima I sland area was deposited mainly in the early S antonian to early C ampanian which is consistent with biostratigraphic ages. Additionally, zircon age distributions of the two tuff samples from the upper part of the H inoshima F ormation do not show a distinct youngest peak of eruption age but characteristics of detrital zircons suggestive of maximum depositional age of the host sediments. These results demonstrate that the mean age of the youngest zircon age cluster of a tuff sample does not always indicate depositional age of the tuff, and statistical evaluation of age data is effective to determine depositional age of a tuff bed using zircon U – Pb ages.