BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
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Detrital zircon U–Pb age of the Jurassic accretionary complex in the western area of Lake Towada located between Akita and Aomori prefectures, Northeast Japan.
Takayuki Uchino
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2018 Volume 69 Issue 1 Pages 37-46

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Abstract

Jurassic accretionary complexes are broadly distributed in the North Kitakami Belt in the Kitakami Massif, Northeast Japan. Meanwhile, the accretionary complexes rarely occur in the western area of the N–S-trending Ou Mountain Range because they are broadly covered and intruded by the Cenozoic erathem. Therefore, the accretionary complexes in the western area provide insufficient geoinformation: their geologic age and correlation to the accretionary complexes in the Kitakami Massif. In this study, the U–Pb ages of detrital zircon from sandstone were examined to understand the geologic age of the accretionary complexes, which are sparsely distributed in the western area of Lake Towada within the Ou Mountain Range. Consequently, 174.6 ± 0.7 Ma was obtained as a weighted mean age of the youngest age component of grain-age distribution (i.e., youngest cluster). Therefore, it has been confirmed that the sandstone was deposited after Middle Jurassic. A pattern of the relative probability of the detrital zircon ages shows the distribution of intensive peaks for the Permian–Jurassic period of the Phanerozoic and minor peaks for Paleoproterozoic. This pattern is considerably similar to that obtained for the Middle Jurassic–Lower Cretaceous shallow-marine deposits in the South Kitakami Belt. The geologic age of the Mesozoic accretionary complexes in the Tohoku area shows a younging trend from the Late Triassic to earliest Cretaceous toward the Pacific Ocean according to previous studies. Based on this younging trend, the accretionary complex in the western area of Lake Towada probably correlates to the Middle Jurassic accretionary complex.

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© 2018 National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan
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