Age of Initial Submarine Volcanism in the Paleo-Tsushima Basin and Implications for Submarine Volcanism in the Opening Stage of the Japan Sea in Northern Kyushu

Takashi Ninomiya,Shoichi Shimoyama,Hideki Iwano,Toshihiro Takahashi,Sho Taniguchi,Tohru Danhara

doi:10.3390/geosciences11090363

Takashi Ninomiya, Shoichi Shimoyama + Show 4 more

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https://doi.org/10.3390/geosciences11090363

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Abstract

The Tsushima Lapilli Tuff, the thickest tuff in the Taishu Group on Tsushima Island, underwent a thermal event after deposition, and has not previously yielded a reliable age because various ages have been reported. This study clarifies the eruption age and thermal history of the Tsushima Lapilli Tuff based on fission-track (FT) and U–Pb dating of zircon grains using laser ablation inductively coupled plasma mass spectrometry (ICP-LA-MS) and evaluates submarine volcanism during deposition of the Taishu Group in the southwestern Japan Sea, as well as volcanism change on Tsushima Island. This study revealed that thermal events caused rejuvenation in some single-grain FT ages after deposition in the Tsushima Group, and that the eruption age of the Tsushima Lapilli Tuff was 16.2 ± 0.7 Ma; the age of the largest submarine volcanism event in the Taishu Group in Tsushima Island was thus determined. On the basis of our previous studies, this age and tectonism strongly indicate that felsic submarine volcanism occurred between 18 and 16 Ma, accompanied by rapid subsidence, and the volcanism changed from felsic volcanism originating from melting of old continental crust by asthenospheric upwelling to mafic volcanism originating from small-scale lithospheric mantle upwelling from 13.6 Ma onward.

Highlights

Strata containing abundant pyroclastic rocks deposited during the opening stage of the Japan Sea (23–15 Ma) are distributed along the Japan Sea coast from southern Hokkaido to northern Kyushu (e.g., [1])
The pyroclastic strata are key to clarifying the volcanism and tectonism sequence of the opening stages of the Japan Sea, and numerous studies have been performed for that purpose (e.g., [2–4])
The Miocene Taishu Group, widely distributed in the southwestern Japan Sea, is an important group because it connects the Green Tuff region and the Miocene groups distributed in northern Kyushu such as the Goto Group in the Goto Islands and Nojima Group in the Sasebo district [5]

Summary

Introduction

Strata containing abundant pyroclastic rocks deposited during the opening stage of the Japan Sea (23–15 Ma) are distributed along the Japan Sea coast from southern Hokkaido to northern Kyushu (e.g., [1]). The pyroclastic strata are key to clarifying the volcanism and tectonism sequence of the opening stages of the Japan Sea, and numerous studies have been performed for that purpose (e.g., [2–4]). The Miocene Taishu Group, widely distributed in the southwestern Japan Sea, is an important group because it connects the Green Tuff region and the Miocene groups distributed in northern Kyushu such as the Goto Group in the Goto Islands and Nojima Group in the Sasebo district [5]. The Taishu Group is a thick marine group (>5000 m) containing abundant pyroclastic rocks. The Taishu Group has been suggested to have been deposited between the early Eocene and early Miocene, and the age of the group has been regarded as evidence supporting the idea that the Japan

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