A large caldera cluster consisting of at least four calderas (Omine, Odai, Kumano‐North and Kumano calderas) existed in the central–southern part of the Kii Peninsula approximately 14–15 Ma. On the other hand, thick Middle Miocene ash‐flow tuffs, referred to as the Muro Ash‐flow Tuff and the Sekibutsu Tuff Member, are distributed in the northern part of the Kii Peninsula. Although these tuffs are considered to have erupted from the caldera cluster in the central‐southern Kii Peninsula, identifying the source caldera in the cluster has been controversial because of similarities in the petrological characteristics and identical radiometric ages of the volcaniclastic rocks of these calderas. We successfully discriminated the characteristics of the eruptive products of each caldera in the caldera cluster based on the apatite trace‐element compositions of the pyroclastic dikes and ash‐flow tuffs of the calderas. We also demonstrated that the source caldera of at least the lower main part of the Muro Ash‐flow Tuff and the Sekibutsu Tuff Member was the Odai Caldera, which is located in the central Kii Peninsula. Our findings show possible correlations among the pyroclastic conduits and ash‐flow tuffs of the caldera‐fill and/or outflow deposits, even in cases where they have been densely welded and diagenetically altered. This method is useful for the study of deeply eroded ancient calderas.

中文翻译：

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基于磷灰石痕量元素组成的基伊半岛中新世中灰凝灰岩源火山口的鉴定

在基伊半岛中南部大约14-15 Ma处，存在着一个由至少四个火山口（大峰，乌代，熊野北部和熊野火山口）组成的大型火山口群。另一方面，在纪伊半岛的北部分布着厚的中新世中度灰烬凝灰岩，被称为Muro灰烬凝灰岩和Sekibutsu凝灰岩成员。尽管这些凝灰岩被认为是从纪伊半岛中南部的火山口喷发而来的，但由于这些火山口的火山碎屑岩的岩石学特征和相同的辐射年龄，确​​定该火山喷发源中的火山口一直存在争议。我们根据火山灰碎石的火山灰岩中的磷灰石微量元素组成和火山灰的灰泥凝灰岩，成功地辨别了火山灰群中每个火山灰的爆发产物的特征。我们还证明，至少Muro灰流凝灰岩下部和Sekibutsu凝灰岩成员的下部主要火山口是位于纪伊半岛中部的Odai Caldera。我们的研究结果表明，即使在火山灰密实地焊接和径向改变的情况下，火山碎屑充填和/或流出沉积物的火山碎屑导管与灰泥凝灰岩之间也可能存在相关性。该方法对于研究深度侵蚀的古代破火山口很有用。我们还证明，至少Muro灰流凝灰岩下部和Sekibutsu凝灰岩成员的下部主要火山口是位于纪伊半岛中部的Odai Caldera。我们的研究结果表明，即使在火山灰密实地焊接和径向改变的情况下，火山碎屑充填和/或流出沉积物的火山碎屑导管与灰泥凝灰岩之间也可能存在相关性。该方法对于研究深度侵蚀的古代破火山口很有用。我们还证明，至少Muro灰流凝灰岩下部和Sekibutsu凝灰岩成员的下部主要火山口是位于纪伊半岛中部的Odai Caldera。我们的研究结果表明，即使在火山灰密实地焊接和径向改变的情况下，火山碎屑充填和/或流出沉积物的火山碎屑导管与灰泥凝灰岩之间也可能存在相关性。该方法对于研究深度侵蚀的古代破火山口很有用。