Abstract In tephrochronology, trace-element compositions of apatite phenocrysts are useful because they change in response to various magmatic conditions as apatite crystallizes. Moreover, because apatite tolerates burial diagenesis and welding processes without chemical changes, its trace-element compositions are a powerful tool for correlating pre-Quaternary tephra; however, this method is not extensively applied. The Hirosegawa Tuff, composed of a pair of Pliocene ash-fall and ash-flow tuffs, is a distinctive marker tephra that is used in geological mapping and for correlating sedimentary rocks in the eastern part of central NE Japan. However, the source volcano of the Hirosegawa Tuff has not been identified because many calderas coexisted in NE Japan during the Pliocene. Analysis of the trace-element compositions of apatite, major element compositions of ilmenite, and U-Pb zircon ages demonstrate that, depending on the area, the previously mapped Hirosegawa Tuff comprises different volcanic ejecta. Furthermore, this study identified that the source volcano of the Hirosegawa Tuff in the type section was the Shiroishi Caldera, located 50 km south of Sendai City.

中文翻译：

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基于磷灰石微量元素成分和锆石U-Pb年龄识别日本东北部上新世灰流凝灰岩源火山口

摘要 在地质年代学中，磷灰石斑晶的微量元素组成是有用的，因为当磷灰石结晶时，它们会响应各种岩浆条件而发生变化。此外，由于磷灰石可以耐受埋藏成岩和焊接过程而不会发生化学变化，因此其微量元素成分是关联第四纪前火山灰的有力工具；然而，这种方法并没有被广泛应用。广濑川凝灰岩由一对上新世落灰凝灰岩和灰流凝灰岩组成，是一种独特的标记 tephra，用于地质绘图和关联日本东北中部东部的沉积岩。然而，广濑川凝灰岩的源火山尚未确定，因为在上新世期间日本东北部有许多火山口共存。磷灰石微量元素组成分析，钛铁矿的主要元素组成和 U-Pb 锆石年龄表明，根据地区的不同，先前绘制的广濑川凝灰岩包含不同的火山喷发物。此外，这项研究确定了类型剖面中广濑川凝灰岩的源火山是位于仙台市以南 50 公里处的白石火山口。