DATE2025.09.03 #Press Releases

Unraveling the Origin of the “Peak of Volcanic Activity” in Japan

Summary

A research team consisting of Ken Yamaoka (Researcher), Daisuke Sato (Senior Researcher), and Kazune Mikuni (Researcher) of the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), together with Tokiyuki Morohoshi (Graduate Student) of the Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, has clarified the cause of ignimbrite flare-ups in the Japanese Islands during the Cretaceous to Paleogene periods by analyzing the isotopic compositions of elements contained in igneous rocks distributed across the Japanese Islands and the Korean Peninsula.

Ignimbrite flare-ups refer to a phenomenon in which large caldera-forming eruptions occur repeatedly within the same region over geologically short timescales. This phenomenon has been confirmed in various parts of the world and is known to have occurred in the Japanese Islands between the Late Cretaceous and Early Paleogene (approximately 90 to 60 million years ago). Frequent large-scale caldera-forming eruptions can exert significant influence on the Earth’s surface environment, yet their causes have long been debated and remain unclear.

In this study, the team compiled and organized numerous previously reported results on the isotopic compositions of strontium (Sr) and neodymium (Nd) in igneous rocks from the Cretaceous to Paleogene periods across the Japanese Islands and the Korean Peninsula. They demonstrated that the isotopic composition of magma underwent a rapid change around 100 million years ago. Furthermore, they examined how the temporal changes in the chemical composition of related magmas corresponded to the geological settings in which these rocks formed.

As a result, the researchers revealed that ignimbrite flare-ups in Japan were triggered by the influx of hot mantle material into the base of the continental plate immediately prior to the events. This influx of hot mantle is thought to have been caused by “slab rollback,” a process in which the edge of an old oceanic plate spread beneath the continent deforms by rolling back toward the mantle. These findings are expected to contribute to elucidating the causes of ignimbrite flare-ups worldwide, including those in the circum-Pacific region.

The details of this research were published in Progress in Earth and Planetary Science on September 2, 2025.

Figure：Mechanism of ignimbrite flare-ups in Japan during the Cretaceous–Paleogene

Links

National Institute of Advanced Industrial Science and Technology (AIST)

Journals

Journal name	Progress in Earth and Planetary Science
Title of paper	Ignimbrite flare-up in Late Cretaceous–Paleocene Japan empowered by hot mantle inflow