担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

<jats:title>Abstract</jats:title>
<jats:p>We conducted paleomagnetic analysis of two late Pleistocene caldera-forming eruption deposits, the Aso-4 tephra from the Aso caldera in Kyushu and Kp II/III deposits from the Kutcharo caldera in Hokkaido Japan, to constrain the time scales of the successive tephra layers and evaluate their chronological relationships. Aso-4 tephra covers most of the Japanese archipelago and is known as a representative, late Pleistocene time marker. Kp II/III deposits are distributed in eastern Hokkaido and subdivided into three subunits (Kp III, Kp III -ash, and Kp II in ascending order). We investigated the detailed stratigraphy of Aso-4 tephra and Kp II/III deposits. Kp II/III deposits directly overlie Aso-4 tephra at the observed outcrop, while a thin (&lt; 1 cm) brown weathered ash layer recognized between Kp III-ash and Kp II indicates an eruption hiatus. Oriented cube samples were collected from Aso-4 tephra and Kp II/III deposits and were subjected to thermal demagnetization experiments to determine their characteristic remanent magnetization (ChRM). The mean ChRM directions for Kp III, Kp III-ash, and Kp II are distinguishable at the 95% confidence interval (α<jats:sub>95</jats:sub>). Based on the angular difference in ChRM directions and the maximum rate of change observed for the archaeomagnetic secular variation curve in Japan, we suggest that the time gaps between Kp III and Kp III -ash was at least 71 ± 34 years and that between Kp III -ash and Kp II was at least155 ± 28 years. Mean ChRM direction of the Aso-4 tephra was also well determined (α<jats:sub>95</jats:sub> = 3.0°) and shows good agreement with the published data. Mean ChRM direction of the Aso-4 tephra is indistinguishable from that of the Kp III which directly overlies Aso-4 tephra. These results indicate that both caldera-forming eruptions of Kp III in Hokkaido and Aso-4 in Kyushu occurred only within a few decades. They can be considered to be an example of “synchronous caldera-forming eruptions” where they are located &gt; 1,500 km apart.</jats:p>
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<jats:bold>Graphical Abstract</jats:bold>
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DOI： 10.1186/s40623-025-02230-9

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担当区分：筆頭著者,　責任著者  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

<jats:title>Abstract</jats:title><jats:p>To constrain the age and duration of large-scale caldera-forming eruptions, we measured paleomagnetic directions of pyroclastic deposits from the 30 ka Aira caldera eruption sequence, and the 60–45 ka Iwato pyroclastic flow deposits around Aira caldera in southern Kyushu, Japan. The 30 ka Aira caldera eruption sequence consists of Osumi pumice fall (OS), Tarumizu pyroclastic flow deposit (TM), Ito ignimbrite (IT) and co-ignimbrite ash (AT), in ascending order. Oriented samples were collected by drilling for OS, TM and welded ignimbrites, and by cubing for non-welded (unconsolidated) pyroclastic flow deposit. We systematically sampled Ito ignimbrite with the degree of welding as: non-welded (IT1), moderately welded (IT2), and strongly welded (IT3) facies that is limitedly distributed in north of Aira caldera. Mean paleomagnetic directions of OS, TM, IT1 and IT2 are consistent with those previously reported for AT and welded facies of IT. Although OS samples were collected from multiple pumice clasts at proximal locations, we obtained well-defined mean paleomagnetic directions corresponding to those of co-eruptive pyroclastic flow (TM). This suggests that even clast-supported and non-welded pumice fall can retain thermoremanent magnetization at the time of deposition. Significance tests for our mean paleomagnetic directions showed that of all sequential units of the Aira caldera-forming eruption deposits, only IT3 has a different paleomagnetic direction. Based on reported paleosecular variation changing rates in Japan, and on the angular difference associated with error of the two paleosecular directions, we estimate the time gap between IT3 and IT2, to be 24.3 ± 16.3 years. A conductive cooling model explains this time difference as due to differences in cooling time between quickly, and slowly cooled parts of a thick single ignimbrite unit. Although the possibility that multiple flow units occurred within tens of years of each other cannot be excluded, there are no observations of clear flow unit boundaries in the Ito ignimbrite to support the suggestion that the Aira caldera-forming eruption sequence was deposited within a shorter time than years. In addition, the age of Iwato pyroclastic flow deposit, which has been situated between 60 and 45 ka, was estimated by calculating the angular distance between the mean paleomagnetic direction and the modeled secular variation curve from the GGF100 ka. As the result, we determine the most probable age to be around 56 ka.</jats:p>
<jats:p><jats:bold>Graphical abstract</jats:bold></jats:p>

DOI： 10.1186/s40623-024-02089-2

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jvolgeores.2024.108125

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DOI： 10.18940/kazan.69.2_79

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開催年月日： 2024年10月

会議種別：ポスター発表  

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開催年月日： 2024年10月

会議種別：口頭発表（一般）  

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開催年月日： 2024年9月

会議種別：ポスター発表  

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開催年月日： 2023年10月

会議種別：口頭発表（一般）  

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開催年月日： 2023年1月 - 2023年2月

会議種別：ポスター発表  

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