[S-EM15] 地磁気・古地磁気・岩石磁気

[SEM15-P16] 阿蘇2/1溶岩の古地磁気学的研究

*望月 伸竜¹、大西 優輝²、石丸 聡子¹ (1.熊本大学大学院先端科学研究部　基礎科学部門　地球環境科学分野、2.熊本大学理学部)

キーワード：古地磁気方位、古地磁気永年変化、阿蘇２、秋田溶岩、岩戸溶岩、瀬田裏溶岩

We conducted a paleomagnetic study on lavas in the Aso caldera wall and out of the Aso caldera, called Aso-2/1 lavas. Stratigraphic levels of these lavas were recognized above Aso-1 pyroclastic flow deposit and below the Aso-2 pyroclastic flow deposit. We collected oriented samples from each of Hokamaki, Matoishi, Togawa, Tamaraigawa, Setaura, and Akita lavas, and the Aso-2 pyroclastic flow deposit. Paleomagnetic directional measurements using alternating field demagnetization were made on the samples. Our paleodirection results combined with the previous data indicate estimates on the temporal gaps between a lava and the Aso-2 pyroclastic flow deposit, and the temporal gaps between lava flows. The paleomagnetic direction of the Akita lava is indistinguishable from that of the Aso-2 pyroclastic flow deposit; this result indicates the Akita lava extruded just before the Aso-2 eruption. In contrast, the paleomagnetic direction of the Setaura lava differs by more than 15 degree from that of the Aso-2 pyroclastic flow deposit; this suggest a temporal gap of 300 year or longer. We will show a modified stratigraphic relationship of the Aso-2/1 lavas based on our paleomagnetic data.