[S-EM37_30PM1] 地磁気・古地磁気・岩石磁気

[SEM37-13] 本州東部に分布するZnp-Ohtaテフラの古地磁気と相対回転運動

*星 博幸¹、二村 昇² (1.愛知教育大学、2.豊橋市立二川南小学校)

キーワード：本州東部, 古地磁気, 鮮新世, 相対回転, テクトニクス, Znp-Ohtaテフラ

We present paleomagnetic data suggesting relative tectonic rotations in eastern Honshu since 3.9 Ma. Samples were collected from a widespread ash bed, called the Znp-Ohta tephra, at three localities. One is the Tomioka locality located to the east of the Abukuma Mountains, where the ash bed (local name = SF4.5 tephra) was samples at three sites. The other two are the Miyobara and Kohsaka localities on the Boso Peninsula, where the ash bed (local name = An85 tephra) was sampled at three sites at each locality. Stepwise demagnetization was performed on all specimens, and the principal component analysis was applied to the demagnetization data to extract characteristic remanent magnetization (ChRM) components. At Tomioka, site-mean ChRM directions were determined at all sites. They are tightly clustered after tilt correction and have a southerly direction of reverse polarity. Interestingly, the direction is deflected significantly counterclockwise with respect to the direction of the correlative tephra at Chita in central Honshu (Hoshi & Deguchi, 2013). At Miyobara and Kohsaka, the locality-mean ChRM directions are significantly different to each other. The paleodeclination of Miyobara is similar to that of Tomioka, and the paleodeclination of Kohsaka is almost identical to that of Chita. The difference in paleodeclination between Miyobara and Kohsaka seems to be related to the difference in the general geological trend of Neogene strata on the Boso Peninsula, suggesting relative rotation on the peninsula. Our results imply that in eastern Honshu, relative rotations have taken place at local and regional scales since the Pliocene.