Paleomagnetism of the Miocene Igneous Rocks in the Uchiyama Area, Central Japan.

Abstract

Paleomagnetism of the Miocene igneous rocks in the Uchiyama area, central Japan, have been determined in an effort to clarify the rotation of the Kanto Mountains located on the east wing of the sharp bent structure of the pre-Neogene basement rocks (Kanto Syntaxis). A mean tilt-corrected paleomagnetic direction of the Yaekubo Formation (D = -145.3°, I = -51.2°, α95 = 4.4°) shows eastward deflected declination indicating the clockwise rotation of the east wing of the Kanto Syntaxis. The radiometric ages of the andesite lava in the Yaekubo Formation (11.9 ± 0.9 Ma, 12.2 ± 0.3 Ma and 12.4 ± 0.4 Ma) signify that the about 35° clockwise rotation of the east wing of the Kanto Syntaxis occurred since 12 Ma. Along with the previous paleomagnetic studies in the Kanto Mountains and in its adjacent area into consideration, we can conclude that the lateral bending of the Kanto Syntaxis was formed in the Middle to Late Miocene.