Early Miocene paleomagnetic results from the Ninohe area, NE Japan: Implications for arc rotation and intra-arc differential rotations

Abstract

We have carried out a paleomagnetic study on well-dated Early Miocene volcanic rocks from the Ninohe area in northern NE Japan. Dacitic welded tuffs ranging from 24 to 21 Ma possess westerly paleomagnetic directions with normal polarity (formation-mean: D/I = 294.5°/44.2° with α 95 = 8.3°, 8 sites), while the andesite flows formed at 17 Ma exhibit southerly directions with reversed polarity (D/I = 186.6°/-61.9°, 2 sites). A positive conglomerate test assures the stability of high-temperature components of remanent magnetization. Our results demonstrate that northern NE Japan rotated counter-clockwise through more than 60° between 21 and 17 Ma, most likely in association with the opening of the Japan Sea. The rotation of northern NE Japan thus preceded the about 15 Ma rapid clockwise rotation of SW Japan, and was synchronous with the possible pre-16 Ma southward translation of it. In comparison with published data, we further suggest that intra-arc block rotations occurred in the back-arc region of NE Japan during and after the arc rotation.

Paleomagnetic evidence for Miocene transtensional deformations at the eastern margin of the Japan Sea

“…There are two lines of evidence. First, the frontal arc, such as the Kadonosawa district (Hayashida, 1994;Hoshi and Matsubara, 1998), rotated as much as the inner arc. Second, the counterclockwise block rotations in the backarc region should have resulted in the left-lateral displacement of the blocks with respect to the less rotational frontal arc.…”

Paleomagnetism of the Ishikoshi Andesite: a Middle Miocene paleomagnetic pole for northeastern Japan and tectonic implications

“…1997; Hoshi and Matsubara, 1998;Takahashi et al, 1999). The geology of the Ishikoshi area was described in a series of geological maps published by the Geological Survey of Japan (Matsuno, 1967;Takeuchi and Kaneko, 1996).…”

“…Otofuji et al (1985bOtofuji et al ( , 1994 proposed a simple kinematic model involving the fan-shaped opening of the Japan Sea, in which northeastern Japan rotated simultaneously with the clockwise rotation of southwestern Japan at about 15 Ma (Middle Miocene). In contrast to this interpretation, some paleomagnetic measurements suggest that the rotation of northeastern Japan was a few million years earlier than that of southwestern Japan (Yamazaki, 1989;Tanaka et al, 1991;Hoshi and Takahashi, 1997;Hoshi and Matsubara, 1998;Takahashi et al, 1999). A review of paleomagnetic data led to the conclusion that the rotation of northeastern Japan was in the Early Miocene (approx.…”

“…For example, Hirooka et al (1990) and Momose et al (1990) reported northwesterly directions from sediments in the back-arc region that were dated biostratigraphically at 15-14 Ma. Such directions are considered to represent intra-arc block rotation during or after the formation of the Japan Sea (Oda et al, 1989;Hirooka et al, 1990;Hoshi and Matsubara, 1998;Yamaji et al, 1999;Mino et al, 2001). Yamaji et al (1999) argued that the block rotation was associated with transtensional deformation.…”

The block rotation in the Uetsu area, Northern Part of Niigata Prefecture, Japan

“…Paleomagnetic studies have shown that NE Japan consisted primarily of counter-clockwise (CCW) rotating blocks when the Japan Sea opened (Sasajima, 1981;Otofuji et al, 1985Otofuji et al, , 1994Hoshi and Matsubara, 1998;Yamaji et al, 1999). However, clockwise (CW) deflections are reported from the Takadate, Yanagawa, Matsushima areas, indicating CW rotations (Oda et al, 1989;Yamazaki, 1989).…”