Paleomagnetism of the Lower to Middle Miocene Series in the Yatsuo area, eastern part of southwest Japan: clockwise rotation and marine transgression during a short period

Abstract

Process of the tectonic rotation related to Japan Sea opening is viewed from tilt-corrected paleomagnetic data obtained from the Early to Middle Miocene sequence in the Yatsuo area on the Japan Sea coast, eastern part of southwest Japan. Progressive demagnetization experiments have been executed on samples obtained from two routes along the Yamada and Wada Rivers, and successfully isolated stable primary magnetic components in 16 sites. Together with data of previous studies, tilt-corrected reliable paleomagnetic directions comprising 10 normal and 27 reversed polarity sites of the Yatsuo Group on accurate stratigraphic positions show systematic temporal variation of easterly deflection in declinations. On the basis of our presented magnetostratigraphy, Yatsuo Group is assigned from the late Early to early Middle Miocene. Significant stage of rotation as much as 30 is specified during late Early Miocene between a period of active volcanism and subsequent period of marine transgression. We suggest that the Japan Sea opening event had a final phase of rapid rotation around the late Early Miocene, which seems to have caused marine transgression in relation to remarkable subsidence along the Japan Sea coast.

Instantaneous paleomagnetic record from the Miocene Kozagawa Dike of the Kumano Acidic Rocks, Kii Peninsula, Southwest Japan: cautionary note on tectonic interpretation

“…(); 9, H oshi & Y okoyama (); 10, I toh & I to (); 11, T amaki et al . (). (b) G eological map of the K umano A cidic R ocks ( KAR ), simplified from A ramaki & H ada () and K awakami et al .…”

“…; Itoh & Kitada ; Tamaki et al . ). Early Miocene or older directions ( ca 23–16 Ma) generally yield northeast declinations, which have been interpreted as showing that Southwest Japan has experienced a clockwise rotation.…”

“…Extensive paleomagnetic studies of the circum-Japan Sea region (i.e., Japan, South Korea, northeast China, and eastern Russia) have been carried out since the 1980s to understand the tectonic evolution of this region. In Southwest Japan, remanent magnetization (or remanence) directions of Miocene age have been documented from a number of areas in order to constrain the tectonics of Southwest Japan, particularly those associated with the back-arc opening of the Japan Sea (e.g., Otofuji 1996;Ishikawa 1997;Hoshi et al 2000;Iwaki & Itoh 2000;Hoshi & Yokoyama 2001;Kojima et al 2001;Shimada et al 2001;Itoh & Kitada 2003;Tamaki et al 2006). Early Miocene or older directions (ca 23-16 Ma) generally yield northeast declinations, which have been interpreted as showing that Southwest Japan has experienced a clockwise rotation.…”

“…Because previous paleomagnetic studies of the KAR have all been published in the Japanese literature, here we briefly review these studies. Torii & Ishikawa (1986); 3-6, Torii (1983);7, Hoshi et al (2000); 8, Otofuji et al (1991);9, Hoshi & Yokoyama (2001); 10, Itoh & Ito (1989); 11, Tamaki et al (2006) Tagami (1982) conducted the first paleomagnetic investigation of the KAR based on a suite of rhyolite (11 sites), tuff (8 sites), and granite porphyry (6 sites) samples. Stepwise alternating-field (AFD) and thermal demagnetization (ThD) was carried out on pilot samples, and the remaining samples were subjected to blanket demagnetization (Butler 1992).…”

Timing of clockwise rotation of Southwest Japan: constraints from new middle Miocene paleomagnetic results

“…The data from Izumo also suggest that clockwise rotation was complete by 15 Ma. Furthermore, studies conducted in other areas of Southwest Japan have provided timeaveraged mean directions suggesting little or no rotation since 15 Ma (Nakajima et al 1990;Itoh et al 2000;Hoshi et al 2000b;Hoshi and Yokoyama 2001;Tamaki et al 2006;Hoshi and Sano 2013).…”