[SGL36-P02] Paleomagnetism and Neogene tectonic rotation of the upper Amatsu Formation, the Awa Group, distributed in the Boso Peninsula, central Japan
Keywords:The Amatsu Formation, Paleomagnetism, Neogene tectonic rotation
Here, we report a reliable magnetostratigraphy and try to discuss about the tectonic rotation suggested by Okada and Okamura (2005).
Shimota et al. (2016) obtained paleomagnetic data from the entire Amatsu Formation exposed along the Shikoma River, which shows more tuffaceous lilthofacies rather than other region, which might have stable magnetic signals. Demagnetization results were displayed on both of the Zijderveld and equal area projection diagrams. Characteristic remanent magnetization (ChRM) was determined by fitting the least squares line to the linear vector endpoint trajectory (Kirschvink 1980). For each site, a site-mean direction was calculated from the ChRM directions. The reversal test (McFadden and McElhinny., 1990) on those results passed as the class C, indicating that the polarities are reliable. Therefore, those site-mean directions were estimate as primary component, the overall mean direction (D = 29.5°, I = 53.0°, α95 = 9.3°) is calculated. Comparing a declination of Okada and Okamura (2005), this declination was smaller by about 20°. As this cause, we presumed that the central part of the Boso Peninsula has complica ted geologic structure due to the development of numerous folds, faults and flexures (Kodama et al., 1990). So, a difference block rotation possibly occurred at the each block.
To discuss the above, we present new paleomagnetic data from the upper Amatsu Formation exposed along the Aikawa River in Takeoka area, Futtsu city, Chiba Prefecture on the west side and the Kanayama River reservoirs along the Kamogawa river in the Kamogawa city, the same prefecture on the east side. Based on the key beds, we correlated the result of paleomagnetic direction in the same time slice at area by area.
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