Paleomagnetic evidence for the clockwise rotation of Southwest Japan |
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| Authors: | Yo-ichiro Otofuji Takaaki Matsuda |
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| Institution: | 1. Department of Geology and Mineralogy, Faculty of Science, Kyoto University, Kyoto 606Japan;2. Department of Geology, Himeji Institute of Technology, Himeji 671-22Japan |
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| Abstract: | Over 500 oriented samples of felsic rocks of Cretaceous to Middle Miocene age were collected along the Go¯River in the central part of Southwest Japan, in an attempt to detect the process of tectonic rotation of Southwest Japan from the paleomagnetic view point. Thermal demagnetization was successful in isolating characteristic directions from the remanent magnetization of samples. Reliability of the paleomagnetic direction is ascertained through the agreement of directions from different kinds of rocks as well as the presence of both normal and reversed polarities. The paleomagnetic results establish that Southwest Japan began to rotate clockwise through58 ± 14° later than 28 Ma and ceased its motion by about 12 Ma. Southwest Japan has undergone no detectable north-south translation since 28 Ma. These results imply that southwest Japan was rotated about the pivot around 34°N, 129°E between 28 Ma and 12 Ma in association with the opening of the Japan Sea. |
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