Paleomagnetic stratigraphy of the Late Cenozoic formations in the Togo area, Hokusatsu district, southern Kyushu, Japan

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Paleomagnetic studies were carried out on the Late Cenozoic rocks in the Togo area, Hokusatsu district, southern Kyushu. Paleomagnetic data were obtained from twelve sites of the Togo and Kasayama Formations, and Togo Andesites. These data sets are primary natural remanent magnetizations because of a positive result of the reversal test. The Togo Formation and hornblende andesite lava of Togo Andesites have reversed polarity magnetizations. The basaltic andesite lava of the Togo Andesites which is the uppermost layer of the Late Pliocene succession in the area has a normal one. The K-Ar age of the basaltic andesite lava is 2.9 ± 0.2Ma. Consequently, the norma polarity of the lava corresponds to the C2An.1n normal polarity subchron (2.58-3.04 Ma) and the Togo Formation may be correlated with the C2An.1r reversed polarity subchron (3.04-3.11 Ma) which is just before the C2An.1n. The results from the polarity sequence reveal that the Togo Formation is lower horizon than the Nagano Formation of which age is 1.8-2.6 Ma, although the Togo Formation has been thought to be the same horizon of the Nagano Formation. The overall mean direction of Pliocene rocks in the Togo area is Dec = 330°, Inc = +45°, α_<95> = 13°, and accords with the paleomagnetic directions of Middle Miocene to Pliocene in southern Kyushu. The deflection in southern Kyushu becomes small until 0° at Early Quaternary time. The Togo Formation having westward deflection seems to be older than the Nagano Formation of no westward deflection from the consideration of a counterclockwise rotation. The estimation of these tectonic aspects is concordant with the results from the polarity sequence.
鹿児島大学の論文
2003-12-30

Paleomagnetic stratigraphy of the Late Cenozoic formations in the Togo area, Hokusatsu district, southern Kyushu, Japan

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