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＜紀要論文＞
鹿児島県八重山付近の火山岩類・火砕流 : 堆積物の古地磁気
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| 概要 | Paleomagnetic measurements were made on samples collected from the Plio-Pleistocene volcanic rocks and pyroclastic flow deposits in the vicinity of the Mt. Yaeyama. The remanent magnetization was meas...ured on about 400 oriented samples from 57 sampling sites. One or two pilot samples at each sampling site were progressively demagnetized in the alternating field up to 600 Oe. The results are summarized in Table 2. The virtual geomagnetic pole (V. G. P.) positions for the volcanic rocks and the pyroclastic flow deposits, except for the samples from the lower pyroclastic flow (2) (Nos. 35, 36, 37) of the Nagano Formation, are distributed around the present geographic pole. The lower pyroclastic flow (2) (Nos. 35, 36, 37) of the Nagano Formation shows the intermediate directions of NRM. The intermediate directions of NRM of the lower pyroclastic flow (2) seem to have been magnetized during the change of the main geomagnetic field. The Pliocene older lavas seem to have been formed in the Gauss normal epoch. The ages of the lower pyroclastic flow (1) and (2) of the Nagano Formation with the normal magnetizations correspond to the Olduvai event or the Reunion event in the Matuyama reversed epoch. Accordingly, these pyroclastic flow deposits seem to be older than the Goino pyroclastic flow deposit. The date of the Pleistocene younger lavas (Yaeyama basalts, Iwashita andesite) with the reversed magnetizations correspond to the younger part of the Matuyama reversed epoch. The late Pleistocene pyroclastic flow deposits (lower Kakuto and Ata) show the normal magnetizations.続きを見る |
| 目次 | I． まえがき II．層序と試料採取地 III. 自然残留磁気の安定性 IV. 測定結果 V. 考察 VI. まとめ |
詳細
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| 登録日 | 2021.10.27 |
| 更新日 | 2022.06.20 |