Heki, K., M. Kono and Y. Hamano, Rotation of the Peruvian Block from Palaeomagnetic studies of the Central Andes

Nature, 305, 514-516, 1983.

初めて外国雑誌へ投稿した論文。博士課程1年の夏に海外学術調査「中部アンデスの 地球物理学的研究」の一員として2ヶ月ペルー、チリに滞在して試料採取、1ヶ月カリフォル ニア大学サンタ・バーバラ校のFuller研究室に滞在して超伝導磁力計によって残留磁化を測定、 その結果をまとめて博士3年の春に論文投稿したもの。ペルー、チリ国境付近のアンデス山脈 の折れ曲がりに関して、その北と南の岩石の残留磁化の偏角が系統的に異なることを発見。過 去にまっすぐだったアンデス山脈が曲がって現在の形になったと結論づけています。その後欧 米の古地磁気研究者によってこの事実は検証され、アンデス山脈の短縮変形とアルチプラーノ の形成に関するひとつの拘束条件を与えています。

Palaeomagnetic studies were performed on the rocks of the Central Andes to test the hypothesis of oroclinal bending of the Andes around the Peru-Chile border. Natural remanent magnetization of Mesozoic volcanic and sedimentary rocks of Peru shows a counterclockwise shift of declination by several tens of degrees relative to the field directions of the same ages in the stable South American craton. Two Mesozoic dyke swarms from Arica region (northermost Chile) also indicate about 20 degrees of declination shift in a counterclockwise sense. These results suggest a considerable amount of counterclockwise rotation of larger area north of Arica, that is, oroclinal bending of the Andes around some hinge near the Peru-Chile border. One Neogene dyke swarm sampled in central Peru also gave declination which deviates counterclockwisely by about 15 degrees. If this declination shift is a result of the wide-area tectonic rotation as suggested by the Mesozoic rocks, oroclinal bending appears to have continued until relatively recent times.


日置幸介 (email: heki@ep.sci.hokudai.ac.jp)