| 講演要旨(和文) | | 海底熱水鉱床の存在が確認されている久米島沖熱水活動域を対象として，JAMSTEC研究船を用いた精密地球物理調査を実施した．より広域スケールの詳細な海底下磁化構造や密度構造を明らかにできれば，熱水活動域周辺の火山活動の特徴や熱水活動域の空間的広がりが明らかになるだけでなく，熱水鉱床の成因の理解が進むことが期待される．本調査では，系統的な測線により，詳細な地磁気，重力，海底地形データを取得した．取得したデータから磁化強度分布，およびブーゲー重力異常を計算した．その結果，磁化強度分布において，海底火山などの海丘に対応する磁化強度分布と，東北東−西南西走向の線構造をもつ磁化強度分布の2つの特徴を明らかにした．これらは，海底火山の活動と背弧のリフティングに伴う火山活動に起因するものと考えられる．また，熱水活動域が低磁化強度分布域とブーゲー重力異常の勾配が急なエリアに対応することを明らかにした． |
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| | 講演要旨(英文) | | We have conducted detailed surface geophysical surveys around the hydrothermal sites off Kumejima island in the Mid-Okinawa Trough. New hydrothermal active area was recently discovered off Kumejima island and the existence of hydrothermal mineral deposits were confirmed by seafloor surveys and rock samplings by ROV. In order to clarify characteristics of magmatic activities and spatial distribution of hydrothermal active area, and further understand the genesis of hydrothermal deposits, the dense magnetic, gravity and bathymetric data were collected during the YK16-10 and YK16-12 cruises aboard the R/V Yokosuka and the KR16-16 cruise aboard the R/V Kairei. The distribution of magnetization and Bouguer gravity anomalies were calculated from the collected magnetic and free-air gravity anomalies and bathymetric data. Finally, we revealed that different types of sub-seafloor magnetic features probably caused by magmatic activities by submarine volcanoes and back-arc rifting and that the hydrothermal site off Kumejima island corresponds to the reduced magnetization zone with the higher gradient part of the Bouguer gravity anomalies. |
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