1988年Sonne号航海による南部・中部沖繩トラフでの地殻熱流量測定

A detailed heat flow survey was carried out near the axis in the southern and middle Okinawa Trough on cruise SO56 of R/V Sonne in 1988, and 50 new heat flow values were determined. Emphasis was put on closely-spaced heat flow measurements around knolls and small basins near the trough axis in order to clarify the nature of thermal anomalies, which were expected to be related to hydrothermal activity. In the axial graben of the southern Okinawa Trough, heat flow values obtained within 2 km of an axial volcano (the Yaeyama Central Knoll) were less than 50mW/m2 and showed large scatter. These low heat flow values can be explained as they are measured in the recharge area of the hydrothermal circulation, which is presumed to discharge at the Yaeyama Central Knoll. In the axial part of the middle Okinawa Trough, heat flow values measured in a basin to the east of the Natsushima-84 Deep, which was known to have high heat flow, were 710±690mW/m2. This indicates that the thermally active area extends along the central axis of the trough. High and variable heat flow (360±220mW/m2) was also found in a cauldron, about 35km to the south of the axis of the middle Okinawa Trough. Heat flow increases toward the northeastern wall of the cauldron, where the hydrothermal ore deposits were discovered.1988年6月に行われた研究船Sonne号による航海において,南部・中部沖縄トラフでの地殻熱流量測定を行った.本航海では,以下に示すようないくつかの小区域において,シービームによる地形調査, OFOS(海底曳航式TV・カメラ)による海底観察,ドレッジ・グラブ・ボックスコアラーによる採泥調査,採水およびマルチゾンデによる地球化学的観測,地殻熱流量測定が詳細に行われ,背弧海盆における熱水活動とそれに伴う熱水性鉱床の探索がなされた