海洋鑽探計畫─子計畫九：南沖繩海槽海洋鑽探計畫井位的震測調查

Abstract

本計畫是海洋鑽探研究整合型計畫項 下的一子計畫，也是中法地球科學合作研 究台灣弧陸碰撞與板塊隱沒及弧後擴張系 統的合作計劃。計畫之目的在於利用反射 震測技術來探討南沖繩海槽地區的構造， 並提供在該地區進行鑽探研究所需的反射 震測剖面。計畫執行初期即提供相關震測 剖面為我國學者提出在南沖繩海槽南端進 行鑽井研究之場址調查資料。該井位並獲 海洋鑽探計畫(ODP) 通過，於2001 年4 月 底成功完成鑽探 (ODP1202 井位)。另外， 為因應我國學者在南沖繩海槽研究重點在 於火成岩活動以及熱液噴發作用，本計畫 結合震測與磁力異常資料，辨識在南沖繩 海槽南端的火成岩體分布及其與構造之關 係。 從震測剖面分析，南沖繩海槽南端可 分為東海陸棚區、陸棚半地塹區、盆地區、 中央火成岩高區、琉球島弧半地塹區、琉 球島弧高區等六個構造區。而磁力異常分 析結果顯示，磁力資料可協助辨識震測剖 面中觀察到的信號混亂區之本質是否為火 成岩體。本研究發現火成岩活動幾乎遍佈 南沖繩海槽南端，而以海槽中央的火成岩 高區最密集。

This project is a sub-project of the ODP integrated project, and also is a Taiwan-France cooperative research project. The purpose of this study is to understand the crustal structure and volcanic activities in the Southern Okinawa Trough (SOT). To support the ODP drilling proposal submitted by several scientists (including the author of this report) to drill in the SOT, seismic reflection profiles have been provided to the Site Survey Panel of the ODP. The proposed site has since been successfully drilled in late April of 2001 (ODP site 1202). Due to the strong interests in the volcanic and hydrothermal activities found in the studied area, the focus of this study thus has been shifted to identify the volcanic bodies and their distribution in the SOT. 3 From seismic reflection profile analyses, we have divided the SOT into six structural provinces, namely the East China Sea shelf, the half graben shelf belt, the basins, the central volcanic high, the Ryukyu arc half graben belt, and the Ryukyu arc high. Magnetic anomaly patterns are used to confirm the volcanic bodies observed on the seismic reflection profiles, while high frequency magnetic anomaly map provides the areal distribution of the volcanic bodies. This study shows that volcanic bodies (both intrusion and extrusion) distribute widely in the SOT, and especially concentrated in the central volcanic high.