Annotated record of the detailed examination of Mn deposits from DSDP Leg 58 (Holes 442A, 442B, 443, 444, 444A, 445, 446, 446A)@en

The JOIDES Active Margin Panel for Leg 58 decided that the drilling would occur in the north Philippine Sea, namely, the Shikoku Basin, the Daito Ridge and Basin province. The Shikoku Basin sites were selected to solve several problems concerning back-arc basins formed by ocean-floor spreading. The main objectives were: (1) to determine the age of the oldest sediment, so as to calibrate magnetic-anomaly ages and to provide a test for various spreading models suggested for the basin; (2) to investigate the mineralogy, petrology, and chemistry of basalt samples recovered by drilling, and to compare there basalts with those of midocean ridges, so as to understand the nature and source of magmatic materials in these basins; (3) to determine the distribution of sediment types in time, and to relate that distribution to the tectonic history of the basin.JOIDES活动边缘专题组（JOIDES Active Margin Panel）针对第58航次（Leg 58）确定，钻探作业将在菲律宾海北部开展，具体区域包括四国盆地（Shikoku Basin）以及大东海岭及盆地群（Daito Ridge and Basin province）。遴选四国盆地的钻探站位，旨在解决与洋壳扩张（ocean-floor spreading）形成的弧后盆地（back-arc basins）相关的多项科学问题。本次钻探的核心目标如下：（1）测定最古老沉积物的形成年代，以此校准磁异常年龄（magnetic-anomaly ages），并对该盆地已提出的各类扩张模型开展验证；（2）研究钻探获取的玄武岩样品的矿物学、岩石学及地球化学特征，并将此类玄武岩与洋中脊（midocean ridges）玄武岩进行对比，以厘清此类盆地中岩浆物质的性质与来源；（3）明确沉积物类型的时间分布规律，并将该分布特征与盆地的构造演化历史相结合。