Annotated record of the detailed examination of Mn deposits from DSDP Leg 21 (Sites 204, 205)

The oceanic region between the Tonga-Kermadec Trench and New Zealand to the east and Australia to the west (see map at the back of this volume) has long been regarded as an anomalous region. Prior to development of the plate tectonic theory, it was known that the eastern boundary of the region was tectonically active, the western relatively passive. The DSDP Leg 21 overall objective was to provide initial coring data which would aid in reconstructing the tectonic history and relative plate movements of the Pacific and Indian crustal plates and determining the age of the tectonic features contained within the Tasman Sea region. In particular, the age and biostratigraphy of the oldest Pacific crustal section now being subducted into the Tonga-Kermadec Trench (Site 204) and the age and composition of the South Fiji Basin and of the basement rock (Site 205).

本卷卷末附图所示的、位于汤加-克马德克海沟（Tonga-Kermadec Trench）东侧新西兰与西侧澳大利亚之间的洋域，长期以来被视为异常构造区域。在板块构造理论发展完善之前，学界便已知晓该区域东边界构造活动活跃，西边界则相对平静。深海钻探计划（Deep Sea Drilling Project, DSDP）第21航次的总体目标为获取初始取心数据，以此助力重建太平洋与印度洋地壳板块的构造演化历史及相对板块运动，并确定塔斯曼海区域内各类构造特征的形成年代。具体而言，本次航次重点研究两项核心内容：一是当前正俯冲入汤加-克马德克海沟的最古老太平洋地壳剖面（204站位）的形成年代与生物地层学特征；二是南斐济盆地及基底岩（205站位）的形成年代与物质组成。