Annotated record of the detailed examination of Mn deposits from the GEORSTOM III NORD (R/V Le Noroit) cruise stations

The D'Entrecasteaux Zone (Southwest Pacific) is an arched submarine horst- and graben structure, which extends from the northern end of the New Caledonia ridge to the western border of the New Hebrides island arc. A review of the bathymetry, seismic-reflection data, paleomagnetism, gravimetry, seismology and DSDP data available for this area is combined with a study of basaltic samples dredged along the horsts of this regional fracture zone. These basalts show strong petrographic and chemical affinities with MORB. Their fissiontrack ages range between 56 Ma (Paleocene-Eocene boundary) and 36 Ma (Eocene-Oligocene boundary). It is suggested that the D'Entrecasteaux Zone represents the northern arcuate extension of the northeast-dipping Eocene subduction/obduction zone, located along the New Caledonia/Loyalty Islands ridge, while its present morphology appeared from post-obduction extensional movements, resulting in a progressive uplift of basaltic ocean floor since Middle Miocene times.当特尔卡斯托带（D'Entrecasteaux Zone）地处西南太平洋，为弧形海底地垒-地堑构造，其展布范围从新喀里多尼亚海岭北端延伸至新赫布里底岛弧的西部边界。本研究整合了该区域已公开的海底地形测量数据、地震反射资料、古地磁数据、重力测量结果、地震学数据及深海钻探计划（Deep Sea Drilling Project, DSDP）资料，并结合沿该区域断裂带内地垒拖网采集的玄武岩样品开展分析。这些玄武岩与洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）展现出显著的岩石学与地球化学亲缘性，其裂变径迹年龄介于56 Ma（古新世-始新世界限）与36 Ma（始新世-渐新世界限）之间。研究认为，当特尔卡斯托带代表了沿新喀里多尼亚/洛亚尔提海岭分布、向东北倾斜的始新世俯冲/仰冲带的北弧形延伸部分；而其现今地貌则形成于仰冲后的伸展运动，自中中新世以来，玄武质洋底持续逐步抬升。