被动大陆边缘:从大陆张裂到海底扩张

PASSIVE MARGINS: FROM CONTINENTAL RIFTING TO OCEANIC SPREADING

被动边缘是研究大陆张裂、破裂到海底扩张的关键。ODP103、149、173航次对伊比利亚—纽芬兰非火山型共轭边缘的研究,证实了洋陆过渡带和低角度拆离断层的存在,其中洋陆过渡带中广泛出现蛇纹岩化地幔橄榄岩,钻探结果支持不对称单剪模式。ODP104、152、163航次对挪威—格陵兰东南火山型共轭边缘的调查,揭示了典型的向海倾斜反射层(SDRS)的特征,反映了岩浆活动在边缘形成中的主导作用。为了进一步了解大陆从张裂到破裂到洋底扩张过程的一系列学术问题,需要在IODP阶段继续对共轭被动边缘以及包括冲绳海槽和南海在内的典型地区,通过钻探、采样和观测进行更深入的研究。

Passive margin study has been at the core of scientific ocean drilling because it provide important information on processes in continental extension, breakup, and the eventual formation of new oceanic spreading centers. In this paper, ODP investigations in the evolution and characteristic of volcanic & nonvolcanic passive margins have been briefly introduced. Drilling on the IberiaNewfoundland nonvolcanic margin by ODP Legs 103, 149 and 173 have demonstrated clearly that lowangle detachment faults have contributed to the unroofing and formation of continentocean transition zone, resulting in the exposure of serpentinized and tectonized mantle peridotite. Results from ODP Leg 104, 152 and 163 on volcanic passive margin of NorwayGreenland conjugate pair suggest that the magmatic processes have played a major role in the thinning of crust and the final breakup. Drilling results so far support an asymmetric simple shear mode for the formation of nonvolcanic margins. ODP explorations also reveal characteristics of seismic seawarddipping reflections. For a better understanding of the processes from continental extension to breakup to the final oceanic spreading, further indepth studies are required in the IODP phase by drilling, sampling across a full rift system on conjugate margin pairs and other locations such as Okinawa Trough and the South China Sea. 