活动大陆边缘的板片窗构造

SLAB WINDOW IN THE ACTIVE CONTINENTAL MARGIN

正俯冲的洋中脊的持续扩张作用将会使该洋中脊两侧的洋壳板片之间形成一个持续加宽的间隙,这个间隙称为板片窗。板片窗往往形成于小于10Ma左右具浮力的大洋岩石圈俯冲时期。板片窗形态依赖于3个主要因素:板块的相对运动、俯冲前的洋脊—转换断层组合样式、俯冲角度。影响板片窗形态的次要因素还有热侵蚀、相变等因素。在板片窗出现的活动大陆边缘,软流圈、岩石圈、大气圈、水圈发生独特的多圈层相互作用,是地球系统最为活跃的地带。由于该地带的洋底消减往往与生长轴呈一定角度相交,不仅引起盆地的不对称消减,而且使得板片窗之上的活动大陆边缘的构造、岩浆、成矿和热效应明显不同于洋中脊平行于俯冲带的消减作用产生的构造、岩浆、成矿和热效应。

Progressive divergence of a subducting ridge will produce a slab window which forms and continues to expand between the subducted parts of the diverging oceanic plates. A slab window often forms at the subduction time of negative buoyant oceanic lithosphere of less than 10 Ma in age. The shape and size of a slab window are mainly controlled by the re-subduction ridge-transform-trench configuration, slab dip angles and vectors of plate convergence. The other factors to influence the shape and size of the slab window are still thermal erosion, phase change and others. The effects of slab windows on ancient convergent margin, the most active region in the Earth system, induce the multi-spheric interactions between asthenosphere, lithosphere, atmosphere and hydrosphere. Because the subduction of oceanic crust in the region is often intersected at a certain angle with the spreading axis, it is not only to induce asymmetric consumption of the oceanic basin, but also to produce the anomalous tectonics, magmatism, mineralization and thermal evolution of the overriding plate which are obviously different from those of the subduction of mid-ocean ridge parallel to subduction zone.