无震脊或海山链俯冲对超俯冲带处的地质效应

Geological effects of aseismic ridges or seamount chains subduction on the supra-subduction zone

全球海底分布着众多的无震脊或海山链,且在太平洋、印度洋及大西洋均存在靠近俯冲带的海岭。除小安德列斯弧外的巴拉克达脊和蒂勃朗脊起源自转换断层外,一般认为它们由与板块构造动力学迥异的地幔柱动力学所形成的。在板块汇聚边缘处,与扩张脊处所形成的正常洋壳一起,无震脊或海山链俯冲于陆缘弧或洋内弧之下,其对弧及弧后地区的地质效应(构造、地貌、地震以及岩浆作用等)有别于正常洋壳俯冲。无震脊或海山链的俯冲通常造成俯冲带地区的上驮板块的局部异常抬升、俯冲剥蚀作用效应的加强、海沟的向陆迁移以及地震强度的增加。同时,无震脊或海山链俯冲时,其携带的具富集地球化学特征的物质不仅影响着地幔地球化学,也对弧及弧后火山熔岩化学产生明显影响,并对超俯冲地区的热液矿床的形成产生重要影响。最后,本文指出了我国有关无震脊或海山链俯冲的可能的研究方向包括黄岩海山链俯冲对吕宋岛弧的可能影响、印度洋无震脊俯冲对青藏高原局部地区的影响,有我国学者参与的IODP344航次的研究对象——科科斯脊俯冲对哥斯达黎加地震成因的效应以及位于西太平洋地区靠近俯冲带的一些无震脊等。

There distributed numerous aseismic ridges and seamount chains in global seafloor. Of them, some remarkable ridges close to subduction zones exist in Pacific Ocean, Indian Ocean and Atlantic Ocean. In addition to Barracuda and Tiburon ridges （close to the Lesser Antilles arc） originating from transform fault, the genesis of most intra-plate aseismic ridges and seamount chains is related to mantle geodynamies （different from plate tectonics）. At plate convergent margins, these aseismic ridges and seamount chains, together with normal oceanic crust formed in spreading mid-oceanic ridges, have been or are subducted be- neath continental arc or intra-oeeanie arc. The geological effects （e. g, structure, morphology, earthquake and magmatism） of the subduction of aseismic ridges and seamount chains on supra-subduction zones （SSZ） are obviously different from those of normal oceanic crust. The subduction of aseismic ridges and seamount chains often cause locally abnormal elevations of upper plate, enhancing subduction-induced ero- sion, landward displacement of trench, and the enhancement of intensity of earthquakes. Meanwhile, when aseismic ridges and seamount chains are subducted, they not only affect mantle geochemistry due to its entrained enriched geochemical characteristics, but play a significant role on geochemistry of are and back-are lavas and the formation of hydrothermal deposits on the SSZ setting. Finally, this paper point out possible research areas related to the subduction of aseimic ridges and seamount chains in China as follows, such as possible effects of subduction of the Huangyandao seamount chain on Luzon arc, effects of subduc- tion of several aseismic ridges in the Indian Ocean on local areas of Tibetan Plateau, and effects of subduetion of the Cocos ridge on the Costa Rica seismogenesis （targeted area of IODP leg 344）, and some aseismic ridges （close to the Subduction zone） dispersed in west Pacific, etc.