摘要
深地震探测、大洋钻探及野外露头观测等技术方法的联合运用,极大地推动了对大陆边缘地质过程的认识。目前对大陆边缘,尤其是对被动大陆边缘的结构、演化和发育机制的认识,正在经历一场前所未有的变革。文章从基本的概念和分类开始,综述了全球已探测到的几种主要大陆边缘类型的盆地结构、深地壳?岩石圈结构、圈层速度、沉降特点和破裂方式的研究进展,讨论了被动大陆边缘的发育和演化的机制。综合已有研究进展,指出富岩浆型和贫岩浆型陆缘在裂前和裂陷期具有相似的岩石组成和裂陷结构特征,只是在破裂前后由于岩浆量的不同而发生了结构的分异。贫岩浆型陆缘中的全岩石圈断裂型、上地壳过渡型、下地壳剥露型、上地幔剥露型,甚至下地壳 上地幔剥露的组合类型陆缘,是被动陆缘在张裂期由于岩石圈各层流变结构等因素的差异发生分异演化的结果。贫岩浆型陆缘下地壳高速体主要来源于地幔蛇纹岩化,而富岩浆型陆缘则主要来源于高温地幔熔融产生的底侵或侵入,局部可能继承了前张裂期的高速变质岩体。上述大陆边缘研究成果为研究南海的结构和演化提供了很好的对比和借鉴。
With the comprehensive utilization of deep reflection and refraction seismic data,ocean drilling program and field outcrops,great progress was made in understanding continental margin. Especially on the structure,evolution and formation mechanisms of passive continental margins,which are undergoing a paradigm shift. Starting from basic concept and classification,this paper reviewed the deep crustal to lithospheric structure,the layer velocity,the subsidence feature,and the breakup pattern of several types of passive continental margins based on recent seismic explorations. Then,mechanisms of passive continental margin formation were discussed. Based on existing research progress,we found that magma-poor and magma-rich margins may have lots of similarities in pre-rift and syn-rift stages,either in lithological components or rifting structures. They just differentiated during breakup depending on whether there was the involvement of hot mantle. During rifting stage,passive continental margin may evolve into four or more types,such as the whole lithospheric breakup type,the upper crust remnant type,the lower crust exhumation type,the upper mantle exhumation type,among others. The different rheological structures,stretching rate and mantle temperature are among the most important factors affecting the marginal structure evolution. Mechanism for high velocity lower crust is summarized. Usually,serpentinization of exhumed mantle is responsible for magma-poor margin,whereas underplating caused by high temperature mantle is responsible for magma-rich margin. Inherited high-grade metamorphic rocks were suggested to be one of the other causes. The above research progresses on passive continental margins provide us references to the research of the South China Sea.