太平洋板块中—新生代构造演化及板块重建

MESO-CENOZOIC TECTONIC EVOLUTION AND PLATE RECONSTRUCTION OF THE PACIFIC PLATE

太平洋板块是一个中生代以来形成的地球上最大的大洋板块,但其起源机制、结构构造、构造演化等始终不清楚。太平洋板块内部的复杂性更是未受到重视,其内部的大火成岩省、海山链、微洋块、微陆块及其下部更深层地幔的微幔块都非常发育,这些复杂板内或板下构造代表的地球动力学含义亟待解决。文章基于最新的板块重建结果,试图分析其运动学过程,揭示太平洋板块形成与演化机制。研究表明,太平洋板块起源于RRR三节点,但不是一个纯粹的完整大洋板块,其增生演化过程经历了非威尔逊旋回模式,其板缘经历了一些外来微陆块或微洋块的并入,其内部也因各种原因出现了一些新生微洋块,总体表现为一个碎片化的镶嵌式板内格局。太平洋板块记录了与邻区板块相互作用的重要构造事件,大约55Ma左右开始俯冲到东亚陆缘,导致东亚陆缘短暂的北西—南东向伸展,随后受印度—欧亚碰撞动力系统和太平洋俯冲动力系统联合控制,总体处于右行右阶的拉分背景,形成了一系列盆地群,俯冲后撤等逐渐形成了双俯冲系统。太平洋板块还记录了深浅部耦合过程,下地幔中的太平洋LLSVP通过遥相关对上部岩石圈微板块、大火成岩省分布具有决定性作用;火山链或热点揭示板块运动同时,也反映深浅部物质交换过程,海山群也揭示太平洋板块之下软流圈并非单一对流胞,其对流格局的多样性尚待深入研究。

The Pacific Plate is the largest oceanic plate on the Earth since Mesozoic,but its original mechanism,structure and tectonic evolution are still unclear.The complexity of the interior of the Pacific Plate has not been taken seriously.Large igneous provinces,seamount chains,oceanic micro-blocks,continental micro-blocks and mantle micro-blocks in the deeper mantle in or under the Pacific Plate are well developed.The geodynamic implications of these complex intraplate or sub-plate structures need to be solved urgently.Based on the latest results of plate reconstruction,this paper attempts to analyze its kinematic process and to reveal the formation and evolution mechanism of the Pacific Plate.The results show that the Pacific Plate originated from the RRR triple junction,but it was not a pure oceanic plate.Its accretion and evolutionary processes have undergone a non-Wilson cycle model.Its margins have undergone the incorporation of some exotic continental or oceanic micro-blocks,and some new oceanic micro-blocks have involved and appeared in its interior for various reasons.It made the Pacific Plate show as a fragmented mosaic pattern.The Pacific Plate recorded important tectonic events interacting with the adjacent tectonic plates.At about 55 Ma,it began to subduct under the East Asian continental margin,resulting in a short NW-SE-directed extension of the East Asian continental margin,which was subsequently jointly controlled by the Indian-Eurasian collisional dynamic system and the Pacific subduction dynamic system,and generally formed some pull-apart basins under the right-lateral dextral strike slipping.Then due to subduction retreat,this region gradually developed a double subduction system.The Pacific Plate also recorded the deep-shallow coupling process,and the Pacific LLSVP in the lower mantle played a decisive role in the distribution of the upper lithospheric micro-plates and large igneous provinces.In addition,volcanic chains or hotspots not only reveal plate movement,but also reflect the process of material exchange between deep and shallow parts,and seamounts also reveal the mantle flow under the Pacific Plate.The mantle circulation is not a single convective cell,and the diversity of its convective pattern needs to be further studied.