中国科学院海洋研究所机构知识库

  俯冲带的物质循环和变形以及裂谷的形成和演化是近十年来国内外重大计划的重要研究内容，因此俯冲及扩张构造是目前国际研究的热点。菲律宾海板块内发育了全球典型的沟-弧-盆体系，同时保存了不同发育阶段的俯冲和扩张构造，是全球扩张及俯冲动力学研究的理想实验室。

  本文主要基于中国科学院海洋研究所2015-2017年采集的高分辨率多道地震、多波束数据，结合最新的重磁数据，采用多道地震解释、重-磁-震联合正反演、沉积盆地分析和数值模拟等方法，对西太平洋典型扩张、俯冲构造的地球物理特征进行系统研究，并尝试探讨晚始新世以来菲律宾海板块和卡罗琳板块相互作用区的演化模式，从而完善菲律宾海板块的演化历史。

  研究结果表明，西菲律宾海盆内中央海盆裂谷东西两侧的沉积、地壳结构存在明显差异。早渐新世之前，裂谷西部沉积凹陷较为发育，地壳内部无杂乱反射，扩张中心体现了岩浆供应充足条件控制下的快速扩张特征；早渐新世之后，裂谷东侧沉积物发育较少，地壳内部杂乱反射特征明显，扩张中心体现了少量岩浆活动与走滑拉张作用控制下的慢速扩张特征。

  晚渐新世，热点火山作用重塑卡罗琳海盆，大规模玄武岩流喷出 地表形成卡罗琳洋脊，在地震剖面上表现为层状的壳内反射和光滑的基底。强烈的火山活动导致卡罗琳海盆内先存沉积物的破坏。洋底高原与菲律宾海板块东南边界的碰撞阻碍了雅浦海沟俯冲活动的进行，同时，碰撞过程是导致雅浦与马里亚纳俯冲带逐渐分离的原因。晚渐新世-中新世，随着热点火山活动的减弱，卡罗琳洋脊基底之上逐渐发育沉积物。早中新世-中中新世，卡罗琳洋脊在远场应力、地幔柱热效应等综合因素下发生裂解，形成索罗尔海槽，张裂活动导致洋脊的上覆沉积物发育广泛的破裂不整合。中新世，俯冲过程活跃，索罗尔海槽张裂过程产生的大量断裂，卡罗琳洋脊前缘临近雅浦海沟处发生挠曲断裂作用，导致地垒地堑断裂带形成。由于俯冲板片上洋底高原、海山及断裂带的存在，雅浦俯冲系统在极慢的汇聚速率下发生了俯冲侵蚀作用，导致上覆菲律宾海板块地壳的破坏。

  总之，渐新世以来，古雅浦-马里亚纳俯冲带的迁移对菲律宾海板块的构造演化产生了重要的影响。由于太平洋板块的后撤，帕里西维拉海盆的形成，诱发了中央海盆裂谷的晚期伸展，使得西菲律宾海盆进一步扩张。卡罗琳板块内洋底高原的形成，限制了古雅浦俯冲带的后撤过程，随后，洋底高原的俯冲造成了菲律宾海板块的侵蚀。渐新世以来，俯冲带的演化对菲律宾海板的构造样式有重要的影响。

  The material circulation and deformation of the subduction zones, and the formation and evolution of the rifts are the important research contents of the major projects at home and abroad in the last decade. Thus, researches of the extensional and subduction structures are one of the international research hotspots at present. The Philippine Sea Plate possesses the typical trench-arc-basin systems in the world and preserves multi-stage extensional and subduction structures. Thus, the Philippine Sea Plate is an ideal laboratory for the study of global extension and subduction dynamics.

  Based on the latest high-resolution multichannel seismic and multibeam data collected by Institute of Oceanology, Chinese Academy of Sciences in 2015-2017, combined with the gravity and magnetic data, we use multichannel seismic interpretation, gravity-magnetic-seismic joint modelling and inversion, sedimentary basin analysis and numerical simulation methods to systematically study the geophysical characteristics of the typical extensional and subduction structures in the western Pacific. We try to explore the evolutionary model for the interaction area between the Philippine Sea Plate and the Caroline Plate, and further improve the researches for the evolutionary history of the Philippine Sea Plate since late Eocene.

  Our results show that obvious differences in the sedimentary and crustal structures appeared between the eastern and western Central Basin Fault in the West Philippine Basin. Before the early Oligocene, sedimentary sags were developed, and there was no disordered reflection within the crust of western Central Basin Fault, indicating the fast-spreading characteristics induced by the sufficient magma supply. Since the early Oligocene, less sedimentary basins were developed and disordered reflection occurred within the crust of eastern Central Basin Fault, proving that minor magmatic activities and strike slip tension control the late extension events of the West Philippine Basin.

  In the late Oligocene, hotspot volcanism remolded the Caroline Plate. Large-scale lava flow erupted at the surface forming the Caroline Ridge. Based on the seismic profiles, lava flow formed the layered instracrustal reflections and smooth basement. Intensive volcanism resulted in the destruction of preexisting sediments in the Caroline Basins. The collision between the oceanic plateau and the southeast boundary of the Philippine Sea Plate hindered the subduction process at the Yap Trench. This collision process induced the gradual separation of the Yap and Mariana subduction zones. During the late Oligocene-Miocene, sediments gradually developed on the smooth basement of the Caroline Ridge with the hotspot volcanism weakening. During the early-middle Miocene, the Caroline Ridge rifting was induced by the far-field stress and other comprehensive factors, forming the Sorol Trough. The rifting led to the widespread unconformity appearing within the overlying sediments. In the Miocene, numerous normal faults produced by the rifting of the Sorol Trough that weakened the crustal strength of the Caroline Ridge. The subduction process was active and thus led to the formation of horst and graben structures near the Yap Trench. Due to the subducting of oceanic plateau, seamounts and fault zones, the Yap subduction zone has experienced the subduction erosion with a extremely slow convergence rate.

  Above all, the migration of Proto-Yap-Mariana subduction zone has an important influence on the tectonic evolution of the Philippine Sea Plate since Oligocene. Because of the Pacific Plate retreat, the spreading of the Parece Vela Basin induced the late extension of the Central Basin Fault, which further led to the extension of the West Philippine Basin. The formation of the oceanic plateau in the Caroline Plate limited the retreat process of the Proto-Yap subduction zone. Subsequently, the subducting Caroline Ridge causes the erosional process of the Philippine Sea Plate. Thus, the evolution of subduction zone controls the tectonic style of the Philippine Sea Plate since Oligocene.