雅浦沟-弧体系构造演化过程

Tectonic evolution of the Yap trench-arc system

雅浦沟-弧体系具有十分独特的地质特征,雅浦岛弧以变质岩为主,岛弧岩浆作用较为缺乏,同时雅浦沟-弧距离异常短,增生楔缺失。在总结雅浦沟-弧系统及其邻区的地球化学、地球物理以及构造特征等证据的基础上,探讨了雅浦沟-弧系统的构造演化过程。雅浦岛上的变质基底具有相对较高的K2O含量、高Ti含量以及较低的87Sr/86Sr比值,表明雅浦岛上的变质基底为帕里西维拉海盆洋壳的一部分。雅浦海沟东侧存在一块水深较深的三角形区域将雅浦岛弧与加罗林海岭间隔开来,地球物理特征显示该区域并没有受到加罗林热点的影响,说明加罗林海岭并没有与雅浦岛弧直接碰撞。结合帕里西维拉海盆在20~15Ma的NE-SW向扩张以及与之相关的海盆东西两侧洋壳发生的左旋相对移动,推测雅浦海沟很可能是雅浦岛弧东侧的扩张中心暴露转变成的俯冲带,而雅浦海沟东侧的三角形区域则为俯冲板片重新暴露的结果。

The geological characteristics of the Yap trench-arc system is quite unique,which is dominated by metamorphic rocks and lack of island arc magmatism.Meanwhile,the trench-island distance of the Yap trench-arc system is abnormally short and the accretion wedge is absent.In this paper,the tectonic evolution of the Yap trench-arc system is discussed on the basis of geochemical,geophysical and tectonic data. The metamorphic basement of Yap island has relatively high K2O,Ti and low 87Sr/86Sr ratio,which indicates that the basement is once the oceanic crust of the Parece-Vela basin.A deep triangular area is located on the east side of the Yap trench which separates the Yap island arc from the Caroline ridge.The geophysical characteristics of this triangular area demonstrate that the area has not been affected by the Caroline Hotspot,and then the Caroline ridge does not collide with the Yap island arc directly.Considering the spreading of the Parece-Vela basin in NESW trending at 20~15 Ma and the relative sinistral movement of the oceanic crust on both sides of the Parece-Vela basin,the Yap trench is probably a subduction zone formed by the exposure of the spreading center on the eastern side of the Yap island arc,while the triangular area on the eastern side of the Yap trench is caused by the re-exposure of the subduction plates.