Tectonic evolution of the Yap trench-arc system

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 NE-SW 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.