Absence of quaternary volcanism suggests super-slow subduction at the Yap arc-trench system in the West Pacific Ocean

Subduction initiation and termination are important components of plate tectonic processes. The Yap subduction system is an ideal natural laboratory to investigate the geodynamics of oceanic plateau–subduction zone interaction. This study presents new K-Ar age determinations and geochemical compositions of volcanic rocks collected from the Yap Arc. The available age data from literatures and this study indicate that the southern Yap Arc was volcanically active at ca. 14.2 Ma and ca. 3.4 Ma, with an additional record at ca. 7.6 Ma. The extremely limited and scattered distribution of volcanic rocks, together with the super-slow subduction rate (3–6 mm/yr), confirms the weakening of magmatic activity at the Yap Arc. The volcanic rocks belong to the subalkaline magma series. Geochemical modelling shows that the basalts can be generated by 2–10% partial melting of spinel lherzolite in a heterogeneous sub-Yap arc mantle, with negligible contribution from subduction components. This synthesis integrates new geochronological and geochemical data with previously published regional observations, and proposes that the arrival and jamming of the Caroline Plateau at the Yap Trench was the key factor responsible for slowing down the subduction process.