The seismic Moho structure of Shatsky Rise oceanic plateau, northwest Pacific Ocean

Oceanic plateaus are large igneous provinces formed by extraordinary eruptions that create thick oceanic crust, whose structure is poorly known owing to the lack of deep-penetration seismic data. Multichannel seismic (MCS) reflection and wide-angle refraction data allow us to show Moho structure beneath a large part of the Shatsky Rise oceanic plateau in the northwest Pacific Ocean. Moho reflectors in the two data sets can be connected to trace the interface from the adjacent abyssal plain across much of the interior. The reflectors display varied character in continuity, shape, and amplitude, similar to characteristics reported in other locations. Beneath normal crust, the Moho is observed at ∼13 km depth (∼7 km below the seafloor) in MCS data and disappears at ∼20 km depth (∼17 km below the seafloor) beneath the high plateau. Moho at the distal flanks dips downward towards the center with slopes of ∼0.5°–1°, increasing to 3°–5° at the middle flanks. Seismic Moho topography is consistent with Airy isostasy, confirming this widely-applied assumption. Data from this study show that crustal thickness between the massifs in the interior of the plateau is nearly twice normal crustal thickness, despite the fact that this crust records apparently normal seafloor spreading magnetic lineations. The Moho model allows improved estimates of plateau area (5.33×105 km2) and volume (6.90×106 km3), the latter assuming that the entire crust was formed by Shatsky Rise volcanism because the massifs formed at spreading ridges. This study is unique in showing Moho depth and structure over an extraordinarily large area beneath an oceanic plateau, giving insight to plateau structure and formation. •Combined reflection and refraction seismic sounding shows the seismic Moho structure.•Seismic Moho reveals the crustal thickness over the Shatsky Rise oceanic plateau.•Seismic Moho interface is consistent with complete Airy isostatic compensation.•Seismic Moho observations provide a direct test of the commonly-used Airy model.•Thickness of crust recording magnetic anomalies is twice that of normal ocean crust.