An Immense Shield Volcano within Shatsky Rise Oceanic Plateau, Northwest Pacific

Most oceanic plateaus are immense basaltic constructs that represent extraordinary flux of magma between mantle and crust. Their structures, eruption processes, and evolution remain unclear because they are remote, submerged, and therefore difficult to study. Shatsky Rise, which formed during the Mesozoic at a triple junction, is one of the largest oceanic plateaus. Volcanic material from Shatsky Rise was cored by Integrated Ocean Drilling Program (IODP) Expedition 324. Cores from Tamu Massif, the largest and oldest edifice, are characterized by massive sheet flows, similar to those in continental flood basalt provinces. Subsequently, 2D multichannel seismic reflection profiles were collected by the R/V Marcus G. Langseth over Tamu Massif and show subparallel reflectors deep within the edifice. Correlation with drilling results shows that the intra-basement reflectors are likely the boundaries between lava flow packages. These data show that Tamu Massif is a single, immense shield volcano. It is constructed of massive lava flows emanating from the volcano center, forming a broad shield with anomalously low slopes likely owing to high effusion rate. It may be the largest single volcano on Earth, comparable with the largest in the solar system. These findings imply that oceanic plateaus can form by massive outpouring of lava from a single center. They also document a different class of oceanic volcano, distinct by its size and morphology from the thousands of common seamounts found throughout the oceans.