Secondary Cones of the Shatsky Rise and Implications for Late-Stage Volcanism Atop Oceanic Plateaus

Abstract

Oceanic plateaus are large igneous provinces in the oceans, created by massive underwater eruptions, but their late-stage volcanism is poorly understood. With the addition of recent high-quality bathymetric data to existing data, 286 secondary cones were discovered over Shatsky Rise oceanic plateau. These cones with steeper flank slopes (mean 6.1° ± 4.4°) and smaller sizes (102–1923 m in height) are morphologically distinct from the plateau, and they are thought to have formed after the main volcanic episodes. Cone height and characteristic height (420 m) are close to seamounts in the Pacific Ocean, whereas greater than those in the Atlantic Ocean. Mean flatness of Shatsky Rise’s cones (0.25 ± 0.20) are similar to that of seamounts in both Pacific and Atlantic Oceans, but notably density in cone distribution (0.56 km ⁻³) and their mean slope are significantly lower than those of seamounts in the two oceans. Lower slopes of secondary cones within Shatsky Rise may be explained by higher effusion rates of remaining magma. Although cone formation was expected to have a link to rifting by seafloor spreading, weak relationship between cone orientation and magnetic anomaly pattern implies that the expectation is negative. Moreover, weak correlation between the cone height and depth indicates it is not true that volcanic cones grow taller when they occur closer to the massif summits with thicker oceanic crust, which was suggested as the increase in hydraulic pressure. Cone height and flatness are also not strongly related, implying that remaining magma supply was too limited to foster the cones to critical height.