Bathymetry of Shatsky Rise, northwest Pacific Ocean: Implications for ocean plateau development at a triple junction

Oceanic plateaus are large igneous edifices thought to have been created by nascent mantle plumes, but owing to sparse data, their origins remain unce rtain. Understanding plateau evolution is important because they are signif icant ocean features and may provide clues about mantle plume dynamics. We constructed a bathymetry map of Shatsky Rise, a large Pacific plateau, comb ining multibeam and wide-beam echosounder data from 87 cruises and U.S. Nav y multibeam contours. The rise consists of three large, isolated volcanic e difices (massifs), surrounded by nearly normal lithosphere, a linear volcan ic ridge, and a group of about 80 scattered seamounts. Massif flank slopes are typically gentle (similar to 1.5 degrees) and often parallel magnetic l ineations or fracture zones. The slope angles imply effusive volcanism, sim ilar to flood basalts, whereas the rise shape suggests formation near the P acific-Izanagi-Farallon triple junction with modification of volcano flanks by spreading-ridge tectonics. Edifice sizes and inferred ages imply a tren d of decreasing volume and age from southwest to northeast. Furthermore, ga ps between massifs suggest episodic volcanism. Existing data are broadly co nsistent with the "plume head" hypothesis wherein the largest edifice forme d by massive plume head eruptions, the ridge formed from the plume tail, an d the two massifs in between represent a transition. Seamounts east of the rise are morphologically distinct, which suggests that they may have been f ormed by a different source or mechanism than Shatsky Rise proper.