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

摘要

Oceanic plateaus are large igneous edifices thought to have been created by nascent mantle plumes, but owing to sparse data, their origins remain uncertain. Understanding plateau evolution is important because they are significant ocean features and may provide clues about mantle plume dynamics. We constructed a bathymetry map of Shatsky Rise, a large Pacific plateau, combining multibeam and wide-beam echosounder data from 87 cruises and U. S. Navy multibeam contours. The rise consists of three large, isolated volcanic edifices (massifs), surrounded by nearly normal lithosphere, a linear volcanic ridge, and a group of about 80 scattered seamounts. Massif flank slopes are typically gentle (approx 1.5 deg) and often parallel magnetic lineations or fracture zones. The slope angles imply effusive volcanism, similar to flood basalts, whereas the rise shape suggests formation near the Pacific-Izanagi-Farallon triple junction with modification of volcano flanks by spreading-ridge tectonics. Edifice sizes and inferred ages imply a trend of decreasing volume and age from southwest to northeast. Furthermore, gaps between massifs suggest episodic volcanism. Existing data are broadly consistent with the "plume head" hypothesis wherein the largest edifice formed by massive plume head eruptions, the ridge formed from the plume tail, and the two massifs in between represent a transition. Seamounts east of the rise are morphologically distinct, which suggests that they may have been formed by a different source or mechanism than Shatsky Rise proper.