Magnetic lineations within Shatsky Rise, northwest Pacific Ocean: Implications for hot spot‐triple junction interaction and oceanic plateau formation

Abstract

Oceanic plateaus are major ocean features, yet their origins and development are poorly understood. Many are huge piles of basalt, and it is widely accepted that mantle plumes are their source, perhaps from eruptions of the voluminous head of an emerging plume. Shatsky Rise is a basaltic plateau that formed during a period of geomagnetic reversals, unlike many mid‐Cretaceous plateaus, so magnetic data can help us understand its tectonic history. In this study, we analyzed magnetic anomaly data from 131 cruises over and around Shatsky Rise and constructed a magnetic lineation chart for tectonic interpretation. A significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs, indicating nearly normal lithosphere, and between large volcanic edifices. Many lineations form bights near the rise axis and show former locations of the Pacific‐Izanagi‐Farallon triple junction. They indicate that the junction was in a ridge‐ridge‐ridge (RRR) configuration and closely followed the rise axis from chron M20 (146 Ma) to chron M4 (127 Ma). Lineation and bight geometries indicate that the triple junction jumped northeastward at least nine times, often apparently in response to volcanic activity from the mantle plume. Some jumps, however, appear related to ridge reorientations. Numerous features within the rise are parallel to lineations or lineation offsets, implying that the plateau formed near the triple junction and was modified by ridge faulting. Most of our observations support the hypothesis that Shatsky Rise was formed by a mantle plume that captured a triple junction.