Sager et al. (1999) inferred that Shatsky Rise was formed by plume-related volcanism near a triple junction from about M21 to M1 (147 to 124 Ma). The three large highs and the normal lithosphere between them imply that volcanism was episodic, with separate pulses building each of the highs. The volume trend implies that the first eruption was extraordinarily large and that subsequent eruptions were of diminishing size.
As indicated by the narrow time gap between the age of the underlying lithosphere and oldest sediments drilled at Site 306, Shatsky Rise evidently began forming near the Jurassic-Cretaceous boundary with rapid, massive eruptions that formed the South High (Sager and Han, 1993). This nearly coincided with an 800-km eastward jump of the Pacific-Izanagi-Farallon triple junction and a reorientation of the Pacific-Izanagi Ridge between M21 and M19 (148-145 Ma) (Sager et al., 1988). Whether this large jump was caused by the eruption of the South High is unclear, but morphology and anomaly positions imply that the volcanic edifice formed slightly off-ridge and affected the ridge positions (Sager et al., 1999). Ridge jumps also occurred at about the time of formation of the Central and North Highs (M16-MI5 and M14, 138 and 136 Ma, respectively), moving the triple junction farther northeast (Nakanishi et al., 1999). The shape of the rise implies that the plates were moving rapidly southwest relative to the mantle plume (~1400 km in the 22 m.y. between M20 and M1), so the ridge jumps may have occurred to keep the spreading ridges located atop or near the plume (Sager et al., 1999).