Origin of the 43 Ma Bend Along the Hawaiian-Emperor Seamount Chain: Problem and Solution

The Hawaiian-Emperor Seamount chain (H-E SMC) on the Pacific Plate Figs. 4.1 and 4.2 a,b) is the best-defined hotspot track on the Earth. If hotspots are surface manifestations of deep, fixed sources of mantle plumes (Morgan 1971, 1981), then the along-track volcanic age progression away from Hawaii (e.g., Clague and Dalrymple 1989) must record the direction, absolute velocity, and possible changes of the Pacific Plate motion. This would suggest that the prominent ∼43 Ma Bend along the H-E SMC reflects a sudden change in Pacific Plate motion direction by ∼60°. However, the actual cause of the 43Ma Bend is unknown. A leading hypothesis is that the collision between India and Eurasia some ∼45 Ma ago might have triggered the sudden reorientation of the Pacific Plate motion from northward to northwestward, hence the 43Ma Bend (Dalrymple and Clauge 1976; Patriat and Achache 1984).This collision, however, is shown to have had no effect on the Pacific Plate motion (Lithgow-Bertelloni and Richards 1998). The lack of apparent mechanism for such a sudden change in Pacific Plate motion direction led to the speculation (Norton 1995) that the ∼43 Ma Bend may have resulted from a southward drift of the Hawaiian hotspot prior to ∼43 Ma. Indeed, recent paleomagnetic studies (Tarduno and Gee 1995; Tarduno and Cottrel 1997; Christensen 1998; Sager 2002), plate reconstructions (Acton and Gordon 1994; Norton 1995, 2000; DiVenere and Kent 1999; Raymond et al. 2000), mantle flow models (Steinberger and O’Connell 2000), and statistical analysis of plate motions using seamount geochronology (Koppers et al. 2001) tall indicate that hotspots are not fixed, but they move individually or in groups at speeds up to 60 mm yr−1.