MagNetZ With Trond Torsvik (2022/09/12) - The mind-bending mystery of the Hawaiian-Emperor Bend
Channel: MagNetZ
Date: 2022-09-20

The mind-bending mystery of the Hawaiian-Emperor Bend

The video is also available for download at: https://earthref.org/ERDA/2538/
and can be referenced with the doi: 10.7288/V4/ERDA/2538

Title: The mind-bending mystery of the Hawaiian-Emperor Bend
Author: Trond Torsvik from CEED at the University of Oslo, Norway

The Hawaiian-Emperor Chain is one of the most spectacular geological features on Earth. Wilson (1963) was the first to suggest that the Hawaiian Islands could be explained by the motion of the Pacific plate over a focused spot of melting in the mantle. The focused spot was later termed a ‘hotspot’ by Morgan (1971) who proposed that hotspots are sourced by deep mantle plumes, which remain fixed relative to each other and to the mantle. Morgan (1972) later built the first kinematic model that defined absolute plate motions in a fixed hotspot reference frame, and in this model, the Hawaiian-Emperor Bend (HEB) was attributed to a change in the absolute motion of the Pacific plate at the time of the bend formation. 
 
Many hotspot reference frames have subsequently been proposed, but explaining the HEB has proven problematic for frames assuming hotspot fixity, and Norton (1995), for example, argued that the bend must rather reflect the motion of a non-stationary hotspot. Paleomagnetic data have proven helpful for testing the non-stationary hotspot hypothesis. If the volcanic chain was produced by a hotspot fixed in the mantle reference frame, and the rotation of the entire solid Earth (mantle and lithosphere) with respect to the spin axis (that is, true polar wander, TPW) were negligible, then the paleolatitudes inferred from paleomagnetic analyses of volcanic rocks recovered from the Hawaiian-Emperor Seamounts should correspond to the present day latitude of Hawaii. However, the paleolatitudes of the Emperor Seamounts (e.g., Tarduno et al. 2003) show a distinct trend of lower latitudes with decreasing age, apparently providing evidence for southward motion of the Hawaiian hotspot between 80 and 47 Ma), but this could be due to both motion of the hotspot and motion of the pole (TPW) with respect to the deep mantle. 
 
The idea that the hotspot was mobile during this time interval has been generally accepted by the geoscientific community, although with some dissenting voices. Most geodynamic models predict a drift of the Hawaii hotspot to the south, and several recent studies argue that a rapid southward motion of the Hawaiian hotspot that ceased at 47 Ma can explain the formation of the HEB without requiring a significant change in the Pacific plate motion around that time. Here I demonstrate from basic geometrical considerations that southward hotspot drift cannot be a sole or dominant mechanism for the formation of HEB. While southward hotspot drift has resulted in more northerly positions of the Emperor Seamounts as they are observed today, formation of the HEB cannot be explained without invoking a prominent change in the direction of Pacific plate motion around 47 Ma. 
 
References 
Wilson, J.T. 1963. A possible origin of the Hawaiian Islands. Can. J. Phys. 41, 863–870. 
Morgan, W.J. 1971. Convection plumes in the lower mantle. Nature 230, 42–43. 
Morgan, W.J. 1972. Plate motions and deep mantle convection. GSA Memoir 132, 7–22 (1972). 
Norton, I.O. 1995. Plate motions in the North Pacific: the 43Ma nonevent. Tectonics 14, 1080–1094. 
Tarduno, J.A. et al. 2003. The Emperor Seamounts: southward motion of the Hawaiian Hotspot Plume in Earth’s Mantle. Science 301, 1064–1069.I: 10.1038 




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00:00 - Intro
00:46 - Presentation
26:35 - Questions
36:12 - Announcements