Page 116 - Global Tectonics

THE FRAMEWORK OF PLATE TECTONICS 103

150˚ 160˚ 170˚ 180˚ 190˚ 200˚ 210˚
Western Aleutians

50˚

64.7 ( Suiko )

56.2 ( Nintoku )
40˚
48.1 ( Koko )

42.4 ( Daikakuji )
38.7 ( Abbott )
30˚ 27.7 ( Midway )
10.3 ( Necker )
A31 7.2 ( Nihoa )
( 67.7 )
A27 2.6 ( Koolau )
( 61.1 ) A25
( 56.1 ) A20 A13 1.03 ( Kahoolawe )
20˚ ( 42.5 ) ( 33.5 ) A6 A5 0
( 20.1 ) ( 10.9 )

Figure 5.10 Predicted Hawaiian hotspot track (solid line) from plate reconstructions assuming that the Indo-Atlantic
hotspots are fixed. Ages in Ma (redrawn from Steinberger & O’Connell, 2000, by permission of the American Geophysical

Union. Copyright © 2000 American Geophysical Union).

implies that its position is not fixed relative to the approximately 60 Ma, was a result of rifting of litho-

other major hotspots in the Indo-Atlantic domain. sphere that had already been thinned by its proximity
However one can use the absolute motions derived to a hotspot, rather than the arrival of a plume head.
from the other hotspots (Müller et al., 1993) to predict In contrast to this interpretation, however, there is
the track of the Iceland hotspot on the assumption considerable doubt, on the basis of geochemical and

that it is fixed in relation to this frame of reference. geophysical data, that the Iceland hotspot is fed by a
Such an analysis has been conducted by Lawver & deep mantle plume (Section 12.10). The Iceland
Müller (1994) with intriguing results (Fig. 5.11). The hotspot is therefore something of an enigma.
track can be projected back to 130 Ma, at which time
the hotspot would have been beneath the northern
margin of Ellesmere Island in the Canadian Arctic.
Lawver & Müller (1994) suggest that such a track 5.6 TRUE POLAR
might explain the formation of the Mendeleyev and
Alpha Ridges in the Canadian Basin of the Arctic WANDER
Ocean and the mid-Cretaceous volcanic rocks of Axel
Heiberg Island and northern Ellesmere Island. At
60 Ma the hotspot is predicted to have been beneath In Section 3.6 it was demonstrated that paleomagnetic
West Greenland where there are volcanics of this age, techniques can be used to construct apparent polar
for example on Disko Island. At 40 Ma it would have wandering paths which track the motions of plates with
been beneath East Greenland which may explain the respect to the magnetic north pole and hence, using an
anomalous post-drift uplift of this area. On this model axial geocentric dipole model, the spin axis of the Earth.
the North Atlantic igneous province, initiated at In Section 5.5 it was suggested that hotspots are nearly