Page 117 - Global Tectonics

104 CHAPTER 5

MR
Canada
Alpha Ridge
Basin Lomonosov Ridge

120 W 30 E
AHI
130
120
EI
110 80 N

100
90 W Greenland 0
Baffin Bay 70 60
90

80 70 50
40
70 N 30 20
10 0

Iceland
60 W 30 W

Figure 5.11 Predicted hotspot track assuming that the Iceland hotspot is fixed relative to the other Indo-Atlantic

hotspots of Fig. 5.9. Position of hotspot at 10 Ma intervals is indicated by solid dots. AHI, Axel Heiberg Island; EI,
Ellesmere Island; MR, Mendeleyev Ridge. Dashed line, continent–ocean boundary based on bathymetry. Gap between

70 Ma positions results from sea floor created after the passage of the Labrador Sea Ridge over the hotspot at 70 Ma

(modified and redrawn from Lawver & Müller, 1994, courtesy of the Geological Society of America).

stationary in the mantle, and so their trajectories provide is obtained. This is then compared with the track of the
a record of the motions of plates with respect to the axis of the hotspot reference frame as viewed from the

mantle. A combination of these two methods can be fixed continent. The TPW path is then determined by
used to test if there has been any relative movement calculating the angular rotation that shifts the global
between the mantle and the Earth’s spin axis. This phe- mean paleomagnetic pole of a certain age to the north
nomenon is known as true polar wander (TPW). pole, and then applying the same rotation to the hotspot
The method employed to investigate TPW is as pole of the same age (Courtillot & Besse, 1987).
follows. Paleomagnetic pole positions for the past The TPW path for the past 200 Ma, obtained by
200 Ma are compiled for a number of continents that Besse & Courtillot (2002), is shown in Fig. 5.12. Their
are separated by spreading oceans so that their relative analysis utilizes paleomagnetic data from six continents,

motions can be reconstructed from magnetic lineation sea floor spreading data from the Atlantic and Indian
data (Section 4.1.7). The pole positions are then cor- Oceans, and the Indo-Atlantic hotspot reference frame
rected for the rotations relative to a single continent of Müller et al. (1993) for the past 130 Ma, and of Morgan
(usually Africa) experienced as a result of sea fl oor (1983) for the period from 130 to 200 Ma. They conclude
spreading since the time for which they apply. In this that as much as 30° of true polar wander has occurred
way a composite or global apparent polar wander path in the past 200 Ma, and that the movement of the pole