Short Notes: A Continental Drift Flip Book

Computers & Geoscieaces, Vol. 2, pp. 113-116. Pergamon Press, 1976. Printed in Great Britain

SHORT NOTES A CONTINENTAL DRIFT 'FLIP BOOK' CHRISTOPHERR. SCOTESE Department of GeologicalSciences, University of Illinois,Chicago,IL 60680,U.S.A. (Received 8 November 1975)

This set of Phanerozoic reconstructions (Fig. 1) can be made into an animated cartoon of continental drift. World maps, plotted on a mercator base, illustrate the changing positions of the continents during the past 350 million years. If the individual reconstructions are cut out and arranged in sequence, the continents can be animated by slowly 'flipping' through the pages. The computer-drawn continental drift reconstructions were produced using Euler's theorem which states that any point p, on the surface of a sphere can be rotated to any new position r, given the appropriate pole g, and angle of rotation 0.

The reconstructions presented here are based mainly on the work of Smith, Briden and Drewry (1973). Subsequent modifications include recent interpetations concerning the position of plate boundaries in Asia (Terman, 1973; McKerrow, 1974, personal comm.) and the tectonic history of the Mediterranean (Dewey and others, 1973). Eastern Siberia is adjoined to North America rather than Asia (Churkin, 1972) and Florida, along with much of Central Europe, is attached to Gondwana (McKerrow and Ziegler, 1972). FORTRAN programs written for an IBM 370 were used to drive a CALCOMP incremental plotter which generated the maps shown in Figure 1. By linearly interpolating the finite rotations, maps at 10 and 20 million year intervals were produced. A 3-rain animation also was produced using this technique; however, a much finer time interval was used (300,00 years) (Scotese and Baker, 1975).

r = (cos 0)p + (1 - cos 0)(p- g)g + (sin 0)g × p

where p, r and g are unit vectors passing through the center of the sphere. Similar coordinate transformations can be made using orthogonal rotation matrices or quaternions (Francheteau, 1970). The poles of rotation needed to reassemble the continents were calculated from the fit of rifted continental margins and the superposition of linear magnetic anomalies of similar age. Where information from the ocean floor was not available, the relative positions of the major land masses were approximated based on evidence of ancient subduction zones, continental collisions, and faunal differentiation. The continents were oriented with respect to latitude by restoring the mean magnetic pole of the reassembly, determined from the cluster of rotated paleomagnetic poles, with the geographic pole of the map. Longitude remains uncertain and is fixed to an arbitrarily chosen continent.

REFERENCES

Churkin, M., 1972, Western boundary of the North American continental plate in Asia: Geol. Soc. America Bull., v. 83, no. 1, p. 1027-1036. Dewey, J. F., Pitman, W. C., Ryan, W. B. F., and Bonnin, J., 1973, Plate tectonics and evolution of the Alpine system: Geol. Soc. America Bull., v. 84, p. 3137-3180. Francheteau, J., 1970, unpubl, doctorial disseration, Scripps Inst. Oceanog. McKerrow, W. S., and Ziegler, A. M., 1972, Paleozoic oceans: Nature Phys. Sci., v. 240, no. 100, p. 92-94. Scotese, C. R., and Baker, D. W., 1975, Continental drift reconstructions and animation: Jour. Geol. Ed, v. 4, Smith, A. G., Briden, I. C., and Drewry, G. E., 1973, Phanerozoic world maps: Sp. Pap. in Palacontolology No. 12,Palaeontologists Assoc., p. 1--42. Terman, M. J., 1973, Tectonic map of China and Mongolia (1:5,000,000): Geol. Soc. America.

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