Depth Distribution in Ocean Basins and Plate Tectonics

Abstract

IN this article I shall show that relationships between the movement of lithospheric plates1–3 and the depths of the sea floor are leading towards a quantitative theory of the distribution of oceanic depths, and that some predictions can be made. Several principal lithospheric plates have now been recognized; their relative motion over the mantle is described by a rotation of one plate relative to an adjacent plate4–6. The rotation requires two parameters to locate the pole of relative rotation, and one to specify the magnitude of the angular velocity. The direction of spreading is along small circles concentric about the pole of rotation and the velocity of spreading varies as the sine of the distance (measured in degrees of arc) from that pole, to a maximum at a distance of 90° along the equator of rotation. The angular velocity of rotation is the same everywhere. In the Atlantic Ocean the fracture zones between about 60° N and 10° S are very nearly small circles centred about a pole near the southern tip of Greenland (62 ± 5° N, 36 ± 2° W), and the spreading rates approximately agree with the velocities required for the opening of the North Atlantic about this pole1,3.