Analysis of the positions of the mid-ocean ridge network and of the orientations of individual spreading segments indicates that the main ridge systems display meridional symmetry. The pole of symmetry, based upon two independent analyses, is located between Iceland and Greenland at lat 65°N, long 40°W and describes both the average orientation of spreading lines and the trends of the main ridge systems. This geometric pattern appears to have existed in the past, as demonstrated for 55 m.y. ago. The high-latitude pole of meridional symmetry plus the latitude dependence of plate velocities, both now and in the past, suggest a rotational control on the positions of ocean ridges and plate motions.

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