Plate Sub-rotations

The kinematics of plates is defined by Euler pole and angular velocity. However, during their journey, plates may be affected by additional simultaneous rotations (i.e., subrotations) while they are rotating about their Euler poles. The kinematic description of this particular plate motion requires a different analytical approach: two angular velocities and two poles are necessary to completely describe plate displacements. If a subrotation occurs, none of the points on a plate moves along circles of the Euler pole but, instead, follows cycloid trajectories because of the combination of the two simultaneous rotations. Regardless of the forces that move the lithosphere, every time a plate experiences a subrotation, an additional force (or resisting) force could act on the plate, generating the two-rotation motion. In the hot spot reference frame, we applied this model to the North America plate, investigating its past motion for a time interval Dt = 43 Ma up to the present and comparing results with those obtained by Gordon and Jurdy (1986). This application shows how the different positions of the North America plate over most of the Cenozoic can be reconstructed by two-rotation plate kinematics.