Guiding of Tectonic Plate Motions by Transform Faults and Mid-Ocean Ridges

Abstract

Transform faults are strike-slip faults that accommodate lateral offsets between spreading segments of mid-ocean ridges. Because plates cannot move perpendicular to them, transform faults may exert a control on plate motions that has not been considered earlier. To improve some discrepancies between the predicted and observed plate motions, we introduce a force that resists plate motions parallel to mid-oceanic ridges (an alternative to a force perpendicular to the transform faults) into a larger-scale force balance that has previously been used to predict plate movements. Using three different misfit functions: misfit in direction, misfit in amplitude, and misfit in both direction and amplitude together, we constrain the magnitude of the new force, and compare its values to that of the major plate-driving forces. Our estimates of the ridge-parallel resistance expressed as a stress at plate boundaries are in a range between 16.5 and 44.0~MPa (assuming an average lithospheric thickness of 10~km at transform faults). The model previously used to predict plate motions is generally most improved when we use a value at the lower end of this range, but the improvement is typically minor. Our estimates of the actual force are between 0.8 and \num{2.1e11}~N/m, which is two orders of magnitude smaller than the expected value of the slab pull force, and one order of magnitude smaller than an estimate for ridge push. In general, even though the contribution of the ridge-parallel resistance to the force balance is relatively small, it slightly improves the predictions of the plate motions.