Ridge forces, absolute plate motions, and the intraplate stress field

Abstract

Torque poles are calculated for a variety of possible forces acting on the plates, including ridge push, slab pull, and collisional resistance. These torque poles are then compared to the directions of absolute plate motions. There is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the North American, South American, Pacific, Cocos, and Eurasian plates. Simple slab pull torques correlate well with absolute motion azimuths for the Pacific, Nazca, and Cocos plates and moderately well with the absolute motion azimuth of the IndoAustralian plate. Collisional resistance torque poles correlate with the absolute motion azimuth of the Eurasian plate only. The correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves. Torque poles for various forces are also compared with several long‐wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions. In general, ridge torque directions agree well with the orientations of maximum horizontal stresses for stable North America, western Europe, and South America and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag. Collisional resistance forces can also explain the alignment of stresses in western Europe. For the IndoAustralian plate, the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate. Other processes, in addition to collisional resistance, must be important for the Indo‐Australian plate. Ridge push forces may account for a significant portion of the long‐wavelength features of the intraplate stress field, especially away from continental collisions. Such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism. As previously suggested, slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates.

3-D geomechanical–numerical model of the contemporary crustal stress state in the Alberta Basin (Canada)

“…An assumption was that the same forces driving plate tectonics are the major control on the stress field, which is confirmed in first order (e.g. Richardson, 1992;Zoback et al, 1989;Zoback, 1992).…”

Transform push, oblique subduction resistance, and intraplate stress of the Juan de Fuca Plate

“…For a 2-D model, the effect of basal drag is represented by a body force9 and the total body force acting on the plate is the vector combination of ridge slide and basal drag. Basal drag is probably very small, of the orders of 10 '2 MPa [Richardson, 1992] Even if we assume an unreasonably large basal drag of 1 MPa, the total body force vector will only be rotated clockwise by 5 ø without appreciable magnitude changeø Such a small effect can be neglected. However, for a large oceanic plate with a significant portion older than 80 Ma, the effect of basal drag integrated over the whole plate may be comparable to that of ridge slide, because for plates older than 80 Ma, ridge slide diminishes, but basal drag does not.…”

Seismic anisotropy inferred from direct <i>S</i>-wave-derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau

“…The first one is a simple asthenospheric model (Richardson, 1992), proposed to explain the decoupling of the crust and mantle by the intrusion of a mechanically weak layer, such as the asthenosphere, into the crust. Whenever a mechanically weak layer is present in between the crust and mantle, the force acting on the crustal region cannot be transmitted into the mantle.…”