Cenozoic global plate motions

Abstract

Cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean‐lithosphere reference frame. Plate motions were analyzed over six time intervals divided by ages (10, 25, 43, 48, and 56 Ma) chosen, as much as possible, to coincide with key plate reorganizations. Alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the Pacific and North American plates. The circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the Atlantic region are assumed to be fixed relative to the hot spots in the Pacific region. Throughout the Cenozoic, the hot spot and mean‐lithosphere reference frames have been in continual, slow relative motion. The rate of motion is nonuniform, however, most of the motion having occurred during the middle Cenozoic. The net Cenozoic rotation of the lithosphere relative to the hot spots is described by a right‐handed rotation of 7° about a Euler pole at 46°S, 87°E, which yields a 5° displacement of the north poles of the two reference frames. This motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other. Analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the Cenozoic. Plate speeds correlate with latitude, plates moving faster near the equator than near the poles throughout the Cenozoic. As at present, continental plates (except for the Indian plate) moved slower than oceanic plates throughout the Cenozoic. Even the structure of the velocity fields as revealed in a contour of root‐mean‐square velocities in equatorial bands persists throughout the Cenozoic. The migration of the paleomagnetic axis over time is also compared to the hot spot and mean‐lithosphere reference frames. The paleomagnetic axis has shifted 5°–10° relative to the hot spot frame, and a lesser amount relative to the mean‐lithosphere frame.

Great earthquakes and slab pull: interaction between seismic coupling and plate–slab coupling

“…If seismic coupling is strengthened by one of these mechanisms, weakened plate^slab coupling and increased slab suction would lead to additional locking, and possibly a rapid slowing of the subducting plate. Because it does not require changes in the mantle density ¢eld, which evolves over tens of millions of years, this slablocking feedback mechanism may provide an explanation for the observation that plate motions occasionally change directions and speeds in only a few million years [37,40,50]. For example, the sharp bend in the Hawaiian^Emperor seamount chain could be explained if the Aleutian subduction zone became locked at about 43 Ma.…”

“…Because Conrad and Lithgow-Bertelloni [13] found that only slabs in the upper mantle contribute to the slab pull force, we sum the excess weight of all upper mantle slab material that is part of a continuous history of subduction at each subduction zone. We use a model of slab locations [11,36] that is derived from estimates of Cenozoic and Mesozoic plate motions [11,37]. We then calculate the slab suction forces on each plate from a model of instantaneous mantle £ow driven by lower mantle slabs [10,11].…”

“…2a), which are obtained [13] from compiled rotation poles for all plates [37] combined with recently updated estimates for the relative motion of Africa and South America [41]. We evaluate each prediction of plate motions by calculating its mis¢t with observed plate motions.…”

Are the Pacific and Indo–Atlantic hotspots fixed? Testing the plate circuit through Antarctica

“…From this fixed reference frame the 'absolute' motions of lithospheric plates might be measured (e.g. [5,6]). However, tests of hotspot fixity have shown a significant discrepancy between the Hawaiian-Emperor and Indo-Atlantic hotspots (e.g.…”

Reconstructing plate-motion changes in the presence of finite-rotations noise

“…In the past, the issue of data noise might have been deemed of second-order importance, because finite rotations were typically reconstructed at resolutions of ~10 Myr 14 . This yields small noise-tosignal ratios when computing Euler vectors directly by differentiation, with respect to time, of stage rotations obtained from two consecutive finite-rotation matrices.…”