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Geochemistry, Geophysics, Geosystems 13, 4 (2012) Q04001
The role of slabs and oceanic plate geometry in the net rotation of the lithosphere, trench motions, and slab return flow
M. Gerault 1, 2, T. W. Becker 2, B. J.P. Kaus 2, Claudio Faccenna 3, Louis Moresi 4, Laurent Husson 1, 5

[1] Absolute plate motion models with respect to a deep mantle reference frame (e.g., hot spots) typically contain some net rotation (NR) of the lithosphere. Global mantle flow models for the present-day plate setting reproduce similarly oriented NRs but with amplitudes significantly smaller than those found in some high NR Pacific hot spot reference frames. It is therefore important to understand the mechanisms of NR excitation, which we attempt here with two-dimensional cylindrical models of an idealized Pacific domain. We study the influence of slab properties, oceanic ridge position, continental keels, and a weak asthenospheric layer on NR and trench migration. Fast slab return flow develops in models with stiff slabs and moderate slab dips. Rapid NRs, comparable to the high NR Pacific hot spot reference frames, are primarily induced by asymmetric slab dips, in particular a shallow slab beneath South America and a steep slab in the western Pacific. A scaling relationship links the amplitude of NR to plate size, slab dip angle, and slab viscosity. Asymmetric ridge positions also promote NR through asymmetric plate sizes. Continental keels have less impact, in contrast to what has been found in earlier global studies. Several models yield unidirectional Pacific trench motions, such as slab advance in the western Pacific and, simultaneously, slab retreat in the eastern Pacific. Our model provides a physical explanation for NR generation in the present-day Pacific setting and hints at mechanisms for the temporal evolution of the basin.
1 :  Géosciences Rennes (GR)
CNRS : UMR6118 – INSU – Observatoire des Sciences de l'Univers de Rennes – Université de Rennes 1
2 :  Department of Earth Sciences, University of Southern California Los Angeles
3 :  Università “Roma TRE”, Dipartimento Scienze Geologiche, Roma
4 :  School of Mathematical Sciences
Monash University
5 :  Laboratoire de Planétologie et Géodynamique de Nantes (LPGN)
CNRS : UMR6112 – INSU – Université de Nantes
Systèmes Tectoniques
Planète et Univers/Sciences de la Terre/Tectonique

Sciences de l'environnement/Milieux et Changements globaux
lithosphere-mantle interactions – net rotation of the lithosphere – slab dynamics – trench motions.
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husson-g3-1.pdf(4.2 MB)