Global Model of the Integrated Strength of Oceanic Lithosphere and Ridge-push Transmission

Abstract:

Global models of the integrated lithospheric strength of oceanic plates and ridge-push force are presented. To assess the transmission of ridge-push related stress in oceanic plates, ridge-push force and lithospheric strength are compared. The integrated strength of oceanic plate has been estimated using plate cooling model and relevant rheology of the crust and upper mantle. The strength analysis includes Low-Temperature Plasticity (LTP) and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from thermal state of oceanic lithosphere, crustal age and seafloor depth data. The results of modelling show that both lithospheric strength and ridge-push force are age dependent. Old oceanic plates can be as strong as ~ 11 TN m^-1. For plates of the same age, the magnitude of ridge-push force is in the order of ~ 3.5 TN m^-1.The transmission of ridge-push is mainly controlled by the rheology and predominant tectonic condition in the plates. If the rheology of oceanic lithosphere is dry, the estimated lithospheric strength is larger than the ridge-push force at all ages for compressional tectonic regimes and at old ages for extension (> 75 Ma). Under such consideration, the ridge-push related stresses may not dissipate in a form of intraplate deformation. Instead, the stresses may be transmitted in the plate. If an oceanic lithosphere has wet rheology, the strength of young plates (< 75 Ma) is much less than the ridge-push force for extensional and compressional tectonic regimes. Consequently, the stress associated with ridge-push may result in intraplate deformation. This depends, however, on the balance of force resulting from far field forces, basal shear traction and Gravitational Potential Energy of elevated regions. In particular, strong basal shear traction can balance the ridge-push force, and as a result, the oceanic lithosphere may respond by deformation. The consideration of LTP in the upper mantle has negligible effect on the total strength of lithosphere, and hence, on the relation between lithospheric strength and ridge-push transmission.