Calculations of the 3D stress fields in mid-ocean ridge systems: a fluid-structure interaction (FSI) modelling approach

Abstract

Mid-ocean ridge (MOR) systems form multi-layered mechanical structures, constituted by a solid elastic crustal layer and an underlying melt-rich mush complex (MC) in the mantle. This article presents a new integrated solid-fluid modelling approach to show the development of complexly heterogeneous stress field in MORs. The modelling is implemented in two steps: 1) simulation of multi-ordered 3D convective circulations, produced by decompression melting in the mushy region, subjected to random thermal perturbations, and 2) mechanical coupling of the sub-ridge mushy regions with the overlying elastic crustal layer within a mathematical framework of fluid-structure interaction (FSI) mechanics. Using an enthalpy-porosity-based fluid-formulation of uppermost mantle the model accounts for a one-way FSI interaction for transmission of viscous forces of the MC region to the overlying upper crust. It is demonstrated from the model runs that a MOR spontaneously develops strongly heterogeneous stress fields on a time scale of million years, characterized by their segmented patterns. The stress mapping reveals a distinct 30 km wide axial zone of ridge-normal tensile stresses ( < 250 MPa), flanked by ridge-parallel linear belts of ridge-normal compression (median < 100 MPa). The FSI model results suggest that ridge-parallel compression belts can develop in MORs without involving flexural bending of lithospheric plates. In addition, a MOR system produces narrow along-axis compressional zones transverse to the ridge axis, resulting in segmentation of the stress field on a wavelength of 40-150 km. These segmented stress fields conforms to the second-order magmatic segmentation patterns of MORs, as reported in the literature.