Axial Topography of Mid-ocean Ridge Systems: the Role of Underlying Melt Dynamics

Abstract:

Mid-ocean ridges (MORs) are one of the most remarkable planetary scale geodynamic features on Earth’s surface. Despite a significant progress in ocean floor mapping, numerical modelling and their theoretical formulations, the origin of axial topography has remained an open ended issue in plate tectonics. By combing Darcy-Stokes flow schemes with an enthalpy-based thermodynamic formulation, we propose a one-way fluid-structure interaction (FSI) model to demonstrate how sub-ridge magma-mush viscosity (μ_eff) can modulate the axial topography of a MOR. This model takes into account the dynamics of mushy region and crustal layer in the framework of FSI interaction, defined by the Robin-Neumann transmission condition. Based on the theory of suspension rheology, we vary μ_eff in the range 10¹⁰ - 10¹³ Pa s, covering the values applicable to most of the MORs in terms of limiting depth and height of axial topography. The 3D FSI models allow us to constrain μ_eff required for the formation of axial highs (10¹² -10¹³ Pa s) and valleys (10¹⁰ -10¹¹ Pa s). This study also provides an alternative explanation for off-axis ridge-parallel second-order hill topography as a consequence of ridge-normal compressive stress localization in linear belts on either flank of the axis. We support the FSI model interpretations with the available bathymetric data of MOR topography.