Asymmetry of thermal structure at slow-spreading ridges: Geodynamics and numerical modeling

Tectonic evolution at spreading centers is commonly considered symmetric along mid-ocean ridges, when modeling with relative plate motions and steady-state processes. However, tectonic features are generally asymmetric, as provided by geological a geophysical data. A better way to understand dynamics of the lithosphere at mid-ocean ridges, and lithosphere/mantle interactions corresponds to absolute plate kinematic analyses, i.e., with respect to the mantle, modeling time-dependent tectonic processes. We performed numerical simulations of plate-driven mantle flow beneath slow mid-ocean ridges and we considered a time-dependent flow induced by the motion of overlying rigid plates in an incompressible viscous mantle, using plate velocities obtained in the hotspot reference frame, as boundary conditions. This implies that plates along a ridge, and the ridge itself, move toward the same direction, but with different velocities, relative to the mantle, and the separation between plates triggers mantle upwelling. Numerical solutions for viscosity flow beneath plates that thicken with increasing age are presented. The mantle can be modeled as a viscous fluid, and its dynamics can be described using the Stokes equations and thermal effects, and a finite element approach has been adopted to obtain numerical solutions. Results show an asymmetric thickening of oceanic plates along the ridge, as suggested by the observations, and provide useful relationships between mantle temperature and thickness of the oceanic lithosphere.