A subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration

The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (nu(S perpendicular to)) at the surface into its subducting plate motion component (nu(SP perpendicular to)) and trench migration component (nu(T perpendicular to)). Geodynamic models of progressive subduction demonstrate such dependence with five distinct slab geometries and corresponding partitioning ratios (nu(SP perpendicular to)/nu(S perpendicular to)): slab draping (nu(SP perpendicular to)/nu(S perpendicular to) = similar to 1.5). The model findings have been applied to subduction zones in nature with well-resolved slab geometries, for which subduction partitioning ratios have been calculated during the last 20 million years in two global reference frames: the Indo-Atlantic and Pacific hotspot reference frames. The model-nature comparison determines in which reference frame subduction partitioning ratios are most in agreement with observed slab geometries. In the Indo-Atlantic frame, five (out of five) selected subduction zone segments with well-resolved slab geometries, plate velocities and trench velocities (Japan, Izu-Bonin, Mariana, Tonga, Kermadec) agree with the geodynamic model predictions, as calculated subduction partitioning ratios match the observed slab geometries. In the Pacific frame the partitioning ratio of only one subduction zone segment (Izu-Bonin) matches observations. It is thus concluded that the Indo-Atlantic hotspot reference frame is preferred over the Pacific one as a subduction zone reference frame in which to describe plate motions, subduction kinematics and mantle flow.