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

Abstract

[1] The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (vS⊥) at the surface into its subducting plate motion component (vSP⊥) and trench migration component (vT⊥). Geodynamic models of progressive subduction demonstrate such dependence with five distinct slab geometries and corresponding partitioning ratios (vSP⊥/vS⊥): slab draping (vSP⊥/vS⊥ ≤ 0.5), slab draping with recumbent folds (0.5 < vSP⊥/vS⊥ < ∼0.8), slab piling (∼0.8 ≤ vSP⊥/vS⊥ ≤ ∼1.2), slab roll-over with recumbent folds (∼1.2 < vSP⊥/vS⊥ < ∼1.5) and slab roll-over (vSP⊥/vS⊥ ≥ ∼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.