Structural versus thermal inheritance controlling the location of compression-induced subduction initiation

New subduction zones may initiate either in intra-oceanic setting or in the vicinity of rifted margins. At both sites, the requirement of subduction initiation is the efficient strain localization and sufficient in-situ external forcing to overcome the shear and bending resistance of the lithosphere. While the age-dependent negative buoyancy of the oceanic lithosphere is the greatest at the ocean-continent boundary and therefore, rifted margin should be more favorable sites for subduction initiation, the increasing mechanical coupling between the oceanic and continental domains and the coeval strengthening of the rifted margin have been suggested to limit subduction initiation along the ocean-continent boundary to the first few tens of million years after continental break-up. This, in particular, suggests that the duration of the transitional interval between rifting and plate convergence plays a crucial role in determining the location of subduction initiation.

In this study, we investigated compression-induced subduction initiation in young and narrow oceanic basins, where the thermo-tectonic age of the rifted margin is low and thus, it is weak and more prone to strain localization. By using the I3ELVIS-FDSPM numerical code, we tested the duration of the plate motion reversal from rifting to convergence, and evaluated the role of the associated structural and thermo-rheological inheritance in controlling the location of subduction initiation. The models tracked the dynamic changes in the lithospheric strength and strain patterns, while the applied two-way coupling between the high-resolution 3D geodynamical and surface processes models allowed for the joint analysis of the crustal tectonics, thermal structure, melting, topography evolution, and the erosion-sedimentation processes.

The results show that abrupt plate motion changes lead to ridge-inversion and subsequent intra-oceanic subduction initiation along the extinct spreading ridge, controlled by the inherited thermal- and melt-induced weakening effects of the shallow lithosphere-asthenosphere boundary. In contrast, when the transition between rifting and plate convergence exceeds a few million years, strain localization is linked to inherited lithospheric-scale weak zones, such as pre-existing suture zones underneath the continental margin, while the inherited thermal structure no longer exerts a substantial influence on the location of subduction initiation. These modeling inferences align with observations from natural subduction initiation sites, such as the Algerian margin and the eastern Japan Sea.