Subduction Initiation at the Solomon Back‐Arc Basin: Contributions From Both Island Arc Rheological Strength and Oceanic Plateau Collision

Abstract

It is generally accepted that the subduction polarity reversal (SPR) results from the strong collision of two plates. Yet, the SPR of the Solomon Back‐arc Basin is started in the “soft docking” stage, and the mechanism by which the “soft docking” induced subduction initiation (SI) remains elusive. We find that the mass depletion of the plateau influences the evolution of the subduction patterns during SI. And the island arc rheological strength affects the development of the shear zone between an island arc and back‐arc basin which favors SI. What's more, with the increase of the rheological strength difference, the SI is more easily to occur, and the contribution of the plateau collision to SI weakens. Hence, by combining the available geological evidence, we suggest that the Solomon Island Arc rheological strength and the Ontong‐Java plateau collision jointly controlled the SI during the “soft docking” stage.

Plain Language Summary

Plateau collision has been considered an important factor for the subduction initiation (SI). However, the SI of the Solomon Sea Basin occurred during the “soft docking” stage, which is unique from the traditional understanding of SI. Our numerical model shows that the rheological strength difference between the SIA and the Solomon Sea Basin results in the conjugate shear zone with a high strain rate during the “soft docking” stage. The conjugate shear zone with a high strain rate as a natural weak zone is conducive to inducing SI. Moreover, while the SI (the San Cristobal Trench) occurs, the OJP likes a “wall” has resulted in the uplift of the SIA and the distinct evolution of subduction patterns.

Key Points

• The subduction initiation at the SSB results from joint contributions of both SIA rheological strength and OJP collision

• The island arc affects the development of shear zone between an island arc and back‐arc basin, which favors subduction initiation

• The mass depletion of the lithospheric mantle in the OJP influences the evolution of subduction patterns after subduction initiation