Subduction Polarity Reversal: Induced or Spontaneous?

Subduction polarity reversal (SPR) is the subduction initiation process following the arc‐continent collision. Previous models emphasized the need for the external compressional force to induce it. However, the explanation of different geological structures in the reported SPR zones was poor. Based on our new thermomechanical model, we confirm the possibility of establishing a spontaneous SPR system, which is self‐sustained by negative buoyancy. The spontaneous SPR will occur when the whole overriding oceanic plate has a small plastic strength, while the arc‐continent collision system with a strong overriding plate and a limited weak back‐arc/arc structure prefers the compression‐induced SPR. Moreover, a rather young oceanic plate (≤20 Ma) can trigger the SPR without any weak area. This study provides new insights into the different initiation mechanisms and evolutionary pathways of the potential Cenozoic SPR events in Ryukyu, Kamchatka, and New Hebrides. Plain Language Summary Subduction polarity reversal (SPR) is a geological process consisting of two successive subductions in opposite directions. An initial intra‐oceanic subduction system forms an arc structure, which will collide with a continent or other buoyant blocks, triggering the second subduction with opposite polarity. SPR is the key process in Wilson's cycle, in which the original passive continental margin is transformed into an active continental margin. However, it is still uncertain how the SPR was initiated. In this study, we developed a numerical model to study the initiation of SPR and identified two modes: Spontaneous SPR and induced SPR. The plastic strength and age of the overriding oceanic plate in the arc‐continent collision system control the initiation modes. Our results can be applied to explain the different evolutionary pathways of the Cenozoic SPR events in Ryukyu, Kamchatka, and New Hebrides. Key Points Lithospheric weakness is conducive to the occurrence of subduction polarity reversal (SPR) Spontaneous SPR will occur when the arc‐continent collision system includes a weak overriding oceanic plate The duration of the spontaneous SPR is 3–5 Myrs shorter than the induced one