Mid-Ocean Ridge obstruction Cause A New Subduction zone

Izu-Bonin-Mariana (IBM) subduction zone, which situated in the western Pacific and eastern Japan, is a major segment of the Pacific subduction system. Based on the geochemical investigations of ophiolites (Ishizuka et al., 2011), IBM is generally considered initiated approximately 52–51 Ma through a gravitational collapse across the transform fault. And then the subsequential spontaneous subduction of IBM began, which corroborated by numerical simulations (Maunder et al., 2020; Ritter et al., 2024). However, recent studies indicate that the IBM has involved horizontal convergence in its subduction initiation (Li et al., 2022). Two-dimensional geodynamic models have verified that the early-stage IBM subduction pattern dominated by horizontal compression is consistent with geochemical observation (Liu et al., 2024), whereas the source of such horizontal forces remains unclear.

Geological reconstructions reveal that the initiation of IBM was synchronous with the subduction of Izanagi-Pacific Ridge. Based on that, we hypothesize that the subduction of the mid-ocean ridge played a important role in the initiation of this new subduction. To verify this idea, we use the 3D thermomechanical coupled numerical code I3VIS to construct a subduction model incorporating both the Izanagi-Pacific Ridge and the transform fault where IBM subduction initiated. Model results demonstrate that when the Izanagi-Pacific Ridge caused subduction obstruction, stress redistributed laterally, thereby inducing horizontal compression along the transform fault. The new subduction was first triggered locally, and then gradually expanded across the entire transform fault, ultimately forming the full-scale initiation of the new subduction zone.

This model confirms that the subduction obstruction of the mid-ocean ridge can redistribute local stress to lateral weak structures, thereby triggering the transition or expansion of the new subduction zone, which as a potential process for the initiation of the IBM subduction. This proposed model validates a new mechanics of subduction initiation driven by indirect factors, and provides novel insights into subduction dynamics.

 

Ishizuka, O., Tani, K., Reagan, M.K., Kanayama, K., Umino, S., Harigane, Y., Sakamoto, I., Miyajima, Y., Yuasa, M., Dunkley, D.J., 2011. The timescales of subduction initiation and subsequent evolution of an oceanic island arc. Earth Planet. Sci. Lett. 306, 229–240.

Maunder, B., Prytulak, J., Goes, S., Reagan, M., 2020. Rapid subduction initiation and magmatism in the western pacific driven by internal vertical forces. Nat. Commun. 11, 1874.

Ritter, S., Balázs, A., Ribeiro, J., Gerya, T., 2024. Magmatic fingerprints of subduction initiation and mature subduction: numerical modelling and observations from the izu-bonin-mariana system. Front. Earth Sci. 12, 1286468.

Li, H.-Y., Li, X., Ryan, J.G., Zhang, C., Xu, Y.-G., 2022. Boron isotopes in boninites document rapid changes in slab inputs during subduction initiation. Nat. Commun. 13, 993.

Liu, Liang, Li, H.-Y., Liu, Lijun, Ryan, J.G., Morgan, J.P., Ren, K.-X., Xu, Y.-G., 2024. Horizontally forced initiation of the izu-bonin-mariana subduction zone. Commun. Earth Environ. 5, 91.