Modelling ridge jumps in back-arc basins at different scales

<p>The structure of oceanic back-arc basins reflects the dynamics of the subduction zone they are associated with. Often, the basement of these basins is not only composed of oceanic crust, but also of exhumed mantle, fragments of continental crust, intrusive magmatic bodies, and a complex mid-ocean ridge system characterised by distinct relocations of the spreading centre. These features are a direct consequence of the transient nature of subduction zones. Here, we show results from different types of numerical models that aim at understanding how back-arc basins are shaped by subduction dynamics.</p><p>We present 3D numerical models of back-arc spreading centre jumps evolving naturally in a homogeneous subduction system surrounded by continents without a trigger event (Schliffke et al., 2022). We find that jumps to a new spreading centre occur when the resistance on the boundary transform faults enabling relative motion of back-arc and neighbouring plates is larger than the resistance to break the overriding plate closer to trench. Time and distance of spreading centres jumps are, thus, controlled by the ratio between the transform fault and overriding plate strengths. We also present results from 2D numerical models of lithospheric extension with asymmetric and time-dependent boundary conditions that simulate multiple phases of extension due to episodic trench retreat (Magni et al., 2021). We show that multiphase extension can result in asymmetric margins, mantle exhumation and continental fragment formations. We find that the duration of the first extensional phase controls the final architecture of the basin. Finally, we show that our models can explain many features observed in present-day and extinct back-arc basins.</p><p><em>Magni, V., Naliboff, J., Prada, M., & Gaina, C. (2021). Ridge Jumps and Mantle Exhumation in Back-Arc Basins. Geosciences, 11(11), 475.</em></p><p><em>Schliffke,</em><em> N., van Hunen,</em><em> J., Gueydan,</em><em> F., Magni,</em><em> V., & Allen</em><em>, M (2022). Episodic back-arc spreading centre jumps controlled by transform fault to overriding plate strength ratio</em><em>. Accepted for publication in </em><em>Nature Communications.</em></p><p>&#160;</p><p>&#160;</p>