Suction-induced subduction initiation in passive margins: insights from 3d numerical models

Despite extensive studies on conversion of passive margins into active ones, our knowledge about how an Atlantic-type of passive margin may convert into a new subduction zone is still inadequate. At Atlantic-type of passive margins, negative buoyancy of the old oceanic plates provides a gravitational driving force which may facilitate onset of a new subduction. However, increasing of lithospheric strength with aging makes it difficult to break an old oceanic plate, hindering spontaneous subduction initiation. Several mechanisms to assist subduction initiation in passive margins such as water weakening (Regenauer-Lieb et al., 2001), sediment loading (Cloetingh et al., 1982), collapse of old oceanic plates along STEP faults (Baes et al., 2011), propagation of subduction along passive margins (Zhou et al., 2020), subduction of young oceanic plates along passive margins induced by external converging forces (Zhong and Li, 2019) or suction forces coming from detached slabs within mantle and/or neighboring subduction zones (Baes and Soblev 2017) have been proposed. In this study, we aim to investigate suction-induced subduction initiation, using 3d models. Previous study of subduction initiation triggered by mantle suction force was based on 2d numerical models (Baes and Soblev 2017). As we expect that considering three-dimensionality of the earth may make the rupturing of the lithosphere more difficult, 3d numerical models may lead to different conclusions than those of 2d ones. To investigate this issue, we setup 3d numerical experiments with dimensions of 1800 km*800 km* 400 km, using ASPECT finite element code (Bangerth et al., 2015). Primarily model results show that suction forces can cause weakening and eventually delamination of parts of continental lithosphere. Delamination of mantle lithosphere along with plastic deformation of upper parts of lithosphere result in decoupling of oceanic and continental lithosphere. This is followed by sinking of oceanic plate into the mantle and sea floor spreading in the forearc. References: Baes et al., 2011. Geophys. J. Int. Baes, M., Sobolev, S., 2017. Geochem. Geophys. Geosyst. Bangerth et al., 2015. User Manual. Cloetingh et al., 1982. Nature. Regenauer-Lieb et al., 2001. Science. Zhong, X, Li, Z.-H., 2019. Geophys. Res. Lett. Zhou et al., 2020. Science Advances.