3D numerical modeling of suction-induced subduction initiation at passive margins

Conversion of a passive margin, which is the transition between oceanic and continental lithosphere formed by sedimentation above an ancient rift, into an active converging plate boundary is still ambiguous. According to the Wilson Cycle (Wilson, 1966), which describes the repeated opening and closing of the oceans, the collapse of a passive margin is a key factor in the closing phase of the Wilson Cycle. However, the lack of any Cenozoic examples of conversion of passive margins into subduction zones and the existence of old oceanic plates along Atlantic passive margins indicate the difficulty of subduction initiation at passive margins. Due to lack of observational evidence, modeling studies play a key role in understanding the kinematics and dynamics of transforming a passive into active margin. During the last decades, they proposed several facilitating mechanisms to collapse a passive margin such as sediment loading (Cloetingh et al., 1982), water weakening (Regenauer-Lieb et al., 2001), STEP faults (Subduction-Transform-Edge-Propagator; Govers and Wortel, 2005) near passive margins (Baes et al., 2011), mantle suction forces derived from detached slabs and/or neighboring subduction zones (Baes and Sobolev, 2017), convergence forces induced from neighboring plates (Zhong and Li, 2019) and propagation of subduction along passive margins (Baes and Sobolev, 2017; Zhou et al., 2020).

 In this study, we extend the work of  Baes and Sobolev (2017) by using 3D models. As breaking a 3D lithosphere is more difficult than a 2D plate, 3D numerical models may lead to different conclusions than those of 2d ones. To study the effect of mantle suction flow on the destabilisation of passive margins, we set up 3D models, using the ASPECT finite element code (Kronbichler et al., 2012). We investigate the effect of different parameters such as the magnitude, spatial size and location of suction flow, the age of oceanic lithosphere and the existence of a STEP (Subduction-Transform-Edge-Propagator; Govers and Wortel, 2005) fault near margin. Our preliminary results show over-thrusting of continental crust from the earliest stage of deformation. This continued over-thrusting along with suction force, which imposes shear stresses below the lithosphere, causes breaking of the oceanic plate and its sinking into the mantle and eventually subduction initiation at the passive margin. The time of subduction initiation, which depends on several factors such as magnitude and location of the suction force, is more than 30 Myr indicating difficulty in the converting passive margins into converging plate boundaries. We believe that subduction initiation at some Atlantic passive margins such as those in the north of the South Sandwich subduction zone, southwest of the Iberia and north of the Caribbean region, where considerable suction forces induced by sinking slabs or neighboring subduction zones are available, will occur in a few tens of million years.

 

References:

Baes et al., 2011. Geophys. J. Int.

Baes, and Sobolev, 2017. Geochem. Geophys. Geosyst.

Cloetingh et al., 1982. Nature.

Govers and Wortel, 2005, Earth Planet. Sci. Lett.

Kronbichler et al., 2012, Geophys. J. Int.

Regenauer-Lieb et al., 2001. Sci.

Wilson, 1966, Nature

Zhou et al., 2020. Sci. Adv.

Zhong and Li, 2019. Geophys. Res. Lett.