Subduction initiation: attempted vs. sustained

Abstract:

Mature subduction is mainly driven by the negative buoyancy of the cold oceanic lithosphere relative to the underlying mantle. Subduction intitiation mechanisms are more difficult to understand due to more complex physics involved in this process. Many spontaneous and induced subduction initiation scenarios have been identified whereas only some are characteristic for the present-day plate tectonics (Stern and Gerya, 2018, Tectonophysics). In the last 100 Ma subduction initiated predominantly in oceans thereby indicating that heterogeneous oceanic plate interiors are more favorable for subduction initiation than passive margins (Crameri et al., 2020, Nature Communications). The research predominantly focused on “successful” subduction initiation cases in which new self-sustained subduction zones formed. However, it is also crucial to identify and investigate “failed” subduction initiation attempts, in which subduction initiation has been arrested at some early stage. Such cases are common in numerical geodynamic models and allow outlining the parameter space for stability of different scenarios. Importantly, subduction initiation and sustainability may be governed by very different physics. In particular, plume-induced subduction initiation is characteristic for both Earth (Whattam and Stern, 2014, Gondwana Research) and Venus (Gulcher et al., 2020, Nature Geoscience) but only on Earth this process produced stable subduction zones. The sustainability is likely controlled by the presence of pressurized aqueous fluids along the subduction interface (Gerya et al., 2008, Geology) but it requires long initiation stage controlled by different forcing and weakening mechanisms responsible for creating respectively the sufficient slab pull and the weak hydrated subduction interface. In particular, apparent absence/scarcity of modern examples of subduction initiation at passive margins does not necessarily mean that subduction does not attempt to frequently initiate there. Therefore it seems critical to broaden the subduction initiation research by systematically confronting attempted vs. sustained cases. In this work, few examples of “successful” and “failed” subduction initiation scenarios are compared based on geodynamic models and natural observations.