Abstract
The thermo-mechanical evolution of the Earth's mantle is largely controlled by the dynamics of subduction zones, which connect the surface tectonic plates with the interior. However, little is known about the systematics of where subduction initiates and ceases within the framework of global plate motions and evolving continental configurations. Here, we investigate where new subduction zones preferentially form, and where they endure and cease using statistical analysis of large-scale simulations of mantle convection that feature self-consistent plate–like lithospheric behaviour and continental drift in the spherical annulus geometry. We juxtapose the results of numerical modelling with subduction histories retrieved from plate tectonic reconstruction models and from seismic tomography. Numerical models show that subduction initiation is largely controlled by the strength of the lithosphere and by the length of continental margins (for 2D models, the number of continental margins). Strong lithosphere favours subduction inception in the vicinity of the continents while for weak lithosphere the distribution of subduction initiation follows a random process distribution. Reconstructions suggest that subduction initiation and cessation on Earth is also not randomly distributed within the oceans, and more subduction zones cease in the vicinity of continental margins compared to subduction initiation. Our model results also suggest that intra-oceanic subduction initiation is more prevalent during times of supercontinent assembly (e.g. Pangea) compared to more recent continental dispersal, consistent with recent interpretations of relict slabs in seismic tomography.
Highlights
Subduction of the rigid plates is a fundamental process in Earth evolution, allowing chemical cycling between the surface and the deep mantle [Kerrick, 2001]
We compare the results of numerical simulations with distributions of subduction initiation and cessation retrieved from plate tectonics reconstructions and seismic tomography models
Subduction zones that are formed at continental margins tend to stay there, while subduction zones formed within the oceans migrate and merge with other intra-oceanic subduction zones, or reach continental margins where subduction usually continues, changing polarity before eventually ceasing
Summary
Subduction of the rigid plates is a fundamental process in Earth evolution, allowing chemical cycling between the surface and the deep mantle [Kerrick, 2001]. The surface and interior of the planet are interconnected within a self-organized system in which subduction arises from an instability of the top boundary layer, while it induces convective currents and pulls tectonic plates [Lowman, 2011; Coltice et al, 2017]. Little is known about subduction inception in the setting of global tectonics with floating continental rafts. How far from the continents do new subduction zones preferentially form? How do plate motions influence subduction inception? At which locations with respect to the position of the continental margins do subduction zones cease?. Few examples of active subduction inception or cessation are available to study. Young subduction systems can be found at the Mussau Trench [Hegarty et al, 1982] and Yap
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