Horizontal mantle flow controls subduction dynamics

E Ficini,L Dal Zilio,T V Gerya,C Doglioni

doi:10.1038/s41598-017-06551-y

E Ficini, L Dal Zilio + Show 2 more

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https://doi.org/10.1038/s41598-017-06551-y

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Abstract

It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age –the main control on buoyancy– exhibits little correlation with most of the present-day subduction velocities and slab dips. “West”-directed subduction zones are on average steeper (~65°) than “East”-directed (~27°). Also, a “westerly”-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an “easterly”-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

Highlights

It is generally accepted that subduction is driven by downgoing-plate negative buoyancy
These asymmetries are striking when comparing the western Pacific slabs and orogens and the eastern Pacific subduction zones, which cannot be explained solely by variations in the age-dependent negative buoyancy of the subducting lithosphere[11, 15, 19, 20]
The same asymmetric features can be recognized worldwide, for instance, comparing the W-directed Atlantic subduction zones and the NE-directed Dinarides-Zagros-Himalayas-Indonesia subduction zones, and it seems rather to be related to the geographic polarity of subduction. In support of this hypothesis, geometrical asymmetries and geophysical constraints along subduction zones would point to a “westerly” polarized drift of plates[21], which implies a relative opposed flow of the underlying Earth’s mantle. This relative motion is presumably allowed by the presence of a rheologically weak sub-lithospheric low seismic velocity zone (LVZ) located at about 100–200 km depth, where low-degree (~1–2%) melting causes an abrupt drop in the velocity of seismic waves and a low viscosity of the asthenosphere (~1017–1019 Pa s)[22,23,24]

Summary

Introduction

It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. E- or NE- directed slabs are shallower (seismicity generally ends at about 300 km, apart from some deeper clusters close to the upper-lower mantle transition)[18] and are less steep (Fig. 1); there is no typical back-arc basin opening but instead they build high-topography double-verging orogens with associated two shallower, slow subsiding (

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