Continental underplating after slab break-off

V Magni,M.B Allen,J Van Hunen,P Bouilhol

doi:10.1016/j.epsl.2017.06.017

V Magni, M.B Allen + Show 2 more

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https://doi.org/10.1016/j.epsl.2017.06.017

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Abstract

We present three-dimensional numerical models to investigate the dynamics of continental collision, and in particular what happens to the subducted continental lithosphere after oceanic slab break-off. We find that in some scenarios the subducting continental lithosphere underthrusts the overriding plate not immediately after it enters the trench, but after oceanic slab break-off. In this case, the continental plate first subducts with a steep angle and then, after the slab breaks off at depth, it rises back towards the surface and flattens below the overriding plate, forming a thick horizontal layer of continental crust that extends for about 200 km beyond the suture. This type of behaviour depends on the width of the oceanic plate marginal to the collision zone: wide oceanic margins promote continental underplating and marginal back-arc basins; narrow margins do not show such underplating unless a far field force is applied. Our models show that, as the subducted continental lithosphere rises, the mantle wedge progressively migrates away from the suture and the continental crust heats up, reaching temperatures >900 °C. This heating might lead to crustal melting, and resultant magmatism. We observe a sharp peak in the overriding plate rock uplift right after the occurrence of slab break-off. Afterwards, during underplating, the maximum rock uplift is smaller, but the affected area is much wider (up to 350 km). These results can be used to explain the dynamics that led to the present-day crustal configuration of the India–Eurasia collision zone and its consequences for the regional tectonic and magmatic evolution.

Highlights

The dynamics of continental collision are complex due to the many forces acting in the system at the same time and the many factors that can affect them
Our results show that for the underplating to occur after break-off an additional force is needed; this force could be provided by a far field push on the subducting plate or by the mantle flow and slab deformation associated with the flanking oceanic subduction
We performed 3D numerical models to study the dynamics of continental collision and, the underplating of the subducting continental plate beneath the overriding plate

Summary

Introduction

The dynamics of continental collision are complex due to the many forces acting in the system at the same time and the many factors that can affect them. In the Apennines and the Carpathians many studies suggested that delamination of the lithospheric mantle from the continental crust occurred, leaving a thin layer of crust as the lithospheric mantle keeps subducting Seismic studies that focused more on the architecture of the Himalayan area, showed that the Indian continental lithosphere lies sub-horizontally underneath Eurasia for about 200 km north of the suture zone (Nábělek et al, 2009; Chen et al, 2010). This configuration has been suggested to be present in ancient orogenies

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