The geodynamic conditions for the formation of the Andes experimentally explored

Oceanic plates plunge into the mantle along subduction zones, sinking beneath another plate, usually a continental one. This process, facilitated by the density of the plunging oceanic plate, usually generates little deformation. Indeed, apart from the formation of an accretionary prism¹ at the very front of the boundary between the two plates, deformation of the upper plate is usually neutral or extensive. The Andes, however, represent an exception in the present era, with major compressive deformation along the western margin of the South American continent, generating one of the highest reliefs observed on Earth, from the ocean trough to the high peaks of the Altiplano.

A team of researchers from the IPGP, Géosciences Rennes and ISTerre have experimentally explored the geodynamic conditions under which such deformation of the upper plate could be made possible in a context of oceanic subduction. A novel experimental setup was used to set in motion glucose syrup, used as an analogue for the Earth’s mantle, in order to create a mantle flow. This generates a tensile force on the plates, which can either support or oppose subduction depending on its direction. The result is a compressive deformation of the upper plate when it is fixed and the mantle flow circulates in the direction of subduction of the oceanic plate. The integration of several silicone bands of different viscosities in the upper plate confirms the role played by lithospheric resistance in the location of the deformation, with a significantly greater amount of deformation in the least viscous silicone band, i.e. the weakest (orange band in the figure).