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The geodynamic conditions for the formation of the Andes experimentally explored

A team of researchers has used a novel experimental setup to explore the geodynamic conditions under which compressive deformation of the upper tectonic plate might be possible in a context of oceanic subduction.

The geodynamic conditions for the formation of the Andes experimentally explored

© Nicolas Prieto - Unsplash

Publication date: 29/11/2023

Press, Research

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).

Comparison between model 5 of Habel et al. (2023) (A, B) and the special case of the Andes at ~20°S (C, cross-section of the Andes modified from Armijo et al., 2015). Model 5 is illustrated through an oblique top view (A) and a side view (B) of the experimental setup. In this model, the top plate is attached to the backwall and is pre-structured, with a lower viscosity silicone band (orange). The imposed mantle flow, with a velocity of 10 cm/year (scaled), is in the direction of subduction. In this case, the upper plate deforms, and the deformation is preferentially located in the orange silicone band.

These innovative results provide a better understanding of the conditions that may have led to Andean orogenesis2. They have been published in Tektonika, a recently launched Diamond Open-Access journal3.

 

1. Accumulation of sediments of oceanic origin which do not pass through subduction, in the form of imbricated tectonic scales.

2. Formation of the Andes mountain range.

3. Type of journal that allows scientists to read and publish in open access and free of charge, while being evaluated by their peers.

 

Ref: Habel T. , Replumaz A., Guillaume B., Simoes M., Geffroy T., Kermarrec J.-J., Lacassin R., Upper-plate shortening and mountain-building in the context of mantle-driven oceanic subduction, Tektonika, 1 (2), doi:10.55575/tektonika2023.1.2.39, 2023.

The data resulting from this work is freely accessible in the IPGP Research Collection: https://doi.org/10.18715/IPGP.2023.ldbm60lm

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