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The crustal structure and kinematics of the Central Andes revisited

Since the advent of plate tectonics, a distinction has been made between mountain ranges formed by the collision of continental blocks, the typical example being the Himalayas, and those formed by the subduction of an oceanic plate at the edge of a continent, such as the Andes.

The crustal structure and kinematics of the Central Andes revisited

Publication date: 15/05/2018

General public, Press, Research

Related themes : Earth System Science

The two types of competing models for the orogeny of the Central Andes at 33.5°S: (a) classical model, (b) alternative model (this work)

The genesis of the imposing relief of the Andes and Altiplano, stretching for more than 5,000 km along the west coast of South America, remains the subject of debate. A recent controversy has pitted two classes of tectonic models against each other in an attempt to explain its formation (Figure 1): the “classic” view of crustal-scale thrusting opposed to subduction (towards the interior of the South American continent) has been called into question by a model published in 2010 and 2015 by researchers at the IPGP. In this alternative model, the chain starts on the west-andin chevauchement, synthetic to subduction, before developing in a bivergent manner and then growing towards the continent.

In an article recently published in Tectonics, Magali Riesner and colleagues (from the tectonics teams at IPGP and the University of Chile) reassess these divergent models by constructing a crustal-scale structural section at the latitude of Santiago de Chile (33.5°S). Using this section, based on 3D mapping of the deformed geological series, and combining it with all the available geological data, the authors reconstruct the kinematic evolution of the Andean orogen at this latitude. The proposed evolution (Figure 2) involves the progressive uplift of a basement massif – the ‘Cordillera Frontale’ – above the west-verging crustal thrust – the ‘West Andean Thrust’ or WAT. The displacement on the WAT, estimated here at between 30 and 55 km, is essentially transferred to the fold and thrust chain of the “Cordillera Principal” to the west. In this model, the famous Aconcagua fold and thrust belt (AFTB) is only a secondary structure above the WAT and the basement culmination of the Cordillera Frontale. The research team shows that the structure, kinematics and mechanics of the Andean orogeny – and by extension of all the Cordilleran chains – are comparable to those of collision chains of the Alpine or Himalayan type.

Kinematic evolution of the Andes chain at 33.5°S

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