Uplift of the western border of the Altiplano on a west-vergent thrust system, Northern Chile

doi:10.1016/0895-9811(96)00004-1

Journal of South American Earth Sciences

Volume 9, Issues 3–4, May–July 1996, Pages 171-181

https://doi.org/10.1016/0895-9811(96)00004-1 Get rights and content

Abstract

A high angle, west-vergent thrust system (WTS) located along the western border of the Altiplano in Northern Chile caused the westward translation of the metamorphic pre-Cambrian basement and Mesozoic rocks over late Tertiary deposits. This WTS, which was essential to the build-up of the western Altiplano, developed principally between 15 and 4.8 Ma. The chronological sequence of faults indicate a back-thrusting. The WTS forms an overstep thrust sequence with vertical throws increasing from West to East and exposes in this direction increasingly older units over younger ones.

Taking the paleolake deposits of the Chucal Formation (25-19 Ma) and the ignimbrites of Oxaya Formation (19 Ma) as two regional reference levels, it is possible to calculate a 4,000 ± 200 m uplift associated to the WTS and a 392 ± 20 m/Ma uplift rate.

The WTS on the west side of de Altiplano and the east vergent thrust and fold belt on the east border, indicate that this plateau is essentially a compressive asymmetric structure, formed by two thrust “belts” with opposing vergencies.

Resumen

El borde occidental del Altiplano está formado por un sistema fallado y plegado de alto ángulo con vergencia hacia el Oeste (WTS). Este sistema involucra el alzamiento de un basamento metamórfico de edad precámbrica y secuencias sedimentarias del Mesozoico, falladas sobre unidades sedimentarias y volcánicas de edad terciaria media y superior.

El alzamiento principal del Altiplano, en el extremo norte de Chile, se habría desarrollado entre los 15 y 4.8 Ma y habría sido facilitado por este sistema de fallas, cuya edad es menor hacia el antepaís y cuyo desplazamiento vertical aumenta en la misma dirección. Tomando como niveles de referencia regional las ignimbritas de la Formación Oxaya y la paleoelevación a la cual fueron generadas las sedimentitas de la Formación Chucal (lacustre, 25-19 Ma), el alzamiento tectónico asociado al WTS habría sido del orden de los 4.000 ± 200 m con una tasa de 392 ± 20 m/Ma.

La existencia de un sistema fallado de vergencia occidental en el borde oeste del Altiplano indica que esta megaunidad es, esencialmente, una estructura compresiva asimétrica formada por dos sistemas de empuje de vergencias opuestas: el sistema de empuje de las Sierras Subandinas y el WTS, ambos iniciados durante el Oligoceno.

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Uplift of the western border of the Altiplano on a west-vergent thrust system, Northern Chile

Abstract

Resumen

Journal of South American Earth Sciences

Earth and Planetary Science Letters

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