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

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.