Abstract

RAMOS, Victor A.. Darwin at Puente del Inca: observations on theformation of the Inca's bridge and mountain building. Rev. Asoc. Geol. Argent. [online]. 2009, vol.64, n.1, pp.170-179. ISSN 0004-4822.

Theanalyses of the observations of Charles Darwin at Puente del Inca, during hissecond journey across the High Andes drew attention on two different aspects ofthe geological characteristics of this classic area. Most of his descriptionson the characteristics and the origin of the natural bridge were not published,mainly due to his poor impression of Puente del Inca. However, the applicationof the uniformitarian principles shows that it was formed as an ice bridgeassociated with snow and debris avalanches later on cemented by the mineralsprecipitated by the adjacent hot-water springs. Darwin's observations on the complexstructural section at Puente del Inca, together with his findings of shallowwater marine fossil mollusks in the thick stratigraphic column of the areainterfingered with volcanic rocks, led him to speculate on several geologicalprocesses. Based on his geological observations, Darwin argued on the mountain uplift, thesubsidence of the marine bottom, the episodic lateral growth of the cordillera,and their association with earthquakes and volcanic activity, which was animportant advance in the uniformitarian hypothesis of mountain uplift proposedby Charles Lyell. Darwin was able to recognize the episodic nature of mountain uplift, and basedon these premises he concluded that the Andes were still undergoing uplift. Takenas a whole, his ideas anticipated in many years some of the premises of thegeosynclinal theory, and current hypothesis on foreland migration of the foldand thrust belts.

Keywords : Andes; Subsidence; Volcanism; Mountain uplift; Lateral growth; Ice-bridge.

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