Abstract

The truncation of orogenic trends at the modern Chilean coast, paleocurrent indicators, and facies distributions indicating the derivation of sediment from sialic sources in the present-day Pacific have suggested to students of the Paleozoic foundation of the Andes that a "south east Pacific continent" may have been located oceanward of the present margin in Paleozoic time. These features are well represented in the middle Paleozoic siliciclastic platform-deeper basin system in northern Chile. Furthermore, the Middle Devonian platform sections contain brachiopods both of Malvinokaffric and Eastern Americas realm affinity. Sedimentological and tectonic features are consistent with the evolution of the basin in a Devonian and early Carboniferous extensional regime, which was succeeded by the inception of subduction by oblique convergence in the late Carboniferous. The extensional regime was possibly governed by the clockwise motion of Laurentia along the proto-Andean margin, as recently proposed by Ian Dalziel; subduction of Pacific oceanic crust then began in the wake of Laurentia moving toward its Permian position in the Pangea supercontinent.

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