Abstract
The Subandean fault system is believed to be the most extensive tectonic feature of the South American Andes. The following discussion is restricted to its role in the tectonics of Peru and Ecuador. A summary of the regional tectonic features and their histories for Peru and Ecuador is presented in order to orient the reader. The fault system lies along the eastern front of the Andean ranges demarking the Andean uplift to the west and the potential petroleum province of the Subandean basin to the east. The arcuate trace of this system, as well as the trends of the Andean ranges and the Subandean basin, parallels the configuration of the western margin of the Brazilian and Guayana Precambrian shields. The Andean uplift contains Precambrian and Mesozoic plutonic intrusions, Paleozoic metamorphic rocks, Paleozoic, Mesozoic, and Tertiary sedimentary rocks, and Tertiary volcanics. Metamorphic and sedimentary formations are highly deformed by folding and faulting and are commonly mineralized. The Subandean basin contains a thick sedimentary sequence of Paleozoic, Mesozoic, and Tertiary rocks which overlie a basement of Precambrian igneous and metamorphic rocks similar to that of the shield regions. Foreland folds developed east of the fault system are generally faulted along the eastern flanks and correspond structurally to the compression deformation characteristic of the Andean uplift. Degree of folding and faulting diminishes eastward toward the shield regions. The Subandean fault system is an imbricate zone of west-dipping reverse strike faults along which the western blocks are elevated with respect to the eastern blocks. Stratigraphic separations of as much as 15,000 feet have been observed along faults of this system. It is possible that other types of movement, especially lateral movement, have occurred along this system during its history. A set of younger cross faults has subsequently offset the Subandean system.
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